Photoacoustic techniques can supplement conventional imaging techniques in breast cancer diagnostics.
From first tests on patients using the ‘photoacoustic mammoscope’ developed by the University of Twente, researcher dr. Srirang Manohar concludes that the images obtained add valuable information about the vascularisation of a tumor. The research has been done in cooperation with the Medisch Spectrum Twente hospital in Enschede, and the results are published in the online journal Optics Express.
In four out of five cases the photoacoustic images of the ‘suspect’ breast area show areas of high intensity around the tumor. The scientists attribute this to the vascularisation of the tumor: a tumor is fed by a large number of tiny blood vessels. These small vessels are not well visible on an X-ray mammogram, but they can indicate the malignancy of the tumor. In this way, photoacoustics has a potential in adding information to conventional X-ray and ultrasound mammography.
In one of the cases now published in Optics Express, the X-ray apparently shows a benignant tumor, while the photoacoustic scan shows a ring-shaped area of high intensity: this may imply malignancy.
Listening to light
The Twente photoacoustic mammoscope (PAM) developed by scientists of the University of Twente, uses pulsed light from a laser, with which part of the breast is scanned. Absorption of the light by a blood vessel, for example, results in local heating, yielding a pressure wave. This pressure wave can be detected as ultrasound. By calculating the origin of the pressure wave, the location of the vessel can be visualized. Direct measurement of the light shining through tissue would be an alternative, but light is scattered highly and therefore it is complicated to reconstruct an adequate image. Using only ultrasound instead, would not result in detailed visualization of the blood vessels, as blood does hardly reflect ultrasound. The combination of light and ultrasound takes away the respective disadvantages: ultrasound will not be scattered and the effect of light on the bloodvessels can be measured using the photoacoustic signal.
The PAM-scan is, unlike in conventional X-ray mammography, taken with the patient in a lying position. The breast is just mildly compressed. The current examination takes about half an hour, but with faster ultrasound detectors this can be improved.
The research published by dr. Srirang Manohar shows the usefulness of the new technique in imaging the vascularisation of the tumor. Further research is required to determine to what extent this new information tells more about the nature of the tumor. Larger scale clinical studies are required for that.
The research of dr. Srirang Manohar has been done within the BMTI Institute for Biomedical Technology of the University of Twente, together with the Surgery and Radiology departments of the Medical Spectrum Twente hospital in Enschede. Manohar is supported by the Dutch Technology Foundation STW and the Netherlands Organisation for Scientific Research NWO.
The article ‘Initial results of in vivo non-invasive cancer imaging in the human breast using near-infrared photoacoustics’ appears in the online journal Optics Express. The authors are Srirang Manohar, Susanne Vaartjes, Johan van Hespen (University of Twente/BMTI), Joost Klaase, Frank van den Engh (Medisch Spectrum Twente), Wiendelt Steenbergen (UT/BMTI) en Ton van Leeuwen (UT/BMTI and AMC Laser Centre, University of Amsterdam).
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