Tumor holograms

Researchers at Purdue University and Imperial College, London have created a holographic imaging system capable of visualizing structure inside living tissue. The researchers used optical coherence imaging (OCI), a technique that directly records complete images of thin tissue sections with a video camera. Tissue readily reflects image-bearing infrared light, but it also strongly diffuses the light, an effect that would ordinarily overwhelm the coherent pictures. The key to the OCI technique is a dynamic holographic film—a 100-layer photorefractive quantum-well device—that filters out the diffused, incoherent background light but passes the coherent, full-frame images to a camera. By adjusting the relative delay between the image beam and the reference beam in the OCI system’s imaging interferometer, the researchers control the depth of the image plane and thereby assemble a slice-by-slice tour through a tumor while leaving the tissue intact. Application of the OCI technique to cultured rat tumors (see image ) revealed structures that appeared to be dead tissue and calcifications much like those found in human cancers. The researchers say that holographic OCI could offer a nondestructive alternative to ionizing x rays and micro-sectioning methods for studying living tissue. (P. Yu et al., Appl. Phys. Lett. 83 , 575, 2003 http://dx.doi.org/10.1063/1.1594830 .)