This blog simplifies the core concepts of Digital Imaging and Communications in Medicine (DICOM) to help one get started whether as a developer entering healthcare sector, or as a student or as a professional doctor in healthcare. As a quick reference, it serves as a practical introduction to DICOM for beginners, breaking down standard terms and concepts.
What is DICOM?
In simple terms, (DICOM) is the international standard for storing, transmitting, and displaying medical imaging data information. It is the equivalent of a “PDF for medical images”, only far more detailed. DICOM for beginners often starts
DICOM provides a standard way to manage and work with the images and metadata (like patient name, scan type, acquired timestamps) across different imaging devices. This ensures that the image acquired is correctly interpreted on other software.
The Importance of DICOM
Medical imaging involves diverse devices: CT scanners, MRI machines, ultrasound units, X-ray systems, and more.
Without a common standard:
- Images might not be interoperable.
- Patient data could be mismatched or lost.
- Execution of diagnosis and patient care continuity could be compromised.
DICOM Components
The following is the breakdown of the core building blocks of DICOM:
1. Images with Metadata
A DICOM file consists of two areas:
- The actual image (e.g., a slice of an MRI scan)
- Metadata like patient ID, modality (scan type), body part, timestamp, etc.
2. DICOM Tags
There are metadata stored as key-value pairs in DICOM files, and these are known as DICOM tags. Each attribute is defined by a tag number, like (0010,0010) for “Patient Name”. Please refer to the DICOM Library for a searchable list of tags.
3. SOP Classes
SOP stands for Service-Object Pair. The SOP Classes define the type of objects e.g., CT image, structured report and the actions allowed on it e.g., store, retrieve.
For example:
- 1.2.840.10008. 5.1.4.1.1.77.1.5.4= Ophthalmic Tomography Image Storage SOP Class
4. UIDs
The UIDs are unique identifiers assigned to each DICOM object so that it can be referenced precisely across systems.
Real-Time DICOM and Streaming
Traditional DICOM, works very well with stored images. However, when it comes to real-time scenarios like surgery feeds or ultrasound video, it requires a standard to be followed wherein the DICOM PS3.22 (Real-Time Communication) plays a key role.
It defines how DICOM metadata can be synchronized with audio/video streams using protocols like RTP (Real-Time Transport Protocol), enabling real-time viewing and interpretation of data without storing it first.
This applies to various sectors like:
- Optical Coherence Tomography
- Robotic surgeries
- Live ultrasound scanning
- AI-assisted diagnostic streaming
Consider a hospital where one machine takes an MRI, another displays it, and a third machine stores it for long-term record keeping. When no standards are followed, it would be exceedingly difficult for machines to communicate with each other. DICOM ensures that different systems can work together, that medical data follows a standard structure and that secured image transfers are possible along with accurate results.
The Core Concepts of Digital Imaging and Communications in Medicine (DICOM)
The core concepts of DICOM can be distributed as follows:
1. DICOM Files
A DICOM file is not just an image like a JPEG or PNG. It contains:
- Image data or Pixel data (e.g., OP, OPT, MRI scan)
- Metadata which are also known as attributes (e.g., patient name, scan date, equipment used)
The DICOM files have “. dcm” extension followed by an application-defined file naming convention.
2. DICOM Structure
Every DICOM file is made up of data elements or attributes. Each data element includes:
- A tag: A tag is a unique identifier to represent data, like (0010,0010) for a patient name.
- A VR (Value Representation): Describes the type of data (e.g., text, date, number, name) described in two letters.
- A value: The actual content or the value of the attribute (e.g., “Smith Jones”).
Consider the following example:
(0010,0010) PN [Smith Jones] Patient’s Name
(0008,0020) DA [20250801] Study Date
In the above example, the (0010, 0010) is the tag, PN is the value representation for Person Name, a value is represented in the [] brackets and finally the DICOM attribute.
3. DICOM Network
DICOM is not merely about files storing the patient data, it also defines how the systems communicate.
For every communication there is a user and a provider with whom the user tries to establish a communication like the application trying to connect with the database. This is based on:
- SCP: Service Class Provider (e.g., a PACS server) – typically, a server that provides a DICOM network service and performs operations requested by an entity.
- SCU: Service Class User (e.g., a user application, an imaging device/workstation) – typically, a client that uses a DICOM network service.
Communication requires services to function as a bridge, to send the requests and receive the responses back. They use services like:
- C-STORE: Storing an image
- C-FIND: Searching for studies
- C-MOVE / C-GET: Retrieve data
For e.g., The DICOM component establishes a connection then sends a C-FIND-RQ for searching data and receives a response as a C-FIND-RSP.
4. DICOM Hierarchy
DICOM follows a hierarchy for data:
Patient –> Study –> Series –> Image
- Patient: The individual undergoing imaging
- Study: A medical exam (e.g., a scan of the eye, an MRI session)
- Series: A set of related images (e.g., retina scan, brain scans)
- Image: A single DICOM image
This hierarchical structure makes it easy to manage and retrieve medical images.
Working with DICOM as a beginner, seems confusing but here is how you can start exploring DICOM hands-on with pre-defined tools in market.
Tools for Viewing DICOM Files
- MicroDicom (Windows)
- Weasis (cross-platform, Java-based)
- PowerDicom
- ImageJ + DICOM plugin (cross-platform)
These tools let you open .dcm files and explore the embedded metadata and images. There are many options available in the market.
Best Practices
- Use the correct SOP Class UIDs (e.g., Secondary Capture Image Storage).
- Maintain the integrity of the image by not overwriting the original instances.
- Tag derived images with appropriate Image Type (0008,0008).
Common Challenges for Beginners
- DICOM images are large and may pan over multiple files.
- DICOM standards support private tags for organizations, vendors add private and undocumented fields which are difficult to understand.
- It is exceedingly difficult to go through a massive document as tye DICOM standard consists of over 3,000 pages.
Final Thoughts
DICOM is the backbone of modern medical imaging. It is a powerful tool or a system that enables doctors, radiologists, and developers to provide better patient care. Start small, explore real files, and do not be afraid to explore things in a sandbox. In the long run, you will be navigating DICOM datasets like a pro. We recommend starting with simple use cases like viewing, reading metadata, and understanding the file structure before deep diving into networking or PACS integration.
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