New PET scanner halves radiation dose and fits inside an MR scanner
By Doug Hendrie
August 23, 2012
So you’re unlucky enough to be hit with the real C-word: cancer. That sucks. But what can be worse is that many current medical scanning techniques come with large levels of radiation. The current practice of combining PET (Positron emission tomography) and CT (computerized tomography) scans produces good images, but the cost is high: a dose of radiation ten times the background amount the average human gets in a year. And that’s just one scan. Many cancer patients have to endure multiple scans. A new PET scanner from physicists at the University of Oslo (UiO) cuts the radiation dose in half and is also small enough to fit inside an MR scanner. Although it was developed for animals, the researchers say it could be easily adapted for human clinical examinations.
Although PET scans provide a spatial image of the location of cancer cells inside the body, they can be hard to interpret without an anatomical picture of the skeleton and soft tissue. This can be provided by a CT or MR (magnetic resonance) scan. Despite providing better images of soft tissue than CT and not emitting ionizing radiation like CT, MR is more expensive and takes much longer. For these reasons, the majority of hospitals currently combine PET and CT scans.
PET technology is also split into two different types, which have each been adapted for a particular use. The first is for the clinical examination of patients, while the second is optimized for scans on animals used in the search for new and improved cancer treatments. Siemens and Philips recently launched a combination PET/MR scanner for clinical examination of patients and now particle physicists at UiO have become the first to develop a specially adapted PET/MT scanner for animals.
"The high resolution in our PET scanner provides better images, and the high sensitivity makes it possible to use only half as much radioactivity in the examinations without it affecting the image quality," says Erlend Bolle, a researcher in particle physics in the Department of Physics at UiO. "This opens new possibilities in research, and may also contribute to reducing radiation in clinical scanners, especially within mammography and brain scans. We therefore hope that Philips and Siemens find our technology interesting."
To make the new scanner, Bolle and his three colleagues, David Volgyes, Michael Rissi and Kim-Eigard Hines, borrowed an idea from the Large Hadron Collider, which relies heavily on advanced particle detection. In old PET scanners, radioactive isotopes are glued to sugar molecules and injected into the body. One hour later, the PET scanner picks up the areas where the sugar has been gobbled up fast. That’s where the greedy cancer cells are.
The problem is that the scanner sometimes has trouble picking up the photons shot out by the radioactive gamma particles when they hit the detectors at an angle. But in the new scanner, a cunning new five-layer arrangement captures all the photons and measures the position in three dimensions. And while current scanners position patients centrally and some distance from the detector to ensure the photons hit the detector at as straight an angle as possible, the UiO PET scanner can capture a good image even if the test animal is lying right next to the detector.
"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," says Bolle.
Because the new PET scanner is small enough to be placed inside an MR machine, allowing both the PET and MR images to be captured at once, time is not only saved when capturing images. It also cuts out the need for medical personnel to correct any errors that can occur when two images are combined after they have been taken.
The new technology also brings a different form factor to the medical scanners. Traditionally these have been circular, with a gap between each detector block through which photons can disappear. The new scanner is square, providing full coverage on all sides.
Although the team developed the scanner for use with animals, Bolle says, "it can easily be rebuilt for hospital use."
Source: University of Oslo
Update: This story was updated on August 27, 2012 to correct a number of errors that were pointed out by helpful commenters (RCMD1 and Australian).
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