Marc Kachelriess PhD, Presenter: Nothing to Disclose

Michael Knaup PhD, Abstract Co-Author: Nothing to Disclose

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

To improve temporal resolution in cardiac CT by using N x-ray tubes and N detector arrays simultaneously.

Temporal resolution can be improved by increasing the rotation speed. Using multiple x-ray sources is an alternative [Proc. IEEE 71(3):308-319, 1983][Med. Phys. 28(7):1466-1471, 2001]. We consider a spiral cone-beam CT scanner that has N tubes and N detectors mounted and call this device a multi-threaded or N-threaded CT scanner. Aiming for improved image quality the relative temporal resolution is studied as a function of heart rate and scan overlap (i.e. the pitch value) for various geometrical configurations assuming multi-segment phase-correlated image reconstruction. The parameters to optimize for are the number of threads N and the azimuthal and longitudinal interthread angles. Due to practical reasons we restrict ourselves to double-threaded (N=2) and triple-threaded (N=3) scanners although our algorithms can cope with any number of threads. We further have generalized the EPBP image reconstruction algorithm [Med. Phys. 31(6):1623-1641, 2004] to allow for 3D and 4D image reconstruction from multi-threaded circular, sequential and spiral cone-beam scans. Our approach was evaluated using simulated 64- and 256-slice data of a thorax and of a cardiac motion phantom.

For N=2 we found the optimum whenever the angle between the tubes is 90° and when both threads are mounted in the same axial plane. Mounting the threads with a longitudinal offset (z-offset) results in a slight reduction of the temporal resolution only. The optimum interthread angles for N=3 are 60° or 120°; both result in identical temporal resolution values. The mean temporal resolution achievable with an optimized multi-threaded CT scanner is a factor of N better than the mean temporal resolution obtained with a single-threaded scanner. Image quality improves accordingly regarding motion artifacts and cone-beam artifacts.

Theoretical considerations and reconstructions of simulated data show that improvements (increase of temporal resolution and a reduction of cone-beam artifacts) by a factor of N can be expected with N-threaded CT scanners.

Kachelriess, M, Knaup, M, Kalender, W, High-Speed Cardiac Imaging Using Multi-Threaded Spiral Cone-Beam CT.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4405225.html