Quantitative magnetization transfer imaging in Alzheimer disease

Multimodality imaging of neurodegenerative disorders with a focus on multiparametric magnetic resonance and molecular imaging

Neurodegenerative diseases afflict a large number of persons worldwide, with the prevalence and incidence of dementia rapidly increasing. Despite their prevalence, clinical diagnosis of dementia syndromes remains imperfect with limited specificity. Conventional structural-based imaging techniques also lack the accuracy necessary for confident diagnosis. Multiparametric magnetic resonance imaging and molecular imaging provide the promise of improving specificity and sensitivity in the diagnosis of neurodegenerative disease as well as therapeutic monitoring of monoclonal antibody therapy. This educational review will briefly focus on the epidemiology, clinical presentation, and pathologic findings of common and uncommon neurodegenerative diseases. Imaging features of each disease spanning from conventional magnetic resonance sequences to advanced multiparametric methods such as resting-state functional magnetic resonance imaging and arterial spin labeling imaging will be described in detail. Additionally, the review will explore the findings of each diagnosis on molecular imaging including single-photon emission computed tomography and positron emission tomography with a variety of clinically used and experimental radiotracers. The literature and clinical cases provided demonstrate the power of advanced magnetic resonance imaging and molecular techniques in the diagnosis of neurodegenerative diseases and areas of future and ongoing research. With the advent of combined positron emission tomography/magnetic resonance imaging scanners, hybrid protocols utilizing both techniques are an attractive option for improving the evaluation of neurodegenerative diseases.

Macromolecular Proton Fraction as a Myelin Biomarker: Principles, Validation, and Applications

Macromolecular proton fraction (MPF) is a quantitative MRI parameter describing the magnetization transfer (MT) effect and defined as a relative amount of protons bound to biological macromolecules with restricted molecular motion, which participate in magnetic cross-relaxation with water protons. MPF attracted significant interest during past decade as a biomarker of myelin. The purpose of this mini review is to provide a brief but comprehensive summary of MPF mapping methods, histological validation studies, and MPF applications in neuroscience. Technically, MPF maps can be obtained using a variety of quantitative MT methods. Some of them enable clinically reasonable scan time and resolution. Recent studies demonstrated the feasibility of MPF mapping using standard clinical MRI pulse sequences, thus substantially enhancing the method availability. A number of studies in animal models demonstrated strong correlations between MPF and histological markers of myelin with a minor influence of potential confounders. Histological studies validated the capability of MPF to monitor both demyelination and re-myelination. Clinical applications of MPF have been mainly focused on multiple sclerosis where this method provided new insights into both white and gray matter pathology. Besides, several studies used MPF to investigate myelin role in other neurological and psychiatric conditions. Another promising area of MPF applications is the brain development studies. MPF demonstrated the capabilities to quantitatively characterize the earliest stage of myelination during prenatal brain maturation and protracted myelin development in adolescence. In summary, MPF mapping provides a technically mature and comprehensively validated myelin imaging technology for various preclinical and clinical neuroscience applications.

Pattern of Altered Magnetization Transfer Rate in Alzheimer's Disease

BACKGROUND

Biomarkers for Alzheimer's disease (AD) are crucial for early diagnosis and treatment monitoring once disease modifying therapies become available.

OBJECTIVE

This study aims to quantify the forward magnetization transfer rate (kfor) map from brain tissue water to macromolecular protons and use it to identify the brain regions with abnormal kfor in AD and AD progression.

METHODS

From the Cardiovascular Health Study (CHS) cognition study, magnetization transfer imaging (MTI) was acquired at baseline from 63 participants, including 20 normal controls (NC), 18 with mild cognitive impairment (MCI), and 25 AD subjects. Of those, 53 participants completed a follow-up MRI scan and were divided into four groups: 15 stable NC, 12 NC-to-MCI, 12 stable MCI, and 14 MCI/AD-to-AD subjects. kfor maps were compared across NC, MCI, and AD groups at baseline for the cross-sectional study and across four longitudinal groups for the longitudinal study.

RESULTS

We found a lower kfor in the frontal gray matter (GM), parietal GM, frontal corona radiata (CR) white matter (WM) tracts, frontal and parietal superior longitudinal fasciculus (SLF) WM tracts in AD relative to both NC and MCI. Further, we observed progressive decreases of kfor in the frontal GM, parietal GM, frontal and parietal CR WM tracts, and parietal SLF WM tracts in stable MCI. In the parietal GM, parietal CR WM tracts, and parietal SLF WM tracts, we found trend differences between MCI/AD-to-AD and stable NC.

CONCLUSION

Forward magnetization transfer rate is a promising biomarker for AD diagnosis and progression.

Saturation Transfer MRI for Detection of Metabolic and Microstructural Impairments Underlying Neurodegeneration in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common causes of dementia and difficult to study as the pool of subjects is highly heterogeneous. Saturation transfer (ST) magnetic resonance imaging (MRI) methods are quantitative modalities with potential for non-invasive identification and tracking of various aspects of AD pathology. In this review we cover ST-MRI studies in both humans and animal models of AD over the past 20 years. A number of magnetization transfer (MT) studies have shown promising results in human brain. Increased computing power enables more quantitative MT studies, while access to higher magnetic fields improves the specificity of chemical exchange saturation transfer (CEST) techniques. While much work remains to be done, results so far are very encouraging. MT is sensitive to patterns of AD-related pathological changes, improving differential diagnosis, and CEST is sensitive to particular pathological processes which could greatly assist in the development and monitoring of therapeutic treatments of this currently incurable disease.

Deep neural network based CEST and AREX processing: Application in imaging a model of Alzheimer's disease at 3 T

PURPOSE

To optimize and apply deep neural network based CEST (deepCEST) and apparent exchange dependent-relaxation (deepAREX) for imaging the mouse brain with Alzheimer's disease (AD) at 3T MRI.

METHODS

CEST and T₁ data of central and anterior brain slices of 10 AD mice and 10 age-matched wild type (WT) mice were acquired at a 3T animal MRI scanner. The networks of deepCEST/deepAREX were optimized and trained on the WT data. The CEST/AREX contrasts of AD and WT mice predicted by the networks were analyzed and further validated by immunohistochemistry.

