Transcript Optimization of Phase Contrast Imaging

Optimization of Phase
Contrast Imaging
Luke Powers
Chris Weaver
Jonathan Fermo
Alfred Luk
BME 273, Group 22
04/06/2005
Phase-Contrast Radiography

Traditional radiography uses
differences in absorption to
develop images

Phase-contrast Radiography
(PC-R) uses differences in
refraction and diffraction of
the x-ray beam as it passes
through the object

Results in enhanced edge
effects in image compared to
those found in absorption
images
Objectives
 Build
a device that aids in testing Phase
Contrast Radiography parameters
 Computer controlled movement of the
object and detector
 Maintain high control accuracy in order
to pick up edges in tissue
PC-R Potential
 Edge
Enhancements
 Has
potential to detect objects that are
invisible on conventional radiography due
to edge enhancements in images.
 Monochromatic
 Tunable
to specific wavelengths
 Monochromatic beam reduces excess
radiation dosage to patient.
Spatial Coherence
λR1
d 
f
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Description of the divergence of a wave
Desire a very large spatial coherence (d):
decrease focal spot size (f)
increase source-object distance (R1)
Waves similar enough for interference patterns to
form when passing through edges of object
Edge Effects
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Waves near edges are
bent
Waves not touching or
passing through are not
affected
Edge enhancement
seen on film
Angle shift insignificant
at close distances
Producing Phase Contrast
z


I ( x )  I ( x ) z  0 1 
 " ( x) 
 2

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Image has two components: absorption and phase
Wavelength is tunable due to monochromatic source
Components functions of position
Goal is to divide out absorption
Absorption component  detector touching object
Magnification Effect
R 1  R2
Mag 
R1
z


I ( x )  I ( x ) z  0 1 
 " ( x) 
 2


Changing R1+R2
 Size of two images are not equal
 Scale images to account for magnification
 Most likely shrink I to Iabs for division
 Poor accuracy will result in production of false edges
Our Device
Main Uses:
• Optimizing distances for PC imaging of specific
objects/tissues
• Produce reproducible images
• Produce no false edge effects
• Images using scattering, defines pixel resolution
< 150 microns
Additional Uses:
• Rotational movement for CT images
Programming
 Inputs:
 LabView
GUI: positions, energy
 Outputs:
 Time/Date
 Image
#
 Angle and x, y, z positions
 Energy Used
Advisors

Advisors:
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Frank E. Carroll, M.D.
Gary Shearer
Robert Traeger
Principal Investigator:

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Edwin Donnelly, M.D.,
Ph.D. from Vanderbilt in
Biomedical Engineering
Facilities
 W.M.
Keck Free
Electron Laser
Center at
Vanderbilt
 Vanderbilt BME
Department
Resources

Monochromatic Xray source at FEL
 LabVIEW and
Virtual Instruments
 Stages, controllers,
etc… for design
construction
provided by FEL &
outside contractors
Design Schematic
-Detector has z-stage movement (1m)
-Object has x (6cm), y (5cm), rotational
(360 degrees) movement
Components
Selected Components
Microcontroller Linear Translation Stage (z)
Questions?