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Robert I. Grossman - One of the best experts on this subject based on the ideXlab platform.
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Magnetization Transfer imaging in progressive multifocal leukoencephalopathy
Neurology, 1997Co-Authors: Scott E. Kasner, Steven Galetta, Joseph C. Mcgowan, Robert I. GrossmanAbstract:Article abstract-We report a patient with biopsy-proven progressive multifocal leukoencephalopathy (PML) who was serially imaged with MRI and Magnetization Transfer imaging. The Magnetization Transfer ratio (MTR) was profoundly and significantly diminished when compared with normal control subjects. The pattern of MTR was distinct from that of MS and periventricular ischemic white matter disease. Magnetization Transfer imaging techniques may aid in the differential diagnosis of PML. NEUROLOGY 1997;48: 534-536
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Multiple sclerosis lesions: relationship between MR enhancement pattern and Magnetization Transfer effect.
AJNR. American journal of neuroradiology, 1996Co-Authors: Jeffrey R. Petrella, Joseph C. Mcgowan, Robert I. Grossman, Gregory Campbell, Jeffrey A. CohenAbstract:PURPOSE To investigate the relationship between the enhancement pattern of a multiple sclerosis lesion and its Magnetization Transfer effect. METHODS Fifty-four lesions were chosen from 29 patients with multiple sclerosis on the basis of enhancement pattern on contrast-enhanced T1-weighted MR images. They included 14 homogeneously enhancing lesions, 26 nonenhancing lesions, and 14 ring-enhancing lesions. Magnetization Transfer ratios of the homogeneously enhancing lesions, nonenhancing lesions, and central portion of the ring-enhancing lesions were measured. Means were calculated and compared. RESULTS The Magnetization Transfer ratios for homogeneously enhancing lesions were higher (mean, 32.2%; SD, 3.4%) than those for nonenhancing lesions (mean 29.4%; SD, 4.3%) and for the central portion of ring-enhancing lesions (mean, 24.5%; SD, 4.0%). Significant differences were found between the ring-enhancing lesions and the homogeneously enhancing lesions and between the ring-enhancing lesions and the nonenhancing lesions. CONCLUSION We found a relationship between decreased Magnetization Transfer ratios and those enhancement patterns in which myelin is known to be decreased histopathologically. Thus, use of the Magnetization Transfer technique may increase the specificity of MR imaging in assessing the extent of residual myelination in multiple sclerosis lesions.
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Characterization of multiple sclerosis plaques with T1-weighted MR and quantitative Magnetization Transfer
AJNR. American journal of neuroradiology, 1995Co-Authors: Laurie A. Loevner, Joseph C. Mcgowan, Robert I. Grossman, Karen N. Ramer, Jeffrey A. CohenAbstract:PURPOSE To investigate the relationship between the appearance of multiple sclerosis lesions identified on unenhanced T1-weighted images and their corresponding Magnetization Transfer ratios. METHODS A total of 119 white matter lesions seen on T2-weighted images in 17 patients with multiple sclerosis were evaluated. Axial T1-weighted images were used to classify the lesions as isointense to white matter (10 lesions), hypointense to white matter but hyperintense to gray matter (44 lesions), hypointense to gray matter (59 lesions), and relatively isointense to cerebrospinal fluid (6 lesions). The Magnetization Transfer ratio of each lesion was calculated, and an average Magnetization Transfer ratio for each subcategory was determined. RESULTS The Magnetization Transfer ratio values became progressively lower with increasing hypointensity of lesions on T1-weighted images. The average Magnetization Transfer ratio for lesions isointense to white matter, hypointense to white matter but hyperintense to gray matter, hypointense to gray matter, and relatively isointense to cerebrospinal fluid was 34.90 +/- 2.67 mean +/- SD), 30.93 +/- 3.57, 27.27 +/- 3.56, and 23.62 +/- 2.83, respectively. All groups were significantly different from each other. CONCLUSION Lesions isointense to white matter exhibited higher Magnetization Transfer ratio values than lesions that were hypointense. These findings are consistent with relative preservation of the myelin structure in the former, perhaps indicating that these lesions are predominantly inflammatory (edematous) in nature. The proportionately lower Magnetization Transfer ratio values of lesions that appear progressively more hypointense on T1-weighted images may reflect varying degrees of demyelination, with increasing lesion hypointensity corresponding to more breakdown in the macromolecular structure. These results suggest that T1-weighted images may be useful in characterizing the underlying pathologic substrate in multiple sclerosis plaques.
