Marcel Van Straten PhD, Presenter: Nothing to Disclose

Marcel L. Dijkshoorn DSc, Abstract Co-Author: Nothing to Disclose

Gabriel P. Krestin MD, PhD, Abstract Co-Author: Nothing to Disclose

Wiro Niessen PhD, Abstract Co-Author: Nothing to Disclose

To develop and validate a method for the assessment of the temporal resolution in ECG-gated cardiac CT.

Temporal resolution is defined here as the width of the cardiac phase sensitivity profile (PSP), analogue to the width of the slice sensitivity profile. The PSP was derived from the response to a step function generated by virtually instantaneously introducing an aluminium rod (diameter 10 mm) into the scan plane, during an ECG-gated cardiac CT acquisition. The heartbeat at which the rod appeared was identified, and multi-phase reconstructions were made at the corresponding z-position (increment 1% of the R-R interval). A simulated ECG-signal of 75 bpm was used. Measurements were performed with the rod at the isocenter and 11, 15, and 19 cm off-center. At each rod position, the experiment was repeated 12 times. Both a first generation (Somatom Definition, Siemens, Germany) and a second generation (Somatom Definition Flash) dual-source CT scanner were used, these having rotation times of 330 and 285 ms, respectively.

At the isocenter, the step response could be very well described by a linear function. Temporal resolution was found to match the nominal resolution of 83 ms and 75 ms for the first and second generation scanner, respectively. Both the inaccuracy and imprecision of the repeated measurements were small (~1 ms). Off-center, the step response could not always be described by a linear function, actual resolution deviated significantly from the nominal resolution, and larger standard deviations were found. This last can be explained by the random starting angle of the x-ray tube. For example, for the first generation scanner resolution (mean±standard deviation) was 107±6, 162±23, and 168±27 ms at 11, 15, and 19 cm from the isocenter, respectively. The influence of the limited field of measurement of the second tube (radius 13 cm) can be appreciated by the large difference between the 11 and 15 cm off-center positions.

An accurate, precise, and easy to perform method for quantification of temporal resolution in CT has been introduced and validated for state-of-the-art dual-source CT. Only at the center of rotation, temporal resolution was equal to the nominal resolution.

Knowledge of temporal resolution characteristics of a CT scanner allows for comparison between scanners and optimization of scanning protocols in for example coronary CT angiography.

Van Straten, M, Dijkshoorn, M, Krestin, G, Niessen, W, Assessment of Temporal Resolution at Multiple Positions in the Axial Plane for First and Second Generation Dual-source CT Scanners.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8001664.html