Influence of Bowtie Filter and Patient Positioning on In-plane Dose Distribution and Image Quality in ECG-gated CT

Abstract

In electrocardiographic (ECG)-gated computed tomography (CT) for diagnosis of cardiac diseases, radiation dose and image quality are optimized by limiting field of view (FOV) and centering on the heart. However, it is necessary to set wide FOV with large bowtie filter depending on patient positioning or various diagnoses such as aortic diseases. The purpose of this study is to clarify influence of bowtie filter and patient positioning on in-plane dose distribution, organ-absorbed dose, image quality in ECG-gated CT. In-plane dose distribution and organ-absorbed dose were evaluated with radio photoluminescence glass dosimeters, and signal-to-noise ratio (SNR) were measured for evaluation of image quality. The bowtie filter was used small (S) and large (L). With automatic exposure control, volume computed tomography dose index was 55.3 mGy at S and 71.8 mGy at L. The phantom was positioned on the heart of phantom (Heart) and the center of phantom (Body). In Heart-L compared with Heart-S, organ-absorbed dose was 1.29 times at breasts. In Heart-S compared with Body-S, in-plane dose distribution was increased 25% at left anterior and decreased 20% at right posterior. In SNR, S and L were decreased from 50 mm off-center. To set appropriate bowtie filter and positioning was reduced radiation dose and improved image quality in ECG-gated CT.