Sarcopenia-defined as significant loss of muscle-is associated with cachexia and frailty. Specific diagnostic criteria for sarcopenia continue to evolve, but imaging can play a role in the detection and quantification of muscle depletion. Emerging evidence indicates that sarcopenia is a relevant predictor of quality and quantity of life, particularly in patients who are elderly, have cancer, or undergo surgery.

Seventy-nine magnetic resonance (MR) studies of the knee were reviewed in an evaluation of the ability of MR imaging to demonstrate arthroscopically proved anterior cruciate ligament (ACL) tears. MR findings were also compared with the findings of two commonly applied clinical tests of ACL instability: the Lachman test and the anterior drawer test. The sensitivity of MR imaging was 94% (17 of 18), compared with 78% (14 of 18) for the anterior drawer test and 89% (16 of 18) for the Lachman test. The specificity was 100% for all three. Three MR criteria were applied: irregularity or a wavy contour of the anterior margin of the ligament, high-signal-intensity change within the substance of the ligament on T2-weighted images, and discontinuity of that substance. The sagittal T2-weighted image was especially helpful, producing an "arthrographic" effect, in which the anterior margin of the ACL is outlined by high-signal-intensity joint fluid. By demonstrating ACL and other extrameniscal lesions, MR imaging may help clarify the mechanisms of knee injury.

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The purpose of this study was to determine the accuracy of radiographic and magnetic resonance imaging techniques in preoperative sizing for allograft meniscus transplantation. Twelve cadaveric knee specimens underwent sequential radiographs, magnetic resonance imaging scans, and arthrotomy. Meniscus dimensions were measured in multiple planes for the purpose of determining accuracy of imaging studies in comparison with actual meniscus dimensions. Overall, magnetic resonance imaging proved only slightly more accurate than conventional radiography. The mean difference between magnetic resonance imaging measurements and actual meniscus dimensions was 2.25 +/- 2.04 mm. The mean difference between radiographic measurements and actual meniscus dimensions was 2.35 +/- 1.79 mm. Neither imaging technique was accurate for measuring individual meniscus dimensions, with only 35% of images measuring within 2 mm of actual meniscus dimensions. Using less stringent criteria for accuracy (within 5 mm), radiography and magnetic resonance imaging were 79% and 83% reliable, respectively. Failure to obtain true anteroposterior or lateral images (15 degrees of external and internal rotation) increased measurement inaccuracy. Intraobserver agreement was significantly higher for magnetic resonance imaging than for radiography. Further research into the development of alternative techniques for more reliable meniscus sizing and better understanding of the tolerance for meniscus size mismatch is necessary.

Purpose: To investigate a tetrahedral diffusion gradient encoding scheme to measure the diffusion tensor in vivo for human calf muscle. Materials and Methods:The theoretical TE which maximizes the signal-to-noise ratio (SNR) of the diffusion images was derived for both the orthogonal and tetrahedral sampling strategies and the SNR advantage verified experimentally. A diffusion echo-planar imaging (EPI) sequence was used to image five volunteers. Gradient cycling and geometric averaging was performed to eliminate cross-terms between the imaging and diffusion gradients.Results: Trace diffusion coefficients in human muscle are spatially invariant and have low intersubject variability (Ͻ4%). Images of the off-diagonal terms confirm the anisotropy of muscle, and fiber orientation maps were derived from these off-diagonal images. A noninvariant index of anisotropy, A ratio (average value: 1.28), was found to be less susceptible to noise than the invariant index. Conclusion: