Examination Protocol

All patients are examined with the use of a Siemens Vision and Avanto 1.5-T, or Trio 3T high-field scanner (Erlangen, Germany). A flexible surface coil is used exclusively for high spatial resolution and signal-to-noise ratio. Before the MRA examination, all patients receive an intra-articular injection of 10 mL to 20 mL of saline-diluted Gd-DOTA 0.0025 mmolGd/mL (Artirem^R, Guerbert AG, Paris) into the hip joint with the use of fluoroscopic guidance. Patients are positioned supine under a C-arm, and the hip is placed slightly in external rotation to relax the anterior capsule. After the disinfection and sterile draping of the injection site, the injection is performed with a 22-gauge, spinal, obtuse-cut–angle needle, which helps to prevent injection into the capsular tissue or any extravasation. Between the injection and MR examination, a maximum time allowance of 10 minutes is preferred. The patients are then positioned supine, and the lower extremities are fixed with 20 degrees of internal rotation to prevent motion during scanning, to generate a standard version of the femoral neck, and to control the position of the pelvis.

After a short localizer in three planes, the examination continues with an axial T1-weighted sequence (repetition time [TR] 650, echo time [TE] 20, 200 mm × 200 mm field of view, 224 × 512 matrix, 4-mm section thickness with a 0.2-mm section gap, 17 slices, 3 minutes and 44 seconds). The sequence is centered on the femoral head, and it covers the whole joint (Figure 4-1).

Figure 4–1 A, Coronal scout view showing the right hip joint. The white lines overlying the joint represent the slices of the transverse T1-weighted sequence. B, Transverse slice through the acetabulum just above the joint space. C, Transverse slice through the midsection of the joint. The white arrow shows the normal anterior joint capsule.

The second sequence is an axial FLASH sequence with a few thin slices that is centered on the upper joint space. This sequence is used to evaluate the version of the acetabulum, and it also helps with the assessment for subcortical hypersclerosis of the rim as well as for the presence of synovial cysts (TR 550, TE 10, flip angle of 90 degrees, 120 mm × 120 mm field of view, 256 × 256 matrix, 2-mm section thickness with a 0.1-mm section gap, 11 slices, 3 minutes and 6 seconds; Figure 4-2).

Figure 4–2 A, Coronal scout view showing the right hip joint. The white lines overlying the joint represent the slices of the transverse FLASH sequence. B, Transverse slice through the acetabulum just above the joint space. The white arrow points to the attachment of the rectus femoris tendon (pars recta) at the spina iliaca anterior inferior. C, Transverse slice through the uppermost part of the joint. The short white arrow points to the anterior acetabular rim; the long white arrow points to the posterior acetabular rim.

Next is a coronal–oblique proton-density l–weighted (PDW) thin-slice sequence (TR 3200, TE 15, 120 mm × 120 mm field of view, 256 × 256 matrix, 2-mm section thickness with a 0.1-mm section gap, 23 slices, 5 minutes). This sequence is aligned perpendicular to the femoral neck, and it is marked on the axial T1W sequence (Figure 4-3).

Figure 4–3 A, Slice from the T1-weighted transverse sequence as a localizer for the coronal-oblique PDW sequence. The white lines overlying the joint represent the coronal-oblique PDW sequence. B, Coronal-oblique slice through the midsection of the joint. The white arrow points at a slightly enlarged, hypointense lateral labrum.

A second PDW sequence in the sagittal direction (TR 3200, TE 15, 120 mm × 120 mm field of view, 256 × 256 matrix, 2-mm section thickness with a 0.2-mm section gap, 23 slices, 5 minutes and 37 seconds) is applied as the next step (Figure 4-4).

Figure 4–4 A, Coronal scout view showing the right hip joint. The white lines overlying the joint represent the slices of the sagittal PDW sequence. Sagittal slices through the hip joint showing B, a bony apposition at the femoral neck (white arrow), and C, a torn labrum (white arrow).

Finally, a radial PDW sequence (Figure 4-5) is used in which all slices are oriented basically orthogonal to the acetabular rim and labrum. This sequence is based on a sagittal oblique localizer, which is marked on the PDW coronal sequence, and it runs parallel with the sagittal oblique course of the acetabulum. The MRA imaging parameters are as follows: TR 2000, TE 15, 260 mm × 260 mm field of view, 266 × 512 matrix, 4-mm section thickness, 16 slices, 4 minutes and 43 seconds. In the center of the radial sequence, where the slices cross over, the signal wipes out. This produces a broad line without signal on the image, which affects the quality of the image. The more slices in a sequence, the broader the no-signal line gets. To reduce this artifact, this sequence is split into two sequences of eight slices each. The whole examination, including the hip injection, lasts about 50 to 60 minutes.

Figure 4–5 A, Slice from the coronal-oblique sequence. The white lines overlying the femoral neck represent the slices of the radial scout view plane. B, Radial scout view with overlying slices of the radial PDW sequence. C, Slice from the radial PDW sequence showing a secondary metaphyseal bump at the femoral neck, characteristic for pincer impingement (white arrow).

Interpretation and Findings

There are numerous methods that address how best to interpret MR images of the hip. We prefer to look first at the bony structures, beginning with the acetabulum, and we then proceed to the soft-tissue structures.