The Impacts of Vertical Off-Centring, Localiser Direction, Phantom Positioning and Tube Voltage on CT Number Accuracy: An Experimental Study.

Background: This study investigates the effects of vertical off-centring, localiser direction, tube voltage, and phantom positioning (supine and prone) on computed tomography (CT) numbers and radiation dose. Methods: An anthropomorphic phantom was scanned using a Discovery CT750 HD­128 slice (GE Healthcare) scanner at different tube voltages (80, 120, and 140 kVp). Images employing 0° and 180° localisers were acquired in supine and prone positions for each vertical off-centring (±100, ±60, and ±30 mm from the iso-centre). CT numbers and displayed volume CT dose index (CTDIvol) were recorded. The relationship between dose variation and CT number was investigated. Results: The maximum changes in CT number between the two phantom positions as a function of vertical-off-centring were for the upper thorax 34 HU (0° localiser, 120 kVp), mid thorax 43 HU (180° localiser, 80 kVp), and for the abdominal section 31 HU (0° localiser, 80 kVp) in the prone position. A strong positive correlation was reported between the variation in dose and CT number (r = 0.969, p < 0.001); 95% CI (0.93, 0.99). Conclusions: Patient positioning demands an approach with a high degree of accuracy, especially in cases where clinical decisions depend on CT number accuracy for tissue lesion characterisation.

Variation in digital breast tomosynthesis image quality at differing heights above the detector.

INTRODUCTION: The aim of this preliminary work was to determine if image quality in digital breast tomosynthesis (DBT) changes when tomosynthesis image slices were obtained at differing heights above the detector and in differing breast thicknesses. METHODS: A CIRS Model 020 BR3D breast imaging phantom was used to obtain the DBT images. The images were also acquired at different tube voltages, and each exposure was determined by the automatic exposure control system. Contrast-to-noise ratio (CNR) and figure-of-merit (FOM) values were obtained and compared. RESULTS: At a phantom thickness of 5 cm or greater, there was a significant reduction (P ≤ 0.05) of image CNR values obtained from the images near the top of the phantom to those obtained near the bottom of the phantom. When the phantom thickness was 4 cm, there was no significant difference in CNR values between DBT images acquired at any height in the phantom. FOM values generally showed no difference when images were obtained at differing heights above the detector. CONCLUSION: Image quality, as measured by the CNR, was reduced when tomosynthesis slice image heights were at the top of the phantom and when the thickness of the phantom was more than 4 cm. From this preliminary work, clinicians need to be aware that DBT images obtained near the top of the breast, when breast thickness is greater than 4 cm, may have reduced image quality. Further work is needed to fully assess any DBT image quality changes when images are obtained near the top of the breast.

0° vs. 180° CT localiser: The effect of vertical off-centring, phantom positioning and tube voltage on dose optimisation in multidetector computed tomography.

INTRODUCTION: Patient positioning is an essential consideration for the optimisation of radiation dose during CT examinations. The study objectives seek to explore the effects of vertical off-centring, localiser direction (0° and 180°), and phantom positioning (supine and prone) on radiation dose, using three different tube voltages in multidetector computed tomography (MDCT) imaging. METHODS: The trunk of a PBU-60 anthropomorphic phantom was imaged using a Discovery CT750 HD - 128 slice (GE Healthcare). Images employing 0° and 180° localisers were acquired in supine and prone orientation for each combination of vertical off-centring (±100, ±60 and ±30 mm) and different tube voltages (80, 120 and 140 kVp), using the system's automatic tube current modulation (ATCM) function. The displayed volume CT dose index (CTDIvol ) and dose length product (DLP) were recorded. RESULTS: With incremental table off-centring of ±100 mm, the dose at 120 kVp in the supine position ranged from 63% to 196% (0° localiser) and from 66% to 191% (180° localiser) as compared to iso-centre. While in the prone position, the dose ranged from 62% to 195% (0° localiser); and 62% to 193% (180° localiser), with a notable dose increase at higher tube voltages. Dose variation and vertical off-centring showed a significant relationship for both 0° and 180° localisers (r = 0.94 and 0.96, respectively, P < 0.001). The CTDIvol variation between supine and prone phantom positions at ±100 mm off-centring was 0.22 mGy (2.9%), and 0.19 mGy (2.3%) when the 0° and 180 ° localisers were utilised, respectively. CONCLUSIONS: Phantom off-centring and localiser direction evidenced large dose variation. It is recommended that the 0° localiser is employed during CT examinations, in order to minimise the potential additional radiation dose which may result from off-centring and the use of lower tube voltages where clinically appropriate.

