Computed Tomography References The Essential Physics of Medical Imaging 2 nd ed n. Bushberg J.T. et.al Computed Tomography 2 nd ed n : Seeram Physics of Radiology : Wolboarst A.B.

COMPUTED TOMOGRAPHY Invented by Godfrey Hounsfield in 1971 Won the Nobel Prize in Medicine in 1979 shared with Alan Cormack Alan Cormack developed the image reconstruction method in CT Radon developed the mathematical principles of CT in 1917

Computed Tomography Produces a cross sectional image of linear attenuation coefficients of a slice of tissue attenuation coefficients of a slice of tissue by measuring the transmitted x-ray intensity through the slice by measuring the transmitted x-ray intensity through the slice

Hounsfield Scanner 160 measurements during translation 180 angular positions Image size = 80x80 = 6400 unknowns Number of equations = 160x180=28800 Number of equations > Number of unknowns, Solution is possible

Tomographic Reconstruction Methods Filteredback Projection Method Direct Fourier Transform Method Iteration Method

Back Projection Method Projection elements are divided uniformly amongst pixels in projection path Non zero activity outside the true location of the object

Filtered Back Projection Acquire projection profiles at N projection angles Do 1D FT of each profile Filter each k space profile Inverse FT each filtered profile to obtain filtered profile in space domain Back project the filtered profile FBP is the most widely used reconstruction method in CT

Image reconstruction Filtered back projection of the data corresponding to a single slice produces the image of that slice. Repeating the above procedure for all slices gives the 3D image.