PACS stands for Picture Archive and Communications System. As its name suggests, it is a way to store the digital images produced by different medical devices. Due to the nature of PACS, they are made up of various components that are, in turn, all part of a net infrastructure that connects them together.
PACS | Purpose and objectives
PACS has several objectives that they strive towards, and the first of them is to provide image administration. They act as the database or storage for these images and provide a way to manage them.
Also, these devices should allow easy viewing of said images. Although it is easy to store different file formats, making the device able to view them is a different story. When storing files, the device does not need to know what the data it's storing means but, this does not stay true when we refer to displaying the data. In this case, the device has to interpret and compute how to load the image with its associated metadata. The reason for this is that doctors and medical personnel have to be able to view these images as an aid to provide a more accurate diagnosis.
Moreover, medical providers should be able to send them easily to any location inside the hospital, which would pose a significant advantage over physical imaging that has to be moved by hospital staff.
Lastly, PACS provides security and easy recoverability of medical images. It has to provide an access system with different levels corresponding to the level of clearance the hospital wishes to grant each individual. Furthermore, the system has to store these files for an extended period to ensure they will be available for years to come.
The components of a PACS can be divided into levels according to their function. The first level corresponds to its origin, the devices that allow for image acquisition, also known as modalities, like ultrasound or x-ray machines. These modalities have their images collected by acquisition gateway computers that take the image in its raw format and transform it into a standard format that the PACS can later store.
The next step in this chain is the stations that allow doctors and hospital staff to view and analyze the images produced by the previous level. Logically, the next step would be to save these images so they can be viewed later on, and that would be the database and the "Archive" component of the system. PACS has two ways to store files for such purposes: short-term and long-term. The first one is designed for fast retrieval, while the other is designed for long-lasting archiving and, consequently, will take longer to retrieve any particular image from the archive. The fourth component connects all these components; it's a communication network that can be as close as a connection between a modality and a gateway computer or as big as connecting different hospitals.
PACS | Interconnection of equipment
Not long ago, each manufacturer had its standards and specifications, causing equipment from different brands to not talk to each other, and sometimes not even different models of the same manufacturer could do so. This quickly became a problem, and thus the need for standardization to become stronger.
DICOM or Digital Imaging and Communication in Medicine was designed to connect different components in a PACS. The aim was to have a file type and a transfer standard built on top of TCP/IP that would allow sending, managing, and storing the images produced by the modalities. With this in mind, DICOM was made to be a file format and a file transfer method. The DICOM file type includes all it needs to replace the traditional printed images used. The main component is the image itself. However, doctors often record patient demographics on or near these images, and the solution should then support this to be a viable replacement. Hence, DICOM files included the image and metadata of the patient demographics with an associated "DICOM image type" used to categorize the file.
As an example, let's review the process of taking an x-ray. First, the image is taken as a digital radiography image and then classified as a DICOM image type, also known as a SOP class. Then, the image and the metadata are combined into a DICOM file, and extra information is represented as DICOM tags; this could be anything from a patient name to the Date of Service. Hence, these tags can then be used to search, filter the files, and help use the digital hanging protocol.
You might ask what this is, and it's exactly as it sounds. Previously, when doctors got an x-ray, they would hang them on a bright backlight to analyze them. They often had many of these x-rays, so a "hanging protocol" was put in place to allow the different x-rays to have a logical order based on what they showed. This was replicated using a "digital" hanging protocol that used the metadata inside a DICOM file when transitioning to digital. This allowed placing the images in order automatically and hence, repeating what was done previously, but this time, instead of the twelve images that fit on top of a backlight, they could be a hundred.
PACS in healthcare | Conclusion
To summarize, PACS came out of a need to replace traditional medical imaging and take it into the new digital era. In turn, this digital health solution provides a way to store, manage and view images, and works together with DICOM to standardize different medical equipment.