Magnetization Transfer MR Imaging Research Articles

Comparative analysis of [18F]F-FAPI PET/CT, [18F]F-FDG PET/CT and magnetization transfer MR imaging to detect intestinal fibrosis in Crohn's disease: A prospective animal model and human cohort study.

Accurately and early detection of intestinal fibrosis in Crohn's disease (CD) is crucial for clinical management yet remains an unmet need. Fibroblast activation protein inhibitor (FAPI) PET/CT has emerged as a promising tool to assess fibrosis. We aimed to investigate the diagnostic capability of [18F]F-FAPI PET/CT in detecting intestinal fibrosis and compared it with[18F]F-FDG PET/CT and magnetization transfer MR imaging (MTI). Twenty-two rats underwent TNBS treatment to simulate fibrosis development, followed by three quantitative imaging sessions within one week. Mean and maximum standardized uptake values (SUVmean and SUVmax) were calculated on[18F]F-FAPI and [18F]F-FDG PET/CT, along with normalized magnetization transfer ratio on MTI. Intestinal fibrosis was assessed pathologically, with MTI serving as imaging standard for fibrosis. The diagnostic efficacy of imaging parameters in fibrosis was compared using pathological and imaging standards. Ten patients with 34 bowel strictures were prospectively recruited to validate their diagnostic performance, using the identical imaging protocol. In CD patients, the accuracy of FAPI uptake (both AUCs = 0.87, both P ≤ 0.01) in distinguishing non-to-mild from moderate-to-severe fibrosis was higher than FDG uptake (both AUCs = 0.82, P ≤ 0.01) and comparable to MTI (AUCs = 0.90, P ≤ 0.001). In rats, FAPI uptake responded earlier to fibrosis development than FDG and MTI; consistently, during early phase, FAPI uptake showed a stronger correlation (SUVmean: R = 0.69) with pathological fibrosis than FDG (SUVmean: R = 0.17) and MTI (R = 0.52). The diagnostic efficacy of [18F]F-FAPI PET/CT in detecting CD fibrosis is superior to [18F]F-FDG PET/CT and comparable to MTI, exhibiting great potential for early detection of intestinal fibrosis.

P376 A prospective multi-model study on diagnostic performance of 18F-FAPI PET/CT in comparison with 18F-FDG PET/CT or magnetization transfer MR imaging to detect intestinal fibrosis in Crohn’s disease

Abstract Background Accurate and early detection of Crohn's disease (CD) induced intestinal fibrosis is crucial for effective clinical management, yet it remains an unmet requirement. The magnetization transfer MR Imaging (MTI) was reported to offer high accurancy for detection of intestinal fibrosis. Recently, the utilization of fibroblast activating protein inhibitor (FAPI) PET/CT has emerged as a promising tool for assessing fibrosis. The diagnostic efficacy of 18F-FAPI PET/CT in detecting intestinal fibrosis was compared with that of 18F-FDG PET/CT and MTI. Methods Twenty-two rats were treated with TNBS for 2-4 weeks to simulate fibrosis development, and multi-model quantitative imaging was performed during a week. The mean and maximum standardized uptake values (SUVmean and SUVmax) were calculated on 18F-FAPI and 18F-FDG PET/CT, as well as the normalized magnetization transfer ratio on MTI (normalized MTR). Pathological evaluation of intestinal fibrosis was performed, and MTI was used as the imaging standard for fibrotic analysis. Imaging and pathological criteria were used to compare the diagnostic effects of fibrosis imaging parameters. Ten patients with 34 cases of intestinal stenosis were prospectively recruited to validate their diagnostic performance using the same imaging protocol. Results In patients, the accuracy of MTI (AUCs=0.90-0.91, P≤0.05) was comparable to FAPI uptake (AUCs=0.80-0.87, both P≤0.01) but higher than that of FDG uptake in distinguishing between non-to-mild and moderate-to-severe fibrosis (AUCs=0.53-0.82, P=0.01-0.36). In rats, FAPI uptake showed a rapid response to intestinal fibrosis at an early disease phase (week 0-2) and demonstrated a significant increasing trend with prolonged treatment duration (week 0-4;). In contrast, normalized MTR and FDG uptake presented only a minimal response at week 2 and did not correlate so clearly with treatment duration. Consistently, in early disease phase (rats treated till week 2), the correlations of FAPI uptake (SUVmean: R=0.69) with fibrotic scores were stronger than those of FDG uptake (SUVmean: R=0.17) and normalized MTR (R=0.52). In late disease phase (rats treated till week 3 or 4), normalized MTR (R=0.93) showed stronger correlations with fibrotic scores than FAPI uptake (SUVmean: R=0.55) or FDG uptake (SUVmean: R=0.19). Conclusion In accurately identifying early-stage intestinal fibrosis, 18F-FAPI PET/CT demonstrates vast potential and outperforms the performance of the other two imaging modalities, warranting further research. However, 18F-FAPI PET/CT offer an equal performance for characterization of intestinal fibrosis with MTI and has significant advantages compared to 18F-FDG PET/CT in the whole disease course from Crohn's disease.

