Šejla Trožić SLIKANJE MEDENICE STOJE Z IN BREZ ODMIKA MEHKEGA TKIVA: PRIMERJAVA KAKOVOSTI SLIKE IN DOZNE OBREMENITVE

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UNIVERZA V LJUBLJANI ZDRAVSTVENA FAKULTETA

RADIOLOŠKA TEHNOLOGIJA, 2. STOPNJA

Šejla Trožić

SLIKANJE MEDENICE STOJE Z IN BREZ ODMIKA MEHKEGA TKIVA: PRIMERJAVA KAKOVOSTI

SLIKE IN DOZNE OBREMENITVE

magistrsko delo

ERECT PELVIC X-RAY WITH AND WITHOUT FAT TISSUE REMOVAL: COMPARISON OF IMAGE

QUALITY AND RADIATION DOSE

master thesis

Mentor: doc. dr. Nejc Mekiš

Somentor: dr. Andrew England

Recenzent: doc. dr. Damijan Škrk

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ACKNOWLEDGEMENTS

I would like to express my sincere gratitude to my mentor doc. dr. Nejc Mekiš and my co-mentor dr. Andrew England for providing guidance and helpful feedback on this thesis, for all of their support, encouragement and patience.

Besides my supervisors, I would like to thank the Head of Radiographers Mrs. Martina Dolšak, the Head of Radiology, Mrs. Vanja Kos, and the medical director Mrs. Tea Stegne Ignjatovič for allowing me to conduct a research in Community Health Centre Ljubljana - unit Centre. I am also thankful to all the radiographers in this facility for their help and patience while we were collecting data for a research. Special thanks to Mrs. Larisa Vengar, Mrs. Žana Blagojević and Mr. Duško Zagoranski, the radiologists, for their help, time and effort in image quality evaluation. I am also extremely grateful to all the patients who decided to participate in this research.

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IZVLEČEK

Uvod: Najpogosteje uporabljena radiografska projekcija pri slikanju medenice in kolkov je AP projekcija v ležečem položaju, vendar nekateri menijo, da bi bilo bolje izvajati slikanje medenice stoje, saj bi s tem dobili diagnostično bolj uporabne informacije. V predhodni študiji, kjer so primerjali AP slikanje medenice stoje in leže pa so poročali o višji dozi in slabši kakovosti rentgenogramov pri slikanju medenice stoje. Namen: Namen raziskave je bil ugotoviti, ali se kakovost rentgenogramov in prejeta doza razlikujeta pri dveh različnih načinih slikanja medenice stoje - z odmikom in brez odmika mehkega tkiva. Metode dela:

Meritve so bile razdeljene na dva dela. Prvi del je obsegal študijo na fantomu, kjer smo izbrali trak, ki ni povzročal vidnih artefaktov na rentgenogramu. S tem trakom so si pacienti v drugem delu študije umaknili tkivo s področja slikanja. Drugi del študije je bil izveden na 60-ih pacientih, ki so bili napoteni na rentgensko slikanje medenice stoje. Bili so naključno razdeljeni v dve skupini z enakim številom. Polovica jih je umaknila tkivo s področja slikanja, druga polovica pa ne. Pri vseh smo izmerili obseg pasu in bokov, telesno višino in maso, DAP, velikost polja, razdaljo med goriščem in objektom slikanja, tokovni sunek (mAs) in napetost (kV). Naknadno smo iz meritev še izračunali indeks telesne mase, vstopno kožno dozo in efektivno dozo. Dobljene slike so ocenili trije radiologi. Rezultati: V prvem delu raziskave smo ugotovili, da tanka trikotna ruta ne povzroča artefaktov na rentgenogramu. Opazili smo statistično značilne razlike v obsegu pasu pred in po umiku mehkega tkiva (p<0.001), saj se je le-ta zmanjšal za 4.7%. Pri obsegu bokov pred in po umiku tkiva ni bilo statistično značilnih razlik (p=0.211). DAP je bil za 38.5% nižji v skupini pacientov, ki so umaknili tkivo med preiskavo (p=0.001). Prav tako je bila tudi vstopna kožna doza nižja v omenjeni skupini pacientov, in sicer za 44% (p<0.001). Efektivna doza se je znižala za 38.7% pri tistih, ki so umaknili tkivo s področja slikanja (p<0.001). Kolčna sklepa (p=0.001), trochantri (p=0.021), acetabulum (p<0.001), vratova stegnenice (p=0.021), medula in korteks medenice (p=0.009), križnica in križnične odprtine (p=0.008) ter mehka tkiva medenice in kolkov (p=0.039) so bili bolj vidni na slikah z odmikom mehkega tkiva. Statistično značilnih razlik med skupinama pacientov nismo našli pri prikazu sakroiliakalnih sklepov (p=0.055), črevničnih grebenov (p=0.060) in vej sramnice in sednice (p=0.166). Skupna ocena slik je bila višja v skupini z odmikom mehkega tkiva (p=0.004).

Razprava in zaključek: Ugotovili smo, da se pri slikanju medenice stoje z odmikom maščobnega tkiva znižajo DAP, vstopna kožna doza in efektivna doza, hkrati pa se izboljša tudi kakovost slike, saj z odmikanjem mehkega tkiva s področja slikanja postajajo bolj vidne anatomske strukture medenice in kolkov.

Ključne besede: slikanje medenice stoje, odmik mehkega tkiva, kakovost slike, dozna obremenitev

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ABSTRACT

Introduction: The most commonly used projection for pelvic and hip radiography is the supine AP projection, but some studies advocate that it would be better to perform it in erect position as this would provide more diagnostically useful information. According to a previous study they reported reduced image quality and increased radiation dose for erect pelvic imaging in larger patients as they compared it to the supine pelvic X-ray. Purpose:

The purpose of this study is to determine whether the radiation dose and image quality differ between two different erect pelvic radiographic procedures, with and without fat tissue removal. Methods: The measurements were divided into two parts. In the first part we determined which band did not produce artefacts on the resultant X-ray image when displacing fat tissue on the phantom. The second part was performed on 60 patients referred for erect pelvic imaging. They were randomly divided into two equal groups, half of them removed the fat tissue from the region of interest and the other group did not. We measured waist and hip circumference, height, weight, DAP, primary field size, source-to-skin distance, mAs and kV. BMI, ESD and effective dose were subsequently calculated. The images were evaluated by three radiologists. Results: In the phantom study we found that a thin cotton triangular bandage does not show any visible artefacts. The waist circumference before and after tissue removal was statistically different (p<0.001), as the thickness decreased by 4.7%, while hip circumference before and after removal was not statistically different (p=0.211). DAP was 38.5% lower in a group of patients with tissue removal (p=0.001). The ESD was 44% lower in a group in which patients moved the fat tissue from the region of interest (p<0.001). The effective dose was reduced by 38.7% in a group of patients with soft tissue removal (p<0.001). Hip joints (p=0.001), trochanters (p=0.021), acetabula (p<0.001), femoral necks (p=0.021), medulla and cortex of the pelvis (p=0.009), sacrum and its foramina (p=0.008) and the pelvic/hip soft tissues (p=0.039) were more visible on images obtained with fat tissue removal and were also statistically different. We found no significant differences between groups in visualisation of sacroiliac joints (p=0.055), the iliac crests (p=0.060) and the pubic/ischial rami (p=0.166). The total image score was higher in the patients with fat tissue removal (p=0.004). Discussion and conclusion: In this study we found that when taking a pelvic radiograph in the erect position, while moving fat tissue from the region of interest, the patient dose area product, the entrance skin dose and the effective dose decreases. This also affects the image quality, as it increases with the removal of the tissue and most of the anatomical structures of the pelvis are better visualised.

