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.

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Related in: MedlinePlus

Relative caffeine signal versus the number of mean free paths (MFPs) of the overlying Intralipid phantom. The solid lines are power-law fits (along with 95% confidence intervals), and the error bars represent 95% confidence intervals for the mean of each measurement.
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f4: Relative caffeine signal versus the number of mean free paths (MFPs) of the overlying Intralipid phantom. The solid lines are power-law fits (along with 95% confidence intervals), and the error bars represent 95% confidence intervals for the mean of each measurement.

Mentions: The magnitude of the caffeine signal versus the number of scattering mean free paths () of the overlying Intralipid phantom is plotted in Fig. 4. The signal is plotted on a relative scale, normalized by the signal strength of pure caffeine with a 0% Intralipid overlying layer. The absolute signal strength is not directly compared here because the specific instrument parameters (e.g., illumination power and sensor integration time) are not related to the signal attenuation rates, i.e., these parameters may be varied to increase or decrease absolute signal (or SNR) of either instrument, but not the attenuation rate. Power-law relationships between the MFPs of each phantom and the corresponding caffeine signal measured by each instrument were established by linear least-squares fitting of the logarithm-transformed data. Approximately 90% of the variance in the caffeine signal is described by these fits ( and 0.93 for the coded aperture and slit-based instruments, respectively).


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)

Relative caffeine signal versus the number of mean free paths (MFPs) of the overlying Intralipid phantom. The solid lines are power-law fits (along with 95% confidence intervals), and the error bars represent 95% confidence intervals for the mean of each measurement.
© Copyright Policy
Related In: Results  -  Collection

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

f4: Relative caffeine signal versus the number of mean free paths (MFPs) of the overlying Intralipid phantom. The solid lines are power-law fits (along with 95% confidence intervals), and the error bars represent 95% confidence intervals for the mean of each measurement.
Mentions: The magnitude of the caffeine signal versus the number of scattering mean free paths () of the overlying Intralipid phantom is plotted in Fig. 4. The signal is plotted on a relative scale, normalized by the signal strength of pure caffeine with a 0% Intralipid overlying layer. The absolute signal strength is not directly compared here because the specific instrument parameters (e.g., illumination power and sensor integration time) are not related to the signal attenuation rates, i.e., these parameters may be varied to increase or decrease absolute signal (or SNR) of either instrument, but not the attenuation rate. Power-law relationships between the MFPs of each phantom and the corresponding caffeine signal measured by each instrument were established by linear least-squares fitting of the logarithm-transformed data. Approximately 90% of the variance in the caffeine signal is described by these fits ( and 0.93 for the coded aperture and slit-based instruments, respectively).

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