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Magnetization Transfer in multiple sclerosis
Annals of Neurology, 1994Co-Authors: Robert I. GrossmanAbstract:Magnetization Transfer (MT) is a technique that has the potential for detecting changes in myelin. The rigid macromolecular structure of myelin is the physical basis of MT. By using off-resonance irradiation, macromolecular protons can be saturated. These protons then exchange with free-water protons and produce a decrease in signal intensity of the free-water protons. This can be quantitated by using a Magnetization Transfer ratio (MTR) of signal intensities (M o -M s /M o .M o represents the signal intensity without off-resonance irradiation, and M s represents the signal intensity with off-resonance irradiation). This method has been sensitive to changes in a spectrum of white-maiter lesions, including an edema model (EAE), and regions of apparent myelin loss in patients with multiple sclerosis (MS)
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Magnetization Transfer: theory and clinical applications in neuroradiology.
Radiographics : a review publication of the Radiological Society of North America Inc, 1994Co-Authors: Robert I. Grossman, Karen N. Ramer, John M. Gomori, F J Lexa, Mitchell D. SchnallAbstract:Magnetization Transfer, a new technique for improving image contrast in magnetic resonance (MR) imaging, is based on application of off-resonance radio-frequency pulses and observing their effects on MR images, as well as measuring the signal intensity with and without application of the pulses (ie, Magnetization Transfer ratio [MTR]). MTRs can be used to detect changes in the structural status of brain parenchyma that may or may not be visible with standard MR techniques. Use of MTRs may allow subcategorization of multiple sclerosis lesions into those with very low MTR (demyelinated lesions) and slightly decreased MTR (edematous lesions). In cases of wallerian degeneration, use of MTRs appears to allow reliable detection of changes undetectable with MR imaging or even light microscopy. In cases of infection with human immunodeficiency virus, MTRs seem to indicate that the macromolecular structure of white matter remains intact until relatively late in the course of disease. In cases of metastatic disease...
Joseph C. Mcgowan - One of the best experts on this subject based on the ideXlab platform.
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Magnetic resonance imaging and Magnetization Transfer
Advances in Imaging and Electron Physics, 2001Co-Authors: Joseph C. McgowanAbstract:Publisher Summary This chapter reviews the fundamentals of magnetic resonance and magnetic resonance imaging to motivate a discussion of a technique aimed at probing interactions between magnetic resonance imaging (MRI)-visible water protons and protons of larger molecules of physiologic interest. The underlying assumption for this technique is that a Magnetization state may be Transferred between such protons, and thus it is referred to as Magnetization Transfer (MT). Contrast obtained via this mechanism is called “Magnetization Transfer contrast” (MTC) and imaging that reflects MTC is known as “Magnetization Transfer imaging” (MTI). Applications of MTI are discussed in the chapter, together with analysis techniques being developed to exploit the MT phenomenon. Although the fundamental phenomena of magnetic resonance are described by quantum mechanics, the observations that are essential to the arguments can be explained with classical arguments, and this is nearly always the case for the purpose of application to medical imaging and diagnosis.
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Magnetization Transfer imaging of the canine brain: a review.
Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology As, 2001Co-Authors: Charles H. Vite, Joseph C. McgowanAbstract:Magnetization Transfer imaging is a modality capable of examining the non-water components of brain tissue by examining the effects they have on water protons. It may be used qualitatively to increase the visibility of lesions seen during magnetic resonance angiography and following the administration of an intravenous paramagnetic contrast medium. Quantitatively, it can be used to examine the effect of pathology on Magnetization Transfer contrast, to provide a measurement of myelination, as well as to quantify disease progression in trauma, neoplasia, neurodegeneration and other disorders of the brain. This paper reviews the theory of Magnetization Transfer imaging, its applications, and provides an example of its use in examining the canine brain.
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The physical basis of Magnetization Transfer imaging.
Neurology, 1999Co-Authors: Joseph C. McgowanAbstract:Article abstract-Magnetization Transfer imaging (MTI) refers to an application of magnetic resonance imaging (MRI) designed as a means of exploring characteristics of non-water components in tissue. Compared with conventional MR imaging, where differences in brightness on images reflect differences in observed relaxation times, MTI theory incorporates the influence of additional parameters, specifically those reflecting the exchange of protons between molecules of water and molecules of more-solid, structural components. Thus, MTI offers the potential of a window on tissue structure, and structural components that are normally not resolvable with MRI. The theory arises from the idea that the spin Magnetization of macromolecular components of tissue can be indirectly observed via observation of the conventionally visible spins of tissue water. The extent of influence of the Magnetization Transfer process can be reflected in a normalized index derived from two magnetic resonance images, which is known as the Magnetization Transfer ratio. Exploitation of this effect is of current interest in multiple sclerosis because it offers the potential for gains in specificity as well as sensitivity of the magnetic resonance examination.
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Magnetization Transfer imaging in progressive multifocal leukoencephalopathy
Neurology, 1997Co-Authors: Scott E. Kasner, Steven Galetta, Joseph C. Mcgowan, Robert I. GrossmanAbstract:Article abstract-We report a patient with biopsy-proven progressive multifocal leukoencephalopathy (PML) who was serially imaged with MRI and Magnetization Transfer imaging. The Magnetization Transfer ratio (MTR) was profoundly and significantly diminished when compared with normal control subjects. The pattern of MTR was distinct from that of MS and periventricular ischemic white matter disease. Magnetization Transfer imaging techniques may aid in the differential diagnosis of PML. NEUROLOGY 1997;48: 534-536
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Multiple sclerosis lesions: relationship between MR enhancement pattern and Magnetization Transfer effect.
AJNR. American journal of neuroradiology, 1996Co-Authors: Jeffrey R. Petrella, Joseph C. Mcgowan, Robert I. Grossman, Gregory Campbell, Jeffrey A. CohenAbstract:PURPOSE To investigate the relationship between the enhancement pattern of a multiple sclerosis lesion and its Magnetization Transfer effect. METHODS Fifty-four lesions were chosen from 29 patients with multiple sclerosis on the basis of enhancement pattern on contrast-enhanced T1-weighted MR images. They included 14 homogeneously enhancing lesions, 26 nonenhancing lesions, and 14 ring-enhancing lesions. Magnetization Transfer ratios of the homogeneously enhancing lesions, nonenhancing lesions, and central portion of the ring-enhancing lesions were measured. Means were calculated and compared. RESULTS The Magnetization Transfer ratios for homogeneously enhancing lesions were higher (mean, 32.2%; SD, 3.4%) than those for nonenhancing lesions (mean 29.4%; SD, 4.3%) and for the central portion of ring-enhancing lesions (mean, 24.5%; SD, 4.0%). Significant differences were found between the ring-enhancing lesions and the homogeneously enhancing lesions and between the ring-enhancing lesions and the nonenhancing lesions. CONCLUSION We found a relationship between decreased Magnetization Transfer ratios and those enhancement patterns in which myelin is known to be decreased histopathologically. Thus, use of the Magnetization Transfer technique may increase the specificity of MR imaging in assessing the extent of residual myelination in multiple sclerosis lesions.
