Diffusion-tensor magnetic resonance imaging (DT-MRI) offers great potential for understanding structure-function relationships in human skeletal muscles. The purposes of this study were to demonstrate the feasibility of using in vivo human DT-MRI fiber tracking data for making pennation angle measurements and to test the hypothesis that heterogeneity in the orientation of the tibialis anterior (TA) muscle's aponeurosis would lead to heterogeneity in pennation angle. Eight healthy subjects (5 male) were studied. T(1)-weighted anatomical MRI and DT-MRI data were acquired of the TA muscle. Fibers were tracked from the TA's aponeurosis by following the principal eigenvector. The orientations of the aponeurosis and muscle fiber tracts in the laboratory frame of reference and the orientation of the fiber tracts with respect to the aponeurosis [i.e., the pennation angle (theta)] were determined. The muscle fiber orientations, when expressed relative to the laboratory frame of reference, did not change as functions of superior-to-inferior position. The sagittal and coronal orientations of the aponeurosis did not change in practically significant manners either, but the aponeurosis' axial orientation changed by approximately 40 degrees . As a result, the mean value for theta decreased from 16.3 (SD 6.9) to 11.4 degrees (SD 5.0) along the muscle's superior-to-inferior direction. The mean value of theta was greater in the deep than in the superficial compartment. We conclude that pennation angle measurements of human muscle made using DT-MRI muscle fiber tracking are feasible and reveal that in the foot-head direction, there is heterogeneity in the pennation properties of the human TA muscle.

Purpose To evaluate a chemical shift-based fat quantification technique in the rotator cuff muscles in comparison with the semi-quantitative Goutallier fat infiltration classification (GC) and to assess their relationship with clinical parameters. Materials and Methods The shoulders of 57 patients were imaged using a 3T MR scanner. The rotator cuff muscles were assessed for fat infiltration using GC by two radiologists and an orthopedic surgeon. Sequences included oblique-sagittal T1-, T2- and proton density-weighted fast spin echo, and six-echo gradient echo. The iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) was used to measure fat fraction. Pain and range of motion of the shoulder were recorded. Results Fat fraction values were significantly correlated with GC grades (p< 0.0001, kappa>0.9) showing consistent increase with GC grades (grade=0, 0%–5.59%; grade=1, 1.1%–9.70%; grade=2, 6.44%–14.86%; grade=3, 15.25%–17.77%; grade=4, 19.85%–29.63%). A significant correlation between fat infiltration of the subscapularis muscle quantified with IDEAL versus a) deficit in internal rotation (Spearman Rank Correlation Coefficient=0.39, 95% CI 0.13–0.60, p<0.01) and b) pain (Spearman Rank Correlation coefficient=0.313, 95% CI 0.049–0.536, p=0.02) was found but was not seen between the clinical parameters and GC grades. Additionally, only quantitative fat infiltration measures of the supraspinatus muscle were significantly correlated with a deficit in abduction (Spearman Rank Correlation Coefficient=0.45, 95% CI 0.20–0.60, p<0.01). Conclusion We concluded that an accurate and highly reproducible fat quantification in the rotator cuff muscles using water-fat MRI techniques is possible and significantly correlates with shoulder pain and range of motion.

OBJECTIVE To evaluate the longitudinal reproducibility and variations of cartilage T1ρ and T2 measurements using different coils, MR systems and sites. METHODS Single-Site study: Phantom data were collected monthly for up to 29 months on four GE 3T MR systems. Data from phantoms and human subjects were collected on two MR systems using the same model of coil; and were collected on one MR system using two models of coils. Multi-site study: Three participating sites used the same model of MR systems and coils, and identical imaging protocols. Phantom data were collected monthly. Human subjects were scanned and rescanned on the same day at each site. Two traveling human subjects were scanned at all three sites. RESULTS Single-Site Study: The phantom longitudinal RMS-CVs ranged from 1.8% to 2.7% for T1ρ and 1.8% to 2.8% for T2. Significant differences were found in T1ρ and T2 values using different MR systems and coils. Multi-Site Study: The phantom longitudinal RMS-CVs ranged from 1.3% to 2.6% for T1ρ and 1.2% to 2.7% for T2. Across three sites (n=16), the in-vivo scan-rescan RMS-CV was 3.1% and 4.0% for T1ρ and T2, respectively. Phantom T1ρ and T2 values were significantly different between three sites but highly correlated (R>0.99). No significant difference was found in T1ρ and T2 values of traveling controls, with cross-site RMS-CV as 4.9% and 4.4% for T1ρ and T2, respectively. CONCLUSION With careful quality control and cross-calibration, quantitative MRI can be readily applied in multi-site studies and clinical trials for evaluating cartilage degeneration.

