Timothy J. Mosher

Spatial variation in cartilage T2 of the knee

Technical limitations imposed by resolution and B1 homogeneity have thus far limited quantitative in vivo T2 mapping of cartilage to the patella. The purpose of this study is to develop T2 mapping of the femoral/tibial joint and assess regional variability of cartilage T2 in the knee. Quantitative in vivo T2 mapping of the knee was performed on 15 asymptomatic adults (age, 22–44) using a 3T MR scanner. There is a consistent pattern of spatial variation in cartilage T2 with longer values near the articular surface. The greatest variation occurs in the patella, where T2 increases from 45.3 ± 2.5 msec at a normalized distance of 0.33–67 ± 5.5 msec at a distance of 1.0. These results demonstrate feasibility of performing in vivo T2 mapping of femoral tibial cartilage. Except for the superficial 15% where T2 values are lower, the spatial variation in T2 of femoral and tibial cartilage is similar to patellar cartilage. J. Magn. Reson. Imaging 2001;14:50–55.

Articular Cartilage in the Knee: Current MR Imaging Techniques and Applications in Clinical Practice and Research

Magnetic resonance (MR) imaging is the most important imaging modality for the evaluation of traumatic or degenerative cartilaginous lesions in the knee. It is a powerful noninvasive tool for detecting such lesions and monitoring the effects of pharmacologic and surgical therapy. The specific MR imaging techniques used for these purposes can be divided into two broad categories according to their usefulness for morphologic or compositional evaluation. To assess the structure of knee cartilage, standard spin-echo (SE) and gradient-recalled echo (GRE) sequences, fast SE sequences, and three-dimensional SE and GRE sequences are available. These techniques allow the detection of morphologic defects in the articular cartilage of the knee and are commonly used in research for semiquantitative and quantitative assessments of cartilage. To evaluate the collagen network and proteoglycan content in the knee cartilage matrix, compositional assessment techniques such as T2 mapping, delayed gadolinium-enhanced MR imaging of cartilage (or dGEMRIC), T1ρ imaging, sodium imaging, and diffusion-weighted imaging are available. These techniques may be used in various combinations and at various magnetic field strengths in clinical and research settings to improve the characterization of changes in cartilage.

Skeletal muscle metaboreceptor exercise responses are attenuated in heart failure.

Background Resting sympathetic nervous system activity is increased in heart failure. Whether sympathetic nervous system responses during exercise are increased is controversial. Futhermore, the role of muscle metaboreceptors and central command in regulating sympa-thetic outflow has been largely unexplored. Methods and Results Muscle sympathetic nerve activity (MSNA, peroneal nerve) was measured in nine heart failure subjects and eight age-matched control subjects during static exercise (30%o maximal voluntary contraction) for 2 minutes and during a period of posthand-grip regional circulatory arrest. This maneuver isolates the metaboreceptor contribution to sympathetic nervous system responses. MSNA responses were similar during static exercise in the two groups. During posthandgrip regional circulatory arrest we observed a marked attenuation in MSNA responses in the heart failure subjects (15% increase in heart failure versus 57% increase in control subjects). A cold pressor test demonstrated a normal MSNA response to a potent nonspecific stimulus in the heart failure subjects (heart failure subjects, 141% increase; control subjects, 215% increase; NS). Nuclear magnetic resonance spectroscopy studies in five separate heart failure subjects and five control subjects suggested that the attenuated metaboreceptor response in heart failure was not due to reduced H+ production. Conclusions Skeletal muscle metaboreceptor responses are impaired in heart failure. Because MSNA responses during static exercise are similar in the two groups, mechanisms aside from metaboreceptor stimulation must be important in increasing sympathetic nervous system activity.

Measures of Molecular Composition and Structure in Osteoarthritis

Osteoarthritis involves ongoing degradative and healing processes that occur at the molecular level in multiple tissues in the joint in response to a number of biochemical and mechanical factors. Understanding these dynamic processes before they affect the structural aspects of the joint motivates the need for metrics to better visualize the compositional and structural molecular aspects of the tissues in vivo. As reviewed here, most of the work to date in this regard has been focused on magnetic resonance imaging approaches for interrogating molecular features of cartilage, including T2 mapping, T1rho mapping, delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC), and sodium imaging. Specific examples illustrate new opportunities and insights emerging from these methods.

