Safe performance of magnetic resonance of the heart in patients with magnetic resonance conditional pacemaker systems: the safety issue of the ESTIMATE study.

BACKGROUND: No published data exist about the safety of diagnostic magnetic resonance (MR) of the heart performed in a larger series of patients implanted with MR conditional pacemakers (PM). The purpose of our study is to analyse safety and potential alterations of electrical lead parameters in patients implanted with the EnRhythm/Advisa MRI SureScan PM with 5086MRI leads (Medtronic Inc.) during and after MR of the heart at 1.5 Tesla. METHODS: Patients enrolled in this single center pilot study who underwent non-clinically indicated diagnostic MR of the heart were included in this analysis. Heart MR was performed for analyses of potential changes in right and left ventricular functional parameters under right ventricular pacing at 80 and 110 bpm. Atrial/ventricular sensing, atrial/ventricular pacing capture threshold [PCT], and pacing impedances were assessed immediately before, during, and immediately after MR, as well at 3 and 15 months post MR. RESULTS: Thirty-six patients (mean age 69 ± 13 years; high degree AV block 18 [50%]) underwent MR of the heart. No MR related adverse events occurred during MR or thereafter. Ventricular sensing differed significantly between the FU immediately after MR (10.3 ± 5.3 mV) and the baseline FU (9.8 ± 5.3 mV; p < 0.05). Despite PCT [V/0.4ms] was not significantly different between the FUs (baseline: 0.84 ± 0.27; in-between MR scans: 0.82 ± 0.27; immediately after MR: 0.84 ± 0.24; 3-month: 0.85 ± 0.23; 15-month: 0.90 ± 0.67; p = ns), 7 patients (19%) showed PCT increases by 100% (max. PCT measured: 1.0 V) at the 3-month FU compared to baseline. RV pacing impedance [Ω/5V] differed significantly at the FU in-between MR scans (516 ± 47), and at the 15-month FU (482 ± 58) compared to baseline (508 ± 75). CONCLUSION: The results of our study suggest MR of the heart to be safe in patients with the MR conditional EnRhythm/Advisa system, albeit although noticeable but clinically irrelevant ventricular PCT changes were observed.

Magnetic resonance fiber density mapping of age-related white matter changes.

OBJECTIVES: To introduce fiber density mapping (FDM) for investigation of age-related white matter (WM) changes and to compare its capabilities with conventional diffusion tensor imaging (DTI) post-processing. METHODS: DTI data with 1.9 mm(3) isotropic voxels were acquired from 44 healthy volunteers (18-88 years) at 3T. FDM is a 3-step approach which includes diagonalization of the diffusion tensor, fiber reconstruction for the whole brain, and calculation of fiber density (FD) values. Maps of fractional anisotropy (FA) and mean diffusivity (MD) were additionally calculated. Voxel-based analyses were performed to determine volume clusters of significant correlation with age. Bivariate linear regression models and Hotelling-Williams tests were used to detect significant differences between correlations. RESULTS: FDM detected a larger WM volume affected by age-related changes concomitant with fewer significant clusters compared to FA and MD. This indicates that WM alterations due to normal aging occur rather globally than locally. FD values showed a significant stronger correlation with age in frontal lobes (prefrontal and precentral gyrus), limbic lobes (cingulate and parahippocampal gyrus), the corpus callosum (genu) and temporal lobes. CONCLUSIONS: FDM shows higher sensitivity for detection of age-related WM changes because it includes all surrounding fiber structures into the evaluation of each DTI data voxel.

Magnetic resonance velocity mapping of 3D cerebrospinal fluid flow dynamics in hydrocephalus: preliminary results.

