2D PACS has had its day in the sun, now 3D PACS is moving in

For the past 15 years, most PACS have performed the basic tasks of taking in images, archiving them, sending them to workstations for display, and hopefully not losing them. In the early days of PACS, in the late 1990s, that was considered plenty, given that the predecessor was film. Every system had the ability to zoom and pan and window and level. They could even flip and rotate images, which any picture managing software can do today. Measurement tools were also a given.

Over time, as CT scanners were able to slice thinner and thinner sections of the body, isometric data sets became available and the voxel (volume element) entered the vocabulary of medical imaging. It soon became apparent that new possibilities in manipulating the data to produce multiplanar reformations (MPRs) and maximum intensity projections (MIPs), as well as volume and surface renderings, could be realized.

These images have proven highly useful to the radiologist and referring clinician for both diagnosis and preoperative planning. But the software to perform these 3D renderings was often complex to use and typically found on only one or two separate computers in the department. To manipulate a set of images, they would have to be transferred to one of these workstations, and then someone, either a radiologist or a technician, would have to spend a fair amount of time adjusting the software to obtain a useful view of the data. Afterward, only a small set of key views would be captured and sent back to the PACS for archiving and review and the rest of the 3D model would be thrown away.

There was good reason for this. Radiologists used to look at about 30 slices of the head, about 60 slices of the chest, and about 80 slices of the abdomen and pelvis. This has not changed, even with the advent of multislice CT scanners. In fact, what most of these scanners do is acquire images in razor-thin slices, 0.5 or 0.6 mm, and average them together to make the typical 2.5-mm, 5-mm, or 10-mm–thick slices radiologists are used to seeing. So what was the point of making devices able to acquire the thin slices?

The answer is 3D. And that is why every CT vendor tries to package a 3D workstation with its scanner. It's not just because they want to sell you more; it's because it takes good 3D processing to bring out many of the benefits of the new scanners over older or less advanced ones. But as beautiful as the images are that the vendor may be able to produce on that workstation, it is still physically fixed in one location, typically. And more important, is not integrated with the PACS. Even if the workstation is accessible remotely, it is often disruptive to a radiologist to have to put PACS aside, push an exam to the 3D system, manipulate it there, and then push back to PACS only a few sample 2D captures of the 3D model.