Characterization of the Magic Angle Effect in the Equine Deep Digital Flexor Tendon Using a Low‐field Magnetic Resonance System

Abstract

Three isolated equine limbs were imaged with a low-field magnetic resonance system with a vertical magnetic field. Each limb was scanned in multiple positions with mild variation of the angle between the magnetic field and the long axis of the limb. When the long axis of the limb was not perpendicular to the magnetic field, a linear hyperintense signal was present at the palmar aspect of one of the deep digital flexor tendon lobes, at the level of the navicular bone and collateral sesamoidean ligaments, in proton density and T1-weighted pulse sequences. With increased angulation of the limb, the palmar hyperintense signal extended farther distally and proximally and additional signal hyperintensity was present at the dorsal aspect of the distal part of the other lobe of the deep digital flexor tendon. Increased signal intensity was also present in the collateral ligament of the distal interphalangeal joint on the same side as the palmar hyperintense signal in the tendon. The changes in the deep digital flexor tendon are due to the specific orientation of fibers at the palmar and dorsal aspect of the tendon, which is responsible for focal manifestation of the magic angle effect. Careful positioning of the limb perpendicular to the magnetic field can prevent this phenomenon. The association of palmar increased signal intensity in the deep digital flexor tendon with increased signal in the collateral ligament of the distal interphalangeal joint on the same side should be recognized as manifestations of the magic angle effect. Veterinary

Influence of the position of the foot on MRI signal in the deep digital flexor tendon and collateral ligaments of the distal interphalangeal joint in the standing horse

“…Similar changes have been reported previously with a low field MR system used with horses under general anaesthesia (Spriet et al 2007;Spriet and McKnight 2009). The orientation of the magnetic field relative to the limb in those studies is equivalent to the equine standing MR system used in this study, which accounts for the similar changes observed with the 2 systems.…”

“…Such changes in signal intensity have been recognised in MR imaging of the foot of horses under general anaesthesia, both with high field (Busoni and Snaps 2002) and low field (Spriet et al 2007;Spriet and McKnight 2009) MR systems. Standing equine MR systems have a configuration similar to recumbent low field MR systems, with the magnetic field perpendicular to the sagittal plane of the limb.…”

Anatomical, magnetic resonance imaging and histological findings in the accessory ligament of the deep digital flexor tendon of forelimbs in nonlame horses

“…In the horse, a MAE has been described in the DDFT (Busoni and Snaps 2002; Dyson et al . 2003; Spriet and McKnight 2009; Spriet and Zwingenberger 2009), the oblique sesamoidean ligaments (Smith et al . 2008) and in the collateral ligaments of the distal interphalangeal joint (Spriet et al .…”

New methods to study the composition and structure of the extracellular matrix in natural and bioengineered tissues

“…However, this only holds when the cartilage is completely isotropically-oriented with respect to the B 0 field since otherwise the so-called magic-angle effect has also to be considered, i.e., the appearance of individual cartilage layers depends on the angle between the sample and the static B 0 field 107 . Very similar effects are also observed when bone and tendon 108 samples are investigated in dependence on the orientation of the sample with respect to the magnetic field.…”