Differentiating Pyogenic Brain Abscesses and Tuberculous using Magnetization Transfer MR Imaging and in Vivo Proton MR Spectroscopy

Objective: To find whether in vivo proton MR spectroscopy and magnetization transfer (MT) MR imaging can be used to differentiate between tuberculous brain abscess and pyogenic brain abscess. Study Design: Retrospective Place and duration: Radiology Department of Ibn_e_Sina Hospital Multan from January 2021 to January 2022. Methodology: The study included 15 subjects with brain abscesses who underwent in vivo MR spectroscopy, MT MR imaging and conventional MR imaging. Those with other systemic diseases were excluded. These techniques were also performed on 10 sex and age-matched control subjects for comparing MT ratios in normal and diseased parenchymal locations. 13 tuberculous abscesses were found in 4 patients, and 20 pyogenic abscesses were found in 11 patients. MT MR imaging and in vivo MR spectroscopy were used to evaluate suspected brain abscesses. Results: The mean MT ratio of the pyogenic brain abscesses was 25.55±1.60.MR spectroscopy showed that in pyogenic abscesses level of amino acids (valine, isoleucine, leucine) was 0.8 ppm and lipid and lactate was 1.2 ppm. Additionally, acetate, 1.91 ppm; glycine, 3.55 ppm; succinate,2.40 ppm and alanine, 1.47 pm were also seen. Four patients had 13 tuberculous abscesses. The mean MT ratio obtained from tuberculous abscesses was 19.87±1.54, which was significantly lower compared to the cortical grey matter, deep grey matter, white matter and pyogenic abscess (p<.001). Conclusion: MT ratios in tuberculous brain abscesses were lower than in pyogenic abscesses. In vivo, MR spectroscopy in pyogenic abscesses did not show amino acids. Tuberculous brain abscess can be differentiated from the pyogenic abscess by using both in vivo MR spectroscopy and MT MR imaging. Keywords: Pyogenic brain abscess, tuberculous brain abscess, MR spectroscopy

Assessment of Achilles Tendon Changes After Long-Distance Running Using Ultrashort Echo Time Magnetization Transfer MR Imaging.

