Stanislav Zabic

Acceleration of ML iterative algorithms for CT by the use of fast start images

This report develops a new strategy for the acceleration of a maximum likelihood (ML) iterative reconstruction algorithm for CT, by selecting a starting image which is closer to the solution of the ML algorithm than the commonly used filtered backprojection image. The starting image is obtained by passing both the acquired projection data and the reconstructed volume though a novel de-noising algorithm which uses the same image penalty function as the ML reconstruction. Clinical examples suggest that a savings of 5-10 iterations of the separable paraboloidal surrogates algorithm per volume is possible when using this new acceleration strategy.

Evaluation of an iterative model-based reconstruction algorithm for low-tube-voltage (80 kVp) computed tomography angiography.

Abstract. The objective of this study was to investigate the improvement in diagnostic quality of an iterative model–based reconstruction (IMBR) algorithm for low-tube-voltage (80-kVp) and low-tube-current in abdominal computed tomography angiography (CTA). A total of 11 patients were imaged on a 256-slice multidetector computed tomography for visualization of the aorta. For all patients, three different reconstructions from the low-tube-voltage data are generated: filtered backprojection (FBP), IMBR, and a mixture of both IMBR+FBP. To determine the diagnostic value of IMBR-based reconstructions, the image quality was assessed. With IMBR-based reconstructions, image noise could be significantly reduced, which was confirmed by a highly improved contrast-to-noise ratio. In the image quality assessment, radiologists were able to reliably detect more third-order and higher aortic branches in the IMBR reconstructions compared to FBP reconstructions. The effective dose level was, on average, 3.0 mSv for 80-kVp acquisitions. Low-tube-voltage CTAs significantly improve vascular contrast as presented by others; however, this effect in combination with IMBR enabled yet another substantial improvement of diagnostic quality. For IMBR, a significant improvement of image quality and a decreased radiation dose at low-tube-voltage can be reported.

Prospectively gated cardiac CT

Future cardiac CT protocols will utilize large area detectors with whole heart scans performed within one heartbeat. For such scans, accurate prospective ECG gating is essential to capture the heart at the correct phase. This report addresses one of the main factors affecting the prospective gating accuracy: the ability to predict the cardiac phase from the ECG signal. Two different scanning methods with equal average dose utilization along with 6 different prediction algorithms are compared and evaluated on 245 patient ECG signals. In general, all the algorithms performed comparably while, perhaps surprisingly, the best scan method was to rescan the patient as necessary as opposed to elongating a single scan.