The reliability of CT numbers as absolute values for diagnostic scanning, dental imaging, and radiation therapy simulation: A narrative review.

BACKGROUND AND PURPOSE: The purpose of this review was to examine the reported factors that affect the reliability of Computed Tomography (CT) numbers and their impact on clinical applications in diagnostic scanning, dental imaging, and radiation therapy dose calculation. METHODS: A comprehensive search of the literature was conducted using Medline (PubMed), Google Scholar, and Ovid databases which were searched using the keywords CT number variability, CT number accuracy and uniformity, tube voltage, patient positioning, patient off-centring, and size dependence. A narrative summary was used to compile the findings under the overarching theme. DISCUSSION: A total of 47 articles were identified to address the aim of this review. There is clear evidence that CT numbers are highly dependent on the energy level applied based on the effective atomic number of the scanned tissue. Furthermore, body size and anatomical location have also indicated an influence on measured CT numbers, especially for high-density materials such as bone tissue and dental implants. Patient off-centring was reported during CT imaging, affecting dose and CT number reliability, which was demonstrated to be dependent on the shaping filter size. CONCLUSION: CT number accuracy for all energy levels, body sizes, anatomical locations, and degrees of patient off-centring is observed to be a variable under certain common conditions. This has significant implications for several clinical applications. It is crucial for those involved in CT imaging to understand the limitations of their CT system to ensure radiologists and operators avoid potential pitfalls associated with using CT numbers as absolute values for diagnostic scanning, dental imaging, and radiation therapy dose calculation.

The recent advances, drawbacks, and the future directions of CMRI in the diagnosis of IHD.

Ischemic heart disease (IHD), also known as coronary artery disease (CAD), is a leading cause of morbidity and mortality in adults. The aims of this research were to study the recent advances on the prognostic and diagnostic value, drawbacks, and the future directions of cardiac magnetic resonance imaging (CMRI) in the diagnosis of IHD. One hundred patients with IHD who had been clinically diagnosed were enrolled in this study prospectively. CMRI; Siemens Magnetom Sola 1.5 T MRI scanner was used to examine the patients. To confirm the diagnosis, conventional coronary angiography was used. CMRI revealed that the left ventricular (LV) volumes and systolic function of male and female patients differed by age decile were 28.9 ± 3.5%; 32 ± 1.7%, 53.3 ± 11.2; 58 ± 6.6 ml, 100.6 ± 7.1; 98.3 ± 14.7 bpm, 5.4 ± 1.4; 5.8 ± 1.5 L/min, 189 ± 14.3; 180 ± 10.9 ml, and 136 ± 3.1; 123 ± 4.4 ml for the left ventricle ejection fraction (LVEF), stroke volume (SV), heart rate, cardiac output, end diastolic volume (EDV), and end systolic volume (ESV), respectively. CMRI has sensitivity, specificity, and accuracy of 97%, 33.33%, and 95.15%, respectively. Finally, CMRI provides a comprehensive assessment of LV function, myocardial perfusion, and viability, as well as coronary anatomy.

Using aluminum for scatter control in mammography: preliminary work using measurements of CNR and FOM.