Long-distance running is a common cause of Achilles tendinopathy. A reliable magnetic resonance imaging (MRI) technique to track early changes in the tendon caused by running could facilitate more effective interventions to combat progression. To evaluate an ultrashort echo time sequence with magnetization transfer preparation (UTE-MT) in the detection of changes in Achilles tendons of amateur marathon runners before and after long-distance running. Prospective. Thirty-two runners (19 enrolled for full marathons and 13 enrolled for half-marathons) and 5 healthy non-runners. 3.0 T; UTE-MT and dual-echo UTE for T2* assessment (UTE-T2*). MRI was performed 1-week pre-race, 2-days post-race, and 4-weeks post-race. UTE-MT ratio (UTE-MTR) and UTE-T2* of tendon were measured by two independent radiologists who were blinded to the scan time point and participant data. The Achilles tendon was divided into six regions of interest (ROIs) for data analysis, namely the insertion part (INS), middle part (MID), muscle-tendon junction (MTJ), tendon-bone insertion (TBI), tendon-muscle insertion (TMI), and whole tendon (bulk). Analysis of variance and Friedman's rank tests were used to evaluate changes in UTE-MTR and UTE-T2* between time points. Tukey test and Bonferroni method were used for further comparisons. P < 0.05 was considered significant. The UTE-MTR values of most tendon ROIs changed significantly between the measured time points, except for the INS region (P=0.1977). Conversely, the UTE-T2* values only showed significant changes in the MID and TBI regions. Paired comparisons showed that the UTE-MTR decreases in the MTJ, MID, TMI, and bulk regions at 2-days post-race were significant compared to measures taken pre-race and 4-weeks post-race. For UTE-T2* measurements, significant differences were observed only for the MID region between pre-race and 2-days post-race (P=0.0408, 95% CI: 0.0061, 0.1973), and for the TBI region between pre-race and 4-weeks post-race (P=0.0473, 95% CI: 0.0013, 0.1766). The UTE-MT sequence is able to detect biochemical changes in the Achilles tendon after long-distance running. 2 TECHNICAL EFFICACY: Stage 1.

Noninvasive Assessment of Renal Fibrosis with Magnetization Transfer MR Imaging: Validation and Evaluation in Murine Renal Artery Stenosis

Purpose To test the utility of magnetization transfer imaging in detecting and monitoring the progression of renal fibrosis in mice with unilateral renal artery stenosis. Materials and Methods This prospective study was approved by the Institutional Animal Care and Use Committee. Renal artery stenosis surgery (n = 10) or sham surgery (n = 5) was performed, and the stenotic and contralateral kidneys were studied longitudinally in vivo at baseline and 2, 4, and 6 weeks after surgery. After a 16.4-T magnetic resonance imaging examination, magnetization transfer ratio was measured as an index of fibrosis (guided by parameters selected in preliminary phantom studies). In addition, renal volume, perfusion, blood flow, and oxygenation were assessed. Fibrosis was subsequently measured ex vivo by means of histologic analysis and hydroxyproline assay. The Wilcoxon rank sum or signed rank test was used for statistical comparisons between or within groups, and Pearson and Spearman rank correlation was used to compare fibrosis measured in vivo and ex vivo. Results In the stenotic kidney, the median magnetization transfer ratio showed progressive increases from baseline to 6 weeks after surgery (increases of 13.7% [P = .0006] and 21.3% [P = .0005] in cortex and medulla, respectively), which were accompanied by a progressive loss in renal volume, perfusion, blood flow, and oxygenation. The 6-week magnetization transfer ratio map showed good correlation with fibrosis measured ex vivo (Pearson r = 0.9038 and Spearman ρ = 0.8107 [P = .0002 vs trichrome staining]; r = 0.9540 and ρ = 0.8821 [P < .0001 vs Sirius red staining]; and r = 0.8429 and ρ = 0.7607 [P = .001 vs hydroxyproline assay]). Conclusion Magnetization transfer imaging was used successfully to measure and longitudinally monitor the progression of renal fibrosis in mice with unilateral renal artery stenosis. © RSNA, 2016 Online supplemental material is available for this article.

Amide Proton Transfer (APT) MR imaging and Magnetization Transfer (MT) MR imaging of pediatric brain development.

To quantify the brain maturation process during childhood using combined amide proton transfer (APT) and conventional magnetization transfer (MT) imaging at 3 Tesla. Eighty-two neurodevelopmentally normal children (44 males and 38 females; age range, 2-190months) were imaged using an APT/MT imaging protocol with multiple saturation frequency offsets. The APT-weighted (APTW) and MT ratio (MTR) signals were quantitatively analyzed in multiple brain areas. Age-related changes in MTR and APTW were evaluated with a non-linear regression analysis. The APTW signals followed a decreasing exponential curve with age in all brain regions measured (R(2) = 0.7-0.8 for the corpus callosum, frontal and occipital white matter, and centrum semiovale). The most significant changes appeared within the first year. At maturation, larger decreases in APTW and lower APTW values were found in the white matter. On the contrary, the MTR signals followed an increasing exponential curve with age in the same brain regions measured, with the most significant changes appearing within the initial 2years. There was an inverse correlation between the MTR and APTW signal intensities during brain maturation. Together with MT imaging, protein-based APT imaging can provide additional information in assessing brain myelination in the paediatric population. • APTW signals followed a decreasing exponential curve with age. • The most significant APTW changes appeared within the first year • At maturation, larger APTW decreases and lower APTW appeared in white matter • MTR signals followed an increasing exponential curve with age.

