Jason G. Parker

Motion estimation for cardiac emission tomography by optical flow methods.

This paper describes a new method for estimating the 3D, non-rigid object motion in a time sequence of images. The method is a generalization of a standard optical flow algorithm that is incorporated into a successive quadratic approximation framework. The method was evaluated for gated cardiac emission tomography using images obtained from a mathematical, 4D phantom and a physical, dynamic phantom. The results showed that the proposed method offers improved motion estimation accuracy relative to the standard optical flow method. Convergence of the proposed algorithm was evidenced with a monotonically decreasing objective function value with iteration. Practical application of the motion estimation method in cardiac emission tomography includes quantitative myocardial motion estimation and 4D, motion-compensated image reconstruction.

Respiratory motion correction in gated cardiac SPECT using quaternion-based, rigid-body registration

In this article, a new method is introduced for estimating the motion of the heart due to respiration in gated cardiac SPECT using a rigid-body model with rotation parametrized by a unit quaternion. The method is based on minimizing the sum of squared errors between the reference and the deformed frames resulting from the usual optical flow constraint by using an optimized conjugate gradient routine. This method does not require any user-defined parameters or penalty terms, which simplifies its use in a clinical setting. Using a mathematical phantom, the method was quantitatively compared to the principal axis method, as well as an iterative method in which the rotation matrix was represented by Euler angles. The quaternion-based method was shown to be substantially more accurate and robust across a wide range of extramyocardial activity levels than the principal axis method. Compared with the Euler angle representation, the quaternion-based method resulted in similar accuracy but a significant reduction in computation times. Finally, the quaternion-based method was investigated using a respiratory-gated cardiac SPECT acquisition of a human subject. The motion-corrected image has increased sharpness and myocardial uniformity compared to the uncorrected image.

Enhanced control of dorsolateral prefrontal cortex neurophysiology with real-time functional magnetic resonance imaging (rt-fMRI) neurofeedback training and working memory practice.

Real-time functional magnetic resonance imaging (rt-fMRI) neurofeedback can be used to train localized, conscious regulation of blood oxygen level-dependent (BOLD) signals. As a therapeutic technique, rt-fMRI neurofeedback reduces the symptoms of a variety of neurologic disorders. To date, few studies have investigated the use of self-regulation training using rt-fMRI neurofeedback to enhance cognitive performance. This work investigates the utility of rt-fMRI neurofeedback as a tool to enhance human cognition by training healthy individuals to consciously control activity in the left dorsolateral prefrontal cortex (DLPFC). A cohort of 18 healthy participants in the experimental group underwent rt-fMRI neurofeedback from the left DLPFC in five training sessions across two weeks while 7 participants in the control group underwent similar training outside the MRI and without rt-fMRI neurofeedback. Working memory (WM) performance was evaluated on two testing days separated by the five rt-fMRI neurofeedback sessions using two computerized tests. We investigated the ability to control the BOLD signal across training sessions and WM performance across the two testing days. The group with rt-fMRI neurofeedback demonstrated a significant increase in the ability to self-regulate the BOLD signal in the left DLPFC across sessions. WM performance showed differential improvement between testing days one and two across the groups with the highest increases observed in the rt-fMRI neurofeedback group. These results provide evidence that individuals can quickly gain the ability to consciously control the left DLPFC, and this training results in improvements of WM performance beyond that of training alone.

Functional MRI mapping of visual function and selective attention for performance assessment and presurgical planning using conjunctive visual search

Accurate mapping of visual function and selective attention using fMRI is important in the study of human performance as well as in presurgical treatment planning of lesions in or near visual centers of the brain. Conjunctive visual search (CVS) is a useful tool for mapping visual function during fMRI because of its greater activation extent compared with high‐capacity parallel search processes.

