Experts in Japan have devised a simple way to glean more detailed
information out of standard medical imaging scans. A research team made up
of atomic physicists and nuclear medicine experts at the University of Tokyo
and the National Institute of Radiological Sciences (NIRS) has designed a
timer that can enable positron emission tomography (PET) scanners to detect
the oxygen concentration of tissues throughout patients' bodies. This
upgrade to PET scanners may lead to a future of better cancer treatment by
quickly identifying parts of tumors with more aggressive cell growth.
"Patients' experience in this future PET scan will be the same as now.
Medical teams' experience of conducting the scan will also be the same, just
with more useful information at the end," said nuclear medicine physician
Dr. Miwako Takahashi from the NIRS, a co-author of the research publication
in Communication Physics.
"This was a quick project for us, and I think it should also become a very
fast medical advance for real patients within the next decade. Medical
device companies can apply this method very economically, I hope," said
Assistant Professor Kengo Shibuya from the University of Tokyo Graduate
School of Arts and Sciences, first author of the publication.
PET scans
The positrons that PET scans are named for are the positively charged
antimatter forms of electrons. Due to their tiny size and extremely low
mass, positrons pose no danger in medical applications. Positrons produce
gamma rays, which are electromagnetic waves similar to X-rays, but with
shorter wavelengths.
When receiving a PET scan, a patient receives a small amount of very weakly
radioactive liquid, often composed of modified sugar molecules, usually
injected into their blood. The liquid circulates for a short period of time.
Differences in blood flow or metabolism affect how the radioactivity is
distributed. The patient then lies in a large, tube-shaped PET scanner. As
the radioactive liquid emits positrons that then decay into gamma rays,
rings of gamma-ray detectors map the locations of gamma rays emitted from
the patient's body.
Doctors request PET scans when they need information about not just the
structure, but also the metabolic function of tissues inside the body.
Detecting oxygen concentration using the same PET scan would add another
layer of useful information about the body's function.
Oxygen concentration measured in nanoseconds
The life of a positron is a choice of two very short paths, both of which
begin when a positron is "born" as it is released from the radioactive PET
scan liquid. On the shorter path, the positron immediately collides with an
electron and produces gamma rays. On the slightly longer path, the positron
initially transforms into another type of particle called a positronium,
which then decays into gamma rays. Either way, the lifetime of a positron
inside a human body is not longer than 20 nanoseconds, or one
fifty-millionth of a second.
"The outcome is the same, but the lifetime is not. Our proposal is to
distinguish the lifetimes of positrons using a PET scan with a timer so that
we can map oxygen concentrations inside patients' bodies," said Shibuya.
Shibuya and his colleagues developed a life expectancy chart for positrons
using a miniaturized PET scanner to time the formation and decay of
positrons in liquids with known concentrations of oxygen.
The research team's new results reveal that when oxygen concentration is
high, the shorter path is more likely. Researchers predict that their
technique will be able to detect the absolute oxygen concentration in any
tissue of a patient's body based on the lifetime of positrons during a PET
scan.
Detecting the lifetime of positrons is possible using the same gamma-ray
detectors that PET scans already use. The research team predicts that the
majority of work to transfer this research from the lab to the bedside
will be on upgrading gamma-ray detectors and software so that the
gamma-ray detectors can record not just location, but accurate time data
as well.
"It should not be much of a cost increase for development of instruments,"
said Professor Taiga Yamaya, a co-author of the research publication and
leader of the Imaging Physics Group at the NIRS.
Enhanced PET scans for more effective cancer treatment
Medical experts have long understood that low oxygen concentrations in
tumors can impede cancer treatment for two reasons: First, a low oxygen
level in a tumor is often caused by insufficient blood flow, which is more
common in fast-growing, aggressive tumors that are harder to treat.
Second, low oxygen levels make radiation less effective because the
desired cancer cell-killing effects of radiation treatment are achieved in
part by the radiation energy converting oxygen present in the cells into
DNA-damaging free radicals.
Thus, detecting the concentration of oxygen in body tissues would inform
medical experts how to more effectively attack tumors inside patients.
"We imagine targeting more intense radiation treatment to the aggressive,
low-oxygen concentration areas of a tumor and targeting lower-intensity
treatment to other areas of the same tumor to give patients better
outcomes and less side effects," said Takahashi.
Shibuya says that the team of researchers was inspired to put into
practice a theoretical model about the ability for positrons to reveal
oxygen concentration published last year by researchers in Poland. The
project went from concept to publication in just a few months even with
COVID-19 pandemic-related restrictions.
Shibuya and colleagues are now aiming to expand their work to find any
other medical details that may be revealed by the lifetime of a positron.
More information:
Kengo Shibuya, Haruo Saito, Fumihiko Nishikido, Miwako Takahashi, and
Taiga Yamaya. 2020. Oxygen sensing ability of positronium atom for tumor
hypoxia imaging. Communication Physics. DOI:
10.1038/s42005-020-00440-z
A link to the original paper is broken. Please use
ReplyDeletehttps://www.nature.com/articles/s42005-020-00440-z
or
https://doi.org/10.1038/s42005-020-00440-z.
I am happy if the web master modify this link.