OBJECTIVES: To investigate the detectability of CSF flow alterations in the ventricular system of patients with hydrocephalus using time-resolved 3D MR velocity mapping. METHODS: MR velocity mapping was performed in 21 consecutive hydrocephalus patients and 21 age-matched volunteers using a 3D phase-contrast (PC) sequence. Velocity vectors and particle path lines were calculated for visualisation of flow dynamics. CSF flow was classified as "hypomotile flow" if it showed attenuated dynamics and as "hypermotile flow" if it showed increased dynamics compared with volunteers. Diagnostic efficacy was compared with routine 2D cine PC-MRI. RESULTS: Seven patients showed hypomotile CSF flow: six had non-communicating hydrocephalus due to aqueductal stenosis. One showed oscillating flow between the lateral ventricles after craniotomy for intracranial haemorrhage. Seven patients showed normal flow: six had hydrocephalus ex vacuo due to brain atrophy. One patient who underwent ventriculostomy 10 years ago showed a flow path through the opening. Seven patients showed hypermotile flow: three had normal pressure hydrocephalus, three had dementia, and in one the diagnosis remained unclear. The diagnostic efficacy of velocity mapping was significantly higher except for that of aqueductal stenosis. CONCLUSIONS: Our approach may be useful for diagnosis, therapy planning, and follow-up of different kinds of hydrocephalus.

Triggered non-contrast enhanced MR angiography of peripheral arteries: optimization of systolic and diastolic time delays for electrocardiographic triggering.

The purpose of this study was to determine the optimal systolic and diastolic time delays for electrocardiographic triggering of a non-contrast media enhanced MR angiography using a 3-dimensional fast spin echo sequence in patients suffering from peripheral arterial disease. 12 patients with suspected peripheral arterial disease were examined on a 1.5 T Philips Achieva MR scanner. A cardiac-triggered Volumetric Isotropic T2-weighted fast spin echo sequence was performed using variable trigger delays for systolic and diastolic phase. The signal in the popliteal arteries and anterior tibial arteries of the systolic and diastolic images was measured and optimal delay times for systolic and diastolic phase were determined. Minimum signal to noise ratio (SNR) appears at the time difference ΔT=-21 ms on systolic images of the popliteal arteries. In the anterior tibial arteries the minimum SNR is significantly higher and appears at the time difference ΔT=-14 ms. Diastolic delay times must be chosen as long or as short as possible depending on heart rate. In peripheral vessels triggered non-contrast MR angiography can yield results which are comparable with contrast enhanced MRA techniques. It is crucial to optimize timing parameters.

High-resolution cartilage imaging of the knee at 3T: basic evaluation of modern isotropic 3D MR-sequences.

PURPOSE: To evaluate qualitative and quantitative image quality parameters of isotropic three-dimensional (3D) cartilage-imaging magnetic resonance (MR)-sequences at 3T. MATERIALS AND METHODS: The knees of 10 healthy volunteers (mean age, 24.4±5.6 years) were scanned at a 3T MR scanner with water-excited 3D Fast-Low Angle Shot (FLASH), True Fast Imaging with Steady-state Precession (TrueFISP), Sampling Perfection with Application-optimized Contrast using different flip-angle Evolutions (SPACE) as well as conventional and two individually weighted Double-Echo Steady-State (DESS) sequences. The MR images were evaluated qualitatively and quantitatively (signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), SNR efficiency, CNR efficiency). Quantitative parameters were compared by means of a Tukey-test and sequences were ranked according to SNR/CNR, SNR/CNR efficiency and qualitative image grading. RESULTS: The highest SNR was measured for SPACE (34.0±5.6), the highest CNR/CNR efficiency (cartilage/fluid) for the individually weighted DESS (46.9±18.0/2.18±0.84). SPACE, individually weighted and conventional DESS were ranked best with respect to SNR/CNR and SNR/CNR efficiency. The DESS sequences also performed best in the qualitative evaluation. TrueFISP performed worse, FLASH worst. The individually weighted DESS sequences were generally better than the conventional DESS with the significant increase of cartilage-fluid contrast (46.9±18.0/31.9±11.4 versus 22.0±7.3) as main advantage. CONCLUSION: Individually weighted DESS is the most promising candidate; all tested sequences performed better than FLASH.

Fiber density mapping of gliomas: histopathologic evaluation of a diffusion-tensor imaging data processing method.

