Faculty Bibliography

PURPOSE: : To assess the use of 3-dimensional (3D) MR imaging of the ankle with the 3D-turbo-spin-echo-sequence 3D-"Sampling Perfection with Application optimized Contrast using different flip angle Evolutions" (SPACE), as compared with 2-dimensional-turbo-spin-echo-sequence. MATERIAL AND METHODS: : After internal review board's approval and informed consent, 15 healthy volunteers and 45 consecutive patients were examined at 3 T with isotropic fat-saturated moderately T2-weighted 3D-SPACE (voxel size: 0.6 mm/acquisition time: 6:43 minutes) featuring radial k-space reordering for optimized contrast. Signal- and contrast-to-noise ratios (SNR; CNR, respectively) were calculated with the subtraction method. Using free 3D reconstructions, 2 radiologists independently assessed depiction of cartilage, ligaments, and tendons, as well as detection and grading of abnormalities of these structures (5-point Likert scale) compared with conventional 2-dimensional-TSE-sequences (voxel size: 0.4 x 0.4 x 3 mm/total acquisition time: 11 minutes). Statistical analysis was performed with Wilcoxon signed rank tests, 95% and 99% confidence intervals and weighted kappa coefficients. RESULTS: : SNR and CNR of fluid/cartilage were significantly higher for 3D-SPACE (P < 0.05). The isotropic voxel size facilitated improved depiction of the medial and lateral ankle ligaments with significant differences for the calcaneofibular ligament and the anteromedial ligament complex (P < 0.05). In the patient cohort, cartilage and spring ligaments were also significantly better depicted (P < 0.05). However, there were no significant differences in the number or in the diagnostic confidence of detected cartilage, ligament, or tendon abnormalities. Interreader correlation was good (kappa = 0.69-0.71) for both sequences. The correlation between the 2 sequences was excellent (kappa = 0.84-0.85). CONCLUSION: : 3D-SPACE allows 3D acquisition and assessment of the ankle and facilitates depiction of the complex ankle anatomy at sufficient SNR and CNR.

Purpose:To investigate technical feasibility, test-retest reproducibility, and the ability to differentiate healthy subjects from subjects with osteoarthritis (OA) with diffusion-tensor (DT) imaging parameters and T2 relaxation time.Materials and Methods:This study was approved by the institutional review board and was HIPAA compliant. All subjects provided written informed consent. DT imaging parameters and T2 (resolution = 0.6 x 0.6 x 2 mm) of patellar cartilage were measured at 7.0 T in 16 healthy volunteers and 10 patients with OA with subtle inhomogeneous signal intensity but no signs of cartilage erosion at clinical magnetic resonance (MR) imaging. Ten volunteers were imaged twice to determine test-retest reproducibility. After cartilage segmentation, maps of mean apparent diffusion coefficient (ADC), fractional anisotropy (FA), and T2 relaxation time were calculated. Differences for ADC, FA, and T2 between the healthy and OA populations were assessed with nonparametric tests. The ability of each MR imaging parameter to help discriminate healthy subjects from subjects with OA was assessed by using receiver operating characteristic curve analysis.Results:Test-retest reproducibility was better than 10% for mean ADC (8.1%), FA (9.7%), and T2 (5.9%). Mean ADC and FA differed significantly (P < .01) between the OA and healthy populations, but T2 did not. For ADC, the optimal threshold to differentiate both populations was 1.2 x 10(-3) mm(2)/sec, achieving specificity of 1.0 (16 of 16) and sensitivity of 0.80 (eight of 10). For FA, the optimal threshold was 0.25, yielding specificity of 0.88 (14 of 16) and sensitivity of 0.80 (eight of 10). T2 showed poor differentiation between groups (optimal threshold = 22.9 msec, specificity = 0.69 [11 of 16], sensitivity = 0.60 [six of 10]).Conclusion:In vivo DT imaging of patellar cartilage is feasible, has good test-retest reproducibility, and may be accurate in discriminating healthy subjects from subjects with OA. ADC and FA are two promising biomarkers for early OA.(c) RSNA, 2011

PURPOSE: The purpose of this study was to analyze potential quantitative and qualitative changes of the knee cartilage and joint indicative of early posttraumatic OA 4 years after ACL-reconstruction and to correlate the MRI-findings with the clinical outcome (CO). MATERIALS AND METHODS: 1.5 T MRI-scans were performed on 9 patients post-op and 4 years later. Using a high-resolution T 1-w-fs-FLASH-3D-sequence cartilage volume (cVol) and thickness (mTh) were quantified. Using standard PD-w fs and T 1-w sequences qualitative changes of the joint structures were analyzed based on the WORMS-score. CO was rated by an orthopaedic surgeon using Lysholm-score, OAK-score, Tegner-activity-score (TAS), and Arthrometer KT-1000 testing. RESULTS: Mean changes of cVol were -1.8 % (range: -5.9 %; + 0.7 %) and of mTh -0.8 % (range: -3.0 %; + 1.1 %). No significant change (95 %-CI) could be identified for any compartment. Three patients developed new peripatellar ostheophytes, acute trauma related changes mostly decreased. Mean outcome of Lysholm-score and OAK-score were 90 pts and 86 pts, mean TAS was 4.3 pts. Average maximum tibial translation reached 5.2 mm comparing to 6.7 mm on the healthy contralateral side. CONCLUSION: Despite a tendency towards decreased cVol and mTh 4 years after ACL-reconstruction qMRI revealed no significant cartilage loss. Newly developing osteophytes did not match with the observed good CO. This small pilot study motivates future quantitative and qualitative-structural MRI-based assessment of articular cartilage and other joint structures in order to improve diagnostic tools for the detection of early OA