Keywords: erect pelvic radiography, fat tissue removal, image quality, radiation dose

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TABLE OF FIGURES

Figure 1 : Anterosuperior view of pelvic girdle (Schuenke et al., 2010) ...2 Figure 2: Optimal AP erect pelvic X-ray (Community Health Centre Ljubljana - unit Centre, 2020). ...6 Figure 3: A rubber exercise band (upper left corner), a cotton cloth folded into a band (upper right corner), an elastic cotton bandage (lower left corner) and a thin cotton triangular bandage (lower right corner) ... 23 Figure 4: Distributed BMI values in groups divided by tissue removal ... 25 Figure 5: The distribution of primary field size data in groups divided by tissue removal . 27 Figure 6: Distributed DAP values in groups divided by tissue removal ... 28 Figure 7: Distributed ESD values in groups divided by tissue removal ... 29 Figure 8: Distributed effective dose values in groups divided by tissue removal ... 30 Figure 9: The distribution of evaluation scores for visualisation of hip joints in groups divided by tissue removal ... 33 Figure 10: The distribution of evaluation scores for visualisation of trochanters in groups divided by tissue removal ... 34 Figure 11: The distribution of evaluation scores for visualisation of sacroiliac joints in groups divided by tissue removal ... 35 Figure 12: The distribution of evaluation scores for visualisation of iliac crests in groups divided by tissue removal ... 36 Figure 13: The distribution of evaluation scores for visualisation of acetabula in groups divided by tissue removal ... 37 Figure 14: The distribution of evaluation scores for visualisation of pubic/ischial rami in groups divided by tissue removal ... 38 Figure 15 : The distribution of evaluation scores for visualisation of femoral necks in groups divided by tissue removal ... 39 Figure 16: The distribution of evaluation scores for visualisation of medulla and cortex of the pelvis in groups divided by tissue removal ... 40 Figure 17: The distribution of evaluation scores for visualisation of sacrum and its foramina in groups divided by tissue removal ... 41 Figure 18: The distribution of evaluation scores for visualisation of pelvic/hip soft tissues in

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TABLE OF TABLES

Table 1: BMI classification (World Health Organization/Europe, 2021) ... 12

Table 2: Comparison of suggested parameters for digital pelvic radiography (European Commission, 2004) and parameters we used in phantom study on Siemens Multix/Vertix Unit ... 16

Table 3: Comparison of suggested parameters for digital pelvic radiography (European Commission, 2004) and parameters we used in patient study on Siemens Axiom Aristos FX Plus Unit ... 19

Table 4: Measured tube output for each value of tube potential ... 20

Table 5: Statistical analysis of BMI for group of patients with and without fat tissue removal ... 24

Table 6: Statistical analysis of waist and hip circumference between both groups of patients ... 26

Table 7: Statistical analysis of waist and hip circumference before and after fat tissue removal ... 26

Table 8: Statistical analysis of primary field size for group of patients with and without fat tissue removal ... 26

Table 9: Statistical analysis of DAP for group of patients with and without fat tissue removal ... 27

Table 10: Statistical analysis of ESD for group of patients with and without fat tissue removal ... 28

Table 11: Statistical analysis of effective dose for group of patients with and without fat tissue removal ... 29

Table 12: The reliability between radiologist 1 and 2 ... 31

Table 15: Statistical analysis of evaluation score of visualisation of hip joints in groups with and without fat tissue removal ... 32

Table 16: Statistical analysis of evaluation score of visualisation of trochanters in groups with and without fat tissue removal ... 33 Table 17: Statistical analysis of evaluation score of visualisation of sacroiliac joints in groups

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Table 18: Statistical analysis of evaluation score of visualisation of iliac crests in groups with and without fat tissue removal ... 35 Table 19: Statistical analysis of evaluation score of visualisation of acetabula in groups with and without fat tissue removal ... 36 Table 20: Statistical analysis of evaluation score of visualisation of pubic/ischial rami in groups with and without fat tissue removal... 37 Table 21: Statistical analysis of evaluation score of visualisation of femoral necks in groups with and without fat tissue removal ... 38 Table 22: Statistical analysis of evaluation score of visualisation of medulla and cortex of the pelvis in groups with and without fat tissue removal ... 39 Table 23: Statistical analysis of evaluation score of visualisation of sacrum and its foramina in groups with and without fat tissue removal... 40 Table 24: Statistical analysis of evaluation score of visualisation of pelvic/hip soft tissues in groups with and without fat tissue removal... 41 Table 25: Statistical analysis of total image score in groups with and without fat tissue

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LIST OF ABBREVIATIONS

AEC ALARA AP

Automatic Exposure Control As Low As Reasonably Achievable Anteroposterior

ATLS BMI BSF CR CT

Advanced Trauma Life Support Body Mass Index

Backscatter factor Computed Radiography Computed Tomography DAP

DDH DR ESD FAI IQR kV mAs

Dose Area Product Dysplasia of the hip Digital Radiography Entrance Skin Dose

Femoroacetabular impingement Interquartile range

Kilovolt (tube potential)

Miliampere-second (tube current and exposure time product) OA

QA ROI SID SPD

Osteoarthritis Quality assurance Region of interest

Source to image distance Source to patient distance

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1 INTRODUCTION

Plain radiography is a simple, quick, and widely used diagnostic imaging technique. It is considered the first diagnostic test for most musculoskeletal problems, especially pathological changes of the pelvis and hips (Mand, 2018; O’Sullivan, Goergen, 2017). Pelvic and hip radiography is a very common examination; however, it is also one of the five examinations in which patients receive the highest radiation dose from radiography (Chiron et al., 2017; European Union, 2014).

The most commonly used radiographic projection for pelvic and hip radiography is the supine anteroposterior (AP) projection, which is taken when the patient is lying on his or her back during the exposure (Campbell, 2005). However, hip pain usually occurs during daily functional activities such as walking and running, and some advocate that it would be better to perform pelvic imaging in erect position as this would provide more diagnostically useful information, such as functional anatomy (Flintham et al., 2021; Alzyoud et al., 2018; Jackson et al., 2016). In addition to these findings, Fuchs-Winkelmann and colleagues (2008) found in their study that erect pelvic radiography is also more useful for assessing the width of the space around the hip joint.

Alzyoud (2019) compared the image quality and the radiation doses received between two imaging projections – AP erect (weight-bearing) and AP supine (lying). In this thesis the author reported reduced image quality and increased radiation dose for erect pelvic imaging in larger patients. The reason for this result is that soft tissue descends due to gravity, which increases the AP thickness in the pelvic region. The resultant effect is poor image quality and an increased dose (Flintham et al., 2017).