PURPOSE: To evaluate fiber density mapping (FDM) in the quantification of the extent of destruction of white matter (WM) structures in the center, transition zone, and border zone of intracranial gliomas. MATERIALS AND METHODS: This retrospective study was approved by the institutional review board. Diffusion-tensor imaging (DTI) and magnetic resonance (MR) imaging-guided biopsies were performed in 20 patients with glioma. FDM is a three-step approach that includes diagonalization of the diffusion tensor, fiber reconstruction for the whole brain, and calculation of fiber density values. Coregistration of FDM data with MR imaging data used for stereotactic biopsy guidance enabled us to correlate these results with histopathologic findings. Data were analyzed by using regression analyses and Hoetelling-Williams and Wilcoxon signed rank tests. RESULTS: Histopathologic correlation revealed strong negative correlations with both the logarithm of tumor cell number (CN) (R = -0.825) and the percentage of tumor infiltration (TI) (R = -0.909). Complete destruction of WM structures was found when the percentage of TI was 60% or greater and when the tumor CN was 150 or greater. We estimated a fiber density value of 18 as a limit in the identification of fiber structures that are infiltrated with tumor yet are still potentially functional. CONCLUSION: FDM provides histologic insight into the structure of WM; therefore, it may help prevent posttreatment neurologic deficits when planning therapy of brain tumors.

Insight into the patterns of cerebrospinal fluid flow in the human ventricular system using MR velocity mapping.

The patterns of cerebrospinal fluid (CSF) flow within the human ventricular system are still not fully understood in all their complexity. Knowledge is based on either the interpretation of CSF flow curves or computational simulations. Both approaches only provide an incomplete insight into the spatial and temporal dynamics of CSF flow. Time-resolved three-dimensional magnetic resonance velocity mapping has previously been used to investigate normal and pathologic blood flow patterns in the human vascular system. Here we used this technique to study the spatial and temporal dynamics of CSF flow in the ventricular system of 40 normal volunteers. Classification of the patterns of CSF flow based on calculation of three-dimensional particle path lines over the cardiac cycle revealed one uniform flow pattern for the lateral ventricles, three categories for the third and two categories for the fourth ventricle. We found no significant aging effects on either the presence of a specific CSF flow pattern or on CSF flow velocities. Our results provide the first detailed demonstration of the patterns of CSF flow within the human ventricular system.

MR imaging of the knee: Improvement of signal and contrast efficiency of T1-weighted turbo spin echo sequences by applying a driven equilibrium (DRIVE) pulse.

The purpose of this study was to assess the effect of a driven equilibrium (DRIVE) pulse incorporated in a standard T1-weighted turbo spin echo (TSE) sequence as used in our routine MRI protocol for examination of pathologies of the knee. Sixteen consecutive patients with knee disorders were examined using the routine MRI protocol, including T1-weighted TSE-sequences with and without a DRIVE pulse. Signal-to-noise ratios (SNRs) and contrast-to-noise ratio (CNR) of anatomical structures and pathologies were calculated and compared for both sequences. The differences in diagnostic value of the T1-weighted images with and without DRIVE pulse were assessed. SNR was significantly higher on images acquired with DRIVE pulse for fluid, effusion, cartilage and bone. Differences in the SNR of meniscus and muscle between the two sequences were not statistically significant. CNR was significantly increased between muscle and effusion, fluid and cartilage, fluid and meniscus, cartilage and meniscus, bone and cartilage on images acquired using the DRIVE pulse. Diagnostic value of the T1-weighted images was found to be improved for delineation of anatomic structures and for diagnosing a variety of pathologies when a DRIVE pulse is incorporated in the sequence. Incorporation of a DRIVE pulse into a standard T1-weighted TSE-sequence leads to significant increase of SNR and CNR of both, anatomical structures and pathologies, and consequently to an increase in diagnostic value within the same acquisition time.

Hypothenar hammer syndrome: Long-term follow-up of selective thrombolysis by 3.0-T MR angiography.