Full-field digital mammography (FFDM) systems provide the current gold standard in mammographic examinations. Although FFDM provides the lowest mammographic doses, the radiation dose to the breast during mammographic examinations is still a concern. Thus, image quality optimization at the lowest dose is a major goal. In planar X-ray imaging, thin sheets of aluminum (Al) are used as filtration to reduce the number of low-energy X-ray photons reaching the patient. The goal of this work was to evaluate whether Al can be used in FFDM to remove scatter radiation from reaching the image detector, hence improving image quality. Doses were compared with the use of a grid. A Hologic Selenia mammographic unit was used to acquire images of two phantoms, namely, the ACR phantom and a Perspex phantom of 5 cm. Images were acquired using two tube voltages (kVp) and filter combinations under two exposure/dose conditions. Al sheets of various thicknesses were placed between the phantom and the image detector. Contrast-to-noise ratio (CNR) and figure of merit (FOM) values were measured and compared with images acquired using a grid. When a constant dose was delivered to the image detector, the highest CNR was achieved using a grid; however, the highest FOM values were achieved when using 0.05 mm thick Al sheets. This study successfully demonstrates that thin sheets of Al can be used in mammography examinations to reduce scattered radiation and improve image quality, as indicated by the measured CNR values. Given the limitations of this work, further kVp and target/filter combinations and various methods of image quality measurement need to be studied.

Evaluation of radiographers' knowledge and attitudes of image quality optimisation in paediatric digital radiography in Saudi Arabia and Australia: a survey-based study.

INTRODUCTION: Digital radiography (DR) systems enable radiographers to reduce the radiation dose to patients while maintaining optimised image quality. However, concerns still exist about paediatric patients who may be exposed to an increased level of radiation dose which is not needed for clinical practice. The purpose of this study was to evaluate the knowledge, awareness and attitudes, in terms of image quality optimisation of radiographers undertaking paediatric DR in Australia and Saudi Arabia. METHODS: A survey-based study was devised and distributed to radiographers from Australia and Saudi Arabia. Questions focused on Australian and Saudi Arabian radiographers' knowledge and attitude of paediatric DR examinations. RESULTS: There were 376 participants who responded to the survey from both countries. A major finding showed that most participants lack knowledge in the area of paediatric DR examinations. Most participants from Australia had received no formal training in paediatric digital radiography (79%), whereas nearly half of the participants from Saudi Arabia received no training (45%). Approximately three out of four radiographers from both countries believed that when using DR they did not need to change the way they collimate the beam as DR images can be cropped using post-processing methods. CONCLUSION: The finding of this study demonstrates that radiographers from both countries should improve their understanding and clinical use of DR in paediatric imaging. More education and training for both students and clinicians is needed to enhance radiographer performance in digital radiography and improve their clinical practices.

Validity of Using Accreditation Phantom in Quality Control of Digital Tomosynthesis.

AIM: This study was undertaken to compare the two image-quality phantoms commonly used in full-field digital mammography (FFDM) and digital breast tomosynthesis (DBT) imaging. METHODS: Mammography units with two targets and three filters resulting in three possible target/filter combinations and two kVp values which are widely used (28 and 32) were used for the comparison. The automatic exposure control system was used in combination with the selected kVp. The CIRS 15 mammographic accreditation phantom (MAP) and CIRS 20 (BR3D) breast imaging phantom were used with the three target/filter combinations and two kVp values. A total of 24 images were acquired and evaluated. Image score was determined as the smallest sized object detectable. The data were analyzed by using Mann-Whitney test. RESULTS: There were significant (p<0.001) differences between the detectability of fibers present in the two phantoms, but there were no differences in the detectability of specks. CONCLUSION: The finding in FFDM and DBT showed there were significant differences between the two phantoms (p<0.02) in fibers and specks visibility. The CIRS 20 phantom provided greater visibility of smaller structures, while the MAP was more suitable for assessing image quality of both FFDM and DBT imaging systems.

Occupational radiation exposure to nursing staff during cardiovascular fluoroscopic procedures: A review of the literature.

Fluoroscopy is a method used to provide real time x-ray imaging of the body during medical procedures to assist with medical diagnosis and treatment. Recent technological advances have seen an increase in the number of fluoroscopic examinations being performed. Nurses are an integral part of the team conducting fluoroscopic investigations and are often located close to the patient resulting in an occupational exposure to radiation. The purpose of this review was to examine recent literature which investigates occupational exposure received by nursing staff during cardiovascular fluoroscopic procedures. Articles published between 2011 and 2017 have been searched and comprehensively reviewed on the referenced medical search engines. Twenty-four relevant studies were identified among which seventeen investigated nursing dose comparative to operator dose. Seven researched the effectiveness of interventions in reducing occupational exposure to nursing staff. While doctors remain at the highest risk of exposure during procedures, evidence suggests that nursing staff may be at risk of exceeding recommended dose limits in some circumstances. There is also evidence of inconsistent use of personal protection such as lead glasses and skull caps by nursing staff to minimize radiation exposure. Conclusions: The review has highlighted a lack of published literature focussing on dose to nurses. There is a need for future research in this area to inform nursing staff of factors which may contribute to high occupational doses and of methods for minimizing the risk of exposure, particularly regarding the importance of utilizing radiation protective equipment.