In view of pelvic radiography being so diagnostically useful, it would be useful to investigate examinations in which patients manually displace soft tissues from the pelvic region during imaging. This is important as studies have shown that inferior soft tissue displacement increases received radiation dose and decreases image quality, because of the limitations described in the previous studies (Flintham et al., 2021; Alzyoud, 2019; Metaxas et al., 2018).

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1.1 General anatomy of the pelvic girdle

The entire structure of pelvic girdle is formed by the two pelvic bones (hip bones), the sacrum and the coccyx, which are parts of the spine (Figure 1). The hip bones unite anteriorly at the pubic symphysis and posteriorly with the sacrum at the sacroiliac joints (Tortora, Derrickson, 2014; Drake et al., 2010). Each of the two pelvic bones consist of three fused bones: an upper ilium, a lower and anterior pubis, and a lower and posterior ischium. These bones are separated by cartilage at birth and fuse together by 23 years of age (Tortora, Derrickson, 2014).

Figure 1 : Anterosuperior view of pelvic girdle (Schuenke et al., 2010).

The ilium is the largest of the three components of the pelvic bone. A ridge on the medial surface separates the ilium into an upper and lower part. The lower part, the body, is one of the components of a large articular socked called acetabulum, which forms the hip joint with the femoral head and is located on the lateral surface of the hip bone. The upper portion forms a flat, fan-shaped "wing" called the ala (Tortora, Derrickson, 2014; Drake et al., 2010).

The iliac crest is the superior border of the ilium and ends anteriorly in the spina iliaca anterior superior. Below this is the anterior inferior iliac spine and posteriorly the iliac crest ends in the posterior inferior iliac spine. The spines are important because they form the attachment for the tendons of the muscles of the trunk, hip, and thighs (Tortora, Derrickson, 2014).

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The ischium consists of the upper body and a lower ramus on each side of the pelvis, which is the part of the ischium that fuses with the pubis. The ramus and pubis together surround the obturator foramen. It is closed by a flat connective tissue membrane, obturator membrane, through which blood vessels and nerves pass (Tortora, Derrickson, 2014; Drake et al., 2010).

The pubic bone consists of an upper ramus, a lower ramus, and a body. The pubic crest is the anterior, upper limit of the body, and at its later end is the tuberculum pubicum. The symphysis pubica is the joint between two hip bones and consists of a disc of fibrocartilage.

The pubic symphysis is formed by the fusion of the inferior rami of the two pubic bones (Tortora, Derrickson, 2014).

The sacrum is a triangular shaped bone formed by the fusion of five sacral vertebrae. It provides a strong foundation for the pelvic girdle as it is positioned in the posterior portion of the pelvic cavity, medial to the two hip bones, where it forms the sacroiliac joint with each hip bone (Tortora, Derrickson, 2014). The sacrum has a base and an apex. The base articulates with the fifth lumbar vertebra and forms the lumbosacral joint and the apex articulates with the coccyx (Drake et al., 2010). The anterior aspect of the sacrum is concave and faces the pelvic cavity. It has four transverse ridges that mark the junction of the sacral vertebral bodies, and at the end of these ridges are four pairs of anterior sacral foramina. The posterior surface of the sacrum has a median sacral ridge, a lateral sacral ridge, and four pairs of posterior sacral foramina that connect to the anterior sacral foramina to allow the passage of blood vessels and nerves (Tortora, Derrickson, 2014).

The coccyx is a small terminal part of the spine and consists of four coccygeal vertebrae fused together. Its base is directed upward and bears a facet for articulation with the sacrum and two horns, one on each side, directed upward to articulate with a similar horn directed downward from the sacrum (Drake et al., 2010).

1.2 Clinical indications for pelvic radiography

Pelvic and hip images are almost always obtained to rule out bony abnormalities or underlying structural fractures that are a frequent and potentially serious injury in patients who have undergone blunt trauma (Mand, 2018; Holmes, Wisner, 2012). It is very important to identify these injuries early, because both temporary and operative stabilization may be

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needed due to possible life-threatening haemorrhage that may occur. The Advanced Trauma Life Support protocol (ATLS) recommends that immediately after the primary examination patients with this kind of trauma undergo AP pelvic radiography in the supine position (Holmes, Wisner, 2012).

Radiography of pelvis and hips is also used to find the cause of many symptoms such as pain, swelling or deformity and for diagnosis and evaluation of arthropathy, metabolic bone disease and malignancies (Durani, 2021; Parker et al., 2017). Pelvic malignant lesions are not uncommon and despite other advanced imaging diagnostic modalities, conventional radiography still remains the gold standard for the initial evaluation and diagnosis of bone tumours. Tumours like Ewing’s sarcoma, plasma cell myeloma, lymphoma and metastatic disease primarily localize to hematopoietic marrow, which predominates in the bony pelvis until later in life (Girish et al., 2012). The distribution of red bone marrow changes due to the patient’s age, so these neoplasms can manifest in both, axial and appendicular skeleton including the pelvis. Some of these tumours can be difficult to diagnose because of the variability in the appearances, especially primary tumours and metastases, but some can be diagnosed simply with conventional radiography, such as osteogenic sarcoma or multiple myeloma. Osteogenic sarcoma is malignant tumour that shows with people below the age of 40 and radiographically can be seen as extensive bone formation, also described as ‘cloudy appearance’. Multiple myeloma, also known as plasmacytoma, is the most common primary bone neoplasm in the elderly, above the age of 40 years (Girish et al., 2012). Such radiographic appearances can be variable, so they can appear as punched-out lytic bony lesions or osteopenia (Girish et al., 2012).

Images of pelvis and hips can also help detect conditions such as sacroiliitis – inflammation of sacroiliac joints, hip dislocations and ankylosing spondylitis which causes stiffness of the spine or sacroiliac joints (Krans, 2017). Furthermore, pelvic X-ray images are also usually required in preoperative hip surgical planning and also after surgery for follow-up of total hip replacement (Chiron et al., 2017). However, in recent years many orthopaedic surgeons prefer AP pelvic images to be undertaken in erect position, since this provides a greater indication of the functional position of acetabular coverage and joint appositions (Yang et al., 2019).

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1.3 Patient positioning for erect pelvic radiography

Erect pelvic radiography is performed in the AP projection with the patient standing in front of the wall stand so that his/her lower back is in contact with the surface of the image detector. The arms are placed across the chest, out of the region of interest (ROI) (Lipovec et al., 2016). The patient's legs are extended and rotated inward 15-20 degrees so that the feet are positioned so that the toes are touching, and the heels are approximately 20-24 cm apart. The rotation of the legs is important to overcome the normal anteversion of the femoral necks so that their longitudinal axes are parallel to the detector (Ahmad, 2003).

From the surgeon's point of view, this position is significant for assessing the femoral neck angle, lateral hip offset and for comparison with the unaffected hip (Shaikh, 2018).

The midsagittal plane of the patient's body is parallel to the detector and centred on its midline. The pelvis should not be rotated, the distance from the surface of the wall stand detector to each anterior superior iliac spine is equal (Ahmad, 2003).

