Incorrectly placed gonad shields: Effect on CT automatic exposure correction from four different scanners

THE EFFECT OF OUT-OF-PLANE PATIENT SHIELDING ON CT RADIATION EXPOSURE AND TUBE CURRENT MODULATIONS: A PHANTOM STUDY ACROSS THREE VENDORS

The aim of this study was to evaluate how out-of-plane patient shielding affects radiation exposure parameters and tube current modulation on different vendors' computed tomography (CT) scanners. Helical CT scans were performed using two homogenous phantoms to mimic patient attenuation. Four CT scanners from three vendors were investigated by varying the distance of the patient shield from the border of the imaging volume. Scans were performed with a shield placed before and after the localizer. Changes in volume computed tomography dose index (CTDIvol), dose-length product (DLP) and tube current-time products were studied. Out-of-field lead shield increased the CTDIvol and DLP values for each scanner at least for one scan setting when the shield was present in the localizer. The most notable changes were recorded with >1.3 pitch values when the shield was closest to the scanned volume (2.5 cm), and the scan direction was towards the shield. The usage of patient shields in the localizer CT scans can disturb TCM even when placed 7.5 cm away from the edge of the scan.

Impact of Overlying Personal Items on CT Dose with Use of Automated Tube Current Modulation-Pilot Investigation

PURPOSE

To determine the incidence and impact of overlying radiopaque personal items (e.g., cellular phones, zippers) on CT dose and image quality with use of automated tube current modulation.

METHODS

Topogram images from 100 consecutive adult outpatient CT abdomen pelvis studies were retrospectively reviewed, and the number and type of overlying radiopaque personal items were recorded. Additionally, an anthropomorphic phantom was imaged with overlying personal items 1) present in topogram and axial images; 2) present in topogram but removed prior to axial acquisition; and 3) present in topogram positioned outside the field of view of the axial acquisition. dose length product (DLP) and CT dose index volume (CTDIvol) were compared to acquisitions performed without overlying personal items. Image noise was evaluated by assessing the standard deviation of Hounsfield units at the level of the overlying personal item.

RESULTS

Overlying personal items were visible in topogram images for 55% of CT exams and included underwires (38% of exams), zippers (7%), and cellular phones (1%). DLP increased when a cellular phone was present in the topogram whether or not it was removed before axial image acquisition (3.7% p = 0.002, combined AutomA and SmartmA), and image noise increased (144%, p = 0.002; AutomA). No increase in dose or image noise was observed with overlying zippers or underwires or when any object was visible in the topogram outside the field of view of the axial images.

CONCLUSIONS

Overlying personal items were observed in the majority of abdominopelvic CT scans. Large overlying radiopaque personal items resulted in increased dose and increased image noise. Removal of all overlying personal items will result in optimized dose and image quality.