CT Users Group

Alexis Moore

Medical Physics Department, Leeds General Infirmary

Abstract

The IGE HiSpeed CT/i scanner has several patient dose reducing features. SmartHelical™ is the latest of these features and is a new piece of software which IGE claim allows the patient dose to be reduced by 20-30% whilst maintaining image quality. When SmartHelical™ is selected the CT machine scans a slightly longer section than is defined by the operator, and the effective slice thickness is increased by 10-20%. An improved reconstruction algorithm is used to improve the image quality for a given tube current. The General Infirmary at Leeds obtained a copy of the software on "flex trial" in order to evaluate the software clinically and to verify the predicted dose reduction. Noise measurements were made using one of the phantoms which was available with the scanner. Data was acquired using a water section for the different tube voltages, slice thicknesses, pitches and software filters using varying mAs values in both SmartHelical™ and standard Helical modes. A second set of data was collected for Teflon, plex and polystyrene with varying slice thicknesses and mAs values in both modes. An exponential decay curve was fitted to each data set, and the value of the mAs where the curve reached a plateau determined. The noise was determined for this mAs in Helical mode and the value of the mAs with a similar amount of noise in SmartHelical™ mode was determined. This enabled the prediction of the amount of mAs reduction achievable in SmartHelical™ mode whilst maintaining image quality.

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