51
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Cercignani M, Basile B, Spanò B, Comanducci G, Fasano F, Caltagirone C, Nocentini U, Bozzali M. Investigation of quantitative magnetisation transfer parameters of lesions and normal appearing white matter in multiple sclerosis. NMR IN BIOMEDICINE 2009; 22:646-53. [PMID: 19322806 DOI: 10.1002/nbm.1379] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The aim of this study was to use quantitative magnetisation transfer (MT) imaging to assess the different pathological substrates of tissue damage in multiple sclerosis (MS) and examine whether the MT parameters may be used to explain the disability in relapsing remitting (RR) MS. Thirteen patients with RRMS and 14 healthy controls were prescribed conventional MRI and quantitative MT imaging at 3.0 T. A two-pool model of MT (where A refers to the free pool and B to the macromolecular pool) was fitted to the data yielding a longitudinal relaxation rate R(A), a relative size F of macromolecular pool, transverse relaxation times T(2) (A) and T(2) (B) for the two pools and a forward exchange rate RM(0) (B). The MT ratio (MTR) was also computed. The mean MT parameters of the normal appearing white matter (NAWM) and of lesions in patients, and of white matter in controls were estimated. MT parameters were significantly different between lesions and NAWM in patients, and between the NAWM and the white matter of controls (with the exception of T(2) (B) and the MTR). Two models were investigated using ordered logistic regression, with the expanded disability status scale (EDSS) as the dependent variable. In the first one, mean NAWM MT parameters and lesion load were entered as explanatory variables; in the second one, mean MT variables within lesions and lesion load were entered as explanatory variables. Unexpectedly, T(2) (B) was the parameter most significantly associated with EDSS in NAWM. This parameter might represent a weighted average of the relaxation times of spins with different molecular environments, and therefore its variation could indicate a change in the balance between subpopulations of macromolecular spins. Conversely, in lesions, RM(0) (B), T(2) (B), F, R(A), and lesion load significantly predicted disability only when combined together. This might reflect the complex interaction between demyelination, remyelination, gliosis, inflammation and axonal loss taking place within lesions.
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Affiliation(s)
- M Cercignani
- Neuroimaging Laboratory, Fondazione Santa Lucia, Via Ardeatina 306, Rome, Italy.
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52
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Schwenzer NF, Martirosian P, Machann J, Schraml C, Steidle G, Claussen CD, Schick F. Aging effects on human calf muscle properties assessed by MRI at 3 Tesla. J Magn Reson Imaging 2009; 29:1346-54. [PMID: 19472391 DOI: 10.1002/jmri.21789] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Affiliation(s)
- Nina F Schwenzer
- Department of Diagnostic and Interventional Radiology, Eberhard-Karls University, Tübingen, Germany.
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53
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Boulant N, Mangin JF, Amadon A. Counteracting radio frequency inhomogeneity in the human brain at 7 Tesla using strongly modulating pulses. Magn Reson Med 2009; 61:1165-72. [DOI: 10.1002/mrm.21955] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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54
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Springer F, Martirosian P, Machann J, Schwenzer NF, Claussen CD, Schick F. Magnetization transfer contrast imaging in bovine and human cortical bone applying an ultrashort echo time sequence at 3 Tesla. Magn Reson Med 2009; 61:1040-8. [PMID: 19267348 DOI: 10.1002/mrm.21866] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Fabian Springer
- Department of Diagnostic and Interventional Radiology, University Hospital Tübingen, Tübingen, Germany.
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55
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Boulant N. T1 and T2 effects during radio-frequency pulses in spoiled gradient echo sequences. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 197:213-218. [PMID: 19171495 DOI: 10.1016/j.jmr.2008.12.023] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 12/29/2008] [Accepted: 12/30/2008] [Indexed: 05/27/2023]
Abstract
Finite pulse durations in diverse pulse schemes lead to the reduction of the magnitude of the magnetization vector due to T(1) and T(2) effects during the radio-frequency pulses. This paper presents an analysis of the steady state signal in the presence of relaxation effects during radio-frequency pulses in MRI spoiled gradient echo sequences. It is shown that minor attenuations of the magnetization vector can have dramatic consequences on the measured signal, and may thus entail a loss in SNR benefits at high static magnetic fields if a careful analysis is not performed. It is emphasized that it is the time-integrated magnetization vector trajectory that matters for these effects and not only the pulse duration. Some experimental results obtained on a phantom at 3T verify this analysis.
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Affiliation(s)
- Nicolas Boulant
- CEA, DSV, I2BM, NeuroSpin, LRMN, Gif sur Yvette 91191, France.
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56
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Helms G, Dathe H, Kallenberg K, Dechent P. High-resolution maps of magnetization transfer with inherent correction for RF inhomogeneity and T1 relaxation obtained from 3D FLASH MRI. Magn Reson Med 2009; 60:1396-407. [PMID: 19025906 DOI: 10.1002/mrm.21732] [Citation(s) in RCA: 216] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
An empirical equation for the magnetization transfer (MT) FLASH signal is derived by analogy to dual-excitation FLASH, introducing a novel semiquantitative parameter for MT, the percentage saturation imposed by one MT pulse during TR. This parameter is obtained by a linear transformation of the inverse signal, using two reference experiments of proton density and T(1) weighting. The influence of sequence parameters on the MT saturation was studied. An 8.5-min protocol for brain imaging at 3 T was based on nonselective sagittal 3D-FLASH at 1.25 mm isotropic resolution using partial acquisition techniques (TR/TE/alpha = 25ms/4.9ms/5 degrees or 11ms/4.9ms/15 degrees for the T(1) reference). A 12.8 ms Gaussian MT pulse was applied 2.2 kHz off-resonance with 540 degrees flip angle. The MT saturation maps showed an excellent contrast in the brain due to clearly separated distributions for white and gray matter and cerebrospinal fluid. Within the limits of the approximation (excitation <15 degrees , TR/T(1) less sign 1) the MT term depends mainly on TR, the energy and offset of the MT pulse, but hardly on excitation and T(1) relaxation. It is inherently compensated for inhomogeneities of receive and transmit RF fields. The MT saturation appeared to be a sensitive parameter to depict MS lesions and alterations of normal-appearing white matter.
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Affiliation(s)
- Gunther Helms
- MR-Forschung in der Neurologie und Psychiatrie, Universitätsmedizin Göttingen, Göttingen, Germany.
