Small Animal PET/CT Scanner Open for Molecular Imaging Research
Kai-Yuan Tzen
Director, Department of Nuclear Medicine, National Taiwan University Hospital
With the support from the Ministry of Education, the National Taiwan University and
the Neurobiology and Cognitive Science Center of NTU, a PET/CT scanner dedicated
for small animal research was installed in the PET Center of the Department of
Nuclear Medicine of the National Taiwan University Hospital in 2007. This system
was opened for service since November 23, 2007. (Fig. 1.)
This small animal PET/CT scanner is a combination of a small animal PET scanner
and a small animal CT scanner. The PET (positron emission tomography) scanner is
used to image the distribution of in vivo biomolecular events such as glucose
metabolism, cellular proliferation, etc., in the rodents. (Fig. 2-3.) The CT
(computerized tomography) scanner is used to provide additional anatomical structure
for better localization of the three dimensional distribution of PET activity in the
studied animals. This service will provide researchers in all the fields of molecular
imaging.
The first human PET scanner was invented in 1974 and was mainly used for research
relating to neurology and then cardiology in early years. In combination with the
synthesis of 18F labeled fluoro-deoxy-glucose (18F-FDG, a glucose analogue) in 1978,
FDG-PET scan became a very useful non-invasive diagnostic imaging tool for cancer
patients in the past 10 years. PET scan is now playing an important role in the study
and clinical application in various human diseases in the fields of oncology,
neurology and cardiology.
Application of this molecular imaging technique in small animal research is only
made possible after the improvement of the resolution of the PET scanner by modern
imaging instrumentation and technologies. With the need for molecular imaging in
modern molecular medicine and molecular biology in genomics and proteomics
research, small animal PET scanner became more and more popular in recent years.
The spatial resolution is improved gradually and approaching 1 mm (1 L in volume)
now. This makes the PET images of the small animals match closely those of a
classical autoradiography.(Fig. 4.) Thus sometimes it is called “in vivo
autoradiography”.
Our small animal PET scanner was originally developed in year 2000 by the National
Institutes of Health with the name of ATLAS (Advanced Technology Laboratory
Animal Scanner). It was later commercialized by GE Healthcare with the name of
eXplore Vista DR. By using this small animal PET scanner in research works, we can
do longitudinal studies without sacrificing so many animals as in the past. We can
measure the distribution of very sensitive targeting bio-markers in the animals at the
level of picomolar order.
The PET Center of the Department of Nuclear Medicine of the National Taiwan
University Hospital set up the Cyclotron & Radiopharmaceutical facilities in 2005.
Short half-lived PET agents, with the half-lives ranging from 2-108 minutes, were
produced for clinical and basic research. With the help of the consultant, Dr. ChyngYann Shiue, retired professor from University of Pennsylvania, this Center is now
able to provide several positron labeled radiopharmaceuticals for measuring the
metabolic and molecular functions in human research and clinical applications. For
example, 18F-FDG is used for measuring glycolysis or glucose metabolism in the
cancer cells. 18F-FDOPA is used for measuring the function of an enzyme called
AADC (aromatic amino-acid decarboxylase) in the basal ganglia of the human brain
or some neuroendocrine tumors. 18F-FLT (fluoro-thymidine) is used for measuring the
proliferation of cancer cells. 18F-choline is used for measuring the choline metabolism
of the cell membrane. Now with the collaboration of the small animal PET/CT
scanner, more and more molecular imaging studies using various animal models to
evaluate or characterize human diseases are possible through the use of various kinds
of PET probes.
All researchers from the University are encouraged to utilize this brand new imaging
system for the research in proteomics and genomics fields. For further information in
starting a research using this small animal PET, please contact Dr. Kai-Yuan Tzen,
Director of Department of Nuclear Medicine, National Taiwan University Hospital at
tzenky@ntuh.gov.tw.
Fig. 1. Director Kai-Yuan Tzen of Department of Nuclear Medicine explaining the
small animal PET/CT scanner to President Si-Chen Lee.
Fig. 2. The GE eXplore Vista DR PET/CT scanner and the rat during scanning.
Fig. 3. In an one-side deafened rat, the sound stimulation can be seen transmitted to
the inferior colliculus (yellow arrow) and auditory cortex (red arrow) on the opposite
side. (courtesy of Dr. Te-Huei Yeh and Dr. Wei-Chung Hsu of Department of
Otolaryngology)
Fig. 4. The small animal PET scan (left) and the autoradiography (right), from:
Chatziioannou AF. Mol Imaging Biol. 2002;4:47-63. PET scanners dedicated to
molecular imaging of small animal models.