Tumor Fly-Through Movies

Researchers at Purdue University and the Imperial College of Science in London have created a real-time holographic system to acquire a fly-through movie of living tissue using infrared light and a special, semiconductor holographic film. The acquired images showed structure inside rat tumors that, with conventional techniques, would only be visible if the tumor was sectioned into thin slices or imaged with ionizing radiation.

The researchers created the fly-through movie using optical coherence imaging (OCI). OCI is related to the more widely known optical coherence tomography (OCT). However, OCT involves scanning a laser beam through a sample and gathering information point by point, which then must be assembled into a complete image. OCI, on the other hand, captures complete images of thin tissue sections that can be recorded directly with a video camera.

The key to the holographic OCI technique is a dynamic holographic film that filters out the scattered, incoherent background light but passes the coherent, full-frame images to a camera. Tissue readily reflects image-bearing infrared light, but it also strongly scatters the light, and without coherence filtering the scattered light would overwhelm the coherent pictures.

By adjusting the relative delay between the image beam and the reference beam in the OCI system's imaging interferometer, the researchers (Ping Yu, 765-494-3004, pingyu@physics.purdue.edu, David Nolte, 765-494-3013, nolte@physics.purdue.edu) could control the depth of the images and assemble a slice-by-slice tour through a tumor while leaving the tissue intact.

Application of the OCI technique to cultured rat tumors revealed structures that appeared to be necroses (regions of dead tissue) and calcifications much like those found in human cancers (see image).

Ultimately, the researchers explain, holographic OCI could offer a nondestructive alternative to x-rays and microsectioning methods for studying living tissue. (P. Yu et al., Applied Physics Letters, 21 July 2003.)