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57
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Perrin JS, Leonard G, Perron M, Pike GB, Pitiot A, Richer L, Veillette S, Pausova Z, Paus T. Sex differences in the growth of white matter during adolescence. Neuroimage 2009; 45:1055-66. [PMID: 19349224 DOI: 10.1016/j.neuroimage.2009.01.023] [Citation(s) in RCA: 156] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2008] [Revised: 12/05/2008] [Accepted: 01/13/2009] [Indexed: 11/28/2022] Open
Abstract
The purpose of this study was to examine sex differences in the maturation of white matter during adolescence (12 to 18 years of age). We measured lobular volumes of white matter and white-matter "density" throughout the brain using T1-weighted images, and estimated the myelination index using magnetisation-transfer ratio (MTR). In male adolescents, we observed age-related increases in white-matter lobular volumes accompanied by decreases in the lobular values of white-matter MTR. White-matter density in the putative cortico-spinal tract (pCST) decreased with age. In female adolescents, on the other hand, we found only small age-related increase in white-matter volumes and no age-related changes in white-matter MTR, with the exception of the frontal lobe where MTR increased. White-matter density in the pCST also increased with age. These results suggest that sex-specific mechanisms may underlie the growth of white matter during adolescence. We speculate that these mechanisms involve primarily age-related increases in axonal calibre in males and increased myelination in females.
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Affiliation(s)
- J S Perrin
- Brain and Body Centre, University of Nottingham, UK
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58
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Growth of white matter in the adolescent brain: role of testosterone and androgen receptor. J Neurosci 2008; 28:9519-24. [PMID: 18799683 DOI: 10.1523/jneurosci.1212-08.2008] [Citation(s) in RCA: 234] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The growth of white matter during human adolescence shows a striking sexual dimorphism; the volume of white matter increases with age slightly in girls and steeply in boys. Here, we provide evidence supporting the role of androgen receptor (AR) in mediating the effect of testosterone on white matter. In a large sample of typically developing adolescents (n = 408, 204 males), we used magnetic resonance imaging and acquired T1-weighted and magnetization transfer ratio (MTR) images. We also measured plasma levels of testosterone and genotyped a functional polymorphism in the AR gene, namely the number of CAG repeats in exon 1 believed to be inversely proportional to the AR transcriptional activity. We found that the testosterone-related increase of white-matter volume was stronger in male adolescents with the lower versus higher number of CAG repeats in the AR gene, with testosterone explaining, respectively, 26 and 8% of variance in the volume. The MTR results suggest that this growth is not related to myelination; the MTR decreased with age in male adolescents. We speculate that testosterone affects axonal caliber rather than the thickness of the myelin sheath.
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59
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Gloor M, Scheffler K, Bieri O. Quantitative magnetization transfer imaging using balanced SSFP. Magn Reson Med 2008; 60:691-700. [DOI: 10.1002/mrm.21705] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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60
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Ou X, Gochberg DF. MT effects and T1 quantification in single-slice spoiled gradient echo imaging. Magn Reson Med 2008; 59:835-45. [PMID: 18302249 PMCID: PMC4186261 DOI: 10.1002/mrm.21550] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2007] [Accepted: 12/12/2007] [Indexed: 02/02/2023]
Abstract
We investigated magnetization transfer (MT) effects on the steady-state MR signal for a sample subjected to a series of identical on-resonance RF pulses, such as would be experienced while imaging a single slice using a spoiled gradient echo sequence. The MT coupling terms for a two-pool system were added to the Bloch equations and we derived the resulting steady-state signal equation and compared this result to the conventional signal equation without MT effects. The steady-state signal is increased by a few percent of the equilibrium magnetization because of MT. One consequence of this MT effect is inaccuracy in T(1) values determined via conventional steady-state gradient echo methods. (Theory predicts greater than 10% errors in T(1) for white matter when using short TR.) A second consequence is the ability to quantify the relaxation and MT parameters by fitting the gradient echo steady state signal to the signal equation appropriately modified to include MT effects. The theory was tested in samples of MnCl(2), cross-linked bovine serum albumin (BSA), and cross-linked BSA + MnCl(2).
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Affiliation(s)
- Xiawei Ou
- Department of Radiology, Vanderbilt University Institute of Imaging Science, Nashville, Tennessee 37232-2310, USA.
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61
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Systematic Variation of Off-Resonance Prepulses for Clinical Magnetization Transfer Contrast Imaging at 0.2, 1.5, and 3.0 Tesla. Invest Radiol 2008; 43:16-26. [DOI: 10.1097/rli.0b013e3181559949] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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62
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Paus T, Nawazkhan I, Leonard G, Perron M, Pike GB, Pitiot A, Richer L, Veillette S, Pausova Z. Corpus callosum in adolescent offspring exposed prenatally to maternal cigarette smoking. Neuroimage 2007; 40:435-441. [PMID: 18221892 DOI: 10.1016/j.neuroimage.2007.10.066] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Revised: 09/29/2007] [Accepted: 10/05/2007] [Indexed: 11/15/2022] Open
Abstract
Teratogens, such as alcohol or anti-epileptic drugs, affect the size of the corpus callosum. Here we report findings obtained in a case-control study that investigated possible effects of teratogens contained in cigarette smoke on the size and structural properties of this structure. We recruited and scanned with magnetic resonance imaging a total of 408 adolescents (12 to 18 years of age); a subsample of 300 adolescents is considered in this report. Cases (n=146) were exposed to maternal cigarette smoking during pregnancy; non-exposed controls (n=154) were matched to cases by maternal education. We measured the size of corpus callosum (CC) and its sections (corrected for brain size), as well as mean values of magnetization-transfer ratio (MTR) in each CC section. Corpus callosum, and especially its posterior part, was smaller in the exposed vs. non-exposed female adolescents; no significant effects were found in males. Exposed and non-exposed subjects did not differ in the MTR-based index of myelination in either gender in any CC section. Given the lack of exposure effect on the myelination index, this finding might reflect a lower number of inter-hemispheric connections in female offspring of mothers who smoked during pregnancy.
