Guangzhi Cao, Presenter: Researcher, General Electric Company

Suresh Narayanan MS, Abstract Co-Author: Employee, General Electric Company

Jean-Baptiste Thibault, Abstract Co-Author: Employee, General Electric Company

Jiang Hsieh PhD, Abstract Co-Author: Employee, General Electric Company

Roy Nilsen, Abstract Co-Author: Employee, General Electric Company

To reduce the over-beaming dose in conventional helical scans by acquiring and reconstructing the same image volume using a reduced scan range through an axial-like reconstruction algorithm that makes better use of the data.

In the proposed framework, the reconstruction volume is split into two types of regions along the z-direction when the helical scan range is reduced: one central region where conventional reconstruction methods are applied and two boundary regions on each side that have historically not been recoverable. In the boundary regions an axial-like reconstruction algorithm which combines 3D view-weighting and modified back-projection is introduced. The 3D view-weighting satisfies consistency condition for a ray and its conjugate ray while taking into account the view-angle, cone-angle and the distance from the image slice to the center view in a unified framework. The same view range as the edge slice of the central region is used for reconstructing the boundary region, which results in smooth transition and makes the reconstruction similar to axial reconstruction.

Extensive experiments and observer study have been performed using both phantom and clinical scan data on volumetric CT scanners with various detector configurations and helical pitches. Experimental results demonstrated for the same prescribed image volume the xray scan range can be reduced by up to ¼ of the x-ray beam width in z on each end of the helix compared to conventional scans. This means we may save an additional 8% and 5% dose in routine chest and abdomen scans, respectively, on top of the dose saving achieved with the dynamic collimation method. The proposed method has also been applied to multi-energy CT scans with similar results.

A new axial-like helical reconstruction method is proposed that reconstructs the prescribed image volume with a reduced xray scan range through intelligent view weighting and back-projection. Experimental results indicate the new method can reduce the over-beaming dose significantly. The method can be easily applied to different helical modes and multi-energy scans.

The proposed method can readily be applied to routine CT helical scans only with software changes, which would result in significant over-beaming dose reduction.

Cao, G, Narayanan, S, Thibault, J, Hsieh, J, Nilsen, R, Over-beaming Dose Reduction Using an Axial-like Reconstruction Method in Helical Scans.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11006320.html