DICOM Modalities: Types, Codes, and Modality Tags

A DICOM modality is the code that tells every system in the imaging chain what kind of device or process produced a series of images. MR means magnetic resonance, CT means computed tomography, PT means PET, and dozens of other values cover everything from ultrasound to radiotherapy plans. This guide explains what a DICOM modality is, lists the current modality types and codes, shows how the Modality tag (0008,0060) behaves in real data, and covers what to watch for when you work with multi-modality imaging across sites and systems.

What Is a DICOM Modality?

In the DICOM standard, a modality describes the type of device, process, or method that originally acquired or produced the data in a series. It is stored as a short uppercase code in the Modality attribute, tag (0008,0060), which sits at the series level. A CT scanner produces a series with the value CT, an MRI scanner produces MR, and a PET scanner produces PT. DICOM, which stands for Digital Imaging and Communications in Medicine, is the international standard for handling, storing, and exchanging medical images. Its official site describes it as defining formats for medical images that can be exchanged with the data and quality needed for clinical use. You can read more at the DICOM Standard organization.

Modality codes are not only for scanners. The standard also uses them for derived and non-imaging objects, such as segmentations (SEG), structured reports (SR), and radiotherapy plans (RTPLAN). That is why a code list that only covers scanners will miss real values you meet in production data. The rest of this guide separates the codes into groups so you can find what you need quickly, explains how the tag behaves in real datasets, and points out the mistakes that most often cause trouble in imaging pipelines.

DICOM Modality Types and Codes

The tables below are based on the Modality defined terms in Part 3 of the DICOM Standard, which is updated several times a year. Always confirm against the current edition of the standard before building rules that depend on a specific value, because new codes are added and old ones are retired over time.

Common Medical Imaging Modalities

These eleven codes account for most of the images in hospital and clinical trial archives.

A few of these codes are easy to confuse. CR and DX both describe projection X-ray, but CR comes from phosphor plate systems while DX comes from direct digital detectors, and RG is used for film that has been digitized. PT and NM are both nuclear techniques, but PT covers positron emission tomography and NM covers gamma camera imaging, including SPECT. MR is a single value for every magnetic resonance sequence, so a brain MRI, a cardiac MRI, and an MR angiogram all share it. The finer distinction comes from other attributes, such as the series description, the protocol name, and the sequence parameters.

In a clinical trial, this shared vocabulary is what allows a protocol to say "baseline CT and PET within 28 days" and have every site, vendor, and reader interpret it the same way. Imaging manuals usually list the required modality for each visit, and the modality tag is the first check that a received series matches that requirement.

Specialty DICOM Acquisition Modalities

These codes describe specialized devices, including ophthalmic instruments, intravascular catheters, microscopes, and dental or surface imaging systems. They appear less often in general radiology but are common in ophthalmology, cardiology, pathology, and dermatology datasets.

Non-Imaging and Derived DICOM Modalities

Some modality values describe waveforms, documents, or objects created from other data rather than a scanner. This group includes physiological signals, radiotherapy objects, segmentations, reports, and presentation states. The code OT (Other) is a catch-all for anything that does not fit another category.

Retired DICOM Modality Codes

Older archives still contain values that the standard has since retired. You will not see them on new equipment, but you may need to map them when you migrate or pool historical data. Several were folded into current codes. For example, SPECT was ST and is now handled under NM, and echocardiography was EC and is now US.

What Does the DICOM Modality Tag (0008,0060) Mean?

The Modality tag (0008,0060) is a required attribute in the General Series module. It has a single value per series, and it is one of the first things a system reads when it receives images. The tag is a code string, so values are uppercase and short, and they should come from the defined terms in the standard. A related attribute, Modalities in Study (0008,0061), lists all the modalities present in a study, which is how a PET/CT exam can be labeled with both PT and CT.

One point surprises many teams: the modality value does not always match the name of the object type it appears in. The standard notes that the modality may not match the name of the information object definition. A digitized film, a secondary capture image, or a converted file may carry OT or another value that does not reflect the original scanner. When data quality matters, check the modality alongside the SOP Class, the manufacturer, and other series attributes instead of relying on a single tag. Our guide to DICOM metadata extraction shows how these attributes are read at scale.

