Radiation dose reduction in medical CT through equally sloped tomography

Purpose: A Fourier-based iterative algorithm, termed equally sloped tomography (EST), in conjunction with advanced regularization methods, has been applied to reduce the radiation dose 15 in medical CT. To quantify the amount of CT dose reduction achievable by EST, image quality phantom and an anonymous pediatric patient data sets were acquired from a Siemens SOMATOM Sensation 64 scanner. Methods: EST iterates back and forth between real and Fourier space utilizing the pseudo-polar fast Fourier transform (PPFFT). In each iteration, physical constraints and mathematical 20 regularization are enforced in real space, while the measured data is applied in Fourier space. The algorithm, monitored by an error metric, is guided towards a global minimum that is consistent with the measured data. To prevent any human intervention, the algorithm is automatically terminated when no further improvement can be made. Quantitative comparisons are conducted on the filtered back projection (FBP) and EST reconstructions at different flux 25 settings using signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs). Results: Based on the phantom and anonymous pediatric patient data sets and the image quantification metrics such as SNRs and CNRs, our experimental results demonstrate that the 39mAs EST reconstructions produce comparable or better image quality, resolution and contrast than the 140mAs FBP reconstructions. 30 Conclusions: As the radiation dose is linearly proportional to the x-ray flux, our results suggest that EST enable a reduction of the CT dose by ~70% while producing comparable or better image quality, contrast and resolution than the conventional reconstruction method. Compared to other iterative algorithms, EST takes advantage of the best features in both real and Fourier space iterative algorithms: i) eliminating the need for interpolation in Fourier space, 2) utilizing the 35 PPFFT that is algebraically exact and computationally fast, and 3) searching for a global minimum using the measured data through an iterative process in conjunction with advanced mathematical regularization. While we demonstrate the radiation dose reduction with fan-beam CT data in this article, EST can also be extended to circular/helical cone-beam geometry through the rebinning process. 40