eceu692 subsurface imaging course notes part 3: imaging with light (2) hyperspectral imaging

January 2004 Chuck DiMarzio, Northeastern University 10471-3-1

ECEU692Subsurface Imaging

Course NotesPart 3: Imaging with Light (2)

Hyperspectral Imaging

Profs. Brooks and DiMarzio

Northeastern University

Spring 2004

January 2004 Chuck DiMarzio, Northeastern University 10471-3-2

Hyperspectral Imaging Concepts

• Absorption• Spectroscopy• Scattering• Reflectance

Spectroscopy• Imaging• Hyperspectral Imaging• The Data Cube

ER-2

AVIRIS

January 2004 Chuck DiMarzio, Northeastern University 10471-3-3

Beer’s Law

dzLzLdzzLdL

Ldz

dL

zeLL 0

January 2004 Chuck DiMarzio, Northeastern University 10471-3-4

Sample Absorption Spectra

Data from Van Assendelft, O. W., Spectrophotometry of Haemoglobin Derivatives, Springfield, IL: Thomas, 1970.

Graph by DiMarzio, Warner, Dwyer, Northeastern University, 1994

686

Hb

HbO2 aS

peci

fic

Abs

orpt

ion,

/cm

/M

, Wavelength, nm

January 2004 Chuck DiMarzio, Northeastern University 10471-3-5

Light in a Turbid Medium

• Specular Components– Fresnel Coefficients

– Beer’s Law

• Diffuse Components– More Complicated

• Some Examples– Paint

– Clouds

January 2004 Chuck DiMarzio, Northeastern University 10471-3-6

Reflectance Spectroscopy;Weak Scattering

January 2004 Chuck DiMarzio, Northeastern University 10471-3-7

A Simple Model

a(1)=C11(1)+ C22(1)

a(2)=C11(2)+ C22(2)

Two Measurements, Two Equations, and Two Unknowns

Later, Prof. Brooks will talk about inverting these equations

January 2004 Chuck DiMarzio, Northeastern University 10471-3-8

Reflectance Spectroscopy;Strong Scattering

No Hb

HbO2

Hb

January 2004 Chuck DiMarzio, Northeastern University 10471-3-9

Pulse Oximeter

• 2 LED’s– Different IR

Wavelengths

• DC Components– Total Hb, HbO2, Other

Absorbers

• Pulsatile Component– Arterial Hb, HbO2

January 2004 Chuck DiMarzio, Northeastern University 10471-3-10

Hyperspectral Imaging Overview• Definition (Multi-, Hyper, Ultra-Spectral)• The Data Cube• Image Acquisition Hardware, Data Visualization• HOSIS - Hyperspectral Oxygen Saturation

Imaging System: – CCD

– Lyot Filter

– Digital Imaging

January 2004 Chuck DiMarzio, Northeastern University 10471-3-11

Hyperspectral Imaging

• Definitions?– Imaging in multiple

bands with width less than (10%?) of the center frequency

– Imaging in more than (25?) bands

– Imaging in Contiguous Bands

x

y

The Hyperspectral“Data Cube”

January 2004 Chuck DiMarzio, Northeastern University 10471-3-12

Hyperspectral Imaging Hardware Concepts (1)

• Camera Coordinates are Spatial

• Successive Images are Different Wavelengths

TunableFilter

B/WCamera

x

y

January 2004 Chuck DiMarzio, Northeastern University 10471-3-13

Hyperspectral Imaging Hardware Concepts (2)

• Pushbroom Scan– Airborne or Vehicle Mounted?

– Camera Coordinates are y, – Successive Scans are Different

values of x

x

y

January 2004 Chuck DiMarzio, Northeastern University 10471-3-14

HOSIS Instrumentation Block Diagram

Computer System with Video Board

Processed Images

Tunable FilterSee SupplementaryNotes

CCD Camera

Halogen Lamp

Target Tissue

Thanks to Peter Dwyer atLucid Technologies, MGH, and NU

January 2004 Chuck DiMarzio, Northeastern University 10471-3-15

Quantitative Imaging

• Quantitative Calculations– Difficult

– Subject to Change

• Calibration Standards– Light Level

– Reflectance

DarkWhite

DarkTarget

R

• Sources of Variation– Light Source

– Camera Sensitivity

– Filter Losses

– Geometry

– Atmosphere?

– Other?