RESULTS

After optimization and training on CEST data of WT mice, deepCEST/deepAREX could rapidly (~1 s) generate precise CEST and AREX results for unseen CEST data of AD mice, indicating the accuracy and generalization of the networks. Significant lower amide weighted (3.5 ppm) signal related to amyloid β-peptide (Aβ) plaque depositions, which was validated by immunohistochemistry results, was detected in both central and anterior brain slices of AD mice compared to WT mice. Decreased magnetization transfer (MT) signal was also found in AD mice especially in the anterior slice.

CONCLUSION

DeepCEST/deepAREX could rapidly generate accurate CEST/AREX contrasts in animal study. The well-optimized deepCEST/deepAREX have potential for AD differentiation at 3T MRI.

Improved MR fingerprinting for relaxation measurement in the presence of semisolid magnetization transfer

PURPOSE

To characterize and minimize the magnetization transfer (MT) effect in MR fingerprinting (MRF) relaxation measurements with a 2-pool (2P) MT model of multiple tissue types.

THEORY AND METHODS

Semisolid MT effect in MRF was modeled using 2P Bloch-McConnell equations. The combinations of MT parameters of multiple tissues (white [WM] and gray matter [GM]) were used to build the MRF dictionary. Both 1-pool (1P) and 2P models were simulated to characterize the dependence on MT. Relaxations measured using MRF with spin-echo saturation-recovery (SR) or inversion-recovery preparations were compared with conventional SR-prepared T1 and multiple spin-echo T2 measurements. The simulations results were validated with phantoms and brain tissue samples.

RESULTS

The MRF signal was different from the 1P and 2P models. 1P MRF produced significantly (P < .05) underestimated T1 in WM (20-30%) and GM (7-10%), while 2P MRF measured consistent T1 and T2 in both WM and GM with conventional measurements (pairwise test P > .1; correlated P < .05). Simulations showed that SR-prepared MRF measuring T1 had much less errors against the variation of the macromolecular fraction. Compared with inversion-recovery preparation, SR-prepared MRF produced higher relaxation correlations (R > 0.9) with conventional measurements in both WM and GM across samples, suggesting that SR-prepared MRF was less sensitive to the compositive effect of multiple MT parameters variations.

CONCLUSIONS

2P MRF using a combination of MT parameters for multiple tissue types can measure consistent relaxations with conventional methods. With the 2P models, SR-prepared MRF would provide an option for robust relaxation measurement under heterogeneous MT.

Quantitative Magnetization Transfer of White Matter Tracts Correlates with Diffusion Tensor Imaging Indices in Predicting the Conversion from Mild Cognitive Impairment to Alzheimer's Disease

Patients with amnestic mild cognitive impairment (aMCI) have higher probability to develop Alzheimer's disease (AD) than elderly controls. The detection of subtle changes in brain structure associated with disease progression and the development of tools to identify patients at high risk for dementia in a short time is crucial. Here, we used probabilistic white matter (WM) tractography to explore microstructural alterations within the main association, limbic, and commissural pathways in aMCI patients who converted to AD after 1 year follow-up (MCIconverters) and those who remained stable (MCIstable). Both diffusion tensor imaging (DTI) and quantitative magnetization transfer (qMT) parameters have been considered for a comprehensive pathophysiological characterization of the WM damage. Overall, tract-specific parameters derived from qMT and DTI at baseline were able to differentiate aMCI patients who converted to AD from those who remained stable in time. In particular, the qMT exchange rate, RMB0, of the right uncinate fasciculus was significantly decreased in MCIconverters, whereas fractional anisotropy was significantly decreased in the bilateral superior cingulum in MCIconverters compared to MCIstable. These results confirm the involvement of WM and particularly of association fibers in the progression of AD, highlighting disconnection as a potential mechanism.

Low duty-cycle pulsed irradiation reduces magnetization transfer and increases the inhomogeneous magnetization transfer effect

Intense off-resonant RF irradiation can lead to saturation of the macromolecular pool magnetization and enhance bound pool dipolar order responsible for the inhomogeneous magnetization transfer (ihMT) effect, but the intensity of RF power in human imaging studies is limited by safety constraints on RF heating. High RF intensities can still be achieved if applied in short pulses with low duty-cycle. Here we investigate the benefits of low duty-cycle irradiation for MT and ihMT studies with both theoretical and experimental methods. Solutions for pulsed irradiation of a two-pool model including dipolar order effects were implemented. Experiments were conducted at 3 T in the brain and through the calf of healthy human subjects. 2D echo planar images were acquired following a preparation of RF irradiation with a 2 s train of 5 ms pulses repeated from between 10 to 100 ms for duty-cycles (DCs) of 50% to 5%, and at varying offset frequencies, and time averaged RF powers. MT and ihMT data were measured in regions of interest within gray matter, white matter and muscle, and fit to the model. RF irradiation effects on signal intensity were reduced at 5% relative to 50% DCs. This reduced RF effect was much larger for single than dual frequency irradiation. 5% DC irradiation reduced single and dual frequency MT ratios but increased ihMT ratios up to 3 fold in brain tissues. Muscle ihMT increased by an even larger factor, depending on the frequency and applied power. The model predicted these changes with duty-cycle. The model fit the data well and constrained model parameters. Low duty-cycle pulsed irradiation reduces MT effects and markedly increases dipolar order effects. This approach is an attractive method to enhance ihMT signal-to-noise ratio and demonstrates a measurable ihMT effect in muscle tissue at 3 T under acceptable specific absorption rates. The effects of duty-cycle changes demonstrated in a separate MT/ihMT preparation provide a route for new applications in magnetization-prepared MRI sequences.

T1, diffusion tensor, and quantitative magnetization transfer imaging of the hippocampus in an Alzheimer's disease mouse model

Alzheimer's disease (AD) pathology causes microstructural changes in the brain. These changes, if quantified with magnetic resonance imaging (MRI), could be studied for use as an early biomarker for AD. The aim of our study was to determine if T₁ relaxation, diffusion tensor imaging (DTI), and quantitative magnetization transfer imaging (qMTI) metrics could reveal changes within the hippocampus and surrounding white matter structures in ex vivo transgenic mouse brains overexpressing human amyloid precursor protein with the Swedish mutation. Delineation of hippocampal cell layers using DTI color maps allows more detailed analysis of T₁-weighted imaging, DTI, and qMTI metrics, compared with segmentation of gross anatomy based on relaxation images, and with analysis of DTI or qMTI metrics alone. These alterations are observed in the absence of robust intracellular Aβ accumulation or plaque deposition as revealed by histology. This work demonstrates that multiparametric quantitative MRI methods are useful for characterizing changes within the hippocampal substructures and surrounding white matter tracts of mouse models of AD.

