Summarized by: Name: AGNES Purwidyantri Student ID No: D

Biophotonics is the science of generating and harnessing light (photons) to image, detect and manipulate biological materials What is Biophotonics?

Optical Manipulation

Transfection The transfer of exogenous DNA into a cell

Femtosecond Laser Mediated Cell Membrane Poration Photoporation: the use of light to permeabilise cells. First inspired from a Tirlapur and Konig, Nature 2002: Used a near-infrared, femtosecond-pulsed laser beam (λ 800 nm) from an 80-MHz titanium–sapphire laser, with a mean power of 50–100 mW and tightly focused using a high-numerical-aperture objective

Linear Fluorescence Microscopy

OPTICAL BIOPSY: The in situ imaging of tissue microstructure with a resolution approaching that of histology, but without the need for tissue excision and processing

Optical Coherence Tomography Three-dimensional imaging technique with ultrahigh spatial resolution even in highly scattering media Based on measurements of the reflected light from tissue discontinuities e.g. the epidermis-dermis junction. Based on interferometry involves interference between the reflected light and the reference beam. 8

OCT vs. standard imaging 9 1 mm1 cm10 cm Penetration depth (log) 1  m 10  m 100  m 1 mm Resolution (log) OCT Confocal microscopy Ultrasound Standard clinical High frequency

OCT in non-invasive diagnostics Ophthalmology diagnosing retinal diseases. Dermatology skin diseases, early detection of skin cancers. Cardio-vascular diseases vulnerable plaque detection. Endoscopy (fiber-optic devices) gastrology, … Functional imaging Doppler OCT, spectroscopic OCT, optical properties, PS-OCT. 10 Guided surgery – delicate procedures – brain surgery,  knee surgery,  …

The OCT setup 11 Broadband source Detector Fiber-optic beamsplitter Tissue Scanning reference mirror Computer Amplifier Bandpass filter

Interference 12 Michelson interferometer light source Detector Coherent source Partially coherent source

Construction of image 13

Normal Eye 14 Nominal width of scan: 2.8 mm 250 microns Humphrey

UHR-OCT versus commercial OCT 15 W. Drexler et al., “Ultrahigh-resolution ophthalmic optical coherence tomography”, Nature Medicine 7, (2001)

System perspective 16 OCT imaging engine Resolution Reference delay scanning Doppler/polarization/spectroscopy Detection Frequency domain Light sources Superluminescent diodes Semiconductor amplifiers Femtosecond lasers … Beam delivery and probes Hand-held probe Catheter Ophthalmoscope Microscope Image & signal processing Motion reduction Speckle reduction Image enhancement Rendering algorithms … Computer control Drive system Real-time display Data management

Choosing the light source Four primary considerations wavelength, bandwidth, power (in a single-transverse-mode), stability; portability, ease-of-use, etc. 17

Choose light source – wavelength Light propagation (Monte Carlo simulation) 18 Incident light Ballistic component “Snake” component Diffuse reflectance Absorption Diffuse transmittance

Ultra-high resolution OCT Broad bandwidth sources solid-state lasers, sub-5 fs pulse; Ti:Al2O3 (Spectral bandwidth: 350 nm demonstrated), other lasers/wavelengths available or needed. Special interferometers and fiber optics support for broad spectral range, dispersion balanced, current system used for OCT: 260 nm bandwidth, ~1.5µm resolution. Chromatically corrected optics aberrations can decrease resolution and SNR. Broad bandwidth detectors and electronics dual balance detection, low noise circuitry necessary. 19

Scanning devices Piezo or motorized scanning devices ideal for both longitudinal and lateral scanning. Galvanic mirrors Resonance scanners Helical mirrors longitudinal scanning. Fiber stretcher longitudinal scanning. 20

RSOD (Rapid Scanning Optical Delay line) setup 21

RSOD in the lab Peter E. Andersen, Optics and Plasma Research Department 22

Clinically adapted systems 23

BCC II Layers Thinning of layers 24 L. K. Jensen, MSc thesis (in Danish), 2003 [data obtained at Lund Medical Laser Centre, courtesy K. Svanberg].

OCT: Figures-of-merit – summary Dynamic range 100 dB (or better). Resolution (typical) 1-10 micrometers. Penetration depth depending on wavelength/tissue, 1-2 mm (typically) for 1300 nm in skin tissue. Axial and lateral resolutions are decoupled important for applications. Pixel density is related to spatial resolution and image acquisition time N z =2*L z /dz, N x =2*L x /dx, image acq. time: T=N x *f s, scan velocity: v s =L z *f s. Image acquisition seconds or less, real-time OCT. Clinical adaptation interfaced to standard equipment, fiber-optic devices, endoscopes. 25

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