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Chapter 1
What Is DICOM?
“When working toward the solution of a problem,
it always helps if you know the answer.”
Murphy’s Law
You can walk with this question into the most modern, digital, state-of-theart hospital and spend hours looking for someone who could answer it correctly. We all get used to buzz words and acronyms, and rarely think about
their meanings. Unfortunately, nothing distances you more from success than
not knowing what you are dealing with!
DICOM stands for Digital Imaging and COmmunications in Medicine and
represents years of effort to create the most universal and fundamental standard in digital medical imaging. As such, it provides all the necessary tools for
the diagnostically accurate representation and processing of medical imaging
data. Moreover, contrary to popular belief, DICOM is not just an image or file
format. It is an all-encompassing data transfer, storage, and display protocol
built and designed to cover all functional aspects of digital medical imaging
(which is why many view DICOM as a set of standards, rather than a single
standard). Without a doubt, DICOM truly governs practical digital medicine.
Another important acronym that seemingly all DICOM companies plug
into their names is PACS (Picture Archiving and Communication Systems).
PACS are medical systems (consisting of necessary hardware and software) designed and used to run digital medical imaging. They comprise digital image
acquisition devices (modalities – such as computed tomography (CT) scanners,
or ultrasound), digital image archives (where the acquired images are stored),
and workstations (where radiologists view the images). When you play with
your digital camera (modality), store the images on your computer (archive),
and send them to your friends (reviewers), you use the exact same model. Of
course, PACS take the model to a much more complex level (Fig. 1).
PACS are directly related to DICOM. Their functionality is DICOM-driven,
which ensures their interoperability. For that reason, any PACS device or software comes with its own DICOM Conformance Statement, which is a very
important document explaining the extent to which the device supports the
DICOM standard. In essence, PACS bring the DICOM standard to life.
One can hardly imagine modern-day digital medicine without DICOM and
PACS. The DICOM standard – conceived over 20 years ago – plays an integral
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Chapter 1
What is DICOM?
Fig. 1 Major Picture Archiving and Communication System (PACS) components. Image
acquisition devices (modalities) store images on a digital archive. From there images are
accessed by radiologists at the viewing workstations
role in the digital medicine evolution, ensuring the highest diagnostic standards and the best performance. DICOM has truly shaped the landscape of
contemporary medicine by providing:
1. A universal standard of digital medicine. All current, digital image-acquisition devices produce DICOM images and communicate through DICOM
networks. Current medical workflow is implicitly controlled by a multitude
of DICOM rules, which will be reviewed in this book.
2. Excellent image quality. For example, DICOM supports up to 65,536
(16 bits) shades of gray for monochrome image display, thus capturing the
slightest nuances in medical imaging. In comparison, converting DICOM
images into JPEGs or bitmaps (BMP), always limited to 256 shades of gray,
often makes them impractical for diagnostic reading. DICOM takes advantage of the most current and advanced digital image representation techniques to provide the utmost diagnostic image quality.
3. Full support for numerous image-acquisition parameters and different data
types. Not only does DICOM store the images, but it also records a multitude of other image-related parameters such as patient 3D position, physical sizes of objects in the image, slice thickness, image exposure parameters, and so on. These data immensely enrich the informational content
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of DICOM images, and facilitate the processing and interpretation of the
image data in various ways (for example, creating 3D images from several
sequences of two-dimensional CT slices).
4. Complete encoding of medical data. DICOM files and messages use more
than 2000 standardized attributes (DICOM data dictionary) to convey various medical data from patient name to image color depth, to current patient diagnosis. These data are often essential for accurate diagnostics, and
capture all aspects of the current radiology.
5. Clarity in describing digital imaging devices and their functionality – the
backbone of any medical imaging project. DICOM defines medical device
functionality in very precise and device-independent terms. Working with
medical devices through their DICOM interfaces becomes a very straightforward process, leaving little room for errors.
At the time this book was written, the DICOM standard consisted of 16 volumes (from 1–18, volumes 9 and 13 being retired) known as parts, and traditionally numbered from PS3.1 to PS3.18.1 The last publicly available revision of
the standard, performed in 2007, was used.2
1 Number 3 representing DICOM 3.0, the current version of the standard.
2 See DICOM home page at NEMA’s Web site, http://medical.nema.org. When this
book was in print, DICOM version 2008 was released.
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