The radiologist’s gerbil wheel: interpreting images every 3-4 seconds eight hours a day at Mayo Clinic

If today’s workload of a radiologist seems to be akin to being a gerbil running inside a wire wheel, the analogy is not so farfetched. That is what radiologists interpreting CT and MRI examinations are doing, according to a study published online July 22, 2015 in Academic Radiology. Based on 255 uninterrupted eight-hour workdays per year, radiologists are needing to review one image every three to four seconds to meet workload demands.

It’s an undisputed fact that the number of CT and MRI examinations being performed have increased significantly in hospitals throughout the United States. A team of researchers from the Clinical Investigator Training Program at the College of Medicine at Mayo Clinic in Rochester, MN, decided to identify trends in utilization of cross-sectional modalities, specifically CT and MRI examinations. They decided to determine changes in utilization, information creation, and radiologist workload over a 10 year time span starting in 1999.

Lead author Robert J. McDonald, M.D., Ph.D. and colleagues determined from their analysis of over 1.5 million CT and MRI exam performed during this time period that increases in radiologist workload are driven more by increases in image content within each CT and MRI examination than increased utilization of these modalities. Although there was a steady increase in the number of CT and MRI exams performed each year at Mayo Clinic, the number of radiologists hired to read them increased steadily. In fact, the average number of CT exams decreased slightly.

At Mayo Clinic, interpretation responsibilities and work assignments (called worklines) have historically divided by modality, study type, and subspecialty. Over the 10 year time span, staff radiologists interpreting CT exams had between five to 37 years experience; radiologists interpreting MRI exams had between five to 31 years experience. The radiology department went filmless in 2004, but had been using PACS technology for CT and MRI interpretation since 1999.

The analysis identified:

  • the total number of CT (994,471) exams and MRI (522,678) exams interpreted;
  • the percentage increase of CT exams (68%) and MRI exams (85%) from Year 1 and Year 10;
  • the total number of exams interpreted for each modality per year. This represented a 1300% increase in CT images from Year 1 and Year 10, and an increase of 540% for MRI exams.

To determine the imaging workload of an individual radiologist, the team calculated the number of exams and images interpreted per assigned staff workline per year and the number of images interpreted per minute per staff workline, normalized to a 255 day year and uninterrupted eight hour workday. They determined that the average CT exam increased from 82 images in 1999 to 679 images in 2010. For MRI, the average increased from 164 images to 570 images respectively.Neuro, body and chest CT studies were the predominant contributors to observed increases in imaging workload. They also demonstrated the greatest increases in number of interpreted images over the study period. For MRI exams, neuro studies were the predominant contributor to workload increases. They accounted for 60.7% of interpreted MRI images.

Staffing of course increased. Dedicated CT worklines increased from 13 to 27, and dedicated MRI worklines from 13 to 21. However, when normalized to an uninterrupted eigh-hour workday, the average number of images requiring interpretation per minute increased nearly sevenfold for CT and fourfold for MRI interpretation.

The research team identified four factors responsible for increases in utilization:

  • A transition in evidence-based medicine showing the superiority of CT and MRI images to conventional radiographs;
  • Ongoing technological improvements in advanced imaging modalities and software;
  • Technological advances increasing the speed with which both CT and MRI images can be acquired and image-processed;
  • Technological advancements leading to the development of new imaging applications;
  • The use of cross-sectional imaging as a defensive tool in response to medicolegal risks.

“There has been little done to mitigate the impact of increases in imaging content on workload,” the authors note. They conclude, “The effect of increased examination content on fatigue and interpretation accuracy remains a relatively undefined clinical problem and merits additional investigation.”


  1. McDonald RJ, Schwartz KM, Eckel LJ, et al. The Effects of Changes in Utilization and Technological Advancements of Cross-Sectional Imaging on Radiologist Workload. Acad Radiol. Published online July 22, 2015.
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