University of Utrecht Developing A New Dual Image System For Medical X-ray And Gamma Ray Diagnosis And Treatment.

University of Utrecht Developing A New Dual Image System For Medical X-ray And Gamma Ray Diagnosis And Treatment.

       I have mentioned medical images with radioactive isotopes occasionally in this blog. Today I am going to delve into detail on a recent development in using radioisotopes in diagnostics and treatment. Researchers at the Utrecht University in the Netherlands have built a prototype device that combines a fluoroscope, a flat panel X-ray detector, combined with a gamma ray camera. They have used computer simulation to show how the device could be improved.
       Usually when creating such a hybrid device in the past that combined two different imaging modalities, one of the modalities was applied after the other. The problem with this approach was that if the patient moved at all between the application of the two different techniques, the resulting combination of images could be misaligned.
      The new device from the Utrecht team captures images from both techniques simultaneously which insures that the two images are properly aligned. This new device may be able to supply clinicians with anatomical data that cannot be captured by medical imaging systems currently in use.
      There was a previous attempt to combine fluoroscopy and nuclear imaging to simultaneously capture both images. Four gamma cameras with pinhole collimators were placed around the X-ray source on the opposite side of the patient from the X-ray detector. In order to create the final gamma image, the distribution of energy from the gamma emitter had to be combined into one image from the four separate images. Sandra van der Velden, the first author of the report on the Utrecht work, said, “This was computationally quite demanding, required complicated hardware integration, and resulted in a lower resolution of the nuclear images.”
       The Utrecht team has shown that they can capture useful images even when a single gamma camera with a cone-beam collimator is positioned behind the X-ray detector. Composite images that are created in this way are naturally co-registered. This means that diagnostic and therapeutic radioisotopes can be tracked within the anatomical context shown by the fluoroscopy.
       X-ray detectors are sensitive photon energies of 30-120 kiloelectron volts. Gamma ray detectors are sensitive to photon energies of 140 kiloelectron volts. This means that in the new device, the gamma photons are captured after they pass through the X-ray detector so system sensitive for gamma rays is degraded. In order to counter this, the Utrecht team has removed some of the lead shielding and structural aluminum from the flat panel X-ray receiver.
      The Utrecht experiments with radioactive sources in moving phantoms showed that the interference by the X-ray detector reduced the sensitivity by between 45% and 60%. However, the images were still free of artifacts and were useful. The spatial resolution of the gamma camera was not affected. The presence of a radioisotope in the field of view of the X-ray detector had no impact on its’s performance.
       Computer modeling indicates that the performance of the new device could be improved by reducing the thickness of the aluminum in the X-ray detector. This would reduce the attenuation of the gamma ray signal by 27% to 35%. This reduction of thickness in the X-ray detector would permit the gamma ray camera to be moved closer to the patient which will improve its resolution.
       While, the new device being developed in Utrecht will have broad application, the Utrecht team is focusing on a particular medical procedure called radioembolization for liver cancer. Currently nuclear imaging is used to predict the uptake of the radioisotope in the liver. Then, up to a week or more later, the treatment is carried out and monitored by the fluoroscope.
       Not only is the delay inconvenient to the patient, a catheter has to be inserted twice which carries its own dangers. If the hospital can carry out both procedures in the same day with the new device, it will be more convenient, safer and the results of imaging more accurate than the current technique.
      Van der Velden said, “We are currently working on a clinical prototype, which is at this moment being constructed. We plan to perform a clinical trial with that prototype, to show that radioembolization procedures can be improved. This will open up the possibility to perform it in one day, instead of the current two-step process, which takes one or two weeks.”