Validation of a Monte Carlo code system for grid evaluation with interference effect on Rayleigh scattering.

Anti-scatter grids are commonly used in x-ray imaging systems to reduce scatter radiation reaching the image receptor. Anti-scatter grid performance and validation can be simulated through use of Monte Carlo (MC) methods. Our recently reported work has modified existing MC codes resulting in improved performance when simulating x-ray imaging. The aim of this work is to validate the transmission of x-ray photons in grids from the recently reported new MC codes against experimental results and results previously reported in other literature. The results of this work show that the scatter-to-primary ratio (SPR), the transmissions of primary (T p), scatter (T s), and total (T t) radiation determined using this new MC code system have strong agreement with the experimental results and the results reported in the literature. T p, T s, T t, and SPR determined in this new MC simulation code system are valid. These results also show that the interference effect on Rayleigh scattering should not be neglected in both mammographic and general grids' evaluation. Our new MC simulation code system has been shown to be valid and can be used for analysing and evaluating the designs of grids.

Low-Contrast Detail Phantom: Proof of Concept.

PURPOSE: To investigate the concept of filling the air gaps of the conventional contrast detail phantom (CDP) with various concentrations of contrast media, and to develop a variable level of attenuation-level differential phantoms that could be more appropriate for contrast measurements in some radiology cases. METHODS: Images were acquired using the digital radiography system of the traditional CDP (Perspex/air hole phantom) and the novel form of CDP where the air holes were replaced with attenuating material. In this study, two different attenuating materials were introduced, water and a 30% concentration of iodine-based contrast medium. Image quality was assessed using automated processing to calculate the image quality factor (IQF)inv. RESULTS AND DISCUSSION: Phantom studies indicate that lower contrast levels are obtained when CDP holes are filled with water and a 30% concentration of iodine contrast media than those observed for air/Perspex or traditional CDP. As an example, when a 5-mAs beam is used the IQFinv values are 5.32 in the case of air filling the holes; however, when these holes are filled with water under the same conditions, the value of the IQFinv drops to 2.55, and to 2.83 when 30% of contrast media is used. Other concentrations were also tested. These results indicate that it is possible to extend the contrast scale in these phantoms to include ranges that are more realistic for a patient's body than just air and tissue-equivalent material. CONCLUSIONS: These findings indicate that the proposed extension of the contrast scales allows smaller changes in contrast to be discerned. This is due to the small attenuation differences of the subject materials (e.g, 30% contrast liquid and wax) from the traditional form of CDP (material/air). This suggests that the low form of the CDP may have a useful role in assessing image quality in planar radiology as an evaluation tool to better represent low-subject contrast imaging requirements.

Factors influencing the development and implementation of advanced radiographer practice in Australia - a qualitative study using an interpretative phenomenological approach.

INTRODUCTION: The purpose of this study was to explore the factors influencing the implementation or the lack of implementation of advanced practitioner role in Australia. METHODS: This study uses an interpretative phenomenological approach to explore the in-depth real life issues, which surround the advanced practitioner as a solution to radiologist workforce shortages in Australia. Research participants are radiographers, radiation therapists and health managers registered with the Australian Institute of Radiography (AIR) and holding senior professional and AIR Board positions with knowledge of current advanced practice. RESULTS: In total, seven interviews were conducted revealing education, governance, technical, people issues, change management, government, costs and timing as critical factors influencing advanced practice in Australia. CONCLUSIONS: Seven participants in this study perceived an advanced practice role might have major benefits and a positive impact on the immediate and long-term management of patients. Another finding is the greater respect and appreciation of each other's roles and expertise within the multidisciplinary healthcare team. Engagement is required of the critical stakeholders that have been identified as 'blockers' (radiologists, health departments) as well as identified allies (e.g. emergency clinicians, supportive radiologists, patient advocacy groups). The research supports that the AIR has a role to play for the professional identity of radiographers and shaping the advanced practice role in Australia.

