Originally published on JS PACS, March 7, 2009. Part of the Radiology Workflow series.
A common question I hear new PACS administrators ask is, “What is meant by prefetching?”
In the PACS environment, a prefetch is when studies are retrieved from the permanent archive and restored to the local cache. This typically happens when an order for a particular patient is entered into the RIS. When that order comes through to the PACS via an HL7 message, the system goes and retrieves the appropriate prior studies on that same patient. These are typically of the same modality and body part as the current order. Advanced prefetching can be based on a combination of factors, such as modality and body part.
An example would be a chest x-ray. If a patient is having a chest x-ray today and in the past had some chest CT scans as well as chest x-rays, you would only want to prefetch the previous chest x-rays. Conversely, if that same patient was coming in for a chest CT, you would want to pull back from the archive all prior chest x-rays and chest CTs.
Spending some time with your radiologists discussing which studies are considered relevant priors is important. If the time is not spent in advance, it will be lost at interpretation time. When a radiologist opens a study to read and the most relevant prior is not available, it has to be manually retrieved right then. That takes additional resources and slows down report turnaround time, which is an important radiology workflow metric. Another area affected by poorly planned retrieval is hanging protocols. If hanging protocols are built to include specific prior studies and those studies are not correctly retrieved from the archive, the hanging protocols will not work as well.
Again, spending time with the radiologists and having a thorough discussion of which relevant priors are needed for reading is imperative. Areas where extra time should be spent are the common multi-modality body parts such as the abdomen, pelvis, and chest.