UBC Theses and Dissertations
Comparison of combinations of various levels of GraSE and compressed sensing on luminal water imaging measurements in MRI Bohnet, Barry
Several methods have been developed to decrease scanning times including gradient-and-spin echo (GraSE) imaging, and compressed sensing. One of the benefits of both techniques is that they can decrease scan time to varying degrees by changing the GraSE factor or sampling level. An electronic phantom was created to model a single slice multi-echo magnetic resonance imaging (acquisitions using different GraSE factors, sampling levels, and signal-to-noise ratios (SNRs). The image included two types of prostatic tissue, peripheral zone and transitional zone, both with the signal composed of two different T2 decay values. LWI analysis was applied to the resulting images and the resulting T2 decay values and luminal water fraction (LWF) measurements were compared with a modeled multi-echo spin echo sequence without noise. The results of comparing the error with the theoretical scan times suggest that if scan times are comparable, the errors will be comparable. As the SNR decreased preference shifted towards using lower GraSE when possible. Next a celery phantom was scanned because it shows two T2 components with values similar to those found in an in-vivo prostate. 3D GraSE Images were acquired with different GraSE factors and had simulated undersampling to various degrees. Measurements of the reconstructions were compared to the fully sampled GraSE factor 3 images and agreed with the previous result that similar scan times lead to similar errors, showing no preference for a higher or lower GraSE factor. Lastly one patient had 3D multi-echo GraSE images taken of their prostate. Images had a simulated undersampling of various levels and reconstructions were compared to the fully sampled GraSE factor 3 images. Again, similar scan times resulted in similar error measurements. For the celery and human prostate scans, selected combinations of GraSE factor and sampling levels were simulated with one hundred different sampling schemes each in order to observe the variability due to the chosen sampling scheme. Following our method of fully sampling the central 33% of k-space and randomly sampling the remainder, the results strongly suggest that different sampling schemes of the same level have little effect on the resulting LWF and T2 measurements.
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