magnetic resonance imaging

how does MRI work

forms an image by mapping out the distribution of hydrogen nuclei

how is an MRI signal produced pt 1

MR machine has very strong magnetic field which aligns magnetic fields of hydrogen atoms in patient to produce net magnetisation

Net Magnetic Vector (NMV)

the magnetic field produced as a result of the alignment of hydrogen nuclei in the body, is a vector because it has a direction and magnitude

how is an MR signal produced pt 2

patient's magnetism is superimposed by machine's magnetism so are separated by bombarding patient with radiofrequencies to give their NMV energy, moving NMV's magnetic field to a higher energy procession state

how is an MR signal produced pt 3

radiofrequency waves turned off so NMV to move back to more stable state, emitting a wave

lamor frequency

frequency of procession, equal to frequency of radiowaves

advantages of MRI

no ionising radiation, images directly acquired in multiple planes, superior soft tissue contrast, allows images to be weighted to visualise different tissues

disadvantages of MRI

need to be screened before getting an MRI, long scans, uncomfortable, very expensive, susceptible to artefacts