The central ray lies midway between the anterior superior iliac spine and the pubis symphysis. Laterally, the collimation extends to the skin margins, superiorly about 2.5 to 3.8 cm above the iliac crests, and inferiorly to the proximal third of the thigh (Lampignano, Kendrick, 2017).

Anatomical structures that should be shown on the pelvic X-ray (Figure 2) are both hip bones (ossa coxae), the fifth lumbar vertebra (vertebra lumbalis V), and the sacrum with the intervening joint, the coccyx (os coccygis), both sacroiliac joints (articulation sacroiliaca), the head of the femur (caput femoris), the neck of the femur (collum femoris), greater and lesser trochanters (trochanter majus et minus) and proximal third of the body of the femur (Lipovec et al., 2016).

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Figure 2: Optimal AP erect pelvic X-ray (Community Health Centre Ljubljana - unit Centre, 2020).

1.4 Radiographic technique for AP pelvis radiography

The recommended radiographic technique for pelvic radiography in the AP projection has been described in the literature (European Commission, 2004) :

 Grid table or vertical stand with moving grid should be used as radiographic device.

 Nominal focal spot value should be 1.3 mm or less.

 Total filtration should be 3 mm of aluminium or more.

 The anti-scatter grid with ratio 10 and 40 lines/cm should be used.

 Source to image distance should be 115 cm - it can also vary between 100 and 150 cm.

 Tube potential should be between 75 to 90 kV.

 Automatic exposure control with central chamber should be used.

 Exposure time should be 400 ms or less.

It should be noted that these criteria (European Commission, 2004) were developed in a film-screen era and are based on the opinion of an expert committee. To the author’s knowledge, there are no other more recent recommendations which address the above limitations.

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1.5 Image criteria

The goal of any radiographic examination is to obtain an optimal radiographic image of an organ or organ system that can be evaluated according to certain standards, also called image quality criteria. General and specific criteria are used to assess the quality of radiographic images. General criteria are used to evaluate all images, regardless of the anatomical structure on the image. This is used to evaluate the photographic (contrast) and geometric properties of the images (spatial resolution, noise, and size distortion), the absence of artefacts, the radiographic projection and the anatomical side of the body, and the patient's identification data (Lipovec et al., 2016).

Using specific criteria, radiographic practitioners evaluate each projection independently, depending on the area of interest and the importance of the anatomy that needs to be depicted on the resultant X-ray image (Lipovec et al., 2016). According to Mraity et al. (2016) the optimum image quality criteria for an AP pelvis projection should include adequate visualisation of the left and the right hip joints, the greater and lesser trochanters, iliac crests, femoral necks and sacroiliac joints. The pubic and ischial rami should also be adequately visualised and so does the sacrum and its intervertebral foramina. The proximal femora should be demonstrated adequately. As for the technical and positioning related items there should be appropriate differentiation between soft tissues, use of correct exposure factors, the image should be sufficient for diagnostic purposes, the medulla, the cortex of the pelvis and the body of fifth lumbar vertebra should be adequately demonstrated, the obturator foramina should be symmetrical, both acetabula should be visualised clearly, the rotation and axial tilting should be within acceptable limits and fine bony detail should be sufficiently demonstrated (Mraity et al., 2016).

1.6 Radiation dose in plain pelvic radiography and comparison of erect and supine pelvic imaging

Medical imaging has become an indispensable part of healthcare today, as it is used to diagnose diseases and injuries. The rapid growth and expansion of diagnostic imaging over the past two decades is a good thing, as it means that imaging modalities are constantly being developed and used in new ways to benefit patients (Hendee, O’Connor, 2012). However, many of these diagnostic imaging modalities use ionising radiation, and the before

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mentioned expansion of medical imaging has increased radiation exposure to patients worldwide. It is well known that exposure to X-rays poses some risk for the development of cancer or genetic effects, therefore the basic radiation protection concept is ALARA, which means to keep exposure to X-ray examinations As Low As Reasonably Achievable (Aliasgharzadeh et al., 2015). It is important to know and monitor the radiation dose received by patients during radiological examinations in order to estimate the potential harm that may occur to the patients undergoing the examination and use it as an indicator to ensure image quality. With this in mind, radiographers strive to keep radiation doses as low as possible without compromising image quality (Aliasgharzadeh et al., 2015; Mratiy, 2015).

The radiation exposure of patients is estimated using a quantity termed ‘effective dose’

(Zdešar et al., 2000). It is used in radiation protection to calculate the annual radiation exposure of workers and the general public. It does not represent a real radiation dose to an individual, but it is a calculated number that provides an approximate measure of stochastic risk. It is determined by calculating all organ equivalent doses, averaging male and female values, and weighting each organ by a tissue weighting factor. At the end, all double- weighted organ equivalent doses are summed (Fisher, Fahey, 2017). In addition to the effective dose, we also use the skin entrance dose (ESD), which is measured on the patient's skin and is defined as the absorbed dose in the air at the point where the X-ray beam enters the patient's body. It is the sum of the direct X-ray beam and the backscattered radiation from the patient. The contribution due to scattered radiation depends on the imaging technique and the size of the patient - the larger the patient, the higher the scattered radiation (Aliasgharzadeh et al., 2015; Zdešar et al., 2000).

In 2014, the European Union conducted a survey of the population dose from medical imaging, they included 36 countries in their survey, including Slovenia (European Union, 2014). The average effective dose for radiography of the pelvis and hips in Slovenia was 0.52 mSv, while the average for all European countries was 0.71 mSv, with a range between 0.21 and 2 mSv. In addition to comparing the effective doses for the pelvic radiography between countries, the doses for thorax/chest, abdomen, cervical, lumbar and thoracic spine, and mammography were also calculated. The results showed that patients receive the highest doses during radiological examination of the lumbar spine, abdomen and pelvis (European Union, 2014).

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Aliasgharzadeh et al. (2015) reached the same conclusion when they measured ESD in four different hospitals for the eight most commonly performed radiographic examinations, including AP pelvic radiography. They measured a relatively high ESD in patients undergoing pelvic radiography. Within their work hospital ESD measurements were 1.21, 2.89, 2.70 and 2.80 mGy. Compared with the ESD values of other radiographic examinations, only abdominal and lumbar spine radiography had higher doses than pelvic radiography. To reduce the absorbed dose, they recommend a large distance between the patient and the X-ray source, a high tube potential and a low tube current, but to this extent to obtain good image quality (Aliasgharzadeh et al., 2015). Kloth et al. (2015) suggest acquiring pelvic X-ray images with a reduced radiation exposure, they compared pelvic images obtained with digital radiography (DR) using a 400 exposure class (recommended for skeletal X-rays) and 800 (reduced dose). Exposure class is similar to speed class, which was traditionally used with film-screen systems. The results showed reduced radiation exposure by 42% in comparison to standard radiation dose, without affecting image quality.

Alzyoud (2019) performed a study in which she compared radiation dose and image quality between supine and erect AP pelvic projections. Within this work AP thickness increased by 13%, 24% and 19% in the upright position for normal, overweight, and obese patients respectively, based on BMI classification groups, when changing supine and erect positions.

