1. Lecture 25 Review

2. Medical Optics and Lasers Application of optical methods to medicine Why optical methods? –Non-invasive –No side-effects –High resolution –Functional information –Real-time information –Cost effective –Portable

3. Medical Optics and Lasers Optical methods based on interactions of light with matter (biological sample) –Basic Principles –Absorption –Scattering Multiple scattering/Diffusion Single scattering –Fluorescence –Microscopy –Optical Coherence Tomography –Photodynamic therapy

4. Light as a wave Period time Monochromatic (only one wavelength/frequency) waves traveling in phase Monochromatic (only one wavelength/frequency) waves traveling out of phase Phase=  =  t-kz

5. Matter: Basic principles The basic unit of matter is the atom Atoms consist of a nucleus surrounded by electron(s) It is impossible to know exactly both the location and velocity of a particle at the same time Describe the probability of finding a particle within a given space in terms of a wave function, 

7. Particle in a box The particle confined in a one-dimensional box of length a, represents a simple case, with well-defined wavefunctions and corresponding energy levels n can be any positive integer, 1,2,3…, and represents the number of nodes (places where the wavefunction is zero) Only discrete energy levels are available to the particle in a box----energy is quantized

8. Atomic orbitals: Quantum numbers Principal quantum number, n –Has integral values of 1,2,3…… and is related to size and energy of the orbital Angular quantum number, l –Can have values of 0 to n-1 for each value of n and relates to the angular momentum of the electron in an orbital; it defines the shape of the orbital Magnetic quantum number, m l –Can have integral values between l and - l, including zero and relates to the orientation in space of the angular momentum. Electron spin quantum number, m s –This quantum number only has two values: ½ and –½ and relates to spin orientation

9. Molecular orbitals Molecular orbitals (chemical bonds) originate from the overlap of occupied atomic orbitals Bonding molecular orbitals –are lower in energy than corresponding atomic orbitals (stabilizes the molecule) Anti-bonding orbitals –are higher in energy than corresponding atomic orbitals and destabilizes the molecule  bonds –involve overlapping s and p orbitals along the line joining the nuclei of the bond-forming atoms  bonds –involve p and d orbitals overlapping above and below the line joining the nuclei of the bond-forming atoms

10. Hybrid orbitals and conjugated bonds The four 2p orbitals can combine to form these  orbitals, arranged according to energy, with the lowest energy  orbital at the bottom. Can you think of a set of wavefunctions that may describe what is going on? These are similar to the wavefunctions we got for a particle in the box, with the length of the box corresponding to the length of the carbon chain

11. Principles of laser operation Stimulated emission Population inversion Laser cavity –Main components –Gain and logarithmic losses –Two vs. three vs. four-level systems –Properties of laser light –Homojunction/heterojunction semiconductor lasers

12. Cell and Tissue basics Basic components of a cell –Nucleus –Mitochondria –Lysosomes –ER –Golgi Basic components of epithelial tissues –Types of epithelia –Connective tissue –Basement membrane

13. Light-tissue interactions scattering –elastic scattering multiple scattering absorption fluorescence single scattering Optical methods are based on different types of light-matter interactions to provide structural, biochemical, physiological and morphological information

14. Tissue optical properties There are two main tissue optical properties which characterize light-tissue interactions and determine therapeutic or diagnostic outcome: –Absorption coefficient:  a (cm -1 )  a =  a *N a =(A/L)*ln10  a =atomic absorption cross section (cm 2 ) N a =# of absorbing molecules/unit volume (cm -3 ) A=Absorbance L=sample length –Scattering coefficient:  s (cm -1 )  s =  s *Ns  s =atomic scattering cross section (cm 2 ) N s =# of scattering molecules/unit volume (cm -3 )

15. Tissue absorption Major tissue absorbers include: Hemoglobin, lipids (beta carotene), melanin, water, proteins Oxy and deoxy hemoglobin have distinct spectra. Optical measurements can provide information on tissue oxygenation, oxygen consumption, blood hemodynamics