G. Bruce Pike - One of the best experts on this subject based on the ideXlab platform.
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Iterative optimization method for design of quantitative Magnetization Transfer imaging experiments.
Magnetic resonance in medicine, 2011Co-Authors: Ives R. Levesque, John G. Sled, G. Bruce PikeAbstract:Quantitative Magnetization Transfer imaging (QMTI) using spoiled gradient echo sequences with pulsed off-resonance saturation can be a time-consuming technique. A method is presented for selection of an optimum experimental design for quantitative Magnetization Transfer imaging based on the iterative reduction of a discrete sampling of the Z-spectrum. The applicability of the technique is demonstrated for human brain white matter imaging at 1.5 T and 3 T, and optimal designs are produced to target specific model parameters. The optimal number of measurements and the signal-to-noise ratio required for stable parameter estimation are also investigated. In vivo imaging results demonstrate that this optimal design approach substantially improves parameter map quality. The iterative method presented here provides an advantage over free form optimal design methods, in that pragmatic design constraints are readily incorporated. In particular, the presented method avoids clustering and repeated measures in the final experimental design, an attractive feature for the purpose of Magnetization Transfer model validation. The iterative optimal design technique is general and can be applied to any method of quantitative Magnetization Transfer imaging. Magn Reson Med, 2011. © 2011 Wiley-Liss, Inc.
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Reproducibility of quantitative Magnetization-Transfer imaging parameters from repeated measurements†
Magnetic resonance in medicine, 2010Co-Authors: Ives R. Levesque, John G. Sled, Sridar Narayanan, Paul S. Giacomini, Luciana Ribeiro, Douglas L. Arnold, G. Bruce PikeAbstract:Quantitative Magnetization-Transfer imaging methods provide in vivo estimates of parameters of the two-pool model for Magnetization-Transfer in tissue. The goal of this study was to evaluate the reproducibility of quantitative Magnetization-Transfer imaging parameter estimates in healthy subjects. Magnetization-Transfer–weighted and T1 relaxometry data were acquired in five healthy subjects at multiple time points, and the variability of the resulting fitted Magnetization-Transfer parameters was evaluated. The impact of subsampling the Magnetization-Transfer data and correcting field inhomogeneities was also evaluated. The key parameters measured in this study had an average variability, across time points, of 4.7% for the relative size of the restricted pool (F), 7.3% for the forward exchange constant (kf), 1.9% for the free pool spin-lattice relaxation constant (R1f), 4.5% for the T2 of the free pool (T2f), and 2.3% for the T2 of the restricted pool (T2r). Our findings show that serial quantitative Magnetization-Transfer imaging experiments can be performed reliably, with good reproducibility of the model parameter estimates, and demonstrate the reproducibility of acquisition schemes with fewer Magnetization-Transfer contrasts. This establishes the feasibility of this technique for monitoring patients affected by degenerative white matter diseases while providing critical data to estimate the statistical power of such studies. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.
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Magnetization Transfer contrast MRI of musculoskeletal neoplasms
Skeletal radiology, 1995Co-Authors: Katharine L. Hopkins, G. Bruce Pike, Sheila G. Moore, Nina N. Loh, Gabrielle Bergman, Gary H. GloverAbstract:Magnetic resonance imaging (MRI) examinations were performed in 15 patients with musculoskeletal neoplasms to assess the value of Magnetization Transfer contrast in tumor characterization. Multiplanar gradient-recalled echo sequences (TR 500-600/TE 15-20/flip angle 20–30°) were performed first without and then with Magnetization Transfer contrast generated by a zero degree binomial pulse (MPGR and MTMPGR). Standard T1-weighted spin echo images (SE; TR 300-400/TE 12-20) and either T2-weighted SE (TR 2000-2900/TE 70-80) or T2-weighted fast spin echo (FSE; TR 4000-5000/TE 100-119 effective) images were also obtained. Signal intensities on MTMPGR scans were compared to those on MPGR scans for both tumors and normal tissues. Signal intensity ratios (SIR) and contrast-to-noise ratios (CNR) were also compared for all sequences. MTMPGR images provided better contrast between pathologic tissues and muscle than did standard MPGR images, increasing both conspicuity of lesions and definition of tumor/muscle interfaces. Benign and malignant tumors, with the exception of lipoma, underwent similar degrees of Magnetization Transfer and could not be distinguished by this technique.
