Spatial and spectral performance of a chromotomosynthetic hyperspectral imaging system

Abstract

The spatial and spectral resolutions achievable by a prototype rotating prism chromotomosynthetic imaging (CTI) system operating in the visible spectrum are described. The instrument creates hyperspectral imagery by collecting a set of 2D images with each spectrally projected at a different rotation angle of the prism. Mathematical reconstruction techniques that have been well tested in the field of medical physics are used to reconstruct the data to produce the 3D hyperspectral image. The instrument operates with a 100 mm focusing lens in the spectral range of 400-900 nm with a field of view of 71.6 mrad and angular resolution of 0.8-1.6 μrad. The spectral resolution is 0.6 nm at the shortest wavelengths, degrading to over 10 nm at the longest wavelengths. Measurements using a point-like target show that performance is limited by chromatic aberration. The system model is slightly inaccurate due to poor estimation of detector spatial resolution, this is corrected based on results improving model performance. As with traditional dispersion technology, calibration of the transformed wavelength axis is required, though with this technology calibration improves both spectral and spatial resolution. While this prototype does not operate at high speeds, components exist which will allow for CTI systems to generate hyperspectral video imagery at rates greater than 100 Hz.

Chromotomosynthesis for high speed hyperspectral imagery

“…There is chromatic aberration observed with this system which limits overall spatial and spectral resolution. The spectral resolution ranges from 1 -10 nm with the direct vision prism (DVP) dispersion poorest at the longest wavelengths [26] The distance between L3 and the detector is used as an adjustable focus and is currently chosen so that best focus is achieved at 635 nm to optimize the spectral resolution in the red. The full field of view is 71.6 mrad and provides an angular resolution of 0.8-1.6 μrad.…”

“…A basic schematic of the AFIT CTI system is displayed in Figure 1 and has been described previously [26,28]. The detector is a PI-MAX Gen II intensified RB fast-gate 1024x1024 array with responsivity primarily in the 400 -850 nm region.…”

“…We recently developed a CTI system uses a rotating direct vision prism (DVP) to collect 2-D projections of spectral imagery function of prism rotation angle, θ [26]. These projections can be mathematically reconstructed to produce both a wideband, undispersed 2-D image of the target and a 3-D hyperspectral image cube [27].…”

Instrumental error in chromotomosynthetic hyperspectral imaging

“…1 and has been described in detail previously [14]. The system features a two-element DVP with an undispersed wavelength of λ c ≈ 548 nm, which is centered on and rotates about the optical axis.…”

“…A backprojection algorithm with optional filtering for point source image reconstruction does not significantly degrade the native spatial and spectral resolution in a reconstructed plane of interest when the system linear dispersion and other instrument properties are adequately characterized [13][14][15]. However, two factors must be considered that can diminish the observed performance in a reconstructed spectral bin.…”