DICOM is an acronym for Digital Imaging Communications in Medicine. In short DICOM is a standard method used to allow interoperability and interconnection between medical imaging devices as well as a standard format (similar to JPEG, TIFF etc.) used to transfer medical images. The degree of interoperability that a particular piece of medical equipment is capable of is defined in a DICOM Conformance statement that comes with DICOM compatible equipment.
A standard imaging format is essential to the medical community because this allows different hospitals to use equipment from different manufacturers. Basically, DICOM was developed to avoid a situation like we have with computer software where many windows based programs and documents won't work on a Mac. Theoretically (see below), if you use DICOM compliant equipment, your GE CT scanner or ultrasound machine will be able to communicate with your FUJI printer and KODAK archiving system. This interoperability should increase competition in the marketplace which should (theoretically) reduce costs.
The DICOM standard is very much like a language. As with any language, there exists vocabulary and grammar. These linguistic elements enable people to communicate. These elements by themselves, however, are not enough to understand the context of dialog. There are rules that apply to different applications of any language. For example, if you said to someone: "Are you having a bad day" where the emphasis is placed on the word day, they would think that you were truly concerned about how their day is going. However, you could make the exact same statement by saying: "Are you having a bad day" where the emphasis is placed on the word you, they would think that you were being sarcastic. The DICOM standard is really no different; the DICOM Data Dictionary defines the vocabulary, the DICOM Data Structure and Semantics defines the grammar, and the DICOM Application Profile defines the context of the discussion. The storage medium and/or physical network (e.g. Ethernet) represent the communication channel (e.g., telephone, FAX, or E-mail).
Unfortunately, DICOM is still a relatively new format and adoption by the different equipment manufacturers is somewhat less than universal. Therefore, the term “DICOM” compliant” is relatively useless because manufacturers can comply with bit and pieces of the DICOM standard. As such, different pieces of equipment that conform to different aspects of DICOM will not be able to communicate to one another. For example: DICOM defines several categories of capabilities or service classes. A scanner that supports DICOM print class will not be able to communicate with an image archiving system that supports only storage service class.
Therefore, a DICOM conformance statement is provided by the manufacturer stating exactly how it is conformant. One should be able to determine from the statement which equipment will obviously not be conformant. However, it is more difficult to tell which ones will be able to communicate. It is recommended to hire an expert to help you understand the DICOM conformance statement (A good idea since the DICOM conformance statement for one GE CR unit was 65 pages long!). Keep in mind that the DICOM conformance statement is a starting point for validation of DICOM compatibility not an ultimate assurance of equipment interoperability.
As stated previously, one part of the DICOM standard defines a file format for the distribution of images. You are probably familiar with other file formats such as JPEG or TIFF. A DICOM image is unique in that in addition to the image (which can contain information in three dimensions) there is additional information about the patient's name, the type of scan, image dimensions etc. stored in an image header. As a result, these images require a special DICOM viewer in order to look at these images. (i.e. you will not be able to open them if you do not have a DICOM viewer installed on your computer). Fortunately, there are a number of free DICOM viewers available. You will see that these DICOM viewers allow you to view and manipulate the images as if you were at a CT or MRI workstation in the hospital. For example, you can alter the window level and width of a DICOM CT or MRI image.
One additional point to note about the DICOM image is that software using DICOM to store images generally has safeguards to prevent alteration of the original image. A DICOM image is part of the medical record so safeguards should be in place to prevent alteration of the original image. Remember, you can alter the image (rotate it, change levels etc.) on your computer screen using a DICOM viewer but you will not be able to save the changes you made without a paper trail.
You may not have had exposure to DICOM in the past. However, as a veterinarian, you will certainly be exposed to DICOM in the future. For example, a salesman may tell you that their machine is DICOM compliant and you will need to know how to evaluate that statement. Additionally, you may receive DICOM images if you refer an animal for a CT, MRI, or ultrasound and you will need to know how to view these images.
UPDATE: It appears that there are now several vendors that market their digital radiography equipment and mention the word DICOM in their literature. To the uninitiated this makes these products seem DICOM compliant, however, in reality, these products do little to ensure connectivity between the different imaging products in your hospital. If you have any questions about the DICOM compatibility of a product you are considering purchasing I encourage you to contact your local veterinary radiologist or vet school.
In conclusion, DICOM is both a standard that allows different pieces of medical equipment communicate with one another and a type of image file. DICOM images can only be viewed with a DICOM viewer.