Indirect MR arthrography: concepts and controversies.

Indirect MR arthrography involves intravenous injection of a standard dose of Gadolinium contrast followed, in delayed fashion, by MR imaging. Contrast in taken up by the joint at a rate dependent on a variety of factors including synovial area, vascularity, permeability, and pre-existing joint effusion. Patient acceptance is higher than with direct intra-articular injection, and logical considerations (e.g., not needing a radiologist present) make this an attractive alternative to direct MR arthrography. At best, an indirect MR arthrography exam can look virtually identical to a direct MR arthrogram. However, the radiologist should be aware that vascular tissue inside and outside the joint will enhance, which may be considered either an advantage or disadvantage. Additionally, since all compartments of the joint enhance, information regarding abnormal communication of contrast material is absent. Suboptimal exams occur due to the need for diffusion of contrast into the joint. Exercise can help improve the quality of exams. Using an adequate time delay is essential for optimizing indirect MR arthrography.