Few events in the imaging arena have commanded more attention
than the current revolution going on in nuclear medicine. The spark
for this revolution is the development of technology that permits
the widespread use of the powerful tumor imaging agent, F-18
fluorodeoxyglucose (FDG). Over the last 20 years, positron emission
tomography (PET) imaging has developed an impressive body of data
concerning FDG applications in oncology.
As Dr. Henry Wagner points out below, these advances were
restricted to only a limited number of patients. The capital cost
of dedicated PET equipment and the lack of widespread availability
of FDG impeded the spread of the technology. Commercial
radiopharmacies already are delivering FDG and will be expanding
their role in the future.
With the advent of gamma camera FDG imaging, the number of sites
capable of imaging FDG will increase by 50% this year alone.
Although there are limitations to the technology, overall it
enhances the diagnosis of tumor distribution in a number of
diseases, ranging from lymphoma to lung cancer. Multicenter
clinical trials currently are under way to define more precisely
the accuracy and document the impact on patient management of FDG
imaging on gamma cameras.
Indeed, we are fortunate to have Dr. Henry N. Wagner, Jr.,
prepare the review below for us. Dr. Wagner is one of the best
known nuclear physicians in the country. His involvement with PET
imaging over the last few years gives him a unique perspective on
this issue. We are pleased to present this brief introduction to
the state of a new art.
Robert E. Henkin, MD, FACNP, FACR
Professor, Department of Nuclear Medicine
Loyola University Medical Center
A postgraduate course entitled "Nuclear Oncology: From Genetics
to Patient Care," was held at Johns Hopkins Medical Institutions
between April 7 and 9, 1997. Investigators from around the world
presented increasing evidence that Fluorine-18 deoxyglucose
coincidence imaging helps detect metastatic cancer of the head and
neck, breast, lung, liver, and colon.
Dr. Peter Valk, of the Northern California PET Imaging Center,
who has performed over 3,000 PET studies with FDG in patients with
cancer, reported the impact of FDG studies in the care of patients
with brain tumors, head and neck cancer, and non-small cell lung
cancer. In those patients with brain tumors, the FDG study is
indicated when an MRI or CT shows new areas of contrast enhancement
that may represent either residual or recurrent tumor or radiation
necrosis. The demonstration of major survival differences between
patients with and without FDG accumulation in these lesions further
validates the use of PET for differentiation of recurrent tumor
from radiation necrosis.
Dr. Valk further described a study comprised of 33 patients with
known or suspected recurrence of squamous cell cancer of the head
and neck. FDG imaging was more accurate than CT or MRI in detecting
local or regional recurrence. FDG studies often revealed
unsuspected distant metastatic cancer. In 99 patients with lung
cancer, FDG was more accurate than CT in the diagnosis of
metastatic mediastinal nodes and distant metastases. Detection of
unsuspected metastatic disease by PET resulted in a decrease in the
number of patients who underwent thoracotomy directed at the
removal of all cancer.1-3
Dr. Richard Wahl, of the University of Michigan, summarized a
worldwide literature search on the use of PET FDG studies to
separate lung cancer from benign disease in patients with solitary
pulmonary nodules on chest radiographs. FDG was useful in nodules
greater than 1 cm in diameter. A recent multicenter study found PET
to be greater than 90% sensitive in determining whether a solitary
pulmonary nodule was malignant, with an acceptably small number of
Dr. David Mankoff reviewed data concerning FDG studies in breast
cancer. Whole-body PET imaging was used to detect recurrent or
metastatic disease. Both FDG and carbon-11 methionine were helpful
in determining the response of the lesions to therapy. At Mankoff's
institution, the University of Washington, FDG PET studies provided
new staging information in over 60% of the patients and
significantly affected therapy in approximately 89% of the
Dr. Paul Shreve, of the University of Michigan, reported his
preliminary results in the use of dual-headed coincidence imaging
with a modified SPECT system. In studies of 34 patients with
non-small cell lung cancer, he compared the results of dual-headed
gamma camera coincidence imaging to a dedicated PET system. Dr.
Shreve reported that, in nearly every case, the results were the
same; however, in many cases, the definition of the lesions was
better with the dedicated PET than with the dual-headed system.
