T1ρ mapping of pediatric epiphyseal and articular cartilage in the knee

Abstract

Purpose: To evaluate the feasibility of measuring T1ρ values in epiphyseal cartilage in children, we have conducted a novel study of spin locking techniques. Adult articular cartilage has been widely studied with spin locking techniques by magnetic resonance imaging. However, no results are available for in vivo T1ρ imaging of developing cartilage.

Materials and methods: Ten volunteers of age 6 ± 3 years were recruited to have T1ρ mapping performed on the knee at the conclusion of their clinical study. T1ρ maps were generated using a spin-lock cluster followed by a fast spin-echo imaging sequence. Regions of interest (ROIs) were placed in non-load-bearing (NLB), load-bearing (LB), and articular cartilage.

Results: Student's t-tests were performed to compare means among the ROIs. Mean T1ρ for epiphyseal and articular cartilage was 49.8 ± 9 and 76.6 ± 7 ms, respectively. LB and NLB T1ρ vales were 47.1 ± 9.5 and 52.5 ± 9 ms, respectively. Significant differences were found in T1ρ values between epiphyseal and articular cartilage layers (P = 0.0001). No difference in T1ρ was observed between NLB and LB layers. A modest trend was also noted for epiphyseal and articular cartilage regions with age.

Conclusion: It is feasible to quantify differences in epiphyseal and articular cartilage layers with SL techniques. T1ρ holds promise as a noninvasive method of studying normal and abnormal developmental states of cartilage in children.

Keywords: 3T; T1ρ; cartilage; spin lock.

Figure 1

a: A T2-weighted turbo spin echo (TSE) sagittal scan of the knee used to plan ROI for the T_1ρ map shown in Figure 1b. The red ROI is articular cartilage, the yellow ROI is LB epiphyseal cartilage, and the green ROI is NLB epiphyseal cartilage. b: T_1ρ map of the same subject as shown in Figure 1a. A maximum threshold of 120 ms was applied to the T_1ρ map, and the soft tissue and patellar regions were removed for clarity. The color scale is given in ms. Note approximately a 25 ms difference in articular and epiphyseal cartilage T_1ρ values.

Figure 2

a: T2-weighted turbo spin echo (TSE) axial scan of the trochlea and patella used to plan ROI for the T_1ρ map in Figure 2b. The red ROI is the patellar articular cartilage, the blue ROI is the patellar epiphyseal cartilage, the green ROI is the trochlear articular cartilage, and the yellow ROI is the trochlear epiphyseal cartilage. Uniform T_1ρ maps were more difficult to achieve in this orientation as evidenced by the low signal intensity in the lateral trochea. This region was avoided when placing ROI. b: T_1ρ map of the same subject as shown in Figure 2b. A maximum threshold of 120 ms was applied to the T_1ρ map, and the soft tissue regions were removed for clarity. The color scale is also given in ms. Note approximately a 25 ms difference in articular and epiphyseal cartilage T_1ρ values.

Figure 3

Pulse sequence used to record T_1ρ-weighted fast spin-echo images.

Figure 4

a: Distal femur cartilage T_1ρ values at 3T (ms ± SD). Articular = 76.6 ± 6.9, Load-bearing epiphyseal = 47.1 ± 9.5, non–load-bearing epiphyseal = 52.5 ± 8.9, average epiphyseal = 49.8 ± 9.0. b: patella and trochlear cartilage T_1ρ values at 3T (ms ± SD). Patella articular = 66.1 ± 17.8, patella epiphyseal = 43.0 ± 10.6, trochlea articular = 67.9 ± 14.3, trochlea epiphyseal = 56.7 ± 12.3. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Figure 5

Plot of cartilage R_1ρ values (1/T_1ρ) versus age at 3T. Note the epiphyseal cartilage relaxation rates always exceed the articular cartilage relaxation rates. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]