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Affiliation(s)
- T Paus
- Brain and Body Centre, University of Nottingham, UK; Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.
| | - I Nawazkhan
- Brain and Body Centre, University of Nottingham, UK
| | - G Leonard
- Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada
| | - M Perron
- Université de Montreal, Montreal, Quebec, Canada; Groupe ECOBES, CEGEP Jonquiere, Jonquiere, Quebec, Canada
| | - G B Pike
- Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada
| | - A Pitiot
- Brain and Body Centre, University of Nottingham, UK
| | - L Richer
- Department of Psychology, University of Quebec in Chicoutimi, Chicoutimi, Quebec, Canada
| | - S Veillette
- Université de Montreal, Montreal, Quebec, Canada; Groupe ECOBES, CEGEP Jonquiere, Jonquiere, Quebec, Canada
| | - Z Pausova
- Brain and Body Centre, University of Nottingham, UK; Université de Montreal, Montreal, Quebec, Canada
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63
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Abstract
Modeling the effects of clinical magnetization transfer (MT) scans, which generate contrast using short, shaped radiofrequency (RF) pulses (pulsed MT), is complex and time-consuming. As a result, several studies have proposed approximate methods for a simplified analysis of the experimental data. However, potential differences in the MT parameters estimated by each method may complicate the comparison of reported results. In this study we evaluated three approximate methods currently used in quantitative MT (qMT) studies. In the first part of the investigation, an MT modeling technique that makes minimal approximations, other than the use of a two-pool tissue representation, was developed and validated. Subsequently, this technique served as a standard against which to evaluate the other, more approximate models. Each model was used to fit experimental data from samples of wild-type (WT) and shiverer mouse spinal cord, as well as simulated data generated by our minimal approximation modeling technique. The results of this study demonstrate that the approximations used in pulsed MT modeling are quite robust. In particular, it was shown that the semisolid pool fraction, M(0)(B), which is known to correlate strongly with myelin content, and the transverse relaxation time of macromolecular protons, T(2)(B), could be evaluated with reasonable accuracy regardless of the model used.
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Affiliation(s)
- Sharon Portnoy
- Department of Medical Biophysics, University of Toronto, Toronto, Canada
| | - Greg J Stanisz
- Department of Medical Biophysics, University of Toronto, Toronto, Canada
- Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Canada
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64
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Pausova Z, Paus T, Abrahamowicz M, Almerigi J, Arbour N, Bernard M, Gaudet D, Hanzalek P, Hamet P, Evans AC, Kramer M, Laberge L, Leal SM, Leonard G, Lerner J, Lerner RM, Mathieu J, Perron M, Pike B, Pitiot A, Richer L, Séguin JR, Syme C, Toro R, Tremblay RE, Veillette S, Watkins K. Genes, maternal smoking, and the offspring brain and body during adolescence: design of the Saguenay Youth Study. Hum Brain Mapp 2007; 28:502-18. [PMID: 17469173 PMCID: PMC6174527 DOI: 10.1002/hbm.20402] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2006] [Revised: 03/06/2007] [Accepted: 03/09/2007] [Indexed: 12/12/2022] Open
Abstract
The search for genes of complex traits is aided by the availability of multiple quantitative phenotypes collected in geographically isolated populations. Here we provide rationale for a large-scale study of gene-environment interactions influencing brain and behavior and cardiovascular and metabolic health in adolescence, namely the Saguenay Youth Study (SYS). The SYS is a retrospective study of long-term consequences of prenatal exposure to maternal cigarette smoking (PEMCS) in which multiple quantitative phenotypes are acquired over five sessions (telephone interview, home, hospital, laboratory, and school). To facilitate the search for genes that modify an individual's response to an in utero environment (i.e. PEMCS), the study is family-based (adolescent sibships) and is carried out in a relatively geographically isolated population of the Saguenay Lac-Saint-Jean (SLSJ) region in Quebec, Canada. DNA is acquired in both biological parents and in adolescent siblings. A genome-wide scan will be carried out with sib-pair linkage analyses, and fine mapping of identified loci will be done with family-based association analyses. Adolescent sibships (12-18 years of age; two or more siblings per family) are recruited in high schools throughout the SLSJ region; only children of French-Canadian origin are included. Based on a telephone interview, potential participants are classified as exposed or nonexposed prenatally to maternal cigarette smoking; the two groups are matched for the level of maternal education and the attended school. A total of 500 adolescent participants in each group will be recruited and phenotyped. The following types of datasets are collected in all adolescent participants: (1) magnetic resonance images of brain, abdominal fat, and kidneys, (2) standardized and computer-based neuropsychological tests, (3) hospital-based cardiovascular, body-composition and metabolic assessments, and (4) questionnaire-derived measures (e.g. life habits such as eating and physical activity; drug, alcohol use and delinquency; psychiatric symptoms; personality; home and school environment; academic and vocational attitudes). Parents complete a medical questionnaire, home-environment questionnaire, a handedness questionnaire, and a questionnaire about their current alcohol and drug use, depression, anxiety, and current and past antisocial behavior. To date, we have fully phenotyped a total of 408 adolescent participants. Here we provide the description of the SYS and, using the initial sample, we present information on ascertainment, demographics of the exposed and nonexposed adolescents and their parents, and the initial MRI-based assessment of familiality in the brain size and the volumes of grey and white matter.
