Medical Imaging: X-rays to CT Zach Simmons UST Physics

History X-Rays: Wilhelm Conrad Röntgen, 1895 –Medical applications immediately apparent –Safety concerns not immediately apparent –Basically remained unchanged until CT Computerized Tomography (CT) : first practical realization appeared in the 1970’s First commercial CT scanner: invented in 1971 by Godfrey Hounsfield, thanks to EMI and the Beatles

X-Rays: Bremsstrahlung anode cathode

OK, so: Different types of tissue attenuate x-rays at different rates, causing there to be contrast in intensity transmitted to the resulting image depending on the tissue –Beer’s law: –Some example attenuation coefficients: µ air =0, µ bone =.48/cm, µ muscle =.180/cm -to give you an idea: about 40% attenuation in 1cm of bone

X-Ray Radiography Projection of a 3D person onto a 2D film

CT Scanner

CT (Computerized Tomography) is where it gets interesting: -Yields slices, instead of a “shadow” -This is the simplest scanning configuration; there’s lots more complicated geometries and this isn’t how modern CT scanners work.

Projections:

Some Math:

But wait there’s more:

Improvements/other: 1980’s Spiral CT and different geometries Fluoroscopy Higher resolution Faster scans also improves quality 3-D image reconstruction 3-D image reconstruction

Questions?

Sources: Books: Cho, Z.H. Foundations of Medical Imaging, New York: John Wiley & Sons, Inc Webb, S. Ed. The physics of Medical Imaging, New York: Adam Hilger, Pics: Slide 1: Slide 3: Slide 5: Slide 6: Slide 7: Webb, p Slide 8: Webb, p.107 Slide 12: