Instrumental error in chromotomosynthetic hyperspectral imaging

Abstract

Chromotomosynthetic imaging (CTI) is a method of convolving spatial and spectral information that can be reconstructed into a hyperspectral image cube using the same transforms employed in medical tomosynthesis. A direct vision prism instrument operating in the visible (400-725 nm) with 0.6 mrad instantaneous field of view (IFOV) and 0.6-10 nm spectral resolution has been constructed and characterized. Reconstruction of hyperspectral data cubes requires an estimation of the instrument component properties that define the forward transform. We analyze the systematic instrumental error in collected projection data resulting from prism spectral dispersion, prism alignment, detector array position, and prism rotation angle. The shifting and broadening of both the spectral lineshape function and the spatial point spread function in the reconstructed hyperspectral imagery is compared with experimental results for monochromatic point sources. The shorter wavelength (λ<500 nm) region where the prism has the highest spectral dispersion suffers mostly from degradation of spectral resolution in the presence of systematic error, while longer wavelengths (λ>600 nm) suffer mostly from a shift of the spectral peaks. The quality of the reconstructed hyperspectral imagery is most sensitive to the misalignment of the prism rotation mount. With less than 1° total angular error in the two axes of freedom, spectral resolution was degraded by as much as a factor of 2 in the blue spectral region. For larger errors than this, spectral peaks begin to split into bimodal distributions, and spatial point response functions are reconstructed in rings with radii proportional to wavelength and spatial resolution.

Review of spectral imaging technology in biomedical engineering: achievements and challenges

“…146 In recent years, various interferometric spectral imaging systems and sensors have been developed and used for biomedical analysis, such as the spectral karyotyping (SKY), dynamic monitoring of biomolecular interactions, and live epithelial cancer cells analysis. 20,109,147,148 Besides the interferometer, some other devices such as the rotating direct vision prism, 149,150 VIF, 78 CVF, LVF, 42,151 and the dispersion of optical rotation 152 can also be used to form biomedical staring imagers. Although the staring biomedical spectral imagers do not need to scan in the spatial dimension, most of them still need to scan in the spectral dimension.…”

“…163 Significant loss in spatial resolution due to prism mount misalignment in a chromotomosynthetic HSI system has been analyzed by Bostick et al They found that the relative effect is less in the shorter-wavelength region, which indicates that spatial performance is also affected by wavelength. 149 However, astigmatism is not a problem in a spectral confocal laser scanning system because the laser submits single points from the FOV sequentially, not multiple points simultaneously. For a line-scanning spectral imaging system, the spatial resolution in the direction of the slit width is affected by the slit width, whereas the spatial resolution along the slit length is usually affected by the magnification and camera pixel size, 44 while for a spectral filters-based imaging system, the spatial resolution is also related to the types of tunable filters (AOTF, LCTF, etc.)…”

Chromotomosynthesis for high speed hyperspectral imagery

“…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.…”

Classification of visible point sources using hyperspectral chromotomosynthetic imagery

“…21,22 Each projection (frame) of data taken by the CTI represents a two-dimensional (2-D) spectrograph, which can be exploited to analyze high frequency changes in spectral content. 28 For these reasons, spectral resolution is inferior to that of more conventional techniques such as imaging Fourier transform spectrometers and traditional scanning systems. Perhaps the most important attribute of CTI is the ability to collect complete HSI data cubes at rates easily exceeding 10 Hz, limited only by the detector array read rates.…”