Summary

This study compared 3D and 2D T1rho mapping for detecting early cartilage lesions in ACL injury patients. Results showed that 3D T1rho mapping was significantly more accurate and sensitive than 2D mapping, making it a superior tool for early diagnosis and monitoring of cartilage damage.

Abstract

Introduction

T1rho mapping has gained attention as a quantitative and non-invasive method for assessing early cartilage lesions. Conventional two-dimensional (2D) midsagittal slice imaging may inadequately capture the full extent of these lesions. In contrast, three-dimensional (3D) imaging may potentially enhance the detection of early cartilage damage. This study aimed to investigate the effectiveness of 3D versus 2D T1rho mapping in detecting early cartilage lesions and compare the diagnostic accuracy of these two methods.

Methods

All patients provided informed consent, and the study was approved by our University Ethics Committee. The study included 51 patients (30 men and 21 women; mean age, 24 years; range, 13–40 years) with isolated anterior cruciate ligament (ACL) injuries, as these frequently present with early cartilage lesions such as cartilage fissures, particularly in the medial femoral condyle (MFC). Patients requiring additional surgeries or those with knee osteoarthritis visible on radiographs were excluded. One year after ACL reconstruction, patients underwent 3T MRI of both knees during second-look arthroscopy at the time of hardware removal. Commercially available software was used to analyze the images, focusing on the weight-bearing areas of the MFC. Regions of interest (ROI) were manually set, and the T1rho values were measured by 2D and 3D methods. The relationship between the T1rho values and cartilage lesions was evaluated by dividing the patients into group E (early cartilage lesions) and group I (intact macroscopically) based on the arthroscopic findings. The contralateral knee served as an internal control. Receiver operating characteristic (ROC) curves assessed the detectability of T1rho values.

Results

Arthroscopy identified early cartilage lesions in 31 MFCs, all of which were classified as ICRS grade 1 or 2. No significant demographic or clinical differences were observed between Groups E and I regarding age, sex, height, weight, surgery waiting time, presence of meniscus injury, positive pivot shift test, Lachman test, and Knee Injury and Osteoarthritis Outcome Score (KOOS). T1rho values in Group E were significantly higher than those in Group I and the control group (p < 0.05) in both 3D and 2D mapping. ROC curve analysis revealed an area under the curve (AUC) of 0.99 for 3D mapping and 0.80 for 2D mapping (p < 0.01). The sensitivity was 96.8% for 3D imaging and 77.4% for 2D imaging, with both methods showing 100% specificity. The accuracy was 97.1% for 3D images and 79.4% for 2D images. Reproducibility, assessed via intra-observer and inter-observer intraclass correlation coefficients, was 0.85/0.90 for 3D and 0.94/0.83 for 2D mapping.

Conclusions

Reliable and reproducible methods for evaluating early cartilage degeneration are crucial for early intervention and effective management before advanced osteoarthritis develops. This study found that T1rho values were significantly higher in early cartilage lesions than in intact cartilages. Additionally, 3D T1rho mapping demonstrated superior accuracy to 2D mapping in detecting early cartilage lesions, suggesting that it is a more effective tool for early diagnosis and monitoring.