A generic, geometric cocalibration method for a combined system of fluorescence molecular tomography and microcomputed tomography with arbitrarily shaped objects.

TLDR: A cocalibration method is proposed for the combined system of FMT&mCT, which could be performed with no restriction on the system geometry, calibration phantoms or imaging objects.

Abstract: Purpose: A combined system of fluorescence molecular tomography and microcomputed tomography (FMT&mCT) can provide molecular and anatomical information of small animals in a single study with intrinsically coregistered images. The anatomical information provided by the mCT subsystem is commonly used as a reference to locate the fluorophore distribution or asa priori structural information to improve the performance of FMT. Therefore, the transformation between the coordinate systems of the subsystem needs to be determined in advanced. Methods: A cocalibration method for the combined system of FMT&mCT is proposed. First, linear models are adopted to describe the galvano mirrors and the charge-coupled device(CCD)camera in the FMT subsystem. Second, the position and orientation of the galvano mirrors are determined with the input voltages of the galvano mirrors and the markers, whose positions are predetermined. The position, orientation and normalized pixel size of the CCDcamera are obtained by analysing the projections of a point-like marker at different positions. Finally, the orientation and position of sources and the corresponding relationship between the detectors and their projections on the image plane are predicted. Because the positions of the markers are acquired with mCT, the registration of the FMT and mCT could be realized by direct image fusion. Results: The accuracy and consistency of this method in the presence of noise is evaluated by computer simulation. Next, a practical implementation for an experimental FMT&mCT system is carried out and validated. The maximum prediction error of the source positions on the surface of a cylindrical phantom is within 0.375 mm and that of the projections of a point-like marker is within 0.629 pixel. Finally, imaging experiments of the fluorophore distribution in a cylindrical phantom and a phantom with a complex shape demonstrate the feasibility of the proposed method. Conclusions: This method is universal in FMT&mCT, which could be performed with no restriction on the system geometry, calibration phantoms or imaging objects.