Optical Absorption Contrast
Optical Absorption Contrast - Related Videos
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This protocol highlights the principles and practical applications of Phase and Differential Interference Contrast (DIC)...
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Optical-resolution photoacoustic microscopy (OR-PAM) is an emerging technology capable of imaging optical absorption contrasts in vivo with cellular resolution and sensitivity. Here, we provide a visualized instruction on the experimental protocols of OR-PAM, including system configuration, system alignment, typical in vivo experimental procedures, and functional imaging schemes.
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This video illustrates a method, using a clinical 3 T scanner, for contrast-enhanced MR imaging of the naïve mouse visual projection and for repetitive and longitudinal in vivo studies of optic nerve degeneration associated with acute optic nerve crush injury and chronic optic nerve degeneration in knock-out mice (p50KO).
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Drug Absorption: Factors Affecting GI Absorption
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2023
The process of oral drug absorption can be influenced by several factors. Weakly acidic drugs tend to be absorbed more readily from the stomach due to their nonionized state. However, absorption may be less efficient in the upper intestine, where drugs are often ionized. Interestingly, despite the stomach's apparent advantage for drug absorption, its mucous layer can hinder diffusion. Its surface area is also smaller than the intestine's, which can further slow down the absorption rate. In...
FAQs
Contrast depends on three linked variables: absorber concentration, optical path length, and wavelength. Greater concentration or a longer path causes stronger attenuation of incident light, while changing wavelength alters how strongly a molecule absorbs. Selecting wavelengths with different absorption properties therefore changes the measured signal and can help distinguish materials or tissue regions with different composition.
Selected wavelengths determine which absorbing molecules contribute most strongly to the measurement. Because absorption properties vary with wavelength, a wavelength choice can emphasize one material or tissue component relative to another. Comparing signals across appropriate wavelengths can therefore provide information about molecular composition or blood distribution rather than merely showing overall light intensity.
Photoacoustic imaging converts absorbed optical energy into a different detectable signal. A light pulse is absorbed locally, producing thermoelastic expansion that generates ultrasound waves. Detecting those waves links the measured response to where absorption occurred, whereas conventional optical measurements may rely on transmitted, reflected, or emitted light. This provides complementary structural and compositional information.
A typical measurement begins by illuminating the sample or tissue at selected wavelengths and recording the resulting transmitted, reflected, or emitted signal. The signal changes are then interpreted in relation to absorption, concentration, and path length. If photoacoustic detection is used, the system instead records ultrasound generated after pulsed absorption, enabling localized absorption measurements.
In bioengineering, these measurements are useful when noninvasive characterization of biological systems is needed. Optical and photoacoustic approaches can reveal tissue structure, blood distribution, and molecular composition. Their outputs support monitoring and diagnostic investigations, while photoacoustic detection adds information from localized absorption through the ultrasound signal generated after pulsed illumination.
For engineered tissues, absorption contrast can help evaluate how optical signals vary across a biological construct. Measurements may provide information related to tissue structure, blood distribution, or molecular composition, depending on the selected approach and wavelengths. This characterization supports monitoring of the construct and assessment of its biological organization without requiring invasive examination.