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A statistical approach to high-quality CT reconstruction at low radiation doses for real-time guidance and navigation

The advent of 64-slice computed tomography (CT) with high-speed scanning makes CT a highly attractive and powerful tool for navigating image-guided procedures. For interactive navigation, scanning will need to be performed over extended time periods or even continuously. However, continuous CT is likely to expose the patient and the physician to potentially unsafe levels of radiation. Before CT can be used appropriately for navigational purposes, the dose problem must be solved. Simple dose reduction is not adequate, because it degrades image quality. This problem can be overcome if the traditional filtered back-projection (FBP) reconstruction is replaced with the maximum likelihood expectation maximization (MLEM) approach. MLEM is more accurate in that it incorporates Poisson statistics of the noisy projection data, especially at low doses. Our study shows that MLEM reconstruction is able to reduce x-ray dose from 200 to 11 mAs (the lowest dose-simulator setting in the present study) without significant image degradation. Taking advantage of modern CT scanners and specialized hardware, it may be possible to perform continuous CT scanning at acceptable radiation doses for intraoperative visualization and navigation.