Combined T1‐T2 mapping of human femoro‐tibial cartilage with turbo‐mixed imaging at 1.5T

Abstract

Purpose:To evaluate the influence of Gd-DTPA on cartilage T2 mapping using turbo-mixed (tMIX) imaging, and to show the possible usefulness of the tMIX technique for simultaneously acquiring T1 and T2 information in cartilage. Materials and Methods:Twenty volunteers underwent MRI of the knee using the tMIX sequence before and after gadolinium administration. T1 and T2 maps were calculated. The mean T1 was determined on the pre-and postcontrast T1 maps. T2 relaxation values before and after gadolinium administration were statistically analyzed. Results:The obtained relaxation values are in correspondence with previously published data. The mean T1 before gadolinium administration was 449 msec Ϯ 34.2 msec (SD), and after gadolinium administration it was 357 msec Ϯ 55.8 msec (SD). The postcontrast T1 relaxation range was 221.5-572.8 msec. The mean T2 of the precontrast T2 maps was 34.2 msec Ϯ 3.1 msec (SD), and the mean T2 of the postcontrast T2 maps was 32.5 msec Ϯ 3.1 msec (SD). These are statistically significant different values. A correction for the postcontrast T2 values, using a back-calculation algorithm, yielded a 98% correlation with the precontrast T2 values. Conclusion:The absolute difference of pre-and postcontrast T2 is very small and is ruled out using the backcalculation algorithm. Combined T1-T2 tMIX cartilage mapping is a valuable alternative for separate T1 and T2 cartilage mapping. MAGNETIC RESONANCE IMAGING (MRI), by virtue of its multiplanar capacity and excellent soft-tissue contrast, is a unique scanning technique for articular cartilage. While the ability to depict the cartilaginous anatomy represents a major advance in the evaluation of chondral abnormalities, a further advantage would be the ability to image and quantify functionally relevant macromolecules within the cartilage itself that are affected by degeneration. Two MRI techniques that have demonstrated promise in this regard are quantitative T2 mapping and T1 mapping after Gd-DTPA administration, known as delayed gadolinium-enhanced MRI of cartilage (dGEMRIC). Current research suggests that these techniques are complementary, with T2 mapping providing information on structural integrity of the collagen matrix (1-4), and dGEMRIC identifying regions of proteoglycan loss (5-7). The major disadvantages in the application of both techniques are the total length of the scan time needed (approximately 18 minutes) and the geometric mismatch between the acquired images. This geometric mismatch is induced by the technique itself, since T2 mapping is performed before gadolinium administration and dGEMRIC is performed after gadolinium administration. Combining both techniques would resolve this issue, and should deal with the influence of administered gadolinium on T2 mapping. The purpose of our study was to evaluate combined T1-T2 mapping of human cartilage using the turbo-mixed (tMIX) technique (8) and to investigate the influence of administered gadolinium on obtained T2 cartilage maps with this technique. MATERIALS AND METHODS TechniqueThe...

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