What is DICOM? How does DICOM Work?

1895, Wilhelm Roentgen discovered the use of X-RAYs.  In 1903, physicists Marie Curie, Pierre Curie and Henri Becquerel were awarded the nobel peace prize for the discovery of radiation.  Their names live on today.  Their accomplishments have shaped the world.  In particular, medical imaging.

Until recently, X-rays were still being printing unto films.  These films, would need to be processed in a dark room, washed, dried then hung up against a lightsource for a radiologist to view them.  

In the digital age today, this process is almost completely obsolete.  Images are transferred directly from the X-ray device to a display monitor of the radiologist almost immediately after capture.  The images are stored in a DICOM file format and transferred using a DICOM operation.  DICOM is both the file type and method of transfer.  

Legacy Imaging

In the old days, an X-RAY film will typically be placed in a physical folder with patient demographics.  The folder would contain contents such as name, patient ID, DOB, and reason for exam.  Some demographics can be written directly onto the X-RAY film itself.  For example, the name of the patient.  The films will be physically up hung against a bright back light. The films are arranged based on a specific protocol.  This deliberate arrangement is based on the type of exam that was performed.  This is called a hanging protocol.  As the films are being reviewed, a radiologist can make notes with a marker or sticker such as measurements and arrows directly on the X-RAY. These are annotations.

Modern Imaging

With the advent of technology this process is entirely digital.  Let’s review a modern X-RAY image.

The X-RAY is captured as a computed radiograph (CR) or digital radiography (DX) image.  The X-RAY is classified as a specific DICOM image type.  This classification is called a SOP class.  The image itself and the patient demographics (the metadata) are combined into a DICOM file.  This DICOM file has a specific method of TCP/IP communication which allows the file to be transferred to another DICOM system in a standard method.

“Wait what”

Okay let’s start over.  If this is your first time hearing any of this, it does sound like techno babble.  In the old days, when an X-RAY film is developed, the patient demographics can be printed directly on the film itself.  Since the X-RAY today is now digital, the image and the demographics are combined into one file.  Each line of information can be considered a DICOM tag.  For example, a tag for patient name.  A tag of the date of service.  So on.   These tags are helpful in the organization of the patient images.  A user can search for these images based on the data within the DICOM tags.

For the sake of organization and standardization, each medical image must fall into a specific category.  The category is determined by NEMA, the smart guys behind the DICOM standard.  For example, the X-RAY images created by the device will be stored as a Computed Radiography Image Storage SOP class (1.2.840.10008.5.1.4.1.1.1).   Other devices that use DICOM will know what a Computed Radiography Image Storage is.  Other devices will know how to store, transfer, query and view a Computed Radiography Image Storage.  The most common system that has the ability to transfer, store, query and view these image types is a PACS.  CR images are sent from the X-RAY device to a PACS for storage.

The Picture Archive and Communications System (PACS) is the digital solution to storage, transfer and viewing of medical grade imaging.  The PACS has become the software solution in medical imaging technology for the past three decades. This has been apparent in the radiology departments. Other departments have been slow to catch on such as cardiology and nuclear medicine. However, by today’s standards most of our medical imaging has been converted to digital format. Most PACS images are stored and transferred in DICOM format.

Again, decades ago, images were physically hung up against a light in a specific order for the radiologist to read.  Today, the PACS replaces this functionality with digital hanging protocols.  When a specific study is opened in the PACS, the system knows to display the images in a specific manner based on study type.  The radiologist can still make annotations on the images, except now it’s digital.  Annotations such as measurements and arrows are stored in the PACS as KO or PR objects.  These can be made available for other PACS users to view as well.  As you can see, DICOM & PACS is a replacement and improvement of real world functionality.

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