Magnetic resonance imaging: Difference between revisions

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In [[diagnostic imaging]], '''magnetic resonance imaging''' (commonly known as an '''MRI scan''') 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."<ref>{{MeSH}}</ref> MRI is commonly used in [[neuroimaging]].
'''Magnetic resonance imaging''' (also known as '''Nuclear Magnetic Resonance imaging''' or as an '''MRI scan''') is a [[non-destructive imaging]] technique with a wide range of applications in the [[materials science]]s and [[life sciences]], including [[diagnostic imaging]] and [[neuroimaging]]. It employs the principle of [[nuclear magnetic resonance]] and is thus, in essence, a variant of [[NMR spectroscopy]] in which the exchange of information with the sample of interest is achieved by radiofrequency pulses at [[isotope]]-specific energy levels. The main difference between MR spectroscopy and MR imaging (the ''N'' is often dropped to avoid confusion with [[nuclear energy]]) is that the static [[magnetic field]] used in the former is supplemented in the latter by
space-encoding magnetic [[field gradient]]s which allow to combine the chemical information (or parts thereof) with spatial information to generate isotope-specific images.  


==Classification==
==Classification==
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* [[Magnetic resonance spectroscopy]]<ref>Fisher M, Prichard JW, Warach S. New magnetic resonance techniques for acute ischemic stroke. JAMA. 1995 Sep 20;274(11):908-11. PMID 7674506</ref>
* [[Magnetic resonance spectroscopy]]<ref>Fisher M, Prichard JW, Warach S. New magnetic resonance techniques for acute ischemic stroke. JAMA. 1995 Sep 20;274(11):908-11. PMID 7674506</ref>
* [[Magnetic resonance microscopy]] - concerned with imaging at resolutions around or below about 100µm
* [[Magnetic resonance microscopy]] - concerned with imaging at resolutions around or below about 100µm
* [[Localized spectroscopy]] - combines MR spectroscopy and MR imaging by providing spectroscopic information from specific spatial locations within the sample
* [[Chemical-shift imaging]] - combines MR spectroscopy and MR imaging by providing information about the spatial distribution of spectroscopically visible [[chemical bond]]s within the sample
* [[Cine magnetic resonance imaging]] is primarily used in cardiology.
* [[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).
* [[Diffusion magnetic resonance imaging]] usually uses echo-planar imaging and  measures changes in the apparent diffusion coefficient (ADC).

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Magnetic resonance imaging (also known as Nuclear Magnetic Resonance imaging or as an MRI scan) is a non-destructive imaging technique with a wide range of applications in the materials sciences and life sciences, including diagnostic imaging and neuroimaging. It employs the principle of nuclear magnetic resonance and is thus, in essence, a variant of NMR spectroscopy in which the exchange of information with the sample of interest is achieved by radiofrequency pulses at isotope-specific energy levels. The main difference between MR spectroscopy and MR imaging (the N is often dropped to avoid confusion with nuclear energy) is that the static magnetic field used in the former is supplemented in the latter by space-encoding magnetic field gradients which allow to combine the chemical information (or parts thereof) with spatial information to generate isotope-specific images.

Classification

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]

MRI pulse sequences
Pulse sequence Description Application
Standard pulse sequences
Spin echo Proton density (water) thoracic imaging
T1 relaxation time Spin-lattice (longitudinal) relaxation time. Short repitition time (TR) & echo time (TE) More solid and less mobile molecules (including lipids, cerebral white matter, yellow bone marrow) are bright.
T1 images can be obtained faster.
T1 images better display gadolinium contrast medium[7]
T2 relaxation time Spin-spin (transverse) relaxation time. Long TR & TE 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)    

Interpretation

The accuracy of interpretation depends on the quality of both the MRI machine used and the quality of the radiologist.[10]

References

  1. 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
  2. Gilman S. Imaging the brain. First of two parts. N Engl J Med. 1998 Mar 19;338(12):812-20. PMID 9504943
  3. Gilman S. Imaging the brain. Second of two parts. N Engl J Med. 1998 Mar 26;338(13):889-96. PMID 9516225
  4. Fisher M, Prichard JW, Warach S. New magnetic resonance techniques for acute ischemic stroke. JAMA. 1995 Sep 20;274(11):908-11. PMID 7674506
  5. 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
  6. Hendee WR, Morgan CJ. Magnetic resonance imaging. Part II--Clinical applications. West J Med. 1984 Nov;141(5):638-48. PMID 6516335
  7. 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
  8. Edelman RR, Warach S. Magnetic resonance imaging - Second of Two Parts. N Engl J Med. 1993 Mar 18;328(11):785-91. PMID 8369029
  9. Berger A. Magnetic resonance imaging. BMJ. 2002 Jan 5;324(7328):35. PMID 11777806
  10. The Scan That Didn’t Scan - NYTimes.com.