Photoacoustic images show blood vessels around breast tumour

Photoacoustic image showing a ring shaped area indicating tumour vascularisation. This is the image of an area at a depth of 12 millimetres from the breast surface.

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 tumour. The research has been done in cooperation with the Medisch Spectrum Twente hospital, 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 tumour. The scientists attribute this to the vascularisation of the tumour: a tumour is fed by a large number of tiny blood vessels. These small vessels are not very visible on an X-ray mammogram, but they can indicate the malignancy of the tumour. 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 tumour, 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 blood vessels can be measured using the photoacoustic signal.

Faster

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 tumour. Further research is required to determine to what extent this new information tells more about the nature of the tumour. 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.