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Measuring the Attenuation Coefficient of Biological Materials

Measuring the Attenuation Coefficient of Biological Materials. Sarah DeLeo Kyle Gautreaux Shreya Purohit Eric Richard. Introductions. Many uses for medical physics Radiation therapy, x-ray imaging, etc. Attenuation occurs when photons pass through a material.

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Measuring the Attenuation Coefficient of Biological Materials

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  1. Measuring the Attenuation Coefficient of Biological Materials Sarah DeLeo Kyle Gautreaux Shreya Purohit Eric Richard

  2. Introductions • Many uses for medical physics • Radiation therapy, x-ray imaging, etc. • Attenuation occurs when photons pass through a material. • This value can change as the thickness and density of different materials change. • When plotted on a graph, (charge vs. thickness) the attenuation coefficient can be found based on the slope of the line.

  3. Purpose: • The purpose of this experiment was to find the attenuation coefficient of a biological material. • Materials tested: • Polymethyl methacrylate – PMMA (plexiglass) • This was used to simulate water • Bone (synthetic)

  4. Procedure

  5. CAMD Equipment Synchrotron Beam line

  6. CAMD Equipment Beam line schematic, with multiple gates for control. “Hutches”

  7. Experiment Setup • Plates of plexiglass were setup vertically on a stage • This allows the materials being tested to move in and out of the beam current • The readings are being taken by an ionization chamber, housed inside a plexiglass plate • The experiment was run several times for plates of different thicknesses until a desired depth was obtained

  8. Experimental Setup • Experiment was repeated for thicknesses of synthetic bone • The Ionization chamber then measures charge differential created by the induced current within the chamber.

  9. Experimental Setup • An Electrometer is used to measure the difference in electrical charge within the ionization chamber. • Computer uses LabU program to control the stage height and the number of times the sample is passed through the photon current

  10. Results

  11. Figure 1: Charge (10-8 Coulombs) vs. Penetration Depth in Plexiglass (polymethyl methacrylate – PMMA). The exponential trend line shows the exponential decay of charge with increasing penetration. Attenuation (absorbtion) coefficient (µ) can be off the formula to be .2181 (1/cm). • Density = 1.184756 g/cm3 • µ/ρ = 0.184089 cm2/g

  12. Figure 2: Charge (10-8 Coulombs) vs. Penetration Depth in synthetic bone. The exponential trend line shows the exponential decay of charge with increasing penetration. Attenuation (absorbtion) coefficient (µ) can be off the formula to be .7509 (1/cm).

  13. Conclusion • µ Plexiglass = .2181 (1/cm) • µ Synthetic Bone = .7509 (1/cm) • The mass attenuation coefficient of the plexiglass was calculated by dividing the density of the plexiglass and compared to the calculated value on the NIST website. The numbers did not correlate exactly but there were multiple factors of error that contributed to this inaccuracy. • http://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/pmma.html

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