Multislice helical computed tomography: Image reconstruction algorithms, implementations, and clinical evaluations

Abstract

The development of multislice computed tomography (MSCT), which incorporates a multirow detector, has been desired for higher longitudinal (z) spatial resolution, longer volume coverage, shorter scan time, and other clinical requirements. Therefore, the purpose of this study was to develop one of the key technologies, image reconstruction algorithms, that cover most scanning applications: (1) step-and-shoot (nonhelical) scan, (2) standard helical reconstruction, (3) higher temporal resolution and dynamic volumetric (cine) imaging, and (4) better in-plane (trans-axial) spatial resolution.First, applying the fan-beam reconstruction algorithm was validated for the step-and-shoot mode: there is no practical problem in MSCT with narrow cone angle. Second, helical filter interpolation (HFI) with z filtering was proposed for standard helical reconstruction after a unique z-sampling pattern in multislice helical CT was investigated. HFI can increase the helical pitch three times as fast as the single-slice CT while keeping the same image quality. Clinical evaluation demonstrated the usefulness of HFI. This method has been implemented on most of the multislice helical CT scanners available worldwide. Third, helical half-scanning with time-shift (TS) technique was used to overcome the insufficient in-plane temporal resolution of HFI. This improved the image quality of cardiac, lung, and vascular imaging substantially. TS not only allows us to take full advantage of the high temporal resolution but also enables cine imaging even in helical scanning. Last, two algorithms were proposed for improving the in-plane spatial resolution. They successfully depict fine structures such as the otitis chain in the middle ear.