Biomedical subjects

C S Bosch

Publications and source records attributed to C S Bosch.

3 recordsLinked to original sources

PubMed1995

Model-based maximum-likelihood estimation for phase- and frequency-encoded magnetic-resonance-imaging data.

A maximum-likelihood (ML)-based magnetic-resonance-imaging (MRI) reconstruction algorithm is established, based on frequency- and phase-encoded data. The model on which the ML method is based is a superposition of exponentially decaying, sinc-modulated sinusoids, arising from the basic Bloch equations for MR spectroscopy, modified to account for the distribution of resonance frequencies and phases used for spatial localization in the image field. Spatial-localizing gradients are assumed to be known linear functions of spatial coordinate position, with the x-encode (frequency) gradient applied continuously during the full duration of data collection, and the y-encode (phase) gradient applied during varying time periods before data collection. A single-voxel emitter becomes sinc-modulated in the x, y directions at rates proportional to voxel size and gradient strengths in the x-encode and y-encode directions. The full two-dimensional MRI signal becomes a superposition of sinc-modulated, exponentially decaying, single-sinusoid emitters, one for each voxel. The ML estimation of spin-density and spin-spin relaxation decay time images becomes a nonlinear least-squares optimization problem; it is solved using an iterative expectation-maximization algorithm for estimating multiple modulated sinusoids in noise. Phantom studies are presented, demonstrating the accuracy of the model and the application of the algorithm to spin-density and spin-spin relaxation decay time profiles.

Algorithms↗

PubMed1994

An evaluation of the sensitivity of the intravoxel incoherent motion (IVIM) method of blood flow measurement to changes in cerebral blood flow.

To evaluate the sensitivity of the intravoxel incoherent motion (IVIM) technique to changes in cerebral blood flow, we made measurements of IVIM parameters in rat brain under conditions of altered arterial pCO2. The arterial pCO2 was varied over a range which would be expected to change cerebral blood flow from roughly 50 to 500 ml/(100 g.min). The IVIM measurements were made with suppression of extravascular water signal. The parameters f' (the apparent fraction of spins which have "fast" pseudodiffusion), D1* (the "fast-pseudodiffusion") coefficient), and D2* (the "slow-pseudodiffusion" coefficient) all showed statistically significant positive linear correlations with arterial pCO2. These results suggest that the IVIM method, when used with suppression of extravascular water signal, is sensitive to changes in blood flow.

Animals↗

PubMed1993

In vivo NMR imaging and spectroscopic investigation of renal pathology in lean and obese rat kidneys.

Diabetic nephropathy is a major cause of end-stage renal failure. While our understanding of the pathogenesis of nephropathy is incomplete, progressive glomerular injury appears to play a significant role in the decline of renal function. Proton NMR spectroscopy and imaging techniques were used to address changes in renal pathology associated with glomerular mesangial expansion in vivo in kidneys from spontaneously obese and lean (control) littermate Zucker rats. Fully functioning rat kidneys were surgically exposed and externalized for direct NMR signal detection via a coil placed around the organ. High-resolution (78 microns in plane) proton images were obtained at 4.7 T magnetic field strength revealing fine structure within the well-defined cortical and medullary regions. The obese rat kidney images were distinct in appearance from the lean kidney images and exhibited marked cortical expansion as well as increased overall kidney size. Enlargement of mean glomerular diameter was verified histologically in the obese kidneys as compared with the lean kidneys. Proton T1 and T2 relaxation times were determined from the entire kidney using standard spectroscopic techniques, and from specific regions within the kidney from multiple T1- and T-2 weighted images. Additionally, image contrast enhancement resulting from saturation transfer between protons in restricted-mobility environments and mobile water protons within the kidney was investigated in the lean and obese rat kidneys using magnetization-transfer imaging techniques. At the early stage of renal injury examined in this study, diseased and healthy kidneys could not be differentiated on the basis of relaxation times alone. The magnitude of saturation transfer obtained in cortical tissue in the lean and obese kidneys was also not statistically significantly different. However, the magnitude of saturation transfer achieved in the medullary tissue of obese kidneys was statistically significantly less than that achieved in lean kidneys.

Animals↗