AJR: ASIR cuts CTC radiation dose by 50%

CT Colonoscopy Image Source: TeraRecon

Adaptive statistical iterative reconstruction (ASIR), a newly adapted CT reconstruction technique, can help reduce CT colonography (CTC) radiation dose by 50 percent, according to a study published in the July issue of the American Journal of Roentgenology.

The study sought to evaluate the feasibility of preserving CTC image quality using reduced radiation dose with ASIR--a new method for reconstructing CT data that uses a mathematical model to remove individual projections that are noisy and deviate from the model. The end result is a marked reduction in image noise, according to the study authors, who added that the selective reduction in image noise produces a higher quality image at lower radiation dose.

Current CTC dose stands at half conventional CT dose because of the high contrast between the soft tissue wall and air attenuation in the lumen; however, further reductions are desirable, particularly for a screening study that may impact a large number of patients.

“Despite the fact that the radiation dose delivered by CTC was already low and a lack of conclusive data regarding risk from medical radiation, radiologists strive to reduce dose at every opportunity,” explained lead author C. Daniel Johnson, MD,  professor of radiology at the Mayo Clinic in Scottsdale, Ariz.

The two-part, single-center study first imaged a colon phantom at 50 mAs (approximately 5 mSv) and at 10-40 mAs (approximately 1-4 mSv) using six different ASIR levels. Researchers assessed 2D and 3D image quality and noise to determine optimal dose and ASIR settings for the patient portion of the study. They scanned  18 patients at a standard CTC dose of 50 mAs (approximately 5 mSv) and at a reduced dose of 25 mAS (approximately 2.5 mSv) using 40 percent ASIR.

Three experienced CTC radiologists reviewed patient image data and independently graded image quality, image noise and image sharpness for three similar anatomic sites in the colon in each patient.

“In patients, no significant image quality differences were identified between standard- and low-dose images using ASIR,” said Johnson. The phantom study showed image noise reduction that correlated with a higher percentage of ASIR.

“The results of this pilot study show that the radiation dose during CTC can be reduced 50 percent below currently accepted low-dose techniques without significantly affecting image quality when ASIR is used,” said Johnson. 

The authors recommend further clinical evaluation in a larger patient group.