Erich Salomonowitz

Three‐dimensional delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) for in vivo evaluation of reparative cartilage after matrix‐associated autologous chondrocyte transplantation at 3.0T: Preliminary results

To use a 3D gradient‐echo (GRE) sequence with two flip angles for delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) to evaluate relative glycosaminoglycan content of repair tissue after matrix‐associated autologous chondrocyte transplantation (MACT).

The intravertebral vacuum phenomenon.

An intravertebral vacuum phenomenon was observed within 19 vertebrae of 17 patients. It represents a non-healing vertebral fracture. Three possible pathologic mechanisms are discussed: ischemic bone necrosis, trauma with ensuing ischemic necrosis, and intraosseous disc prolapse. The intravertebral vacuum phenomenon was found in two patients with multiple myeloma and thus does not exclude the presence of malignancy in the affected bone. Radiographs obtained during traction or extension may be of diagnostic value.

Diffusion tensor imaging and optimized fiber tracking in glioma patients: Histopathologic evaluation of tumor-invaded white matter structures

Fiber tracking is increasingly used to plan and guide neurosurgical procedures of intracranial tumors in the vicinity of functionally important areas of the brain. However, valid data concerning the reliability of tracking with respect to the actual pathoanatomical situation are lacking. We retrospectively correlated fiber tracking based on magnetic resonance (MR) DT imaging with the histopathological data of 25 patients with WHO grade II and III gliomas. Fiber tracking using the Fiber Assignment by Continuous Tracking (FACT) method was performed to investigate the integrity of white matter tracts in the surrounding border zone of the lesions. The tracking procedure was stopped when fractional anisotropy (FA) thresholds = 0.1, 0.15, 0.2, 0.25, and 0.3, or a tract turning angle >60 degrees were encountered. In 9 patients we were able to reconstruct brain fiber tracts at biopsy loci (2-32% tumor infiltration) using an FA threshold of 0.15 and 0.2, but not for a threshold of 0.25 or 0.3. The neurological outcome demonstrated potential tumor cell infiltration of functionally intact brain fiber tracts in the range of 2-8%. These findings may be useful in planning therapeutic approaches to gliomas in the vicinity of eloquent brain regions.

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 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.

Metabolic Imaging of Cerebral Gliomas: Spatial Correlation of Changes in O-(2-18F-Fluoroethyl)-l-Tyrosine PET and Proton Magnetic Resonance Spectroscopic Imaging

The aim of this study was to determine the spatial correlation of O-(2-18F-fluoroethyl)-l-tyrosine (18F-FET) uptake and the concentrations of choline (Cho), creatine (Cr), and total N-acetylaspartate (tNAA) determined with proton magnetic resonance spectroscopic imaging (1H MRSI) in cerebral gliomas for the multimodal evaluation of metabolic changes. Methods: 18F-FET PET and 2-dimensional 1H MRSI were performed in 15 patients with cerebral gliomas of World Health Organization (WHO) grades II–IV. PET and 1H MRSI datasets were coregistered by use of mutual information. On the basis of their levels of 18F-FET uptake, 4 different areas in a tumor (maximum, strong, moderate, and low 18F-FET uptake) were defined on PET slices as being congruent with the volume of interest in the 1H MRSI experiment. 18F-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 18F-FET uptake, the concentration of tNAA (R = −0.588) and the Cho/tNAA ratio (R = 0.945) correlated significantly with 18F-FET uptake. In the areas with strong and moderate 18F-FET uptake, only the Cho/tNAA ratios (R = 0.811 and R = 0.531, respectively) were significantly associated with amino acid transport. At low 18F-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 1H MRSI and 18F-FET uptake in normal brain tissue. Maximum 18F-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 18F-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 1H MRSI. The significant correlation coefficients detected for Cr in regions with low 18F-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 1H MRSI to define tumor boundaries in a manner analogous to that of amino acid PET.

High-resolution cartilage imaging of the knee at 3 T: 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.

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.

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.