Reading the tag is straightforward in most tools. In Python with the open-source pydicom library, the value is available as the Modality attribute of a loaded dataset, and command-line utilities such as dcmdump print it as (0008,0060). At scale, teams extract the tag for every instance into an index so that they can count series by modality, spot unexpected values, and compare what each site sent against what the protocol requires. For studies that combine sites, this simple inventory often reveals problems early, such as a site that sends only secondary captures or a scanner that uses a non-standard value.

Developers should also plan for values that fall outside the list. Real datasets contain retired codes, vendor-specific entries, and missing or empty attributes. A robust pipeline validates against the current defined terms, maps retired values where the meaning is clear, and flags anything else for review instead of failing silently.

DICOM Modality Codes vs. Common Imaging Names

Clinicians and researchers use everyday names, and those names often differ from the DICOM value. This mismatch is a common source of errors in scripts, filters, and protocol documents. The table below maps familiar terms to the code the standard expects.

How DICOM Modalities Work Across Imaging Systems

Modality codes are the routing labels of an imaging workflow. Scanners set them, PACS and archives read them, and worklists and rules depend on them. A research PACS or imaging platform uses modality to sort studies, apply hanging protocols, assign reading queues, and decide which quality checks to run. Downstream tools do the same: viewers choose display settings, and analysis pipelines select the series they can process. The steps in medical image preprocessing, such as resampling and normalization, often depend on the modality to choose the right method.

In multi-site imaging trials, modality consistency becomes a data quality control. Each site may label the same protocol slightly differently, or send a secondary capture instead of the original series. Checking the modality on receipt, alongside protocol parameters, helps catch wrong series, missing exams, and mislabeled data before they reach central review. Privacy tools must also keep the attribute intact while removing identifiers. See our overview of DICOM anonymization for how this balance works in practice.

Because trials often combine CT, MR, PET, and ultrasound from many scanners, a shared understanding of these codes supports the same standardization that reliable endpoints depend on. Read more in our articles on medical imaging data and medical imaging strategy.

Several recurring issues are worth building checks for:

• Secondary captures labeled OT. Screenshots or exported images carry little of the original acquisition detail and may not be usable for measurement.
• Combined exams. PET/CT and similar studies contain several series with different modality values, and each series needs to be handled on its own terms.
• Derived objects mixed with source images. Segmentations, structured reports, and presentation states share a study with the original scans and can be picked up by mistake if filters only look at the study level.
• Legacy values. Historical archives can hold retired codes that current tools no longer recognize.
• Inconsistent labeling between sites. Different scanners and configurations can describe the same protocol in different ways, so modality should be checked together with other series attributes.

DICOM Modality Codes Provide a Common Language for Imaging Data

A modality code is a small piece of metadata with a large effect. It lets systems from different vendors agree on what an image is, where it came from, and how it should be handled. Teams that know the current list, understand the difference between codes and everyday names, and check modality as part of quality control avoid many avoidable problems in imaging pipelines. If you manage imaging data across sites, Collective Minds can help you receive, check, and organize it in one place. That includes reading modality and other DICOM attributes on receipt, flagging series that do not match the protocol, and keeping every image traceable from the site to the final read. Whether you are building a pipeline, running a multi-site trial, or auditing an archive, treat the modality tag as a quality signal and not just a label.

Frequently Asked Questions About DICOM Modalities

What is the DICOM modality code for MRI?

The DICOM modality code for MRI is MR, which stands for Magnetic Resonance. It is stored in the Modality tag (0008,0060). MR is also used for related techniques such as MR angiography and spectroscopy, since the older MA and MS codes are retired.

What is the DICOM modality code for PET?

The code for PET is PT, defined as positron emission tomography. In a combined PET/CT exam, the PET series carries PT and the CT series carries CT, and the study lists both under Modalities in Study (0008,0061).

What does OT mean in DICOM?

OT means Other. It is the catch-all value for data that does not fit another defined modality, and it is often seen on secondary capture images and converted files. Because OT says little about how an image was acquired, teams should check other attributes before relying on it.

Can a DICOM modality represent something other than an imaging scanner?

Yes. The standard includes modality values for objects such as structured reports (SR), segmentations (SEG), presentation states (PR), radiotherapy plans (RTPLAN), and waveforms such as ECG and EEG. The Modality attribute describes the device, process, or method that produced the data, which is not always a scanner.

Reviewed by: Pilar Flores Gastellu on September 30, 2026