Xiangyang Tang PhD, Presenter: Former employee, General Electric Company

Suresh Narayanan MS, Abstract Co-Author: Employee, General Electric Company

Jiahua Fan PhD, Abstract Co-Author: Employee, General Electric Company

Jiang Hsieh PhD, Abstract Co-Author: Employee, General Electric Company

Jed Pack, Abstract Co-Author: Employee, General Electric Company

Roy Nilsen, Abstract Co-Author: Employee, General Electric Company

It is well-known that, to take advantage of the capability offered by focal spot wobbling to increase spatial resolution in CT scanner, certain conditions govern the focal spot deflection distance (condition-I) and the number of views (NOV) per gantry rotation (condition-II). An image reconstruction solution for volumetric CT to overcome the constraints imposed by condition-II and its evaluation are presented.

In the native cone beam (CB) geometry, condition-I assures that the latitudinal sampling rate in each virtual view combined from two adjacent actual views is doubled, while condition-II guarantees that the virtual focal spot of the virtual view is unique. A violation of condition-II can cause severe aliasing artifacts. In practice, these two conditions may prevent one from pursuing well-balanced image qualities over clinical applications. In the proposed solution, images are reconstructed in cone-parallel geometry obtained from the native CB geometry through row-wise fan-to-parallel rebinning. In the rebinning, the non-uniform sampling along the view angle direction due to the violation of condition-II is dealt with adequately by an advanced beta-interpolation followed by the conventional gamma-interpolation. This means that, condition-II does not have to be satisfied, so the NOV per gantry rotation can be set accordingly to pursue optimized image qualities. The proposed solution is evaluated by high contrast phantoms simulated by computer and scanned by a volumetric scanner, respectively, in which the enhancement in in-plane resolution at various distance away from the iso-center is quantitatively studied.

The performance evaluation shows that, the proposed solution enables the volumetric CT with focal spot wobbling at arbitrary NOV per rotation to increase its highest in-plane spatial resolution up to 33% while the optimized balance between spatial resolution and noise characteristics can be retained.

With the advanced fan-to-parallel rebinning to reconstruct images in cone-parallel geometry, the conventional condition-II is no longer a prerequisite for volumetric CT with focal spot wobbling to achieve superior in-plane resolution and optimized noise characteristics.

A substantial increase in in-plane spatial resolution is of significant clinical relevance, especially in imaging of cardiovascular and bony structures, such as inner ear and extremities.

Tang, X, Narayanan, S, Fan, J, Hsieh, J, Pack, J, Nilsen, R, Focal Spot Wobbling in Volumetric CT for Diagnostic Imaging: Revisited with Row Wise Fan-to-Parallel Rebinning.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8011422.html