[Basic examination of in-plane spatial resolution in multi-slice CT].

In computed tomography(single-slice spiral CT, conventional CT), in-plane(x-y plane) spatial resolution is consistently identified as depending on the detector density of the in-plane(x-y plane). However, we considered that the in-plane(x-y plane) spatial resolution of multi-slice CT (MSCT) was influenced by an error in the detector's sensitivity to the Z-axis and by the frequency of use of direct row data and complementary row data when the image of spiral pitches(SP) was reconstructed. Our goal in this experiment was to analyze the relationship of the in-plane(x-y plane)spatial resolution of an asymmetric-type detector in MSCT to SP, tube current, and rotation time. By employing a tungsten wire phantom of 0.2 mm in diameter, we examined modulation transfer functions(MTF) by point-spread functions(PSF) of CT-images. Next, using the mean-square-root bandwidth theory, we analyzed the MTF of wire phantoms. The analysis of in-plane(x-y plane) spatial resolution revealed that various tube currents had no effect on the value of the mean-square-root bandwidth. However, rotation time and high spiral pitch did have an effect on mean-square-root bandwidth. Considering the results mentioned above, spiral pitch(z-axis reconstruction algorithm) had a slight effect on in-plane(x-y plane) spatial resolution of asymmetric-type detectors in MSCT. Accordingly, we proposed a new general view of VDDz(view/mm) in MSCT that considered view data density on the Z-axis according to spiral pitch(mm/rotation), rotation time(view/rotation), and slice collimation.