title: Multimodality calibration for simultaneous fluoroscopic and nuclear imaging.
abstract: BACKGROUND
  Simultaneous real-time fluoroscopic and nuclear imaging could benefit image-guided (oncological) procedures. To this end, a hybrid modality is currently being developed by our group, by combining a c-arm with a gamma camera and a four-pinhole collimator. Accurate determination of the system parameters that describe the position of the x-ray tube, x-ray detector, gamma camera, and collimators is crucial to optimize image quality. The purpose of this study was to develop a calibration method that estimates the system parameters used for reconstruction. A multimodality phantom consisting of five point sources was created. First, nuclear and fluoroscopic images of the phantom were acquired at several distances from the image intensifier. The system parameters were acquired using physical measurement, and multimodality images of the phantom were reconstructed. The resolution and co-registration error of the point sources were determined as a measure of image quality. Next, the system parameters were estimated using a calibration method, which adjusted the parameters in the reconstruction algorithm, until the resolution and co-registration were optimized. For evaluation, multimodality images of a second set of phantom acquisitions were reconstructed using calibrated parameter sets. Subsequently, the resolution and co-registration error of the point sources were determined as a measure of image quality. This procedure was performed five times for different noise simulations. In addition, simultaneously acquired fluoroscopic and nuclear images of two moving syringes were obtained with parameter sets from before and after calibration.
  
  
  RESULTS
  The mean FWHM was significantly lower after calibration than before calibration for 21 out of 25 point sources. The mean co-registration error was significantly lower after calibration than before calibration for all point sources. The simultaneously acquired fluoroscopic and nuclear images showed improved co-registration after calibration as compared with before calibration.
  
  
  CONCLUSIONS
  A calibration method was presented that improves the resolution and co-registration of simultaneously acquired hybrid fluoroscopic and nuclear images by estimating the geometric parameter set as compared with a parameter set acquired by direct physical measurement.
authors: Radiology and Nuclear Medicine, UMC Utrecht, P.O. Box 85500, 3508 GA, Utrecht, the Netherlands. cbeijst@umcutrecht.nl.|Image Sciences Institute, UMC Utrecht, P.O. Box 85500, 3508 GA, Utrecht, the Netherlands. cbeijst@umcutrecht.nl.
authors: Casper
authors: http://orcid.org/0000-0003-1672-3230
authors: C
authors: Beijst
authors: Radiology and Nuclear Medicine, UMC Utrecht, P.O. Box 85500, 3508 GA, Utrecht, the Netherlands.|Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
authors: Mattijs
authors: M
authors: Elschot
authors: Radiology and Nuclear Medicine, UMC Utrecht, P.O. Box 85500, 3508 GA, Utrecht, the Netherlands.|Image Sciences Institute, UMC Utrecht, P.O. Box 85500, 3508 GA, Utrecht, the Netherlands.
authors: Sandra
authors: S
authors: van der Velden
authors: Radiology and Nuclear Medicine, UMC Utrecht, P.O. Box 85500, 3508 GA, Utrecht, the Netherlands.
authors: Hugo W A M
authors: HW
authors: de Jong
keywords: Calibration; Dynamic imaging; Fluoroscopy; Hybrid imaging; Interventional; Nuclear imaging; Scintigraphy; X-ray; c-arm