OBJECTIVE: To assess the long-term outcome of selective thrombolysis in patients with hypothenar hammer syndrome by 3.0-T magnetic resonance (MR) angiography. MATERIALS AND METHODS: Seven patients (6 men, 1 woman; mean age, 58.6 +/- 14.4 years) were investigated. Long-term follow-up examinations (9-11 years post-interventional) were based on 3.0-T MR angiography. Pre- versus post-thrombolysis images and post-thrombolysis versus long-term follow-up images were compared with respect to arterial diameter. Additionally, changes in patients' symptoms were assessed. RESULTS: The long-term follow-up examination showed worse contrast filling of the ulnar digits compared to the immediately post-interventional angiographic images only in one patient (14.3%), whereas worse contrast filling of the deep palmar arch or the ulnar artery was registered in three patients (42.9%). Three of seven patients (42.9%) reported worse symptoms, two patients (28.6%) stable symptoms at the long-term follow-up MR angiography. In two patients (28.6%) the change of symptoms could not be observed due to missing post-interventional clinical data. CONCLUSIONS: At the long-term follow-up, clinically, mild progression was found rather often, whereas with respect to imaging findings progression at the ulnar digits was rare. We assume that collateral vessels might play a major role in the post-interventional follow-up. In many instances the patients' symptoms are not in line with the angiographic findings.

Accelerated time-resolved three-dimensional MR velocity mapping of blood flow patterns in the aorta using SENSE and k-t BLAST.

PURPOSE: To assess the feasibility and potential limitations of the acceleration techniques SENSE and k-t BLAST for time-resolved three-dimensional (3D) velocity mapping of aortic blood flow. Furthermore, to quantify differences in peak velocity versus heart phase curves. MATERIALS AND METHODS: Time-resolved 3D blood flow patterns were investigated in eleven volunteers and two patients suffering from aortic diseases with accelerated PC-MR sequences either in combination with SENSE (R=2) or k-t BLAST (6-fold). Both sequences showed similar data acquisition times and hence acceleration efficiency. Flow-field streamlines were calculated and visualized using the GTFlow software tool in order to reconstruct 3D aortic blood flow patterns. Differences between the peak velocities from single-slice PC-MRI experiments using SENSE 2 and k-t BLAST 6 were calculated for the whole cardiac cycle and averaged for all volunteers. RESULTS: Reconstruction of 3D flow patterns in volunteers revealed attenuations in blood flow dynamics for k-t BLAST 6 compared to SENSE 2 in terms of 3D streamlines showing fewer and less distinct vortices and reduction in peak velocity, which is caused by temporal blurring. Solely by time-resolved 3D MR velocity mapping in combination with SENSE detected pathologic blood flow patterns in patients with aortic diseases. For volunteers, we found a broadening and flattering of the peak velocity versus heart phase diagram between the two acceleration techniques, which is an evidence for the temporal blurring of the k-t BLAST approach. CONCLUSION: We demonstrated the feasibility of SENSE and detected potential limitations of k-t BLAST when used for time-resolved 3D velocity mapping. The effects of higher k-t BLAST acceleration factors have to be considered for application in 3D velocity mapping.

Diffusion-weighted imaging for the follow-up of patients after matrix-associated autologous chondrocyte transplantation.

OBJECTIVE: To evaluate the use of diffusion-weighted imaging (DWI) for the assessment of cartilage maturation in patients after matrix-associated autologous chondrocyte transplantation (MACT). MATERIALS AND METHODS: Fifteen patients after MACT were examined by 3.0-T magnetic-resonance-tomography; the examination was up to 13 month after surgery in group 1, and later than 13 month after surgery in group 2. Both groups had a follow-up one-year later. DWI was acquired using a steady-state gradient-echo sequence. Mean values of the diffusion quotients of regions of interest within cartilage repair tissue and of reference regions were assessed. Each region-of-interest was subdivided into a deep, and a superficial area. RESULTS: Mean diffusion quotients of cartilage repair tissues were 1.44 (baseline), and 1.44 (follow-up). Mean diffusion quotients of reference tissues were 1.29 (baseline) and 1.28 (follow-up). At the follow-up diffusion quotients of cartilage repair tissue were significantly higher than those of reference cartilage. In group 1 the diffusion quotients were significantly lower at the follow-up (1.45 versus 1.65); in group 2 no statistically significant differences between follow-up (1.39) and baseline (1.41) were found. Reference cartilages and cartilage repair tissues of group 2 showed a decrease of diffusion quotients from the deep to the superficial area being stable at the follow-up. In group 1 initially a significant increase (1.49 versus 1.78) of the diffusion quotients from deep to superficial area of the cartilage repair tissue was found changing into a decrease (1.65 versus 1.52) at the follow-up. CONCLUSIONS: DWI detected changes of diffusion within cartilage repair tissue that may reflect cartilage maturation. Changes in diffusity occurred up to two years after surgery and were stable later. Zonal variations within cartilage could be measured.

