Algorithm for image reconstruction in multi-slice helical CT

Abstract

Efforts are being made to develop a new type of CT system that can scan volumes over a large range within a short time with thin slice images. One of the most promising approaches is the combination of helical scanning with multi-slice CT, which involves several detector arrays stacked in the z direction. However, the algorithm for image reconstruction remains one of the biggest problems in multi-slice CT. Two helical interpolation methods for single-slice CT, 360LI and 180LI, were used a starting points and extended to multi-slice CT. The extended methods, however, had a serious image quality problem due to the following three reasons: (1) excessively close slice positions of the complementary and direct data, resulting in a larger sampling interval; (2) the existence of several discontinuous changeovers in pairs of data samples for interpolation; and (3) the existence of cone angles. Therefore we have proposed a new algorithm to overcome the problem. It consists of the following three parts: (1) optimized sampling scan; (2) filter interpolation; and (3) fan-beam reconstruction. Optimized sampling scan refers to a special type of multi-slice helical scan developed to shift the slice position of complementary data and to acquire data with a much smaller sampling interval in the z direction. Filter interpolation refers to a filtering process performed in the z direction using several data. The normal fan-beam reconstruction technique is used. The section sensitivity profile (SSP) and image quality for four-array multi-slice CT were investigated by computer simulations. Combinations of three types of optimized sampling scan and various filter widths were used. The algorithm enables us to achieve acceptable image quality and spatial resolution at a scanning speed that is about three times faster than that for single-slice CT. The noise characteristics show that the proposed algorithm efficiently utilizes the data collected with optimized sampling scan. The new algorithm allows suitable combinations of scan and filter parameters to be selected to meet the purpose of each examination.

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

“…This property indicated that the reconstruction algorithm of 64HM changes over a partial scan reconstruction algorithm at a pitch factor of 1.0. Hence, to adjust the TR for various projection data for 64HM, we deduced that a weighting function that regulates the range of required projection data to the z-direction based on a modified reconstruction algorithm of a helical filter interpolation and a helical half-scanning was used [2].…”

“…In contrast, the TR of the helical acquisition mode to which image reconstruction is performed from z-axis interpolation is closely related to the gantry rotation time and specific interpolation method applied [2]. Thus, because CT images are reconstructed from projection data corresponding to each detector and complex interpolation algorithms [2][3][4], the TR of the helical acquisition mode may not necessarily be equal to the gantry rotation time of a multi-detector CT [5].…”

Temporally Targeted Imaging Method Applied to ECG-Gated Computed Tomography

“…For small cone-angles fan beam formulas may be applied directly to interpolated helical data (32)(33)(34)(35). For the moderate cone-angles of current state-of-the-art 64-slice scanners, FDK-type approximations that utilize heuristic filtering and exact 3D backprojection may be employed (17,(36)(37)(38).…”

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

“…The reconstruction algorithm of the Somatom VZ system and helical filter interpolation (HFI) for the 4-channel mode of the Aquilion 16 system have been previously described [11,12], and the weight functions for helical interpolation of these reconstruction algorithms were known. Thus, these two CT systems could be used to compare the measured and theoretical TSPs.…”