Quantitative Magnetization Transfer in Monitoring Glioblastoma (GBM) Response to Therapy

Quantitative magnetization transfer (qMT) was used as a biomarker to monitor glioblastoma (GBM) response to chemo-radiation and identify the earliest time-point qMT could differentiate progressors from non-progressors. Nineteen GBM patients were recruited and MRI-scanned before (Day0), two weeks (Day14), and four weeks (Day28) into the treatment, and one month after the end of the treatment (Day70). Comprehensive qMT data was acquired, and a two-pool MT model was fit to the data. Response was determined at 3-8 months following the end of chemo-radiation. The amount of magnetization transfer ([Formula: see text]) was significantly lower in GBM compared to normal appearing white matter (p < 0.001). Statistically significant difference was observed in [Formula: see text] at Day0 between non-progressors (1.06 ± 0.24) and progressors (1.64 ± 0.48), with p = 0.006. Changes in several qMT parameters between Day14 and Day0 were able to differentiate the two cohorts with [Formula: see text] providing the best separation (relative [Formula: see text] = 1.34 ± 0.21, relative [Formula: see text] = 1.07 ± 0.08, p = 0.031). Thus, qMT characteristics of GBM are more sensitive to treatment effects compared to clinically used metrics. qMT could assess tumor aggressiveness and identify early progressors even before the treatment. Changes in qMT parameters within the first 14 days of the treatment were capable of separating early progressors from non-progressors, making qMT a promising biomarker to guide adaptive radiotherapy for GBM.

Pool size ratio of the substantia nigra in Parkinson's disease derived from two different quantitative magnetization transfer approaches

PURPOSE

We sought to measure quantitative magnetization transfer (qMT) properties of the substantia nigra pars compacta (SNc) in patients with Parkinson's disease (PD) and healthy controls (HCs) using a full qMT analysis and determine whether a rapid single-point measurement yields equivalent results for pool size ratio (PSR).

METHODS

Sixteen different MT-prepared MRI scans were obtained at 3 T from 16 PD patients and eight HCs, along with B1, B0, and relaxation time maps. Maps of PSR, free and macromolecular pool transverse relaxation times ([Formula: see text], [Formula: see text]) and rate of MT exchange between pools (k _mf ) were generated using a full qMT model. PSR maps were also generated using a single-point qMT model requiring just two MT-prepared images. qMT parameter values of the SNc, red nucleus, cerebral crus, and gray matter were compared between groups and methods.

RESULTS

PSR of the SNc was the only qMT parameter to differ significantly between groups (p < 0.05). PSR measured via single-point analysis was less variable than with the full MT model, provided slightly better differentiation of PD patients from HCs (area under curve 0.77 vs. 0.75) with sensitivity of 0.75 and specificity of 0.87, and was better than transverse relaxation time in distinguishing PD patients from HCs (area under curve 0.71, sensitivity 0.87, and specificity 0.50).

CONCLUSION

The increased PSR observed in the SNc of PD patients may provide a novel biomarker of PD, possibly associated with an increased macromolecular content. Single-point PSR mapping with reduced variability and shorter scan times relative to the full qMT model appears clinically feasible.

Quantitative two-dimensional ultrashort echo time magnetization transfer (2D UTE-MT) imaging of cortical bone

PURPOSE

To investigate quantitative 2D ultrashort echo time magnetization transfer (UTE-MT) imaging in ex vivo bovine cortical bone and in vivo human tibial cortical bone.

METHODS

Data were acquired from five fresh bovine cortical bone samples and five healthy volunteer tibial cortical bones using a 2D UTE-MT sequence on a clinical 3T scanner. The 2D UTE-MT sequence used four or five MT powers with five frequency offsets. Results were analyzed with a two-pool quantitative MT model, providing measurements of macromolecular fraction (f), macromolecular proton transverse relaxation times (T_2m ), proton exchange rates from water/macromolecular to the macromolecular/water pool (RM_0m /RM_0w ), and spin-lattice relaxation rate of water pool (R_1w ). A sequential air-drying study for a small bovine cortical bone chip was used to investigate whether above MT modeling parameters were sensitive to the water loss.

RESULTS

Mean fresh bovine cortical bone values for f, T_2m , R_1w , RM_0m , and RM_0w were 59.9 ± 7.3%, 14.6 ± 0.3 μs, 9.9 ± 2.4 s^-1 , 17.9 ± 3.6 s^-1 , and 11.8 ± 2.0 s^-1 , respectively. Mean in vivo human cortical bone values for f, T_2m , R_1w , RM_0m and RM_0w were 54.5 ± 4.9%, 15.4 ± 0.6 μs, 8.9 ± 1.1 s^-1 , 11.5 ± 3.5 s^-1 , and 9.5 ± 1.9 s^-1 , respectively. The sequential air-drying study shows that f, RM_0m , and R_1w were increased with longer drying time.

CONCLUSION

UTE-MT two-pool modeling provides novel and useful quantitative information for cortical bone. Magn Reson Med 79:1941-1949, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Associations between brain white matter integrity and disease severity in obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized by recurrent upper airway blockage, with continued diaphragmatic efforts to breathe during sleep. Brain structural changes in OSA appear in various regions, including white matter sites that mediate autonomic, mood, cognitive, and respiratory control. However, the relationships between brain white matter changes and disease severity in OSA are unclear. This study examines associations between an index of tissue integrity, magnetization transfer (MT) ratio values (which show MT between free and proton pools associated with tissue membranes and macromolecules), and disease severity (apnea-hypopnea index [AHI]) in OSA subjects. We collected whole-brain MT imaging data from 19 newly diagnosed, treatment-naïve OSA subjects (50.4 ± 8.6 years of age, 13 males, AHI 39.7 ± 24.3 events/hr], using a 3.0-Tesla MRI scanner. With these data, whole-brain MT ratio maps were calculated, normalized to common space, smoothed, and correlated with AHI scores by using partial correlation analyses (covariates, age and gender; P < 0.005). Multiple brain sites in OSA subjects, including superior and inferior frontal regions, ventral medial prefrontal cortex and nearby white matter, midfrontal white matter, insula, cingulate and cingulum bundle, internal and external capsules, caudate nuclei and putamen, basal forebrain, hypothalamus, corpus callosum, and temporal regions, showed principally lateralized negative correlations (P < 0.005). These regions showed significant correlations even with correction for multiple comparisons (cluster-level, family-wise error, P < 0.05), except for a few superior frontal areas. Predominantly negative correlations emerged between local MT values and OSA disease severity, indicating potential usefulness of MT imaging for examining the OSA condition. These findings indicate that OSA severity plays a significant role in white matter injury. © 2016 Wiley Periodicals, Inc.