Longitudinal assessment of mouse renal injury using high-resolution anatomic and magnetization transfer MR imaging

The purpose of this study is to evaluate the utility of high-resolution non-invasive endogenous high-field MRI methods for the longitudinal structural and quantitative assessments of mouse kidney disease using the model of unilateral ureter obstruction (UUO). T1-weighted, T2-weighted and magnetization transfer (MT) imaging protocols were optimized to improve the regional contrast in mouse kidney. Conventional T1 and T2 weighted images were collected in UUO mice on day 0 (~3h), day 1, day 3 and day 6 after injury, on a 7T small animal MRI system. Cortical and medullary thickness, corticomedullary contrast and Magnetization Transfer Ratio (MTR) were assessed longitudinally. Masson trichrome staining was used to histologically assess changes in tissue microstructure. Over the course of UUO progression there were significant (p<0.05) changes in thickness of cortex and outer medulla, and regional changes in T2 signal intensity and MTR values. Histological changes included tubular cell death, tubular dilation, urine retention, and interstitial fibrosis, assessed by histology. The MRI measures of renal cortical and medullary atrophy, cortical–medullary differentiation and MTR changes provide an endogenous, non-invasive and quantitative evaluation of renal morphology and tissue composition during UUO progression.

Magnetization Transfer MR Imaging Demonstrates Degeneration of the Subcortical and Cortical Gray Matter in Huntington Disease

GM is typically affected in HD since the presymptomatic stage. Our aim was to investigate with MT MR imaging the microstructural changes of the residual brain subcortical and cortical GM in carriers of the HD gene and to preliminarily assess their correlation with the clinical features. Fifteen HD gene carriers with a range of clinical severity and 15 age- and sex-matched healthy controls underwent MT MR imaging on a 1.5T scanner. The MT ratio was measured automatically in several subcortical and cortical GM regions (striatal nuclei; thalami; and the neocortex of the frontal, temporal, parietal, and occipital lobes) by using FLS tools. The MT ratio was significantly (P < .05 with Bonferroni correction for multiple comparison) decreased in all subcortical structures except the putamen and decreased diffusely in the cerebral cortex of HD carriers compared with controls. Close correlation was observed between the subcortical and cortical regional MT ratios and several clinical variables, including disease duration, motor disability, and scores in timed neuropsychological tests. MT imaging demonstrates degeneration of the subcortical and cortical GM in HD carriers and might serve, along with volumetric assessment, as a surrogate marker in future clinical trials of HD.

Multi-parametric classification of Alzheimer's disease and mild cognitive impairment: The impact of quantitative magnetization transfer MR imaging

Multi-parametric and quantitative magnetic resonance imaging (MRI) techniques have come into the focus of interest, both as a research and diagnostic modality for the evaluation of patients suffering from mild cognitive decline and overt dementia. In this study we address the question, if disease related quantitative magnetization transfer effects (qMT) within the intra- and extracellular matrices of the hippocampus may aid in the differentiation between clinically diagnosed patients with Alzheimer disease (AD), patients with mild cognitive impairment (MCI) and healthy controls. We evaluated 22 patients with AD ( n = 12) and MCI ( n = 10) and 22 healthy elderly ( n = 12) and younger ( n = 10) controls with multi-parametric MRI. Neuropsychological testing was performed in patients and elderly controls ( n = 34). In order to quantify the qMT effects, the absorption spectrum was sampled at relevant off-resonance frequencies. The qMT-parameters were calculated according to a two-pool spin-bath model including the T1- and T2 relaxation parameters of the free pool, determined in separate experiments. Histograms (fixed bin-size) of the normalized qMT-parameter values ( z-scores) within the anterior and posterior hippocampus (hippocampal head and body) were subjected to a fuzzy- c-means classification algorithm with downstreamed PCA projection. The within-cluster sums of point-to-centroid distances were used to examine the effects of qMT- and diffusion anisotropy parameters on the discrimination of healthy volunteers, patients with Alzheimer and MCIs. The qMT-parameters T2 r (T2 of the restricted pool) and F (fractional pool size) differentiated between the three groups (control, MCI and AD) in the anterior hippocampus. In our cohort, the MT ratio, as proposed in previous reports, did not differentiate between MCI and AD or healthy controls and MCI, but between healthy controls and AD.