Diffusion-weighted MR imaging with background body signal suppression (DWIBS) for the diagnosis of malignant and benign breast lesions.

The purpose of this study was to evaluate the efficacy of diffusion-weighted MR imaging with background body signal suppression (DWIBS) and a conventional DWI (cDWI) sequence for the detection of breast lesions. Fifty consecutive patients with suspected breast lesions underwent DWIBS and cDWI at 1.5 T. The routine protocol consisted of a short TI inversion recovery (STIR) sequence and a dynamic contrast-enhanced T1-weighted sequence. Apparent diffusion coefficient (ADC) and exponential ADC (eADC) values of the lesions were calculated. Receiver operating characteristic (ROC) analyses and qualitative evaluation of lesion detectability and conspicuity were performed. Thirty-six lesions were detected in 30 patients by using the routine protocol. DWIBS detected 34 lesions (94%) and cDWI detected 26 lesions (72%). The conspicuity of fibroadenomas was significantly (P = 0.007) better for DWIBS. ADC and eADC values of tumour were significantly different between DWIBS and cDWI. DWIBS is superior to cDWI in the visualization of malignant and benign lesions in the breast.

Accelerated phase-contrast MR imaging: comparison of k-t BLAST with SENSE and Doppler ultrasound for velocity and flow measurements in the aorta.

PURPOSE: To evaluate differences in velocity and flow measurements in the aorta between accelerated phase-contrast (PC) magnetic resonance imaging (MRI) using SENSE and k-t BLAST and in peak velocity to Doppler ultrasound. MATERIALS AND METHODS: Two-dimensional PC-MRI perpendicular to the ascending and descending aorta was performed in 11 volunteers using SENSE (R = 2) and k-t BLAST (2-, 4-, 6-, and 8-fold). Peak velocity, mean velocity, and stroke volume of the accelerated PC-MRI experiments were correlated. Peak velocities were compared to Doppler ultrasound. RESULTS: All acceleration techniques showed significant correlations for peak velocity with Doppler ultrasound. However, k-t BLAST 6 and 8 showed a significant underestimation. Strong correlations between SENSE and k-t BLAST were found for all three parameters. Significant differences in peak velocity were found between SENSE and all k-t BLAST experiments, but not for 2-fold k-t BLAST in the ascending aorta, and 2- and 4-fold k-t BLAST in the descending aorta. For mean velocity no significant differences were found. Stroke volume showed significant differences for all k-t BLAST experiments in the ascending and for 6- and 8-fold k-t BLAST in the descending aorta. CONCLUSION: Peak velocity of accelerated PC-MRI correlated with CW Doppler measurements, but high k-t BLAST acceleration factors lead to a significant underestimation. SENSE with R = 2 and 2-fold k-t BLAST are most highly correlated in phase-contrast flow measurements.

Quantitative T2 mapping during follow-up after matrix-associated autologous chondrocyte transplantation (MACT): full-thickness and zonal evaluation to visualize the maturation of cartilage repair tissue.

