Visualization of wrist anatomy-a comparison between 7T and 3T MRI

Abstract

Objective: Injuries to the wrist are, due to its small size and complex anatomical structures, difficult to assess by MR, and surgical interventions such as diagnostic arthroscopy are often necessary. Therefore, improved visualization using non-invasive methods could be of clinical value. As a first step of improvement, the purpose of this study was to evaluate visualization of anatomical structures at 7T compared with 3T MR.

Methods: Eighteen healthy volunteers (three males and three females from each age decade between 20 and 49 years) were examined with 7T and 3T MR. Four musculoskeletal radiologists graded 2D and 3D images on a five-level grading scale for visibility of ligaments, cartilage, nerves, trabecular bone, and tendons, as well as overall image quality (i.e., edge sharpness, perceived tissue contrast, and presence of artefacts). Statistical analysis was done using a visual grading characteristics (VGC) analysis.

Results: Visibility of cartilage, trabecular bone, tendons, nerves, and ligaments was graded significantly higher at 7T with an area under the curve (AUC_VGC) of 0.62-0.88 (95% confidence interval [CI] 0.50-0.97, p = < 0.0001-0.03) using either 2D or 3D imaging. Imaging with 3T was not graded as superior to 7T for any structure. Image quality was also significantly superior at 7T, except for artefacts, where no significant differences were found.

Conclusions: Tendons, trabecular bone, nerves, and ligaments were all significantly better visualized at 7T compared to 3T.

Key points: • MRI of the wrist at 7T with a commercially available wrist coil is feasible at similar acquisition times as for 3T MRI. • The current study showed 7T to be superior to 3T in the visualization of anatomical structures of the wrist, including ligaments, tendons, nerves, and trabecular bone. • Image quality was significantly superior at 7T, except for artefacts, where no significant differences were found.

Keywords: Area under curve; Carpal joints; Cartilage, articular; Ligaments; Triangular fibrocartilage.

Fig. 1

VGC analysis comparing grading between 7T and 3T imaging. If the bar showing the area under curve, AUC_VGC including the range bar (i.e., the 95% confidence interval) is above 0.5, 7T imaging was on average graded significantly better than 3T imaging. Wider confidence intervals imply lower observer agreement. 2D, two-dimensional; 3D, three-dimensional; AUC, area under the curve; ECU, extensor carpi ulnaris; LTL, lunotriquetral ligament; SLL, scapholunate ligament; TFCC, triangular fibrocartilage complex; VGC, visual grading characteristics. 2D, two-dimensional; 3D, three-dimensional; AUC, area under curve; ECU, extensor carpi ulnaris; LTL, lunotriquetral ligament; SLL, scapholunate ligament; TFCC, triangular fibrocartilage complex

Fig. 2

A 32-year-old male healthy volunteer (a, b), a 22-year-old male healthy volunteer (c, d), and a 27-year-old female healthy volunteer (e, f). a A 7 T 0.5-mm-thick coronal 3D PD TSE section and (b) a 3 T 0.5-mm-thick coronal 3D PD SPACE section with a depiction of the ulnar styloid attachment (arrowheads), the foveal attachment (arrow), and the radial attachment (arrowhead) of the TFCC. c A 7 T 0.5-mm-thick axial 3D PD TSE section and (d) a 3 T 0.5-mm-thick axial 3D PD SPACE section with visualization of the dorsal portion (arrow), and the palmar portion (arrowhead) of the SLL. e A 7 T 0.5-mm-thick coronal 3D PD TSE section and (f) a 3 T 0.5-mm-thick coronal 3D PD SPACE section depicts the dorsal portion of the SLL (arrowheads). 3D, three-dimensional; PD, proton density; S, scaphoid; SLL, scapholunate ligament; SPACE, “sampling perfection with application-optimized contrasts using different flip angle evolution”; TFCC, triangular fibrocartilage complex; TSE, turbo spin echo

Fig. 3

A 39-year-old male healthy volunteer. a A 7 T and (b) a 3 T coronal 2D PD-weighted section, showing the articular cartilage (arrowheads) between the hamate and the triquetrum. Articulate cartilage between other bones is also visible. c a 7 T and (d) a 3 T axial 2D PD-weighted section, showing the median (arrow), and ulnar nerve (arrowhead), at the level of the pisiform bone. 2D, two-dimensional; H, hamate; P, pisiform; PD, proton density; T, triquetrum

Fig. 4

A 42-year-old male healthy volunteer (a, b) and a 29-year-old male healthy volunteer (c, d). a A 7 T and (b) a 3 T axial 2D PD-weighted section, with a depiction of the ECU tendon (arrow) at the dorsal groove of the ulnar head. c A 7 T and (d) a 3 T coronal T1-weighted section, illustrating visualization of bone structure. 2D, two-dimensional; ECU, extensor carpi ulnaris; PD, proton density; U, ulna