Technical Principles and Applications of Multislice Spiral CT

Abstract

With the introduction of multislice computed tomography (CT) into clinical practice a new era began, leading to the possibility of nearly isotropic voxel imaging and high-quality reconstructions. The main drawbacks of single-slice spiral CT are insufficient volume coverage of the patient within the time of one breath hold and missing spatial resolution in the z-axis due to wide collimation. Larger volume coverage and improved axial resolution may be achieved by simultaneous acquisition of more than one slice and by a shorter rotation time. In 1998, all major CT manufacturers introduced multislice CT systems offering increased scan speed, improved axial resolution, and better utilization of the tube output. These new devices typically offer simultaneous acquisition of four slices at 0.5 s rotation time, thus increasing the performance of a single-slice CT scanner at 1 s rotation time by a factor of 8. This increased performance allows for the optimization of different clinical parameters: for example, the examination time for a standard protocol may be reduced by a factor of 8, which is clinically important in a variety of instances, such as in dealing with trauma or uncooperative patients. Alternatively, the scan range may be extended correspondingly, as for oncological screening or for CT angiographies (CTAs) of the extremities. Most important, however, is the capacity to scan a given volume in a given time with considerably smaller slice width, thus to approach the ideal of isotropic resolution. Chest and abdomen examinations may be routinely performed with 1.25-mm slice width on a 4-slice CT system, obtaining high-quality image data for volumetric visualization, evaluation, and quantification. As a consequence, volumetric viewing and diagnosis in a volumetric mode have become integrated elements of the routine workflow.