10.1117/2.1200812.1394 Novel hyperspectral imager aids surgeons Karel Zuzak, Robert Francis, Jack Smith, Chad Tracy, Jeffrey Cadeddu, and Edward Livingston Illuminating bodily tissues with a digital micromirror device enables non-invasive characterization of living tissue based on chemistry and morphology. When performing open or endoscopic surgery, it is often difficult to differentiate between neighboring tissues. For example, when removing the gallbladder, it is important not to damage the com- mon bile duct. If we could non-invasively distinguish the bile duct from surrounding arteries, the surgeon would know better where to cut. Spectroscopy has been used for decades to characterize chem- ical and biological molecules based on their spectral signatures, that is, the way they reflect or absorb different wavelengths of light. It is well-documented that oxygenated tissue reflects dif- ferent wavelengths of light at different intensities than deoxy- genated tissue. 1 In the same way, gallbladder and bile duct tis- sue has a different spectral signature than surrounding anatom- ical structures such as the liver and blood vessels. 2 In hyper- spectral imaging, we capture a series of images while scanning through wavelengths of light. Each processed image pixel cor- responds to the spectrum for that point on the image. We then compare each spectrum to known spectral signatures to deter- mine which tissue they match, or their level of oxygenation. Liquid crystal tunable filters (LCTF) have been used previously to scan through the wavelengths of light, generating only one processed image every 30s. We have developed a new hyper- spectral imager which uses a programmable digital micromirror device (DMD) from Texas Instruments DLP R  Products group to generate over three processed images per second. The primary limitation of the previous LCTF system is that only single bandpasses of narrow bandwidth light can be fil- tered at a time. 3 The new system has a DLP DMD-based spectral illumination light source (OL 490, Optronic Labs). 4 In the DMD source, broadband light is diffracted through a slit, reflected from a grid of digitally-controlled programmable micromirrors, and optically directed to a focal plane array (FPA, or digital cam- Figure 1. DMD-based hyperspectral imager for medical imaging. era) through a liquid light guide (LLG), similar to an optical fiber that has an increased capacity for transmitting light. Figure 1 shows the experimental setup. By controlling the state of each mirror individually, the source illuminates tissue with a pro- grammed selection of wavelengths of light and the camera mea- sures the reflection of that spectrum. The programmed spectrum may simply be a single bandpass—similar to the LCTF output— or a more complex combination of wavelengths that cannot be duplicated by the LCTF. Since the DMD hyperspectral imager Continued on next page