Analysis of post-contraction MRI signal intensity (SI) transients may allow noninvasive studies of microvascular reactivity and blood oxygenation recovery. The purpose of this study was to determine the physiological basis for post-contraction changes in short-echo (6 ms) and long-echo (46 ms) gradient-echo (GRE) MRI signals (S 6 and S 46 , respectively). Six healthy subjects were studied with the use of dual GRE MRI and near-infrared spectroscopy (NIRS). As the site of oxygen delivery and substrate exchange to the peripheral tissues of the body, the microcirculation has important roles in maintaining the health and function of these tissues. Because the microcirculation adapts positively to exercise training (1) and is pathologically altered in various diseases, such as diabetes (2), it is important to assess microcirculatory function in order to understand normal, adaptational, and pathological physiology. In particular there is a need for noninvasive protocols to examine microvascular function during and after a challenge, such as isometric muscle contractions.Elevated intramuscular pressure during isometric contractions compresses the vessels of the microcirculation along the fascicular lines (3). This compression causes a rapid ejection of venous blood, decreasing the total muscle and limb volumes (4), and restricts arterial inflow to the muscle for those portions of the cardiac cycle in which the intramuscular pressure exceeds the blood's hydrostatic pressure (5). Following the contraction, local, rapid increases in blood flow and volume occur in order to resupply the tissue with the oxygen that was consumed by the muscle. This reactive hyperemia has been shown to be inversely related to the degree of mechanical occlusion, and directly related to the metabolic regulators of vasodilation that are released in the tissue (6).One noninvasive technique for examining hemodynamic events in the microcirculation is near-infrared spectroscopy (NIRS), which exploits the relative ease of nearinfrared light transmission through tissues and the differential absorption of this light by oxyhemoglobin (HbO 2 ) and deoxyhemoglobin (HHb). Although one must consider the confounding influences of subcutaneous fat thickness (7,8) and the similar absorption spectrum of myoglobin when interpreting NIRS data, this technique is generally quite useful for following the changes in total hemoglobin concentration ([THb]) and HbO 2 saturation (%HbO 2 ) during and after exercise or other physiologic events. The depth of light penetration for NIRS is generally considered to be about half of the light emitter-detector spacing (9), and is about 2 cm for most NIRS devices. This depth is a limitation when perfusion or oxygen extraction heterogeneity is present (as previously demonstrated in healthy subjects (10 -12) and peripheral vascular disease patients (13)), when deep muscles are activated, and when there is an appreciable subcutaneous fat layer thickness.Functional MRI (fMRI) methods can overcome the depth-sampling limitations of NIRS. ...

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Altered knee kinematics following ACL reconstruction may predispose patients to the development of early onset posttraumatic osteoarthritis. The goal of our study was to examine the longitudinal interrelationship between altered tibial position relative to the femur and cartilage health measured by quantitative T 1r MRI. Twenty-five patients with isolated unilateral ACL injury underwent kinematic and cartilage T 1r MRI at baseline prior to ACL reconstruction and then at 1-year post-reconstruction. Tibial position relative to the femur in the anterior-posterior plane was calculated as well as cartilage T 1r relaxation values in the injured and uninjured knee. At baseline prior to ACL reconstruction, the tibia was in a significantly more anterior position relative to the femur in the ACL deficient knee compared to the healthy contralateral knee. This difference was no longer present at 1-year follow-up. Additionally, the side-side difference in tibial position correlated to increased cartilage Keywords: ACL injury; post-traumatic osteoarthritis; knee kinematics; quantitative imaging Anterior cruciate ligament injuries are one of the most common ligamentous injuries of the knee, sustained by roughly 1 in 3,000 people per year in the United States.1 Mostly affecting a young and healthy population, ACL injury leads to pain and instability and can predispose the patient to secondary damage to other structures in the knee such as cartilage and the meniscus. 2,3 Previous studies have demonstrated that on average, 50% of patients will have radiological evidence of osteoarthritis 10-15 years following initial ACL injury.2 Additionally, patients with post-traumatic osteoarthritis are on average 15-20 years younger than patients with primary degenerative osteoarthritis. 4 Although the cause of this early onset post-traumatic osteoarthritis is not completely understood, altered knee kinematics following ACL injury and reconstruction may play a role in its development. Many different methods, including gait analysis, dual-plane fluoroscopy, and magnetic resonance (MR)-based kinematics, have been utilized to study kinematics in the ACL deficient and reconstructed knee.5-8 While ACL reconstruction has been shown to correct knee laxity, studies have demonstrated that tibiofemoral mechanics, such as tibial position, anterior tibial translation, and internal tibial rotation are not restored following ACL reconstruction. 9-11Recent advancements in quantitative magnetic resonance imaging (MRI) provide the ability to reliably detect changes in cartilage structure and health far before radiographic evidence of cartilage damage occurs. 12-14Previous work has demonstrated that T 1r is correlated to the concentration of proteoglycan in the cartilage matrix in histological analysis of bovine 14,15 and human cartilage specimens. 16,17 In vivo work has also shown that T 1r values increase in animal models with cartilage damage, 18 as well in human subjects with osteoarthritis. 12,13,[19][20][21][22][23] In addition to these cross-...

