The Twente Photoacoustic Mammoscope. Image courtesy of Michelle Heijblom, University of Twente. |
X-ray
mammography is an important diagnostic tool in the fight against breast
cancer, but it has certain drawbacks that limit its effectiveness. For
example, it can give in false positive and negative results; it also
exposes women to low doses of ionizing radiation, which – while accepted
as safe—still carry some risk.
In
the first phase of clinical testing of a new imaging device,
researchers from Netherlands’ University of Twente and Medisch Spectrum
Twente Hospital in Oldenzaal used photoacoustics—light-induced
sound—rather than ionizing radiation to detect and visualize breast
tumors. The team’s preliminary results, which were conducted on 12
patients with diagnosed malignancies and reported today in the Optical
Society’s (OSA) open-access journal Optics Express,
provide proof-of-concept support that the technology can distinguish
malignant tissue by providing high-contrast images of tumors.
“While
we’re very early in the development of this new technology, it is
promising. Our hope is that these early results will one day lead to the
development of a safe, comfortable, and accurate alternative or adjunct
to conventional techniques for detecting breast tumors,” explained
researcher Michelle Heijblom, a Ph.D. student at the University of
Twente.
Photoacoustics,
a hybrid optical and acoustical imaging technique, builds on the
established technology of using red and infrared light to image tissue
and detect tumors. This technology, called optical mammography, reveals
malignancies because blood hemoglobin readily absorbs the longer, redder
wavelengths of light, which reveals a clear contrast between
blood-vessel dense tumor areas and normal vessel environments. However,
it is difficult to target the specific area to be imaged with this
approach.
|
As
a means of improving this, the researchers combined the light-based
system’s ability to distinguish between benign and malignant tissue with
ultrasound to achieve superior targeting ability. The result of their
refinements is a specialized instrument, the Twente Photoacoustic
Mammoscope (PAM), which was first tested in 2007.
The
device is built into a hospital bed, where the patient lies prone and
positions her breast for imaging. Laser light at a wavelength of 1,064 nm scans the breast. Because there is increased absorption of
the light in malignant tissue the temperature slightly increases. With
the rise in temperature, thermal expansion creates a pressure wave,
which is detected by an ultrasound detector placed on one side of the
breast. The resulting photoacoustic signals are then processed by the
PAM system and reconstructed into images. These images reveal abnormal
areas of high intensity (tumor tissue) as compared to areas of low
intensity (benign tissue). This is one of the first times that the
technique has been tested on breast cancer patients.
By
comparing the photoacoustic data with conventional diagnostic X-rays,
ultrasound imaging, MRI, and tissue exams, the researchers showed that
malignancies produced a distinct photoacoustic signal that is
potentially clinically useful for making a diagnosis of breast cancer.
The team also observed that the photoacoustic contrast of the malignant
tissue is higher than the contrast provided by the conventional X-ray
mammographies.
In
looking to the future, notes Heijblom, “PAM needs some technical
improvements before it is a really valuable clinical tool for diagnosis
or treatment of breast cancer. Our next step is to make those
improvements and then evaluate less obvious potential tumors, benign
lesions, and normal breasts with it.”
Source: Optical Society of America
