Mammograpy without X-rays, using photoacoustic technique

May 10, 2012

Images of a breast carcinoma: X-ray image (left) and photoacoustic image (right) (credit: University of Twente/Optics Express)

Researchers from Netherlands’ University of Twente and Medisch Spectrum Twente Hospital in Oldenzaal have found that photoacoustics — laser-induced sound — can detect and visualize breast tumors at higher contrast than X-rays and MRI while avoiding ionizing radiation and toxic contrast agents.

“While we’re very early in the development of this new technology, it is promising,” explained researcher Michelle Heijblom, a Ph.D. student at the University of Twente. ”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.”

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.

So the researchers added ultrasound, achieving superior targeting ability. The result of their refinements is a specialized instrument, the Twente Photoacoustic Mammoscope (PAM), which was first tested in 2007.

How the Photoacoustic Mammoscope works

The device is built into a hospital bed, where the patient lies prone and positions her breast for imaging. Near-IR laser light at a wavelength of 1,064 nanometers 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 thermoelastic pressure wave, which is detected by an ultrasound detector placed on one side of the breast.

Diagnostic mammograms of a 31 mm ductal carcinoma in a breast: (a) X-ray, (b) ultrasound, (c) MRI, (d) photoacoustic image showing upper and lower abnormalities, (e-f) photoacoustic images of upper and lower abnormalities (credit: University of Twente/Optics Express)

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 conventional X-ray mammographies. In all ten malignancies they studied, photoacoustic imaging was able to visualize a confined high-contrast region at the true lesion depth and in all cases, the contrast was higher than observed on x-ray.

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.”

Ref.: M. Heijblom et al., Visualizing breast cancer using the Twente photoacoustic mammoscope: What do we learn from twelve new patient measurements?, Optics Express, 2012, DOI: 10.1364/OE.20.011582 (open access)