Diffuse Optical Tomography

Ishtiaque Ahmed and Jonathan McDonald

University of Minnesota

Methods of Experimental Physics Spring 2013

Introduction

Diffusive Optical Tomography is the imaging of solid objects within diffusive medium using electromagnetic waves. Many imaging device utilizes the tomographic properties of electromagnetic waves such as X-rays, MRI, PET scans. This high energy waves are highly penetrating and produce image of targets very accurately. Human body has 57% water by mass. High energy waves are highly absorbed in water. These highly absorbing waves possess great potential to cause harm to the tissue cells by damaging the DNA or causing mutation of cells which leads to cancer.

Unlike other medical imaging method, diffuse optical tomography uses waves of lower energy such as visible light to near infrared in electromagnetic spectrum. This range of waves has the least absorption properties in liquids (Fig 1). This makes diffuse optical tomography the optimal method compared to other scans like X-rays and MRI. In diffusive medium, electromagnetic wave undergoes scattering and absorption while interacting with the particles in the medium. The lower the energy of the wave, the lesser penetrating it is. Thus it undergoes more scattering and absorption in the medium then high energy waves. This makes it a challenge to image objects accurately in diffusive medium using

Results

Where the intensity at the surface of the medium, d is the depth of the medium and n is the separation distance from the LED and bottom of the bowl. We used a concentration of 0.5629 grams/ liter and calculated attenuation coefficient was 0.8079±0.0468. Setting the attenuation coefficient and integrating over a range of disk radii between 1 and 2 cm, we observed intensity spectrum between our experimental scan and the theoretical model at an attenuation coefficient of 0.80. The similarity was observed in a contour plot for normalized intensities versus distance from the origin in the x and y direction. From our experimental plot, we determined the radius of our disk to be 1.6±0.224 cm. Whereas our disk was 1cm in radius. Our calculated value was 2.67 away from our expected value.

Experimental scan that we achieved (not normalized).