This month’s column introduces new technology from GE Medical Systems, the Millennium VG gamma camera. The camera offers functional anatomic mapping as well as digital x-ray tomography. The system is said to be a breakthrough in diagnostic accuracy given it’s ability to more accurately localize lesions detected by abnormal radionuclide uptake.
Imaging specialists can now more accurately localize lesions
detected by abnormal radionuclide uptake with a system that
simultaneously acquires an anatomic map. With new technology
promoted as a powerful merger of form and function a fusion of
anatomy and physiology a gamma camera equipped with digital x-ray
tomography provides tomographic slices that show the structural
landmarks of radionuclide activity.
X-ray anatomic landmarks acquired by Millennium VG gamma
Unveiled at The Society of Nuclear Medicine's (SNM) 46th Annual
Meeting (held June 1999 in Los Angeles), the functional anatomic
mapping technology developed for the Millennium VG evolved from the
1998 acquisition of Elscint's nuclear medicine business (Haifa,
Israel) by GE Medical Systems (Milwaukee). The system is now
undergoing clinical evaluation at Vanderbilt University Medical
Center (Nashville), Duke University Medical Center (Durham, NC),
and Hadassa and Rambam Hospitals (Israel). With marketing clearance
from the Food and Drug Administration (FDA) pending, GE expects the
system to become available commercially by the end of the year
"I believe that this technology is a defining moment in nuclear
medicine, and will have a tremendous impact on how we practice
nuclear medicine in the future," said Martin Sandler, MD, vice
chairman of radiology and radiological sciences at Vanderbilt.
"Knowing the precise location of the disease, monitoring the
response to therapy, and noninvasively differentiating benign from
malignant lesions is critical to good patient care," Dr. Sandler
"Anatomic mapping is a major breakthrough in nuclear medicine
and it's going to improve patient care over the next several
years," said R. Edward Coleman, MD, director of nuclear medicine
and vice president of the Department of Radiology at Duke.
Ever since tomographic anatomy became clinically routine with
x-ray computed tomography (CT) and magnetic resonance (MR), nuclear
medicine pioneers have pursued techniques for correlating or fusing
those images with radionuclide studies. Years ago at the low-tech
end of the spectrum, transparent plastic templates with anatomic
maps were produced to overlay on single-photon emission computed
tomography (SPECT) films to help localize lesions. Today, there are
sophisticated techniques for fusing the digital data from SPECT,
positron emission tomography (PET), CT, and MR, but the technology
is not ready for everyday clinical practice.
Localization and attenuation correction
The functional anatomic mapping available from GE is not a
fusion of a diagnostic CT scan with a SPECT scan (or with a
dualhead, coincidence-detection, positron-emission scan). Instead,
it is a method of providing tomographic x-ray anatomic landmarks
for the radionuclide image. The x-ray and radionuclide data are
acquired simultaneously, without moving the patient, which should
eliminate registration problems inherent in fusing separately
Beth Klein, GE's general manager of global nuclear medicine and
PET, pointed out that functional anatomic mapping can rise to meet
two key challenges in today's nuclear medicine practice:
(1) Localization-Although nuclear medicine has progressed to the
point where radionuclide studies quite accurately detect the
presence and extent of disease, precise and accurate localization
has remained elusive.
(2) Attenuation correction-In addition to providing anatomic map
images, the x-ray transmission data can also serve to correct for
attenuation in the radionuclide emission data, which will be
particularly helpful in nuclear cardiology.
Advantages of a slip-ring gantry
The x-ray tomography in functional anatomic mapping comes from a
combination of a low-dose x-ray tube (about 300 millirads of
exposure to the patient) and a solid-state digital x-ray detector
mounted directly on the slip-ring gantry. The low-dose x-ray tube
in the GE gamma camera exposes the patient to about one-tenth the
radiation of a diagnostic CT scan, according to Nathan Hermony,
manager of GE's Nuclear Medicine R&D, Engineering, and
Manufacturing Center of Excellence (Haifa, Israel).
The slip-ring gantry design allows for continuous revolution of
the gamma detectors, x-ray tube, and x-ray detectors around the
patient, "making it possible to cover the entire volume without
breaks, pauses, or the need to 'rewind' the detectors after one or
two revolutions," explained Mr. Hermony. Although most x-ray
computed tomography (CT) systems have slip-ring technology, he
added, very few gamma camera systems have it.
