Magic angle effect: a relevant artifact in MR neurography at 3T?

Area of Science:

• Medical Imaging
• Neuroscience
• Biophysics

Background:

• Magnetic Resonance Neurography (MRN) is an emerging technique for diagnosing peripheral nerve disorders.
• The impact of magnetic susceptibility (MA) on intraneural T2 signal in MRN requires clarification to prevent false-positive findings.

Purpose of the Study:

• To investigate the influence of MA on intraneural T2 signal in healthy subjects.
• To determine if MA-induced T2 signal changes can be distinguished from neuropathic lesions.

Main Methods:

• MRN of the sciatic nerve was performed at 3T in 25 healthy subjects.
• Apparent T2 (T2(app)) was calculated at various angles (0°–55°) relative to B0 using a DE-TSE sequence.
• Intraneural contrast-to-noise ratios (CNRs) were compared between healthy subjects and 14 patients with neuropathic lesions using a TIRM sequence.

Main Results:

• T2(app) significantly increased with MA angle in healthy subjects (74.5 ms at 0° to 104.0 ms at 55°).
• Intraneural CNR increased with MA, but remained substantially lower in healthy subjects compared to patients even at maximum MA (55°).

Conclusions:

• Neuropathic lesions are clearly distinguishable from MA-induced increases in intraneural T2 signal.
• False-positive determination of neuropathic lesions due to MA is unlikely, even at maximum MA (55°).