PURPOSE/OBJECTIVE:The discoid meniscus is a common meniscal anomaly. Symptomatic discoid menisci treated by arthroscopic surgery were examined preoperatively and postoperatively by magnetic resonance imaging (MRI). Aim of this study was to quantify the amount of meniscal resection when treating discoid meniscus in children by partial meniscectomy. The hypothesis was that partial meniscectomy left sufficient amounts of meniscal tissue. METHODS:A quantitative evaluation of meniscal size comparing preoperative and postoperative data after partial meniscectomy was performed by MRI (n = 6). The anteroposterior meniscal diameter and anterior and posterior thickness were measured. The relative postoperative thickness to preoperative thickness was defined. All patients were graded according to Lysholm score and Ikeuchi knee scale. RESULTS:The quantitative MRI evaluation showed a pronounced reduction of the anteroposterior meniscal diameter (42%) and anterior thickness (41%) after partial meniscectomy, whereas the posterior thickness showed a mean increase of 50%. According to Ikeuchi, all clinical postoperative findings were excellent and displayed an increase in Lysholm score. CONCLUSIONS:MRI findings showed that the amount of remaining tissue after partial meniscectomy was smaller than aspired. Especially in the anterior joint, the final size of remaining meniscal tissue was overestimated intraoperatively. It may be concluded that in arthroscopic partial meniscectomy, the final meniscal size, especially in the anterior part of the joint, is difficult to assess. As it is known that the extent of meniscal resection plays a crucial role in the clinical course of discoid menisci, these data claim retentiveness in resecting meniscal tissue.

PURPOSE: The posterior tibial slope has a huge influence on the kinematics of the knee. In several orthopedic interventions such as high tibial osteotomy and unicondylar or bicondylar knee replacement changing, the tibial slope can result in altered knee mechanics. Therefore, an exact preoperative measurement of the posterior tibial slope is mandatory. Several methods are used on conventional radiographs and CT scans, but until now there is no standard validated method. The aim of this study was to compare several methods and imaging techniques to measure the posterior tibial slope and to establish a standard and reliable measurement method by radiography. METHODS: Fourteen knees (seven cadavers) were scanned by a 64-slice CT, a 3T-MRI, and true lateral radiographs were performed. The anatomical references (TPAA = tibial proximal anatomical axis; ATC = anterior tibial cortex; PTC = posterior tibial cortex) and the new computed reference (MPA = mean of PTA and ATC) were compared by short as well as long radiographs, CT scan and MRI. The influence of a malrotation in radiographs of the knees was also analyzed. RESULTS: CT scan and MRI are suitable for the measurement of the medial and lateral posterior tibial slopes, the results of the radiographs varied depending on the method used. The new method (MPA) showed the best correlation to the CT scan (r = 0.997), even on short radiographs (10 cm distal the joint line). CONCLUSION: The measurement of the posterior tibial slope on a short lateral radiograph using the MPA is a reliable method and should be established as a standard. LEVEL OF EVIDENCE: Diagnostic study, Level II

PURPOSE: To measure the systematic error in perfusion and filtration parameters derived from magnetic resonance (MR) renography caused by protein binding of MR contrast agents. MATERIALS AND METHODS: Eight healthy Danish Landrace pigs were examined with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). In four pigs a bolus of gadopentetate-dimeglumine (Gd-DTPA; no protein binding) was injected, followed by gadobenate-dimeglumine (Gd-BOPTA; 10% protein binding). The order was reversed in the other four pigs. A two-compartment filtration model was generalized to allow for protein binding and fitted to whole-cortex region of interest (ROI) curves. Single-kidney plasma flow and volume, tubular flow (or GFR), and tubular transit time of both agents were compared. RESULTS: The data show a strong systematic underestimation (P < 0.001) in GFR by Gd-BOPTA (33 +/- 7.2%), and no significant differences (P > 0.05) in plasma flow (2.2 +/- 18%), plasma volume (-1.7 +/- 7.8%) and tubular transit time (3.1 +/- 7.2%). The order of injection had no significant effect. CONCLUSION: Theory and experiments agree that perfusion parameters of both agents are comparable, whereas GFR is underestimated with Gd-BOPTA due to the dependence of relaxivity on protein content. Hence, GFR cannot be measured with protein-bound contrast agents, but the proposed dual-agent protocol may produce new functional indices measuring protein filtration.

