MR imaging and T2 mapping of femoral cartilage: In vivo determination of the magic angle effect

T. J. Mosher, H. Smith, B. J. Dardzinski, V. J. Schmithorst, M. B. Smith

Research output: Contribution to journalArticlepeer-review

216 Scopus citations


OBJECTIVE. The purpose of this study was to perform a quantitative evaluation of the effect of static magnetic field orientation on cartilage transverse (T2) relaxation time in the intact living joint and to determine the magnitude of the magic angle effect on in vivo femoral cartilage. MATERIALS AND METHODS. Quantitative T2 maps of the femoral-tibial joint were obtained in eight asymptomatic male volunteers using a 3-T magnet. Cartilage T2 profiles (T2 vs normalized distance from subchondral bone) were evaluated as a function of orientation of the radial zone of cartilage with the applied static magnetic field (B0). RESULTS. At a normalized distance of 0.3 from bone, cartilage T2 is 8.6% longer in cartilage oriented 55° to B0 compared with cartilage oriented parallel with B0. Greater orientation variation is observed in more superficial cartilage. At a normalized distance of 0.6, cartilage T2 is 18.3% longer. The greatest orientation effect is observed near the articular surface where T2 is 29.1% longer at 55°. CONCLUSION. The effect of orientation on cartilage T2 is substantially less than that predicted from prior ex vivo studies. The greatest variation in cartilage T2 is observed in the superficial 20% of cartilage. Given the small orientation effect, it is unlikely that the "magic angle effect" accounts for regional differences in cartilage signal intensity observed in clinical imaging. We hypothesize that regional differences in the degree of cartilage compression are primarily responsible for the observed regional differences in cartilage T2.

Original languageEnglish (US)
Pages (from-to)665-669
Number of pages5
JournalAmerican Journal of Roentgenology
Issue number3
StatePublished - 2001

All Science Journal Classification (ASJC) codes

  • Radiology Nuclear Medicine and imaging


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