16. Tissue scattering spectra exhibit a weak wavelength dependence Structural proteins constitute major tissue scattering centers. Cell nuclei and membrane rich organelles (e.g. mitochondria) also scatter light

17. Fluorescence spectra provide a rich source of information on tissue state NADH FAD Collagen Trp Protein expression Structural integrity Metabolic activity Courtesy of Nimmi Ramanujam, University of Wisconsin, Madison

18. Which optical method to use? Three main questions: –What is the required depth of penetration? –What is the acceptable resolution? –What type of information is needed?

19. 1 mm 1 cm10 cm Penetration depth (log) 1  m 10  m 100  m 1 mm Resolution (log) OCT Imaging methods 100 nm 100  m10  m1  m Standard microsc 4-Pi/STED Confocal/multi-photon microscopy Diffuse optical tomography and spectroscopy

20. Spectroscopic methods: Functional information Diffuse reflectance –Penetration depth: microns to centimeters depending on wavelength, souce/detector separation, light delivery/collection geometry –Resolution not well defined –Absorption Tissue oxygen saturation Arterial/venus oxygen saturation Oxygen consumption Hemodynamics –Scattering Structural changes of the matrix May be nuclear changes Light Scattering –Penetration depth: microns to hundreds of microns depending on how highly scattering is the sample –Inelastic scattering (Raman) Information: biochemical composition –Elastic scattering Information –Size distribution of major cell scattering centers (e.g. nuclei, mitochondria) –Cell/tissue organization Resolution –Potential to detect size changes on the order of 100 nanometers Fluorescence –Penetration depth: microns to centimeters depending on implementation, i.e. wavelength, sample optical properties, source/detector geometry –Endogenous fluorescence Cell and tissue biochemistry (NADH/FAD, tryptophan, porphyrins, oxidized lipids Tissue structure (collagen, elastin) –Induced fluorescent protein expression (molecular specificity) –Fluorescent tags Antibodies (antigen expression) Molecular beacons (enzyme activity)

21. Diffuse optical tomography and spectroscopy Applications –Breast cancer detection –Brain function –Oxygen consumption by muscles –Arthritis –atherosclerosis –Pulse oximeter –Jauntice (billirubin) test for neonates

22. Light scattering spectroscopy Cancer detection Detection of pre-cancerous changes –Barrett’s esophagus –Uterine cervix –Oral cancers Biopsy guidance Non-invasive patient monitoring

23. Optical coherence tomography Non-invasive detection of morphological changes Applications –Cancer detection –Eye diseases –Atherosclerosis –Developmental biology

24. Raman scattering Applications –Atherosclerosis –Cancer detection –Blood composition –Bacterial detection

25. Tissue fluorescence Applications –Cancer detection Pre-cancer detection Guide to biopsy Patient monitoring –Atherosclerosis detection –Bacterial infection (?)

26. Microscopy Cell microscopy –Understand basic cell functions in healthy and disease states –Understand role of specific proteins and cell component interactions Tissue/intravital microscopy –Understand cell matrix interactions that govern disease development, progression and regression Drug/therapy development and optimization Early detection

27. Multi-modality optical detection Goal: Acquire morphological and biochemical information to achieve more sensitive/specific detection Combined use of fluorescence, diffuse reflectance and light scattering Combined use of Raman and fluorescence Combined use of OCT and fluorescence Combined use of reflectance and fluorescence imaging

28. Photodynamic therapy Example of light-based therapeutic method Light used to achieve cytotoxicity Optical methods can also be used to tailor dosimetry to patient and monitor/predict therapeutic efficacy Used for treating a variety of conditions from cancer to acne to atherosclerosis

29. Optical methods are a powerful tool for understanding human health and improving disease detection and treatment 0246810 20 18 16 14 12 10 8 6 4 2 0 y (cm) x (cm)