Hyperspectral FT-IR imaging

Figure 6.4 Hyperspectral FT-IR data processing performed simultaneously on four adjacent tissue sections from a cervical biopsy sample. The numbers 1 to 4 identify the individual sections in the figure, (a) A univariate chemical image obtained from the integrated area under the 1275-1190cm region after baseline subtraction (b) A four-cluster map derived from analysis over the 1272-950cm spectral window. The cluster...

At this point, it may be asked if certain parameters can be changed to decrease the measurement time to allow maps to be acquired in reasonable times. Since the size of the remote aperture for most applications is smaller than 250 pm, it is valid to suggest that even smaller detectors should be installed in FT-IR microscopes so that the SNR is optimized for samples that are 50 pm or smaller in dimension. The answer is a very practical one it is simply very difficult to keep the beam aligned with the tighter tolerance required for the beam to be focused accurately on a detector that is smaller than 250 pm. As described later, the situation is different when array detectors with very small pixels are used for hyperspectral imaging. 

By combination of FT-IR hyperspectral imaging and multivariate curve resolution (MCR) analysis, Budevska et al. [77] could identify two separate corn storage proteins, the so-called zeins in maize seed sections. By univariate analysis, these proteins could not be separated from the entire protein complex caused by superimposition of the corresponding amide I signals around 1656 cm . ... 

The first array detectors to be used for FT-IR hyperspectral imaging were focal-plane arrays (FRA) fabricated from InSb. MCT arrays were incorporated shortly thereafter, and these detectors are usually cold-shielded to improve their performance. The individual elements are bump-bonded onto small spheres of indium (a very soft metal). This method of fabrication sometimes led to poor reliability, but this problem has been largely overcome. Details of the construction of FPAs are given by in the paper by Scribner et al. [6]. Most InSb and MCT arrays are square, with 64 X 64, 128 x 128, or 256 x 256 detector elements (pixels) that are 6.25 X 6.25 pm in size. Thus, the entire detector array is less than 0.5 mm on the side. Note also that when such small detectors are used, their NEP is concomitantly small (see Section 7.1). 

As the speed of electronics increased, it became possible to use rapid-scanning interferometers at their lowest scan speed for hyperspectral imaging. The first report of this type of instrument was made by Snively et al. [8] at Purdue University in 1999. Several manufacturers of FT-IR spectrometers claim to have implemented continuous scan imaging for the first time, implying that they developed the idea. Perhaps they intended to say that they implemented it on their company s interferometer for the first time, but Lauterbach s group should be given credit for the original implementation. 

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