High Prevalence of Pelvic and Hip Magnetic Resonance Imaging Findings in Asymptomatic Collegiate and Professional Hockey Players

Background: Prior retrospective studies have reported magnetic resonance imaging (MRI) findings of common adductor–abdominal rectus enthesopathy and acetabular labral tear in athletes treated for athletic pubalgia and hip pain. The true prevalence of these findings and association with symptoms in this population is unknown. Purpose: This study was undertaken to determine the prevalence of pelvic and hip MRI findings and association with clinical symptoms in professional and collegiate hockey players. Study Design: Cross-sectional study; Level of evidence, 3. Methods: The study included 21 professional and 18 collegiate hockey players. Self-reported symptoms were measured using a modified Oswestry Disability Questionnaire. Participants underwent 3-T MRI evaluation of the pelvis and hips. The MRI scans were interpreted independently by 3 musculoskeletal radiologists in 2 sessions separated by 3 months using a 5-point Likert scale to assess for features associated with common adductor–abdominal rectus dysfunction and hip pathology. To estimate prevalence, MRI findings rated 4 or higher on 4 of the 6 interpretations were considered positive. A variance component analysis was applied to determine intrareader and interreader reliability and the lower 95% confidence limits (CLs). Results: No participants reported symptoms related to pelvic or hip disorders. The MRI findings of common adductor–abdominal rectus dysfunction were observed in 14 of 39 participants (36%) and hip pathologic changes in 25 of 39 (64%). There was moderate agreement between readings, with intrareader and interreader reliabilities ranging from 0.37 to 1.00. The interreader reliability was less for evaluation of hip pathologic abnormalities than for groin pathologic abnormalities, with the lowest reliability observed in reporting of hip osteochondral lesions (0.37 with lower 95% CL of 0.22) and fluid in the primary cleft (0.45 with lower 95% CL of 0.29) and perfect reliability in the absence of effusion and abdominal rectus tendon tears. Overall, 30 of 39 (77%) asymptomatic hockey players demonstrated MRI findings of hip or groin pathologic abnormalities. Conclusion: Given the high prevalence of MRI findings in asymptomatic hockey players, it is necessary to cautiously interpret the significance of these findings in association with clinical presentation. Future investigations will determine whether these asymptomatic findings predict future disabilities.

Hydrogen ion concentration is not the sole determinant of muscle metaboreceptor responses in humans.

We examined the effects of exercise conditioning on muscle sympathetic nerve activity (MSNA) during handgrip and posthandgrip circulatory arrest (PHG-CA). Two conditioning stimuli were studied: forearm dominance and bodybuilding. Static handgrip at 30% maximal voluntary contraction followed by PHG-CA led to a rise in MSNA smaller in dominant than in nondominant forearms (99% vs. 222%; P less than 0.02) and in body builders than in normal volunteers (28% vs. 244%; P less than 0.01). Separate 31P NMR experiments showed no effect of dominance on forearm pH but a pH in bodybuilders higher (6.88) than in normal volunteers (6.79; P less than 0.02) during PHG-CA. Our second goal was to determine if factors besides attenuated [H+] contribute to this conditioning effect. If differences in MSNA during exercise were noted at the same pH, then other mechanisms must contribute to the training effect. We measured MSNA during ischemic fatiguing handgrip. No dominance or bodybuilding effect on pH was noted. However, we noted increases in MSNA smaller in dominant than nondominant forearms (212% vs. 322%; P less than 0.02) and in bodybuilders than in normal volunteers (161% vs. 334%; P less than 0.01). In summary, MSNA responses were less during exercise of conditioned limbs. Factors aside from a lessening of muscle acidosis contribute to this effect.

Functional cartilage MRI T2 mapping: evaluating the effect of age and training on knee cartilage response to running

OBJECTIVE To characterize effects of age and physical activity level on cartilage thickness and T2 response immediately after running. DESIGN Institutional review board approval was obtained and all subjects provided informed consent prior to study participation. Cartilage thickness and magnetic resonance imaging (MRI) T2 values of 22 marathon runners and 15 sedentary controls were compared before and after 30 min of running. Runner and control groups were stratified by age<or=45 and >or=46 years. Multi-echo [(Time to Repetition (TR)/Time to Echo (TE) 1500 ms/9-109 ms)] MR images obtained using a 3.0 T scanner were used to calculate thickness and T2 values from the central femoral and tibial cartilage. Baseline cartilage T2 values, and change in cartilage thickness and T2 values after running were compared between the four groups using one-way analysis of variance (ANOVA). RESULTS After running MRI T2 values decreased in superficial femoral (2 ms-4 ms) and tibial (1 ms-3 ms) cartilage along with a decrease in cartilage thickness: (femoral: 4%-8%, tibial: 0%-12%). Smaller decrease in cartilage T2 values were observed in the middle zone of cartilage, and no change was observed in the deepest layer. There was no difference cartilage deformation or T2 response to running as a function of age or level of physical activity. CONCLUSIONS Running results in a measurable decrease in cartilage thickness and MRI T2 values of superficial cartilage consistent with greater compressibility of the superficial cartilage layer. Age and level of physical activity did not alter the T2 response to running.

