What is DICOM ?

There are literally billions of DICOM Images currently in use for clinical care!!

Image Source: I-MED Radiology Network

If you are a Biomedical Engineer, an IT Specialist in the healthcare field, or a Healthcare Data Scientist/Analyst, you’ve probably used or at least heard about DICOM because it’s everywhere related to medical imaging systems.

We will cover some of the most important information related to DICOM like:

• What is DICOM?
• What does a DICOM Data Object contain?
• Image Display Using DICOM.
• DICOM Services.
• A blink in the history of DICOM.
• DICOMweb.

DICOM Logo. Image Source

What is DICOM in General?

DICOM®, Digital Imaging and Communications in Medicine, is the international standard for medical images and related information. It defines the formats for medical images that can be exchanged with the data and quality necessary for clinical use.

DICOM® is implemented in almost every radiology and radiotherapy device (X-ray, CT, MRI, ultrasound, etc.). It is one of the world’s most widely deployed healthcare messaging standards in the world. The International Organization for Standardization recognizes it as the ISO:12052.

What does a DICOM Data Object contain?

DICOM groups information into data sets. That means that a file of a chest x-ray image, for example, actually contains the patient ID within the file, so that the image can never be separated from this information by mistake.

A DICOM object with metadata and image. Image Source

A DICOM data object consists of several attributes, including items such as name, ID, etc., and also one special attribute containing the image pixel data. The attribute of pixel data may contain multiple frames, allowing storage of cine loops or other multi-frame data. Therefore, three- or four-dimensional data can be encapsulated in a single DICOM object.

Image Display Using DICOM:

Given that many newly acquired images are digital, there is a potential to view them on any number of computer systems. Computers as common as a standard personal computer (PC) or as sophisticated as a Picture Archival and Communications System (PACS) workstation may be used to view images. The need for consistent image presentation on this wide selection of workstations has been recognized as part of a broader description of a high-quality display, which is required for medical image presentation. DICOM can promote identical grayscale image display on different monitors and consistent hard-copy images from various printers. This is done using the DICOM grayscale standard display function (GSDF). This standard provides a mathematical definition of the luminance output versus digital input which ensures perceptually equivalent contrast throughout the grayscale range of the display.

DICOM Services:

DICOM consists of many services, most of which involve data transmission over a network. The most common services are:

• DICOM Store Service, which is used to send images or other persistent objects (structured reports, etc.) to a picture archiving and communication system (PACS) or workstation. It is used to transfer DICOM images and other related digital data from a DICOM node to another DICOM node, which allows the exchange of data among multiple devices over the DICOM network.
• DICOM Storage Commitment Service. It is used to confirm that an image has been permanently stored by a device. It is complementary to the DICOM Storage service but more focused on the safekeeping of data concerning this last service.

DICOM Services. SCU refers to Service Class User. SCP refers to Service Class Provider. Image Source

• Query/Retrieve Service. This service enables a workstation to find lists of images or other such objects and then retrieve them from a picture archiving and communication system.
• The DICOM Verification Service is probably the simplest. It is used to verify DICOM connectivity between two DICOM nodes.
• Print Service. This service is used to send images to a DICOM Printer, for example, to print an X-Ray film. There is a standard calibration to help ensure consistency between various display devices, including hard-copy printouts.

DICOM Printing Service. Image Source

• Modality Worklist. Today, most medical centers use information systems such as Hospital Information Systems, HIS, or Radiology Information Systems, RIS, to store patients’ demographics and exam scheduling information. These data are then required during the image acquisition phase at the acquisition modality since digital acquisition devices must know all relevant patient and study information to store them in the digital images they produce. The items in the worklist include relevant details about the subject of the procedure (patient ID, name, sex, and age), the type of procedure (equipment type, procedure description, procedure code), and the procedure order (referring physician, accession number, reason for exam). Before the use of the DICOM Modality Worklist service, the scanner operator was required to manually enter all the relevant details. Manual entry is slower and introduces the risk of misspelled patient names, and other data entry errors.

Modality Worklist Service. Image Source

• Modality Performed Procedure Step Service, which is a complementary service to Modality Worklist. It enables the modality to send a report about a performed examination including data about the images acquired, beginning time, end time, duration of a study, dose delivered, etc. It helps give the radiology department a more precise handle on resource (acquisition station) use.

The history of DICOM:

It all began in 1983 when the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA) joined forces and formed a Standards committee to meet the combined needs of radiologists, physicists, and equipment vendors. The first standard, ACR-NEMA 300, was released in 1985. Later, in 1993 was changed to DICOM. Since then, many highlighted histories and milestones that have been going on. You can refer to this link for more details.

DICOMWeb:

DICOMweb™ is the DICOM Standard for web-based medical imaging. It is a set of RESTful services that enable web developers to unlock the power of healthcare images using industry-standard toolsets. DICOMweb can be implemented directly or as a proxy for the DIMSE services. DIMSE refers to DICOM Message Service Element that provides the mechanism for message exchange between peer Application Entities once an Association between them has been established. DICOMweb offers modern web-based access to DICOM-enabled systems. DICOMweb has multiple main services such as:

• Query: Search for DICOM objects. Query-based on ID for DICOM Objects (QIDO) enables you to search for studies, series, and instances by patient ID, and receive their unique identifiers for further usage (i.e., to retrieve their rendered representations).
• Retrieve: Retrieve DICOM objects (WADO-RS). Or retrieve single DICOM instances (WADO-URI). Web Access to DICOM Objects (WADO) enables you to retrieve specific studies, series, and instances by reference.
• Store: STore Over the Web (STOW) enables you to store specific instances on the server.

