Biomedical subjects

H Eisendrath

Publications and source records attributed to H Eisendrath.

9 recordsLinked to original sources

PubMed1998

Comparison of computer simulated and phantom measured phase variance in the study of trabecular bone.

A new method using magnetic resonance phase images for the assessment of trabecular bone structure has recently been proposed. To test this method, a mathematical model is developed which calculates the phase distribution in gradient echo acquired phase images of a structure of Pyrex glass rods immersed in a copper sulfate solution. Several experiments were performed using a phantom built in the same way as the structure used in the mathematical model. The results from the model are compared with those from the phantom tests, and the influence of resolution and bone area fraction on the phase dispersion is studied. The good correlation between theoretical and experimental results shows that phase variance increases with increasing resolution and bone density. However, the dependence of variance on bone density is less prominent for large pixel sizes.

Bone Density↗

PubMed1997

A comparison between different imaging strategies for diffusion measurements with the centric phase-encoded turboFLASH sequence.

The study compared the results of three centrally reordered phase-encoded turboFLASH sequences for diffusion-weighted imaging (DWI). The sequences were conventional turboFLASH, turboFLASH with subtraction of T1-related effects, and turboFLASH with correction for T1-related effects during the imaging period only. The relative merits were studied with respect to image quality and accuracy by computer simulation and by experimental validation on phantoms and on in vivo rat brain. A T1-related underestimation of the diffusion coefficient ranging from -30% (T1 approximately 200 ms) to -5% (T1 approximately 1 s) was found to exist for the conventional sequence. Image artifacts, caused by longitudinal relaxation during the imaging period, are reflected in calculated diffusion maps. When the correction sequence is used, the artifacts and the systematic errors are reduced but longitudinal relaxation during the delay between preparation and imaging periods remains large enough to induce significant errors (-15% for T1 approximately 200 ms to -3% for T1 approximately 1 s). The subtraction sequence eliminates the influence of T1 effects on the calibrations, but leads to identical artifacts for all diffusion-weighted images.

Animals↗

PubMed1996

Interpretation of flow encoding and quantification in MRI: time domain versus frequency domain.

The traditional approach to flow effects in MRI is based on the gradient moment expansion. Recently, we have presented an alternative description by using linear response theory: the distortions of the velocity waveform induced by the gradient waveforms were analyzed in the frequency domain on the basis of the transfer function. In the present paper, we perform an analysis of flow encoding and quantification in the time domain, on the basis of the impulse response. The analysis shows that flow encoding should be interpreted as a weighted averaging process. Instantaneous flow encoding is determined by the centroid of the impulse response, but care should be taken regarding the physical meaning of the instant of encoding. The relationship of this approach to the frequency domain and gradient moment expansion approaches is clarified. By way of example, some interesting applications are investigated: asymmetrical phase encoding gradients to minimize misregistration and oscillating read-out gradients for flow quantification. A variety of new applications are expected to derive from the combination of both the time and frequency domains.

Magnetic Resonance Imaging↗

PubMed1995

Time resolved flow quantification with MRI using phase methods: a linear systems approach.

Phase-related unsteady (pulsatile) flow effects in MRI have been studied by means of linear response theory. These flow effects can be described in the frequency domain: the influence of the gradients on the phase shift is described by a transfer function, the spectrum of the gradient being the determining factor. An analysis of this transfer function is shown to provide information about the process of flow encoding: instant of encoding, induced distortions and how they are related to the gradient waveform. The connection with the traditional description in terms of the gradient moment expansion has also been investigated and clarified. This approach was applied to study the response of two time-resolved flow quantification techniques (Fourier flow method and phase mapping) by analyzing their amplitude and phase transfer functions. By simulation it is shown that a better interpretation of the measured velocity waveform is obtained and that Fourier analysis in combination with a correction by the inverse transfer function results in an accurate reconstruction of the velocity waveform studied.

Algorithms↗

PubMed1992

Excitation characteristics of adiabatic half-passage RF pulses used in surface coil MR spectroscopy. Application to 13C detection of glycogen in the rat liver.

Properties of sech/tanh and sin/cos half-passage RF pulses are discussed in view of their use in surface coil MR spectroscopy. We focus on the use of these pulses in a regime which is partially adiabatic, i.e. not strictly adiabatic off-resonance, while on-resonance the adiabaticity condition is fulfilled. It is shown that the frequencies of the singular points of the excitation profiles, as well as their number, depend on the B1 field. This leads to a signal intensity reduction from off-resonance spectral regions over much broader ranges than generally believed. We show in particular that with surface coil, sin/cos RF pulses may perform particularly well, providing optimal excitation on resonance and a desired attenuation over a broad spectral range off-resonance. This feature is applied for the in vivo detection of rat liver glycogen by means of 13C MR spectroscopy. Under suitable RF power conditions, a remarkable attenuation of the signals from the saturated carbons of the subcutaneous fat can be achieved.

