CT | About the UW GE CT Protocol Project
Clinically Validated and Dose Optimized
At the University of Wisconsin - Madison, the Departments of Radiology and Medical Physics have been collaborating with the hospital staff to refine CT imaging protocols in an effort to reduce dose, enable the acquisition of more clinically useful images, and reduce the frequency of repeat scans.
The UW CT protocols have been in a constant state of evolution. With the help of the largest medical physics department in the world, UW protocols have been modified so we image gently, but also we image well.
Part of the success of the project is that UW has partnered with GE Healthcare. Collaboration with the GE engineers has allowed us to gain greater insight into the capabilities of each scanner platform. These protocols are now shared with current and future GE CT users. This has the potential to save time and effort for clinical services, particularly those relying on GE scanners. As an example, a study at the William W. Backus hospital presented at the 2011 annual meeting of the Radiological Society of North America (RSNA), revealed that the annual cost of reviewing and optimizing 30 protocols can exceed $150,000.1
This release of UW protocols covers nearly all clinical indications for CT imaging including neuro, MSK, chest, body, vascular, and pediatric. By adjusting the type, amount, and timing of oral and intravenous contrast as well as modifying patient positioning, and scan and reconstruction parameters, each protocol is optimized to enhance potential for accurate diagnosis of a suspect clinical condition.
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.
Each Scanner is Different
Typically when an institution acquires a new CT scanner an existing set of protocols is modified from an older scanner, and transferred to the new one, usually with the help of an application specialist. But it takes time and an understanding of the new scanner's capabilities to fine-tune those protocols so the scanner can be used to full advantage. Instead of this transfer-and-tweak method, for several of the GE scanner platforms, the new protocols are optimized, validated, and take full advantage of the new scanner's capabilities.
Before the protocols could be turned over to GE, UW Radiology had to become ISO compliant (an industry standard for quality). It is not typical for an academic institution to go through this high degree of quality evaluation, but since this is a product intended for public clinical use, it was deemed necessary. An ISO specialist joined the UW team to generate formal documentation of the protocol management and optimization framework that developed organically from our early days of CT. This quality management program meets and or exceeds the AAPM Medical Physics Practice Guidelines which were recently published for CT protocol management.2,3
To ensure that patient exams are accepted internally at the UW Madison, a robust quality assurance (QA) procedure had to be put in place. Every exam read by UW radiologists from CT scanners participating in the GE protocol project is subject to this QA procedure to ensure image quality. The radiologists leave feedback in the form of "good" or "bad" responses and if bad, provide details as to why the image was not adequate for their needs. To date, over 60,000 unique image quality reviews have been received. Drs. Timothy Szczykutowicz, Ph.D. and Robert Bour, M.D. are spearheading the compilation and analysis of the QA data. We routinely analyze the performance of our protocols across each of our scanners, for each of our patient size categories.
This QA data lets us take an aggregate view of our protocol performance, and often spurs changes or consultations between the physicists and clinical staff. That would be difficult to accomplish without an automatic QA system as our protocol set contains hundreds of protocols, each tuned to a specific model of CT scanner.
An Efficient Workflow
Having so many protocols might suggest a negative impact on workflow, but that's not the case. Workflow actually proves.
The first major advantage is that each protocol is tailored to a particular clinical indication. These are often straightforward (such as a known cancer follow-up) and we only employ a single scan sequence. This eliminates those multiple sequence studies that are not needed for diagnosis. Fewer sequences performed means a lower dose to the patient, and shorter study length.4
At many centers, the technologist is left to arbitrarily modify the protocol based on patient weight or BMI. The quality of the scan and dose are then highly dependent on their knowledge and expertise. That's a big responsibility and our protocols take out the guess work out. The scanner user-interface presents the operator with the option of various clinical protocols. Once one is selected and a scout image is obtained, the technologist specifies the body-size-specific protocol based on patient measurements and proceeds with the scan. No time is wasted experimenting with the settings, and scan is accomplished with the optimal dose for that patient and that clinical indication.
Additionally, with timely advanced radiologist protocoling (motivated by insurance pre-approval process), the technologists know exactly how long the patient preparation and the CT scan will take. This benefits patient scheduling and streamlines workflow.
The ultimate goal is to provide a scan that allows a confident diagnosis with an appropriately low dose. The focus in CT has shifted. Just a few years ago, it was on increasing the number of slices and getting better resolution. Now it's time to pull back from the over-pursuit of detail. We want make the diagnosis accurately, quickly, and do it at an appropriate dose.
- Siegelman, Jenifer RQW, and Dustin A. Gress. "Radiology Stewardship and Quality Improvement: The Process and Costs of Implementing a CT Radiation Dose Optimization Committee in a Medium-Sized Community Hospital System." J Am Coll Radiol. 2013 Jun;10(6): 416-22.
- Cody, Dianna D., et al. "AAPM Medical Physics Practice Guideline 1.a: CT Protocol Management and Review Practice Guideline." J Appl Clin Med Phys. 2013 Sep 6;14(5):3-12
- Szczykutowicz, Timothy P., et al. "Compliance with AAPM Practice Guideline 1. a: CT Protocol Management and Review—from the perspective of a university hospital." Journal of Applied Clinical Medical Physics 16.2 (2015).
- Guite KM, Hinshaw JL, Ranallo FN, Lindstrom MJ, Lee FT Jr. "Ionizing Radiation in Abdominal CT: Unindicated Multiphase Scans are an Important Source of Medically Unnecessary Exposure," J Am Coll Radiol. 2011 Nov;8(11):756-61.