Quantitative magnetization transfer MRI of desmoplasia in pancreatic ductal adenocarcinoma xenografts

Quantitative assessment of desmoplasia in pancreatic ductal adenocarcinoma (PDAC) may be critical for staging or prediction of response to therapy. We performed quantitative magnetization transfer (qMT) MRI measurements in 18 mouse xenograft tumors generated from three PDAC cell lines. The qMT parameter bound proton fraction (BPF) was found to be significantly higher in tumors grown using the BxPC-3 cell line (5.31 ± 0.87, mean ± standard deviation) compared with the BPF measured for tumors grown from Panc-1 (3.65 ± 0.60) and Capan-1 (1.50 ± 0.58) cell lines (P < 0.05 for each comparison). Histologic measurements demonstrated a similar trend; BxPC-3 tumors had significantly higher fibrosis levels (percentage of fibrotic tissue area, 6.21 ± 2.10) compared with Panc-1 (2.88 ± 1.13) and Capan-1 (1.69 ± 1.01) tumors. BPF was well correlated with quantitative fibrosis levels (r = 0.77, P < 0.01). Our results indicate that qMT measurements offer the potential to noninvasively quantify fibrosis levels in PDAC mouse xenograft models and thus serve as a valuable in vivo biomarker of desmoplasia in PDAC.

Magnetization transfer contrast imaging reveals amyloid pathology in Alzheimer's disease transgenic mice

The presence of amyloid plaques in the brain is one of the pathological hallmarks of Alzheimer's disease, which might already be present in the early stage of the disease. Therefore it is important to track amyloid plaques as early as possible. In this paper, we report magnetization transfer contrast magnetic resonance imaging (MTC MRI) as a novel approach to detect amyloid plaques in vivo. Two mice models, APP/PS1 and BRI, developing amyloid pathology were investigated with MTC MRI, T2 relaxation measurements and immunohistochemistry (IHC). MT-ratios of several brain regions were compared to T2-values and correlated with quantitative IHC, revealing amyloid load and gliosis in different brain regions. APP/PS1 mice develop large compact plaques, resembling late stage Alzheimer's disease, while rather small and diffuse plaques are deposited in BRI mice, reflecting early stage of Alzheimer's disease. We found significantly higher MT-ratio's in the brain of APP/PS1 mice as compared to their controls and similar trends in BRI mice. A region based MT-ratio and IHC analysis and correlations between MT-ratios and quantitative IHC indicate amyloid plaques as the main substrate for altered MT-ratios in transgenic animals. We additionally demonstrated the improved sensitivity of MTC MRI to amyloid pathology as compared to traditional T2 relaxation measurements. Our results suggest that MTC MRI reveals extensive, and potentially even early amyloid pathology. Further unraveling the MT-effect of each pathological feature during each stage of AD might indicate MTC MRI as a useful diagnostic technique.

Regional analysis of the magnetization transfer ratio of the brain in mild Alzheimer disease and amnestic mild cognitive impairment

BACKGROUND AND PURPOSE

Manually drawn VOI-based analysis shows a decrease in magnetization transfer ratio in the hippocampus of patients with Alzheimer disease. We investigated with whole-brain voxelwise analysis the regional changes of the magnetization transfer ratio in patients with mild Alzheimer disease and patients with amnestic mild cognitive impairment.

MATERIALS AND METHODS

Twenty patients with mild Alzheimer disease, 27 patients with amnestic mild cognitive impairment, and 30 healthy elderly control subjects were examined with high-resolution T1WI and 3-mm-thick magnetization transfer images. Whole-brain voxelwise analysis of magnetization transfer ratio maps was performed by use of Statistical Parametric Mapping 8 software and was supplemented by the analysis of the magnetization transfer ratio in FreeSurfer parcellation-derived VOIs.

RESULTS

Voxelwise analysis showed 2 clusters of significantly decreased magnetization transfer ratio in the left hippocampus and amygdala and in the left posterior mesial temporal cortex (fusiform gyrus) of patients with Alzheimer disease as compared with control subjects but no difference between patients with amnestic mild cognitive impairment and either patients with Alzheimer disease or control subjects. VOI analysis showed that the magnetization transfer ratio in the hippocampus and amygdala was significantly lower (bilaterally) in patients with Alzheimer disease when compared with control subjects (ANOVA with Bonferroni correction, at P < .05). Mean magnetization transfer ratio values in the hippocampus and amygdala in patients with amnestic mild cognitive impairment were between those of healthy control subjects and those of patients with mild Alzheimer disease. Support vector machine-based classification demonstrated improved classification performance after inclusion of magnetization transfer ratio-related features, especially between patients with Alzheimer disease versus healthy subjects.

CONCLUSIONS

Bilateral but asymmetric decrease of magnetization transfer ratio reflecting microstructural changes of the residual GM is present not only in the hippocampus but also in the amygdala in patients with mild Alzheimer disease.

Gender, age-related, and regional differences of the magnetization transfer ratio of the cortical and subcortical brain gray matter

PURPOSE

To explore gender, age-related, and regional differences of magnetization transfer ratio (MTR) of brain cortical and subcortical gray matter (GM).

MATERIALS AND METHODS

In all, 102 healthy subjects (51 women and 51 men; range 25-84 years) were examined with 3-mm thick MT images. We assessed MTR in automatically segmented GM structures including frontal, parietal-insular, temporal, and occipital cortex, caudate, pallidus and putamen, and cerebellar cortex. A general linear model analysis was conducted to ascertain the linear and quadratic relationship among the MTR and gender, age, and anatomical structure.

