SCCT: High-pitch CT slashes pediatric radiation dose
Source: U. Joseph Schoepf, MD
High-pitch, dual-source CT scanners may enable physicians to sustain diagnostic accuracy while allowing up to seven-fold reductions in pediatric radiation dose, according to a study presented this weekend at the Society of Cardiovascular CT (SCCT) in Denver.

“The main difference from a clinical standpoint is that dual-source CT scanners have very high pitch, and that dramatically reduces radiation dose compared to standard pitch,” B. Kelly Han, MD, a pediatric cardiologist at Children’s Heart Clinic and Children’s Hospital of Minnesota in Minneapolis, told Health Imaging News.

“Pitch is how fast the patient goes through the scanner, how fast the image can be acquired. So the flash scanner is about 48 cm in one shot. Standard pitch is anywhere from 0.8 to 1, variable pitch is up to 2.5 or 3, and the highest pitch is 3.4.”

Han and colleagues reviewed 76 coronary CT angiography (CTA) scans for children up to 18 years of age taken between 2007 and early 2011 at Minneapolis Heart Institute in Minnesota.

Patients were divided into three groups: 22 children underwent CTA with a first-generation dual-source scanner with retrospective ECG gating (spiral scan mode) in the first group. The second group consisted of 35 children who underwent second generation dual-source CTA with prospective ECG gating (sequential scan mode). Finally, 19 patients underwent the same protocol as group two but at a high pitch (flash scan mode).

Radiation dose was significantly lower for patients imaged at high pitches, with median age-adjusted doses of 1.8 mSv in the spiral scan group and 1.01 mSv in the sequential scan group, compared with 0.035 mSv for patients who underwent high-pitch coronary CTA.

Dose-length products likewise differed dramatically between the three groups, with median dose-length products of 122 and 62 mGy • cm in groups one and two, respectively, compared with a dose-length product of 17 mGy • cm for the high-pitch group.

Based on a four-point scale, image quality did not differ significantly between the three groups, with the spiral scan group averaging 3.5, while the sequential and flash scan groups showed slightly poorer quality at 3.3 and 3.4, respectively.

Han and colleagues’ findings followed their publication in the May issue of the American Journal of Cardiology (AJC) of similar results in comparing single-source CTA and dual-source, high-pitch CTA.

Among 61 neonates who underwent coronary CTA for complex congenital heart disease, the researchers calculated median dose-length products of 66 mGy • cm for the standard-pitch group and 7 mGy • cm for the high-pitch group, amounting to effective doses of 0.9 and 0.11 mSv, respectively.

Although both of Han et al’s studies showed degradation of image quality for high-pitch scans, with the earlier study showing significant reductions for objective measures, all images were judged to be fully diagnostic. Moreover, upon subsequent intervention in sizable sub-cohorts, all catheter and surgical diagnoses agreed completely with CTA interpretations for both studies.

Han stressed the clinical significance of the dual-source scanners’ accelerated acquisition of images. “The new scanners take between 0.2 and 0.5 seconds to acquire images, so patients can be free-breathing throughout the exams, which is very important for pediatrics.

“And although we still need to intubate some patients, we could radiate a much smaller part of the cardiac cycle and give them much lower doses than in the past, so many fewer patients are needing sedation and anesthesia, without a loss of diagnostic quality,” Han added.

In her view, because all images were fully diagnostic, the drop in dose “absolutely” outweighs the loss of image quality.

“Assuming the average yearly exposure from background radiation is 3 mSv, the dose from the highest pitch scans from this study is equivalent to the average exposure from 2 weeks of background radiation or two round trip flights from New York to Los Angeles,” wrote Han and colleagues in the AJC.

Han predicted that dual-source, high-pitch scanning will have “enormous” implications not just for pediatric imaging, but for radiology as a whole. While recognizing the need to demonstrate the technique’s effectiveness for each subset of patients and disease process, Han noted that a number of studies conducted on adults showed similar results to those of her group.

“I think for much of radiology, trauma and a lot of other areas, the need for sedation and anesthesia will be far lower, and so will radiation dose,” Han concluded.