Riparian Restoration, Success Criteria, and Application to the BART Sabrecat Creek Riparian Restoration Project in Fremont, California

Riparian restoration is a complex, inter-disciplinary field that is open to interpretation by its practitioners. This research reviews some of the critical elements of riparian restoration, including the watershed, surrounding land use, adjacent habitat, and riparian buffers; special-status species, endangered species, and habitat type and structure; invasive species control; water quality and hydrology; and soil and soil microbial communities. Three methods of evaluating restoration projects are discussed, including the Society for Ecological Restoration International Primer, the California Department of Fish and Wildlife (CDFW) California Salmonid Stream Habitat Restoration Manual and CDFW permitting, and the California Rapid Assessment Method. Finally, the BART Sabrecat Creek Riparian Restoration Project is evaluated using the SER Primer

Conjugate-Gradient Preconditioning Methods for Shift-Variant PET Image Reconstruction

Gradient-based iterative methods often converge slowly for tomographic image reconstruction and image restoration problems, but can be accelerated by suitable preconditioners. Diagonal preconditioners offer some improvement in convergence rate, but do not incorporate the structure of the Hessian matrices in imaging problems. Circulant preconditioners can provide remarkable acceleration for inverse problems that are approximately shift-invariant, i.e., for those with approximately block-Toeplitz or block-circulant Hessians. However, in applications with nonuniform noise variance, such as arises from Poisson statistics in emission tomography and in quantum-limited optical imaging, the Hessian of the weighted least-squares objective function is quite shift-variant, and circulant preconditioners perform poorly. Additional shift-variance is caused by edge-preserving regularization methods based on nonquadratic penalty functions. This paper describes new preconditioners that approximate more accurately the Hessian matrices of shift-variant imaging problems. Compared to diagonal or circulant preconditioning, the new preconditioners lead to significantly faster convergence rates for the unconstrained conjugate-gradient (CG) iteration. We also propose a new efficient method for the line-search step required by CG methods. Applications to positron emission tomography (PET) illustrate the method.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85979/1/Fessler85.pd

Combined Diagonal/Fourier Preconditioning Methods for Image Reconstruction in Emission Tomography

Iterative methods for tomographic image reconstruction often converge slowly. Preconditioning methods can often accelerate gradient-based iterations. Previous preconditioning methods for PET reconstruction have used either diagonal or Fourier-based preconditioners. Fourier-based preconditioners are well suited to problems with near-circulant Hessian matrices. However, due to the nonuniform Poisson noise variance in PET, the circulant approximation to the Hessian is suboptimal. This paper shows that a particular combined diagonal/Fourier preconditioner yields a more accurate approximation to the Hessian and gives significantly faster convergence rates than does either preconditioner used alone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85972/1/Fessler135.pd

Benefits of Position–Sensitive Detectors for Source Detection with Known Background

We address the question of whether or not the directional or imaging information offered by a position-sensitive gamma-ray detector improves the detection accuracy when searching for a source of known shape amid a background of known intensity. We formulate the detection problem as a composite hypothesis testing problem and examine the behavior of the generalized likelihood ratio test (GLRT) in terms of the area under the receiver operating characteristic (AUC). Due to the analytical complexity of the GLRT in this case, we examine its asymptotic properties when the number of detected photons is large. We find that a detector of uniform sensitivity can more accurately detect a source when imaging information is used.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85968/1/Fessler245.pd

Benefits of Position-Sensitive Detectors for Radioactive Source Detection

There are many systems for counting photons such as gamma-rays emitted from radioactive sources. Many of these systems are also position-sensitive, which means that the system provides directional information about recorded events. This paper investigates whether or not the additional information provided by position-sensitive capability improves the performance of detecting a point-source in background. We analyze the asymptotic performance of the generalized likelihood ratio test (GLRT) and a test based on the maximum-likelihood (ML) estimate of the source intensity for systems with and without position-sensitive capability. When the background intensity is known and detector sensitivity is spatially uniform, we prove that position-sensitive capability increases the area under the receiver operating characteristic curve (AUC). For cases when detector sensitivity is nonuniform or background intensity is unknown, we provide numerical results to illustrate the effect of the parameters on detection performance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85967/1/Fessler6.pd

Joint Maxiniurn Likelihood Estimation of Emission and Attenuation Densities in PET

Accurate attenuation correction can be performed in PET (positron emission tomography) using transmission scanning to estimate the survival probabilities along each coincidence line. However, since these measurements are typically corrupted by Poisson counting noise, they propagate additional uncertainty into reconstructed images and kinetic parameter estimates. This can be especially true in the thorax where the attenuating medium is heterogeneous and the statistical precision of the transmission scan may be approximately the same as that of the emission data. To account for the Poisson noise in the transmission measurement, the authors have developed a sieve-constrained maximum likelihood algorithm that jointly estimates both the survival probability and the emission intensity. They present some of their initial experiences in using the joint alternate and maximize algorithm with simulated PET data.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85813/1/Fessler119.pd

Treatment of Advanced Emphysema with Emphysematous Lung Sealant (AeriSeal (R))

