Ultra-high field MRI clinical anatomy of the equine fetlock to aid clinical image interpretation

Reasons for performing study:

Interpretation of clinical diagnostic imaging of the equine musculoskeletal system requires accurate reference anatomical materials. In the case of MRI, this includes images acquired from low and high field systems. Using ultra-high field MRI, higher resolution images with small slice thickness and gap suitable for reconstruction in any anatomical plane can be produced.

Objectives:

To describe the normal equine metacarpophalangeal joint using ultra-high field MRI and compare ultra-high and high field MR images.

Study design:

Limbs (n = 14) from horses (n = 5) with no history of orthopaedic disease were frozen at -20°C until imaging. Fetlock joints were scanned using an ultra-high field (7T) MRI unit. T1 (280 slices, thickness = 0.356 mm) and T2 (140 slices, thickness = 0.713 mm) weighted sequences were acquired. Limbs were scanned using a 1.5T MRI unit in transverse, sagittal, and dorsal planes using T1 (60 slices, thickness 2.2–3.5 mm) and T2 (60 slices, thickness 2.2–3.5 mm) sequences. Images were analysed using OsiriX software.

Results:

Ultra-high field MR images visualised the fine detail of trabecular and subchondral bone, the articular cartilage surface of P1 and McIII, the short, oblique, straight and oblique sesamoidean ligaments including origins and insertions, the fasicular structure of superficial digital flexor tendon, deep digital flexor tendon and ligaments and the regional neurovascular structures. Whilst T1 high field images visualised the majority of tissues, structural detail was reduced compared to ultra-high field imaging, margins were less well defined in some instances, e.g. articular cartilage, and a number of smaller structures were indistinct, e.g. short and cruciate sesamoidean ligaments.

Conclusions:

7T MRI produced images of the fetlock with excellent anatomical detail. Future publication of opensource ultra-high field MRI files could aid the interpretation of 0.3T and 1.5T field MR images, especially with the capacity to reconstruct image slices orientated exactly to match those of interest.