The problem with breast imaging modalities such as mammography and ultrasound, is that they are only able to show the morphology (i.e. anatomy) of the underlying tissues. That is why modalities such as magnetic resonance imaging and shear-wave elastography, which provide both anatomical and functional (i.e. physiological) information, are sometimes preferred for diagnosing breast cancer. Angiogenesis is the physiological process by which new blood vessels are formed and is a normal and vital process in growth and development. However, angiogenesis is also a fundamental process that occurs when a tumour changes from benign to malignant.
It therefore stands to reason that an imaging method which is able to detect angiogenesis could offer significant benefits for diagnosing breast cancer. Such a method has indeed been developed by Seno Medical Instruments, based in Texas, that utilises the photo-acoustic effect, also known as the opto-acoustic (OA) effect. Their Imagio system takes advantage of the OA effect – the conversion of laser light energy into sound energy – and is a dual-modality device that integrates OA imaging with conventional ultrasound, enabling co-registered functional and anatomical mapping of breast tumours.
The Imagio system, which has been patented, has a single hand-held probe (seen at left) that incorporates both ultrasound and near infrared (NIR) lasers. It is able to detect the presence of tumour angiogenesis, taking advantage of the fact that malignant and benign lesions have different levels of haemoglobin and oxygen concentration, and has been clinically tested in a multi-centre clinical trial of more than 2,000 patients. The primary purpose of the PIONEER trial was to establish whether it was possible to reduce the number of false-positive assessments and benign biopsies.
In the most recent issue of Radiology, the flagship journal of the Radiological Society of North America (RSNA), a special section focused on breast imaging. Basak Dogan and her colleagues, as an extension of the PIONEER trial, have published a paper entitled “Opto-acoustic imaging and gray-scale ultrasound features of breast cancer: correlation with molecular subtypes.” As seen in the diagram below (© RSNA), the ultrasound image shows a well-defined invasive cancer, while the OA image reveals significant vascularity, with deoxygenated vessels in red and oxygenated vessels in green.
One of the current drawbacks of Imagio is that it is reliant on the skill of the operator because the probe is hand-held. However, the developers envision a next-generation system that will support three-dimensional OA tomography that could enable automated screening for breast cancer. Now that’s something to anticipate.