Novel Imaging Technology Improves Image Quality, Lessens Radiation

Particle physicists have created a novel imaging technology that includes combining the PET and MRI technologies in a way that involves much less radiation than current technology.

Many cancer patients must be examined multiple times to check whether treatment is effective, resulting in very high total radiation exposure. PET (positron emission tomography) scans are harder to interpret if medical staff cannot situate the location of cancer cells in relation to the skeleton and soft tissue. This is done by comparing PET images with an anatomical picture such as CT or MRI scans. Currently, due to the high expense of MRI, most hospitals combine PET and CT, but this combination has a significant weakness.

The team of physicists, at the University of Oslo (UiO; Oslo, Norway), developed a high resolution, high sensitivity technology based on an idea connected to the experiment at CERN (the European Organization for Nuclear Research) in which enormous detectors are used in the largest physics experiment being performed to trace the smallest particles. “We have managed to double the sensitivity. In practice, we can take the pictures twice as fast, or only use half of the radioactive dose in order to get the same image quality as previously,” said Erlend Bolle, PhD and particle physics researcher at UiO. Also, Dr. Bolle and his three colleagues have constructed the PET machine to be so small that it can be placed inside an MRI machine. Both images can thereby be taken simultaneously, further reducing total radiation exposure for patients and providing higher accuracy in that medical personnel do not have to correct for errors that occur when the two images are taken separately and later combined. Presently the technology is in a format specially optimized for use on experimental animals for research. However, Dr. Bolle emphasizes that “it can easily be rebuilt for hospital use.”

One of the great technical challenges that were overcome is that in order to trace the radioactive source, a PET scanner must find which parallel photons are linked. Current detectors have no depth information and therefore cannot reconstruct the positions of the many photons that release only part of their energy on first impact. In the new technology, identifying the locations of all photons is enabled by measuring the positions in three dimensions in a five-layer detector. The new detectors are made from entirely new crystals and light guides such that in each of the five layers of the detectors, crystal pins are placed on top of a transverse layer of light guide fibers. “This is a completely new way of measuring gamma particles,” notes Dr. Bolle. Another important technical improvement incorporated into the new PET scanner enables good image quality to be achieved even if the test animal is lying right next to the detectors.

Among advantages are parts of the new PET scanner that are put together like lego bricks; the system digitalizes the data at an earlier stage than the current PET solutions; the data can be sent to any number of computers; and image processing takes place in parallel with the examination.

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