Introduction to Biophotonics for Medical Applications

Introduction to Biophotonics for Medical Applications

Summarized by:Name: AGNES Purwidyantri

Student ID No: D0228005

Biophotonics is the science of generating and harnessing light (photons) to image,

detect and manipulate biological materials

What is Biophotonics?

Optical Manipulation

TransfectionThe 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

Introduction to Optical Coherence Tomography (OCT)

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

8

Optical Coherence TomographyThree-dimensional imaging technique with

ultrahigh spatial resolution even in highly scattering media

Based on measurements of the reflected light from tissue discontinuitiese.g. the epidermis-dermis junction.

Based on interferometryinvolves interference between the reflected

light and the reference beam.

9

OCT vs. standard imaging

1 mm 1 cm 10 cm

Penetration depth (log)

1 mm

10 mm

100 mm

1 mm

Resolution (log)

OCTConfocalmicroscopy

Ultrasound

Standardclinical

Highfrequency

10

OCT in non-invasive diagnosticsOphthalmology

diagnosing retinal diseases.

Dermatologyskin diseases,early detection of skin

cancers.Cardio-vascular diseases

vulnerable plaque detection.

Endoscopy (fiber-optic devices)gastrology,…

Functional imagingDoppler OCT,spectroscopic OCT,optical properties,PS-OCT.

• Guided surgery– delicate procedures– brain surgery,

knee surgery, …

11

The OCT setup

Broadbandsource

Detector

Fiber-opticbeamsplitte

r

TissueScanningreference mirror

Computer

Amplifier Bandpass filter

12

Interference

- 6 - 4 - 2 0 2 4 6Dl@lD1

1.5

2

2.5

3

derusaeM

ytisnetni

- 6 - 4 - 2 0 2 4 6Dl@lD1

1.5

2

2.5

3

derusaeM

ytisnetni

Michelson interferometer

light source

Detector

Coherent source

Partially coherent source

13

Construction of image

14

Normal Eye

Nominal width of scan: 2.8 mm

250 micronsHumphrey

15

UHR-OCT versus commercial OCT

mm

mm

W. Drexler et al., “Ultrahigh-resolution ophthalmic optical coherencetomography”, Nature Medicine 7, 502-507 (2001)

16

System perspective

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

17

Choosing the light sourceFour primary considerations

wavelength,bandwidth,power (in a single-transverse-mode),stability;

portability, ease-of-use, etc.

18

Choose light source – wavelength

Light propagation (Monte Carlo simulation)

Incident light

Ballistic component

“Snake” component

Diffuse reflectance

Absorption

Diffuse transmittance

19

Ultra-high resolution OCTBroad 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 opticsaberrations can decrease resolution and SNR.Broad bandwidth detectors and electronics

dual balance detection, low noise circuitry necessary.

20

Scanning devicesPiezo or motorized scanning devices

ideal for both longitudinal and lateral scanning.Galvanic mirrorsResonance scannersHelical mirrors

longitudinal scanning.Fiber stretcher

longitudinal scanning.

21

RSOD (Rapid Scanning Optical Delay line) setup

22

RSOD in the lab

Peter E. Andersen, Optics and Plasma Research Department

23

Clinically adapted systems

24

BCC II

LayersThinning of

layers

L. K. Jensen, MSc thesis (in Danish), 2003 [data obtained atLund Medical Laser Centre, courtesy K. Svanberg].

25

OCT: Figures-of-merit – summaryDynamic 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 decoupledimportant for

applications.

Pixel density is related to spatial resolution and image acquisition timeNz=2*Lz/dz,Nx=2*Lx/dx,image acq. time:

T=Nx*fs,scan velocity: vs=Lz*fs.

Image acquisitionseconds or less,real-time OCT.

Clinical adaptationinterfaced to standard

equipment,fiber-optic devices,endoscopes.

Thank You