Iterative reconstruction (IR) algorithms can reduce radiation dose for young patients

According to a recent study published by Clinical Radiology, using adaptive statistical iterative reconstruction (ASIR) and low tube voltage (kV) during non-contrast pediatric cranial computed tomography (cCT) can reduce radiation dose by a significant amount.

Lead author David Kaul, department of radiology at the Charité School of Medicine and University Hospital in Berlin, Germany, and colleagues noted that reducing dose during cCT can be especially difficult.

“Strategies to reduce radiation dose include using ultrasound (US) or magnetic resonance imaging (MRI) instead of CT when possible, as well as dose-saving CT technologies, such as automated tube current modulation and noise reduction filters; however, the potential of these dose reduction technologies is limited when examining through dense skull bone,” the authors wrote. “In addition, lowering the tube potential in the acquisition of cranial CT reduces radiation effectively, but comes at the cost of increased image noise.”

To test the ability of iterative reconstruction (IR) algorithms to reduce dose during cCT, Kaul et al. analyzed images from 78 patients 12 years old and younger. The patients were treated using four different protocols:

Group A (control): 120 kV, filtered back projection (FBP), n=18

Group B: 100 kV, FBP, n=22

Group C: 100 kV, scan and reconstruction performed with 20 percent ASIR, n=20

Group D1: 100 kV, scan and reconstruction performed with 30 percent ASIR, n=18

Group D2: raw data from Group D1 reconstructed using a blending of 40 percent ASIR and 60 percent FBP, n=18

Overall, the study revealed “a significant reduction” of the dose-length product (DLP) in Group C and Group D1/D2. In Group C, that reduction was more than 34 percent; for Group D1/D2, it was more than 64 percent.

Using both signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) to analyze the image quality of the different groups, the authors noted that Group C was comparable to the control group with a few exceptions. Group D1/D2, however, displayed lower quality in a number of ways. The data also showed “a trend towards decreased diagnosis-related confidence in Groups D1 and D2.”

“The protocol used in Group C is considered adequate for everyday clinical imaging, and this CT protocol is now routinely used in paediatric patients in the authors' clinics,” Kaul and colleagues wrote. “The CT protocol with 30 percent ASIR and an increased noise index (Group D1/D2) further reduced both quantitative and qualitative image quality to such an extent that it was not considered adequate for everyday clinical use; however, the quality remains high enough for the diagnosis of life-threatening conditions, such as acute bleeding, fractures, or for the assessment of hydrocephalus.”

According to the authors, this showed that IR algorithms do have the ability to reduce radiation dose.

The study, however, did have limitations. For instance, the authors said, image quality was based on the grades of two radiologists, “which may not have been completely blind.” Also, there were differences in patient ages between the various groups, though all patients did fall in the range of 0 to 12 years old.

Kaul and colleagues also believe there is much more research to be done, saying “further studies might be helpful in determining whether the present results can be applied to other scanners and algorithms.”