Effect of deep digital flexor tendon orientation on magnetic resonance imaging signal intensity in isolated equine limbs-the magic angle effect.

This research explored how the orientation of the deep digital flexor tendon in horse limbs affects the intensity of the magnetic resonance imaging (MRI) signal. It was found that an increased signal intensity was observed at an angle of approximately 55 degrees, a phenomenon referred to as the “magic angle”.

Research method and procedure

• The study used ten normal equine isolated limbs and imaged them using a knee coil in a 1.5 Tesla magnetic field with short echo time sequences.
• MRI was performed on each isolated limb in different positions, including with and without extension of the metacarpophalangeal joint.
• The orientation of the horse’s deep digital flexor tendon was varied between 20 to 60 degrees in relation to the static magnetic field.

Findings

• An increased intensity of the intratendinous signal was observed when the angle between the deep digital flexor tendon and the constant magnetic field was approximately 55 degrees, hence named the “magic angle”.
• The increased signal intensity was observed to be independent of the extension of the metacarpophalangeal joint.

Significance

• Understanding the “magic angle” phenomenon is crucial in interpreting MRI scans of the equine foot. These scans are critical for diagnosing many conditions, and so it’s important to know how the tendon’s orientation can affect the image’s clarity and readability.
• The findings imply that care must be taken when positioning the horse’s foot for an MRI scan and evaluating the results. Misinterpretation could occur if the presence of the magic angle effect is not taken into account, potentially leading to incorrect diagnoses.