Resolution Properties in Regularized Dynamic MRI Reconstruction

In dynamic MRI, one is constantly addressing the tradeoff between spatial and temporal resolution. Regularized reconstruction methods may offer benefits in terms of this tradeoff. However, selection of the regularization parameters is challenging. In this work we examine the spatial and temporal resolution of penalized-likelihood image reconstruction for dynamic MRI, and present an accelerated method for computing the local impulse response. This method may prove advantageous for regularization parameter selection.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85877/1/Fessler228.pd

Temporal Regularization Use in Dynamic Contrast-Enhanced MRI.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) studies demand both high spatial and high temporal resolution. We need high spatial resolution to accurately visualize tissue morphology, and we need high temporal resolution to accurately follow the contrast kinetics of the tissue, which provide clinically important physiological information. We can only acquire so many measurements per unit time, however, and this limited data implies an inherent tradeoff between spatial and temporal resolution in the reconstructed image sequence. Most existing methods undersample the data and then employ some sort of data sharing technique in the k-space domain to recover the ‘missing’ data points. These data sharing schemes are based on an implicit assumption that the dynamic object varies smoothly in time. We present an image reconstruction scheme based on an object domain model that does not attempt any k-space data recovery, but rather explicitly uses the assumption of temporal smoothness in the image domain to estimate the image sequence that best fits the available data. Our proposed method is called Temporal Regularization Use in Image Reconstruction (TRUIR), and is a penalized likelihood formulation that includes spatial and temporal regularization terms in addition to the data fidelity term. This work presents our TRUIR formulation for both single coil and parallel imaging, and explores various aspects of TRUIR reconstructed image sequences. We evaluate the effect of the spatial and temporal regularization parameters on the resolution properties of TRUIR reconstructed image sequences, and present our work toward establishing selection criteria for these parameters. In evaluating our proposed TRUIR method, we focus on the application of DCE-MRI in the characterization and assessment of breast cancer. Our simulation studies model contrast uptake in a dynamic digital breast phantom. Results show that TRUIR reconstructions offer improved temporal dynamics when compared to more traditional frame-by-frame reconstructions, as well as more accurate estimates of kinetic parameters, particularly when TRUIR is used in conjunction with two new proposed k-space sampling trajectories, which are also presented in this work. These new trajectories are also shown to be more robust to regularization parameter choice. Further work is needed to improve TRUIR’s spatial resolution.Ph.D.Biomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/84566/1/kkhalsa_1.pd

Temporal Regularization Use in Dynamic Contrast-Enhanced MRI

I am incredibly grateful to so many people for all of the love, support, and guidance I have received over the years. Of course, I’d like to thank my advisor, Jeff Fessler, who, for better or for worse, convinced me to go to grad school in the first place. He inspired me as an undergrad, and he inspires me still today. I think it’s safe to say that this dissertation wouldn’t exist without Jeff’s endless guidance, patience, and support. Thank you. I also want to thank the other members of my committee: Doug Noll, who first taught me the nuts and bolts of MRI, and whose group meetings and group members were an important part of my graduate education; Tom Chenevert, whose insights and knowledge regarding “real life ” DCE-MRI were invaluable to this research project; an

Disulfiram Attenuates Drug-Primed Reinstatement of Cocaine Seeking via Inhibition of Dopamine β-Hydroxylase

The antialcoholism medication disulfiram (Antabuse) inhibits aldehyde dehydrogenase (ALDH), which results in the accumulation of acetaldehyde upon ethanol ingestion and produces the aversive ‘Antabuse reaction' that deters alcohol consumption. Disulfiram has also been shown to deter cocaine use, even in the absence of an interaction with alcohol, indicating the existence of an ALDH-independent therapeutic mechanism. We hypothesized that disulfiram's inhibition of dopamine β-hydroxylase (DBH), the catecholamine biosynthetic enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic neurons, underlies the drug's ability to treat cocaine dependence. We tested the effects of disulfiram on cocaine and food self-administration behavior and drug-primed reinstatement of cocaine seeking in rats. We then compared the effects of disulfiram with those of the selective DBH inhibitor, nepicastat. Disulfiram, at a dose (100 mg/kg, i.p.) that reduced brain NE by ∼40%, did not alter the response for food or cocaine on a fixed ratio 1 schedule, whereas it completely blocked cocaine-primed (10 mg/kg, i.p.) reinstatement of drug seeking following extinction. A lower dose of disulfiram (10 mg/kg) that did not reduce NE had no effect on cocaine-primed reinstatement. Nepicastat recapitulated the behavioral effects of disulfiram (100 mg/kg) at a dose (50 mg/kg, i.p.) that produced a similar reduction in brain NE. Food-primed reinstatement of food seeking was not impaired by DBH inhibition. Our results suggest that disulfiram's efficacy in the treatment of cocaine addiction is associated with the inhibition of DBH and interference with the ability of environmental stimuli to trigger relapse