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Affiliation(s)
- Zdenka Pausova
- Brain and Body Centre, University of Nottingham, Nottingham, United Kingdom
- Centre de recherche, Centre hospitalier de l'Université de Montreal, Montreal, Quebec, Canada
| | - Tomás˘ Paus
- Brain and Body Centre, University of Nottingham, Nottingham, United Kingdom
- Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada
| | - Michal Abrahamowicz
- Centre de recherche, Centre hospitalier de l'Université de Montreal, Montreal, Quebec, Canada
| | - Jason Almerigi
- Child Development Department, Tufts University, Medford, Massachusetts, USA
| | - Nadine Arbour
- Groupe ECOBES, CEGEP Jonquiere, Jonquiere, Quebec, Canada
| | - Manon Bernard
- Brain and Body Centre, University of Nottingham, Nottingham, United Kingdom
| | - Daniel Gaudet
- Complex hospitalier de la Sagamie, Chicoutimi, Quebec, Canada
| | - Petr Hanzalek
- Brain and Body Centre, University of Nottingham, Nottingham, United Kingdom
| | - Pavel Hamet
- Centre de recherche, Centre hospitalier de l'Université de Montreal, Montreal, Quebec, Canada
| | - Alan C. Evans
- Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada
| | - Michael Kramer
- Montreal Children's Hospital, McGill University, Montreal, Quebec, Canada
| | - Luc Laberge
- Groupe ECOBES, CEGEP Jonquiere, Jonquiere, Quebec, Canada
| | - Susan M. Leal
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA
| | - Gabriel Leonard
- Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada
| | - Jackie Lerner
- Child Development Department, Tufts University, Medford, Massachusetts, USA
| | - Richard M. Lerner
- Child Development Department, Tufts University, Medford, Massachusetts, USA
| | - Jean Mathieu
- Complex hospitalier de la Sagamie, Chicoutimi, Quebec, Canada
| | - Michel Perron
- Groupe ECOBES, CEGEP Jonquiere, Jonquiere, Quebec, Canada
| | - Bruce Pike
- Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada
| | - Alain Pitiot
- Brain and Body Centre, University of Nottingham, Nottingham, United Kingdom
| | - Louis Richer
- Department of Psychology, University of Quebec in Chicoutimi, Chicoutimi, Quebec, Canada
| | - Jean R. Séguin
- Research Unit on Children's Psychosocial Maladjustment (GRIP), University of Montreal, Montreal, Quebec, Canada
| | - Catriona Syme
- Brain and Body Centre, University of Nottingham, Nottingham, United Kingdom
| | - Roberto Toro
- Brain and Body Centre, University of Nottingham, Nottingham, United Kingdom
| | - Richard E. Tremblay
- Research Unit on Children's Psychosocial Maladjustment (GRIP), University of Montreal, Montreal, Quebec, Canada
| | | | - Kate Watkins
- Department of Experimental Psychology, University of Oxford, Oxford, United Kingdom
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65
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Vrenken H, Geurts JJG. Gray and normal-appearing white matter in multiple sclerosis: an MRI perspective. Expert Rev Neurother 2007; 7:271-9. [PMID: 17341175 DOI: 10.1586/14737175.7.3.271] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Besides focal white matter lesions, multiple sclerosis brain tissue also displays abnormalities in the gray matter and the normal-appearing white matter. Recent advances in magnetic resonance imaging studies of both types of tissue are discussed. Herein, normal-appearing white matter abnormalities are being found in quantitative magnetic resonance investigations, consistent with a limited degree of axonal damage and/or demyelination, and an increase of glial cells, but the specific nature of the histopathological changes underlying the quantitative magnetic resonance abnormalities remains unclear. Gray matter studies have demonstrated that much of the disease process remains undetected by conventional magnetic resonance imaging. Although newly developed techniques, such as 3D double-inversion recovery, may greatly improve detection of cortical pathology, it remains important to investigate the resultant effects on the cortical tissue alongside this, by studying integrity of normal-appearing cortical tissue through quantitative magnetic resonance studies, as well as the net neurodegenerative effect through measurements of cortical thickness and cortical atrophy (rates). To improve our understanding of normal-appearing white and gray matter changes, their mutual relations, and their relations to clinical changes, further in vivo magnetic resonance imaging studies are required. Specifically, it is proposed that more spatially specific investigations, ideally utilizing subject-specific anatomical information from, for example, diffusion fiber-tracking techniques, could be used to gain more insight into the relations between normal-appearing white matter changes, cortical changes, magnetic resonance visible focal-lesions, and physical and cognitive deficits.
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Affiliation(s)
- Hugo Vrenken
- MS Center Amsterdam, VU University Medical Center, Department of Physics & Medical Technology, De Boelelaan, Amsterdam, The Netherlands.
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66
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Zhang H, Xie Y. Dynamics of paramagnetic agents by off-resonance rotating frame technique in the presence of magnetization transfer effect. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 184:275-91. [PMID: 17123851 PMCID: PMC1941718 DOI: 10.1016/j.jmr.2006.11.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2006] [Revised: 11/06/2006] [Accepted: 11/06/2006] [Indexed: 05/12/2023]
Abstract
The simple method for measuring the rotational correlation time of paramagnetic ion chelates via off-resonance rotating frame technique is challenged in vivo by the magnetization transfer effect. A theoretical model for the spin relaxation of water protons in the presence of paramagnetic ion chelates and magnetization transfer effect is described. This model considers the competitive relaxations of water protons by the paramagnetic relaxation pathway and the magnetization transfer pathway. The influence of magnetization transfer on the total residual z-magnetization has been quantitatively evaluated in the context of the magnetization map and various difference magnetization profiles for the macromolecule conjugated Gd-DTPA in cross-linked protein gels. The numerical simulations and experimental validations confirm that the rotational correlation time for the paramagnetic ion chelates can be measured even in the presence of strong magnetization transfer. This spin relaxation model also provides novel approaches to enhance the detection sensitivity for paramagnetic labeling by suppressing the spin relaxations caused by the magnetization transfer. The inclusion of the magnetization transfer effect allows us to use the magnetization map as a simulation tool to design efficient paramagnetic labeling targeting at specific tissues, to design experiments running at low RF power depositions, and to optimize the sensitivity for detecting paramagnetic labeling. Thus, the presented method will be a very useful tool for the in vivo applications such as molecular imaging via paramagnetic labeling.
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Affiliation(s)
- Huiming Zhang
- Center for Basic MR Research, Evanston Northwestern Healthcare Research Institute, 1033 University Place, suite 100, Evanston, IL 60201, USA.
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67
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Cercignani M, Alexander DC. Optimal acquisition schemes for in vivo quantitative magnetization transfer MRI. Magn Reson Med 2007; 56:803-10. [PMID: 16902982 DOI: 10.1002/mrm.21003] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This paper uses the theory of Cramer-Rao lower bounds (CRLB) to obtain optimal acquisition schemes for in vivo quantitative magnetization transfer (MT) imaging, although the method is generally applicable to any multiparametric MRI technique. Quantitative MT fits a two-pool model to data collected at different sampling points or settings of amplitude and offset frequency in the MT saturation pulses. Here we use simple objective functions based on the CRLB to optimize sampling strategies for multiple parameters simultaneously, and use simulated annealing to minimize these objective functions with respect to the sampling configuration. Experiments compare optimal schemes derived for quantitative MT in the human white matter (WM) at 1.5T with previously published schemes using both synthetic and human-brain data. Results show large reductions in error of the fitted parameters with the new schemes, which greatly increases the clinical potential of in vivo quantitative MT. Since the sampling-scheme optimization requires specific settings of the MT parameters, we also show that the optimum schemes are robust to these settings within the range of MT parameters observed in the brain.
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Affiliation(s)
- Mara Cercignani
- NMR Research Unit, Department of Neuroinflammation, Institute of Neurology, London, UK.
