SU-E-I-46: Quantitative Effects of Clinical Practice on the Efficiency of CT Tube Current Modulation for Radiation...

CT tube current modulation (TCM) represents one of the most important and efficient methods for radiation dose reduction and has been well accepted. However, the possible influence of clinical practice is likely to be ignored although venders may provide clinical protocols and instructions. This study is designed to further investigate the quantitative effects of clinical operation, including radiograph direction and patient positioning, on the efficiency of TCM by measuring patient radiation dose and image quality.

An anthromorphologic chest phantom was scanned in a Sensation 40 and a lightSpeed 16 CT scanner, respectively, using routine chest protocols with TCM. We first investigated the effects of radiograph direction. Anterior-posterior (AP), lateral, and posterior-anterior (PA) directions were chosen. CTDIvol and dose-length-product (DLP) were recorded for analyses. Our second experiment studied the influence of patient position. First the phantom was positioned at the iso-center then scanned with AP direction. CTDIvols and DLPs were recorded as reference. Then the phantom was moved out of iso-center, up or down 2 and 4 cm respectively then scanned. CTDIvols and DLPs were recorded for comparison. For each setting, image noise was measured.

CTDIvol increases approximately 20% for PA direction, compared to AP or lateral direction which generates similar CTDIvol and DLP with TCM. Image noise for the PA direction is less than those for the AP or lateral directions. CTDIvol increases approximately 9% for LightSpeed 16 and 13% for Sensation 40 when the phantom was moved up 4 cm, while CTDIvol decreases approximately 5% for LightSpeed 16 and 8% for Sensation 40 when the phantom was moved down 4 cm.

Our quantitative study can direct clinical practice to improve the efficiency of CT tube current modulation and reduce patient radiation dose.