Vol 1, No. 2, March 1995

The above AVIRIS data-cube was taken from NASA/JPL FTP site


Well, here we go again. Things are looking good, so far. Our first edition was not also our last. Thanks to readers' encouragement, we are actually starting to believe our own hype, that Hyperspectrum does provide a useful service and that it is good for the readers' (professional) health. Judged by a recent supreme court decision, this newsletter is not considered denigrating to anyone in the work place, so unlike some other subscriptions, there is no need to hide this one from your peers.

In this, as in future issue, we plan to review topics in imaging spectroscopy from the vista of the different disciplines that are a part of the logo above. The similarities in the problems being addressed and the technical approach could be of interest to researchers in diverse fields.

Has anyone noticed the increase in the number of conferences that include sessions on imaging spectroscopy? For the latest list see attachment.

Nahum Gat, Editor

Cancer or Scuds Hunter?
The place is an operating room. A patient undergoes surgery to remove a malignant tumor, and the surgeon tries to locate the remaining few tissue cells into which the cancer has spread. These are the most difficult to spot. A camera-like device is pointed at the exposed flesh. An image appears on a large overhead monitor, and certain areas are delineated and highlighted with false colors that correspond to a probability level of a local malignancy. The technician zooms in and the surgeon decides whether to remove additional tissues.

One of the newest applications for hyperspectral imaging is non- or minimally-invasive photodiagnosis. Conventional spectroscopy is, of course, not a new tool in pathology, and the idea of using spectroscopic techniques in real time and in-vivo, is a natural extension. The problem may be that whereas the pathologist is trained in the interpretation of spectra, very few physicians and surgeons would call themselves experts in this field. The computerized pathologist does the job (for more on photobiology, see Tidbits, Pg. 3).

A computerized pathologist has additional benefits. Human pathologists do get tired at the end of a long day, a condition that may contribute to mistakes. Not all hospitals have a pathologist around the clock, some have none at all. And sending too many biopsies to the lab takes more time to analyze. Enter the imaging spectrometer with the hyperspectral analyzer.

Locating a few malignant cells in a benign background is not unlike finding a camouflaged tank in the woods. The background has its own spectral signature, and so does the target. The background exhibits a spatially non-stationary clutter, and the target signature is masked by the adjacent cells. Furthermore, early stage detection is critical, and at that stage the target may still be classified as "subpixel" in size, meaning that the signature is composed of contributions from both the target and background. And if the malignant cell is covered under a layer of benign cells (camouflage), than the spectral mixing is non-linear. A nice little mathematical problem to solve, that may even tax your Neyman-Pearson formalism!

Unlike conventional spectroscopy, which deals with all these problems as well, imaging spectroscopy provides simultaneous spatial and spectral data. The mathematical algorithms should be able to take advantage of the spatial data to develop image statistics and other parameters which aid in the detection, improving on the capabilities of conventional spectroscopy.

State of the Art
Various methods are investigated for in-vivo photodiagnosis that could be made amenable to hyperspectral analyses, by producing spatio-spectral signatures. Examples, all based on active systems, include elastic scattering (reflection/ excitation spectra), fluorescence spectra using exogenous chromophores (specific photo-reactive compounds that have a preferential affinity to malignant cells [i.e., taggers]), or endogenous (auto-) fluorescence.

Added levels of complexity appear due to the time-dependence of fluorescence signatures, that exhibit an exponential decay, and the multiple scattering and absorption through the intervening tissue (the photon migration problem). The former is not typically associated with tanks and scuds. But the latter is somewhat analogous to atmospheric transmission of a signature. Of course, a few kilometers of atmosphere may be equivalent in optical path density to a millimeter of tissue (or less, depending on the wavelength). No equivalent to the Air Force Geophysics Directorate's LOWTRAN exists yet for transmission calculations, however.

One critical issue is the development of a knowledge base including spectral libraries containing signatures of various tissue types, and the statistics of these signatures.

Photodiagnosis can be used for topical (e.g., skin cancer) or internal organ conditions. In the latter case an endoscope or a fiber optic probe inserted through a hypedermic needle can reach almost any organ. Now, one should agree that instead of snipping polyps for biopsy, photodiagnosis is a more comfortable option during the biannual colonoscopy. Besides cancer detection, hyperspectral techniques may be used for identification of bacterial infection, and other medical conditions.

So, is a real-time, computerized hyperspectral pathologist that exhibits a high probability of detection at a low false alarm rate, under low SNR and poor S/C conditions, coming to operating rooms near you? Don't expect a revolution, but perhaps an evolution.

EOS: For Your Info.
Some interesting instruments for the Earth Observing System (EOS). The MODIS (Moderate Resolution Imaging Spectrometer) with 36 spectral channels: 20 within 0.4-3.0 śm; 16 within 3-15 śm, uses a cross-track scan mirror and a set of linear detector arrays with spectral interference filters providing imagery in 36 bands. The MISR (Multi-Angle Imaging Spectro-Radiometer) uses 9 CCDs operating in a pushbroom mode providing nadir and fore-aft views. Each CCD is covered by 4 banded filters to produce multispectral imagery. The 1st platform slated for launch in 1998, will be placed in a polar sun-synchronous orbit with equatorial crossing time at 10:30 AM, and it is, most imaginatively named AM-1. The chart on the next page shows how the satellite is placed permanently in a 10AM orbit (Ground Hog Day Syndrom [the movie] in space). More information on the EOS system and instruments can be found on the web at http://spso.gsfc.nasa.gov/spso_homepage.html.

Web Surfing.
Other cool places to visit on the Web: The Virtual Tourist at http://wings.buffalo.edu/world/na.html, is a pictorial map of the world to be used to locate web servers using a click with your mouse; and if you want to find and connect to all the government web servers (all branches, agencies) look at http://www.fie.com/www/ us_gov.html.

Have you heard about the new and improved French abortion pill RU-486DX4? It works even faster. How is this related to hyperspectrum? Good question. Who said it has to be...? No, no O.J. trial coverage.

Interesting reading.

Photon Exchange:
The rapid, uncontrolled increase in the use of lasers is creating a shortage of photons in certain colors. Our well-connected free-lancer inside the DC Beltway has informed us that the government is considering a two step approach. In the near term, the use of photons will be taxed; in the long run, the UN will establish a global allocation system and a Photon Exchange Program that will monitor irresponsible utilization and report all such waste. So, remember you read it first here in "Hyperspectrum." We will keep you informed on developments.

We would like to know what hyperspectral data processing software are in use, and what data format are required to read the data-cubes. Can the data be read directly from the sensor, or from a disk? Results will be published in an upcoming issue. See back cover for how to communicate with OKSI.
Meeting Your Interests -- Multi & Hyperspectral Systems: An agenda for the frequent flyer. Conferences, and call for papers, related to multi- and hyperspectral techniques.


Don't be old fashioned. If you organize a conference -- consider including a session on hyperspectral and multispectral imaging. Everyone else does. Then let us know if you want it listed here.


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