Assessment of temporal resolution of multi-detector row computed tomography in helical acquisition mode using the impulse method

Abstract

The purpose of this study was to propose a method for assessing the temporal resolution (TR) of multi-detector row computed tomography (CT) (MDCT) in the helical acquisition mode using temporal impulse signals generated by a metal ball passing through the acquisition plane. An 11-mm diameter metal ball was shot along the central axis at approximately 5 m/s during a helical acquisition, and the temporal sensitivity profile (TSP) was measured from the streak image intensities in the reconstructed helical CT images. To assess the validity, we compared the measured and theoretical TSPs for the 4-channel modes of two MDCT systems. A 64-channel MDCT system was used to compare TSPs and image quality of a motion phantom for the pitch factors P of 0.6, 0.8, 1.0 and 1.2 with a rotation time R of 0.5 s, and for two R/P combinations of 0.5/1.2 and 0.33/0.8. Moreover, the temporal transfer functions (TFs) were calculated from the obtained TSPs. The measured and theoretical TSPs showed perfect agreement.The TSP narrowed with an increase in the pitch factor. The image sharpness of the 0.33/0.8 combination was inferior to that of the 0.5/1.2 combination, despite their almost identical full width at tenth maximum values. The temporal TFs quantitatively confirmed these differences. The TSP results demonstrated that the TR in the helical acquisition mode significantly depended on the pitch factor as well as the rotation time, and the pitch factor and reconstruction algorithm affected the TSP shape.

Temporal resolution measurement of 128-slice dual source and 320-row area detector computed tomography scanners in helical acquisition mode using the impulse method

“…However, because the present study aimed to analyse the TR (FWHM) of the TSP, these result may not sufficiently reflect the overall temporal element in CT images. Therefore, although the detailed relation between the TSP shape and image quality has to be considered as a function of temporal modulation transfer, which was calculated by Fourier transformation of the TSP [11], characterization of the temporal property of the TSP was partly possible using the index of FWHM in our TR measurement.…”

“…In our previous report [11], we proposed a practical method to measure the TR using the impulse method, in which a temporal impulse signal is generated by a small metal ball passing through a gantry rotation plane at a very high speed during the respective scan. The passage of the small metal ball can generate a temporal impulse signal into the projection data.…”

“…Thus, if a temporal impulse signal into the reconstructed image (projection data) of commercial CT scanners can be generated by any method, assessment of the actual TR for all acquisition conditions is possible by TSP analysis. In response to this problem, we previously proposed a practical method to assess the TSP of all acquisition modes using an impulse theorem-based metrology (impulse method) [11].…”

Role of Computed Tomography Scan in Dental Trauma: A Cross-Sectional Study

“…The images were reconstructed to 0.2-mm-interval images. 2,15 Limited cone beam computed tomography. All patients were subjected to LCBCT (PSR 9000N; Asahi Roentgen, Kyoto, Japan).…”