Assessing patterns of T2/T1rho change in grade 1 cartilage lesions of the distal femur using an angle/layer dependent approach

Abstract

Purpose: To assess changes in the patterns of T2 and T1rho values within grade 1 cartilage lesions of osteoarthritis (OA) patients compared to healthy controls.

Materials and methods: Twenty healthy knees and 25 OA knees were examined on a 3 T scanner. Areas of signal heterogeneity within the cartilage of the distal femur were identified using fat suppressed proton density-weighted imagines. T2 and T1rho values in each OA patient with grade 1 lesions were compared to average T2 and T1rho values of the corresponding areas in healthy subjects.

Results: A total of 28 areas including grade 1 lesion were identified. Compared to normal cartilage, the majority of grade 1 cartilage lesions demonstrated either no significant change or a statistically significant increase in both T2 values (18/28, 64%) and T1rho values (23/28, 82%). Compared to T2, T1rho demonstrated a greater proportion of statistically significantly higher values in OA patients than those from the normal controls. However, T2 and T1rho values in grade 1 lesions can be decreased, or demonstrate mixed patterns compared to those in healthy cartilage.

Conclusion: Our results suggest that early degenerative cartilage lesions can demonstrate various patterns of T2 and T1rho changes.

Keywords: Grade 1 lesion; Knee cartilage; Osteoarthritis; T1rho relaxation time; T2 relaxation time.

Figure 1

Comparison of T2 and T1rho values between degenerative legions within (a) all OA patients and (b,c) early and advanced OA patients with corresponding areas in the normal control.

Figure 2

A representative lesion in an OA patient where both T2 and T1rho values were significantly higher than those in the normal control within both the deep and superficial layers. Cartilage signal heterogeneity is observed over the central portion of the medial femoral condyle in the (a) routine FS PDWI, (b) T2 mapping image, and (c) T1rho mapping image. (d) T2 color map and (e) T1rho color map demonstrate increases in values in this area. The relaxation times within the area between the arrows was analyzed and statistically compared between this case and controls.

Figure 3

A representative lesion where both T2 and T1rho values in OA patients were significantly lower than in normal controls within both the deep and superficial layers. Cartilage signal heterogeneity is observed over the trochlea in the (a) routine FSPDWI, (b) T2 mapping image, and (c) T1rhomapping image. (d) T2 color map and (e) T1rho color map demonstrate a mix of increased and decreased in values in this area. Low signal in the most distal trochlea is normally seen, while low signal in the mid trochlea is abnormal. The relaxation times within the area between the arrows was analyzed and statistically compared between this case and controls.

Figure 4

A representative lesion where T2 and T1rho value show a non-synchronized pattern. There was no significant difference in T2 values between this lesion and the normal control cartilage, whereas a significantly higher T1rho value was seen in the OA patient within both the deep and superficial layers. Subtle cartilage signal heterogeneity is observed over the posterior portion of the lateral femoral condyle in the (a) routine FS PDWI, (b) T2mapping image, and (c) T1rho mapping image. (d) T2 color map demonstrates no significant change compared the surrounding cartilage, while (e) T1rho color map demonstrates subtle increase in values in this area. The relaxation times within the area between the arrows was analyzed and statistically compared between this case and controls.

Figure 5

A representative lesion (shaded zone in left graph and area between red lines in right images) where on T2, a mixture of both higher and lower T2 values results in no significant difference on average between the OA patient and the normal control. In distinction, T1rho values in this patient were significantly lower than the normal control in the deep layer, and significantly higher than the control in the superficial layer within the same area.

Figure 6

Comparison of T2 and T1rho value between normal and degenerative cartilage within the vicinity of the magic angle (±50~58°).