The dose-area product (DAP) also increased in the erect position. In the normal-weight group, DAP increased by 42% but was not statistically significant, although there were statistically significant differences in overweight and obese patients, where DAP increased by 55, and 105%, respectively. Changing from the supine to erect position also increased the whole-body absorbed dose by 40%, 50%, and 92% in the normal, overweight, and obese BMI groups, respectively. The effective dose was 38% higher in normal weight patients, 65% higher in overweight patients, and 120% higher in obese patients. The dose results for the normal BMI group of patients were not statistically significant, but for the other two BMI groups they were.

Image quality decreased by 6% in normal-weight patients, 10% in overweight patients, and 15% in obese patients. These results were all statistically significant. Also, the visualisation of the sacrum and sacroiliac joints was worse in the erect position (Alzyoud, 2019). The reason for the decrease in image quality in patients with higher BMI is that as body fat

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increases, the attenuation of the X-ray beam leads to increased noise and lower contrast resolution (Modica et al., 2011).

The study by Alzyoud (2019) also reported statistically significant differences between the supine position and erect AP pelvic position in terms of patient thickness, as AP thickness increased by 16% when moving from the supine to erect position. Based on the patient thickness Metaxas et al. (2018) also reported a lower effective dose in the supine projection during radiography of the abdomen, lumbar spine, and pelvis because in the supine position some of fat tissue shifts laterally, but in the upright position the fat tissue descends and increases AP thickness due to gravity.

Pelvic radiography is commonly used for clinical decision making, including diagnosis, observation, and prediction of developmental dysplasia of the hip (DDH). The position of the patient during this examination is very important in the diagnosis of DDH, as it can influence the information on the image. However, most hospitals tend to take images of the pelvis in the supine position, but these images may differ compared to those taken in the erect position (Fuchs-Winkelmann et al., 2008; Troelsen et al., 2008).

A study by Troelsen and colleagues (2008) was undertaken comparing supine and erect images in patients with DDH. They looked for differences between these two imaging projections in terms of pelvic tilt, joint space width and radiographic parameters of dysplasia, such as centre edge angle and acetabular index. Based on their findings, they recommend AP pelvic images, which should be taken in erect position to best evaluate hip deformities because people, especially young adults with hip deformities, notice symptoms during activities such as running, walking, or jumping. These types of images are most relevant for diagnostic and preoperative evaluation because they provide the best match between hip deformities, symptoms, and functional appearance. Using supine projection in patients with DDH risks misdiagnosing the patient as having acetabular retroversion, which may lead to unnecessary acetabular realignment surgery, resulting in a possible worse outcome for the patient (Troelsen et al., 2008).

Fuchs-Winkelmann et al. (2008) also conducted a study comparing radiographic angle and signs of hip osteoarthrosis (OA) on erect and supine pelvic images in patients with long-term follow-up after closed reduction of the DDH. Their results showed that there was no difference between erect and supine images when evaluating the depth of the acetabulum

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(ACM angle), while the acetabular roof slope (AC angle) was greater, the centre-edge angle was smaller, and the minimum joint space width was smaller in images taken in erect position. These results led to the conclusion that erect pelvic radiography is more accurate than supine radiography in assessing minimum joint space width.

Pullen et al. (2014) investigated the variability of acetabular coverage in images of the pelvis in the supine and erect positions in patients with femoroacetabular impingement (FAI). They reported that changing the pelvic tilt when taking AP supine pelvic X-ray just to meet the standards for adequate supine radiography may artificially affect the screening characterization of the acetabular deformity, meaning that supine pelvic images may not represent the true, functional, erect position of the acetabulum when impingement is involved. Other authors also concluded in their studies (Jackson et al., 2016;

Ross et al., 2015) that the functional position of the pelvis during radiography may influence the signs on the image when evaluating pincer impingement, and if these changes are not appreciated when diagnosing and treating patients with FAI, it may lead to choosing the wrong treatment pathway and poor outcomes later on. Jackson et al. (2016) also reported the results of their study showing a decrease in pelvic tilt on images taken in erect position that corresponded with a lower incidence and severity of radiographic signs of pincer impingement, such as a decreased ischial spine sign, the presence of a crossover sign, and even a small increase in acetabular tilt.

1.7 Plain pelvic radiography in obese patients

Since 1975, global obesity has nearly tripled, reports the World Health Organization (2020).

In 2016, more than 1.9 billion adults aged 18 years and older were overweight and more than 650 million of them were obese (World Health Organization, 2020). In Slovenia, 58.1% of the adult population aged 18 years and older is considered overweight or obese (Statistical Office of the Republic of Slovenia, 2020). Overweight and obesity are defined as excessive fat accumulation that can have harmful effects on health. To determine the nutritional status in adults, we use the classification of body mass index (BMI). It is defined as a person's weight in kilograms divided by their height in meters squared. The BMI classification is divided into six groups based on the effect of excessive body fat on health and well related to obesity (Table 1). This classification was developed as a risk indicator for disease, i.e. as BMI increases, so does the risk of disease (World Health Organization/Europe, 2021).

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Table 1: BMI classification (World Health Organization/Europe, 2021) BMI Nutritional status

Below 18.5 Underweight

18.5–24.9 Normal weight

25.0–29.9 Overweight

30.0–34.9 Obesity class I 35.0–39.9 Obesity class II Above 40 Obesity class III

Radiologic examination of obese patients requires a tailored standard of care, as radiographers need to adjust the procedures based on issues arising from both technical and patient care, such as patients exceeding imaging equipment weight limits, potential motion artefacts due to increased exposure parameters that also increase exposure time, inadequate image detector coverage, and difficulty palpating anatomic landmarks. It also compromises the balance between adequate radiation exposure and minimizing dose (Le et al., 2015).

Previous studies (Efthymiou et al., 2020; Zalokar et al., 2020; Metaxas et al., 2018; Chan et al., 2012; Yanch et al., 2009), investigated the effect of BMI on the radiation dose received in overweight and obese patients. These studies reported an increase in the radiation dose received by these patient groups when compared to those with normal weight, taking into account BMI classification. Chan et al. (2012) found in their study that for each kilogram of weight, there was an increase in effective dose for computed tomography (CT) of the abdomen and pelvis of 0.13 mSv, equivalent to 6.5 chest X-rays per CT examination, and for an increase in BMI of 5 kg/m², there was an increase in effective dose of 1.95 mSv, equivalent to 97.5 chest X-rays per CT examination.

Zalokar et al., 2020 report that in their research, during pelvic AP X-ray examination, DAP increased in a group of overweight patients for 52% and for 135% in a group of obese patients in comparison to the group of patients with normal weight. The increase of effective dose was 46% in overweight patients and 123% in obese patients, both compared to the normal-weight patients. The increase of dose on individual organs was similar to the effective dose, 37% and 107%, respectively. They found image quality differences between normal and overweight group of patients, but not between groups of normal and obese or overweight and obese patients. They also concluded that DAP and effective dose are strongly

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related to BMI and that BMI has a very strong effect on the dose received by the patients during X-ray imaging, so the patients with higher BMI can receive several times higher dose than those with normal body weight (Zalokar et al., 2020).