RESULTS

The effect of gender was borderline (P = 0.07) in all GM structures (with higher MTR values in men), whereas age showed a significant linear as well as quadratic effect in all cortical and subcortical GM structures (P ≤ 0.001). Quadratic age-related decrease in MTR began at about 40 years of age. Mean and standard deviation (SD) of MTR had the following decreasing order: thalamus (58.3 + 0.8), pallidus (56.8 ± 1.3), caudate (55.5 ± 1.6) and putamen (54.6 ± 1.1); temporal (56.8 ± 0.9), parietal-insular (56.8 ± 1.1), frontal (56.5 ± 1.1), occipital (55.4 ± 1.0) and cerebellar (53.2 ± 1.0) cortex. In post-hoc testing, all regional pairwise differences were statistically significant except pallidus vs. temporal or parietal-insular cortex, caudate vs. occipital cortex, frontal vs. parietal-insular or temporal cortex.

CONCLUSION

MTR of the cortical and subcortical brain GM structures decreases quadratically after midlife and shows significant regional differences.

MRI of carriers of the apolipoprotein E e4 allele-evidence for structural differences in normal-appearing brain tissue in e4+ relative to e4- young adults

Apolipoprotein E is a protein involved in cholesterol and lipid transport. The gene coding for this protein has three different alleles: e2, e3 and e4. The e4 allele is recognised as a significant risk factor for the development of Alzheimer's disease in later life. Paradoxically, behavioural and functional evidence has demonstrated that the e4 allele may confer a cognitive advantage to the carrier in youth. In this article, a range of sophisticated and novel structural imaging techniques were used to identify subtle differences in the brain tissue of groups of young e4 and homozygous e3 carriers that might support this paradox. Using voxel-based morphometry of high-resolution structural MR images, we identified a higher white matter volume ratio in e4 relative to homozygous e3 carriers. Furthermore, diffusion tensor imaging and tract-based spatial statistics studies identified increases in axial diffusivity and mode of anisotropy in carriers of the e4 allele. In addition, quantitative magnetisation transfer data were analysed using tract-based spatial statistics. Evidence of a trend towards an increased transverse relaxation time of the bound proton pool was detected in e4 carriers, indicative of altered white matter composition. These changes were found to correlate with indices of cognitive performance across the two groups, supporting the notion that such subtle differences in white matter integrity may confer neural advantages that contribute to cognitive outcomes and, potentially, to performance differences, such as observed here in a test of verbal fluency and reported previously by other researchers. Copyright © 2013 John Wiley & Sons, Ltd.

Quantitative evaluation of MRI and histological characteristics of the 5xFAD Alzheimer mouse brain

Assessment of β-amyloid (Aβ) plaque load in Alzheimer's disease by MRI would provide an important biomarker to monitor disease progression or treatment response. Alterations in tissue structure caused by the presence of Aβ may cause localised changes that can be detected by quantitative T₁ and T₂ relaxation time measurements averaged over larger areas of tissue than that of individual plaques. We constructed depth profiles of the T₁ and T₂ relaxation times of the cerebral cortex with subjacent white matter and hippocampus in six 5xFAD transgenic and six control mice at 11 months of age. We registered these profiles with corresponding profiles of three immunohistochemical markers: β-amyloid; neuron-specific nuclear protein (NeuN), a marker of neuronal cell load; and myelin basic protein (MBP), a marker of myelin load. We found lower T₁ in the 5xFAD transgenic mice compared to wild type control mice at all depths, with maximum sensitivity for detection at specific layers. T₁ negatively correlated with Aβ staining intensity in the 5xFAD mice which had no changes in NeuN and MBP staining compared to wild type mice. We postulate that these relaxation time changes are due to the presence of β-amyloid in the transgenic mice. It may be clinically feasible to develop a similar layered analysis protocol as a biomarker for Alzheimer's disease in humans.

Classification of mild cognitive impairment and Alzheimer disease using model-based MR and magnetization transfer imaging

BACKGROUND AND PURPOSE

Early stratification of degenerative processes is a prerequisite to warrant therapeutic options in prodromal Alzheimer disease. Our aim was to investigate differences in cerebral macromolecular tissue composition between patients with AD, mild cognitive impairment, and age- and sex-matched healthy controls by using model-based magnetization transfer with a binary spin-bath magnetization transfer model and magnetization transfer ratio at 1.5 T.

MATERIALS AND METHODS

We investigated patients with de novo AD (n=18), MCI (n=18), and CTRLs (n=18). A region-of-interest analysis of the entorhinal cortex, hippocampal head and body, insula, and temporal neocortex was performed with fuzzy clustering to associate every subregion to a cluster representative for each group.

RESULTS

Cluster analysis achieved a concordance of 0.92 (50 of 54 subjects) between a combination of the calculated mMT parameters (kf,kr,T2r,F,T2f) in the entorhinal cortex and the neuropsychological diagnosis. The sensitivity and specificity for the discrimination of AD from MCI reached 1 and 0.94, with a positive predictive value of 0.95 and a negative predictive value of 1. Compared with mMT, the concordance for MTR was 0.83 (45 of 54 subjects) with a lower specificity of 0.5 and positive predictive value of 0.67 to discriminate patients with AD and MCI.

CONCLUSIONS

mMT imaging detects macromolecule-related alterations and allows an improved classification of patients with early AD and MCI compared with MTR.

Magnetization transfer imaging in premanifest and manifest huntington disease: a 2-year follow-up

BACKGROUND AND PURPOSE

MTI is a quantitative MR imaging technique that has recently demonstrated structural integrity differences between controls and patients with HD. Potentially, MTI can be used as a biomarker for monitoring disease progression. To establish the value of MTI as a biomarker, we aimed to examine the change in these measures during the course of HD.

MATERIALS AND METHODS

From the Leiden TRACK-HD study, 25 controls, 21 premanifest gene carriers, and 21 patients with manifest HD participated at baseline and during a 2-year follow-up visit. Brain segmentation of the cortical gray matter, white matter, caudate nucleus, putamen, pallidum, thalamus, amygdala, and hippocampus was performed by using the automated tools FAST and FIRST in FSL. Individual MTR values were calculated from these regions, and MTR histograms were constructed.

RESULTS

In the premanifest HD group stage "far from disease onset," a significant increase in MTR peak height of the putamen was observed with time. During the manifest HD stage, neither the mean MTR nor the MTR peak height showed a significant change during a 2-year follow-up.

CONCLUSIONS

MTI-derived measures are not suitable for monitoring in Huntington disease during a 2-year period because there was no decrease in structural integrity detected in any of the manifest HD groups longitudinally. The finding of increased putaminal MTR peak height in the premanifest far from disease onset group could relate to a predegenerative process, compensatory mechanisms, or aberrant development but should be interpreted with caution until future studies confirm this finding.

