Magic angle effect on low field magnetic resonance images in the superficial digital flexor tendon in the equine proximal pastern region.

Recognition of artefacts is an essential component of the accurate interpretation of diagnostic images. This study aimed to investigate the presence of magic angle effect in the superficial digital flexor tendon (SDFT) in the equine proximal pastern region. The proximal pastern of four cadaver limbs was imaged using a 0.27 Tesla magnet with high-resolution sequences that are commonly utilised in clinical equine practice. The limbs were imaged in a neutral position and positions that simulated the horse 'leaning in', 'leaning out' and having internal and external rotation of the distal limb. Signal intensity changes in the SDFT were described and compared. The simulated 'leaning in' and external rotation positions resulted in increased signal intensity in the axial and middle thirds of the lateral half of the SDFT on sequences with short echo times. The simulated 'leaning out' and internal rotation positions resulted in increased signal intensity in the axial and middle thirds of the medial half of the SDFT on sequences with short echo times. These signal intensity changes did not occur or were only mild and inconsistent on T2 fast spin echo sequences with longer echo times. The increases in signal intensity in the SDFT are consistent with a position-induced magic angle artefact that has been noted in clinical cases. Attention to positioning of the equine distal limb is essential during clinical imaging; radiologists should be aware of position-induced artefacts to ensure accurate image interpretation.