Every area of scientific investigation goes through an evolutionary process in which its fundamental ideas are continuously honed and developed, always questioned and more often than not enhanced with newly introduced ideas. By the late eighties, the use of visible and near-infrared light for probing tissue had reached a crossroads. The basic concepts had been developed and tested in experimental settings, but because of limitations in technique and instrumentation, optical imaging and spectroscopy were still far from experiencing widespread deployment in clinical settings.

But then, also in the late eighties, Britton Chance and others spearheaded the development of time- and frequency-resolved techniques, while David Delpy and others advanced the quantitative utility of continuous-wave techniques. These allowed for greater sensitivity and specificity in spectroscopy, one of the most common methods of optical imaging, and so spurred a resurgence of interest in the technique. Before long, clinical application of near-infrared spectroscopy and diffuse optical tomography seemed much more than a remote possibility.

In 1998, Massachusetts General Hospital’s NMR Center and the multi-institutional Center for Innovative Minimally Invasive Therapies (CIMIT) set before themselves a challenge: to advance our understandings of photon migration and diffuse optical tomography and to help introduce optical imaging into the realms of health science and health care as an attractive and viable alternative to traditional imaging techniques. To this end, the NMR Center and CIMIT established what became known as the Photon Migration Imaging Lab.

The Photon Migration Imaging Lab currently conducts research in several areas: near-infrared spectroscopy/diffuse optical tomography of the brain, optical breast imaging and microscopy of cerebral physiology. The members of the lab have published on a range of topics within each of these areas, contributing a great deal to the existing bodies of knowledge and helping to advance photon migration and diffuse optical tomography ever closer to widespread clinical application.

Facilities

The Photon Migration Imaging Lab consists of 4 separate lab facilities for 1) fiber optic and electronics fabrication and testing, 2) instrumentation system development and testing, 3) small animal studies, and 4) human subject testing.

Instrumentation in the Photon Migration Imaging Lab includes:

• A continuous-wave diffuse optical tomography (CW4) imaging system with 18 lasers and 16 detectors (manufactured by TechEn – http://www.techen.com).
• Two additional CW-DOT imaging systems (CW5), each with 32 lasers and 32 detectors (also manufactured by TechEn).
• A time-resolved spectroscopy system with pulsed laser diodes at 4 wavelengths and 4 photon-counting photo-multiplier tubes (manufactured by PicoQuant – http://www.picoquant.com/).
• An ISS system with 16 laser diodes and 4 photomultiplier detectors (Imagent™ functional brain imaging – http://www.iss.com/products/imagent/imagent.htm).
• A time-domain diffuse optical tomography (TD-DOT) imaging system, with an imaged intensified CCD detector and optically multiplexed sources (constructed in-house with the support of Advanced Research Technologies http://www.art.ca).
• A Mai:Tai Titanium:Saphire Laser (manufactured by SpectraPhysics – http://www.spectraphysics.com/).
• 2 Ocean Optics Spectrographs (model S2000).
• 4 Near-infrared spectroscopy systems (NIRS 1 and 2) (custom made by TechEn).
• 8-bit CCD camera (Cohu 4910) and various white light lamps, a mercury xenon lamp (200W, Oriel) with housing and SMA connector, a mercury lamp (200W, Oriel) for speckle microscopy.
• TE-cooled 12-bit CCD (Coolsnap fx, Roper Scientific).
• 50mW diode-pumped solid state laser (532 nm).

Other equipment is as follows.

Electronics: 1 Gs/s digital oscilloscope (HP Infiniium), numerous data acquisition cards, network analyzer, 24-node Linux Beowulf system.

Optical fiber equipment: single-mode, multi-mode and fiber bundles, optical fiber polishing equipment, and optomechanical fiber coupling.

Optomechanical equipment: breadboards for mounting optical components, three-dimensional translation stages, optical mounting hardware, various diode lasers and white light sources and other optics, electro-optics and electronics equipment.

Optics: various lenses, microscope objectives, mirrors, filters, beamsplitters, orthogonal galvanometer mounted mirrors (Cambridge, 6810).