Early structural changes in individuals at risk of familial Alzheimer’s disease: a volumetry and magnetization transfer MR imaging study

Presenilin 1 (PS1) mutation carriers provide the opportunity to asses early features of neurodegeneration in familial Alzheimer's disease (AD). Gray matter (GM) regional volume loss and decrease of magnetization transfer ratio (MTR) consistent with microstructural changes have been reported in sporadic AD. We performed a regional volumetric and MTR analysis in carriers of PS1 mutations. Six non-demented mutated PS1 carriers (5 with memory deficits) and 14 healthy subjects were examined with high resolution T1-weighted images for volumetry and with T2* weighted images for MTR. Cortical GM volume and MTR values were derived. Compared to healthy controls, the GM volume of the left temporal and inferior parietal cortex and the MTR of the temporal cortex bilaterally were significantly decreased in PS1 gene carriers. In the latter, the temporal lobe MTR showed a trend for correlation with memory and executive function scores. Early neurodegeneration in non-demented subjects at risk for familial AD may be associated with atrophy and decreased MTR in the temporal cortex.

High‐resolution, multicontrast three‐dimensional‐MRI characterizes atherosclerotic plaque composition in ApoE–/– mice ex vivo

To systematically investigate intrinsic MR contrast mechanisms that would facilitate plaque characterization and quantification in the aortic root and brachiocephalic artery of ApoE-/- mice ex vivo. To establish unambiguous MR parameters for routinely analyzing atherosclerotic plaque ex vivo at 11.7 T, relaxation times of plaque components were quantitatively assessed. Magnetization transfer and lipid-proton three-dimensional MR imaging was investigated for visualization of collagen- and lipid-rich plaque regions, respectively. A three-dimensional multiecho sequence with a spatial resolution of 47 x 47 x 63 microm was implemented providing a variable degree of T2-weighting. Relaxation time measurements showed clear tissue heterogeneity between atherosclerotic plaque components in the T2-values, but similar T1-values at 11.7 T (T1/T2 mean +/- SD; cellular plaque component: 1.2 +/- 0.3 seconds/26.3 +/- 0.4 msec; fibrofatty plaque component: 1.1 +/- 0.2 seconds/13.7 +/- 2.0 msec). The three-dimensional multiecho sequence allowed the calculation of the intrinsic proton density and T2-maps. The sum of the multiecho data provided strong T2-weighting that facilitated quantification of various components of atherosclerotic plaque in the mouse aortic root and correlated well with histology (P < 0.0001). High-resolution MRI allows for accurate classification and quantification of atherosclerotic plaque components in the aortic root of mice.

Diffusion tensor and magnetization transfer MR imaging of early-onset multiple sclerosis

Multiple sclerosis (MS) is a chronic, demyelinating disease of the central nervous system (CNS) with the onset of symptoms typically occurring between the age of 20 and 40 years. However, in about 3% to 12% of the cases, the onset of the disease is before 16 years of age. This review summarizes the main results obtained by the application of conventional and non-conventional MRI techniques to the assessment of patients with early-onset MS, which showed that the overall amount of CNS damage in these subjects is mild, compared to that typically detected in the adult-form of the disease. This fits with the notion that an early onset of the disease is associated with a more favourable clinical evolution.

