A common question I hear new PACS administrator’s ask is, “What is meant by prefetching?”

In the PACS environment a prefetch is when all the studies are retrieved from permanent archive and are restored to the local cache. This typically happens when an order for a particular patient is entered into the rest system. When that water comes through to the PACS system via an HL7 message, the system will go retrieve the appropriate studies on that same patient. These studies are typically of the same modality and a body part of the current order. Advanced prefetching can’t occur based on a combination of factors such as modality and body part.

An example would be for 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 pre-fetch in the previous chest x-rays. Conversely, if that same patient was coming in for a chest CT, you would then want to pull back from the archive all prior chest x-rays and chest CT’s.

Spending some time with your radiologists discussing what studies are considered relevant when identifying prior studies is important. If time is not spent in advance, it will be lost at interpretation time. When a radiologist opens the study to read and the most relevant prior is not available, it will have to be manually retrieved at that time. This takes additional resources and slows down the radiology report turnaround time which is an important metric regarding radiology workflow. Another area that can be affected by poorly planned retrieval is the hanging protocols. If hanging protocols are developed to contain specific prior studies and those studies are not correctly retrieved from the archive, hanging protocols will not work as well.

Again, spending time with the radiologists and a thorough discussion of what relevant prior is unnecessary for reading is imperative. Some areas where extra time should be devoted to our discussions relating to common multi-modality body part imaging such as the abdomen, pelvis, and the chest.