Investigating the CT localizer radiograph: acquisition parameters, patient centring and their combined influence on radiation dose

Abstract

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.

Effect of Localizer Radiography Projection on Organ Dose at Chest CT with Automatic Tube Current Modulation

“…Our observations indicate that, despite trying to vertically center the phantom as accurate as possible, the attenuation centering was on average too low. Similar findings according to the patient vertical centering were previously reported (9,11,17).…”

“…Some studies suggested that the use of a PA instead of an AP projection for localizer radiography may lead to higher tube currents and, thus, to an increased radiation dose at the CT examination (8,9). However, these studies estimated radiation doses from the CT examination only and did not take into account the dose from localizer radiography as well.…”

“…Vertical centering of the patient plays an essential role in the estimation of the D w for localizer radiography (9,15,16). Ideally, imaging should be performed with the attenuation center of the object in the isocenter.…”

Implications of Patient Centring on Organ Dose in Computed Tomography

“…The apparent object size may be misinterpreted on the localizer radiograph as the system assumes the object is at the isocenter, and implementation of the TCM would be adjusted accordingly (10) . With the object centered below the isocenter, the object's size is estimated to be smaller than the actual size.…”

CT Radiation Dose Management: A Comprehensive Optimization Process for Improving Patient Safety

“…Parakh et al decision software solutions (18,19). After a rigorous review of justification of each scan, radiologists should ensure that patients undergo scanning that is in accordance with the ALARA (as low as reasonably achievable) principle, which is practically done by optimizing each examination through proper patient centering, judicious use of intravenous contrast material, and selecting suitable technical parameters (20)(21)(22). CT manufacturers have also played a critical role by focusing on the development of effective technologies for dose reduction (automatic tube current modulation, iterative reconstruction techniques, dynamic collimation, and dose-efficient detectors), while preserving diagnostic accuracy and image quality (23)(24)(25)(26)(27)(28).…”