Biomedical subjects

Lawrence L Wald

Publications and source records attributed to Lawrence L Wald.

9 recordsLinked to original sources

PubMed2005

Detection of entorhinal layer II using 7Tesla [corrected] magnetic resonance imaging.

The entorhinal cortex lies in the mediotemporal lobe and has major functional, structural, and clinical significance. The entorhinal cortex has a unique cytoarchitecture with large stellate neurons in layer II that form clusters. The entorhinal cortex receives vast sensory association input, and its major output arises from the layer II and III neurons that form the perforant pathway. Clinically, the neurons in layer II are affected with neurofibrillary tangles, one of the two pathological hallmarks of Alzheimer's disease. We describe detection of the entorhinal layer II islands using magnetic resonance imaging. We scanned human autopsied temporal lobe blocks in a 7T human scanner using a solenoid coil. In 70 and 100 microm isotropic data, the entorhinal islands were clearly visible throughout the anterior-posterior extent of entorhinal cortex. Layer II islands were prominent in both the magnetic resonance imaging and corresponding histological sections, showing similar size and shape in two types of data. Area borders and island location based on cytoarchitectural features in the mediotemporal lobe were robustly detected using the magnetic resonance images. Our ex vivo results could break ground for high-resolution in vivo scanning that could ultimately benefit early diagnosis and treatment of neurodegenerative disease.

Entorhinal Cortex↗

PubMed2004

Parallel imaging reconstruction using automatic regularization.

Increased spatiotemporal resolution in MRI can be achieved by the use of parallel acquisition strategies, which simultaneously sample reduced k-space data using the information from multiple receivers to reconstruct full-FOV images. The price for the increased spatiotemporal resolution in parallel MRI is the degradation of the signal-to-noise ratio (SNR) in the final reconstructed images. Part of the SNR reduction results when the spatially correlated nature of the information from the multiple receivers destabilizes the matrix inversion used in the reconstruction of the full-FOV image. In this work, a reconstruction algorithm based on Tikhonov regularization is presented that reduces the SNR loss due to geometric correlations in the spatial information from the array coil elements. Reference scans are utilized as a priori information about the final reconstructed image to provide regularized estimates for the reconstruction using the L-curve technique. This automatic regularization method reduces the average g-factors in phantom images from a two-channel array from 1.47 to 0.80 in twofold sensitivity encoding (SENSE) acceleration. In vivo anatomical images from an eight-channel system show an averaged g-factor reduction of 1.22 to 0.84 in 2.67-fold acceleration.

Algorithms↗

PubMed2003

Stereopsis activates V3A and caudal intraparietal areas in macaques and humans.

Stereopsis, the perception of depth from small differences between the images in the two eyes, provides a rich model for investigating the cortical construction of surfaces and space. Although disparity-tuned cells have been found in a large number of areas in macaque visual cortex, stereoscopic processing in these areas has never been systematically compared using the same stimuli and analysis methods. In order to examine the global architecture of stereoscopic processing in primate visual cortex, we studied fMRI activity in alert, fixating human and macaque subjects. In macaques, we found strongest activation to near/far compared to zero disparity in areas V3, V3A, and CIPS. In humans, we found strongest activation to the same stimuli in areas V3A, V7, the V4d topolog (V4d-topo), and a caudal parietal disparity region (CPDR). Thus, in both primate species a small cluster of areas at the parieto-occipital junction appears to be specialized for stereopsis.

Animals↗

PubMed2003

A wavelet-based approximation of surface coil sensitivity profiles for correction of image intensity inhomogeneity and parallel imaging reconstruction.

We evaluate a wavelet-based algorithm to estimate the coil sensitivity modulation from surface coils. This information is used to improve the image homogeneity of magnetic resonance imaging when a surface coil is used for reception, and to increase image encoding speed by reconstructing images from under-sampled (aliased) acquisitions using parallel magnetic resonance imaging (MRI) methods for higher spatiotemporal image resolutions. The proposed algorithm estimates the spatial sensitivity profile of surface coils from the original anatomical images directly without using the body coil for additional reference scans or using coil position markers for electromagnetic model-based calculations. No prior knowledge about the anatomy is required for the application of the algorithm. The estimation of the coil sensitivity profile based on the wavelet transform of the original image data was found to provide a robust method for removing the slowly varying spatial sensitivity pattern of the surface coil image and recovering full FOV images from two-fold acceleration in 8-channel parallel MRI. The results, using bi-orthogonal Daubechies 97 wavelets and other members in this family, are evaluated for T1-weighted and T2-weighted brain imaging.

Algorithms↗

PubMed2003

Degenerate mode birdcage volume coil for sensitivity-encoded imaging.

A volume birdcage coil for accelerated image encoding with parallel acquisition methods such as SENSE is demonstrated. The coil is degenerately tuned with both the standard homogeneous mode and the first gradient mode of the birdcage coil resonant at the Larmor frequency. Conventional and antisymmetric coupling structures allow imaging from each of these modes simultaneously. The coil for SENSE-type reconstruction with acceleration factors of up to 2-fold is demonstrated. The spatial distribution of the added noise from the SENSE reconstruction (g-factor map) due to geometrical arrangement of the two-channel system is estimated. The spatially averaged g-factors were found to be 1.21, 1.36, and 1.55 for 1.3, 1.6, and 2-fold accelerations, respectively. The system was demonstrated in vivo using accelerated and nonaccelerated anatomical brain images at 1.5 T. The maximal 2-fold acceleration in this dual-mode degenerate birdcage coil offers the potential to extend SENSE-type image reconstruction methods to applications demanding uniform whole brain coverage.