Early detection of cartilage degeneration in the hip may help prevent onset and progression of osteoarthritis in young patients with femoroacetabular impingement. Delayed gadolinium-enhanced MRI of cartilage is sensitive to cartilage glycosaminoglycan loss and could serve as a diagnostic tool for early cartilage degeneration. We propose a new high resolution 2D T(1) mapping saturation-recovery pulse sequence with fast spin echo readout for delayed gadolinium-enhanced magnetic resonance imaging of cartilage of the hip at 3 T. The proposed sequence was validated in a phantom and in 10 hips, using radial imaging planes, against a rigorous multipoint saturation-recovery pulse sequence with fast spin echo readout. T(1) measurements by the two pulse sequences were strongly correlated (R(2) > 0.95) and in excellent agreement (mean difference = -8.7 ms; upper and lower 95% limits of agreement = 64.5 and -81.9 ms, respectively). T(1) measurements were insensitive to B(1+) variation as large as 20%, making the proposed T(1) mapping technique suitable for 3 T. Magn Reson Med, 2011. (c) 2011 Wiley-Liss, Inc

OBJECT: To investigate the relationship of the different diffusion tensor imaging (DTI) parameters (ADC, FA, and first eigenvector (EV)) to the constituents (proteoglycans and collagen), the zonal arrangement of the collagen network, and mechanical loading of articular cartilage. MATERIAL AND METHODS: DTI of eight cartilage-on-bone samples of healthy human patellar cartilage was performed at 17.6 T. Three samples were additionally imaged under indentation loading. After DTI, samples underwent biomechanical testing, safranin-O staining for semiquantitative proteoglycan estimation, and scanning electron microscopy (SEM) for depicting collagen architecture. RESULTS: From the articular surface to the bone-cartilage interface, ADC continuously decreased and FA increased. Cartilage zonal heights calculated from EVs strongly correlated with SEM-derived zonal heights (P < 0.01, r (2)=0.87). Compression reduced ADC in the superficial 30% of cartilage and increased FA in the superficial 5% of cartilage. Reorientation of the EVs indicative of collagen fiber reorientation under the indenter was observed. No significant correlation was found between ADC, FA, and compressive stiffness. CONCLUSIONS: Correlating ADC and FA with proteoglycan and collagen content suggests that diffusion is dominated by different depth-dependent mechanisms within cartilage. Knowledge of the spatial distribution of the DTI parameters and their variation contributes to form a database for future analysis of defective cartilage

Orthopedic surgeons have multiple options available to treat articular cartilage lesions, including microfracture, osteochondral autografting, and autologous chondrocyte implantation. By having basic knowledge of these surgical procedures, radiologists can more accurately interpret imaging studies obtained after surgery. In this article, we briefly review the different types of cartilage repair procedures, their appearance on magnetic resonance imaging (MRI), and pathologic MRI findings associated with postoperative complications. We also briefly discuss advanced MRI techniques (T2 mapping, delayed gadolinium-enhanced MRI of cartilage, sodium MRI) that have been recently used to assess the biochemical composition of repair tissue matrix. MRI can accurately assess the status and health of cartilage repair tissue. By providing this information to orthopedic surgeons, radiologists can play a valuable role in the management of patients who undergo cartilage repair surgery

OBJECTIVE:: To investigate changes of diffusion tensor imaging (DTI) parameters (mean apparent diffusion coefficient [ADC], fractional anisotropy [FA], and first eigenvector) with increasing proteoglycan (PG) extraction of articular cartilage. MATERIAL AND METHODS:: Twelve cylindrical cartilage-on-bone samples were drilled from 4 human patellae (3 per patella). Each sample was divided into 2 pieces. One piece underwent histologic examination to assess the PG content of the native sample by safranin-O staining and its collagen architecture by polarized light microscopy. The other underwent magnetic resonance imaging (MRI) at 17.6 T for DTI measurement. After MRI, 2 of the 3 samples from each patella were immersed in a dilute trypsin solution (0.1 mg/mL), whereas the third sample was kept as a negative control in physiological saline. After incubation (6, 48, 72, and 96 hours), the samples were reimaged, stained for PG content and for the collagen orientation. Maps of ADC, FA, and the orientation of the first eigenvector as well as histology were available for each sample before and after incubation. RESULTS:: PG loss led to increased ADC and reduced safranin-O staining from the articular surface to the bone-cartilage interface. A significant correlation (r = 0.86, P < 0.01) was observed between the change in bulk ADC and PG loss. Regional analysis from the articular surface to the tide mark demonstrated depth dependent significant correlations of ADC and PG loss. FA and first eigenvector as well as polarized light microscopy showed only small changes in the order of magnitude of measurement errors, not correlating with PG loss. CONCLUSION:: Mean diffusivity evidence by the ADC is linearly correlated to progressive PG extraction in articular cartilage. FA and the first eigenvector seem to be specific to the collagen architecture of cartilage. DTI has the potential to become a valuable biomarker for the workup of cartilage degeneration in osteoarthritis, since evaluation of the PG content and collagen architectural properties of cartilage can be performed with a single, non-contrast-enhanced proton-based MRI measurement