How PARISS® and Other Hyperspectral Imaging
Systems Work

Analytical Hyperspectral Systems Convert
Spectral Signatures Into Maps Showing
Target Objects or Conditions

Definitions of "Spectral" Imaging
Spectral Imaging: An all inclusive term that describes systems that characterize aheterogeneous field of objects as a function of their spectra

Multispectral imaging: The characterize a heterogeneous field of objects at multiple, but not necessarily contiguous wavelengths

Hyperspectral imaging (HSI) The characterize a heterogeneous field of objects at multiple contiguous wavelengths

Origins of Hyperspectral imaging (HSI): HSI originated in the remote Earth sensing community. The goal then, as now, was to convert spectroscopic data into an information-rich image. Landsat, other satellites, and fixed wing aircraft are highly successful uses of Multispectral and Hyperspectral Imaging for remote sensing.

It is well understood that most objects present spectral information that correlate well enough to be considered a " fingerprint". Hyperspectral imaging acquires "spectral fingerprints" and creates a spectral "topographical" map showing target spectral objects, or conditions, on a grayscale field of view.

There are Two HSI Methodologies
1. Wavelength Dispersive Imaging Spectrometers (WDSI) These systems use a diffraction grating or a prism to acquire analytically accurate spectral wavelength data in one of the following spectroscopy methods:

Hyperspectral imaging
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  • Absorption (measured in optical density)
  • % Reflection
  • Fluorescence
  • Luminescence, phosphorescence, auto-luminescence...
  • Scattered light. Typically in "Dark-field" often used for characterizing nanoparticles.
  • Instruments, such as the PARISS Hyperspectral Imaging System, can be rendered "radiometric" to compensate for variations in wavelength sensitivity (QE) of the camera.
  • Can be validated using spectroscopic standards

WDSI instruments acquire all wavelength information simultaneously and an unlimited field of view sequentially

2. Electronic bandpass filters that characterize a fixed field of view, by acquiring wavelength data sequentially. The instrument is typically a sensitive camera, such as a CCD, with the "Filter Flipper" located between a focusing lens and the camera chip.

Every camera pixel accumulates a wavelength data point (WDP). If 50 filters are needed to obtain the necessary information, then each pixel will step through and acquire 50 WDP.

Electronic tunable filter (ETF) hardware includes:

  • Liquid Crystal Tunable Filters (LCTF),
  • Acousto Optic Tunable Filters (AOTF) or an
  • Interferometer (In this case filters are not involved, but wavelengths are still acquired sequentially over a fixed field of view)

ETF instruments when used in the life sciences typically:

  • Acquire relative, not analytical data.
  • Rarely if ever calibrated or validated for wavelength accuracy
  • In instruments designed for use in the life sciences, it is unlikely that they compensate for variations in camera sensitivity (QE) as a function of wavelength

Electronic Tunable Filters do not acquire analytical "spectroscopic" data. They do not quantify differences between objects, or conditions.

 
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