MR imaging of cartilage and its repair in the knee - a review

Chondral injuries are common lesions of the knee joint, and many patients could benefit from cartilage repair. Widespread cartilage repair techniques require sophisticated noninvasive follow-up using MRI. In addition to the precise morphological assessment of this area of cartilage repair, the cartilage’s biochemical constitution can be determined using biochemical MRI techniques. The combination of the clinical outcome after cartilage repair together with the morphological and biochemical description of the cartilage repair tissue as well as the surrounding cartilage can lead to an optimal follow-up evaluation. The present article on MR imaging techniques of cartilage repair focuses on morphological description and scoring using techniques from conventional 2D through advanced isotropic 3D MRI sequences. Furthermore the ultrastructure of the repair tissue and the surrounding cartilage is evaluated in-vivo by biochemical T1-delayed gadolinium enhanced MRI of cartilage (dGEMRIC), T2 relaxation, and diffusion-weighted imaging techniques.

Knee Articular Cartilage Damage in Osteoarthritis: Analysis of MR Image Biomarker Reproducibility in ACRIN-PA 4001 Multicenter Trial

PURPOSE To prospectively determine the reproducibility of quantitative magnetic resonance (MR) imaging biomarkers of the morphology and composition (spin lattice relaxation time in rotating frame [T1-ρ], T2) of knee cartilage in a multicenter multivendor trial involving patients with osteoarthritis (OA) and asymptomatic control subjects. MATERIALS AND METHODS This study was HIPAA compliant and approved by the institutional review committees of the participating sites, with written informed consent obtained from all participants. Fifty subjects from five sites who were deemed to have normal knee joints (n = 18), mild OA (n = 16), or moderate OA (n = 16) on the basis of Kellgren-Lawrence scores were enrolled. Each participant underwent four sequential 3-T knee MR imaging examinations with use of the same imager and with 2-63 days (median, 18 days) separating the first and last examinations. Water-excited three-dimensional T1-weighted gradient-echo imaging, T1-ρ imaging, and T2 mapping of cartilage in the axial and coronal planes were performed. Biomarker reproducibility was determined by using intraclass correlation coefficients (ICCs) and root-mean-square coefficients of variation (RMS CVs, expressed as percentages). RESULTS Morphometric biomarkers had high reproducibility, with ICCs of 0.989 or greater and RMS CVs lower than 4%. The largest differences between the healthy subjects and the patients with radiographically detected knee OA were those in T1-ρ values, but precision errors were relatively large. Reproducibility of T1-ρ values was higher in the thicker patellar cartilage (ICC range, 0.86-0.93; RMS CV range, 14%-18%) than in the femorotibial joints (ICC range, 0.20-0.84; RMS CV range, 7%-19%). Good to high reproducibility of T2 was observed, with ICCs ranging from 0.61 to 0.98 and RMS CVs ranging from 4% to 14%. CONCLUSION MR imaging measurements of cartilage morphology, T2, and patellar T1-ρ demonstrated moderate to excellent reproducibility in a clinical trial network.

T2 star relaxation times for assessment of articular cartilage at 3 T: a feasibility study

PurposeT2 mapping techniques use the relaxation constant as an indirect marker of cartilage structure, and the relaxation constant has also been shown to be a sensitive parameter for cartilage evaluation. As a possible additional robust biomarker, T2* relaxation time is a potential, clinically feasible parameter for the biochemical evaluation of articular cartilage.Materials and methodsThe knees of 15 healthy volunteers and 15 patients after microfracture therapy (MFX) were evaluated with a multi-echo spin-echo T2 mapping technique and a multi-echo gradient-echo T2* mapping sequence at 3.0 Tesla MRI. Inline maps, using a log-linear least squares fitting method, were assessed with respect to the zonal dependency of T2 and T2* relaxation for the deep and superficial regions of healthy articular cartilage and cartilage repair tissue.ResultsThere was a statistically significant correlation between T2 and T2* values. Both parameters demonstrated similar spatial dependency, with longer values measured toward the articular surface for healthy articular cartilage. No spatial variation was observed for cartilage repair tissue after MFX.ConclusionsWithin this feasibility study, both T2 and T2* relaxation parameters demonstrated a similar response in the assessment of articular cartilage and cartilage repair tissue. The potential advantages of T2*-mapping of cartilage include faster imaging times and the opportunity for 3D acquisitions, thereby providing greater spatial resolution and complete coverage of the articular surface.