Developments
from CERN could make CT scanners even better at detecting early cancer cells or
other disease indicators. The facility's work to create photon counters that
can count ten million photons per second - up by a factor of one hundred from
previous generation counters - have been integrated into CT systems and had
their first trial run with patients. There are more developments that will have
to take place before the photon-counters can fullfill their full potential, but
early work presented at the meeting looks promising.
While
CERN made the progress in photon counter technology, it has been
representatives from industry who put them together with CT scanners. At the
AIP and AAPM meeting, Reuven Levinson, a Technology Development Leader at GE
Healthcare in the CT Engineering group in Haifa, Israel, announced the first
use of a photon counting CT system on human patients. The CT's X-ray detector
counts the individual photons and measures their energy. Levinson and his team
built the photon counting CT system and had it installed last year at the Rabin
Medical Center in Tel Aviv, Israel.
CT scans,
introduced in the 1970's, revolutionized X-rays by giving doctors a sharper
look inside their patients. Traditional X-rays can only produce straight on 2D-
projection images, while CT scans provide cross sectional slices; revealing
internal structures otherwise concealed by overlying layers. In hospitals, CT
scans are helpful, and in many cases irreplaceable, in diagnosing diseases and
injuries like internal bleeding, strokes, and lung disease. In the US, 68
million CT scans are performed year.
One of the
requirements for CT scanning is that the image must be acquired quickly. As
with photography, if the patient moves during the scan, the final image will be
blurred, so modern CT scanners capture an image in less than 1 second.
These modern CT
systems use x-ray detectors, which operate much like digital cameras, with the
exception that the CT detectors essentially produce "black and white"
photos. The detectors only record the total energy of all the x-rays
transmitted through the patient's body, not the individual energies of each
photon. In the optical range, the energy of a photon determines its color, so
the CT scanners are in a sense color blind.
And for the
most part, CT scanners don't need to see individual photon energies. For the
majority of uses, the black and white photo tells the physician everything they
need to know. But in some cases, "color-sensitive" X-ray detectors
would be beneficial.
Previous
generations of photon counting detectors could count up to only 100,000 x-rays
per second, which was not fast enough to produce an adequate CT image.
That
was until about five years ago when particle physicists at CERN, the facility
in Geneva that is home to the Large Hadon Collider, broke the previous barrier
of photon counting by ten orders of magnitude. In need of highly sensitive
detectors for their experiments hunting subatomic particles, they increased the
capabilities of photon counters to over 10 million photons per second. This
increase would allow a photon counter to measure the energy of each individual
photon striking the detector from a CT scan.
The
results reported by Levinson explained the first use of the photon counting
detecor on humans, yet this can not yet assist in detecting specific types of
cells. To highlight specific cells that the CT scans can target, the team would
like to attach nanoparticles that the photon counter CT system can easily
detect - such as gold or other metals - to biomarkers that will attach to the
target cells. So, attaching gold nanoparticles to a peptide that bonds to
"vulnerable" plaque cells will illuminate the cells in little gold
halos. Another company has reported results using the gold nanoparticles in
rats and rabbits.
Eventually
the same technology could also be used in cancer detection. While many
cancerous tumors are visible on regular CT scanners, there are significant
limitations. A CT scanner cannot distinguish between cancer and normal tissue
following radiation or chemotherapy treatment. The imaging of a tumor
following the anti-cancer treatment is critical in determining the patient's
status and also in evaluating the efficacy of different treatments in curing
the cancer. Current medical practice utilizes PET/CT for the status evaluation
of post-treatment cancer patient, which is an expensive and time consuming
procedure. The challenge would be for CT plus nanoparticle systems to replace
the PET/CT procedure with a simpler, higher resolution and less expensive
alternative.
Spectral x-ray photon counting CT significantly improves contrast-to-noise in images from objects that have been injected with contrast agents that have a "k-edge" in the spectral range of the counting detector.
This improvement has been shown by Philips in Germany and its collaborators in the US. A photon counting detector used for those experiments had been developed by Gamma Medica - Ideas in Norway.
A parallel and independent effort was done by GE in Israel as described in this article.
What did CERN contribute to these efforts ?