Simultaneous Multispectral Imaging in the Visible and Near-Infrared Region:  Applications in Document Authentication and Determination of Chemical Inhomogeneity of Copolymers

Abstract

A new multispectral imaging spectrometer capable of simultaneously recording spectral images in the visible and near-infrared has been developed. In this instrument, an acoustooptic tunable filter is used to diffract an unpolarized incident light into two diffracted beams with orthogonal polarization; one of them is detected by a silicon camera for the visible region while the other beam is detected in the near-infrared region (from 1 to 1.7 microns) with a NIR camera. The imaging spectrometer is sensitive, inexpensive, and field deployable because it is based on the recently available InGaAs focal plane arrays camera, which is low cost and can be sensitively operated at room temperature. Preliminary applications of the imaging spectrometer include measurements of the visible and NIR absorption spectra of ink used to print U.S. currency. Such results may help to characterize samples as well as to control and to ensure the quality of the samples during the production processes. More important are the results obtained on ethylene/vinyl acetate copolymers. The NIR spectral images obtained clearly indicate that these copolymers exhibit a high degree of chemical inhomogeneity. Because of the possibility of inhomogeneity, it is very important that the homogeneity of polymers or copolymers be thoroughly understood before the NIR methods, especially those based on NIR spectrometers equipped with a single-element detector, are used for measurements.

Pulmonary hypertension

“…Near-infrared (NIR) multispectral imaging technique may be the solution to this problem. We have succeeded in developing a novel NIR multispectral imaging (NIR-MSI) instrument that can provide, for the first time, the means to noninvasively, sensitively (single pixel resolution), and rapidly (ms) record not at a single wavelength as in NIR bioimaging instruments but rather on an entire NIR absorption spectrum (as with a Fourier transform [FT]-IR spectrophotometer) and not just one spectrum but rather tens of thousands of spectra at tens of thousands of different locations within a sample during a period as short as a few milliseconds [13][14][15][16][17]. Chemical information derived from these spectra will make it possible to accurately detect and identify any different chemical or biochemical species at many different positions within a sample.…”

“…Because of its advantages, we were able to use the NIR-MSI instrument for studies and measurements that are not possible otherwise. These include the noninvasive and nondestructive authentication of documents (e.g., stock certificates, currency), determination of the chemical inhomogeneity of polymers, kinetics of fast reactions (e.g., curing of epoxy by amine), and detection of combinatorial peptide synthesis [13][14][15][16][17]. It is expected that combined advantages of NIR light (deep tissue penetration) and MSI technique (ability to provide chemical composition and structure at various positions within a sample) enable the NIR-MSI instrument to be uniquely suited for the noninvasive investigation of MCT toxicity in the lung of Sprague-Dawley rats.…”

Multispectral imaging of tablets in blister packaging

“…The inhomogeneity was not observed if the average of a large number of pixels were used. In a similar manner, ethylene/vinyl acetate copolymers were shown to exhibit a high degree of chemical inhomogeneity [10].…”

Multispectral optical imaging combinedin situwith XPS or ToFSIMS and principal component analysis

“…[10] Multispectral imaging in the optical and IR range has been used to identify inhomogeneity in polymers and authenticate documents. [11] There are many applications of multispectral imaging in the analysis and conservation of paintings and other heritage materials. [12] At least one commercial LED-based multispectral imaging instrument [13] is available for operation in air.…”