Essential education: Managing dose

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 - radiation dose, CT

With increasing awareness of the harms that can accompany multidetector CT-related radiation dose, radiologists must fully understand the technology with which they constantly work. A review published in the November issue of the Journal of the American College of Radiology highlights this crucial necessity, emphasizing the essentials of basic CT scan parameters, as well as how they can be manipulated to produce diagnostic images at lower radiation doses for safe imaging.

Siva P. Raman, MD, of John Hopkins University in Baltimore, and colleagues outlined eight CT parameters that can be manipulated to create lower radiation dose protocols. These eight parameters include:

  • Detector configuration; 
  • Tube current; 
  • Tube potential; 
  • Reconstruction algorithm; 
  • Patient positioning; 
  • Scan range; 
  • Reconstructed slice thickness; and
  • Pitch.

“Although there is always an inherent trade-off between image quality or noise and patient radiation dose, in many cases, a reasoned manipulation of these eight parameters can allow the safer imaging of patients (with lower dose) while preserving diagnostic image quality,” explained the researchers.

Automated tube current modulation is used across the board in almost all patients, as increases in the tube current and scan time produce improved image quality and decreased image noise. However, there is a trade-off between these benefits and an increase in patient dose. Radiologists need to be careful about using the software in obese patients, children, and patients with metallic hardware, according to the authors.

Reducing kvP can effectively reduce the dose of radiation exposure during an exam. Low-kVp protocols are particularly useful in thin, non-obese patients during vascular or angiographic studies. An increase in image noise with lower kVp needs to be balanced by an increase in the tube current.

Iterative reconstruction techniques permit the reconstruction of images with improved image quality, even in cases where the radiation dose and contrast-to-noise ratios are low. Once an iterative technique is in place, the dose should be decreased over time until the radiologist is not comfortable with the image quality.

Incorrect positioning of patients in the scanner can be associated with significant radiation dose penalties and can affect image noise too. Attention should particularly focus on pediatric patients when positioning on the scanner gantry.

The scan range should be reduced to the needed minimum for any examination, but especially when an increased range is not necessary for certain structures.

Practical knowledge of all eight parameters will improve quality and safety in patient care.

“When facing increasing criticism regarding CT dose, the best way to tackle the issue is to understand all the factors and parameters that can affect radiation dose and image quality and examine how these can be altered to reduce dose,” wrote Raman and colleagues.