Measurement of regional blood oxygenation and cerebral hemodynamics

An echo planar linewidth mapping technique, Shufflebutt, has allowed temporal measurements of changes in linewidth caused by static inhomogeneities (delta LWSI) and transverse relaxation rate (delta R2) in models of hypoxia and hypercapnia. We demonstrate these changes are due to intravascular susceptibility differences/(delta chi) between the blood and tissue. Contrast agent injections at a delta chi equivalent to that of deoxygenated blood showed a twofold difference between the contrast agent and physiological anoxia values. Hypercapnia decreased both delta LWSI and delta R2 consistent with an increase in blood oxygenation. We attribute these findings to constant oxygen extraction during an increase in blood flow, resulting in less deoxygenated venous blood and thus reduced delta chi. For in vivo perturbations we found that delta R2/delta R2' approximately 0.33, a ratio much different from that measured in whole blood phantoms (delta R2/delta R2' approximately 2). This demonstrates that signal changes in these studies are produced predominantly by dephasing of extravascular protons due to field inhomogeneities produced by intravascular deoxygenated hemoglobin (deoxyHb).     

Graded functional activation in the visuospatial system with the amount of task demand

Immunocompromised hosts have defects in their immune system that make them at risk of developing a variety of infections. In addition, these persons may develop a wide variety of noninfectious disease processes that involve the lung. These disorders may be caused by the underlying disease process. This may be seen with the development of metastatic disease from the underlying neoplasm, or it may represent the development of a malignancy secondary to therapy, as is seen with posttransplant lymphoproliferative disease. The abnormalities may be a result of the therapy used to treat the patients, as is seen with radiation injury to the lung and drug toxicity. Pulmonary edema may occur and be from a wide variety of causes. All of these disease processes may simulate an infectious process and must be differentiated from infection to allow proper therapeutic intervention.     

The Design and Implementation of an On-Line Testable UART

This paper presents the design of a complex integrated circuit realised through a novel on-line test methodology. The circuit and its exact conventional equivalent both have been realised in FPGA technology. As such it represents one of the most complex designs realised to date using on-line test approaches. The approach used—IFIS incorporates dual-rail coding of individual data and a handshaking protocol, which substantially simplifies the detection of failure. Details of the IFIS methodology are given. The IFIS and conventional redesign of a commercial UART are reported, focusing on methodological issues as well as size and speed. Output traces are shown for the IFIS UART on FPGA operating under fault-free conditions and with deliberate failures injected.     

Functional,physiological, and metabolic toolbox for clinical magnetic resonance imaging: Integration of acquisition and analysis strategies

Selected neuroimaging strategies have been integrated into a clinical brain imaging protocol to provide quantitative high-resolution functional, physiological, and metabolic maps to complement exquisitely detailed anatomic images without excessively prolonging the conventional clinical examination or analysis time. The physiological maps of blood pool parameters (relative cerebral blood volume, tissue transit time, and arrival time), apparent diffusion coefficient, tissue water content, and functional neuronal activation maps are derived from series of images acquired with echo-planar imaging. The metabolic map reflecting tissue sodium homeostasis (tissue sodium concentration) is acquired using twisted projection imaging and a customized dual-tuned, dual-quadrature 23Na/1H brain radiofrequency coil that ensures coregistration of data and avoids moving the patient. The different types of acquired images are transferred to a common file format with customized file management software and the corresponding maps are derived by applying appropriate fitting algorithms. Customized software allows rapid interrogation and manipulation of all resultant images and maps for detailed but rapid interpretation, printing, and archiving immediately following completion of acquisition. As all acquisitions and processing are performed by the magnetic resonance technologist, the neuroradiologist is able to focus on the interpretation of this immensely rich data set. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 572–581, 1997     

Specified-resolution wavelet analysis of activation patterns from BOLD contrast fMRI

Functional magnetic resonance (MR) MR imaging (fMRI) with blood-oxygenation-level-dependent (BOLD) contrast localizes neuronal processing of cognitive paradigms. As magnetic resonance signal responses are small, functional mapping requires statistical analysis of temporally averaged image data. Although voxels activating at the paradigm frequency can be identified from the Fourier power spectrum, such analyses collapse the temporal information that is useful to establish consistency of responses during the paradigm. The design of a set of nonorthogonal wavelets of specified frequency resolution within the power spectrum was investigated for extracting desired frequency responses from the noisy signal intensity of individual voxels. These wavelets separate the low-frequency cognitive response to the paradigm from the respiratory and cardiac responses at higher frequencies. The retention of the temporal information, possible by wavelet analysis, allows the MR signal changes to be compared to changes in behavioral responses over the duration of an entire paradigm. The amplitude and time delay of the wavelet specified by the paradigm identify quantitatively the size of the MR signal change and the temporal delay of the hemodynamic BOLD response, respectively. This specified-resolution wavelet analysis was demonstrated for individual voxels and maps through the frontal eye fields using a visually guided saccade paradigm.     

