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

2. 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

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

17. 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

18. Tomographic Reconstruction Methods • Filteredback Projection Method • Direct Fourier Transform Method • Iteration Method

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

22. 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

23. 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.