Magnetization transfer imaging in premanifest and manifest Huntington disease

BACKGROUND AND PURPOSE

MTI has the potential to detect abnormalities in normal-appearing white and gray matter on conventional MR imaging. Early detection methods and disease progression markers are needed in HD research. Therefore, we investigated MTI parameters and their clinical correlates in premanifest and manifest HD.

MATERIALS AND METHODS

From the Leiden TRACK-HD study, 78 participants (28 controls, 25 PMGC, 25 MHD) were included. Brain segmentation of cortical gray matter, white matter, caudate nucleus, putamen, pallidum, thalamus, amygdala, and hippocampus was performed using FSL's automated tools FAST and FIRST. Individual MTR values were calculated from these regions and MTR histograms constructed. Regression analysis of MTR measures from all gene carriers with clinical measures was performed.

RESULTS

MTR peak height was reduced in both cortical gray (P = .01) and white matter (P = .006) in manifest HD compared with controls. Mean MTR was also reduced in cortical gray matter (P = .01) and showed a trend in white matter (P = .052). Deep gray matter structures showed a uniform pattern of reduced MTR values (P < .05). No differences between premanifest gene carriers and controls were found. MTR values correlated with disease burden and motor and cognitive impairment.

CONCLUSIONS

Throughout the brain, disturbances in MTI parameters are apparent in early HD and are homogeneous across white and gray matter. The correlation of MTI with clinical measures indicates the potential to act as a disease monitor in clinical trials. However, our study does not provide evidence for MTI as a marker in premanifest HD.

Longitudinal magnetization transfer imaging in mild to severe Alzheimer disease

BACKGROUND AND PURPOSE

MTI has been proposed as a sensitive technique for studying microstructural brain tissue changes in patients with AD, but the course of these changes over time is largely unknown. We therefore used a placebo-controlled study of memantine to follow the evolution of tissue damage in AD by means of MTR measurements and investigated how MTR changes were related to brain atrophy and cognition.

MATERIALS AND METHODS

Twenty-eight patients (76.5 ± 5.8 years) with mild to moderate AD underwent MTI, brain volume measurements, and cognitive testing at baseline and after 6 and 12 months. Nineteen healthy individuals (73.3 ± 3.2 years) served as controls. MTI was performed with a 2-minute protocol that was optimized for an enhanced MT effect and reduced motion sensitivity. Global and regional MTR measurements served as correlations with brain volumes and the MMSE score.

RESULTS

AD patients had significantly lower global MTR values than controls, and showed a consistent and significant MTR reduction in all regions investigated over a period of 12 months. These MTR changes were paralleled by a brain tissue loss of 2.2% per year. Associations between MTR and cognition were found for the hippocampus, putamen, and thalamus, and were more pronounced in the left hemisphere.

CONCLUSIONS

MTI in AD allows the assessment of ongoing global and regional brain damage independent of atrophy, and therefore appears to be a valuable marker for disease-related tissue changes.

Comprehensive brain analysis with automated high-resolution magnetization transfer measurements

PURPOSE

To enhance the reliability and spatial resolution of magnetization transfer ratio (MTR) measurements for interrogation of subcortical brain regions with an automated volume of interest (VOI) approach.

MATERIALS AND METHODS

A 3D magnetization transfer (MT) sequence was acquired using a scan-rescan imaging protocol in nine healthy volunteers. VOI definition masks for the MTR measurements were generated using FreeSurfer and compared to a manual region of interest (ROI) approach. (The longitudinal stability of MTR was monitored using agar gel phantom over a 5-month period.) Intraclass correlation coefficients (ICCs), coefficients of variation (CVs), and instrumental standard deviation (ISD) were determined.

RESULTS

CVs ranged from 1.29%-2.64% (automated) vs. 1.30%-3.40% (manual). ISDs ranged from 0.62-1.10 pu (automated) vs. 0.68-1.67 pu (manual). The SD of the running difference was 1.70% for the phantom scans. The Bland-Altman method indicated interchangeability of the automated VOI and manual ROI measurements.

CONCLUSION

The automated VOI approach for MTR measurement yielded higher ICCs, lower CVs, and lower ISDs compared to the manual method, supporting the utility of this strategy. These results demonstrate the feasibility of obtaining reliable MTR measurements in hippocampus and other critical subcortical regions.

Quantitative magnetization transfer provides information complementary to grey matter atrophy in Alzheimer's disease brains

Preliminary studies, based on a region-of-interest approach, suggest that quantitative magnetization transfer (qMT), an extension of magnetization transfer imaging, provides complementary information to conventional magnetic resonance imaging (MRI) in the characterisation of Alzheimer's disease (AD). The aim of this study was to extend these findings to the whole brain, using a voxel-wise approach. We recruited 19AD patients and 11 healthy subjects (HS). All subjects had an MRI acquisition at 3.0T including a T(1)-weighted volume, 12 MT-weighted volumes for qMT, and data for computing T(1) and B(1) maps. The T(1)-weighted volumes were processed to yield grey matter (GM) volumetric maps, while the other sequences were used to compute qMT parametric maps of the whole brain. qMT maps were warped to standard space and smoothed, and subsequently compared between groups. Of all the qMT parameters considered, only the forward exchange rate, RM(0)(B), showed significant group differences. These images were therefore retained for the multimodal statistical analysis, designed to locate brain regions of RM(0)(B) differences between AD and HS groups, adjusting for local GM atrophy. Widespread areas of reduced RM(0)(B) were found in AD patients, mainly located in the hippocampus, in the temporal lobe, in the posterior cingulate and in the parietal cortex. These results indicate that, among qMT parameters, RM(0)(B) is the most sensitive to AD pathology. This quantity is altered in the hippocampus of patients with AD (as found by previous works) but also in other brain areas, that PET studies have highlighted as involved with both, reduced glucose metabolism and amyloid β deposition. RM(0)(B) might reflect, through the measurement of the efficiency of MT exchange, some information with a specific pathological counterpart. Given previous evidence of a strict relationship between RM(0)(B) and intracellular pH, an intriguing speculation is that our findings might reflect metabolic changes related to mitochondrial dysfunction, which has been proposed as a contributor to neurodegeneration in AD.

