Background: Clinical progress by the development of multi-slice CT (MSCT) technology beyond 16 slices can more likely be expected from further improved spatial and temporal resolution rather than from a mere increase in the volume coverage speed. We present an evaluation of a recently introduced 64-slice CT (64SCT) system, which makes use of a periodic motion of the focal spot in the longitudinal direction (z-flying focal spot) to double the number of simultaneously acquired slices.
Materials and methods: A recently introduced 64SCT system (SOMATOM Sensation 64, Siemens Medical Solutions, Forchheim, Germany) is being described and tested in first clinical practice, applying the following parameters: z-flying focal spot technology, 64 x 0.6 mm slices; spatial resolution, 0.4 x 0.4 x 0.4 mm; gantry rotation time, 330 ms; temporal resolution, 83-165 ms. Various phantom studies and first clinically implemented protocols are being described, to evaluate the full spectrum of possible applications for this scanner type, with a focus on cardiac imaging.
Results: ECG-gated cardiac scanning with this 64-slice CT system benefits clearly from both the improved temporal resolution and improved spatial resolution. These benefits enable a more reliable assessment of mixed plaques, due to reduced partial-voluming and beam-hardening artefacts caused by calcifications, and holds great promise for the reliable assessment of in-stent stenoses, as stent lumen visibility is clearly improved as compared to earlier MSCT systems. With the increased volume coverage and acquisition speed of the 64SCT system, a comprehensive emergency protocol of the thorax becomes feasible within an acceptable breath-hold time, performing an ECG-gated CT angiography of the complete thoracic vasculature. This protocol enables a detailed assessment of the thoracic aorta, the pulmonary arteries and the coronary arteries in one single examination.
Conclusions: 64SCT Cardiac imaging provides an increased spatial resolution with an isotropic voxel size of 0.4 mm and an improved temporal resolution of 83-165 ms. These benefits hold great promise especially for fast-moving organs requiring detailed imaging, such as the heart and coronary arteries.