Animals↗

PubMed1988

Determinants of water proton T1 in blood serum.

Water proton T1 (10.7 MHz; 7 degrees C) and albumin and globulin contents were measured in the blood serum of 30 normal volunteers. The T1 relaxivity of serum albumin and globulin (i.e., the change of water relaxation rate 1/T1 per concentration unit) was determined in pure albumin and globulin solutions. It is shown that more than 90% of the serum relaxation rate 1/T1 is due to the proteins, making T1 a nonspecific blood parameter. In addition five pathological serum samples were examined, explaining clearly why serum T1 is not a clinically useful measurement.

Blood↗

PubMed1988

Analysis by the Carr-Purcell-Meiboom-Gill sequence of the influence of P388 leukemia and of cis-diamminedichloroplatinum(II) nephrotoxicity on water compartmentalization in kidneys and spleens of mice.

The multiexponential behavior of the decay curves obtained in vitro by a Carr-Purcell-Meiboom-Gill (CPMG) sequence from spleens and kidneys of mice is analyzed. The mice were inoculated with the acute lymphocytic P388 leukemic cells and treated with the anticancer drug cis-diamminedichloroplatinum(II), cis-Pt. Kidneys and spleens of control animals display four relaxation components. The two longest ones were assigned, in the kidneys, in decreasing order of their relaxation time value, to intracellular and extracellular water, respectively. In spleens, the reversed assignment resulted. The two shortest ones are assigned to different tightly bound hydration water compartments, the fastest relaxing one being more greatly influenced by the unobservable crystalline water. No significant systemic effect on the intra- and extracellular water relaxation times could be observed in the kidneys under P388 leukemia inoculation, despite an apparent increase in the intracellular water content. In contrast, drug administration results in the apparent decrease in or even disappearance of the extracellular water component, with an increase in both relaxation time and apparent fraction of the intracellular water. These effects correlate well with changes in the usual nephrotoxicity parameters and are explained in terms of the well-known cell damage in kidneys under cis-platinum administration. A systemic effect under P388 leukemia disease is observed for the spleen, resulting again in the disappearance of the extracellular water component. The latter is related to splenomegaly due to invasion of the organ by leukemic cells during disease development.

Animals↗

PubMed1988

The relationship between serum water proton T1 and protein content in the P388 leukemic mouse and the effect of chemotherapy by cis-diamminedichloroplatinum(II).

Proton NMR longitudinal relaxation times (T1; 10.7 MHz; 37 degrees C) were measured in the kidneys and blood serum of mice inoculated with P388 leukemia, and/or treated with the chemotherapeutic drug cis-diamminedichloroplatinum(II) (cis-Pt). In parallel, serum total protein content, urea and creatinine levels were determined and protein fractions were separated electrophoretically. Serum T1 was found to be 1518 +/- 73 ms (1 SD) in control mice, 1670 +/- 69 ms in leukemic mice, and 1380 +/- 71 ms in the healthy and the leukemic cis-Pt treated mice. The T1 increase in leukemic serum and T1 decrease in the serum of cis-Pt injected mice are attributed to decreased and increased protein contents respectively. A detailed analysis in terms of electrophoretic fractions of serum proteins reveals that the serum relaxation rate 1/T1 is a multilinear function of the mass concentrations of the main serum protein fractions, explaining all serum T1 effects. This makes T1 a non-specific blood parameter. The kidney T1 was found to be 311 +/- 12 ms in normal mice and 334 +/- 20 ms in leukemic mice. A dramatic T1 increase is observed when the mice are injected with cis-Pt; the values are 400 +/- 38 ms and 407 +/- 39 ms for healthy and leukemic mice, respectively. This effect is related to the nephrotoxicity of the drug, as evidenced by serum urea and creatinine levels and protein content being higher than normal.

Animals↗

PubMedDate not supplied

In vivo comparison of MR phase distribution and 1/T2* with morphologic parameters in the distal radius.

A new approach based on the calculation of the phase variance in a region of interest on the phase images of a simple gradient echo sequence, was used to assess the properties of trabecular bone in the distal radius. The phase variance reflects the distribution of field inhomogeneities due to the difference in magnetic susceptibility between bone and marrow in a way similar to T2*. However, the phase variance monitors the intervoxular differences, whereas T2* studies the intravoxular inhomogeneities. In this study of the radius of seven volunteers, both techniques were compared with parameters characterizing trabecular bone structure derived from high resolution MR images. Parameters such as the apparent bone area fraction, trabecular number, thickness and spacing, and box-counting fractal dimension were determined.

Adult↗