Spatial variation inT₁of healthy human articular cartilage of the knee joint

Abstract

ABSTRACT. The longitudiual relaxation time T 1 of native cartilage is frequently assumed to be constant. To redress this, the spatial variation of T 1 in unenhanced healthy human knee cartilage in different compartments and cartilage layers was investigated. Knees of 25 volunteers were examined on a 1.5 T MRI system. A three-dimensional gradient-echo sequence with a variable flip angle, in combination with parallel imaging, was used for rapid T 1 mapping of the whole knee. Regions of interest (ROIs) were defined in five different cartilage segments (medial and lateral femoral cartilage, medial and lateral tibial cartilage and patellar cartilage). Pooled histograms and averaged profiles across the cartilage thickness were generated. The mean values were compared for global variance using the Kruskal-Wallis test and pairwise using the Mann-Whitney U-test. Mean T 1 decreased from 900-1100 ms in superficial cartilage to 400-500 ms in deep cartilage. The averaged T 1 value of the medial femoral cartilage was 702¡68 ms, of the lateral femoral cartilage 630¡75 ms, of the medial tibial cartilage 700¡87 ms, of the lateral tibial cartilage 594¡74 ms and of the patellar cartilage 666¡78 ms. There were significant differences between the medial and lateral compartment (p,0.01). In each cartilage segment, T 1 decreased considerably from superficial to deep cartilage. Only small variations of T 1 between different cartilage segments were found but with a significant difference between the medial and lateral compartments. MRI relaxation parameters are used to evaluate cartilage degradation. T 2 has been investigated extensively and has been demonstrated to vary with water and collagen content and with collagen orientation in the different cartilage layers [1][2][3][4][5][6][7][8].The quantification of the longitudiual relaxation time T 1 of native cartilage has received less attention. In experimental studies, native T 1 has been demonstrated to correlate with mechanical properties [9] and to depend upon the macromolecular structure of cartilage [10]. However, it is frequently assumed to be constant across cartilage [11][12][13]. A few studies have investigated the mean values of a single compartment (Table 1) [10, 14-19] but have not investigated the depth-dependent variation. To our knowledge, no study has systematically compared T 1 of unenhanced human knee cartilage in different cartilage layers and in different cartilage compartments in healthy volunteers.Usually, inversion-recovery (IR) sequences have been used to measure several points in the T 1 relaxation curve. Although this technique provides ideal measurements of T 1 , it is not viable in most studies that require T 1 values of a large volume within a reasonable time. Threedimensional (3D) T 1 mapping techniques were applied for this purpose [17,[20][21][22].The purpose of this study was to investigate the spatial variation of native cartilage T 1 in different compartments and different cartilage layers in healthy human knee joints using a rapid 3D gradient-echo (G...

In vivo transport of Gd‐DTPA2− in human knee cartilage assessed by depth‐wise dGEMRIC analysis

“…Previously, it has been assumed that T 1 of native cartilage is relatively constant (11, 26). However, more recent studies both in vitro and in vivo support our findings (27, 28). Generally, water content of articular cartilage is considered more related to T 2 relaxation time (29–31).…”

Quantitative parametric MRI of articular cartilage: a review of progress and open challenges

“…The exact nature of this relationship is unclear, but is believed to relate more to the PG content of the tissue than the collagen architecture [16]. A systematic survey of native T 1 in different cartilage compartments of healthy human volunteers was undertaken by Wiener et al [17]. In this study, T 1 values were shown to decrease from the superficial cartilage layers to the deep layer, consistent with the dependence of native T 1 values upon the macromolecular construction of cartilage.…”

Functional MR Imaging Mapping of Human Articular Cartilage Response to Loading

“…T1, T1r, T2, and T2* relaxation times displayed concordant regional and zonal changes upon loading. In the unloaded state, T1 values were found to be quite variable, which has been demonstrated before (30). T1 relaxation time is considered more related to the PG than to the collagen content, although the exact biochemical correlate remains unclear (31).…”