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.
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
by measuring the transmitted x-ray
intensity through the slice
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I t I 0e
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.