MEDICAL DIAGNOSTICS: Optical breast imaging shows differentiated tissue

An optical tomography system developed by Imaging Diagnostic Systems Inc. (IDSI; Sunrise, FL) reveals differentiated tissue in breast images, in a technique that the developers hope will eventually augment mammograms as a diagnostic tool.

In the IDSI system, a patient lies face down on the imaging unit with one breast at a time pendulous in an 8-in.-diameter, 10-in.-deep scanning chamber. Earlier versions of the system scanned a near-infrared laser beam over the breast with a rotating polygon, which provided an illumination dwell time per patch of roughly 4 µs (see Laser Focus World, Oct. 1997, p. 113). The illumination source is a Ti:sapphire laser delivering up to 500 mW at 790 nm; melanin does not absorb radiation at these wavelengths, rendering the images independent of skin tone.

To increase dwell time, thereby enhancing image contrast, the new system illuminates the breast tissue directly by delivering the beam with a single-mode silica optical fiber in contact with the skin. Swinging out on an assembly reminiscent of a phonograph tone arm, the fiber makes a complete circuit of the breast, while a circumferential array of large-area photodiodes captures the light scattered by the tissue. After completing a circuit, the fiber shifts vertically by 4 mm and the process is repeated, eventually forming a multislice tomographic image of the breast. The new design increases dwell time to about 0.2 s per patch.

The company has received FDA approval to perform a 20-patient study comparing optical tomography images with conventional mammograms and magnetic resonance imaging (MRI) scans. By following this study with more extensive, multiple-site trials, IDSI researchers hope to compile an image interpretation database that will allow them to use the system to detect breast cancer.