Wall Motion Estimation for Gated Cardiac Emission Tomography: Physical Phantom Evaluation

The purpose of this work was to develop a physical phantom for testing the accuracy of cardiac wall motion estimation algorithms, and to use the phantom to evaluate several motion estimation and reconstruction methods, including a simultaneous image reconstruction/wall motion estimation algorithm we have developed. Our approach was to attach radioactive markers to the myocardial wall of a dynamic cardiac phantom and to trace the motion of the markers throughout the cardiac cycle via gated SPECT acquisition. Then, without moving the phantom, and after the markers were allowed to decay to negligible levels, the myocardium was injected with 99mTc and a gated SPECT scan was acquired. From the gated myocardial emission data, two wall motion estimation methods were evaluated. The first method was by applying an optical flow algorithm to an optimized OSEM reconstruction of the myocardial emission data. The second was by applying our simultaneous image reconstruction/motion estimation algorithm to the myocardial emission data. The error in the estimated motion fields was described by the average Euclidean distance between the motion of the markers and the estimated motion. Values of 0.15 and 0.14 were found for the average Euclidean distance for the optical flow method applied to OSEM and the simultaneous method, respectively. Image quality was also evaluated and, in agreement with our previous findings, the simultaneous method produced myocardial images with improved noise characteristics and better uniformity in terms of the activity distribution within the myocardium.

Performance Evaluation of a Bedside Cardiac SPECT System

This paper reports on the initial performance evaluation of a bedside cardiac PET/SPECT system. The system was designed to move within a hospital to image critically-ill patients, for example, those in intensive care unit (ICU) or emergency room settings, who cannot easily be transported to a conventional SPECT or PET facility. The system uses two compact (25 cm times 25 cm) detectors with pixilated NaI crystals and position sensitive PMTs. The performance is evaluated for both 140 keV (Tc-99m) and 511 keV (F-18) emitters with the system operating in single photon counting (SPECT) mode. The imaging performance metrics for both 140 keV and 511 keV included intrinsic energy resolution, spatial resolution (intrinsic, system, and reconstructed SPECT), detection sensitivity, count rate capability, and uniformity. Results demonstrated an intrinsic energy resolution of 31% at 140 keV and 23% at 511 keV, a planar intrinsic spatial resolution of 5.6 mm full width half-maximum (FWHM) at 140 keV and 6.3 mm FWHM at 511 keV, and a sensitivity of 4.15 countsmiddotmuCi-1 ldr s-1 at 140 keV and 0.67 counts ldr muCi-1 ldr s-1 at 511 keV. To further the study, a SPECT acquisition using a dynamic cardiac phantom was performed, and the resulting reconstructed images are presented.

Performance evaluation of a small field-of-view, mobile PET/SPECT system

This paper reports on the initial performance evaluation of a small field-of-view, mobile PET/SPECT system for bedside imaging. The system was designed to move within a hospital to image patients who cannot easily be transported to a conventional PET or SPECT facility, for example, patients within an intensive care unit (ICU). The focus of the system is cardiac imaging in which both viability (18F fluorodeoxyglucose; FDG) and perfusion (99mTc Sestamibi) images are desired. This paper evaluates the capabilities of the mobile system for acquisitions at both 140 keV (Tc-99 m) and at 511 keV (F-18) operated in single photon counting mode. Parameters evaluated were the planar and reconstructed SPECT spatial resolution, the intrinsic energy resolution, sensitivity, and the count rate capability. Results demonstrate an intrinsic energy resolution of 32% at 140 keV and 23% at 511 keV, a planar intrinsic spatial resolution of 0.56 cm full width half-maximum (FWHM) at 140 keV and 0.61 cm FWHM at 511 keV, a system spatial resolution at 10 cm of 1.14 cm FWHM for both 140 keV and 511 keV, a reconstructed SPECT spatial resolution of 1.37 cm at 140 keV (22 cm radius-of-rotation), a sensitivity of 3.1 countsldrmuC-1ldrs-1 at 140 keV and 0.48 countsldrmuC-1ldrs-1 at 511 keV, and a maximum count rate of 1.46 times 105 counts/s at 140 keV and 1.56 times 105 counts/s at 511 keV.