The purpose of this article was to evaluate the potential of in vivo zonal T2-mapping as a noninvasive tool in the longitudinal visualization of cartilage repair tissue maturation after matrix-associated autologous chondrocyte transplantation (MACT). Fifteen patients were treated with MACT and evaluated cross-sectionally, with a baseline MRI at a follow-up of 19.7 +/- 12.1 months after cartilage transplantation surgery of the knee. In the same 15 patients, 12 months later (31.7 +/- 12.0 months after surgery), a longitudinal 1-year follow-up MRI was obtained. MRI was performed on a 3 Tesla MR scanner; morphological evaluation was performed using a double-echo steady-state sequence; T2 maps were calculated from a multiecho, spin-echo sequence. Quantitative mean (full-thickness) and zonal (deep and superficial) T2 values were calculated in the cartilage repair area and in control cartilage sites. A statistical analysis of variance was performed. Full-tickness T2 values showed no significant difference between sites of healthy cartilage and cartilage repair tissue (p < 0.05). Using zonal T2 evaluation, healthy cartilage showed a significant increase from the deep to superficial cartilage layers (p < 0.05). Cartilage repair tissue after MACT showed no significant zonal increase from deep to superficial cartilage areas during baseline MRI (p > 0.05); however, during the 1-year follow-up, a significant zonal stratification could be observed (p < 0.05). Morphological evaluation showed no significant difference between the baseline and the 1-year follow-up MRI. T2 mapping seems to be more sensitive in revealing changes in the repair tissue compared to morphological MRI. In vivo zonal T2 assessment may be sensitive enough to characterize the maturation of cartilage repair tissue.

Reference data for in vivo magnetic resonance imaging properties of meniscoids in the cervical zygapophyseal joints.

STUDY DESIGN: Prospective in vivo study of meniscoids in the cervical zygapophyseal joints. OBJECTIVE: To generate reference data for in vivo magnetic resonance (MR) imaging properties of meniscoids in the cervical zygapophyseal joints. SUMMARY OF BACKGROUND DATA: Meniscoids, also called synovial folds, are tiny anatomic structures within the zygapophyseal joints. It has been suggested that pathologic conditions of meniscoids may be a potential source of cervical pain. Prior studies were limited to in vitro observations. To identify pathologic conditions of the meniscoids, it is necessary to obtain reference data of basic in vivo MR imaging properties of meniscoids in a healthy population. METHODS: Fifty-six healthy volunteers (33 women, 23 men; mean age 42.0 +/- 17.1 years) were investigated in a 3.0 Tesla MR scanner using high resolution isotropic 3-dimensional sequences. Presence, size, location, and signal intensity of the meniscoids were assessed, and their dependence on sex, age, body mass index, and degenerative changes were analyzed by t test and correlation analysis. RESULTS: There was no significant difference in presence (20.3 +/- 4.8 vs. 19.7 +/- 4.8) and size (3.8 +/- 0.7 mm vs. 4.1 +/- 0.5 mm) of meniscoids between women and men. Presence of meniscoids decreased with increasing age (r = -0.38, P = 0.004). Size of meniscoids did not significantly depend on age (r = 0.02, P = 0.91). Meniscoid entrapment (location) was a rare condition (0.4%). Tissue composition (signal intensities) of the meniscoids was 61.6% mainly fatty, 15.8% mainly fibrous, and 22.6% mixed. CONCLUSION: Basic data about in vivo MR imaging properties of cervical meniscoids in a healthy population have been successfully generated. Subsequent studies may use these data as reference for the identification of meniscoid pathologies.

Proton magnetic resonance spectroscopy in pituitary macroadenomas: preliminary results.