Dieter R. Enzmann - One of the best experts on this subject based on the ideXlab platform.
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Measure of Magnetization Transfer in multiple sclerosis demyelinating plaques, white matter ischemic lesions, and edema.
AJNR. American journal of neuroradiology, 1996Co-Authors: R C Mehta, G B Pike, Dieter R. EnzmannAbstract:PURPOSE To define the percentage of Magnetization Transfer of multiple sclerosis (MS) plaques, ischemic white matter lesions, and vasogenic edema to determine whether this measurement can help differentiate these entities. METHODS Findings were compared in 25 patients with proved MS, 20 patients with white matter ischemic lesions, and 72 patients with white matter edema (caused by tumors, infections, or acute/subacute infarctions) in the periventricular system, centrum semiovale, and subcortical white matter. Magnetization Transfer was performed using an on-resonance binomial pulse. The percentage of Magnetization Transfer of the normal white matter was also calculated. RESULTS Magnetization Transfer was significantly higher in white matter ischemic lesions (range, 31% to 38%; mean, 34% +/- 0.6%) than in demyelinating plaques of MS (range, 19% to 28%; mean, 22.5% +/- 1%) and in edema (range, 29% to 37%; mean, 30.2% +/- 0.4%). No statistical difference in percentage of Magnetization Transfer was found among lesions in the periventricular system (34% +/- 0.6%), centrum semiovale (35% +/- 0.5%), or subcortical white matter (33% +/- 0.6%), or in vasogenic edema associated with tumors, infections, or infarction. CONCLUSION Differences in Magnetization Transfer suggest less change of demyelination in white matter ischemic lesions than in MS plaques and are significantly different in this respect from similar MS plaques. Magnetization Transfer of edema was less than that of normal white matter or fell between ischemic abnormalities and MS plaques. Percentages of Magnetization Transfer below the mid-20% range is highly suggestive of demyelination. Vasogenic edema, our surrogate for increased water content of white matter, caused a decrease in the percentage of Magnetization Transfer.
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Magnetization Transfer MR of the normal adult brain.
AJNR. American journal of neuroradiology, 1995Co-Authors: R C Mehta, G B Pike, Dieter R. EnzmannAbstract:PURPOSE To establish a normal baseline of the percent Magnetization Transfer of gray (cortical and deep) and white matter structures in the brain in healthy adults and to determine whether there are adult age-related differences in these measurements. METHODS Axial T1-weighted scans (800/20 [repetition time/echo time]) with and without Magnetization Transfer were prospectively performed on a 1.5-T MR imaging unit on 68 healthy patients (aged 20 to 76 years). Presaturation and postsaturation Magnetization Transfer images were obtained using an on-resonance binomial pulse. All patients had normal MR scans on all pulse sequences. A calculated "difference" image was used to calculate the percent Magnetization Transfer in multiple specific regions of the brain. In each hemisphere, 9 discrete areas of cortical and deep gray matter and 29 areas of white matter were measured in 68 patients to generate age-related changes in percent Magnetization Transfer in these anatomic regions. Ranges of normal percent Magnetization Transfer in each of the 38 measures were established. RESULTS The percent Magnetization Transfer of the gray matter (28% +/- 2%) was lower than that of the white matter (36% +/- 2%). There was no statistically significant difference in the percent Magnetization Transfer in different areas of gray matter. Deep white matter in the different lobes (percent Magnetization Transfer, 31% to 38%) also showed no differences by age. Percent Magnetization Transfer was the highest in the genu of the corpus callosum (42%), and this was statistically significant compared with other white matter measurements. CONCLUSION There were no statistically significant age-related variations in the percent Magnetization Transfer in healthy adults in gray or white matter. These percent Magnetization Transfer measurements provide baseline normative data, which can be used to measure the extent and severity of white matter changes in disease states.