Alzyoud et al. (2019) performed a study on an anthropomorphic phantom to estimate how increasing body thickness affects radiographic quality and effective dose during pelvic imaging. Within this work the authors simulated fat on the aforementioned phantom, by using commercially available catering lard. The results showed that it is important to adjust the exposure parameters when performing pelvic X-ray examinations in obese patients. They found that the best image quality was obtained when using a tube potential of 70 kV at all fat thicknesses, while when using high tube potentials, 105 and 110 kV, the quality of the X-ray image decreased by about 68%. The effective dose was increased by 856% at 15 cm fat thickness at 80 kV. At 110 kV, the effective dose was lowest for all thicknesses. For all thicknesses used, there were characteristic differences in effective dose when different tube potentials were used, such that the radiation dose increased exponentially with increasing thickness of the imaging object. Acceptable image quality was achieved with a range of imaging parameters, but the optimal tube potential was reached at 70 and 75 kV for all fat thicknesses. This is actually contrary to professional practice, where radiographers usually tend to increase the tube potential with increasing patient thickness. However, the authors suggest that if the primary factor is radiation dose, higher tube potential could be used in pelvic radiography as patient thickness increases (Alzyoud et al., 2019).

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2 PURPOSE

The purpose of this study is to determine whether the radiation dose and image quality differ between two different erect pelvic radiographic procedures, with and without fat tissue removal. Based on the above, this study seeks to determine how much of a difference there is between the radiation doses received by the patient and how does the tissue removal technique affect the resultant images based on established image quality criteria. This study will compare the acquired images and the radiation doses received between patients who will move the fat tissue from the region of interest (pelvis) and those who do not.

Based on the literature review the following research questions have been established:

Q1: How does fat tissue removal during erect pelvic imaging affect the resultant dose area product?

Q2: How does fat tissue removal during erect pelvic imaging affect the patient's entrance skin dose?

Q3: How does fat tissue removal during erect pelvic imaging affect the patient’s effective dose?

Q4: How does fat tissue removal during erect pelvic imaging affect image quality?

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3 METHODS

The measurements were divided into two parts. In the first part, measurements were performed on an anthropomorphic phantom, and in the second part, the experimental methods were performed on 60 patients referred for pelvic imaging in the erect position. The participants were randomly divided into two equal groups, half of them where imaged removing the fat tissue from the region of interest (n=30) and the other group did not remove the tissue from the ROI (n=30).

The exact sample size was calculated based on a preliminary result using the GPower 3.1 analysis tool. The calculated total number of patients was 56, with 28 participants in each group. Based on the calculated sample size, this study has a power of 95% to detect a difference in image quality and doses received between two groups of patients.

3.1 Phantom Study

The measurements were performed in the radiography lab at the Faculty of Health Sciences in Ljubljana on a Siemens Multix/Vertix unit. Standard quality assurance (QA) testing was performed on the equipment prior to the start of the phantom study. The results of the QA tests were within expected tolerances, this was interpreted to mean that the equipment was working correctly.

Siemens Multix/Vertix unit has an option of selecting two different focal points; small (0.6 mm) and large (1.0 mm). In our study, a large focal point was used, which is recommended for large body parts as they require higher exposures and consequently greater tube loading so the heat is distributed over a larger area of the anode, to minimize the X-ray tube damage (Gorham, Brennan, 2010). The total filtration was 2.5 mm of aluminium, and an additional filtration of copper could be added (0.1, 0.2 or 0.3 mm Cu). The additional filtration we used in our phantom study was 0.1 mm copper. We did not vary between different filtrations because in clinical practice, where the patient study was performed, this type of filtration is only used for pelvic radiography.

Optimal exposure parameters were used based on the European Guidelines for Digital Detectors in the DIMOND 3 project (European Commission, 2004). These

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recommendations from European Commission, 2004 are compared in Table 2 with the parameters we used in this part of the study. Our study was performed on the vertical stand at a SID of 150 cm, the antiscatter radiation grid was used focused at 115 cm, as this was the only grid available. The antiscatter grid ratio was 13 with 70 lines/cm. The European Commission, 2004 allows a source to image distance of 150 cm for pelvis X-ray, as the evidence suggests that increasing SID results in reduction of effective and entrance skin dose of the patients (Tugwell et al., 2014). Total filtration was 2.5 mm of aluminium and the additional filtration was 0.1 mm of copper. The nominal focal spot value was 1 mm. The cathode of the X-ray tube was positioned towards the legs and the anode was positioned towards the abdomen, however differences in anode heel orientation were no evaluated in the phantom study, because of the tube’s position which is not changeable. The tube potential was 81 kV and the AEC was selected using both side chambers, this was because there it is generally the lowest dose measured (Kim et al., 2015). The central AEC chamber was positioned head away from the outer two. This radiographic technique was chosen based on the protocol for pelvic radiography of the health care centre where the patient study was performed. In the phantom study Agfa CR plates with a size of 35 cm × 43 cm were used as image receptors. Even though in the facility where clinical acquisitions were performed digital radiography is used, CR was used for the phantom study as DR was not available.

Table 2: Comparison of suggested parameters for digital pelvic radiography (European Commission, 2004) and parameters we used in phantom study on Siemens

Multix/Vertix Unit Suggested parameters for digital pelvic radiography

Siemens Multix/Vertix Unit (computed radiography) Radiographic device Vertical stand or table with

moving grid

Vertical stand with moving grid

Nominal focal spot ≤ 1.3 mm 1 mm

Total filtration ≥ 3 mm Al 2.5 mm Al

Anti-scatter grid r=10; 40 lines/cm r=13; 70 lines/cm Source to image distance 115 cm (it can vary between

100-150cm) 150 cm

Tube potential 75 – 90 kV 81 kV

AEC chambers Central chamber Lateral chambers

Exposure time < 400 ms < 400 ms

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A patient was simulated using the pelvic and lumbar spine phantom RS -113T (Radiology Support Devices, California, USA), which has the same absorption coefficient as a person with a height of 175 cm and a weight of 74 kg. To simulate the first stage of obesity on a phantom, fat equivalent material was added. In our case, we used commercially available catering lard, which we wrapped in cling film, and we also used the cling film to wrap around the phantom to secure the lard to it. The thickness of the lard was 8 cm, the length was approximately 30 cm (the width of the phantom at the pelvic region), and the height was 13 cm (the height of the studied anatomical region on the phantom). We collected bands of different materials - a rubber training band, a cotton cloth folded into a band, an elastic cotton bandage, and a thin triangular cotton bandage. We used these bands to test which one would not produce visible artefacts on the images. We placed the phantom with attached fat anteriorly in front of the wall stand detector - the posterior surface of the phantom was facing the wall stand. We then selected one of the tapes and lifted the fat out of view as much as possible. We attached both sides of the tape to the handles on the left and right sides of the wall stand to ensure that the tape remained in the same position during imaging.

One of the key objectives of the phantom study was to determine which band was radiolucent and did not produce artefacts on the resultant X-ray image when displacing fat tissue from the area of interest.

3.2 Patient Study

In this part of the study we investigated whether image quality and radiation dose differed between the two different types of pelvic radiography in erect position - with and without fat tissue removal.

