Maximum-Likelihood Dual-Energy TomographicImage Reconstruction

Dual-energy (DE) X-ray computed tomography (CT) has shown promise for material characterization and for providing quantitatively accurate CT values in a variety of applications. However, DE-CT has not been used routinely in medicine to date, primarily due to dose considerations. Most methods for DE-CT have used the filtered backprojection method for image reconstruction, leading to suboptimal noise/dose properties. This paper describes a statistical (maximum-likelihood) method for dual-energy X-ray CT that accommodates a wide variety of potential system configurations and measurement noise models. Regularized methods (such as penalized-likelihood or Bayesian estimation) are straightforward extensions. One version of the algorithm monotonically decreases the negative log-likelihood cost function each iteration. An ordered-subsets variation of the algorithm provides a fast and practical version.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85934/1/Fessler172.pd

Design of a dual modality PET/cone beam CT scanner. A feasibility study.

Positron Emission Tomography (PET) is a noninvasive medical imaging modality that provides quantitative information about human physiology. One of the most rapidly expanding areas of PET imaging is cancer diagnosis. The application of PET in cancer diagnosis is, however, hampered by the attenuation of gamma-rays and poor anatomical localization. The attenuation of gamma-rays is typically accounted for by taking a transmission scan with an external gamma-ray source. Radionuclide transmission scans, however, suffer from a high noise level and take a long time to acquire. The second problem---the imprecise anatomical localization of the metabolic changes---is due to the fact that a PET scan contains very little anatomical information. A solution is to superimpose the PET image with a separately obtained X-ray computed tomography (CT) image. Because the two scans are obtained using different scanners with different geometries and protocols, the fusion is not trivial. Also, these methods require expert supervision and are computationally expensive. As another solution, several dual modality PET/CT scanners have recently been developed. These devices, however, are typically very expensive and expose the patient to a high radiation dose. We propose a novel PET/CT design that can be developed at a significantly lower cost and exposes the patient to a lower radiation dose. The CT component is based on cone beam mode of scanning. The cone beam CT (CBCT) scan is used to perform the attenuation correction for the PET scan and is fused with the PET scan to produce a combined anato-metabolic image. We have constructed a CBCT test bench to perform feasibility studies. We successfully performed attenuation correction for a PET scan of a torso phantom and demonstrated that the radiation dose can be significantly lower than in diagnostic CT, while maintaining the quality of the attenuation correction. We further proposed several methods for improving upon the performance of the basic design, to of which we dealt with in more detail. First, we proposed a method for improving the dynamic range of the flat panel detectors. Second, we proposed a statistically motivated dual energy image reconstruction method - DE PWLS.Ph.D.Applied SciencesBiomedical engineeringElectrical engineeringHealth and Environmental SciencesMedical imagingUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123716/2/3096212.pd