The dual-headed coincidence imaging system used by Dr. Shreve
was developed by ADAC Laboratories and is based upon earlier
systems. The use of a gamma camera to image positron emitting
radionuclides, such as Fluorine-18, was first described by Hal
Anger in 1957. Gerd Muehllehner then advanced dual-head coincidence
imaging in the 1970s using analogue detectors, but the images were
limited by low count rate capabilities. He subsequently developed a
dedicated PET imaging system, called PennPET, in the mid 1980s and
formed UGM Laboratories. The PennPET system uses gamma camera
detectors built with high-speed digital electronics to achieve the
necessary counting rates.
ADAC Laboratories and UGM further developed the digital
electronics to enable both single photon and positron coincidence
imaging to be performed with the same dual-headed gamma camera. The
positron imaging is called molecular coincidence detection (MCD)
and was shown by ADAC Laboratories at the annual meeting of the
Society of Nuclear Medicine in 1995. The results were impressive,
and the brain images were deemed "Image of the Year."
Examples of two FDG/MCD studies of patients with lung cancer are
shown in figures 1 and 2. CL, a patient of Dr. John Sweeney at
Boone Hospital, had a positive CT scan revealing a lesion in the
left lower lobe of the lung. On the MCD study, the lesion seen on
the CT had a high FDG uptake. There was no evidence of lymph node
EJ was a patient of Dr. George Sfakianakis at the University of
Miami. The CT scan showed tumor in the left upper lobe but no
lymphadenopathy. The FDG/MCD study showed avid accumulation of FDG
in both the primary tumor and a mediastinal node. The patient had a
left upper lobectomy. Pathology results were positive for squamous
cell carcinoma and metastases in the visualized perihilar lymph
One of the major advantages of a multipurpose dual-headed camera
is that a single imaging device can perform both single-photon
imaging and coincidence imaging. These systems retain the
capability of imaging tracers emitting single photons as well.
Radiopharmaceuticals such as Tc-99m sestamibi or similar agents
used for the detection of multidrug resistance to cancer
chemotherapeutic agents may be imaged. These devices also may study
receptor-imaging agents, such as In-111 somatostatin analogues.
The addition of the coincidence capability to the gamma camera,
by increasing the crystal thickness to five-eighths of an inch, has
not resulted in any significant decrease in the effectiveness of
the camera for technetium-99m or other single-photon-emitting
tracers. The thicker crystal increases the detection efficiency for
Tc-99m by 10%, and higher energy emitters, such as I-131, Ga-67,
and In-111, have even larger increases in the detection efficiency.
This should improve the image quality of scans involving these
radionuclides even further. Thirty systems of this type have been
installed by March 1997.
The coincidence system has four to eight times greater counting
efficiency than the use of high-energy collimators for FDG
collimator-based SPECT for positron-emitters. The dual-headed
coincidence systems have a larger axial field of view than
dedicated PET systems and, therefore, can image a larger area of
the patient with a single acquisition. The spatial resolution of
dual-headed coincidence imaging is less than 5 mm, which compares
favorably with dedicated PET. Most of the dedicated PET systems,
however, have a full ring of detectors around the patient and,
therefore, have a higher geometric efficiency that leads to higher
image quality in clinical studies. Another advantage of dedicated
PET systems is the higher count rate capability. This higher count
rate capability permits the use of 10 mCi of FDG, as compared to 5
mCi used in the coincidence gamma camera system.
At the conclusion of the conference, the attendees unanimously
agreed that FDG imaging will play a major role in the care of many
oncology patients. Half of them responded that the approach that
they themselves would take is to image FDG with a dual-headed
The use of dual-headed coincidence systems will allow more
widespread use of FDG imaging for the management of cancer
patients. Centers that previously have not had access to PET
technology may now be able to offer their patients FDG imaging for
oncology evaluations. AR
1. Gupta NC, Frank AR, Dewan NA, et al: Solitary pulmonary
nodules: Detection of malignancy with PET with
2-[F-18]-fluoro-2-deoxyglucose. Radiology 184:441-444, 1992.
2. Knopp MV, Bischoff HG: Evaluation of pulmonary lesions with
positron emission tomography. Radiologe 34:588-591, 1994.
3. Valk P: Clinical application and cost-effectiveness of PET in
colon cancer. Nucl Med Biol 23:737-743, 1996.