MnDPDP-enhanced magnetization transfer MR imaging: implications for effective liver imaging

The benefit of combining magnetization transfer (MT) MR imaging technique with liver-specific contrast agent manganese dipyridoxyldiphosphate (MnDPDP) was assessed in our experimental investigation. The study was accomplished by imaging a phantom containing serial concentrations of MnDPDP in cross-linked bovine serum albumin (BSA) with various protein concentrations. A 0.1T clinical MR imager with different parameters for MT and conventional MR sequences were used. The combination of an offset frequency of 8 kHz and an amplitude of 25 μT produced nearly maximal MT effect for all protein samples either without MnDPDP or with different MnDPDP concentrations. With long TRs (TR > 200 ms) MT dramatically improved CNR in conjunction with MnDPDP. With short TRs, the gain in CNR with MT was negligible. However, long TRs with increased number of images are beneficial in liver imaging. We conclude that MT like preparation pulse is useful when paramagnetic contrast agents such as MnDPDP are employed.

Comparative evaluation of magnetization transfer MR imaging and in-vivo proton MR spectroscopy in brain tuberculomas

We have compared and analyzed the value of in vivo proton MR spectroscopy (PMRS) and T1 weighted magnetization transfer (MT) MR imaging in tissue characterization of brain tuberculomas. We studied 33 cases of proven intracranial tuberculomas with in vivo PMRS and T1 weighted MT MR imaging. MT ratios from the rim and core of the tuberculomas were calculated and compared with metabolites seen on PMRS. Final diagnosis of tuberculoma was based on histopathology (n = 26) and/or associated tuberculous meningitis (n = 7) in all the cases. Out of the 33 patients who underwent both PMRS and T1 weighted MT MR imaging, spectroscopy showed only lipids at 0.9 ppm, 1.3 ppm, 2.0 ppm, and 2.80 ppm in 26 cases while lipids at 0.9 ppm, 1.3 ppm, 2.0 ppm and 2.80 ppm along with choline at 3.22 ppm was seen in remaining 7 patients. MT ratios from the core or solid necrosis varied from 21–29% while from the rim or cellular region varied from 16–24%. MT ratios from all the 33 lesions were consistent with tuberculomas while PMRS showed choline along with lipids in 7 predominantly cellular lesions simulating a neoplasm. We conclude that T1 weighted MT MR imaging appears to be more consistent in the tissue characterization of brain tuberculomas.

Magnetization Transfer MR Imaging Correlation with Histopathology in Intracranial Tuberculomas

OBJECTIVE: The purpose of this study was to correlate the differences in the magnetization transfer (MT) ratios of different components of the tuberculoma with histopathology and to see whether MT or conventional MR imaging correlates better with histopathology. METHODS: MT T1 and conventional spin echo MR imaging was performed in six patients with intracranial tuberculomas. The tuberculomas were excised as a single mass and ex vivo MR imaging was performed using the same protocol. The gross histopathology was compared with in vivo imaging with respect to the MR signal intensity (MT ratio) in all six specimens. RESULTS: The size of the tuberculomas was larger on MT T1-weighted images compared to T2-weighted images and matched the gross measurements of each specimen. The MT hyperintense rim matched the cellular component of the tuberculoma that was masked on T2-weighted images because of the associated perifocal oedema. The cellular component had a lower MT ratio compared to the necrotic components. CONCLUSION: The outer hyperintense rim and hyperintense strands are due to the cellular infiltrate, noncaseating granulomas, and gliosis while the hypointense core represents solid caseation. The cellular outer rim shows lower MT ratio compared to the core of the tuberculoma. Histological correlation of the cellular and necrotic components of tuberculomas is best shown with MT T1 imaging. Gupta R. K.et al. (2001)Clinical Radiology,56 , 656–663.

