Compositional MR imaging including T2 mapping play an important role in the assessment of early and potentially reversible cartilage damage [1, 9].
The main clinical application for T2 mapping involves the detection of early cartilage damage prior to the onset of symptoms and prior to detection using conventional screening techniques [1, 10].
Combining the anatomical and functional information may enhance our ability to detect early cartilage degeneration, and to distinguish between different stages of degeneration [8].
T2 mapping has been used to describe the composition of hyaline articular cartilage in the knee joint on the basis of collagen structure and hydration. Analyses of T2 relaxation times in the knee have been performed, usually at 1.5T or, more recently, 3.0 T, demonstrating the ability to depict abnormalities before there is evident morphologic change [1, 11].
The results of this study have the potential to deepen our information about the role of compositional imaging T2 mapping sequence in detection of stages of medial knee compartments articular cartilage degeneration beyond the usage of descriptive statistics.
Sensitivity and specificity of conventional techniques, and the absence of a defined threshold to classify OA, have been criticized in previous studies. However, our results show there may be more information.
Compared with other quantitative MRI techniques, T2 mapping has the advantage that it can be performed non-invasively without the injection of contrast agents; also, this sequence and its post-processing software are available in many commercial MRI scanner systems [11, 12].
In our study, the addition of a T2 mapping sequence to a routine MR imaging protocol significantly increased the sensitivity for detecting cartilage lesions within the knee joint, with the greatest improvement occurring in the identification of early cartilage degeneration. Our low sensitivity for detecting early cartilage degeneration by using the morphologic cartilage imaging sequences in the routine MR protocol is similar to the findings of previous studies, which have reported sensitivity values for detecting cartilage fibrillation and superficial partial-thickness cartilage defects
The study showed significant differences in T2 mapping ability to detect degree of cartilage degeneration between the two study groups according to ICRS degeneration grades in the weight-bearing regions of the knee joint (medial patella and trochlea, peripheral medial femoral and tibial, central and peripheral medial femoral and tibial regions).
This agreed with Zhang, et al. [13] for the patellar articular cartilage early changes as well as Apprich, et al. [14] for the medial femoral condyle, where T2 mapping appears to be sensitive to early cartilage changes, but also to the loading state of the joint. Even changes not yet visible in high-resolution MRI might be detectable with quantitative T2 mapping.
Furthermore Hesper et al. [15], who reported that the potential value of T2 mapping as a biomarker for early cartilage degeneration is highlighted by its inclusion in the MRI protocol for the early osteoarthritis.
Advanced quantitative MRI techniques such as T2 mapping are sensitive to subtle cartilage matrix alterations that occur early in the course of OA and therefore, these imaging modalities have the potential to provide biomarkers for disease onset and progression, which could be a meaningful addition in the diagnosis and follow-up of cartilage abnormalities [11, 15].
A study by Hesper et al. [15] concluded that “biochemically sensitive” MRI techniques as T2 mapping are able to add robust biomarkers for osteoarthritis onset and progression with varying degrees of sensitivity and specificity, and therefore could be meaningful assessment tools for the diagnosis and follow-up of cartilage abnormalities.
In our study, the age of presentation of the cases ranged from 13 to 57 years old. Out of the 20/30 (66%) cases presented by knee pain, 15% were anterior 35% medial, 15% lateral, and 35% global. All cases underwent conventional MRI with complementary T2 mapping sequence
T2 mapping despite all the enumerated advantages, and its contribution to enhancing cartilage status assessment, is still in its infancy, as its values are based on several factors, including the biochemical status of the cartilage, physics variables involved in obtaining the mapping, and the physiology of the individual patient. So, the current literature still lacks clinical correlation [4].
A study by Mars, et al. and Zhang, et al. [10, 13] reported that the potential clinical applications of quantitative mapping are vast, but, before the clinical community can take full advantage of this tool, it must be automated, standardized, validated, and have proven reproducibility prior to its implementation into the standard clinical care routine.
T2 mapping may provide the basis for diagnosis and follow-up evaluation of cartilage injury and response to cartilage treatment and repair. Once a set of standardized protocols are developed and proposed, subsequent studies are needed to determine specific values or distribution of values, which are associated with healthy and damaged cartilage [10, 13].
Pedoia et al. and Hesper et al. [12, 15] added that much remains to be understood and certain points have become apparent with the studies that are crucial to the further applications of T2 mapping technique, also added that further studies are needed to address protocol issues for this technique.
T2 mapping has proven to be a useful predictor of cartilage degeneration and repair tissue following surgical intervention in the knee [10].
Surgical approaches to repair focal cartilage damage were introduced several years ago and have shown promising results, but long-term observation of any of the repair techniques still have not been reported. The most commonly applied techniques are microfracture, osteochondral transfer, and autologous chondrocyte implantation [9].
Limitations
The limitation of this study is the lack of histological information or arthroscopic correlation. Further investigations in larger patient groups with histologic correlation would be beneficial in comparing T2 and T2 mapping values. Also, studies in larger number of patients with different age and activity levels are needed to quantify correctly these biochemical mapping methods.