Medical Imaging with the speed of light

Nothing is faster than light, yet we managed to see light travel millimeter by millimeter with a one-trillion-frames-per-second ultra high speed video camera build from a femto second laser and a streak camera. The imaging technique, devised by MIT researcher Raskar, may be useful in medical imaging with light.

Cheap, fast and easy visualization of breast or brain tissue with light within the near infrared (NIR) transparency window (600-1000 nm), is a holy grail in medical imaging because it does not depend on harmful radiation, radioactive substances, or bulky instrumentation. The clinical value of NIR imaging has so far been limited due to the strong inelastic scattering of light in tissue that causes serious image blurring. A challenging solution to the scattering problem is the use of pulsed light sources and time resolved detection of transmitted light because in that case only unscattered photons that go straight can be selected. The bottleneck of this time-of-flight or time-gated approach has been a limited temporal resolution (>100 pico seconds) and a too poor sensitivity.

We have constructed a one-trillion-frames-per-second video camera based on a streak camera and a femto second laser, that combines a 100 times higher time resolution (~1 ps) and photon counting sensitivity. In the movie below it is explained that the time-of-flight camera can fruitfully be used to image objects in strongly scattering media, much better than can be done with continuous laser light. We are developing this time-of-flight camera further by optimizing it for NIR optical imaging in order to (i) better understand light transport in strongly scattering media and (ii) to perform 2D and 3D image reconstruction of realistic tissue equivalent phantoms.