MR detection of hyperacute parenchymal hemorrhage of the brain

OBJECTIVE: This study aimed to assess the effect of contact lens wear on the mucosal defenses of the outer eye against infection. DESIGN: A case-controlled study of daily contact lens wearers in their initial 6 months of contact lens wear. PARTICIPANTS: Contact lens wearers (mean age, 23.1 years; 47 subjects) were compared with age-matched control subjects (mean age, 24.7 years; 44 subjects). INTERVENTION: Outer eye defenses were studied by assay of tear constituents and quantitative conjunctival microbiology. MAIN OUTCOME MEASURES: Antimicrobial activity of tears was studied by assay of total immunoglobulin A (IgA), IgA isotype-specific antibodies reactive with Escherichia coli, Haemophilus influenzae, Staphylococcus epidermidis, albumin and lysozyme, and the ocular surface microbial load determined using quantitative microbiology of the conjunctival sac. RESULTS: The IgA isotype-specific antibodies reactive with E. coli (P = 0.03) and S. epidermidis (P = 0.068) were lower in contact lens wearers, but antibody:albumin ratios were not significantly different in the two groups. Contact lens wear also had no significant effect on tear IgA, albumin, or lysozyme or its ratios with albumin. Bacterial numbers and colonization rates for coagulase-negative staphylococci were greater in contact lens wearers than in age-matched control subjects. Corynebacterium sp. and non-Enterobacteriaceae (P = 0.007) were isolated more frequently and in greater numbers from contact lens wearers. Colonization rates were increased for Corynebacterium sp., but non-Enterobacteriaceae were transient. In both daily contact lens wearers and age-matched control subjects, most conjunctival flora were transient rather than colonizing, and no subject developed an outer eye infection during the study. CONCLUSION: These results suggest that daily contact lens wear does not significantly alter the mucosal defenses of the outer eye that function to eliminate organisms from the conjunctival sac and prevent outer eye infection.     

Toward 20 T magnetic resonance for human brain studies: opportunities for discovery and neuroscience rationale

Magnetic Resonance Materials in Physics, Biology and Medicine - An initiative to design and build magnetic resonance imaging (MRI) and spectroscopy (MRS) instruments at 14 T and beyond to...     

Rapid computation of sodium bioscales using gpu‐accelerated image reconstruction

Quantitative sodium magnetic resonance imaging permits noninvasive measurement of the tissue sodium concentration (TSC) bioscale in the brain. Computing the TSC bioscale requires reconstructing and combining multiple datasets acquired with a non‐Cartesian acquisition that highly oversamples the center of k‐space. Even with an optimized implementation of the algorithm to compute TSC, the overall processing time exceeds the time required to collect data from the human subject. Such a mismatch presents a challenge for sustained sodium imaging to avoid a growing data backlog and provide timely results. The most computationally intensive portions of the TSC calculation have been identified and accelerated using a consumer graphics processing unit (GPU) in addition to a conventional central processing unit (CPU). A recently developed data organization technique called Compact Binning was used along with several existing algorithmic techniques to maximize the scalability and performance of these computationally intensive operations. The resulting GPU+CPU TSC bioscale calculation is more than 15 times faster than a CPU‐only implementation when processing 256 × 256 × 256 data and 2.4 times faster when processing 128 × 128 × 128 data. This eliminates the possibility of a data backlog for quantitative sodium imaging. The accelerated quantification technique is suitable for general three‐dimensional non‐Cartesian acquisitions and may enable more sophisticated imaging techniques that acquire even more data to be used for quantitative sodium imaging. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 29–35, 2013.     

Volumetry and topography of the human brain by magnetic resonance imaging

Software, termed Morph©, is described for the morphometric analysis of magnetic resonance images of the human brain. Algorithms for objective contrast border recognition, surface feature classification, and surface feature contour unfolding are evaluated. Intraoperator and interoperator variabilities and errors were determined to be less than 2% over a group of operators (n = 6) for the known volume of a cerebral hemisphere obtained at autopsy. Volumetric errors were measured to be ± 3% for simulated objects and less than 1% for images of phantoms. Contours of brains of normal elderly subjects (n = 6) and patients with probable Alzheimer's disease (n = 6), segmented into sulcal and gyral features to determine gyrification indices, showed concordance with literature values. Flat maps or topograms were obtained of the convoluted cortex by unfolding the segmented contours. The areas of surface features were readily obtained. The activation of the frontal eye fields (FEF) defined by functional magnetic resonance imaging (fMRI) with an oculomotor control task was mapped onto a topogram of the precentral sulcus. This software provides accurate volumetric analysis with additional topographical tools for characterizing convoluted cortical features and for presenting three‐dimensional fMRI activation patterns as two‐dimensional maps. © 2001 John Wiley & Sons, Inc. Int J Imaging Syst Technol 11, 198–208, 2000     

Changes in fMRI Following Cognitive Rehabilitation in Severe Traumatic Brain Injury: A Case Study.

Objective: To illustrate the relationship between changes in neuropsychological testing and changes in functional magnetic resonance imaging (fMRI) before and after cognitive rehabilitation therapy (CRT). Study Design: Single case study. Setting: Outpatient treatment center. Participant: A woman with history of severe traumatic brain injury (TBI) 16 years before study. Intervention: Individualized CRT using a developmental metacognitive model. Main Outcome Measures: Neuropsychological tests and fMRI imaging performed during an eye movement task and a reading comprehension task. Results: Improvements on some neuropsychological test scores (>1 SD) and changes in the magnitude and distribution of the blood oxygen level dependent (BOLD) response as a function of task performance on both fMRI tasks. Conclusions: Individuals with severe TBI many years postinjury can demonstrate improvements in neuropsychological testing following CRT. Behavioral improvements can be related to changes in brain activity using fMRI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)