OBJECT: The aim of this study was to correlate proton MR (1H-MR) spectroscopy data with histopathological and surgical findings of proliferation and hemorrhage in pituitary macroadenomas. METHODS: Quantitative 1H-MR spectroscopy was performed on a 1.5-T unit in 37 patients with pituitary macroadenomas. A point-resolved spectroscopy sequence (TR 2000 msec, TE 135 msec) with 128 averages and chemical shift selective pulses for water suppression was used. Voxel dimensions were adapted to ensure that the volume of interest was fully located within the lesion and to obtain optimal homogeneity of the magnetic field. In addition, water-unsuppressed spectra (16 averages) were acquired from the same volume of interest for eddy current correction, absolute quantification of metabolite signals, and determination of full width at half maximum of the unsuppressed water peak (FWHM water). Metabolite concentrations of choline-containing compounds (Cho) were computed using the LCModel program and correlated with MIB-1 as a proliferative cell index from a tissue specimen. RESULTS: In 16 patients harboring macroadenomas without hemorrhage, there was a strong positive linear correlation between metabolite concentrations of Cho and the MIB-1 proliferative cell index (R = 0.819, p < 0.001). The metabolite concentrations of Cho ranged from 1.8 to 5.2 mM, and the FWHM water was 4.4-11.7 Hz. Eleven patients had a hemorrhagic adenoma and showed no assignable metabolite concentration of Cho, and the FWHM water was 13.4-24.4 Hz. In 10 patients the size of the lesion was too small (< 20 mm in 2 directions) for the acquisition of MR spectroscopy data. CONCLUSIONS: Quantitative 1H-MR spectroscopy provided important information on the proliferative potential and hemorrhaging of pituitary macroadenomas. These data may be useful for noninvasive structural monitoring of pituitary macroadenomas. Differences in the FWHM water could be explained by iron ions of hemosiderin, which lead to worsened homogeneity of the magnetic field.

Metabolic imaging of cerebral gliomas: spatial correlation of changes in O-(2-18F-fluoroethyl)-L-tyrosine PET and proton magnetic resonance spectroscopic imaging.

UNLABELLED: The aim of this study was to determine the spatial correlation of O-(2-(18)F-fluoroethyl)-L-tyrosine ((18)F-FET) uptake and the concentrations of choline (Cho), creatine (Cr), and total N-acetylaspartate (tNAA) determined with proton magnetic resonance spectroscopic imaging ((1)H MRSI) in cerebral gliomas for the multimodal evaluation of metabolic changes. METHODS: (18)F-FET PET and 2-dimensional (1)H MRSI were performed in 15 patients with cerebral gliomas of World Health Organization (WHO) grades II-IV. PET and (1)H MRSI datasets were coregistered by use of mutual information. On the basis of their levels of (18)F-FET uptake, 4 different areas in a tumor (maximum, strong, moderate, and low (18)F-FET uptake) were defined on PET slices as being congruent with the volume of interest in the (1)H MRSI experiment. (18)F-FET uptake in lesions was evaluated as tumor-to-brain ratios. Metabolite concentrations for Cho, Cr, and tNAA and Cho/tNAA ratios were computed for these 4 areas in the tumor and for the contralateral normal brain. RESULTS: In the area with maximum (18)F-FET uptake, the concentration of tNAA (R= -0.588) and the Cho/tNAA ratio (R=0.945) correlated significantly with (18)F-FET uptake. In the areas with strong and moderate (18)F-FET uptake, only the Cho/tNAA ratios (R=0.811 and R=0.531, respectively) were significantly associated with amino acid transport. At low (18)F-FET uptake, analysis of the correlations of amino acid uptake and metabolite concentrations yielded a significant result only for the concentration of Cr (R=0.626). No correlation was found for metabolite concentrations determined with (1)H MRSI and (18)F-FET uptake in normal brain tissue. Maximum (18)F-FET uptake and the tNAA concentration were significantly different between gliomas of WHO grades II and IV, with P values of 0.032 and 0.016, respectively. CONCLUSION: High (18)F-FET uptake, which is indicative of tumor cell infiltration, associates with neuronal cell loss (tNAA) and changes in ratios between parameters representing membrane proliferation and those of neuronal loss (Cho/tNAA ratio), which can be measured by (1)H MRSI. The significant correlation coefficients detected for Cr in regions with low (18)F-FET uptake suggests an association between the mechanism governing amino acid transport and energy metabolism in areas that are infiltrated by tumor cells to a lesser extent. These findings motivate further research directed at investigating the potential of (1)H MRSI to define tumor boundaries in a manner analogous to that of amino acid PET.

Age-related degradation in the central nervous system: assessment with diffusion-tensor imaging and quantitative fiber tracking.

