A single photon emission computed tomography (SPECT) imaging system can be modeled by a linear operator
H that maps from object space to detector pixels in image space. The singular vectors and singular-value spectra
of H provide useful tools for assessing system performance. The number of voxels used to discretize object space
and the number of collection angles and pixels used to measure image space make the matrix dimensions H
large. As a result, H must be stored sparsely which renders several conventional singular value decomposition
(SVD) methods impractical. We used an iterative power methods SVD algorithm (Lanczos) designed to operate
on very large sparsely stored matrices to calculate the singular vectors and singular-value spectra for two small
animal pinhole SPECT imaging systems: FastSPECT II and M3R. The FastSPECT II system consisted of two
rings of eight scintillation cameras each. The resulting dimensions of H were 68921 voxels by 97344 detector
pixels. The M3R system is a four camera system that was reconfigured to measure image space using a single
scintillation camera. The resulting dimensions of H were 50864 voxels by 6241 detector pixels. In this paper we
present results of the SVD of each system and discuss calculation of the measurement and null space for each
system.
Design of receiver-operating characteristic (ROC)-based paradigm and data analysis methods that capture and adequately address the complexity of clinical decision-making will facilitate the development and evaluation of new image acquisition, reconstruction and processing techniques. We compare the JAFROC (Jackknife free-response ROC) to traditional ROC paradigm and analysis in two image evaluation studies. The first study is designed to address advantages of "free response" features of JAFROC paradigm in a breast lesion detection task. We developed tools allowing the acquisition of FROC-type rating data and use them on a set of simulated scintimammography images. Four observers participated in a small preliminary study. Rating data are then analyzed using traditional ROC and JAFROC techniques. The second study is aimed at comparing the diagnostic quality of myocardial perfusion SPECT (MPS) images obtained with different quantitative image reconstruction and compensation methods in an ongoing clinical trial. The observer assesses status of each of the three main vascular territories for each patient. This experimental set-up uses standardized locations of vascular territories on myocardial polar plot images, and a fixed number of three rating scores per patient. We compare results from the newly available JAFROC versus the traditional ROC analysis technique previously applied in similar studies, using a set of data from an on-going clinical trial. Comparison of two analysis methodologies reveals generally consistent behavior, corresponding to theoretical predictions.
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