Targeting progressive neuroaxonal injury: lessons from multiple sclerosis

Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), are characterized by progressive neuroaxonal injury, suggesting a common pathophysiological pathway. Identification and development of neuroprotective therapies for such diseases has proven a major challenge, particularly because of an already substantial neuroaxonal compromise at the time of initial onset of clinical symptoms. Methods for early identification of neurodegeneration are therefore vital to ensure that neuroprotective therapies are applied as early as possible. Recent investigations have enhanced our understanding of the role of neuroaxonal injury in multiple sclerosis (MS). As MS generally manifests earlier in life and can be diagnosed much earlier in the course of the disease than the above-mentioned 'classic' neurodegenerative diseases, it is possible that MS could be used as a model disease to study degeneration and regeneration of the CNS. The mechanism of neuroaxonal injury in MS is believed to be inflammation-led neurodegeneration; however, the reverse may also be true (i.e. neuroaxonal degeneration may precede inflammation). Animal models of PD, AD and ALS have shown that it is likely that most cases of disease are due to initial inflammation, followed by a degenerative process, providing a parallel between MS and the classic neurodegenerative diseases. Other common factors between MS and the neurodegenerative diseases include iron and mitochondrial dysregulation, abnormalities in α-synuclein and tau protein, and a number of immune mediators. Conventional MRI techniques, using markers such as T2-weighted lesions, gadolinium-enhancing lesions and T1-weighted hypointensities, are readily available and routinely used in clinical practice; however, the utility of these MRI measures to predict disease progression in MS is limited. More recently, MRI techniques that provide more pathology-specific data have been applied in MS studies, including magnetic resonance spectroscopy, magnetization transfer ratio and myelin water imaging. Optical coherence tomography (OCT) is a non-MRI technique that quantifies optic nerve integrity and retinal ganglion cell loss as markers of neuroaxonal injury; more research is needed to evaluate whether information obtained from OCT is a reliable marker of axonal injury and long-term disability in MS. Using these advanced techniques, it may become possible to follow degeneration and regeneration longitudinally in patients with MS and to better differentiate the effects of drugs under investigation. Currently available immune-directed therapies that are approved by the US FDA for the first-line treatment of MS (interferon-β and glatiramer acetate) have been shown to decelerate the inflammatory process in MS; however, such therapy is less effective in preventing the progression of the disease and neuroaxonal injury. The use of MS as a clinical model to study modulation of neuroaxonal injury in the brain could have direct implications for the development of treatment strategies in neurodegenerative diseases such as AD, PD and ALS.

Quantitative magnetisation transfer imaging in glioma: preliminary results

Quantitative magnetisation transfer imaging (qMTI) is an extension of conventional MT techniques and allows the measurement of parameters that reflect tissue ultrastructure through the properties of macromolecule-bound protons; these include the bound proton fraction and the relaxation times of free and bound proton pools. It has been used in multiple sclerosis and Alzheimer's disease, and has shown changes in some of the parameters, particularly the bound proton fraction. The purpose of this pilot study was to assess whether qMTI could distinguish between gliomas and normal brain tissue, and provide proof of principle for its use in tumour characterisation. Eight subjects [three men, five women; mean age, 44 years; range, 27-66 years; seven World Health Organization (WHO) Grade II, one Grade III] with biopsy-proven glioma were imaged with a structural MRI protocol that included three-dimensional qMTI. qMTI parameters were extracted from regions of interest selected from different tumour components visible on conventional MR sequences, normal-appearing peritumoral tissue and distant normal-appearing white matter. All patients gave informed consent and the study was approved by the Local Research Ethics Committee. Almost all of the qMTI parameters detected abnormalities in both glioma and the peritumoral region relative to the distant white matter. In particular, the bound proton fraction was reduced significantly from 6.0 percentage units (pu) [standard deviation (SD), 0.5 pu] in normal-appearing white matter to 1.7 pu (SD = 0.5 pu) in solid tumour and 2.2 pu (SD = 0.5 pu) in peritumoral areas. This work shows that qMTI reveals abnormalities, not only in glioma, but also in the apparently normal tissue surrounding the conventionally defined tumour. Thus, qMTI shows promise for tumour characterisation and for studying tumour boundaries. These preliminary data justify larger studies in a range of different tumour types and grades.

Quantitative magnetization transfer in in vivo healthy human skeletal muscle at 3 T

The value of quantitative MR methods as potential biomarkers in neuromuscular disease is being increasingly recognized. Previous studies of the magnetization transfer ratio have demonstrated sensitivity to muscle disease. The aim of this work was to investigate quantitative magnetization transfer imaging of skeletal muscle in healthy subjects at 3 T to evaluate its potential use in pathological muscle. The lower limb of 10 subjects was imaged using a 3D fast low-angle shot acquisition with variable magnetization transfer saturation pulse frequencies and amplitudes. The data were analyzed with an established quantitative two-pool model of magnetization transfer. T₁ and B₁ amplitude of excitation radiofrequency field maps were acquired and used as inputs to the quantitative magnetization transfer model, allowing properties of the free and restricted proton pools in muscle to be evaluated in seven different muscles in a region of interest analysis. The average restricted pool T₂ relaxation time was found to be 5.9 ± 0.2μs in the soleus muscle and the restricted proton pool fraction was 8 ± 1%. Quantitative magnetization transfer imaging of muscle offers potential new biomarkers in muscle disease within a clinically feasible scan time. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.

Magnetization transfer imaging provides a quantitative measure of chondrogenic differentiation and tissue development

The goal of the present investigation was to test whether quantitative magnetization transfer imaging can be used as a noninvasive evaluation method for engineered cartilage. In this work, we used magnetic resonance imaging (MRI) to monitor the chondrogenesis of stem-cell-based engineered tissue over a 3-week period by measuring on a pixel-by-pixel basis the relaxation times (T₁ and T₂), the apparent diffusion coefficient, and the magnetization transfer parameters: bound proton fraction and cross-relaxation rate (k). Tissue-engineered constructs for generating cartilage were created by seeding mesenchymal stem cells in a gelatin sponge. Every 7 days, tissue samples were analyzed using MRI, histological, and biochemical methods. The MRI measurements were verified by histological analysis, and the imaging data were correlated with biochemical analysis of the developing cartilage matrix for glycosaminoglycan content. The MRI analysis for bound proton fraction and k showed a statistically significant increase that was correlated with the increase of glycosaminoglycan (R = 0.96 and 0.87, respectively, p < 0.05), whereas T₁, T₂, and apparent diffusion coefficient results did not show any significant changes over the 3-week measurement period.

