Limits...
Sensitivity of coded aperture Raman spectroscopy to analytes beneath turbid biological tissue and tissue-simulating phantoms.

Maher JR, Matthews TE, Reid AK, Katz DF, Wax A - J Biomed Opt (2014)

Bottom Line: Traditional slit-based spectrometers have an inherent trade-off between spectral resolution and throughput that can limit their performance when measuring diffuse sources such as light returned from highly scattering biological tissue.Another approach is to change the nature of the instrument by using a coded entrance aperture, which can increase throughput without sacrificing spectral resolution.In this study, two spectrometers, one with a slit-based entrance aperture and the other with a coded aperture, were used to measure Raman spectra of an analyte as a function of the optical properties of an overlying scattering medium.These results demonstrate that the attenuation in signal intensity is more pronounced for the slit-based instrument and highlight the scattering regimes where coded aperture instruments can provide an advantage over traditional slit-based spectrometers.

View Article: PubMed Central - PubMed

Affiliation: Duke University, Department of Biomedical Engineering, Durham, North Carolina 27708, United States.

ABSTRACT
Traditional slit-based spectrometers have an inherent trade-off between spectral resolution and throughput that can limit their performance when measuring diffuse sources such as light returned from highly scattering biological tissue. Recently, multielement fiber bundles have been used to effectively measure diffuse sources, e.g., in the field of spatially offset Raman spectroscopy, by remapping the source (or some region of the source) into a slit shape for delivery to the spectrometer. Another approach is to change the nature of the instrument by using a coded entrance aperture, which can increase throughput without sacrificing spectral resolution.In this study, two spectrometers, one with a slit-based entrance aperture and the other with a coded aperture, were used to measure Raman spectra of an analyte as a function of the optical properties of an overlying scattering medium. Power-law fits reveal that the analyte signal is approximately proportional to the number of transport mean free paths of the scattering medium raised to a power of -0.47 (coded aperture instrument) or -1.09 (slit-based instrument). These results demonstrate that the attenuation in signal intensity is more pronounced for the slit-based instrument and highlight the scattering regimes where coded aperture instruments can provide an advantage over traditional slit-based spectrometers.

Show MeSH

Related in: MedlinePlus

Representative Raman spectra acquired with the slit-based [(a) and (b)] and coded aperture [(c) and (d)] instruments. The measured data were acquired with a 0% [(a) and (c)] or 1% [(b) and (d)] Intralipid overlayer and are well fit by the pure spectral components as evidenced by the small amplitudes of the fit residuals. The signal-to-noise ratio (SNR) and signal-to-background ratio (SBR) of each representative measurement are also provided.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC4221093&req=5

f3: Representative Raman spectra acquired with the slit-based [(a) and (b)] and coded aperture [(c) and (d)] instruments. The measured data were acquired with a 0% [(a) and (c)] or 1% [(b) and (d)] Intralipid overlayer and are well fit by the pure spectral components as evidenced by the small amplitudes of the fit residuals. The signal-to-noise ratio (SNR) and signal-to-background ratio (SBR) of each representative measurement are also provided.

Mentions: The measured spectra (five per sample per instrument) were least-squares fit with a combination of pure spectra of the underlying components, as well as fifth-order polynomial, in order to determine the spectral contribution of the underlying layer of caffeine. Representative spectra acquired with both the slit-based and coded aperture instruments are displayed in Fig. 3. As shown in Fig. 3, interfering signal from the overlying layer was primarily due to fluorescence from the glass microscope slides. As a reminder, the glass slides were used to aid in phantom construction and to facilitate coregistration of measurements acquired with different instruments. Because this interfering signal was not from caffeine or the overlying turbid layer, the glass fluorescence was modeled and removed prior to all subsequent analyses. The figure shows that the relative caffeine signal measured by the slit-based instrument through the overlying 1%-Intralipid sample drops to whereas the coded aperture system retains of the maximum signal. It should also be noted that both instruments were operated above their detection limits, which were defined as a spectral SNR of unity. The SNR of each measurement was calculated as SNR=c·s/c2·σ2,(2)where is the spectrum of pure caffeine, is the spectral contribution of the underlying layer of caffeine, and is the wavelength-dependent variance of the measured spectrum. This expression is equal to the caffeine fit coefficient divided by the uncertainty in the coefficient provided that the model components are orthogonal, and the measurement noise is Gaussian, independent, and identically distributed.33 The SNRs varied between 20 and 730 (slit-based instrument) and 230 and 1870 (coded aperture instrument).


