Common magnetic field strengths range from 0.3 to 3 T, although field strengths as high as 9.4 T or higher are used in research scanners and research instruments for animals or only small test tubes range as high as 20 T. Commercial suppliers are investing in 7 T platforms. For comparison, the Earth's magnetic field averages around 50 μT, less than 1/100,000 times the field strength of a typical MRI
Functional MRI (fMRI) measures signal changes in the brain that are due to changing neural activity:
Hydrogen
is the most frequently imaged nucleus in MRI because it is present in
biological tissues in great abundance. However, any nucleus which has a
net nuclear spin could potentially
be imaged with MRI. Such nuclei include helium-3, carbon-13, oxygen-17,
sodium-23, phosphorus-31 and xenon-129. 23Na and 31P are naturally
abundant in the body, so can be imaged directly
Cerebellar activation maps resulting from electrical stimulation of the left forpaw (LFP) and left hindpaw (LHP) superimposed on high resolution images of the cerebellum. Figures A, B,C and D are from the same rat. Coronal images (A and C) show 5 consecutive 1 mm thick slices located from -1 mm to -5 mm interaurally, sagittal images (B and D) show 6 slices of 1 mm thickness.
Visualization of the orienitation columns at the human brain obtained by fMRI.
Visualization of the orienitation columns at the human brain obtained by fMRI.
Nature Neuroscience 3,
164 - 169 (2000) doi:10.1038/72109 High-resolution mapping of
iso-orientation columns by fMRI Dae-Shik Kim, Timothy Q. Duong
& Seong-Gi Kim