Related Experiment Videos
Intervertebral disks on MR images: variation in signal intensity with the disk-to-magnetic field orientation
1Division of Radiology, Cleveland Clinic Foundation, OH 44195, USA.
Purpose:
To demonstrate and quantitate the magic angle effect in the intervertebral disk.
Materials And Methods:
Magnetic resonance (MR) images of a lumbar intervertebral disk in a healthy volunteer were obtained with MR images with horizontal and vertical magnetic fields. Thin-section spin-echo images of an excised intervertebral disk were obtained with a horizontal field machine at orientations with respect to the main magnetic field between +90 degrees and -90 degrees. T1 and T2 were measured independently in this disk at two orientations.
Results:
Images of the in vivo disk demonstrated a variation in the signal intensity of the anulus fibrosus that was different for the two MR units. The images obtained in the excised intervertebral disk demonstrated a signal intensity variation with disk orientation that was most pronounced in the anterior portion of the anulus. Relaxation time measurements showed the signal intensity reduction to arise from a reduction in T2 with oblique orientations.
Conclusion:
The observed signal intensity variation with disk orientation arises from an anisotropy in T2 caused by the restriction of water associated with collagen in the anulus. The magic angle effect in intervertebral disks will be observed with vertical magnetic field MR imagers.
Insights
The magic angle effect in intervertebral discs causes signal variations due to T2 anisotropy. This phenomenon is observable with vertical magnetic field magnetic resonance (MR) imagers.
Area of Science:
- Biophysics
- Magnetic Resonance Imaging
Background:
- The intervertebral disc is a complex biological structure.
- Magnetic Resonance (MR) imaging is a key tool for visualizing soft tissues.
Purpose of the Study:
- To demonstrate and quantify the magic angle effect in the intervertebral disc.
- To investigate the impact of magnetic field orientation on MR signal intensity.
Main Methods:
- Acquired MR images of a lumbar intervertebral disc in vivo using horizontal and vertical magnetic fields.
- Obtained thin-section spin-echo images of an excised intervertebral disc at various orientations.
- Measured T1 and T2 relaxation times at different orientations.
Main Results:
- In vivo images showed signal intensity variations in the anulus fibrosus dependent on the MR unit.
- Excised disc images revealed orientation-dependent signal intensity variations, particularly in the anterior anulus.
- Relaxation time measurements indicated signal reduction due to decreased T2 at oblique orientations.
Conclusions:
- The signal intensity variation is attributed to T2 anisotropy caused by water restriction within the anulus fibrosus collagen.
- The magic angle effect is expected to be observable in intervertebral discs using vertical magnetic field MR imagers.