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Improved detection of enhancing and nonenhancing lesions of multiple sclerosis with Magnetization Transfer.
AJNR. American journal of neuroradiology, 1995Co-Authors: R C Mehta, G B Pike, Dieter R. EnzmannAbstract:PURPOSE To determine whether Magnetization Transfer imaging can improve visibility of contrast enhancement of multiple sclerosis plaques. METHODS Fifty-nine enhancing and 63 nonenhancing lesions in 10 patients with multiple sclerosis were evaluated to calculate contrast-to-noise ratios on conventional T1-weighted and T1-weighted Magnetization Transfer images. The signal intensity of the lesion and the background (white matter) were measured on precontrast T1-weighted and T1-weighted Magnetization Transfer images (800/20/1 [repetition time/echo time/excitations]) and on postcontrast T1-weighted and T1-weighted Magnetization Transfer images. Mean contrast-to-noise ratios was calculated for all lesions. RESULTS The contrast-to-noise ratio was significantly higher for enhancing and nonenhancing lesions on T1-weighted Magnetization Transfer images than on conventional T1-weighted images. For enhancing lesions, the contrast-to-noise ratio was significantly higher on postcontrast T1-weighted Magnetization Transfer images, 32 +/- 2 compared with 21 +/- 2 on conventional T1-weighted images. Fifty of the 59 enhancing lesions were seen on both the T1-weighted and the T1-weighted Magnetization Transfer images. Nine enhancing lesions were seen only on the postcontrast T1-weighted Magnetization Transfer images. In addition, of 63 nonenhancing lesions seen on proton-density, T2-weighted, and T1-weighted Magnetization Transfer images, 16 were not seen on the conventional T1-weighted images. Seven of the 63 nonenhancing lesions and 7 of the 59 enhancing lesions had high signal intensity on the precontrast T1-weighted Magnetization Transfer images suggestive of lipid signal, a finding not seen on the conventional precontrast T1-weighted images. CONCLUSION Magnetization Transfer improves the visibility of enhancing multiple sclerosis lesions, because they have a higher contrast-to-noise ratio than conventional postcontrast T1-weighted images. High signal intensity on both nonenhancing and enhancing lesions noted only on precontrast T1-weighted Magnetization Transfer suggests a lipid signal was unmasked. If Magnetization Transfer is used in multiple sclerosis patients, a precontrast Magnetization Transfer image is necessary.
Robert S. Balaban - One of the best experts on this subject based on the ideXlab platform.
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Magnetization Transfer characterization of hypertensive cardiomyopathy: significance of tissue water content.
Magnetic resonance in medicine, 1993Co-Authors: Thomas D. Scholz, Toni L. Ceckler, Robert S. BalabanAbstract:Magnetization Transfer measurements offer the potential for specific noninvasive tissue characterization. The goal of the present study was to determine if changes in Magnetization Transfer would accompany the myocardial remodeling that occurs with hypertrophic cardiomyopathy. Using 40-week spontaneously hypertensive rat (SHR) myocardium, T1, T2, and T1 in the presence of off-resonance irradiation (T1sat) were found to be greater compared to Wistar-Kyoto (WKY) controls. The pseudo-first order rate constant of Magnetization Transfer (kfor) was less in 40-week SHR compared with WKY while the ratio of equilibrium Magnetization in the presence and absence of off-resonance irradiation (Ms/M0) was not different. The extent to which observed interspecies differences in tissue water content affected these parameters was investigated by dehydrating normal and hypertrophic myocardium. Significant correlations found between tissue water content and T1, T2, T1sat and kfor, but not Ms/M0, suggested changes in tissue water dominated the observed interspecies differences in relaxation parameters. Thus, ventricular remodeling in hypertrophic cardiomyopathy does not alter Magnetization Transfer though the accompanying change in tissue water content influences water proton relaxation.