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68
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Bieri O, Scheffler K. Optimized balanced steady-state free precession magnetization transfer imaging. Magn Reson Med 2007; 58:511-8. [PMID: 17763346 DOI: 10.1002/mrm.21326] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Balanced steady-state free precession (bSSFP) suffers from a considerable signal loss in tissues. This apparent signal reduction originates from magnetization transfer (MT) and may be reduced by an increase in repetition time or by a reduction in flip angle. In this work, MT effects in bSSFP are modulated by a modification of the bSSFP sequence scheme. Strong signal attenuations are achieved with short radio frequency (RF) pulses in combination with short repetition times, whereas near full, i.e., MT-free, bSSFP signal is obtained by a considerable prolongation of the RF pulse duration. Similar to standard methods, the MT ratio (MTR) in bSSFP depends on several sequence parameters. Optimized bSSFP protocol settings are derived that can be applied to various tissues yielding maximal sensitivity to MT while minimizing contribution from other impurities, such as off-resonances. Evaluation of MT in human brain using such optimized bSSFP protocols shows high correlation with MTR values from commonly used gradient echo (GRE) sequences. In summary, a novel method to generate MTR maps using bSSFP image acquisitions is presented and factors that optimize and influence this contrast are discussed.
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Affiliation(s)
- O Bieri
- MR Physics, Department of Medical Radiology, University of Basel, Basel, Switzerland.
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69
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Cercignani M, Symms MR, Ron M, Barker GJ. 3D MTR measurement: From 1.5 T to 3.0 T. Neuroimage 2006; 31:181-6. [PMID: 16413794 DOI: 10.1016/j.neuroimage.2005.11.028] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2005] [Revised: 11/16/2005] [Accepted: 11/25/2005] [Indexed: 10/25/2022] Open
Abstract
This study investigates some of the issues involved in magnetization transfer ratio (MTR) acquisition, and in particular aims to determine whether high quality in vivo MTR measurements can be made at 3.0 T. The dependency of the MTR white-to-grey matter contrast to noise ratio (CNR) on MT pulse characteristics at 1.5 T and at 3.0 T was investigated using an established two-pool model for MT. The simulations showed that MT pulse parameters optimizing the CNR can be derived for both field strengths. Both the SNR and the CNR of MTR maps at 3.0 T were increased compared to 1.5 T. Images obtained using a safe in vivo MTR acquisition protocol based on results of simulations at 3.0 T are presented.
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Affiliation(s)
- Mara Cercignani
- NMR Research Unit, Department of Neuroinflammation, 6th floor, Queen Square House, Institute of Neurology, Queen Square, London WC1N 3BG, England, UK.
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70
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Helms G, Piringer A. Quantitative magnetization transfer by trains of radio frequency pulses in human brain: extension of a free evolution model to continuous-wave-like conditions. Magn Reson Imaging 2006; 23:723-31. [PMID: 16198827 DOI: 10.1016/j.mri.2005.05.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2004] [Accepted: 05/23/2005] [Indexed: 11/17/2022]
Abstract
A theoretical model of free evolution between repeated magnetic transfer (MT) pulses was extended to continuous-wave (CW)-like conditions showing that only the repetitive "direct" saturation of bulk water changes the transient and stationary behavior. The influence of the pulse repetition period (PR) on progressive saturation was studied in cortical gray matter (GM) and central white matter (WM) under conditions of short periods of free evolution and strong macromolecular saturation. Interpulse delays of 3 ms were achieved in vivo on a 1.5-T MR system with bell-shaped MT pulses of 12-ms duration and nominal flip angles of up to 1440 degrees and single-shot readout by a stimulated echo acquisition mode localization sequence. The frequency offset was chosen between 1 and 3 kHz to avoid excessive direct saturation. The stationary MT ratio (MTR) followed an inverse linear PR dependence, showing a consistent partial saturation of about 90% at zero PR for both WM and GM. Comparison to a relaxation-matched liquid indicated the presence of MT, but not necessarily of direct saturation. The transient behavior indicated considerable direct saturation, but this could also be explained by MT. These inconsistencies showed that the intervals of time evolution in our experiments were too long to be modeled by CW-like conditions. Free evolution takes place during the whole PR rather than during the interpulse delay only. Quantification using the rates of free evolution theory yielded the saturations and rate constants necessary to explain the observed behavior. The theory of rapid CW-like pulsing provides an upper limit for the rate of progressive saturation. This limit is approached at PR below an estimated value of 5 ms. The phenomenological PR dependence of the steady-state MTR may indicate that MT exceeded the direct saturation. Unlike to an idealized CW experiment, the extrapolated value at zero PR is subject to direct effects and not a physically meaningful constant.
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Affiliation(s)
- Gunther Helms
- Section on Experimental Radiology, Department of Diagnostic Radiology, University of Tübingen, DE-72076 Tübingen, Germany.
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71
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Arnold DL, Chen J. Measuring injury and repair of myelin and neurons in multiple sclerosis. ERNST SCHERING RESEARCH FOUNDATION WORKSHOP 2005:173-86. [PMID: 16315614 DOI: 10.1007/3-540-27626-2_10] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Neuroprotection in MS needs to be considered in the context of several pathological processes: limitation of acute inflammatory injury to myelin and axons, remyelination, survival of demyelinated axons, and limitation of more diffuse, nonlesional pathology that affects myelin and axons. Advanced MRI techniques are capable of reporting on all of these different pathological features of MS and will be an important aspect of the assessment of neuroprotection strategies in MS, when these become available.
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Affiliation(s)
- D L Arnold
- Montreal Neurological Institute, McGill University, Quebec, Canada.
