Modality is the term used in radiology to refer to one form of imaging, e.g. CT. It is often used in the plural form, e.g. "various modalities can be employed to evaluate this liver lesion."
More generally, in clinical medicine, the term 'modality' refers to different types of procedures and therapies. For example, modalities of treatment for cancer include chemotherapy, radiotherapy, and surgery.
Imaging modalities
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often cross-sectional radiotracer scanning, e.g. PET, is considered a separate modality from 'traditional' scintigraphy, e.g. bone scans
hybrid modalities, e.g. PET-CT, PET-MRI, SPECT-CT
At times, modalities are subdivided into structural techniques and functional techniques. The former are those modalities that primarily demonstrate the anatomy of body structures, e.g. CT or MRI, and the latter are modalities that emphasize function, such as bone scintigraphy, over the anatomy.
NB: As per the agreed Radiopaedia style guide, when two modalities are combined such as PET and CT, the two modalities are separated by a single dash only, i.e. PET-CT, PET-MRI, etc. We ask contributors not to use any other format.