Optimization of Phase Contrast Imaging

Luke PowersChris Weaver

Jonathan FermoAlfred Luk

BME 273, Group 2204/06/2005

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

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

f

λRd

1

Edge Effects

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

)("

21)()( 0 x

zxIxI z

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

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

1

21

R

RRM

ag

)("

21)()( 0 x

zxIxI z

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, energyOutputs:

Time/Date Image # Angle and x, y, z positions Energy Used

Advisors Advisors:

Frank E. Carroll, M.D. Gary Shearer Robert Traeger

Principal Investigator: Edwin Donnelly, M.D., Ph.D. from Vanderbilt in

Biomedical Engineering

FacilitiesW.M. Keck Free

Electron Laser Center at Vanderbilt

Vanderbilt BME Department

Resources Monochromatic X-

ray 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?