The Value of CT Contrast

If there was a tool available that would automatically improve your job performance by nearly one-third, you’d want to use it, right? (And no, we’re not talking about ChatGPT.) The tool is contrast media, and a new study in JAMA Surgery found that the use of contrast in emergency CT exams improved the diagnostic accuracy of radiologists by 30%.

Radiology has a love-hate relationship with contrast. Contrast media unquestionably improves medical image quality, but it also adds a layer of complexity to imaging operations. Patients have to be screened and monitored for contrast allergies and reactions, IV lines have to be placed, injectors have to be monitored and maintained. 

Radiology researchers and clinicians have explored a variety of methods for non-contrast imaging, in particular in the emergency setting, where the time spent setting up a contrast exam could delay patient care. 

But while the risks of giving contrast are extensively debated, what are the risks of not using it? Researchers from multiple US institutions sought to answer this question in a study of 201 patients who got CT scans in emergency departments for acute abdominal pain over 3 weeks in 2017. All patients were scanned on Siemens Healthineers’ Somatom Force dual-source dual-energy CT scanner.

The original scans were contrast-enhanced, and a dual-energy technique was used to produce non-contrast images. Both sets of images were read by faculty and resident radiologists. Compared to the gold standard of contrast CT at 100%, findings included:

  • Diagnostic accuracy of unenhanced CT was 70%, or 30 percentage points lower than contrast CT
  • Faculty radiologists were more accurate than residents for primary diagnoses (82% vs. 76%), but less accurate for actionable secondary diagnoses (87% vs. 90%)
  • Faculty made fewer false-negative primary diagnoses than residents (38% vs. 62%)
  • False-negative and false-positive results were common (19% and 14%, respectively)

The Takeaway 

Reducing the use of contrast is a worthy goal, but it carries risks of its own, as this study indicates. False-negative interpretations are among the worst kinds of radiology errors with non-contrast exams, and clinicians should weigh the diagnostic penalty of withholding contrast media in the emergency setting, especially given the extremely low rate of contrast reactions in low-risk patients.

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-- The Imaging Wire team