Interaction Between Departments

Over the years as CT scanner complexity increased, Frank Ranallo, Ph.D., Associate Professor of Medical Physics and Radiology at the University of Wisconsin, became closely involved in protocol development. He recognized there was a great opportunity for improving image quality and also lowering radiation dose. He has interacted extensively with the radiologists and evaluated numerous parameters for CT image acquisition and reconstruction. In most protocols, there are over 30 different technical parameters that can be adjusted and all of them were considered fair game for modification.

What is truly unique about the UW protocol optimization project is that for each clinical protocol, there are multiple protocol sub-sets optimized to patient size: adult (3 sets) and pediatric (5 sets). With larger patients, image quality can suffer and arbitrary increases in exposure could improve image quality but at the expense of very high radiation doses. This was the key issue: How do we generate diagnostic quality images at a reasonable dose for all size patients?

At many institutions, there is a single set of technical scan parameters per clinical protocol. Most then rely on automatic exposure control (AEC), to produce the needed dose modification as patient size varies. That’s a good start. But AEC only varies the mA. We tweak multiple parameters: kV, mA, rotation time, pitch, slice thickness, viewing window width and level, iterative reconstruction methods, and more so the end result is maximum dose reduction for specific scanners across the spectrum of body sizes.