Improvements In computed tomography perfusion output using complex singular value decomposition and the maximum slope algorithm

OBJECTIVE: Determine if complex singular value decomposition (cSVD) used as preprocessing in the maximum slope algorithm reduces image noise of resultant physiologic parametric images. Noise will be decreased in the parametric maps of cerebral blood flow (CBF), cerebral blood volume (CBV) as compared to the same algorithm and data set with no cSVD applied. MATERIALS AND METHODS: A set of 10 patients (n=15) underwent a total combined 15 CT perfusion studies upon presenting with stroke symptoms. It was determined these patients suffered from occlusions resulting in a prolonged arrival time of blood to the brain. DICOM data files of these patients scans were selected based on this increased arrival delay. We compared the output of estimation calculations for cerebral blood flow (CBF), and cerebral blood volume (CBV), using preprocessing cSVD against the same scan data with no preprocessing cSVD. Image noise was assessed through the calculation of the standard deviation within specific regions of interest copied to specific areas of grey and white matter as well as CSF space. A decrease in the standard deviation values will indicate improvement in the noise level of the resultant images.. Results for the mean value within the regions of interest are expected to be similar between the groups calculated using cSVD and those calculated under the standard method. This will indicate the presence of minimal bias. RESULTS: Between groups of the standard processing method and the cSVD method standard deviation (SD) reductions were seen in both CBF and CBV values across all three ROIs. In grey matter measures of CBV, SD was reduced an average of 0.0034 mL/100g while measures of CBF saw SD reduced by an average of 0.073 mL/100g/min. In samples of white matter, standard deviations of CBV values were reduced on average by 0.0041mL/100g while CBF SD's were reduced by 0.073 mL/100g/min. CSF ROIs in CBV calculations saw SD reductions averaging 0.0047 mL/100g and reductions of 0.074 mL/100g/min in measures of CBF. Bias within CBV calculations was at most minimal as determined by no significant changes in mean calculated values. Calculations of CBF saw large downward bias in the mean values. CONCLUSIONS: The application of the cSVD method to preprocessing of CT perfusion imaging studies produces an effective method of noise reduction. In calculations of CBV, cSVD noise reduction results in overall improvement. In calculations of CBF, cSVD, while effective in noise reduction, caused mean values to be statistically lower than the standard method. It should be noted that there is currently no evaluation of which values can be considered more accurate physiologically. Simulations of the effect of noise on CBF showed a positive correlation suggesting that the CBF algorithm itself is sensitive to the level of noise

Qualitative and quantitative whole-body MRI assessment of metastatic disease in patients with radio-recurrent prostate cancer

The thesis provides an overview of my research on the evaluation of whole-body magnetic resonance imaging (WB-MRI) as a single step imaging technique for assessment of metastasis in patients presenting with radio-recurrent prostate cancer (PCa). The work presented is the interim analysis of the LOCATE (localising occult prostate cancer metastasis with advanced imaging techniques) prospective clinical trial (study REC number: 15/LO/0776) Chapter 1 provides a literature review of available clinical and research imaging techniques for evaluation of metastatic disease in the radio-recurrent prostate cancer setting. It introduces the WB-MRI techniques employed in chapters 2-5, provides an overview of pathophysiological basis for WB-MRI signal changes and a review of current WB-MRI literature related to PCa. Chapter 2 presents the first part of my research, addressing the repeatability of lymph node and bone lesion size measurements conducted on various sequences on WB- MRI studies. This critical piece of work underpins the development of the reference standard applied for WB-MRI qualitative and quantitative analysis presented in chapters 3 and 4 respectively. Chapter 3 addresses quantitative imaging biomarkers namely signal fat fraction (sFF), apparent diffusion co-efficient (ADC) and signal enhancement ratio (SER) obtained from WB-MRI and assesses each as a classifier of nodal & bony metastatic disease status. Chapter 4 addresses the diagnostic accuracy of WB- MRI as a qualitative imaging modality evaluated by expert radiologists; compared against an enhanced reference standard (involving clinical and imaging 1-year follow-up). Sensitivity/specificity of WB- MRI is determined on a per-patient basis. Sensitivity/specificity analyses of conventional imaging is also provided. Finally, in this chapter, locked sequential read analysis for the whole-body MRI sequences is presented. Chapter 5 is a health economic analysis of imaging techniques evaluated in chapter 3. It was done in collaboration with the health economics team, in order to carry out a cost comparison analyses between whole body MRI and conventional imaging. Chapter 6 is a summary of main findings and discussions from chapters in this thesis. It also dwells on potential applications and future perspectives on some of the imaging techniques explored in this thesis