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72
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Helms G, Piringer A. Simultaneous measurement of saturation and relaxation in human brain by repetitive magnetization transfer pulses. NMR IN BIOMEDICINE 2005; 18:44-50. [PMID: 15455467 DOI: 10.1002/nbm.920] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Magnetization transfer (MT) by equidistant pulse trains can be described as being analogous to progressive partial saturation, where 'direct' saturation of water is amplified by MT contributions that are dependent on macromolecular content and differential saturation. This concept was applied to study the transition to steady state in the human brain using similar MT-pulses as in imaging. Up to 41 bell-shaped MT-pulses of 12 ms duration were applied at frequency offsets between 0.5 and 15 kHz with flip angles between 1080 and 1440 degrees . Central white and parietal gray matter was studied in human subjects using STEAM for localized read-out (TE = 30 ms, TM = 13.7 ms). The apparent degree of saturation, delta(app), and the longitudinal relaxation of the water pool during the pulse repetition period (PR) were fitted to the transient behavior after signal correction for cerebro-spinal fluid. PR was varied between 15 and 100 ms to assess the PR-dependence of the fitted parameters. The MT-term in delta(app) exceeded the direct saturation and attained its maximum at PR > or = 100 ms. The macromolecular pool was only partially saturated by a single MT-pulse. The offset may be increased to 2.5 kHz to reduce direct saturation without sacrificing MT in white matter. The estimated relaxation rates (1.04 +/- 0.11 s(-1) in WM; 0.76 +/- 0.13 s(-1) in GM) were faster than are commonly observed at 1.5 T. The apparent saturation is a measure for MT that is not confounded by relaxation. To maximize MT in brain tissue, MT-pulses should be applied at PR = 100 ms or longer. At shorter PR, a larger steady state saturation is obtained at the cost of increased contributions from direct saturation. Since this accelerates the convergence, PR should be decreased to reach the steady state within a specified time. A faster transition can always be achieved at a reduced frequency offset via increased direct saturation.
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Affiliation(s)
- Gunther Helms
- Section on Experimental Radiology, Department of Diagnostic Radiology, University Hospital, Tübingen, Germany.
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73
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Levesque I, Sled JG, Narayanan S, Santos AC, Brass SD, Francis SJ, Arnold DL, Pike GB. The role of edema and demyelination in chronic T1 black holes: A quantitative magnetization transfer study. J Magn Reson Imaging 2005; 21:103-10. [PMID: 15666408 DOI: 10.1002/jmri.20231] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To use quantitative magnetization transfer imaging (qMTI) in an investigation of T1-weighted hypointensity observed in clinical magnetic resonance imaging (MRI) scans of multiple sclerosis (MS) patients, which has previously been proposed as a more specific indicator of tissue damage than the more commonly detected T2 hyperintensity. MATERIALS AND METHODS A cross-sectional study of 10 MS patients was performed using qMTI. A total of 60 MTI measurements were collected in each patient at a resolution of 2 x 2 x 7 mm, over a range of saturation pulses. The observed T1 and T2 were also measured. qMT model parameters were estimated using a voxel-by-voxel fit. RESULTS A total of 65 T2-hyperintense lesions were identified; 53 were also T1 hypointense. In these black holes, the qMTI-derived semisolid pool fraction F correlated negatively with T(1,obs) (r2 = 0.76; P < 0.0001). The water pool absolute size (PDf) showed a weaker correlation with T(1,obs) (positive, r2 = 0.53; P < 0.0001). The magnetization transfer ratio (MTR) showed a similarly strong correlation with F and a weaker correlation with PDf (r2 = 0.18; P < 0.04). CONCLUSION T1 increases in chronic black holes strongly correlated with the decline in semisolid pool size, and somewhat less to the confounding effect of edema. MTR was less sensitive than T(1,obs) to liquid pool changes associated with edema.
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Affiliation(s)
- Ives Levesque
- McConnell Brain Imaging Centre, Montréal Neurological Institute, McGill University, Montréal, H3A 2B4 Québec, Canada.
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74
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Helms G, Hagberg GE. Pulsed saturation of the standard two-pool model for magnetization transfer. Part I: The steady state. ACTA ACUST UNITED AC 2004. [DOI: 10.1002/cmr.a.20004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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75
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Natt O, Watanabe T, Boretius S, Frahm J, Michaelis T. Magnetization transfer MRI of mouse brain reveals areas of high neural density. Magn Reson Imaging 2003; 21:1113-20. [PMID: 14725918 DOI: 10.1016/j.mri.2003.08.012] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Extending applications of magnetization transfer contrast (MTC) in magnetic resonance imaging (MRI) of the human central nervous system, this work quantitatively describes MTC of the murine brain. As a novel finding, complementing T(1)- and T(2)-weighted MRI, MTC allows for the distinction of densely packed gray matter from normal gray and white matter. Examples include the Purkinje cell layer and the granular cell layer in the mouse cerebellum as well as the delineation of the CA3 subfield of the hippocampus relative to surrounding hippocampal gray matter and white matter tracts such as the hippocampal fimbria. Using a kainate lesion model, the CA3 hyperintensities in MTC and T(1)-weighted MRI are assigned to the densely packed somata of pyramidal cells.
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Affiliation(s)
- O Natt
- Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany.
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76
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Tozer D, Ramani A, Barker GJ, Davies GR, Miller DH, Tofts PS. Quantitative magnetization transfer mapping of bound protons in multiple sclerosis. Magn Reson Med 2003; 50:83-91. [PMID: 12815682 DOI: 10.1002/mrm.10514] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Quantitative analysis of magnetization transfer images has the potential to allow a more thorough characterization of the protons, both bound and free, in a tissue by extracting a number of parameters relating to the NMR properties of the protons and their local environment. This work develops previously presented techniques to produce estimates of parameters such as the bound proton fraction, f, and the transverse relaxation time of the bound pool, T(2B), for the whole brain in a clinically acceptable imaging time. This is achieved by limiting the number of data collected (typically to 10); to collect 28 5-mm slices with a reconstructed resolution of 0.94 x 0.94 mm. The protocol takes 82 sec per data point. The fitting technique is assessed against previous work and for fitting failures. Maps and analysis are presented from a group of seven controls and 20 multiple sclerosis patients. The maps show that the parameters are sensitive to tissue-specific differences and can detect pathological change within lesions. Statistically significant differences in parameters such as T(2B) and f are seen between normal-appearing white matter, multiple sclerosis lesions, and control white matter. Whole-brain histograms of these parameters are also presented, showing differences between patients and controls.
