Is a magic angle effect observed in the collateral ligaments of the distal interphalangeal joint or the oblique sesamoidean ligaments during standing magnetic resonance imaging?
Abstract: Collagen fibers oriented at 55 degrees to the static magnetic field (B0) are characterized by an artifactual increase in signal intensity due to the magic angle effect. We hypothesized that there would be increased signal intensity in the collateral ligaments of the distal interphalangeal joint and oblique sesamoidean ligaments when these ligaments were at angles approaching 55 degrees to a horizontal B0 during standing magnetic resonance (MR) imaging. MR imaging was performed on four cadaver forelimbs in a 0.27 T standing system. Transverse and dorsal images were obtained using various sequences, with limbs angled at 0 degrees, 4 degrees, 8 degrees, and 12 degrees to the vertical. Images were analyzed and the angle of each ligament to B0 determined. Mean signal intensity in the ligament and cortex of the adjacent phalanx was measured and ratios calculated. With subjective interpretation, there was increased signal intensity in the collateral ligaments of the distal interphalangeal joint and oblique sesamoidean ligaments over ranges of angles of 60-78 degrees and 57-69 degrees, respectively, to B0. In fast spin echo (FSE) sequences, with a long echo time (72ms), the effect was less pronounced. FSE sequences can help determine the significance of increased signal intensity within tissues. In spite of limited positions of a limb during standing MR imaging compared with horses under general anesthesia, deviation from a vertical posture sufficient to cause a magic angle effect can still occur in both ligaments tested. Conformation may contribute to the occurrence of the magic angle effect during standing MR imaging. Effort should be made to position horses squarely and to minimize leaning during image acquisition.
Publication Date: 2008-12-05 PubMed ID: 19051639DOI: 10.1111/j.1740-8261.2008.00432.xGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The study investigates whether the magic angle effect, an unintentional increase in signal intensity, can be observed in the ligaments of the distal interphalangeal joint and oblique sesamoidean ligaments during standing magnetic resonance imaging.
Research Methodology
- The researchers performed Magnetic Resonance Imaging (MRI) on four cadaver forelimbs using a 0.27 T standing system.
- Images were obtained at different angles – 0 degrees, 4 degrees, 8 degrees, and 12 degrees – relative to the vertical.
- The images were then analyzed to determine the angle of each ligament to the static magnetic field, known as B0.
- The mean signal intensity within the ligament and the cortex of the adjacent phalanx were measured and their ratios computed.
Observations
- The researchers observed an increase in signal intensity in the collateral ligaments of the distal interphalangeal joint and the oblique sesamoidean ligaments over ranges of angles of 60-78 degrees and 57-69 degrees, respectively, to B0.
- This observation is indicative of the magic angle effect, which is caused by collagen fibers oriented at 55 degrees to B0.
Additional Findings
- When fast spin echo (FSE) sequences were used and had a long echo time (72ms), the magic angle effect was less pronounced, which suggests that FSE sequences can help determine the level of signal intensity within tissues.
- Even with limited limb movement during standing MR imaging compared with anesthetized horses, there was still a noticeable deviation from a vertical posture, enough to cause the magic angle effect in both ligaments tested.
- The conformations of the limbs might also contribute to the occurrence of the magic angle effect during standing MRI.
Implications
- The findings underscore the need for positioning horses squarely and minimising leaning during image acquisition to reduce the occurrence of the magic angle effect.
- The study provides valuable input for improved image interpretation and adequate imaging procedure for both ligaments.
Cite This Article
APA
Smith MA, Dyson SJ, Murray RC.
(2008).
Is a magic angle effect observed in the collateral ligaments of the distal interphalangeal joint or the oblique sesamoidean ligaments during standing magnetic resonance imaging?
Vet Radiol Ultrasound, 49(6), 509-515.
https://doi.org/10.1111/j.1740-8261.2008.00432.x Publication
Researcher Affiliations
- Centre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB87UU. meredith.smith@aht.org.uk
MeSH Terms
- Animals
- Artifacts
- Cadaver
- Collateral Ligaments / anatomy & histology
- Horses / anatomy & histology
- Magnetic Resonance Imaging / methods
- Magnetic Resonance Imaging / veterinary
- Toe Joint / anatomy & histology
Citations
This article has been cited 1 times.- Mizobe F, Okada J, Shinzaki Y, Nomura M, Kato T, Yamada K, Spriet M. Use of standing low-field magnetic resonance imaging to assess oblique distal sesamoidean ligament desmitis in three Thoroughbred racehorses.. J Vet Med Sci 2016 Oct 1;78(9):1475-1480.
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