Figure 1 • DBT imaging system. Photo courtesy of Hologic, Inc.
( www.hologic.com). Used with permission.
Molecular Breast Imaging—
A Subfield of Functional Imaging
dual camera. The dual head provides
higher throughput and increased sensitivity per the manufacturer. PEM uses two
detector plates and is a tomographic (3D)
modality providing 12 images. This allows
for greater accuracy in localizing a lesion.
Only PEM currently offers an image-guided biopsy system. BSGI and MBI are
approved as problem-solving modalities.
PEM is only reimbursed for patients with
biopsy proven cancer.
Initial studies indicate sensitivity that
matches or exceeds breast MR, but with
greater specificity, which may lead to
fewer unnecessary biopsies and accurately
identify breast cancer earlier than MR. For
example, a PEM study of 208 patients
imaged for pre-surgical staging, identified
half the number of false positives with
a resulting specificity of 73% compared
to 43% for MRI. 3 A BSGI study of 75
women with 98 lesions showed that the
combination of mammography with
ultrasound would have missed two cancers; mammography and MRI would have
missed four; while mammography and
BSGI accurately identified all 69 malig-nancies. 4
Molecular imaging captures the physio-logic/metabolic response to radionucleo-tides and is not affected by tissue density.
Approved molecular modalities include
breast specific gamma imaging (BSGI);
molecular breast imaging (MBI); and
positron emission mammography (PEM).
Compared to breast MR, they are less
expensive to purchase, with shorter learning curves, and are easier to interpret. Figure 2 is a PEM scanner.
All use radioactive tracers which cancer
cells uptake at a higher rate and for longer
periods of time than normal cells. Each
is relatively similar in configuration to a
mammography unit allowing positioning
comparison with the mammogram. Minimal compression holds the breast in place.
BSGI is a planar (2D, summation)
modality utilizing one gamma camera.
MBI can be configured with a single or
Figure 2 • PEM scanner. Photo courtesy of Naviscan, Inc.
( www.naviscan.com). Used with permission.