Purpose: To evaluate the repeatability of the dGEMRIC (delayed gadolinium enhanced MRI of cartilage) method in osteoarthritis-prone knee joints for three different T1 quantification techniques: two-dimensional inversion recovery (2D-IR), three-dimensional Look-Locker (3D-LL), and three-dimensional variable flip angle (3D-VFA).
Materials and Methods:Nine subjects were examined twice, with a 2-week interval, using all three measurement techniques. Four regions of interest were defined in the central medial and lateral femoral cartilage. The repeatability was evaluated for each measurement technique. For the 3D techniques, the variation between different slices was also evaluated.Results: Repeatability expressed by root-mean-square coefficient of variation (CV RMS ) showed similar results for 2D-IR and 3D-LL (5.4-8.4%). For 3D-VFA CV RMS was higher (9.3-15.2%). Intraclass correlation coefficient showed both 2D-IR and 3D-LL reliability to be moderate, while 3D-VFA reliability was low. Inter-slice CV RMS and ICC was of the same magnitude as the repeatability. No clear differences could be interpreted between the condyles.Conclusion: Both 2D-IR and 3D-LL perform well in generating repeatable dGEMRIC results, while 3D-VFA results are somewhat inferior. Furthermore, repeatability results in this study are similar to previously published results for healthy subjects. Finally, the positioning of the analyzed images is crucial to generate reliable repeatability results. OSTEOARTHRITIS (OA) IS a common long-term disease characterized by loss and degradation of cartilage, causing pain and dysfunction, commonly affecting the knees. In several previous studies (1-4) a method for identification of early disease related joint cartilage changes has been presented. This method, known as delayed gadolinium enhanced MRI of cartilage (dGEMRIC), provides an estimation of the glycosaminoglycan (GAG) content in the cartilage, which is shown to be decreased at early stages of OA. The technique is based on the principle that the negatively charged contrast agent Gd(DTPA) 2À (Magnevist V R , Scheering AG, Berlin, Germany), distributes in the cartilage in an inverse relationship to the GAG content. In normal cartilage, Gd(DTPA) 2À is repelled by the abundant negatively charged GAG, whereas in conditions of GAG loss, more Gd(DTPA) 2À will be distributed within the cartilage matrix. When the intravenously injected contrast agent has approximately reached its peak concentration in the cartilage, a quantitative measurement of T1 in the cartilage is performed, which will then correlate to the distributed amount of Gd(DTPA) 2À . Hence, longer T1 corresponds to higher cartilage quality and vice versa.Traditionally dGEMRIC has been performed using a two dimensional T1-quantifying inversion recovery (2D-IR) sequence (1,2,4). Recently, however, several methods for performing dGEMRIC in a three-dimensional (3D) volume of interest have emerged. In the long-term, there are many advantages of using 3D sequences for dGEMRIC. With 3D, it will be possible t...