Background: This report summarizes initial tests of an emphysematous lung synthetic polymer sealant (ELS) designed to reduce lung volume in patients with advanced emphysema. Objectives: The primary study objective was to define a therapeutic strategy to optimize treatment safety and effectiveness. Methods: ELS therapy was administered bronchoscopically to 25 patients with heterogeneous emphysema in an open-label, noncontrolled study at 6 centers in Germany. Treatment was performed initially at 2-4 subsegments. After 12 weeks, patients were eligible for repeat therapy to a total of 6 sites. Safety and efficacy were assessed after 6 months. Responses were evaluated in terms of changes from baseline in lung physiology, functional capacity, and health-related quality of life. Follow-up is available for 21 of 25 patients. Results: Treatment was well tolerated. There were no treatment-related deaths (i.e. within 90 days of treatment), and an acceptable short-and long-term safety profile. Physiological and clinical benefits were observed at 24 weeks. Efficacy responses were better among Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage III patients {[}n = 14; change in residual volume/total lung capacity (Delta RV/TLC) = -7.4 +/- 10.3%; Delta forced expiratory volume in 1 s (Delta FEV(1)) = +15.9 +/- 22.6%; change in forced vital capacity (Delta FVC) = +24.1 +/- 22.7%; change in carbon monoxide lung diffusion capacity (Delta DLCO) = +19.3 +/- 34.8%; change in 6-min walk test (Delta 6MWD) = +28.7 +/- 59.6 m; change in Medical Research Council Dyspnea (Delta MRCD) score = -1.0 +/- 1.04 units; change in St. George's Respiratory Questionnaire (Delta SGRQ) score = -9.9 +/- 15.3 units] than for GOLD stage IV patients (n = 7; Delta RV/TLC = -0.5 +/- 6.4%; Delta FEV 1 = +2.3 +/- 12.3%; Delta FVC = +2.6 +/- 21.1%; Delta DLCO = -2.8 +/- 17.2%; Delta 6MWD = +28.3 +/- 58.4 m; Delta MRCD = 0.3 +/- 0.81 units; Delta SGRQ = -6.7 +/- 7.0 units). Conclusions: ELS therapy shows promise for treating patients with advanced heterogeneous emphysema. Additional studies to assess responses in a larger cohort with a longer follow-up are warranted. Copyright (C) 2011 S. Karger AG, Base

Transmission Imaging With Axially Overlapping Cone-Beams

We have shown that cone-beam transmission imaging of medium-energy photons that penetrate the parallel-hole collimators can be used to rapidly estimate attenuation maps for use in reconstruction of cardiac SPECT images. Such a transmission imaging geometry offers the advantages of eliminating the need to mechanically move the point-sources during imaging, and minimizes cross-talk between emission and transmission imaging. The axial extent over which artifact-free attenuation maps can be reconstructed is limited by the cone-beam geometry and source collimation. We investigated irradiation of a single head by multiple point-sources such that their asymmetric cone-beam fields overlap in the axial direction as a method of extending the axial coverage of the patient. This study reports on testing of a penalized-likelihood algorithm for transmission reconstruction of overlapping cone-beams. This algorithm was evaluated through MCAT simulations and applied to transmission measurements of an anthropomorphic phantom. The experimental work consisted of performing a series of flood and transmission measurements on the anthropomorphic phantom with shifted axial locations of point-sources. We summed the projection data from individual measurements to simulate the projection data for a multiple point-source system. With the proposed penalized-Iikelihood algorithm, the full axial extent (20.5 cm) of the anthropomorphic phantom was reconstructed for the overlapping cone-beam geometry with 2 point-sources per camera head.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85904/1/Fessler202.pd

Evaluation of the Ordered-Subset Transmission (OSTR) Algorithm for Transmission Imaging on SPECT Systems Using Axially Overlapping Cone-Beams

Cone-beam transmission imaging employing medium-energy photons which penetrate parallel-hole collimators can be used to rapidly estimate attenuation maps for use in reconstruction of cardiac SPECT images. Such a transmission imaging geometry offers the advantage of eliminating the need to mechanically move the point-sources during imaging, and enables fast sequential transmission scans. The axial extent over which artifact-free attenuation maps can be reconstructed is limited by the cone-beam geometry and point-source collimation. We investigated irradiation of a single head by multiple point-sources whose asymmetric cone-beam fields overlap in the axial direction as a method of extending the axial coverage of the patient. This study reports on the development and testing of a penalized-likelihood algorithm for transmission reconstruction of overlapping asymmetric cone-beams. We evaluated this algorithm and optimized the reconstruction parameters through MCAT phantom simulations. We then and applied the algorithm to transmission measurements of an anthropomorphic phantom. The experimental work consisted of performing a series of flood and transmission measurements on the anthropomorphic phantom with shifted axial locations of point-sources. We summed the projection data from individual measurements to simulate the projection data for a multiple point-source system. With the proposed penalized-likelihood algorithm, the full axial extent (20.5 cm) of the anthropomorphic phantom was reconstructed for the overlapping cone-beam geometry with two point-sources per camera head.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85997/1/Fessler43.pd