A dose comparison survey in CT departments of dedicated paediatric hospitals in Australia and Saudi Arabia.

AIM: To measure and compare computed tomography (CT) radiation doses delivered to patients in public paediatric hospitals in Australia and Saudi Arabia. METHODS: Doses were measured for routine CT scans of the head, chest and abdomen/pelvis for children aged 3-6 years in all dedicated public paediatric hospitals in Australia and Saudi Arabia using a CT phantom measurement cylinder. RESULTS: CT doses, using the departments' protocols for 3-6 year old, varied considerably between hospitals. Measured head doses varied from 137.6 to 528.0 mGy(·)cm, chest doses from 21.9 to 92.5 mGy(·)cm, and abdomen/pelvis doses from 24.9 to 118.0 mGy(·)cm. Mean head and abdomen/pelvis doses delivered in Saudi Arabian paediatric CT departments were significantly higher than those in their Australian equivalents. CONCLUSION: CT dose varies substantially across Australian and Saudi Arabian paediatric hospitals. Therefore, diagnostic reference levels should be established for major anatomical regions to standardise dose.

Clinical Utility of Out-of-Hours Chest Radiographs.

PURPOSE: In Australia, radiology services are provided as full 24-hour services, 24-hour urgent out-of-hours (on-call) services, and business hours-only service. The primary purpose of this study was to determine whether out-of-hours (11 PM-7 AM) chest x-ray (CXR) referrals are consistent with out-of-hours service expectations associated with the cost and inconvenience of calling staff in from home. A secondary objective was to determine whether the mobile chest plain film examinations are consistent with expectations of a patient's increased degree of infirmary. METHOD: A retrospective analysis was undertaken over 6 contiguous months for patients referred from the emergency department for CXRs out-of-hours and within standard hours (in-hours). The study population included 436 out-of-hours patients recruited into the investigation cohort and a matched cohort of 438 CXR examinations performed in-hours. The key information gleaned from the study was concordance or discordance between the clinical details relating to the actual referral and the findings of the CXR. RESULTS: The total sample comprised 414 females (47.4%) and 460 males (52.6%). The mean age was 55.3 years, median was 56.5 years, with a range of 0-97 years. The examination type performed was 8.9% mobile compared with 91.1% departmental for the sample. It was found that there was 43.5% prevalence of abnormalities, 27.0% significant abnormalities, and 8.7% clinically significant abnormality. The predictors found for clinically significant abnormalities were increasing patient age (P < .001) and the need for mobile examination (P < .001). Performing the examination out-of-hours did not predict a clinically significant abnormality (P = .491) and similarly, gender did not predict clinically significant abnormality (P = .152). CONCLUSION: The results suggest that similar approaches to referrals for CXRs are applied in-hours and during the out-of-hours period which are inconsistent with the "urgent" philosophy that should accompany an out-of-hours service. Only increasing patient age and the need for a mobile CXR offered predictors of a clinical significant abnormality and this offers an insight into the potential approach to the development of referral guidelines for out-of-hours procedures.

Computed Radiography and Dosimetry: Some Practical Tips for Dose Optimization Procedures.

This article provides some practical tips for dose optimization in computed radiography (CR). The article will not provide a comprehensive list of all factors that could be changed to optimize patient dose in CR examination. This article will also provide specific manufacturer examples that can be transferred to other manufacturers' CR systems. Due to the relatively large dynamic range of CR, stringent measures have to be put in place to ensure that patients are not being overexposed to ionizing radiation. Manufacturers of CR systems use dose indicators such as S-values, exposure index, and log-mean values to provide an indication of the "dose" received at the imaging plate. Manufacturers also provide a histogram analysis of the image pixel values. This histogram can also be used to evaluate the dose. The dose received at the imaging plate also has an effect on image quality. Radiographic factors of kV, mAs, and source to image distance affect the dose index, the histogram, and hence the image quality. These relationships will be reviewed and practical tips for dose optimization will be discussed.