Low-dose protocol doesnt affect 3D CTC
CHICAGO—Although the diagnostic quality of 2D images produced by ultra low-dose CT colonography (CTC) is not affected by the radiation-lowering protocol, questions have remained as to its applicability with 3D advanced visualization software tools.

According to research presented by team of French scientists at the 94th scientific assembly and annual meeting of the Radiological Society of North America (RSNA) this week, the quality of images for CTC 3D interpretation is not affected by low-dose protocols.

“For CTC, it has been proven that the dose reduction does not affect the quality of the 2D images for a polyp and mass detection,” said Meihdi Cadi, MD, who presented the results of the group’s study. “Our aim was to evaluate the impact of the dose reduction on the 3D endoscopic view.”

The group examined 80 asymptomatic individuals who underwent CTC screening for colorectal cancer with a 64-slice CT system (Brilliance by Philips Healthcare) at the Pitie Saltpietre Hospital in Paris and selected 53 for its testing cohort. Colonic insufflation was achieved through an automated CO2 system from E-Z-EM, he said.

“Individuals were examined at the usual dose of 120 kVp and 100 mAs for supine position while the prone position was acquired at an ultra low dose: 120 kVp and 10 effective mAs,” Cadi reported

For each patient the individual dose exposure was calculated by using the dose length product, he said. The data set was then sent to a 3D workstation (V3D colon from Viatronix) and interpreted by two readers for each acquisition from rectum to cecum, then from cecum to rectum.

One of the readers was experienced with 3D interpretation and one was not, Cadi noted.

The prone acquisition was analyzed first, and then was followed by analysis of the supine acquisition. Image quality was assessed by using a four-point confidence scale, he said.

“The radiation dose was significantly lower on the prone acquisition compared to the supine acquisition: 1.02 mSv and 2.43 mSv respectively,” Cadi said. “The average image quality was rated at 3.9 for the supine acquisition and 3.7 for the prone acquisition, without significant difference.”

The use of an ultra low dose did not affect the 3D endoscopic image quality and led to a significant reduction in patient radiation exposure during a CTC exam, the scientists reported.

“The ultra low-dose CTC protocol did not affect the quality of our 3D endoscopic interpretation,” Cadi stated.