Evaluation of a Clinical fMRI Cueing System Utilizing Complex Scene and Auditory Stimuli for Neurosurgical Treatment Planning of Patients with Cognitive and Physical Deficits

Purpose: The adoption of functional MRI for presurgical planning in neuro-oncology has been limited by the high degree of patient compliance required to generate accurate activation maps. The purpose of this work was to evaluate the brain activation properties and patient head motion associated with a presurgical fMRI cueing system utilizing complex scene and auditory commands to enhance compliance in patients with cognitive and physical deficits. Materials and Methods: An fMRI cueing system which delivered simultaneous audio and video task instructions was compared to a simple visual cueing system across 10 healthy volunteers, each performing two different motor tasks (40 total fMRI acquisitions). Statistical differences between the complex and simple cueing systems were evaluated using a mixed effects modeling method which was able to carry up variances from the individual analyses to the group analysis. Differences in relative head motion between the systems were evaluated using a paired t-test. Results: Both cueing systems demonstrated typical somatotopic activity distributions in the pre- and postcentral gyrus of the left hemisphere. No significant differences were found between the systems in target brain regions. Furthermore, relative head motion using the complex system was found to not differ statistically from the simple method. Conclusion: The fMRI cueing system using complex scene stimuli produced results comparable to a simple cueing system in target regions of the brain. In patients presenting with deficits that lead to noncompliance with fMRI procedures, the use of complex scene stimuli may provide a good alternative to conventional cueing methods.

Volitional down-regulation of the primary auditory cortex via directed attention mediated by real-time fMRI neurofeedback

The present work assessed the efficacy of training volitional down-regulation of the primary auditory cortex (A1) based on real-time functional magnetic resonance imaging neurofeedback (fMRI-NFT). A1 has been shown to be hyperactive in chronic tinnitus patients, and has been implicated as a potential source for the tinnitus percept. 27 healthy volunteers with normal hearing underwent 5 fMRI-NFT sessions: 18 received real neurofeedback and 9 sham neurofeedback. Each session was composed of a simple auditory fMRI followed by 2 runs of A1 fMRI-NFT. The auditory fMRI alternated periods of no auditory with periods of white noise stimulation at 90 dB. A1 activity, defined from a region using the activity during the preceding auditory run, was continuously updated during fMRI-NFT using a simple bar plot, and was accompanied by white noise (90 dB) stimulation for the duration of the scan. Each fMRI-NFT run alternated “relax” periods with “lower” periods. Subjects were instructed to watch the bar during the relax condition and actively reduce the bar by decreasing A1 activation during the lower condition. Average A1 de-activation, representative of the ability to volitionally down-regulate A1, was extracted from each fMRI-NFT run. A1 de-activation was found to increase significantly across training and to be higher in those receiving real neurofeedback. A1 de-activation in sessions 2 and 5 were found to be significantly greater than session 1 in only the group receiving real neurofeedback. The most successful subjects reportedly adopted mindfulness tasks associated with directed attention. For the first time, fMRI-NFT has been applied to teach volitional control of A1 de-activation magnitude over more than 1 session. These are important findings for therapeutic development as the magnitude of A1 activity is altered in tinnitus populations and it is unlikely a single fMRI-NFT session will reverse the effects of tinnitus.

Single Session Low Frequency Left Dorsolateral Prefrontal Transcranial Magnetic Stimulation Changes Neurometabolite Relationships in Healthy Humans

Background: Dorsolateral prefrontal cortex (DLPFC) low frequency repetitive transcranial magnetic stimulation (LF-rTMS) has shown promise as a treatment and investigative tool in the medical and research communities. Researchers have made significant progress elucidating DLPFC LF-rTMS effects—primarily in individuals with psychiatric disorders. However, more efforts investigating underlying molecular changes and establishing links to functional and behavioral outcomes in healthy humans are needed. Objective: We aimed to quantify neuromolecular changes and relate these to functional changes following a single session of DLPFC LF-rTMS in healthy participants. Methods: Eleven participants received sham-controlled neuronavigated 1 Hz rTMS to the region most activated by a 7-letter Sternberg working memory task (SWMT) within the left DLPFC. We quantified SWMT performance, functional magnetic resonance activation and proton Magnetic resonance spectroscopy (MRS) neurometabolite measure changes before and after stimulation. Results: A single LF-rTMS session was not sufficient to change DLPFC neurometabolite levels and these changes did not correlate with DLPFC activation changes. Real rTMS, however, significantly altered neurometabolite correlations (compared to sham rTMS), both with baseline levels and between the metabolites themselves. Additionally, real rTMS was associated with diminished reaction time (RT) performance improvements and increased activation within the motor, somatosensory and lateral occipital cortices. Conclusion: These results show that a single session of LF-rTMS is sufficient to influence metabolite relationships and causes widespread activation in healthy humans. Investigating correlational relationships may provide insight into mechanisms underlying LF-rTMS.