Meetings » 2nd CTUG Meeting » A comparison of methods for measuring the limiting spatial resolution of a CT scanner

A comparison of methods for measuring the limiting spatial resolution of a CT scanner

B Warr, A Hill, N Keat, Dr S Sassi, S Edyvean

ImPACT, St George's Hospital, London


The use of CT as a widespread diagnostic imaging tool necessitates the accurate assessment of a scanner's capabilities, specifically spatial resolution. The test tool provided for the assessment of high contrast spatial resolution is usually a bar pattern for subjective visual analysis. The design of these bar phantoms varies between different manufacturers, and although suitable for QA procedures, it does not allow for reliable comparisons between different scanner models. Therefore, it is important that these subjective checks can be related to one another, as well as the more objective methods used by the ImPACT group. The aim of this project was to determine the correlation between techniques so that fair comparisons can be made when required. Measurements were conducted on an IGE HiSpeed CT/i scanner recently installed at St.George's Hospital, London. We used a range of both objective and subjective methods. These included Fourier analysis of Edge Spread Function data, from our own phantom, to calculate MTF 10% and 50% values, the Droege method of analysis (related to the modulation of a bar pattern) on IGE's own QA phantom and visual analysis on a 'Catphan'. By upgrading our image analysis software we were able to test a new wire insert made to fit into one of ImPACT's existing phantoms, which allows us another method of objectively measuring, via the Point Spread Function, MTF 10% and 50% values for, axial, helical and multi-slice scanning. Results are presented showing the correlation between the different methods.

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