Hip MR Arthrography for Acetabular Labral Tears

It is the authors’ opinion that the MR assessment of labral tears should be performed as an MR arthrogram, employing an array or surface coil and using higher resolution than that employed for routine MR examinations of the hip MR. The authors also believe that these studies should not be attempted on systems with static field strength <1 Tesla, because of the considerable demands placed on these systems to evaluate the labrum, in particular, the need for high resolution and fat saturation. (Not all investigators agree with the necessity of using arthrography, however. At least one investigator maintains that intra-articular contrast is not needed if sufficiently high resolution is employed. A different group of investigators performed MR arthrograms on a group of patients using a 0.5-T system for some patients and a 1.0-T system for others. These investigators did not describe any difference in accuracy between the two systems, although, they did not directly address this issue.) Under fluoroscopic guidance, a small amount of iodinated contrast agent is injected to confirm intra-articular location of the needle. A small amount of dilute Gd-chelate in saline, bupivicaine, and betamethasone is injected into the joint. Bupivicaine, a long-acting anesthetic, is used to confirm the intra-articular origin of the pain, as well as to provide short-term relief of symptoms. Betamethasone, a long-acting steroid, is used to provide somewhat longer-term symptomatic relief. Following the acquisition of a scout sequence in the coronal plane, fat-saturated, T1-weighted, fast-spin echo sequences in the transverse, coronal, and sagittal planes are obtained. Fast spin echo (FSE) sequences are used because fat saturation, when used with short TE FSE sequences, increases the study time much less than when used with short TE conventional spin echo sequences (CSE). The authors also set the second echo of the echo train in the FSE sequence to two times the minimum TE as the effective TE because of reduced blurring compared with use of the first echo. See Kowalchuk et al. (2000) for further discussion of the rationale for using the second echo of a fast-spin echo sequence as well as demonstrating its accuracy for the assessment of knee meniscal tears. To keep this effective TE <30 msec while using the second echo of the train requires relatively strong gradients and wide bandwidth. This type of sequence cannot be performed on all systems. In particular, if the gradients are not sufficiently strong, fat-saturated, T1-weighted CSE sequences are used and more time is taken to perform the study. Other investigators have advocated the use of 3-D, T1-weighted, short TR, gradient sequences. The authors have had no experience with these sequences for this application.