Dirk Ertel, Presenter: Nothing to Disclose

Marc Kachelriess PhD, Abstract Co-Author: Nothing to Disclose

Willi A. Kalender PhD, Abstract Co-Author: Nothing to Disclose

Using multiple x-ray sources is an alternative option to improve the temporal resolution of CT scanners [Med. Phys. 28(7): 1466-1471, 2001]. We want to generate and evaluate a purely rawdata-based synchronization signal for simulated CT scans of the heart with multiple tube-detector-systems (multi-threaded).

The kymogram function represents the temporal variation of the mass and is therefore correlated to the heart rate. It is an alternative to the commonly used concurrent ECG recording for phase-correlated image reconstruction. We simulated rawdata of the heart for CT scanners with N tubes and N detectors. With the usage of a software-based cardio phantom we generated CT rawdata with different heart rates, different scanner geometries and rotation times for N=1,2,3. The kymogram function is generated from the rawdata by a center-of-mass (COM) tracking of the scanned object [Med. Phys., 29 (7):1489-1503, 2002]. Standard protocols of 16- and 64-slice CT scanners were used. To validate our results we used the mean heart rate difference of the kymogram to the simulated ECG as a quality measure.

Our results show that the correlation of the kymogram with the ECG increases with the number of threads. The inconsistency of the projected mass due to beam hardening and scatter leads to a detectable resonance frequency in the case of N=1 and therewith correlates to the error in the kymogram. The variation of the entire projected mass of ±1.7% for N=1 can be reduced to ±0.3% for N=2 and ±0.18% for N=3. With respect to the intersecting tube-detector axes for N=2,3 the required angular integration in the COM calculation can be reduced and therewith the temporal resolution of the kymogram signal can be increased significantly. The improvement for more threads was more pronounced using a 16-slice scanner with lower rotation time.

Synchronization signals on the basis of a kymogram signal correlate well with the ECG using a multi-threaded CT scanner. With a higher number of threads the correlation between the kymogram and the ECG increases and therewith the image quality of a kymogram-based phase-correlated image reconstruction in cardiac CT is improved.

W.A.K.: Consultant to Siemens Medical Solutions

Ertel, D, Kachelriess, M, Kalender, W, Raw Data-based Generation of a Heart Motion Function (Kymogram) Using Multi-Threaded CT Scans of the Heart.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4416369.html