In response to a question about the economic impact of the
system, GE did not provide a list price or an estimated cost per
procedure. However, "when you improve diagnostic accuracy, you
decrease healthcare costs," said Dr. Coleman. With better
evaluation of a tumor, for example, unnecessary surgery can be
avoided and more appropriate chemotherapy can be planned, he
Unlike other tranmission data sources used for attentuation
correction, such as gadolinium or cesium, which are usually
replaced every year, the x-ray tube in the Millennium VG functional
anatomic mapping system should last for the lifetime of the camera.
From this point of view, noted Mr. Harmony, this new technique for
attenuation correction could make more sense economically.
GE illustrated case studies of patients with lung cancer (figure
1), melanoma (figure 2), colon cancer, and breast cancer.
An FDG image fused with x-ray functional anatomic mapping in a
patient with lung cancer.
An FDG image fused with x-ray functional anatomic mapping in a
patient with lymphoma.
Evaluation of lung cancer and lymphoma
Dr. Sandler presented brief case reports of two patients to
illustrate how functional anatomic mapping can help in the
evaluation of lung cancer and lymphoma. Both patients underwent
dual-head, coincidence-detection studies with fluorine-18
In a patient with a history of lung cancer that led to removal
of the left lung, Dr. Sandler showed a diagnostic CT study with a
small nodule in the right lung and an enlarged lymph node in the
mediastinal region. CT, of course, does not indicate whether
nodules or enlarged lymph nodes are benign or malignant. The FDG
image, however, showed increased uptake in both areas. When the
functional anatomic map was superimposed on the FDG image, the
uptake correlated perfectly to the nodule and lymph node, said Dr.
Sandler, providing a noninvasive test that identified metastatic
cancer in the right lung with involvement of the mediastinum.
In a patient with lymphoma, the diagnostic CT study showed
significant shrinkage of an abdominal mass 3 months after
chemotherapy. The dilemma, said Dr. Sandler, was determining
whether the patient was in remission or had active disease. The FDG
scan alone did not show whether the FDG activity was part of the
mass or unrelated to the mass. With functional anatomic mapping,
however, it was clear that the hot spot represented residual tumor
Useful for more than FDG
Although the clinical examples shown at the SNM were FDG
oncology studies, functional anatomic mapping can apply to other
positron emitters used in dual-head, coincidence-detection, gamma
camera systems, or with any radiotracer used for SPECT. For
example, said Dr. Coleman, functional anatomic mapping could become
useful for infection imaging with gallium-67, for monoclonal
antibody studies in patients with cancer, and for nuclear
Improved reconstruction algorithms and radiation therapy
Besides improving the diagnostic accuracy and interpretation of
radionuclide images, said Dr. Coleman, the anatomic map data can
provide two additional benefits: improved radiation therapy
planning and more accurate reconstruction of radionuclide data.
With current technology, a nuclear medicine image is often
overlaid on a CT image from a radiation planning system, "which is
not ideal," said Dr. Coleman. Correlating a SPECT/PET/ anatomic map
image with a radiation planning CT could improve the accuracy of
radiation therapy targeting. In addition, smart algorithms will be
created to use the x-ray transmission data for better
reconstruction of SPECT images, said Dr. Coleman.
X-ray anatomic map: not a diagnostic CT image
When asked whether nuclear medicine technologists will need to
learn CT imaging skills, Dr. Sandler said that the x-ray image
should not be confused with a CT study. "I hope that we identify
clearly what we are doing from the start so we don't create a
tangled web that we have to untangle over the next few months or
years," said Dr. Sandler.
Although the anatomic map image from the GE system is generated
by x-ray tomography, it is not the same as a diag-nostic CT study.
In fact, at the SNM presentation, Drs. Sandler and Coleman always
called the x-ray image an "anatomic map," not a "CT image". The
Millennium VG will not be used as a diagnostic CT. The x-ray
transmission data are used only for attenuation correction and
Every state has different regulations on the use of x-ray
sources, noted Dr. Sandler. In Tennessee, for example, nurses can
perform simple x-ray procedures after completing a relatively short
training program. "We should be able to establish similar training
programs for nuclear medicine technologists," he added. Having an
x-ray tube in a gamma camera will probably be comparable, in
relation to using x-ray equipment in a nuclear medicine department,
to x-ray bone densitometry, he added.
Nuclear medicine: "bigger player"
It is possible that functional anatomic mapping may reduce the
need for some anatomic imaging studies in a diagnostic workup, said
Dr. Sandler, particularly when the main purpose of such studies is
to provide anatomic localization of radionuclide-detected lesions.
Rather than viewing this new technology as a way for nuclear
medicine to take referrals away from other modalities, however, Dr.
Sandler sees it more as a technique for improving diagnostic
accuracy. "I think it will improve the ability of nuclear medicine
to become a 'bigger player," he predicted.