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Development and performance of a sparsity-exploiting algorithm for few-view single photon emission computed tomography (SPECT) reconstruction

Thesis (M. Med. Sc.)--University of Queensland, 2001. / Includes bibliographical references.

This dissertation addresses two problems dealing with detection sensitivity in radiology. First, is a 100-mm format adequate for displaying enhanced radiographic images in a photoelectronic imaging system and can the same format be used for permanent storage of these images? Second, what are the effects of training on the radiologist's sensitivity? Controlled 14-in. x 17-in. x-ray images were reduced to 100 mm to investigate which factors caused the decrement noted in the radiology literature. The 14-in. x 17-in. images used were generated from a 3M phantom. Three levels of kilovolt potential (80 kVp, 110 kVp, and 140 kVp) and two types of film (RPR and Cronex) were used to make the images. Twenty-four images, six for each of four quadrants, contained a simulated lung nodule and six contained no nodule. The 100-mm images were precisely controlled, miniaturized images of the above films. The task of the 16 non-radiologists was to decide if a simulated nodule was present or not. A signal detection experimental paradigm with a 10-point certainty scale was used for analysis. Correction for location was also implemented. For the first problem, results showed that kilovolt potential and film type interacted with the reduction procedure to change the direction of sensitivity (both in the positive and the negative directions) in the reduced format stimulus set, thereby indicating that the 100-mm format was not the main reason for reduced sensitivity noted in the literature. Our conclusion was that the 100-mm format would be suitable for image enhancement displays and for permanent hard copy in a photoelectronic radiologic imaging system. The second problem explores the effects of training on detection and sensitivity. The responses of the untrained observers to the 14-in. x 17-in. images were compared to previously gathered data of the staff and residents of the Arizona Health Sciences Center Radiology Department. Results indicated that the residents, even before formal training, were much better than the untrained observers, but well below the staff, in detection sensitivity. Within 6 months to a year later, they were equivalent to the staff. The main conclusion was that sensitivity does increase with training fairly rapidly and that the findings would be useful in designing further studies to investigate means to speed up or enhance the procedures used to train new radiologists.

A novel MRI method, DIFRAD-FSE (D̲i̲f̲fusion with R̲adial A̲cquisition of D̲ata with F̲ast S̲pin-E̲cho) is presented that enables rapid, high-resolution, multi-shot diffusion-weighted MRI without significant artifacts due to motion. Following a diffusion-weighted spin-echo preparation, multiple radial lines of Fourier data are acquired using spin-echo refocusing. Data can be acquired in either 2D or 3D Fourier space. Motion correction is accomplished via one of four correction techniques: phase correction, shift correction, a combination of the phase and shift correction, or magnitude. Images from a radial data set are reconstructed with filtered back projection reconstruction. Results from human brain imaging will demonstrate the ability of DIFRAD-FSE to acquire high-resolution images without significant artifacts due to motion in both 2D and 3D. Results from liver and heart imaging demonstrate the versatility of the 2D DIFRAD-FSE.

Over the last few years there has been a great demand for noninvasive, dedicated, small-animal imaging systems for biomedical research applications. In this dissertation we will discuss the development and performance of two gamma-ray systems and a dual modality CT/SPECT system. Initially we introduce FASTSPECT, a stationary, scintillator-based, single-photon emission computed tomography (SPECT) system that was originally built as a brain imager. We discuss its transformation into a small-animal imaging system and validate its performance by presenting high-resolution images of phantoms and animals. Furthermore, we discuss the development of an in vivo imaging protocol for rat myocardial models using FASTSPECT. The infarct size obtained from the images is quantified and compared with the myocardial infarct size measured from histology. Semiconductor detectors can exhibit good spatial and energy resolution, and therefore offer a promising alternative to scintillation technology. We discuss the performance of a semiconductor detector system, previously developed in our group, for planar and tomographic imaging of small animals. The same gamma-ray detector is used in a dual modality system for imaging mice. The system combines an anatomical imaging modality, x-ray CT, with a functional modality, SPECT. We present the development of the CT/SPECT system and illustrate its performance by presenting high-resolution images of phantoms and mice. Finally, we introduce a procedure for evaluating estimation methods without the use of a gold standard.