Reconstruction of High Quality CT Angiography from Noisy Cerebral CT Perfusion Data

Purpose: To develop and test a method for the reconstruction of cerebral Computed Tomography (CT) Angiography (CTA) from CT Perfusion data that, with respect to image quality, can substitute for conventional CTA. Method and materials: We propose the temporal Maximum Intensity Projection (tMIP) with prior temporal Guassian filtering as a technique to obtain angiography from CT Perfusion data (perfusion derived CTA, p-CTA). The amount of temporal filtering was evaluated to optimize Contrast-to-Noise Ratio (CNR) in the Circle of Willis (CoW). No spatial filtering was applied. We retrospectively selected 25 consecutive stroke patients who underwent CTP (80 kV, 150 mAs, 25 scans every 2s) and CTA (120 kV, 150 mAs) both with 128 x 0.625 mm collimation. Arterial enhancement was measured in 10 regions of interest (ROI) in the CoW (5 large and 5 small arteries) and image noise in one occipital lobe for perfusion derived CTA (p-CTA), standard tMIP, arterial phase of CTP (a-CTP) and conventional CTA. Results: Optimal CNR in the CoW was obtained at a temporal Gaussian filter strength of 2 seconds and was equal for both large and small arteries. The p-CTA resulted in an average CNR increase of 12% and a noise reduction of 25% compared to standard tMIP. The optimal filter strength was equal for both large and small vessels in the circle of Willis, and for comprised a Gaussian filter with a standard deviation of 2 seconds. The p-CTA was superior to conventional CTA with 23% higher CNR and 42% lower noise and to a-CTP with 42% higher CNR and 119% noise reduction. Conclusion: The presented method is an excellent technique to obtain CT Angiography from CT Perfusion data and renders CTA images with CNR and SNR superior to conventional CTA of the brain. Clinical relevance/application: Obtaining high quality CT Angiography (CTA) from noisy CT Perfusion (CTP) data could obviate an additional CTA scan, reduce total radiation exposure and the amount of contrast material needed.