Slide 1
MRI constructs an image from tissue’s responses
Magnetic resonance imaging, or MRI, uses measured magnetic responses in tissue to construct images of anatomy. It does not take a photograph inside the body.
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MRI is particularly useful for examining soft tissues. Unlike an ordinary photograph, the image depends on how measurements are acquired and reconstructed. Movement during acquisition can blur the result, so producing a clear image involves the patient and the measurement process as well as the scanner.
Slide 2
A strong field establishes an overall magnetic alignment
A strong magnetic field establishes net alignment among hydrogen nuclei in tissue. Nuclei are the centres of atoms; here, net means overall.
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A strong magnetic field establishes a net alignment among hydrogen nuclei in tissue. An explanatory diagram can represent this collective behavior with arrows; those arrows are a model, not literal spinning objects inside cells.
Slide 3
Radio pulses change that state so a response can be measured
Radiofrequency pulses change the tissue’s magnetic state. The subsequent response produces detectable signals.
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Radiofrequency pulses change that magnetic state. The subsequent response produces detectable signals whose behavior depends on the surrounding tissue. Those differences help create contrast between structures in the resulting image.
Slide 4
The signals must also carry information about position
MRI must encode position as well as detect signals. Reconstruction then converts those measurements into an image.
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Image formation requires more than detecting a response. Spatial encoding associates information with position, and reconstruction converts the measurements into an image. Acquisition choices influence how tissue differences appear, so brightness is not a simple photograph of tissue color.
Slide 5
The imaging method still needs its own safety precautions
MRI uses no ionizing radiation. But its strong magnets still require safety screening, including assessment of implants.
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MRI uses no ionizing radiation, but strong magnets still require safety screening, including assessment of implants. Its images depend on tissue properties and measurement choices: a powerful way to examine anatomy, with its own constraints.
Sources
- Magnetic Resonance Imaging (MRI)
NIH, NIBIB