Modalities, in this URL, are two things that share a word: the kind of exam (imaging vs therapy) and the DICOM modality code on the file (CT, MR, US, PT, …). It is a glossary. It is not how the camera makes the pixels. It is not a career on-ramp. It is not “what is a pixel.”
If you meant body → pixels, the four cameras → acquisition of images. If you meant which hole to fill first → medical imaging starter. If you meant what a pixel / RGB / monochrome file is → what is an image. If you meant the DICOM file and the protocol → what is DICOM. If you meant the 3D field → 3D medical imaging.
265 already pointed here for “imaging vs therapy, DICOM modality codes.” 515 already pointed here for the same leftover job. Those splits stand. This page is not a second acquisition article.
PYCAD builds custom web DICOM viewers and imaging models. It does not sell a scanner, a linac, or a “modalities platform.”
Imaging vs therapy
In clinic, “modality” is often just “which machine.” In a toolkit sentence it splits:
| Imaging (diagnostic) modalities | Therapeutic modalities | |
|---|---|---|
| Job | Write a file someone can read: see, measure, stage, follow | Deliver energy or a substance to change tissue |
| Examples | X-ray / CR / DX, CT, MR, US, PT / NM, MG, XA, ES | External-beam RT, brachytherapy, therapeutic US, ablation, a lot of physio “modalities” (heat, TENS) that never write a DICOM |
| The file | Almost always a DICOM image IOD | Sometimes a DICOM (RTIMAGE, RTDOSE, RTPLAN, RTSTRUCT). Often not an image at all |
| What it is not | A treatment | A picture. A portal film is imaging in the service of therapy |
Ultrasound sits in both columns: a diagnostic probe and a therapeutic one are not the same device. Immunotherapy is a treatment; calling it a “modality” in an imaging glossary is how these posts go off the rails. Dropped.
The four-camera physics (CT / MRI / US / PET as how the pixels got there) stays on acquisition. Do not reread it here. A one-line reminder: CT is attenuation, MRI is water, US is echo, PET is a tracer. Therapy dose-volume is dose volume histogram, not this page.
DICOM modality codes
Tag (0008,0060) Modality is a short code that says which kind of equipment produced the instance. A PACS worklist, a hanging protocol, and a viewer’s default window all key off it. A ‘CT’ that opens in a mammography layout is a broken router, not a preference.
The code is not the SOP Class. SOP Class says which information object (a CT image vs an RT structure set vs a waveform). Modality says which camera family. Both matter; this page is the camera family.
Defined Terms live in the DICOM standard (PS3.3, C.7.3.1.1.1 Modality). The list is longer than anyone memorizes. The ones you will actually see:
| Code | Means | Usual file |
|---|---|---|
| CR | Computed radiography (plate) | Projection X-ray |
| DX | Digital radiography (flat panel) | Projection X-ray |
| IO / PX | Intra-oral / panoramic X-ray | Dental projection |
| MG | Mammography | Breast X-ray (often for-presentation + for-processing) |
| CT | Computed tomography | Slice / volume, HU |
| MR | Magnetic resonance | Slice / volume, not HU |
| US | Ultrasound | Frame or cine. Operator-dependent |
| PT | Positron emission tomography | Activity. Often a PT+CT pair |
| NM | Nuclear medicine (incl. SPECT) | Activity, not PET |
| XA / RF / XRF | X-ray angiography / fluoroscopy | Cine projection, a catheter in the picture |
| ES | Endoscopy | A camera in a lumen. Often RGB, still a DICOM |
| OT | Other | The junk drawer. Read the SOP Class |
| RTIMAGE / RTDOSE / RTPLAN / RTSTRUCT | Radiotherapy image / dose / plan / structures | Therapy objects. Not a diagnostic CT even when they look like one |
A ‘CT’ from a linac cone-beam and a ‘CT’ from a diagnostic gantry can share a code and still be different protocols. The code is necessary and not sufficient. SC (secondary capture) is how a screenshot of a report becomes a fake series — treat it as a picture, not a study.
What the code is for
Routing, hanging, and “which viewer tools to offer.” A web DICOM viewer that ignores (0008,0060) will hang a PET like a chest CR. PACS as a library is PACS and DICOM; this page only names why the tag exists.
The same patient can have four codes in one accession (PT + CT + a scout CR + an SC). That is normal. Multi-modal as a research word is several cameras on one question; multi-modal as a PACS word is several codes under one ID.
What this page is not
- Not 265. Acquisition (the physics hop) stays on that URL.
- Not 515. The starter / on-ramp stays on that URL.
- Not 612. Pixels / RGB / monochrome stay on what is an image.
- Not a market size, a physio-CAGR, or a “one platform for every modality” pitch. Dropped.
- Not a PYCAD scanner, linac, or modalities suite. Viewer / model when the file already exists. Case studies.