Opto-acoustic imaging represents a breakthrough in diagnostic imaging technology.
Unlike most imaging modalities (CT, MR, X-ray, Ultrasound, etc.) that look at the structure or anatomy of a region of interest, opto-acoustic imaging looks at the structure, but then also fuses that information with what’s happening functionally in and around the mass of interest. This combination of anatomic and functional imaging is accomplished through the use of light (laser optics) and sound (conventional ultrasound), in real time, to produce high-resolution, high-contrast images to the clinician.
Opto-acoustic imaging looks for the presence of tumor neoangiogenesis, new blood vessels produced by malignant tumors to help supply nutrients to and remove wastes from the tumor. Malignant masses cannot grow larger than 2-3 mm without generating neovessels. The Seno laser wavelengths used were selected to enable visualization of relative amounts of oxygenated and deoxygenated hemoglobin within the vasculature and within masses and their surrounding tissues. Inside vessels supplying and draining a malignant tumor, the hemoglobin gives up its oxygen to the rapidly growing cells and becomes deoxygenated. The combination of hemoglobin concentration and its relative oxygenation has been shown to have good diagnostic accuracy (Academic Radiology 2005; 12:925-933).
- Malignant tumors have increased blood (hemoglobin) concentration with relatively decreased oxygen content.
- Benign growths have variable blood (hemoglobin) concentration with relatively more oxygenation.
Functional information has direct relevance to tumor pathophysiology and supports a clinician’s decision-making as to a lesion’s malignancy and the need for biopsy.
Opto-acoustic imaging may permit the identification of tumors as small as 3 mm and has demonstrated the ability to see submillimeter vascular structures. Early detection is important, because biologically advanced tumors are more capable of metastasis.
TECHNICALLY, WHAT’S HAPPENING?
A short pulse of laser light energy, at a specific wavelength (color), is directed at and illuminates a large volume of tissue in a selected region of the breast. Hemoglobin containing vessels within that volume absorb a portion of the laser energy and convert it to heat energy. The heat creates thermoelastic expansion of the structure (in this case hemoglobin), which generates a sound pressure wave that radiates to the surface of the tissue. The sound wave is then captured by wideband, ultrasonic, piezoelectric transducers, similar to those used for conventional ultrasound. The Imagio™ reconstruction algorithms can then determine the spatial location of those optical absorbers from the captured ‘time-domain’ data. The Imagio™ breast imaging system uses alternating pulses of two different wavelengths of laser light, which can then show the relative difference between oxygenated and deoxygenated hemoglobin.
For more detailed descriptions of the technique and underlying physics, see this publication: Disease Markers 2003, 2004; 123-138.