Iterative reconstruction can cut dose, but know the limits

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Evan Godt, Editorial Director

A pair of recent top-read advanced visualization stories focused on studies of iterative reconstruction and how the technology can benefit patients—but it also has its limits.

The first study, published in Academic Radiology, focused on model-based iterative reconstruction for reduced-dose CT colonography. Authors Varut Vardhanabhuti, FRCR, of the Plymouth University Peninsula Schools of Medicine and Dentistry in the U.K., and colleagues showed that the technology can improve image noise and maintain overall quality while also reducing patient radiation exposure.

For the study, standard-dose and low-dose CT colonography was conducted on 65 symptomatic patients using traditional filtered-back projection, adaptive statistical iterative reconstruction and model-based iterative reconstruction. Results showed the mode-based technique was able to maintain the same level of polyp detection while attaining dose reduction of 47 percent on average.

Another study, however, sought to determine much low-contrast spatial resolution is affected by iterative reconstruction, and found that clinically relevant diagnostic performance might be hampered at reduced dose levels. Published online in Radiology, the study featured scans in the LCR section of the American College of Radiology CT accreditation phantom implanted with 6 mm rods. Cynthia McCollough, PhD, and her colleagues at the Mayo Clinic in Rochester, Minn., used two scanner models at volume CT dose indexes of 8, 12, and 16 mGy.  Both filtered back projection and two manufacturers’ iterative reconstruction techniques were used each at “moderate” and “strong” strengths.

Their results showed that low-contrast spatial resolution was reduced with every reduction in contrast dosage, with reductions of 25-50 percent producing images that were inferior to traditional filtered back projection. Dose reductions of 25 percent could result in the inability to resolve the 6 mm rods in the phantom.

“It is imperative that the ability to detect and characterize low-contrast lesions not be compromised in the pursuit of reduced radiation dose levels,” wrote McCollough and colleagues. “Until sufficient studies have been performed to show that clinically relevant diagnostic performance for low-contrast imaging tasks is maintained or improved at reduced dose levels, use of IR techniques to decrease the appearance of image noise may increase the likelihood of missing clinically important findings, particularly those that are subtle in appearance.”

-Evan Godt
Editor – Health Imaging