T₂ of articular cartilage in the presence of Gd‐DTPA²⁻

Abstract

T 2 information and delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) are both used to characterize articular cartilage. They are currently obtained in separate studies because Gd-DTPA 2؊ (which is needed for dGEMRIC) affects the inherent T 2 information. In this study, T 2 was simulated and then measured at 8.45 T in 20 sections from two human osteochondral samples equilibrated with and without Gd-DTPA 2؊. Both the simulations and data demonstrated that Gd-DTPA 2؊ provides a non-negligible mechanism for relaxation, especially with higher (1 mM) equilibrating Gd-DTPA 2؊ concentrations, and in areas of tissue with high T 2 (due to weak inherent T 2 mechanisms) and high tissue Gd-DTPA 2؊ (due to a low glycosaminoglycan concentration). Nonetheless, T 2 -weighted images of cartilage equilibrated in 1 mM Gd-DTPA 2؊ showed similar T 2 contrast with and without Gd-DTPA 2؊, demonstrating that the impact on T 2 was not great enough to affect identification of T 2 lesions. However, T 2 maps of the same samples showed loss of conspicuity of T 2 abnormalities. We back-calculated inherent T 2 's (T 2,bc ) using a T 2 -relaxivity value from a 20% protein phantom (r 2 ‫؍‬ 9.27 ؎ 0.09 mM ؊1 s ؊1) and the Gd-DTPA 2؊ concentration calculated from T 1,Gd . The back-calculation restored the inherent T 2 conspicuity, and a correlation between T 2 and T 2,bc of r ‫؍‬ 0.934 (P < 0.0001) was found for 80 regions of interest (ROIs) in the sections. Backcalculation of T 2 is therefore a viable technique for obtaining T 2 maps at high equilibrating Gd-DTPA 2؊ concentrations. With T 2 -weighted images and/or low equilibrating Gd-DTPA 2؊ concentrations, it may be feasible to obtain both T 2 and dGEMRIC information in the presence of Gd-DTPA 2؊ without such corrections. These conditions can be designed into ex vivo studies of cartilage. They appear to be applicable for clinical T 2 studies, since pilot clinical data at 1.5 T from three volunteers demonstrated that calculated T 2 maps are comparable before and after "double dose" Gd-DTPA 2؊ (as utilized in clinical dGEMRIC studies). Therefore, it may be possible to perform a comprehensive clinical examination of dGEMRIC, T 2 , and cartilage volume in one scanning session without T 2 data correction.

In vitro determination of biomechanical properties of human articular cartilage in osteoarthritis using multi-parametric MRI

“…The results of our study suggest that prediction of biomechanical parameters for degenerated articular cartilage may not be simply extrapolated from assessment of native tissue. T 2 values were measured in the presence of Gd-DTPA 2À , however, this paramagnetic contrast agent does not influence T 2 values at low equilibrated concentrations [53]. As T 2 is related primarily to the orientation of collagen fibers, one can expect that T 2 would better correlate with biomechanical parameters not measured in this study, such as modulus of rigidity (shear modulus) or tensile strength.…”

Effect of multislice acquisition on T1 and T2 measurements of articular cartilage at 3T

“…To observe the whole cartilage of the patella, medial condyle, or lateral condyle at a time, at least this degree of slice number and interslice gap are required. An ETL ϭ 7, which is comparable with values used for clinical studies (12,27), was used in this study. Theoretically, it is possible to reduce the MT effect by reducing the number of ETL; however, acquisition time will increase inversely proportional to the number of ETL.…”

“…A total of 10 knees were involved in the T 1 measurement study (three men, two women), and the other 10 knees were involved in the T 2 measurement study (three men, two women). Mean age at time of imaging was 31.8 Ϯ 3.9 years [25][26][27][28][29][30][31][32][33][34][35][36] (values are given throughout as mean Ϯ SD [range]) for the T 1 measurement study and 29.5 Ϯ 4.9 years [24 -36] for the T 2 measurement study. Exclusion criteria were history of knee pain or abnormality or trauma of the knee joint requiring medical treatment.…”

Sodium and T1ρ MRI for molecular and diagnostic imaging of articular cartilage

“…Prominent in these are: proton-based methods such as T 2 relaxation mapping (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), delayed gadoliniumenhanced magnetic resonance imaging contrast (dGEM-RIC) (21,22), T 1r relaxation mapping (23)(24)(25)(26) and the direct MRI of sodium (27)(28)(29)(30). T 2 is predominantly affected by changes in collagen content and to a smaller extent in PG in the tissue.…”