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Biosignal and Biomedical Image Processing phần 11

Tham khảo tài liệu 'biosignal and biomedical image processing phần 11', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 388 Chapter 13 Q Reconstruct image using Ram-Lak filter I_RamLak iradon p delta_theta Ram-Lak Q. .Display images. Radon and Inverse Radon Transform Fan Beam Geometry The MATLAB routines for performing the Radon and inverse Radon transform using fan beam geometry are termed fanbeam and ifanbeam respectively and have the form fan fanbeam I D where I is the input image and D is a scalar that specifies the distance between the beam vertex and the center of rotation of the beams. The output fan is a matrix containing the fan bean projection profiles where each column contains the sensor samples at one rotation angle. It is assumed that the sensors have a one-deg. spacing and the rotation angles are spaced equally over 0 to 359 deg. A number of optional input variables specify different geometries sensor spacing and rotation increments. The inverse Radon transform for fan beam projections is specified as I ifanbeam fan D Figure 13.9 Original MR image and reconstructed images using the inverse Radon transform with the Ram-Lak derivative and the cosine filter. The cosine filter s lowpass cutoff has been modified by setting its maximum relative frequency to 0.4. The Ram-Lak reconstruction is not as sharp as the original image and sharpness is reduced further by the cosine filter with its lowered bandwidth. Original image from the MATLAB Image Processing Toolbox. Copyright 19932003 The Math Works Inc. Reprinted with permission. Copyright Marcel Dekker Inc. All rights reserved. Marcel Dekker Inc. 270 Madison Avenue New York New York 10016 TLFeBOOK Image Reconstruction 389 where fan is the matrix of projections and D is the distance between beam vertex and the center of rotation. The output I is the reconstructed image. Again there are a number of optional input arguments specifying the same type of information as in fanbeam. This routine first converts the fan beam geometry into a parallel geometry then applies filtered back-projection as in iradon. During the filtered .