Optics 1&2- Biomedical imaging

Specular reflection, absorption, fluorescence, scattering

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• The breast is surrounded by optical sources and sensors
• High levels of scattering results in banana shaped sensing volumes
• Tomographic reconstruction is still possible and may detect the absorbers in the blood
• You can sense lesions in the breast by detecting increased haemoglobin

• Light does not penetrate through tissue but some may be scattered back to the surface
• 

Can also study brain activation by detecting absorption at two different wavelengths to detect blood volume

• Occurs due to changes in refractive index eg:
• Collagen fibrils
• Maromolecular aggregates
• Lysosomes
• Mittochondira Nuclei
• Cells

Rayleigh scattering 

Mie scattering

When the wavelength of light is Much larger than the size of particles

• scattering cross section σ is dependent on λ
•  σ = 1/ λ⁴
• 

• when wavelength of light is roughly the same as the size of particles
• 

• NIRS brain imaging
• Breast imaging

• 600-1100nm where haemoglobin absorption is low
• 
• With this you can take measruements at two wavelengths to see the relative conc of oxy and deoxy haemoglobin

Problem: scattering of liight makes accurate measurement difficult

Optical tomography but only for thin samples (<10mm).

Otherwise not a particularly realistic scenario

• Useful for photoplethysmography (pulse oximeter)
• Diffuse optical tomography

Absorption varies depending on the concentration of oxy and deoxy haemoglobin

Monitor wavelength at two wavelengths eg 650 and 900nm

• Since blood volume changes from heartbeat you can filter out the AC component etc
• Could use it to monitor heartbeat actually.

• 
• REMEMBER Y AXIS IS cm^-1
• Also the print is small so the y axis numbers are:
• 15000
• 5000
• 1000
• Then the ones towards the right go down in factors of ten
• It goes Electronic,vibrational,Rotational,Translational

Specular and diffuse reflection

• 
• High res
• Wide field of view (100 deg)
• Wide working range of distances
• Not too much chromatic aberration

Use narrow bands light instead of full white light spectrum

• 
• gamma is radiative decay rate
• K is non radiative decay rate

• 
• gamma is raidative decay rate
• K is non radiative decay rate

• White light illumination
• Narrow and illumination
• Fluorescence