Objective: To systematically investigate the effect of CT localizer radiograph acquisition on the tube current modulation and thus radiation dose of the subsequent diagnostic scan. Methods: Localizer radiographs of an abdominal section CT phantom were taken, and the resulting volume CT dose index (CTDIvol) for the diagnostic scan was recorded. Variables included tube potential, the phantom's alignment within the CT scanner gantry in both the vertical and horizontal directions and the X-ray source angle at which the localizer was acquired. Results: Diagnostic scan CTDIvol decreased with increasing tube potential. Vertical (table height) movement was found to affect radiation dose more than horizontal movement, with 650 mm table movement resulting in a standard deviation in the diagnostic scan CTDIvol of 4.4 mGy, compared with 2.5 mGy with 6 50 mm horizontal movement. Correspondingly, localizer angles of 90°or 270°(3 o'clock and 9 o'clock X-ray source positions) were less sensitive overall to alignment errors, with a standard deviation of 2.5 mGy, compared with a 0°or 180°angle, which had a standard deviation of 3.8 mGy. Conclusion: To achieve a consistently optimized radiation dose, the localizer protocol should be paired with the diagnostic acquisition protocol. A final acquisition angle of 90°should be used when possible to minimize dose variation resulting from alignment errors. Advances in knowledge: Localizer parameters that affect radiation output were identified for this scanner system. The importance of tube potential and acquisition angle was highlighted.Radiation exposure from medical imaging remains in the public awareness and has spurred the adoption of several technologies to minimize CT dose.

Colorectal cancer (CRC) is one of the most common malignancies with a dismal prognosis. Indeterminate pulmonary nodules (IPNs) are lung nodules with uncertain nature, generally defined as a noncalcified nodule smaller than 10 mm in diameter or solid nodule no greater than 20 mm at maximum diameter without malignant character. With the widespread use of preoperative staging computed tomography (CT) of the chest and follow-up CT, IPNs are frequently detected in patients with CRC, which makes diagnosis more controversial. Generally, progression to pulmonary metastasis from IPNs is rare. Thus, no further interventions were needed for IPNs in CRC patients. A second reviewing of scans with IPNs by both clinicians and experienced thoracic radiologists may help to obtain a more accurate diagnosis.