Based on the findings of this systematic review that emphasize biomechanical properties of ACL allografts, surgeons should favor the use of central third patellar tendon or looped soft tissue grafts, maximize graft cross-sectional area, and favor grafts from donors younger than 40 years of age while avoiding grafts subjected to radiation doses > 20 kGy, chemical processing, or greater than eight freeze-thaw cycles.

Objective. To analyze region-specific T1r and T2 relaxation times of the hip joint cartilage in relation to presence or absence of radiographic hip osteoarthritis (OA) and presence or absence of magnetic resonance imaging (MRI)-detected cartilage defects.Methods. Weight-bearing radiographs and 3T MRI studies of the hip were obtained from 84 volunteers. Based on Kellgren/Lawrence (K/L) scoring of the radiographs, 54 subjects were classified as healthy controls (K/L grade £1) and 30 were classified as having mild or moderate radiographic hip OA (K/L grades 2 or 3, respectively). Two-dimensional fat-suppressed fast spin-echo MRI sequences were used for semiquantitative clinical scoring of cartilage defects, and a T1r/T2 sequence was used to quantitatively assess the cartilage matrix. The femoral and acetabular cartilage was then segmented into 8 regions and the mean T1r/T2 values were calculated. Differences in T1r and T2 relaxation times were compared between subjects with and those without radiographic hip OA, and those with and those without femoral or acetabular cartilage defects.Results. Higher T1r and T2 relaxation times in the anterior superior and central regions of the acetabular cartilage were seen in individuals with radiographic hip OA and those with acetabular cartilage defects compared to their respective controls (P < 0.05). In the femoral cartilage, the differences in T1r and T2 were not significant for any of the comparisons. Significant differences in the T1r and T2 values (each P < 0.05) were found in more subregions of the cartilage and across the whole cartilage when subjects were stratified based on the presence of MRI-detected cartilage defects than when they were stratified based on the presence of radiographic hip OA.Conclusion. T1r and T2 relaxation parameters are sensitive to the presence of cartilage degeneration. Both parameters may therefore support MRI evidence of cartilage defects of the hip.One in 4 individuals has a lifetime risk of developing symptomatic hip osteoarthritis (OA) by the age of 85 years (1). Individuals with hip OA experience substantial pain and disability, suggesting an urgent clinical need for diagnosis and prevention of hip OA (2,3). Hip OA is typically diagnosed through the use of radiographs, and semiquantitative clinical scores, such as the Kellgren/Lawrence (K/L) scores for radiographic damage (4), are used to quantify the severity of OA. However, diagnosis of OA with the use of radiographs is mostly focused on osteophytes and joint space narrowing, features that are indicative of advanced disease, whereas radiography lacks sensitivity for early changes of the soft tissues, such as cartilage and labrum. Magnetic resonance imaging (MRI) can provide information on hip degeneration at an earlier stage, by allowing visualization of morphologic abnormalities of the cartilage, bone marrow, and labrum (5-8).Early changes in OA consist of proteoglycan loss, changes in water content, and collagen disruption (9).