We introduced and evaluated the techniques LightSpeed VCT uses to reduce X-ray dose and image noise in cardiac helical CT applications. These techniques include the use of much improved VCT data acquisition system (VDAS) with reduced electronic noise; cardiac bowtie that redistributes X-rays to have more signals for heart and much less flux to the peripheries; adaptive post-processing filters to reduce cardiac image noise; and ECG modulated tube currents to concentrate X-ray dose for desired cardiac phases. Phantom and patient scans were used to evaluate the dose saving and noise reduction potentials of these techniques. The results demonstrated that the improved VDAS reduced image noise 15-20% for cardiac imaging. With same scan technique, the use of cardiac bowtie reduced about 10% dose in terms of CTDIw measurement and clinical evaluation demonstrated additional 7% image noise reduction and equivalent image quality with cardiac bowtie vs. regular body bowtie. The adaptive filter generated 15-20% noise reduction while maintaining image resolution and artery sharpness. Finally, the use of ECG modulated mA method provided up to 50% dose reduction based on CTDIw measurements, but the saving potentials depended on the heart rate and cardiac phase selection. For heart rate of 60bpm and ±15% cardiac phase margin, the average dose reduction could be 30%. Since these dose and noise reduction methods are inclusive and can be combined to produce even greater dose/noise reduction. It is reasonable to believe that with VCT we maybe able to acquire cardiac helical CT images with only 30-40% of the dose of older generation 16-slice CT scanners with similar noise level and same slice thickness.
We have developed an adaptive filtering algorithm for cardiac CT scans with EKG-modulated tube current to optimize resolution and noise for different cardiac phases and to provide safety net for cases where end-systole phase is used for coronary imaging. This algorithm has been evaluated using patient cardiac CT scans where lower tube currents are used for the systolic phases. In this paper, we present the evaluation results. The results demonstrated that with the use of the proposed algorithm, we could improve image quality for all cardiac phases, while providing greater noise and streak artifact reduction for systole phases where lower CT dose were used.
Dose is becoming increasingly important for computed tomography clinical practice. It is of general interest to understand the impact that system design can have on dose and image quality. This study addresses the effect of bowtie shape on the dose and contrast-to-noise across the field of view. Simulation of the CT acquisition is used to calculate the energy deposition throughout a numerical phantom for a set of relevant system operating parameters and bowtie shapes. Mean absorbed dose is calculated by summing over the phantom volume and is compared with other typical dose specifications. A more aggressive attenuation profile of the bowtie which offers higher attenuation in the periphery of the field of view can offer the benefit of lower dose but at the expense of reduced contrast-to-noise at the edge of the cross-sectional image.
One new kind of the laser-ultrasonic technique in which a continuous ultrasonic signal is used to record flow-induced traveling time differences of ultrasonic wave, propagation along a measuring sound beam between two laser beams, so-called A Continuous Ultrasonic Signal Method of Laser-Ultrasonic Technique, is presented. This method allows a fast and non-disturbing exploration of the flow field around models in wind tunnels. By using the new method, even an ultrasonic transducer with lower performance could be employed, and there is no need a high-accuracy optical detector.