SAN ANTONIOMeasurement of radiowave absorption could offer a
new noninvasive approach to the identification and diagnosis of
breast cancer, investigators involved in an ongoing evaluation of the
technology reported at the 22nd Annual San Antonio Breast Cancer Symposium.
Called thermoacoustic computed tomography (TCT), the technology takes
advantage of the fact that the dielectric properties of cancer differ
from those of surrounding normal tissues, Kathy Miller, MD, an
oncologist at Indiana University, Indianapolis, said at a symposium
Thermoacoustic CT employs computerized analysis of
ultra-high-frequency (UHF) radiowaves to distinguish breast cancer,
which exhibits increased UHF absorption, from normal tissue. As UHF
energy is absorbed, tissue heats and expands, creating a pressure
wave that propagates through the tissue and that can be detected as
sound, Dr. Miller explained.
A prototype TCT device consists of a hemispherical bowl containing 64
transducers mounted in a spiral array. The bowl is mounted in a shaft
that rotates 360 degrees on its axis. A water-filled cylindrical
waveguide, mounted beneath a cushioned examining table, provides
radiowave illumination to the breast. A patient lies prone on the
table, positioning one breast into an examining tank.
Radiofrequency Energy Pulses
Radiofrequency energy pulses are supplied by a 25 kW generator at an
average repetition rate of 500 Hz. Immediately following each pulse,
the output of the 64 transducers is captured for computer analysis.
After completion of an acquisition series of 2,048 pulses, the bowl
is rotated 1.4 degrees, and the series is repeated. The process is
repeated 256 times during a total acquisition that lasts less than 10
minutes. The pulse sequences are assembled by computer into a
After validation of the technology in preclinical studies involving
excised pig kidneys and a mouse xenograft model, the TCT device
underwent an initial clinical evaluation of five patients with
documented breast cancer. Three patients were imaged at diagnosis,
and two patients had TCT imaging after completion of chemotherapy
that resulted in complete remission.
Dr. Miller reported that TCT revealed areas of thermoacoustic
contrast enhancement corresponding to palpable tumor in the three
patients who had diagnostic scans. In the two treated patients, TCT
yielded normal thermoacoustic images that confirmed the pathologic
This is the first study proving that we can image the breast
with a thermoacous-tic technique and that we can distinguish
cancerous lesions from normal surrounding tissue, Dr. Miller said.
The investigators, in conjunction with Optisonics, Inc.
(Indianapolis), have begun work on a second prototype device that
should offer improved spatial resolution and decreased scan
acquisition time, she said. Additionally, planning has begun for a
clinical trial of TCT for evaluation of response to neoadjuvant chemotherapy.
The neoadjuvant setting is really the ideal way to evaluate a
new imaging technique, Dr. Miller said. The patients will
all have known tumor and will be imaged with more traditional methods
at the same time that they undergo thermo-acoustic imaging.
Preclinical evaluation also continues in an effort to provide more
insight into the physiologic aspects of cancer that contribute to the
characteristics of TCT images.