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Analysis of water-macromolecule proton Magnetization Transfer in articular cartilage.
Magnetic resonance in medicine, 1993Co-Authors: David K. Kim, Toni L. Ceckler, Vincent C. Hascall, Anthony Calabro, Robert S. BalabanAbstract:These studies were designed to establish which structural elements of cartilage are responsible for proton Magnetization Transfer between water (Hf) and macromolecules (Hr) observed in MRI studies on articular cartilage. Saturation Transfer techniques were used to monitor Magnetization Transfer in vitro on samples of the two major constituents of cartilage: collagen and proteoglycan. Articular cartilage samples were also evaluated in vitro before and after the removal of the proteoglycan fraction. Isolated hydrated collagen exhibited a significant proton Magnetization Transfer rate with water. In contrast, proteoglycans exhibited no proton Magnetization Transfer. Articular cartilage, in vitro, exhibited a high degree of Magnetization Transfer with water protons consistent with previous MRI studies in vivo. Enzymatic removal of proteoglycan from the cartilage did not alter the Magnetization Transfer rate between Hr and Hf. These data demonstrate that the structure and concentration of the collagen matrix are the predominant determinants of the Magnetization Transfer process in articular cartilage with little or no contribution from proteoglycans. This specificity of the Magnetization Transfer effect may prove useful in the noninvasive evaluation of cartilage composition and structure in vivo.
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Quantitative 1H Magnetization Transfer imaging in vivo.
Magnetic resonance in medicine, 1991Co-Authors: John Eng, Toni L. Ceckler, Robert S. BalabanAbstract:A major factor contributing to proton (1H) spin-lattice relaxation in biological tissues is believed to be Magnetization Transfer between 1H in free bulk water and 1H restricted motion associated with macromolecules. We have shown recently that saturation Transfer is an effective approach for studying this Magnetization Transfer process. Herein the determination of Magnetization Transfer rates in biological tissues is further analyzed by considering the time and power dependencies of saturation Transfer. Following these analyses, quantitative Magnetization Transfer rate constant image maps were collected from the kidney in vivo. These rate constant images may prove useful in quantitative tissue characterization and in the determination of tissue-specific 1H relaxation mechanisms.
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Lipid bilayer and water proton Magnetization Transfer: effect of cholesterol.
Magnetic resonance in medicine, 1991Co-Authors: Teresa A. Fralix, Toni L. Ceckler, Steven D. Wolff, Sidney A. Simon, Robert S. BalabanAbstract:Magnetization Transfer between macromolecules and water can be a significant factor contributing to tissue water 1H relaxation. Using saturation Transfer techniques, the degree of Magnetization Transfer between the macromolecular matrix and bulk water 1H can be directly measured and Magnetization Transfer contrast (MTC) can be generated in MR images. A significant degree of MTC has been observed in tissues with high plasma membrane content such as kidney and brain. The purpose of this study was to establish whether lipid bilayers, as models for cell membranes, could exchange Magnetization with the water solvent and whether this effect could contribute to MTC observed in intact tissues. Magnetization Transfer was measured in aqueous dispersions of egg phosphatidylcholine (EPC) in the presence and absence of cholesterol. It was found that neither EPC bilayers nor cholesterol by themselves significantly exchanged Magnetization with bulk water 1H. However, as the concentration of cholesterol was increased, the pseudo-first-order Magnetization exchange rate increased to a maximum value of approximately 1 s-1. The cholesterol-induced 1H Magnetization exchange may be related either to longer correlation times of the lipid or to an increase in the number of water molecules associated with the bilayer. These results indicate that EPC-cholesterol bilayers exchange 1H Magnetization with bulk water. These results are consistent with lipid bilayer contributions to bulk water relaxation and MTC in intact biological tissues.