DICOM explained Part 1: What is DICOM, DICOM Tags and Data Sets?

Imaging techniques play an important role in many areas of modern medicine. This applies to diagnostics and therapy, but also to research, for example, in the context of clinical trials. The most important medical image format is DICOM. 

Within clinical projects, utilizing our ClinFlows’ solutions to exchange medical images, we frequently meet users (physicians, study nurses and coordinators) who are not that familiar with the topic “DICOM”. Time for us as DICOM experts to start a series in which we explain the format and obstacles that come when dealing with it (spoiler: among others, it’s about personal data!).

In the coming time, we will gradually publish articles here in which we explain the most important background and facts about DICOM data. We start today with part 1 of our DICOM explained-series, in which you will learn what is behind the abbreviation, how the DICOM format is structured, what makes it so characteristic and what it is used for in healthcare.

DICOM: the format behind the five letters

JPEG, TIFF, PNG – almost everyone knows these file formats of images. DICOM is also an image format, but it is used primarily in the medical industry. The abbreviation DICOM stands for “Digital Imaging and Communications in Medicine”. The term already makes it clear that the format not only includes the respective image data, the pixels or its storage as a specific file format, but that the DICOM standard includes further information, which we will explain in more detail later. The DICOM standard has its origins in the 1970s, when it was still called the ACR/NEMA standard and was initiated by the American College of Radiology and the National Electrical Manufacturers Association. DICOM as we know it today has only existed since 1992. The use of this image format is intended to facilitate and standardize the exchange of medical image data.

DICOM: Open standard to exchange medical images

The DICOM format is one of the so-called open standards, openly accessible and usable by anyone. This allows many medical professionals in the fields of research and clinical practice, diagnostics and therapy to exchange, view and perform measurements of medical images independently of manufacturers.

What are DICOM Headers, DICOM Tags and Data Sets?

A set of medical images in DICOM format usually has the following overall structure: Patient – Exam – Series – Images. That is, a patient undergoes a study or examination, such as a computed tomography (CT) scan. This examination consists of several series, and each series contains multiple images (hundreds or thousands) or multiple frames (like a video, e.g., for echocardiographies).

A DICOM medical image file, such as a single CT slice, consists of two distinct parts. One is the medical image itself, the other is the DICOM header. The DICOM header is a block of data that contains specific information that complements the image, called DICOM tags. This usually includes relevant patient data such as name, age, gender and date of birth, but also a lot of technical data and parameters, such as the device used to generate the images, the names of the surgeon and the administered drugs such as contrast agents, as well as data on the imaging technique, such as pixels, matrix size or the dimensions of the image. This usually facilitates the assignment of an image to a patient. In medical jargon, this data is referred to as attributes. Depending on the image and the circumstances, certain information is mandatory, while other attributes are optional. In addition, the DICOM header has DIN standards, which are defined by law.

What are DICOM Tags good for?

The DICOM Tags are organized as a constant and standardized series; thus, they are used in the management of information belonging to medical image data. The DICOM Tags are assigned as metadata elements to each image object in medicine. These can be segmentations, definitions of surfaces, and registration numbers for the images. The format is used for both standardization and storage of the files, as well as a uniform communication protocol for sharing. As data elements, tags consist of an attribute that is used for identification. Usually they are composed of hexadecimal numbers (XXXX,XXXX) with a comma in the middle. If necessary, a further subdivision into the group and element number is possible. In this way, DICOM tags are easier to read, and patient data can be printed directly on them when developing X-ray images. In this way, the X-ray image and the associated data are combined digitally in one file.

What DICOM Tags are available?

There are a variety of DICOM tags that assist in organizing medical image data as well as searching for them. These include, for example:

Accession Number0008,0050
Procedure Creation Date0014,4076
Patient’s Birth Name0010,1005
Operator’s Name0007,1070
Patient’s ID0010,0020
Patient’s Birth Date0010,0030
Patient’s Body Mass Index0010,1022
Table 1, DICOM Tags

Thanks to the numbers, an extremely large amount of information can be assigned to the images, which is immediately recognized by the medical authorities. By the way: A full list of all DICOM tags can be found at MITA (The Medical Imaging Technology Association) or NEMA here.

In the next part of our DICOM explained series, we will dive deeper into the topic: Among others, you will learn more about the problems that the data contained in DICOM files pose for working with them. Stay tuned!