The second part of the study was conducted at Community Health Centre Ljubljana - unit Centre, from March 2020 to November 2020. The study was performed on 60 patients. We included patients who were ≥18 years old, those with a BMI of ≥25, they had to be referred for the erect pelvic radiography and those who signed the consent form. All of the inclusion criteria had to be met, otherwise patients were excluded from the study. A randomization program built into Microsoft Excel was used to determine which patients were imaged normally - without fat tissue removal and with which ones were imaged with a radiotransparent band to remove fat tissue from the ROI as much as possible. The patient

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held the band with both hands and lifted the soft tissue out of the field of view and with this tissue removal procedure the thickness of the patient in the part of ROI decreased. Waist and hip circumference were measured by placing the tape measure around the patient's waist at the level of the upper edge of the iliac crest and around the hips at the level of the trochanters.

The measurements were taken without the removal of the fat tissue and with removal of the fat tissue and for the patients who did not move the fat tissue during imaging we measured waist and hip circumference once. Measurements of dose area product, field size at the image receptor, source-to-skin distance, tube current and exposure time product (mAs), tube potential (kV) and patient height and weight were also recorded. Based on patients’ height and weight measurements BMI was calculated using the following formula:

𝐵𝑀𝐼 = 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑘𝑔) ℎ𝑒𝑖𝑔ℎ𝑡 (𝑚)²

Before we started this part of the study, we obtained a permission at the Community Health Centre Ljubljana - unit Centre from the Head of Radiographers Mrs. Martina Dolšak; the Head of Radiology, Mrs. Vanja Kos, and the medical director Mrs. Tea Stegne Ignjatovič;

the approval was received on November 13, 2019 (Appendix 8.3). Lastly the approval from the National Medical Ethics Committee was obtained on January 14th, 2020 (Appendix 8.4).

Research acquisition on patients were carried out using a Siemens Axiom Aristos FX Plus unit. Before starting the patient study routine QA testing was performed, and the results fell within expected tolerance.

The total filtration we used was 2.5 mm of aluminium, and the additional filtration was 0.1 mm of copper, grid ratio 15:1 with 80 lines/cm and SID was 150 cm. The image detector is DR amorphous silicon digital flat panel detector size of 43 cm × 43 cm. The central AEC chamber was positioned head away from the outer two, and the lateral ones were selected for pelvic imaging. The cathode of the X-ray tube was above the anode, that means the anode heel orientation was considered, as the cathode was on the thicker side of the body (towards the abdomen) and the anode was positioned towards the legs. The tube potential varied based on patient thickness. If the patient was obese, the tube potential was increased based on their body thickness – the greater the thickness, the higher the tube potential, but not higher than 96 kV. Even if the tube potential varied, on average 81 kV was used. The proposed parameters and the parameters used in this part of the study are compared in Table 3.

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Table 3: Comparison of suggested parameters for digital pelvic radiography (European Commission, 2004) and parameters we used in patient study on Siemens Axiom Aristos FX

Plus Unit

Suggested parameters for digital pelvic radiography

Siemens Axiom Aristos FX Plus Unit

(digital radiography) Radiographic device Vertical stand or table with

moving grid

Vertical stand with moving grid

Nominal focal spot ≤ 1.3 mm 1 mm

Total filtration ≥ 3 mm Al 2.5 mm Al

Anti-scatter grid r=10; 40 lines/cm r=15; 80 lines/cm Source to image distance 115 cm (it can vary between

100-150cm) 150 cm

Tube potential 75 – 90 kV 81 – 96 kV

AEC chambers Central chamber Lateral chambers

Exposure time < 400 ms < 400 ms

Radiation dose was measured using a DAP meter built into the X-ray unit. We then calculated the entrance skin dose (ESD) received by the patients from the tube output using the following formula (International Atomic Energy Agency, 2007) :

𝐸𝑆𝐷 = 𝐵𝑆𝐹 ∗ 𝑌(𝑑) ∗ (100 𝑆𝑃𝐷)

2

∗ 𝐼𝑡

BSF is the backscatter factor, Y(d) means the tube output per mAs measured at a distance of 100 cm. BSF for every patient was 1.4. SPD is the distance between source and patient in cm, and the It is the tube current-time product. SPD and tube current-time product were, based on measurements, different for each patient. To measure Y(d) - the tube output, we placed the dosimeter on the table in the centre of the X-ray beam at a distance of 100 cm from the source to dosimeter. The exposure parameters were set to 10 mAs while we were changing the tube voltage, because we had to measure the tube output for each value of tube potential was used in the patient study. That means we noted the tube output after we took the exposure at 10 mAs and a certain value of kV. After each exposure, we changed the tube

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voltage, but the mAs remained fixed. The tube output varied according to the tube potential we used during patient study and is presented in Table 4.

Table 4: Measured tube output for each value of tube potential Tube potential Tube output Y(d)

81 kV 56.9 μGy/mAs

83 kV 59.5 μGy/mAs

85 kV 62.7 μGy/mAs

87.5 kV 65.7 μGy/mAs

90 kV 69.7 μGy/mAs

96 kV 78.9 μGy/mAs

3.2.1 Effective dose calculation

The effective dose and organ doses were calculated using the PCXMC software (Radiation and Nuclear Safety Authority, Helsinki, Finland). PCXMC uses Monte Carlo calculating method for calculating organ and effective doses of patients in medical X-ray examinations.

The Monte Carlo method mathematically simulates interactions between photons and matter, where photons are emitted from a source into the angle, which is specified by the focal distance and the field size. The photons are followed while they interact with the phantom simulated in the program, according to the probability distributions of the physical process that may happen: photo-electric absorption, coherent scattering or Compton scattering. For each interaction, the energy deposition to the organ is calculated and stored for dose calculation. The effective dose is calculated with the present tissue weighting factors of ICRP Publication 103 (2007) and the old tissue weighting factors of ICRP Publication 60 (1991) (Tapiovaara, Siiskonen, 2008).

When calculating effective dose with PCXMC software, the height and weight for each patient was used. Following this, the program generated a graphical representation of the simulated object in the AP projection. To generate an appropriate X-ray beam spectrum, the Monte Carlo simulation software needed data on the tube potential, number of photons, source to image distance and field size for each patient. For the project, to facilitate calculation of effective dose, the tube potential, anode angle, beam filtration we used together within individual DAP exposure values.

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3.2.2 Image quality evaluation

The obtained X-ray images were evaluated using the ViewDEX software (Sahlgrenska University Hospital, Göteborg, Sweden). ViewDEX (Viewer for Digital Evaluation of X- ray Images) is a software that allows evaluation of digital images. It displays X-ray images along with the image quality criteria scale. The person who is evaluating X-rays selects the number or a letter on a scale that suits their image quality judgement. All of their choices are stored in a log file (Svalkvist et al., 2021).

The images we obtained were evaluated by three radiologists with more than five years of experience. For assessment we used a four-step scale with the numbers from 1 to 4, where number 4 means perfect/optimal image, 3 means good image, 2 moderate image (acceptable for diagnostic purposes) and 1 inadequate image. The radiologists were blinded to whether each image was acquired with or without fat tissue removal.