Sensitivity of coded aperture Raman spectroscopy to analytes beneath turbid biological tissue and tissue-simulating phantoms.

Maher JR, Matthews TE, Reid AK, Katz DF, Wax A - J Biomed Opt (2014)

Representative Raman spectra acquired with the slit-based [(a) and (b)] and coded aperture [(c) and (d)] instruments. The measured data were acquired with a 0% [(a) and (c)] or 1% [(b) and (d)] Intralipid overlayer and are well fit by the pure spectral components as evidenced by the small amplitudes of the fit residuals. The signal-to-noise ratio (SNR) and signal-to-background ratio (SBR) of each representative measurement are also provided.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4221093&req=5

f3: Representative Raman spectra acquired with the slit-based [(a) and (b)] and coded aperture [(c) and (d)] instruments. The measured data were acquired with a 0% [(a) and (c)] or 1% [(b) and (d)] Intralipid overlayer and are well fit by the pure spectral components as evidenced by the small amplitudes of the fit residuals. The signal-to-noise ratio (SNR) and signal-to-background ratio (SBR) of each representative measurement are also provided.
Mentions: The measured spectra (five per sample per instrument) were least-squares fit with a combination of pure spectra of the underlying components, as well as fifth-order polynomial, in order to determine the spectral contribution of the underlying layer of caffeine. Representative spectra acquired with both the slit-based and coded aperture instruments are displayed in Fig. 3. As shown in Fig. 3, interfering signal from the overlying layer was primarily due to fluorescence from the glass microscope slides. As a reminder, the glass slides were used to aid in phantom construction and to facilitate coregistration of measurements acquired with different instruments. Because this interfering signal was not from caffeine or the overlying turbid layer, the glass fluorescence was modeled and removed prior to all subsequent analyses. The figure shows that the relative caffeine signal measured by the slit-based instrument through the overlying 1%-Intralipid sample drops to whereas the coded aperture system retains of the maximum signal. It should also be noted that both instruments were operated above their detection limits, which were defined as a spectral SNR of unity. The SNR of each measurement was calculated as SNR=c·s/c2·σ2,(2)where is the spectrum of pure caffeine, is the spectral contribution of the underlying layer of caffeine, and is the wavelength-dependent variance of the measured spectrum. This expression is equal to the caffeine fit coefficient divided by the uncertainty in the coefficient provided that the model components are orthogonal, and the measurement noise is Gaussian, independent, and identically distributed.33 The SNRs varied between 20 and 730 (slit-based instrument) and 230 and 1870 (coded aperture instrument).

Bottom Line: Traditional slit-based spectrometers have an inherent trade-off between spectral resolution and throughput that can limit their performance when measuring diffuse sources such as light returned from highly scattering biological tissue.Another approach is to change the nature of the instrument by using a coded entrance aperture, which can increase throughput without sacrificing spectral resolution.In this study, two spectrometers, one with a slit-based entrance aperture and the other with a coded aperture, were used to measure Raman spectra of an analyte as a function of the optical properties of an overlying scattering medium.These results demonstrate that the attenuation in signal intensity is more pronounced for the slit-based instrument and highlight the scattering regimes where coded aperture instruments can provide an advantage over traditional slit-based spectrometers.

View Article: PubMed Central - PubMed

Affiliation: Duke University, Department of Biomedical Engineering, Durham, North Carolina 27708, United States.

ABSTRACT
Traditional slit-based spectrometers have an inherent trade-off between spectral resolution and throughput that can limit their performance when measuring diffuse sources such as light returned from highly scattering biological tissue. Recently, multielement fiber bundles have been used to effectively measure diffuse sources, e.g., in the field of spatially offset Raman spectroscopy, by remapping the source (or some region of the source) into a slit shape for delivery to the spectrometer. Another approach is to change the nature of the instrument by using a coded entrance aperture, which can increase throughput without sacrificing spectral resolution.In this study, two spectrometers, one with a slit-based entrance aperture and the other with a coded aperture, were used to measure Raman spectra of an analyte as a function of the optical properties of an overlying scattering medium. Power-law fits reveal that the analyte signal is approximately proportional to the number of transport mean free paths of the scattering medium raised to a power of -0.47 (coded aperture instrument) or -1.09 (slit-based instrument). These results demonstrate that the attenuation in signal intensity is more pronounced for the slit-based instrument and highlight the scattering regimes where coded aperture instruments can provide an advantage over traditional slit-based spectrometers.

Show MeSH
Related in: MedlinePlus