Magnetization transfer and diffusion tensor MR imaging of the optic radiations and calcarine cortex from patients with Leber's hereditary optic neuropathy

Optic nerve abnormalities are easily detectable in patients with Leber's hereditary optic neuropathy (LHON), using magnetic resonance imaging (MRI). However, the presence of structural changes in the optic radiations and calcarine cortex of these patients is still an unresolved issue. In this study, we obtained magnetization transfer (MT) and diffusion tensor (DT) MRI to investigate the integrity of these structures in patients with LHON. Dual echo, MT- and DT-MRI scans of the brain were obtained from 10 men with LHON and 10 healthy sex- and age-matched controls. After image co-registration, we obtained MT ratio (MTR), average diffusivity ( D̄) and fractional anisotropy (FA) maps. MTR, D̄ and FA values for the white matter of the optic radiations and MTR and D̄ values for the calcarine cortex were obtained using a region of interest (ROI) analysis. No macroscopic abnormalities were detected in any of the scans from LHON patients and controls. No statistically significant differences of MTR, D̄ or FA values were found for any of the regions studied in LHON patients and healthy controls. Our results suggest that, in patients with LHON, the optic radiations and the calcarine cortex are spared from structural damage, both at a macroscopic and a microscopic level.

Spin lock and magnetization transfer MR imaging of focal liver lesions

The present study was designed to evaluate tissue contrast characteristics obtained with the spin-lock (SL) technique by comparing the results with those generated with a magnetization transfer(MT)-weighted gradient echo [GRE, echo-time (TE) = 40 ms] sequence. Twenty-eight patients with hepatic hemangiomas ( n = 14), or metastatic liver lesions ( n = 14) were imaged at 0.1 T by using identical imaging parameters. Gradient echo, single–slice off-resonance MT, and multiple-slice SL sequences were obtained. SL and MT-effects were measured from the focal liver lesions and from normal liver parenchyma. In addition, tissue contrast values for the liver lesions were determined. Statistically significant difference between the SL-effects of the hemangiomas and metastases, and also between the MT-effects of the lesions was observed ( p < 0.02). Tissue contrast values for the lesions proved to be quite similar between the SL and MT techniques. Our results indicate that at 0.1 T multiple-slice SL imaging provides MT based tissue contrast characteristics in tissues rich in protein with good imaging efficiency and wide anatomical coverage, and with reduced motion and susceptibility artifacts.

Magnetization transfer contrast: experimental sequence optimization for study of the cerebral substantia alba

A new application for magnetization transfer (MT) MR imaging is the investigation of cerebral white matter. For that a pure MT effect is desirable. Our purpose was the optimization and testing of an MT sequence for investigations of cerebral white matter. Experimental investigations were performed in phantom material and in 5 wistar rats using various frequency offsets (FO) (200 Hz-30,000 Hz). Relative signal suppression (rSS) for the phantom material and for callosal white matter of the rat was calculated. The optimized sequence was tested in 25 healthy volunteers. A relatively pure MT effect was achieved with FO > 4000 Hz. rSS for cerebral white matter structures was generally higher than rSS für cerebral gray matter structures. rSS for cerebral white matter structures ranged from 45-50%. We present a fast MT sequence with high rSS for cerebral white matter and a relatively pure MT effect. Owing to the high rSS-values we expect that this sequence improves differentiation of cerebral white matter lesions. Because of the confusing variety of MT sequence currently described in the literature we believe that standard parameters should be defined to make published results comparable.

Magnetization transfer and spin lock MR imaging of patellar cartilage degeneration at 0.1 T.

To investigate magnetization transfer (MT) parameters and rotating frame relaxation time T1 rho in patellar cartilage at different levels of degeneration. Thirty cadaveric patellae were examined at 0.1 T using the time-dependent saturation-transfer MT technique and the spin lock (SL) technique. In an SL experiment, nuclear spins are locked with a radiofrequency (RF) field, and the locked nuclear magnetization relaxes along the magnetic component of the locking RF field. The specimens were divided into three groups according to the level of cartilage degeneration. MT parameters and T1 rho were measured. The MT effect was greater in degenerated cartilage than in normal cartilage. T1 rho was longer in advanced cartilage degeneration than in intermediate cartilage degeneration. The results suggest that more studies are needed to fully establish the value of SL imaging in cartilage degeneration.

Magnetization transfer and spin lock MR imaging of patellar cartilage degeneration at 0.1 t

Magnetization transfer and spin lock MR imaging of patellar cartilage degeneration at 0.1 t