The images were evaluated according to the following image quality criteria for pelvic radiography (Alzyoud et al., 2019):

 visualisation of hip joints,

 visualisation of trochanters,

 visualisation of sacroiliac joints,

 visualisation of iliac crests,

 visualisation of acetabula,

 visualisation of pubic/ischial rami,

 visualisation of femoral necks,

 visualisation of medulla and cortex of the pelvis,

 visualisation of sacrum and its foramina,

 visualisation of pelvic/hip soft tissues.

After image evaluation scores were received from the radiologists, the average score was calculated for each criterion for each image, so that every image had one average score for each of the criteria. The total score of each image was calculated by adding all image criteria average scores for every evaluated image.

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3.2.3 Statistical analysis

Data were analysed using SPSS version 25 (IBM Inc, Armonk, New York). We proposed to use the Shapiro-Wilk test to determine the normal distribution of all data. For normally distributed data on patient measurements, the T-test for independent samples was used and paired samples T-test was used for dependent data, while the Mann-Whitney U-test was used for independent non-normally distributed data and Wilcoxon test was used for dependent non-normally distributed data. To estimate reliability of the radiologists we used Cohen’s Kappa coefficient. Results are presented with tables and graphs. The significance of p<0.05 was used for all the tests.

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4 RESULTS

In this chapter the results of the research are presented. In the first part, the results of the phantom study will be reported in which the appropriate type of displacement band that is best suited for removing fat tissue from the area of interest during erect pelvic radiography.

It was important that the band did not cause artefacts on the images. In the second part of this chapter, the results of the patient study which compared the image quality ratings and radiation doses received between patients who had the fat tissue removed from the field of view during erect pelvic radiography and those who did not were reported.

4.1 The results of the band comparison (phantom study)

Four bands made of different materials were evaluated. The aim was to test which one was superior in the removal of fat tissue and did not cause any artefacts on the image. A rubber exercise band, a cotton cloth folded into a band, an elastic cotton bandage, and a thin cotton triangular bandage were compared (Figure 3). Four images were acquired, one for each band.

Figure 3: A rubber exercise band (upper left corner), a cotton cloth folded into a band (upper right corner), an elastic cotton bandage (lower left corner) and a thin cotton

triangular bandage (lower right corner)

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Members of the research team (student and supervisors) were responsible for visually evaluating the level of soft tissue displacement and the presence of any related image artefacts. Each band was deemed by consensus adequate to move the simulated fat tissue from the pelvic area, but only one did not show any artefacts on the radiographic image. The cotton cloth folded into the band was most visible on the image. An exercise rubber band and an elastic cotton bandage also caused visible artefacts on the image, but not as much as a cotton cloth. Finally, a thin cotton triangular bandage did not show any visible artefacts, so this was used for the second part of the study.

4.2 The results of the patient study

This part of the study was carried out on 60 patients, of whom 34 were women and 26 men.

The average ± SD age was 67 ± 11 years. The mean ± SD age of the females was 68 ± 12 years and that of the males 67 ± 11 years.

Patients were randomly divided into two equal groups. One half of the participants were in a group where they had to move the fatty tissue from the ROI during the pelvic imaging. For this, they used a thin cotton bandage, which was deemed in the phantom study as the most suitable for lifting the soft (fat) tissue and least visible. Meanwhile, the patients in the second group did not move the tissue away during erect pelvic radiography.

4.2.1 Calculated body mass index of the patients

Out of 60 patients, 22 (36.7%) were overweight according to the BMI classification, 34 (56.7%) had class I obesity and 4 (6.7%) of them had class II obesity. In the group where participants did not have to move fat tissue, the average ± SD BMI was 30.8 ± 3.0 and in the other group where the tissue was moved, the average ± SD BMI was 31.0 ± 2.7. The statistical analysis of body mass index between two inspected groups is shown in Table 5.

Table 5: Statistical analysis of BMI for group of patients with and without fat tissue removal

Group n Mean ± SD. Median Min. Max. p-value Without tissue removal 30 30.8 ± 3.0 31.2 25.5 36.6 0.790

With tissue removal 30 31.0 ± 2.7 30.7 27.2 38.8

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The difference between the compared groups according to BMI values is minimal (0.6%).

Using the T-test for independent samples, it was found that there was no statistically significant difference in BMI between the patients who removed fat tissue and those who did not (p=0.790). The graphical representation of the distributed data within the groups is shown in Figure 4.

Figure 4: Distributed BMI values in groups divided by tissue removal

4.2.2 Measured waist and hip circumference of the patients

In the group of patients with the fat tissue removal, measurements of waist and hip circumference were taken twice, i.e., the first time before and the second time after tissue removal. In the other group, measurements were taken only once. The average ± SD waist circumference in that group was 112.9 ± 7.4 cm and hip circumference was 108.7 ± 7.2 cm (Table 6). Patients who had to remove fat tissue during imaging had mean ± SD waist and hip circumferences of 111.7 ± 5.3 cm and 105.6 ± 6.1 cm, respectively. Raising fat tissue from the region of interest decreased waist circumference to an average of 106.4 ± 5.2 cm, but hip circumference did not change (105.5 ± 6.0 cm). Waist thickness decreased by 4.7%

and hip thickness by 0.1%. The main statistical analysis is shown in Table 7.

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Table 6: Statistical analysis of waist and hip circumference between both groups of patients

Circumference n Mean ± SD. Median Min. Max. p-value Waist – without removal 30 112.9 ± 7.4 113 101 126 0.459

Waist – with removal 30 111.7 ± 5.3 111 101 125

Hips – without removal 30 108.7 ± 7.2 109 95 121 0.077 Hips – with removal 30 105.6 ± 6.1 104 93 118

Using the independent samples T-test there were no statistically significant differences between waist (p=0.459) or hip circumference (p=0.077) of the patients who removed fat tissue during imaging and those who did not.

Table 7: Statistical analysis of waist and hip circumference before and after fat tissue removal

Circumference n Mean ± SD. Median Min. Max. p-value Waist – before removal 30 111.7 ± 5.3 111 101 125 p<0.001

Waist – after removal 30 106.4 ± 5.2 106 95 119

Hips – before removal 30 105.6 ± 6.1 104 93 118 0.211 Hips – after removal 30 105.5 ± 6.0 104 93 118

Using paired samples T-test, it was found that waist circumference before and after tissue removal was statistically different (p<0.001), as the thickness decreased by 4.7%, while hip circumference before and after removal was not statistically different (p=0.211).

4.2.3 Primary field size measurements in patients

The primary field size was measured in all patients. The mean ± SD field size in the group of patients without tissue removal was 1600.6 ± 144.6 cm² and in the group with fat tissue removal was 1604.3 ± 113.4 cm². The rest of the statistical analysis is shown in Table 8.

Table 8: Statistical analysis of primary field size for group of patients with and without fat tissue removal

Group n Mean ± SD. Median Min. Max. p-value Without tissue removal 30 1600.6 ± 144.6 1583.6 1276.8 1831.8 0.743

With tissue removal 30 1604.3 ± 113.4 1583.6 1373.9 1831.8