What makes this PACS software so hard to replicate, to copy, and then to replace in an organization?

The basics are pretty straightforward and well-established; they have been for 25 years or more. The ability to display an image, to zoom in and out on that image, to change the brightness and contrast—what's referred to as the level and the window in the radiology world—to be able to do some fundamental tasks; all of the different PACS systems have been able to do that for 20-plus years. Where you start to differentiate the capabilities is when you drill into the very specialized functionality. For example, a neuroradiologist wants to be able to trace the neurological pathways—in other words, the spinal column or nerve routings through the brain. A vascular radiologist wants to be able to trace blood vessels, the arteries and the veins. Those each require very different and highly specialized tools to indicate the extent of how far you want to trace it. Do you want to trace it from a tiny vessel in the brain all the way down through the heart and into the legs, or do you want to trace the vessels in the lower legs? Or for the neuroradiologist, do you want to trace the spinal column or what's referred to as the neural foramen—in other words, where the nerves branch off of the spinal column and out into a leg or an arm or to the liver or wherever? Each of those requires different algorithms in the software, different levels of specialization of the software engineering, of the testing teams, and of the regulatory affairs teams.

This is a general question on how the PACS industry developed. In other healthcare verticals like hospitals, like life sciences, the industry has evolved under a bundle model; you have the hardware medtech vendor bundled with the software. But here, it seems like it would be the case with GE machines or Siemens or other types of machines. However, the industry has evolved and unbundled, with two leading players getting traction—Sectra and Visage—which are unbundled, software-only. Why is this? If 80% is radiology, I assume that one hospital has a single vendor of radiology machines or a single vendor of cardiology machines.

You identified it exactly. When PACS was first created, going back to the late 1980s and early 1990s, it was 100% provided by the same companies that created the machines that generated those images: GE Healthcare, Siemens, and any others that made those devices. The reason for that was they were the only ones that had access to the information that defined how those images existed and what the file format was. In other words, is it a JPEG, a TIFF, a PNG, or a PDF? Those aren't exactly the formats they were originally; they were proprietary. Nobody else had access to how those images existed if they came off of a GE scanner or a Siemens scanner.