It is confined to regions of tightly bound collagen at 54.74° from the main magnetic field (Bo), and appears hyperintense, thus potentially being mistaken for tendonopathy.
In tightly bound collagens, water molleules are restricted usually causing very short T2 times, accounting for the lack of signal.
When molecules lie at 54.74°, there is lengthening of T2 times with corresponding increase in signal. Thus in short TE sequences, the T2 signal does not decay significantly before the scanner picks up the signal. On the other hand, in long TE sequences (like T2WI), by the time the scanner picks the signal, T2 signal has already decayed.
The reason for this change is due to quantum mechanics: in the set of equations that describe the interaction of spins (their Hamiltonian), there are several terms that are orientation-dependent. Normally, these orientations are averaged over as protons tumble around thermally, but in sites with long-range order these terms can be important. In the case of structured collagen, lots of water binds to the outside of the protein, and therefore exhibits an orientation-dependent effect.
Typical sites include:
- proximal part of the posterior cruciate ligament (PCL)
- peroneal tendons as they hook around the lateral malleolus.
- cartilage can also be affected, e.g. femoral condyles
- supraspinatus tendon
- triangular fibrocartilage complex (if the patient is imaged with the arm elevated)
- infrapatellar tendon at the tibial insertion
It appears that at 3.0T the effects are reduced.
Other non-pathologic causes of high signal within tendons include near tendon insertions, and/or where the tendon normally fans out or merges with other tendons.
Tends to occur only on short TE sequences (e.g. T1, GRE, PD), sequences with a longer TE (e.g. T2 including FSE T2) can be used to avoid this artefact.
- MRI (introduction)
- MR physics
- MR hardware
- signal processing
MRI pulse sequences (abbreviations | parameters)
- spin echo sequences
- inversion recovery sequences
- gradient echo sequences
- fat suppressed imaging sequences
- pulse sequence parameters
- diffusion weighted sequences (DWI)
- perfusion weighted imaging
- saturation recovery sequences
- echo-planar pulse sequences
- metal artifact reduction sequence
- spiral pulse sequences
- MR angiography (and venography)
MR spectroscopy (MRS)
- Hunter's angle
- lactate peak: resonates at 1.3 ppm
- lipids peak: resonate at 1.3 ppm
- alanine peak: resonates at 1.48 ppm
- N-acetylaspartate (NAA) peak: resonates at 2.0
- glutamine-glutamate peak: resonate at 2.2-2.4 ppm
- gamma-aminobutyric acid (GABA) peak: resonate at 2.2-2.4 ppm
- creatine peak: resonates at 3.0 ppm
- choline peak: resonates at 3.2 ppm
- myo-inositol peak: resonates at 3.5 ppm
- functional MRI
- MR hardware and room shielding
- MR software
- patient and physiologic motion
- tissue heterogeneity and foreign bodies
- Fourier transform and Nyqvist sampling theorem
MR contrast agents
- extracellular MRI contrast agents
- hepatobiliary MRI contrast agents
- intravascular (blood pool) MRI contrast agents
- gastrointestinal MRI contrast agents
- tumor-specific MRI contrast agents
- reticuloendothelial MRI contrast agents
- contrast agent safety
- MR safety
- 1. Erickson SJ, Cox IH, Hyde JS et-al. Effect of tendon orientation on MR imaging signal intensity: a manifestation of the "magic angle" phenomenon. Radiology. 1991;181 (2): 389-92. Radiology (abstract) - Pubmed citation
- 2. Erickson SJ, Prost RW, Timins ME. The "magic angle" effect: background physics and clinical relevance. Radiology. 1993;188 (1): 23-5. Radiology (citation) - Pubmed citation
- 3. Kneeland JB. Articular cartilage and the magic angle effect. AJR Am J Roentgenol. 2001;177 (3): 671-2. AJR Am J Roentgenol (full text) - Pubmed citation
- 4. Gold GE, Suh B, Sawyer-glover A et-al. Musculoskeletal MRI at 3.0 T: initial clinical experience. AJR Am J Roentgenol. 2004;183 (5): 1479-86. AJR Am J Roentgenol (full text) - Pubmed citation
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Magic angle effect||✗|
|Magic angle artifact||✗|
|Magic angle artefact||✗|