PURPOSE: To prospectively quantify differences in age-related changes in the diffusivity parameters and fiber characteristics between association, callosal, and projection fibers. MATERIALS AND METHODS: This study was approved by the institutional review board, and informed consent was obtained. Diffusion-tensor imaging data with an isotropic voxel size of 1.9 mm(3) were acquired at 3 T in 38 healthy volunteers (age range, 18-88 years; 18 women). Quantitative fiber tracking was used to calculate fractional anisotropy (FA) and mean diffusivity values, eigenvalues (lambda(1), lambda(2), and lambda(3)), the number of fiber projections, and the number of fiber projections per voxel for three-dimensional reconstructed association, callosal, projection, and total brain fibers. Bivariate linear regression models were used to analyze correlations. Significant differences between correlations were assessed with the Hotelling-Williams test. RESULTS: For FA, the strongest degradation in association fibers and no significant changes in projection fibers were observed. The difference in correlation was significant (P = .002). The number of fiber projections and the number of fiber projections per voxel showed strong to moderate negative correlations that were dependent on age (P < .001) in the three fiber structures and total brain fibers, with the exception of the number of fiber projections per voxel in projection fibers, which showed no significant correlation. The decrease in the number of fiber projections was significantly greater (P = .043) in projection fibers than in total brain fibers, whereas the decrease in the number of fiber projections per voxel was significantly weaker (P = .005). Association fibers showed the largest changes per decade of age for FA (-1.13%) and for the number of fiber projections per voxel (-4.7%), whereas callosal fibers showed the largest changes per decade of age for the number of fiber projections (-10.4%). CONCLUSION: Quantitative fiber tracking enables identification of differences in diffusivity and fiber characteristics due to normal aging.

Quantitative diffusion tensor fiber tracking of age-related changes in the limbic system.

Cerebral white matter is known to undergo degradation with aging, and diffusion tensor imaging (DTI) is capable of revealing the white matter integrity. We assessed age-related changes of quantitative diffusivity parameters and fiber characteristics within the fornix and the cingulum. Thirty-eight healthy subjects aged 18-88 years were examined at 3 Tesla using a 1.9-mm isotropic DTI sequence. Quantitative fiber tracking was performed for 3D-segmentation of the fornix and the cingulum to determine fractional anisotropy (FA), mean diffusivity (MD), eigenvalues (lambda1, lambda2, and lambda3), number of fibers (NoF), and mean NoF/voxel (FpV). In the fornix, all diffusivity parameters (FA, MD, and eigenvalues) were moderately correlated with age. Strong and moderate negative correlations for NoF and FpV were found, respectively. In the cingulum, no correlation was observed between FA and age, and only weak correlations for the other quantitative parameters. Differences in correlations between the fornix and the cingulum were significant for all diffusivity parameters and for NoF, but not for FpV. The strongest relative changes per decade of age were found in the fornix: FA -2.1%, MD 4.2%, NoF -10.6%, and FpV -4.6%. Our quantitative 3D fiber tracking approach shows that the cingulum is resistant to aging while the fornix is not.

Steady-state diffusion imaging for MR in-vivo evaluation of reparative cartilage after matrix-associated autologous chondrocyte transplantation at 3 tesla--preliminary results.

OBJECTIVES: To demonstrate the feasibility of time-reversed fast imaging with steady-state precession (FISP) called PSIF for diffusion-weighted imaging of cartilage and cartilage transplants in a clinical study. MATERIAL AND METHODS: In a cross-sectional study 15 patients underwent MRI using a 3D partially balanced steady-state gradient echo pulse sequence with and without diffusion weighting at two different time points after matrix-associated autologous cartilage transplantation (MACT). Mean diffusion quotients (signal intensity without diffusion-weighting divided by signal intensity with diffusion weighting) within the cartilage transplants were compared to diffusion quotients found in normal cartilage. RESULTS: The global diffusion quotient found in repair cartilage was significantly higher than diffusion values in normal cartilage (p<0.05). There was a decrease between the earlier and the later time point after surgery. CONCLUSIONS: In-vivo diffusion-weighted imaging based on the PSIF technique is possible. Our preliminary results show follow-up of cartilage transplant maturation in patients may provide additional information to morphological assessment.