A fast B1-mapping method for the correction and normalization of magnetization transfer ratio maps at 3 T

In neuroimaging, there is increasing interest in magnetization transfer (MT) techniques which yield information about bound water protons. One of the main applications is the investigation of the myelin integrity in the central nervous system (CNS). However, several problems may arise, in particular at high magnetic field strengths: B1 inhomogeneities may yield deviations of the MT saturation angle and thus non-uniformities of the measured MT ratio (MTR). This effect can be corrected for but requires in general additional time consuming B1 mapping. Furthermore, increased values of the specific absorption rate (SAR) may require a reduction of the saturation angle for individual subjects, impairing comparability of results. In this work, a B1 mapping method based on magnetization-prepared FLASH with slice selective preparation and excitation pulses and correction for relaxation effects is presented, yielding B1 maps with whole brain coverage, an in-plane resolution of 4 mm, a slice thickness of 3 mm, and a clinically acceptable duration of 46 s. The method is tested both in vitro and in vivo and applied in a subsequent in vivo study to show that MTR values in human brain tissue depend approximately linearly on the preparation angle, with a slope similar to values reported for 1.5 T. Calibration data and B1 maps are applied to B1 inhomogeneity corrections of MTR maps. Subsequently, it is shown that B1-corrected MTR maps acquired at reduced preparation angles due to individual SAR restrictions can be normalized, allowing for a direct comparison with maps acquired at the full angle.

Alzheimer's disease: from pathology to therapeutic approaches

Mind how you go: The current strategies for the development of therapies for Alzheimer's disease are very diverse. Particular attention is given to the search for inhibitors (see picture for two examples) of the proteolytic enzyme beta- and gamma-secretase, which inhibits the cleavage of the amyloid precursor proteins into amyloid beta peptides, from which the disease-defining deposits of plaque in the brains of Alzheimer's patients originates.Research on senile dementia and Alzheimer's disease covers an extremely broad range of scientific activities. At the recent international meeting of the Alzheimer's Association (ICAD 2008, Chicago) more than 2200 individual scientific contributions were presented. The aim of this Review is to give an overview of the field and to outline its main areas, starting from behavioral abnormalities and visible pathological findings and then focusing on the molecular details of the pathology. The "amyloid hypothesis" of Alzheimer's disease is given particular attention, since the majority of the ongoing therapeutic approaches are based on its theoretical framework.

Characterization of white matter damage in animal models of multiple sclerosis by magnetization transfer ratio and quantitative mapping of the apparent bound proton fraction f*

Quantitative magnetization transfer magnetic resonance imaging (qMT-MRI) can be used to improve detection of white matter tissue damage in multiple sclerosis (MS) and animal models thereof. To study the correlation between MT parameters and tissue damage, the magnetization transfer ratio (MTR), the parameter f* (closely related to the bound proton fraction) and the bound proton transverse relaxation time T2B of lesions in a model of focal experimental autoimmune encephalomyelitis (EAE) were measured on a 7T animal scanner and data were compared with histological markers indicative for demyelination, axonal density, and tissue damage. A clear spatial correspondence was observed between reduced values of MTR and demyelination in this animal model. We observed two different levels of MTR and f* reduction for these lesions. One was characterized by a pronounced demyelination and the other corresponded to a more severe loss of the cellular matrix. Changes in f* were generally more pronounced than those of MTR in areas of demyelination. Moreover, a reduction of f* was already observed for tissue where MTR was virtually normal. No changes in T2B were observed for the lesions. We conclude that MTR and qMT mapping are efficient and reliable readouts for studying demyelination in animal models of MS, and that the analysis of regional f* might be even superior to the analysis of MTR values. Therefore, quantitative mapping of f* from human brains might also improve the detection of white matter damage in MS.

[Ethical questions in clinical research with the mentally ill]

The review deals with present problems of protecting mentally ill patients who are incompetent to give informed consent to participating in clinical research, and of assessment of the capacity to consent. 1. Clinical trials of drugs on efficacy and safety in incompetent patients are ethically justified and legally admissible if the investigational drug can be expected to exert a direct potential individual benefit and if such trials will be performed under defined criteria to protect these vulnerable patients. In Germany it is questionable how far these prescriptions of the German Drug Law (AMG) are transferable to other than drug research. 2. Research with no direct potential individual benefit or only a group-specific benefit in incompetent patients is controversially discussed. However, it may be ethically justified as an exception, and is in Germany legally admissible only in minors, but not in adults. 3. However, internationally there exists a wide range of legal regulations, terms, interpretations, and practices of research with vulnerable persons. In the past years a shift seems to have developed from normatively oriented discussions to more empirically based investigations. Especially vague but clinically relevant terms in protection declarations or guidelines have been better specified, put in concrete form by anchor examples, and empirically studied. 4. In general the criteria of protecting the dignity and, even if impaired, the autonomy of incompetent patients as subjects for research appear to guarantee a high standard of protection. However, the application of these criteria must be improved by practicable procedures. This is valid particularly for the assessment of the basic criterion whether a patient is capable of consenting or not. 5. Open Questions are formulated as need of research.

Evaluation of the role of magnetization transfer imaging in prostate: a preliminary study

Results of the preliminary study on the evaluation of the role of magnetization transfer imaging (MTI) of prostate in men who had raised prostate-specific antigen (PSA) (>4 ng/ml) or abnormal digital rectal examination (DRE) are reported. MT ratio (MTR) was calculated for 20 patients from the hyper- (normal) and hypo-intense regions (area suspicious of malignancy as seen on T2-weighted MRI) of the peripheral zone (PZ) and the central gland (CG) at 1.5 T. In addition, MTR was calculated for three healthy controls. Mean MTR was also calculated for the whole of the PZ (including hyper- and hypo-intense area) in all patients. Out of 20 patients, biopsy revealed malignancy in 12 patients. Mean MTR value (8.29+/-3.49) for the whole of the PZ of patients who were positive for malignancy on biopsy was statically higher than that observed for patients who were negative for malignancy (6.18+/-3.15). The mean MTR for the whole of the PZ of controls was 6.18+/-1.63 and is similar to that of patients who were negative for malignancy. Furthermore, for patients who showed hyper- (normal portion) and hypo-intense (region suspicious of malignancy) regions of the PZ, the MTR was statistically significantly different. These preliminary results reveal the potential role of MT imaging in the evaluation of prostate cancer.