The store service (STOW-RS). Image Source

• Worklist: Manage worklist items (UPS-RS). The Unified Procedure Step (UPS) enables clients to manage Workitems. It also describes how notifications (including subscriptions) work.
• Capabilities: Discover service enables you to discover the supported services of a particular DICOMweb end-point. The image below represents the use of the Capabilities service.

The capabilities service. Image Source

DICOMwebTM encodes the data in JSON and XML. And this is useful and nicely applicable for health data scientists and machine learning developers. For more details, refer to this link. And you can check more details about DICOMweb resources and attributes by following this link of DICOMweb Cheatsheet.

Conclusion:

DICOM is a set of standards that are created to allow communication across multiple modalities between multiple manufacturers so that all medical machines, that are DICOM-compliant of course, can speak the same language when sending information across a network. All you need is one piece of software, a DICOM reader, to read many medical DICOM images from many different modalities.

In the next blog, I will discuss how to deal with DICOM objects using Python and dive in details beyond just pixels of images.

Thanks For Reading…

Recommendation to read:

To give you a plus ultra understanding what DICOM is and what can you do with DICOM objects, I’ll point out on some links that might be helpful.

• DICOM Service in Azure Health Data Services: The DICOM service is a managed service within Azure Health Data Services that ingests and persists DICOM objects at multiple thousands of images per second. It facilitates communication and transmission of imaging data with any DICOMweb enabled systems or applications via DICOMweb Standard APIs like Store (STOW-RS), Search (QIDO-RS), Retrieve (WADO-RS). You can check this link to see more details about DICOM Service and its great applications, especially for health data scientists and AI engineers. Don’t forget to check the GitHub link of DICOM Server on Azure.
• DICOM Metadata — A Useful Resource for Big Data Analytics:
  This article provides an overview of new ways to represent data by combining patient access and DICOM information, advanced use of medical imaging metadata, analysis of radiation dose and image segmentation, and deep learning for feature engineering to enrich data.
• DICOM Progress: This link provides an overview of the yearly progress of the DICOM. Also, it provides the progress and services they are currently working on it.
• Medical Imaging I.T. Basics: In this blog, Dominic DiFrancesco introduces some of the basic elements for anyone working in healthcare I.T., including some basics of DICOM. I’m sure you’ll find it a great source to read.

References:

[1] “DICOM Standard,” DICOM, [Online]. Available: https://www.dicomstandard.org/about-home. [Accessed 4 12 2022].

[2] “DICOM Concepts,” [Online]. Available: https://www.dicomstandard.org/concepts. [Accessed 4 12 2022].

[3] Kenneth A. Fetterly, Hartwig R. Blume, Michael J. Flynn, and Ehsan Samei, “Introduction to Grayscale Calibration and Related Aspects of Medical Imaging Grade Liquid Crystal Displays,” Journal of Digital Imaging, vol. 21, no. 2, pp. 193–207, 2008.

[4] “Neologica Tutorial DICOMStorage,” Neologica, [Online]. Available: https://www.neologica.it/eng/Tutorial/DICOMStorage. [Accessed 4 12 2022].

[5] “Neologica Tutorial DICOMStorageCommitment,” Neologica, [Online]. Available: https://www.neologica.it/eng/Tutorial/DICOMStorageCommitment. [Accessed 4 12 2022].

[6] “Neologica Tutorial DICOMVerification,” Neologica, [Online]. Available: https://www.neologica.it/eng/Tutorial/DICOMVerification. [Accessed 4 12 2022].

[7] “Neologica Products DICOMMod,” Neologica, [Online]. Available: https://www.neologica.it/eng/Products/DICOMMod. [Accessed 4 12 2022].

[8] “DICOM History,” DICOM, [Online]. Available: https://www.dicomstandard.org/history. [Accessed 4 12 2022].

[9] “DICOMWeb,” DICOM, [Online]. Available: https://www.dicomstandard.org/using/dicomweb. [Accessed 4 12 2022].

[10] “PyDicom DIMSE,” [Online]. Available: https://pydicom.github.io/pynetdicom/stable/reference/dimse.html. [Accessed 4 12 2022].

[11] “DICOMWeb Query,” DICOM, [Online]. Available: https://www.dicomstandard.org/using/dicomweb/query-qido-rs. [Accessed 4 12 2022].

[12] “DICOMWeb Retrieve,” DICOM, [Online]. Available: https://www.dicomstandard.org/using/dicomweb/retrieve-wado-rs-and-wado-uri. [Accessed 4 12 2022].

[13]“DICOMWeb Store,” DICOM, [Online]. Available: https://www.dicomstandard.org/using/dicomweb/store-stow-rs. [Accessed 4 12 2022].

[14] “DICOMWeb Worklist,” DICOM, [Online]. Available: https://www.dicomstandard.org/using/dicomweb/workflow-ups-rs. [Accessed 4 12 2022].

[15] “DICOMWeb Capabilities,” DICOM, [Online]. Available: https://www.dicomstandard.org/using/dicomweb/capabilities. [Accessed 4 12 2022].