Magnetic resonance imaging
Magnetic resonance imaging (commonly known as an MRI scan) is a type of neuroimaging performed in health care. It has been described as a "non-invasive method of demonstrating internal anatomy, based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves - which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques."[1]
Classification
- Echo-planar imaging allows much faster acquisition of images.
- Functional magnetic resonance imaging uses echo-planar imaging and measures changes in oxygenation status of hemoglobin in response to specific sensory or motor stimulation.[2][3][4]
- Magnetic resonance angiography
- Magnetic resonance spectroscopy
- Cine magnetic resonance imaging is primarily used in cardiology.
- Diffusion magnetic resonance imaging usually uses echo-planar imaging and measures changes in the apparent diffusion coefficient (ADC).
Physical principles
In contrast to x-ray computed tomography which is based on the density of electrons in tissues, MRI is based on several properties of protons.[5][6][7][8][9]Atoms with an odd number of protons, such as hydrogen, inherently create a small magnetic field that can be measured, then manipulated by MRI, then measured again as the tissue relaxes after the external field is turned off.[5]
| Pulse sequence | Description | Application |
|---|---|---|
| Standard pulse sequences | ||
| Spin density | Proton density | |
| T1 relaxation time | Spin-lattice (longitudinal) relaxation time. Short TR & TE | Less mobile molecules (including lipids, cerebral white matter, yellow bone marrow) are bright. T1 images can be obtained faster. Long TR & TE T1 images better display gadolinium contrast medium[7] |
| T2 relaxation time | Spin-spin (transverse) relaxation time | Water (including CSF, urine, cysts, abscesses) is bright[7] |
| Other pulse sequences | ||
| DWI (diffusion-weighted imaging) | ||
| ADC (apparent diffusion coefficient) | ||
| GRE (gradient echo) pulse sequences | Blood flow is bright | |
| PWI (perfusion-weighted imaging) | ||
References
- ↑ Anonymous (2024), Magnetic resonance imaging (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ Le Bihan D, Jezzard P, Haxby J, Sadato N, Rueckert L, Mattay V. Functional magnetic resonance imaging of the brain. Ann Intern Med. 1995 Feb 15;122(4):296-303. PMID 7825767
- ↑ Gilman S. Imaging the brain. First of two parts. N Engl J Med. 1998 Mar 19;338(12):812-20. PMID 9504943
- ↑ Gilman S. Imaging the brain. Second of two parts. N Engl J Med. 1998 Mar 26;338(13):889-96. PMID 9516225
- ↑ 5.0 5.1 Hendee WR, Morgan CJ. Magnetic resonance imaging. Part I--physical principles. West J Med. 1984 Oct;141(4):491-500. PMID 6506686
- ↑ Hendee WR, Morgan CJ. Magnetic resonance imaging. Part II--Clinical applications. West J Med. 1984 Nov;141(5):638-48. PMID 6516335
- ↑ 7.0 7.1 7.2 Edelman RR, Warach S. Magnetic resonance imaging - First of Two Parts. N Engl J Med. 1993 Mar 11;328(10):708-16. PMID 8433731
- ↑ Edelman RR, Warach S. Magnetic resonance imaging - Second of Two Parts. N Engl J Med. 1993 Mar 18;328(11):785-91. PMID 8369029
- ↑ Berger A. Magnetic resonance imaging. BMJ. 2002 Jan 5;324(7328):35. PMID 11777806