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Volumetric Cartilage Measurements of Porcine Knee at 1.5-T and 3.0-T MR Imaging: Evaluation of Precision and Accuracy¹

¹ From Musculoskeletal and Quantitative Imaging Research, Department of Radiology, University of California, San Francisco, Calif. Received August 9, 2005; revision requested October 17; revision received November 4; accepted December 1; final version accepted February 6, 2006. Supported by National Institutes of Health grants AR46905 and AG17762. Address correspondence to J.S.B., Institut für Röntgendiagnostik, Technische Universität München, Ismaninger Strasse 22, 81675 München, Germany (e-mail: jsb{at}roe.med.tum.de).

Purpose: To compare the precision and accuracy of 3.0-T and 1.5-T magnetic resonance (MR) imaging in the quantification of cartilage volume by using direct volumetric measurements as a reference standard.

Materials and Methods: The local animal experimentation committee did not require its approval for this study. Porcine knees were obtained from an abattoir. These specimens were used to optimize imaging parameters regarding effective signal-to-noise ratio (SNR_E) and contrast-to-noise ratio (CNR_E) for a fat-saturated spoiled gradient-recalled acquisition in the steady state (SPGR) sequence, a water excitation SPGR sequence, and a fast spin-echo sequence at 3.0 T and a fat-saturated SPGR sequence at 1.5 T. By using the optimized sequences, 18 specimens were imaged in less than 6 minutes per sequence. A fivefold repetition of measurements of four specimens was performed for precision analysis. Cartilage was segmented by using semiautomatic software to calculate the volume. After imaging, the cartilage was scraped off and the volume was measured directly by using a saline-displacement method to calculate accuracy. Precision and accuracy errors were calculated as the root-mean-squares of the single errors per specimen.

Results: SNR_E and CNR_E values, respectively, were highest for the water excitation sequence at 3.0 T (1.81 sec^–1/2 and 1.27 sec^–1/2), followed by the fat-saturated SPGR sequence (1.52 sec^–1/2 and 1.07 sec^–1/2). The fast spin-echo sequence and the fat-saturated SPGR sequence at 1.5 T had lower SNR_E (1.27 sec^–1/2 and 0.59 sec^–1/2, respectively). Accuracy error for MR-based volume calculation at the femur was 5.0%, 3.0%, 21%, and 16% for the water excitation, fat-saturated SPGR, and fast spin-echo sequences at 3.0 T and the fat-saturated SPGR sequence at 1.5 T, respectively.

Conclusion: MR imaging at 3.0 T was shown in our study to better quantify cartilage volume. SNR_E and CNR_E were substantially improved, resulting in significantly higher accuracy in determining cartilage volume.

© RSNA, 2006

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