Effect of arm position, presence of medical devices, and off-centering during acquisition of scout image on automatic tube voltage selection and current modulation in pediatric chest CT

Automatic patient centering in computed tomography: a systematic review and meta-analysis

OBJECTIVE

To comprehensively examine the influence of auto-patient centering technologies on positioning accuracy, radiation dose, image quality, and time efficiency of computed tomography (CT) scans.

MATERIALS AND METHODS

A systematic search of peer-reviewed English publications was performed between January 2000 and November 2023 in PubMed, Embase, CINAHL, Scopus, and Web of Science. Two postgraduate students and an academic lecturer independently reviewed the articles to verify adherence to the inclusion criteria. The QUADAS-2 tool was employed to evaluate study quality. We derived summary estimates on positioning accuracy, radiation dose reduction, image quality, and time efficiency using proportion and meta-analysis methodologies.

RESULTS

Nine studies were identified comparing automatic and manual CT positioning. Automatic positioning improved accuracy by reducing vertical offsets to 7 mm and 4 mm for thorax and abdominal CTs, compared to 19 mm and 18 mm with manual methods. Most studies showed significant reductions in radiation dose, ranging from 5.71 to 31%. Image quality results were mixed, automatic methods generally produced images with less noise, but differences were minimal. Time efficiency was better, with automatic positioning reducing preparation time from 0.48 min versus 0.67 min for manual positioning.

CONCLUSIONS

This review confirms that automatic patient-centering technologies enhance positioning accuracy and decrease preparation times in CT scans. While reductions in radiation doses and some improvements in image quality were observed, the evidence remains mixed. Findings support integrating these technologies into clinical practice to optimize patient care.

KEY POINTS

Question Does automatic patient centering in CT enhance positioning accuracy, reduce radiation exposure, and improve image quality? Findings Findings indicate that automatic centering can optimize image quality, reduce examination times and contribute to overall improvements in imaging efficiency. Clinical relevance Automatic patient centering in CT improves positioning accuracy, minimizes radiation exposure, enhances image quality, and accelerates imaging workflows, contributing to safer, more efficient imaging procedures that benefit patient care.

A comparative study of the CT effective dose in whole-body 18F-FDG PET/CT for arm-raised position and arm-lowered position

INTRODUCTION

This study aimed to investigate and compare the effective dose (ED) delivered by computed tomography (CT) in whole-body positron emission tomography/CT (WB-PET/CT) scans between patients positioned with their arms-raised and those with their arms-lowered during the scan on a large population.

METHODS

The retrospective study involved 785 oncology patients who underwent WB-PET/CT scans with 18F-FDG between January and June 2019. Exclusion criteria were applied, resulting in a final analysis of data from 732 adult patients. All of the patients were measured height and weight, and the ED from CT in WB-PET/CT was estimated using the dose length product value and a conversion factor. Statistical analyses were conducted to explore relationships between factors and the ED. Linear regression analysis was performed to investigate connections between weight and ED, and height and ED. Multiple linear regression was used to predict ED based on sex, weight, and arm position.

RESULTS

The arm-lowered group had a higher ED than the arm-raised group, and the median dose was 1.1 times higher in the arm-lowered group. The difference in ED between the two groups was found to be greater with higher body weight. Arm-position (β = 0.460), sex (β = -0.190), and weight (β = 0.057) were significant predictors of ED.

CONCLUSION

This study demonstrated that arm position, sex, and weight were significant factors influencing the ED from CT scans in WB-PET/CT.

IMPLICATIONS FOR PRACTICE

The research underscores the importance of considering these factors when evaluating radiation exposure in clinical practice, particularly for patients undergoing WB-CT imaging. These findings contribute to a better understanding of the radiation dosimetry associated with different patient positions during WB-PET/CT scans.

Influence of tube and patient positioning in thoracoabdominal CT examinations on radiation exposure-towards a better patient positioning

Although iso-centric patient positioning is enormously important in computed tomography (CT), it is complicated in thoracoabdominal imaging by the varying dimensions of the body. Patient positioning can affect the appearance of the patient on the localiser. Positioned too close to the x-ray tube, a patient appears considerably more voluminous. The goal of this study is to assess the difference in radiation exposure of combined chest and abdomen CT scans between scans with prior 0°- and 180°-localisers in conjunction with patient positioning. In this IRB-approved retrospective study, patients who had two routine thoracoabdominal CT scans on the same CT scanner, one with a prior 0°- and one with a prior 180°-localiser, were included. To evaluate the radiation exposure of the thoracoabdominal CT examination regarding the tube position during the localiser, volumetric computed tomography dose index (CTDIvol), size-specific dose estimate (SSDE), patient diameter and positioning within the iso-centre for three positions (heart, abdomen, femur level) were compared with regard to the tube position during the prior localiser. CT examinations of 114 patients were included. Despite similar patient weight and diameter between the two examinations, SSDE and CTDIvolwas significantly larger (up to 73%) with 180°-localisers. Patient offset from the iso-centre ranged between -9 mm at the centre slice (abdomen level) to -43 mm at the most caudal slice at the pelvis (femur level), causing a significant magnification (p < 0.001) on 180°-localisers with a subsequent increase of the apparent attenuation. The results of this study emphasise the use of 0°-localisers in thoracoabdominal CTs, since 180°-localisers caused patient magnification with subsequent increase in radiation exposure. The advantage of 180°-localisers, namely reducing the dose in thyroid and breast, is eliminated if the dose of the CT scan increases significantly in the abdomen and pelvis.