Iterative Reconstruction Could Half CT Perfusion Dose

Computed tomography perfusion imaging reconstructed with half of the normal dose and iterative reconstruction resulted in a similar objective and diagnostic image quality as the standard dose.

“Protocols of CT perfusion-studies could be changing due to our conclusions,” said Joris M. Niesten, MD, of the department of radiology at University Medical Center Utrecht, Netherlands. “The results of this study are promising, suggesting that a significant dose reduction in head CT perfusion can be achieved when using iterative reconstruction.”

CT perfusion in stroke patients has been shown to increase the diagnostic accuracy of finding potentially reversible ischemia. This procedure is being used in combination with unenhanced CT and CT angiography for a more complete diagnostic picture.

“With the ongoing introduction of full-brain CT perfusion in many centers, the radiation exposure of the CT perfusion will continue to increase, increasing many of the problems associated with CT,” Niesten said.

Therefore, Niesten and colleagues conducted a study to determine if CT perfusion radiation dose could be cut in half without reducing image quality. The study included patients with less than 24 hours since the onset of neurological stroke symptoms. All patients had undergone CT perfusion using a 256-slice multi-detector.

The researchers reconstructed 48 CT perfusion examinations into a standard dose with filtered back projection and a half-dose with middle and high iterative reconstruction. Both objective and subjective image quality was measured. The results of the study were published in European Radiology.

Results indicated that the half-dose CT perfusion with a high iterative reconstruction had similar objective and diagnostic image quality to the standard dose:

·       Grey matter cerebral blood volume (4.4 mL/100 g vs. 4.3 mL/100 g)

·       Contrast-to-noise ratio (1.59 vs. 1.64)

·       Penumbra/infarct index (0.74 vs. 0.73)

·       Mean Likert scale ranking (1.42 vs. 1.49)

Overall image quality was equal for standard dose with filtered back projection and half-dose with high iterative reconstruction. In 25 percent of cases, the standard dose was rated as superior to the half-dose with high iterative reconstruction. However, in 15 percent of cases, the standard dose was rated as inferior.

“As both the objective and diagnostic image quality were comparable despite a 50 percent dose reduction when using iterative reconstruction high, it is unlikely that dose reduction in combination with the use of iterative reconstruction high algorithms will influence diagnostic conclusions and therapeutic decisions,” the researchers wrote. “However, as the subjective overall image quality was still scored inferiorly in about one-quarter of patients with a 50 percent dose reduction using iterative reconstruction, the effect of the decreased overall image quality on the clinical decisions should be further examined.”

Half-dose imaging with filtered back projection and half-dose with middle iterative reconstruction were both considered inferior to standard dose imaging with filtered back projection.