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Affiliation(s)
- D Tozer
- NMR Research Unit, Department of Neuroinflammation, Institute of Neurology, University College London, London, UK
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77
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Henkelman RM, Stanisz GJ, Menezes N, Burstein D. Can MTR be used to assess cartilage in the presence of Gd-DTPA2-? Magn Reson Med 2002; 48:1081-4. [PMID: 12465122 DOI: 10.1002/mrm.10322] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Magnetization transfer (MT) and T(1) and T(2) relaxation of normal, trypsinized, and interleukin-1beta (IL-1beta)-treated cartilage were measured in the absence and presence of Gd-DTPA(2-). Without the addition of Gd-DTPA(2-), neither T(1) nor T(2) showed any significant change with cartilage damage. However, with Gd-DTPA(2-), trypsinized cartilage exhibited substantially shorter T(1) than normal cartilage, as expected due to the glycosaminoglycan (GAG) loss in these samples, and associated increased Gd-DTPA(2-) concentration. The T(2) results were similar, but less dramatic. The MT pseudo first-order exchange rate, RM(0B), did not depend on the contrast agent concentration, as expected, and was significantly faster for trypsinized and slower for IL-1beta-treated cartilage. In both cases, the MT fraction of the macromolecular pool M(0B) decreased while only trypsinized cartilage showed an increase in MT exchange rate R. The MT ratio (MTR) decreased with increasing Gd-DTPA(2-) concentration. However, interpretation of the MTR results in the presence of Gd-DTPA(2-) was complicated due to competing effects of increased longitudinal relaxivity and MT exchange. Therefore, in a cartilage sample with an unknown degree of GAG depletion and some collagen damage, a full MT analysis might be used to probe the molecular state of cartilage, but it would not be possible to use a simple MTR measurement after the administration of Gd-DTPA(2-) to differentially determine the amount of cartilage degradation in the sample.
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Affiliation(s)
- R M Henkelman
- Department of Medical Biophysics, University of Toronto, Toronto, Canada.
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78
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Sled JG, Pike GB. Quantitative imaging of magnetization transfer exchange and relaxation properties in vivo using MRI. Magn Reson Med 2001; 46:923-31. [PMID: 11675644 DOI: 10.1002/mrm.1278] [Citation(s) in RCA: 304] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We describe a novel imaging technique that yields all of the observable properties of the binary spin-bath model for magnetization transfer (MT) and demonstrate this method for in vivo studies of the human head. Based on a new model of the steady-state behavior of the magnetization during a pulsed MT-weighted imaging sequence, this approach yields parametric images of the fractional size of the restricted pool, the magnetization exchange rate, the T(2) of the restricted pool, as well as the relaxation times in the free pool. Validated experimentally on agar gels and samples of uncooked beef, we demonstrate the method's application on two normal subjects and a patient with multiple sclerosis.
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Affiliation(s)
- J G Sled
- McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.
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79
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Vavasour IM, Whittall KP, Li DK, MacKay AL. Different magnetization transfer effects exhibited by the short and long T(2) components in human brain. Magn Reson Med 2000; 44:860-6. [PMID: 11108622 DOI: 10.1002/1522-2594(200012)44:6<860::aid-mrm6>3.0.co;2-c] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Magnetization transfer ratios (MTRs) were measured separately for the two T(2) components in white matter. For both binomial and off-resonance sinc MT pulses, the MTR was larger for the short T(2) component than for the long T(2) component. This differential MT effect disappeared for delays between the MT pulse and the multi-echo pulse sequence longer than 200 msec, indicating exchange between the two components. When using the sinc MT pulse, the MTR for the short T(2) component was similar for different white matter structures, whereas it varied for different white matter structures when using the binomial pulse-a phenomenon attributed to direct saturation. When the sinc pulse frequency was brought closer to resonance, MTRs in white matter and doped water phantoms increased for both components but more so for the shorter T(2) component. This behavior was consistent with a Bloch equation model of direct saturation.
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Affiliation(s)
- I M Vavasour
- Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada
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80
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Sled JG, Pike GB. Quantitative interpretation of magnetization transfer in spoiled gradient echo MRI sequences. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2000; 145:24-36. [PMID: 10873494 DOI: 10.1006/jmre.2000.2059] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A method for analyzing general pulsed magnetization transfer (MT) experiments in which off-resonance saturation pulses are interleaved with on-resonance excitation pulses is presented. We apply this method to develop a steady-state signal equation for MT-weighted spoiled gradient echo sequences and consider approximations that facilitate its rapid computation. Using this equation, we assess various experimental designs for quantitatively imaging the fractional size of the restricted pool, cross-relaxation rate, and T(1) and T(2) relaxation times of the two pools in a binary spin bath system. From experiments on agar gel, this method is shown to reliably and accurately estimate the exchange and relaxation properties of a material in an imaging context, suggesting the feasibility of using this technique in vivo.
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Affiliation(s)
- J G Sled
- McConnell Brain Imaging Centre, McGill University, Montréal, Québec, H3A 2B4, Canada.
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81
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Pike GB, De Stefano N, Narayanan S, Worsley KJ, Pelletier D, Francis GS, Antel JP, Arnold DL. Multiple sclerosis: magnetization transfer MR imaging of white matter before lesion appearance on T2-weighted images. Radiology 2000; 215:824-30. [PMID: 10831705 DOI: 10.1148/radiology.215.3.r00jn02824] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To determine the evolution of magnetization transfer (MT) in white matter regions before and after plaque development in patients with multiple sclerosis (MS). MATERIALS AND METHODS In a 5-year longitudinal evaluation, 30 patients with MS underwent conventional magnetic resonance (MR) imaging, MT MR imaging, and clinical assessment. Cross-sectional data in 12 healthy subjects were also collected. Semiautomated lesion classification with use of T2-weighted MR images was used to measure the time course of the MT ratio (calculated with MR data acquired without and with MT saturation) in every voxel and to help analyze the relationship with the status of lesions depicted on T2-weighted images. RESULTS There was a significant (P <.001) temporal decline in lesion MT ratio after lesion appearance on T2-weighted images. A significant (P <. 001) progressive decline in MT ratio was also present in voxels that later became lesions, prior to initial detection on T2-weighted images. Even 1(1/2) years prior to lesion appearance, the MT ratio (33.3%) in regions destined to become such lesions was significantly (P <.001) lower than that in both white matter in healthy subjects (41.3%) and other normal-appearing white matter in patients with MS (38.1%). CONCLUSION The MT ratio reveals progressive focal abnormalities in MS that antedate by up to 2 years the appearance of lesions on T2-weighted MR images.
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Affiliation(s)
- G B Pike
- McConnell Brain Imaging Center, Montreal Neurological Institute, 3801 University St, Montreal, Québec, Canada.
