Combined ultrasound and near infrared diffused light imaging

The authors have investigated the use of combining near infrared (NIR) diffuse light and ultrasound methods to increase detection sensitivity and specificity of small targets by ultrasound. A line-of-sight optical projection through a test phantom is identified from an amplitude null and a sharp phase transition produced by diffusive waves originating from 2 in-phase (initial phase 0°) and out-of-phase (initial phase 180°) sources. This line-of-sight is scanned across the test phantom. A complete ultrasound B-scan image is recorded at each project line in the optical scan. Each acoustic image plane is bisected by the optical beam path and lies in the optical scan plane. The test phantom simulates acoustic and optical properties of homogeneous tissue. A single small cylinder simulating some breast tumor properties is inserted somewhere in the test phantom. The optical scanning identifies quite well the line-of-sight passing through the tumor simulator. Most of these simulated tumors were at or below the threshold for acoustic detection and were not seen consistently with unguided ultrasound. For tests in which a target was apparently identified optically, the selected line of sight was indicated in each of 3 adjacent ultrasound images. Two radiologist observers were statistically more accurate (83%) in identifying the target location on the optically-selected ultrasound images than in the unmarked images (52%). That is, in these single-target, phantoms of homogeneous background, the optical technique usually provided the correct line-of-sight and ultrasound generally showed the location along that line. Performance of this combined technique in the detection of breast tumors needs further clinical evaluation