New technique for early detection of breast cancer

science to medicine Researchers are now using the principles of Physics to understand signs of breast cancer, writes Sharath Ahuja

Breast cancer is the leading cause of cancer death in females worldwide. Early detection increases the survival rate. X-ray mammography, ultrasonography and magnetic resonance imaging (MRI) are the commonly used imaging modalities for breast cancer detection and diagnosis. All of these techniques have their limitations: X-ray mammography besides possessing ionising hazards, is less sensitive in women with dense breasts. Ultrasonography in breast imaging suffers from poor soft tissue contrast, operator dependence and lack of standardisation. MRI has less sensitivity but suffers from a limited specificity, a relatively high cost and requires the use of a contrast agent.
Since many of these limitations are related to the fundamental nature of the techniques, there is great need for an alternative breast imaging modality to detect and diagnose early stages of cancer with high sensitivity and specificity.

Photoacoustics

In the search for improved imaging modalities for detection and diagnosis of breast cancer, the ability to differentiate between benign cysts and malignant lesions is of great importance. Photoacoustic (PA) imaging is a relatively new imaging modality that has potential for visualising breast malignancies.

To create a photoacoustic image, pulses of laser light are shone onto the tissue being scanned. The light scatters inside the  tissue and gets selectively absorbed by tumors. This is because tumours are associated with high density of blood vessels, and haemoglobin in blood absorbs light strongly. The absorbed light is converted to heat leading to a temperature rise, – just a few thousandths of a degree – that is perfectly safe but not enough to cause the tumour to expand abruptly due to thermoelastic expansion. This leads to the emission of sound waves in the ultrasonic range. An array of sensors placed on the skin picks up these waves, and a computer then uses a process of triangulation to turn the ultrasonic signals into a two or three-dimensional image of what lies beneath. It is an imaging modality that relies on listening to the “sound” generated by “light.”

A team of researchers led by Associate Professor Srirang Manohar, at the University of Twente in the Netherlands, have in recent times developed a prototype of a new imaging tool that may one day help to detect breast cancer early, when it is most treatable. If effective, the new device called the Twente photoacoustic mammoscope (PAM2) would represent an entirely new way of imaging the breast and detecting cancer. Instead of X-rays, which are in traditional mammography, the photoacoustic breast mammoscope uses a combination of infrared light and ultrasound to create a 3-D image of the breast.

In the new technique, infrared light is delivered in billionth-of-a-second pulses to tissue, where it is scattered and absorbed. The high absorption of blood increases the temperature of blood vessels slightly, and this causes them to undergo a slight but rapid expansion. While imperceptible to the patient, this expansion generates detectable ultrasound waves that are used to form a 3D map of the breast vasculature. Since cancer tumours have more blood vessels than the surrounding tissue, they are distinguishable in this image.

In a collaborative effort, researchers from Netherlands’ University of Twente and Medisch Spectrum Twente Hospital in Oldenzaal are now using photoacoustics rather than ionising radiation (such as X-rays) to detect and visualise breast tumors. The team’s preliminary results, which were conducted on 12 patients with diagnosed malignancies, provide proof-of-concept support that the technology can distinguish malignant tissue by providing high-contrast images of tumours. Recent clinical results using PAM have corroborated the earlier results, while showing successful visualisation of malignancies with a superior imaging contrast to X-ray mammography. The next step the researchers say would be to prepare for larger clinical trials.

The first version of the instrument PAM1, which was first tested in 2007, has been upgraded to the present version

PAM2, with several new features which are expected to improve the resolution as well as add to the capability of image, using several different wavelengths of light at once, which in turn is expected to improve detectability. Manohar and his colleagues added that if the instrument were commercialised, it would likely cost less than MRI and X-ray mammography and probably not much more than an ultrasound machine.The instrument will undergo first clinical testing in the middle of 2015.