The influence of patient positioning on radiation dose in CT imaging: A narrative review.

BACKGROUND AND PURPOSE: Although it is fundamental for optimal scanner operation, it is generally accepted that accurate patient centring cannot always be achieved. This review aimed to examine the reported knowledge of the negative impact of patient positioning on radiation dose and image quality during CT imaging. Furthermore, the study evaluated the current optimisation tools and techniques used to improve patient positioning relative to the gantry iso-center. METHODOLOGY: A comprehensive search through the databases PubMed, Ovid, and Google Scholar was performed. Keywords included patient off-centring, patient positioning, localiser radiograph orientation, radiation dose, and automatic patient positioning (including synonyms). The search was limited to full-text articles that were written in English. After initial title and abstract screening, a total of 52 articles were identified to address the aim of the review. No limitations were imposed on the year of publication. RESULTS: Vertical off-centring was reported in up to 95% of patients undergoing chest and abdominal CT examinations, showing a significant influence on radiation dose. Depending on the scanner model and vendor, localiser orientation, bowtie filter used, and patient size, radiation dose varied from a decrease of 36% to an increase of 91%. A significant dose reduction was demonstrated when utilising an AP localiser, aligning with the trend for radiographers to off-center patients below the gantry iso-centre. Utilizing a 3D camera for body contour detection allowed for more accurate patient positioning and promoted further dose reduction. CONCLUSION: Patient positioning has shown significant effects on radiation dose and image quality in CT. Developing a good understanding of the key factors influencing patient dose (off-centring direction, localiser orientation, patient size and bowtie filter selection) is critical in optimising CT scanning practices. Utilising a 3D camera for body contour detection is strongly recommended to improve patient positioning accuracy, image quality and to minimise patient dose.

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.

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.

Impacts of Phantom Off-Center Positioning on CT Numbers and Dose Index CTDIv: An Evaluation of Two CT Scanners from GE.

The purpose of this work is to evaluate the impacts of body off-center positioning on CT numbers and dose index CTDIv of two scanners from GE. HD750 and APEX scanners were used to acquire a PBU60 phantom of Kagaku and a 062M phantom of CIRS respectively. CT images were acquired at various off-center positions under automatic tube current modulation using various peak voltages. CTDIv were recorded for each of the acquisitions. An abdomen section of the PBU60 phantom was used for CT number analysis and tissue inserts of the 062M phantom were filled with water balloons to mimic the human abdomen. CT numbers of central regions of interests were averaged using the Fiji software. As phantoms were lifted above the iso-center, both CTDIv and CT numbers were increased for the HD750 scanner whilst they were approximately constant for the APEX scanner. The measured sizes of anterior-posterior projection images were also increased for both scanners whilst the sizes of lateral projection images were increased for the HD750 scanner but decreased for the APEX scanner. Off-center correction algorithms were implemented in the APEX scanner. Matching the X-ray projection center with the system's iso-center could improve the accuracy of CT imaging.

Knowledge, Attitude and Practice Around Breast Cancer and Mammography Screening Among Jordanian Women.

BACKGROUND: Breast cancer is the most common occurring cancer in women worldwide. To guide current breast cancer screening program, the level of knowledge about breast cancer should be evaluated. This study aims to ascertain the level of breast cancer knowledge including risk factors, signs and symptoms, and early detection methods, especially mammography screening. METHODS: The study was conducted among 1353 Jordanian women from the public using a self-administered questionnaire. Responses to the knowledge test were summed for an overall knowledge score. Comparisons between socio-demographics and knowledge, attitude and practice were also measured using a Chi-square test. RESULTS: About 76% of participants were aware that breast cancer is the most common cancer among women in Jordan. About 53.7% of our participants were rated as having an intermediate level of knowledge regarding risk factors, and 44% were rated as having a good to an excellent level of knowledge about breast cancer signs and symptoms. The participants' level of education was the main factor identified as influencing the participants' knowledge of the risk factors, signs and symptoms, and knowledge of early detection methods of breast cancer. The study sample was rated as having an intermediate level of knowledge regarding mammography screening; however, their participation in this screening method was low. CONCLUSION: Although Jordanian women had an acceptable level of knowledge of breast cancer, the screening rates for mammography were low. These findings suggest that there is a need to provide extra awareness programs for Jordanian women to improve their breast cancer knowledge and practice.

Body size and tube voltage dependent corrections for Hounsfield Unit in medical X-ray computed tomography: theory and experiments.

The purpose of this work is to present a body size and tube voltage dependent correction scheme for the Hounsfield Unit, HU, in medical X-ray Computed Tomography imaging. Boltzmann photon transport equation was employed to study X-ray interaction with bulk water in CT imaging. Experimentally measured X-ray output in body of phantoms and attenuation cross sections of water were employed in the derivation of beam intensity in X-ray imaging. A Somatom Emotion CT scanner from Siemens and electron density phantoms from CIRS were employed to acquire CT images of different body sizes and different tissue materials located at different depths from body's surface. Tube voltage and depth dependent effective attenuation of bulk water was found from theoretical analysis in agreement with measured size-specific correction factors for CTDIvol under different tube voltages. A size and tube voltage dependent correction scheme for the Hounsfield Unit is established. For the same tissue material, body size has much larger impact on the CT number variations than that of depth from the body surface in phantom measurements. Good results were achieved by applying the established correction scheme on the experimentally measured CT number variations under different tube voltages and body sizes.