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82
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83
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Duvvuri U, Roberts DA, Leigh JS, Bolinger L. Magnetization transfer imaging of the brain: A quantitative comparison of results obtained at 1.5 and 4.0 T. J Magn Reson Imaging 1999; 10:527-32. [PMID: 10508319 DOI: 10.1002/(sici)1522-2586(199910)10:4<527::aid-jmri5>3.0.co;2-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The preliminary results of magnetization transfer (MT) imaging on a whole body 4.0 T system are presented. Cooked egg phantoms and several volunteers were imaged on 1.5 and 4.0 T magnets interfaced to GE Signa scanners. The MT ratio (MTR), signal difference to noise ratio (SDNR), and contrast parameters were measured at both fields and compared. Furthermore, single-shot Z-spectroscopy was used to characterize the frequency dependence of the MT phenomenon. The results show that MT imaging can be safely performed at 4.0 T without exceeding limitations of radio frequency power. The MT effect is more pronounced at the higher field, leading to better quality images with higher contrast and SDNR. The Z-spectra are not markedly different at the higher field although the MTR is greater. The potential applications of this technique to study neurodegenerative diseases, as well as, perfusion imaging and angiography are discussed. J. Magn. Reson. Imaging 1999;10:527-532.
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Affiliation(s)
- U Duvvuri
- Department of Radiology, and MMRRCC University of Pennsylvania Medical Center, 3400 Spruce Street, Philadelphia, Pennsylvania 19104, USA
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84
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Abstract
New spectroscopic and imaging methods have been developed for quantitatively measuring magnetization transfer (MT). These methods use trains of radiofrequency (rf) pulses with pulse separations much longer than 1/k(mf) and pulse durations much shorter than 1/k(mf), where k(mf) is the rate of MT from the immobile (macromolecular) protons to the mobile (free water) protons. Signal sensitivity to MT occurs when these pulses affect the mobile and immobile proton pools to different degrees. The signal from water may be quantitatively related to the macromolecular content of the sample using theory. The method has been used to make quantitative measurements of macromolecular content in cross-linked bovine serum albumin and employed in conjunction with echoplanar imaging to produce maps of the spatial distribution of the macromolecular content.
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Affiliation(s)
- D F Gochberg
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA
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85
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Pachot-Clouard M, Vaufrey F, Darrasse L, Toussainti JF. Magnetization transfer characteristics in atherosclerotic plaque components assessed by adapted binomial preparation pulses. MAGMA (NEW YORK, N.Y.) 1998; 7:9-15. [PMID: 9877454 DOI: 10.1007/bf02592251] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Increasing the contrast between atheromatous plaque components is a major issue in cardiovascular MRI research. It would allow one to identify unstable plaque by differentiating the lipid core associated with vulnerability, from the fibrous cap, considered as a factor of stability. T2 and diffusion-weighted imaging have already provided satisfying results. Magnetization transfer (MT) between restricted protons Hr and free-water protons Hf could achieve a different contrast related to collagen and lipoprotein macromolecules present in the fibrous cap and lipid core, respectively. The purpose of this work was to evaluate in vitro the MT effect produced by adapted T2-selective 1-3-3-1 binomial pulses on isolated samples of atheromatous arteries at 3 T. A method based on simulation was used in order to improve the MT specificity: it is shown that 50% 1-3-3-1 pulses (the percentage indicating the level of Hr saturation) allow an estimation of T2r, the Hr T2. Using this technique, magnetization transfer was observed for the first time in atherosclerotic plaque components, an effect more pronounced for the fibrous cap and media than for the lipid core and adventitia. The T2r estimation gave values ranging from 20 to 25 micros for the four samples. This preliminary study provides a basis for establishing an MT imaging sequence of atheromatous arteries, by using 50% 1-3-3-1 pulses calibrated for saturating protons with a 20 micros T2. This MT protocol should be further compared to T2 and diffusion-weighted imaging.
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86
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Bertini I, Luchinat C, Parigi G, Quacquarini G, Marzola P, Cavagna FM. Off-resonance experiments and contrast agents to improve magnetic resonance imaging. Magn Reson Med 1998; 39:124-31. [PMID: 9438446 DOI: 10.1002/mrm.1910390119] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The effect of off-resonance irradiation on the water proton NMR signal intensity has been investigated as follows: (a) in the presence of a paramagnetic probe like manganese(II); (b) in the presence of bovine serum albumin (BSA) and two gadolinium(III) complexes, Gd-DTPA and Gd-BOPTA; (c) in the presence of cross-linked BSA and the two above-mentioned gadolinium(III) complexes. The experimental data have been rationalized on the basis of the available theoretical models. The effectiveness of the two complexes as contrast agents for MRI has been predicted. It is shown that contrast agents providing comparable longitudinal and transverse relaxation rate enhancements are those of general interest for off-resonance magnetization transfer-MRI.
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Affiliation(s)
- I Bertini
- Department of Chemistry, University of Florence, Italy
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87
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Pike GB. Magnetization transfer imaging of multiple sclerosis. ITALIAN JOURNAL OF NEUROLOGICAL SCIENCES 1997; 18:359-65. [PMID: 9494868 DOI: 10.1007/bf02048239] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
While conventional magnetic resonance imaging (MRI) measures signal primarily from the hydrogen nuclei of water, magnetization transfer (MT) MRI indirectly detects macromolecular associated hydrogen nuclei via their magnetic interaction with the observable water. In the normal adult CNS, white matter exhibits the largest MT effect due to the macromolecular content of the highly structured and lipid rich myelin. Pathologies which alter the structural integrity and the relative macromolecular-water composition, such as multiple sclerosis (MS), therefore show abnormal MT. Conventional MRI, which has a high MS lesion detection sensitivity but poor specificity in terms of differentiating the pathological state of a plaque, can thus be supplemented by MT to provide more specific information on the extent of demyelination and axonal loss. In this paper we review the basic concepts of MT imaging and its role in MS lesion characterization.
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Affiliation(s)
- G B Pike
- McConnell Brain Imaging Center, Montreal Neurological Institute, McGill University, Quebec, Canada
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88
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Abstract
Using a two-pool exchange model of magnetization transfer (MT), numeric simulations were developed to predict the time dependence of longitudinal magnetization in both semisolid and liquid pools for arbitrary pulsed radiofrequency (RF) irradiation. Whereas RF excitation of the liquid pool was modeled using the time-dependent Bloch equations, RF saturation of the semisolid pool was described by a time-dependent rate proportional to both the absorption lineshape of the semisolid pool and the square of the RF pulse amplitude. Simulations show good agreement with experimental results for a 4% agar gel aqueous system in which the two-pool kinetics have been well studied previously. These simulations provide a method for interpreting pulsed MT effects, are easily extended to biologic tissues, and provide a basis for optimizing clinical imaging applications that exploit MT contrast.
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Affiliation(s)
- S J Graham
- Department of Medical Biophysics, University of Toronto, Sunnybrook Health Science Centre, Ontario, Canada.
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