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[[File:MRM of stained muscle fibers.jpg|thumb|Top: MRM image of mouse muscle fibers stained with [[ferric ammonium citrate]], scale bar 200 μm. Bottom: conventional micrograph showing the MRM coil.<ref>{{cite journal|doi=10.1038/srep39496|pmid=28045071|pmc=5206738|title=Magnetic Resonance Microscopy (MRM) of Single Mammalian Myofibers and Myonuclei|journal=Scientific Reports|volume=7|pages=39496|year=2017|last1=Lee|first1=Choong H.|last2=Bengtsson|first2=Niclas|last3=Chrzanowski|first3=Stephen M.|last4=Flint|first4=Jeremy J.|last5=Walter|first5=Glenn A.|last6=Blackband|first6=Stephen J.|bibcode=2017NatSR...739496L}}</ref>]]
'''Magnetic resonance microscopy''' (MRM, μMRI) is [[magnetic resonance imaging]] (MRI) at a microscopic level down to the scale of microns.<ref>{{cite journal|pmid=18775619|year=2009|
==Nomenclature==
Magnetic resonance microscopy refers to very high resolution MRI imaging (down to nanometer scale, in some cases comparable with histopathology). The term MR microscopy is most widely used by the High Resolution Magnetic Resonance Imaging department at Duke University, headed by Dr. G. Allan Johnson, and the National High Magnetic Field Lab group at AMRIS, University of Florida/Florida State University.<ref>{{cite journal|doi=10.2174/1877613211101020089|title=21.1 Tesla Magnetic Resonance Imaging Apparatus and Image Interpretation: First Report of a Scientific Advancement|journal=Recent Patents on Medical
== Differences between MRI and MRM ==
* MRM represent a higher evolution of MRI
* [[Angular resolution|Resolution]]: Medical MRI resolution is typically about 1 mm<sup>3</sup>; the desired resolution of MRM is 100 μm<sup>3</sup> or smaller to 10 μm<sup>3</sup>, comparable with histology.▼
* MRM employs a much stronger magnetic field, which is conducted on a much smaller scale. <ref>{{cite web |title=Magnetic Resonance Microscopy (MRM) {{!}} The Embryo Project Encyclopedia |url=https://embryo.asu.edu/pages/magnetic-resonance-microscopy-mrm |website=embryo.asu.edu |publisher=The Embryo Project Encyclopedia |access-date=11 October 2021}}</ref>
* Specimen size: Medical MRI machines are designed so that a patient may fit inside. MRM chambers are usually small, typically less than 1 cm<sup>3</sup> for the imaging of rats, mice and rodents. BrukerBio Spin Company, Billerica, MA specialises in the supply of different microimaging probes (5 mm – 75 mm) for ex vivo/in vivo imaging of excised biological samples.<ref>{{cite journal|pmid=20663627|year=2010|author1=Sharma|first1=R|title=Jet fuel toxicity: Skin damage measured by 900-MHz MRI skin microscopy and visualization by 3D MR image processing|journal=Magnetic Resonance Imaging|volume=28|issue=7|pages=1030–48|last2=Locke|first2=B. R.|doi=10.1016/j.mri.2010.03.045}}</ref>▼
▲* [[Angular resolution|Resolution]]: Medical MRI resolution is typically about 1 mm
▲* Specimen size: Medical MRI machines are designed so that a patient may fit inside. MRM chambers are usually small, typically less than 1 cm<sup>3</sup> for the imaging of rats, mice and rodents. BrukerBio Spin Company, Billerica, MA specialises in the supply of different microimaging probes (5 mm – 75 mm) for ex vivo/in vivo imaging of excised biological samples.<ref>{{cite journal|pmid=20663627|year=2010|
== Current status of MRM ==
Although MRI is very common for medical applications, MRM is still developing in laboratories up to resonance frequencies of 1000 MHz<sup>[1]</sup> (for nuclear magnetic resonance; electron magnetic resonance commonly operates at much higher frequencies). The major barriers for practical MRM include:
* [[Magnetic field]] [[gradient]]: High gradient focus of magnetic resonance in a smaller volume (smaller [[point spread function]]), results in a better spatial resolution. The gradients for MRM are typically 50 to 100 times those of clinical systems. However, the construction of [[radio frequency]] (RF) coils used in MRM does not allow ultrahigh gradients.
* [[Sensitivity (electronics)|Sensitivity]]: Because the voxels for MRM can be 1/100,000 of those in MRI, the signal is proportionately weaker.<ref>{{cite journal|doi=10.1080/01926230490451707|pmid=15503663|url=http://civmxsrv1.duhs.duke.edu/publications/Journal_articles/Maronpot.MRM2004.pdf|title=Applications of Magnetic Resonance Microscopy|journal=Toxicologic Pathology|volume=32|issue=5|pages=42–8|year=2004|last1=Maronpot|first1=Robert R.|last2=Sills|first2=Robert C.|last3=Johnson|first3=G. Allan|citeseerx=10.1.1.1029.6047|s2cid=233584 }}</ref><ref>Sharma, R. [https://www.webmedcentral.com/articlefiles/655999094b6a6eaeccbc273dad1b9bab.pdf Physical Basis of Gadolinium Induced Skin Nephrofibrosis: Testing by Gadolinium-Protein Targeting Assay and Iron Oxide Nanoparticle Based Magnetic Resonance Microscopy]. ISRN Dermatology. 1</ref><ref>{{cite journal|pmid=20577039|year=2010|
== Alternative MRM ==
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{{Commons category|Magnetic resonance microscopy}}
* [http://cbaweb2.med.unc.edu/henson_mrm/pages/mrmfaq.html#MRMAnchor Introduction to Magnetic Resonance Microscopy] Auditory Research Laboratory at the Univ. of North Carolina.
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[[Category:Magnetic resonance imaging]]
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