State one advantage and one disadvantage of magnetic resonance imaging (MRI) compared to X-ray imaging.

Explain why a gradient field is required in nuclear magnetic resonance (NMR) imaging.

Advantage:

no ionizing radiation OR high res images of soft tissue OR 3D images

Disadvantage:

«generally» more expensive OR takes much longer OR less detail of bony structures «than X-ray» OR noisy for patient OR claustrophobic for patient OR cannot be used for patients with metal implants

Do not accept advantages that are also true of X-rays, eg non-invasive.

a gradient field is added to a magnetic field that is originally uniform across patient
the gradient field varies linearly across patient
as the protons relax a «radio frequency» signal is emitted
the emitted signal frequency is proportional to the total strength of the magnetic field
the signal frequency depends on the emission position in the patient