Brain↗

PubMed2003

In vivo tracing of major rat brain pathways using manganese-enhanced magnetic resonance imaging and three-dimensional digital atlasing.

The magnetic resonance imaging (MRI)-detectable T1 contrast agent manganese (Mn2+) has recently been introduced as a neural tracer in rodents, birds, and monkeys. We have tested to what extent this in vivo method is useful for three-dimensional (3-D) survey of connectivity patterns in the rat somatosensory system. A commonly available 3 T human clinical MRI scanner was used to trace neural pathways following focal injection of manganese chloride (MnCl2) in the somatosensory cortex. Six to 10 h after MnCl2 injection, we found significant signal enhancement in major projection systems, including corticocortical, corticostriatal, corticothalamic, corticotectal, corticopontine, and corticospinal pathways. To facilitate the assignment of anatomic localization to the observed Mn2+ signal enhancement, we registered the MRI data with a 3-D digital reconstruction of a stereotaxic rat brain atlas. Across-animal comparison using the digital model allowed demonstration of a corticothalamic 3-D topographic organization in agreement with previously published two-dimensional topographic schemes based on classical neural tracing data. We conclude that anterograde MnCl2/MRI tracing allows rapid analysis of topographic organization across multiple brain regions. The method allows a higher data throughput for 3-D studies of large-scale brain connectivity than conventional methods based on tissue sectioning.

Animals↗

PubMed2003

Comparison of cardiac MRI on 1.5 and 3.0 Tesla clinical whole body systems.

RATIONALE AND OBJECTIVES: A cardiac imaging pilot study was performed on 1.5 and 3.0 Tesla (T) whole body magnetic resonance units equipped with identical gradient sets and geometrically equivalent body coils. The goals were to compare the signal-to-noise (SNR) and contrast-to-noise (CNR) ratios on matched studies conducted at both field strengths and demonstrate the potential for functional and morphologic cardiac evaluation at 3.0 T. METHODS: Short axis cine true fast imaging with steady precession (True FISP) was compared at 1.5 and 3.0 T using the body coil in transmit-receive mode and transmit-only with single loop and phased array receiver coils. SNR of the myocardium and CNR of the ventricular blood and myocardium were calculated from a quantitative region of interest analysis of these data. Additionally at 3.0 T, long axis and 4-chamber cine as well as "dark blood" imaging are demonstrated with sequence and parameter settings comparable to current state of the art for cardiac evaluation at 1.5 T. RESULTS: The 3.0 T data consistently demonstrates increases in SNR when all imaging conditions are closely matched but the increase has a large variability ranging from 20 to 85% depending on the radiofrequency coil configuration. Ventricular blood-myocardium CNR greater than 30 is obtained at 3.0 T, which is comparable to an optimized 1.5 T acquisition despite the specific absorption rate limitation of flip angle to nearly one half the value. The increased SNR at 3.0 T improves detection of fine anatomic detail, such as the chordae tendineae and mitral valve structure. CONCLUSIONS: Increased specific absorption rate can be a limiting fact; however, we have demonstrated that 3.0 T cardiac imaging shows gains in SNR while maintaining the CNR. The SNR gain is advantageous, and phased array coil technology is key for improving cardiac magnetic resonance imaging at 3.0 T.

Aged↗

PubMed2002

Modulation of brain and serum glutamatergic concentrations following a switch from conventional neuroleptics to olanzapine.

BACKGROUND: Recent evidence suggests that effects upon glutamatergic transmission may contribute to the therapeutic action of certain atypical antipsychotic agents. METHODS: Glutamate concentrations were measured in serum and were estimated (Glx/Cr) in cingulate cortex by proton magnetic resonance spectroscopy (MRS) in schizophrenia patients while they were being treated with conventional neuroleptics and then 8 weeks after switching to olanzapine. Serum glutamate concentrations were obtained from 11 subjects, and MRS estimates of Glx/Cr were available from 10 subjects at both time points. RESULTS: Serum glutamate concentrations significantly increased after the switch from conventional agents to olanzapine; brain glutamate (Glx/Cr) did not change significantly; however, brain glutamate (Glx/Cr) concentrations increased significantly in patients who exhibited an improvement in negative symptoms with olanzapine compared with patients with no change or worsening of negative symptoms. CONCLUSIONS: Comparisons performed following the switch from conventional agents to olanzapine are consistent with previous studies of clozapine and provide additional preliminary evidence supporting the hypothesis that effects on excitatory amino acid activity may contribute to olanzapine's efficacy for treating negative symptoms.

Adult↗

PubMedDate not supplied

Brain proton magnetic resonance spectroscopy in Alzheimer disease: changes after treatment with xanomeline.

Patients with mild-to-moderate Alzheimer disease received transdermal xanomeline, an M1-selective cholinergic agonist, or placebo for 4 months. Clinical assessments and proton magnetic resonance spectroscopic imaging examinations were carried out at baseline, and after 8 and 16 weeks of treatment. There was a positive correlation between change from baseline in parietal lobe gray-matter cytosolic choline, expressed in terms of choline/creatine resonance ratios, and cognitive performance as measured with the Alzheimer's Disease Assessment Scale Cognitive Subscale. Specifically, increased levels of cytosolic choline, a precursor pool for acetylcholine synthesis, were associated with greater progression in memory impairment during treatment.

Administration, Cutaneous↗