Fully 3D PET Image Reconstruction Using A Fourier Preconditioned Conjugate-Gradient Algorithm

Since the data sixes in fully 3D PET imaging are very large, iterative image reconstruction algorithms must converge in very few iterations to be useful. One can improve the convergence rate of the conjugate-gradient (CG) algorithm by incorporating preconditioning operators that approximate the inverse of the Hessian of the objective function. If the 3D cylindrical PET geometry were not truncated at the ends, then the Hessian of the penalized least-squares objective function would be approximately shift-invariant, i.e. G'G would be nearly block-circulant, where G is the system matrix. The authors propose a Fourier preconditioner based on this shift-invariant approximation to the Hessian. Results show that this preconditioner significantly accelerates the convergence of the CG algorithm with only a small increase in computation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86015/1/Fessler139.pd

Maximum-Likelihood Transmission Image Reconstruction for Overlapping Transmission Beams

In many transmission imaging geometries, the transmitted "beams" of photons overlap on the detector, such that a detector element may record photons that originated in different sources or source locations and thus traversed different paths through the object. Examples include systems based on scanning line sources or on multiple parallel rod sources. The overlap of these beams has been disregarded by both conventional analytical reconstruction methods as well as by previous statistical reconstruction methods. The authors propose a new algorithm for statistical image reconstruction of attenuation maps that explicitly accounts for overlapping beams in transmission scans. The algorithm is guaranteed to monotonically increase the objective function at each iteration. The availability of this algorithm enables the possibility of deliberately increasing the beam overlap so as to increase count rates. Simulated single photon emission tomography transmission scans based on a multiple line source array demonstrate that the proposed method yields improved resolution/noise tradeoffs relative to "conventional" reconstruction algorithms, both statistical and nonstatistical.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85818/1/Fessler78.pd

Maximum Likelihood Transmission Image Reconstruction for Over lapping Transmission Beams

In many transmission imaging geometries, the transmitted “beams” of photons overlap on the detector, such that a detector element may record photons that originated in different sources or source locations and thus traversed different paths through the object, Examples include systems based on scanning line sources or on multiple parallel rod sources. The overlap of these beams has been disregarded by both conventional analytical reconstruction methods as well as by previous statistical reconstruction methods. We propose a new algorithm for statistical image reconstruction of attenuation maps that explicitly accounts for overlapping beams in transmission scans. The algorithm is guaranteed to monotonically increase the objective function at each iteration. The availability of this algorithm enables the possibility of deliberately increasing the beam overlap so as to increase count rates. Simulated SPECT transmission scans based on a multiple line source array demonstrate that the proposed method yields improved resolution/noise tradeoffs relative to “conventional” reconstruction algorithms, both statistical and nonstatistical.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85817/1/Fessler156.pd

Fast Parallelizable Algorithms for Transmission Image Reconstruction

Presents a new class of algorithm for penalized-likelihood reconstruction of attenuation maps from low-count transmission scans. The authors derive the algorithms by applying to the transmission log-likelihood a variation of the convexity technique developed by De Pierro for the emission case. The new algorithms overcome several limitations associated with previous algorithms. (1) Fewer exponentiations are required than in the transmission EM algorithm or in coordinate-ascent algorithms. (2) The algorithms intrinsically accommodate nonnegativity constraints, unlike many gradient-based methods. (3) The algorithms are easily parallelizable, unlike coordinate-ascent algorithms and perhaps line-search algorithms. The authors show that the algorithms converge faster than several alternatives, even on conventional workstations. They give examples from low-count PET transmission scans and from truncated fan-beam SPECT transmission scans.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86006/1/Fessler136.pd

Deadtime correction for two multihead Anger cameras in 131I dual‐energy‐window‐acquisition mode

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134914/1/mp8162.pd

In vivo mapping of cholinergic terminals in normal aging, Alzheimer's disease, and Parkinson's disease

To map presynaptic cholinergic terminal densities in normal aging (n = 36), Alzheimer's disease (AD) (n = 22), and Parkinson's disease (PD) (n = 15), we performed single-photon emission computed tomography using [ 123 I]iodoben-zovesamicol (IBVM), an in vivo marker of the vesicular acetylcholine transporter. We used coregistered positron emission tomography with [ 18 F]fluorodexyglucose for metabolic assessment and coregistered magnetic resonance imaging for atrophy assessment. In controls (age, 22–91 years), cortical IBVM binding declined only 3.7% per decade. In AD, cortical binding correlated inversely with dementia severity. In mild dementia, binding differed according to age of onset, but metabolism did not. With an onset age of less than 65 years, binding was reduced severely throughout the entire cerebral cortex and hippocapus (about 30%), but with an onset age of 65 years or more, binding reductions were restricted to temporal cortex and hippocampus. In PD without dementia, binding was reduced only in parietal and occipital cortex, but demented PD subjects had extensive cortical binding decreases similar to early-onset AD. We conclude that cholinergic neuron integrity can be monitored in living AD and PD patients, and that it is not so devastated in vivo as suggested by postmortem choline acetylransferase activity (50–80%).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50361/1/410400309_ftp.pd