Meetings » 12th CTUG Meeting » Abstracts

CT Helical Head Scanning

Katherine Dewis, Peter McGookin, Matilda Myekiova, John Crossman

Royal Berkshire Hospital


Alternative protocols for CT head examinations at the Royal Berkshire Hopsital (RBH) have been assessed in order to optimise the procedure and to improve compliance with IRMER (2000). Moreover the current sequential head CT scan used at RBH provides limited diagnsotic information compared to helical scans. The volume reconstructions undertaken on sequential scans can lead to a step image artefact which would not be observed in helical scanning.

Despite the additional diagnostic information gained and the radiologists' approval of the image quality routine helical scanning has not been adopted due to the high effective dose to the patient of approximately 5.6 mSv (in comparison to 2.3 mSv for sequential scanning).

Alternative protocols, which utilise automatic tube current modulation, were tested using a RANDO phantom for measurements of the image quality. These alternative protocols were derived from and similar to a similar GE scanner at a near by hospital. This protocol at the near by hospital was also tested.

In comparison to the original RBH helical protocol these new protocols had differing tube voltage, noise index (the noise index is the parameter used to determine the automatic tube modulation on the GE scanner) and pitch. The initial helical protocol was shown to give a dose of 5.9 mSv to the RANDO phantom, with the alternaitve protocols providing doses in the range of 1.6 mSv to 4.8 mSv. In comparison the current sequential head protocol delivered a dose of 2.7 mSv to the RANDO phantom. The image quality was assessed in terms of noise and signal to noise ratio (SNR) with the aim of matching the noise and SNR levels measured, to determine if lowering the dose had significantly affected the image quality.

A new optimised protocol was identified that provided clinically acceptable image quality but delivered an effective dose of 2.4 mSv. Given the small increase in dose over the sequential scan, the helical scan protocol has been accepted for routine use by RBH.

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