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18 Cards in this Set

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What are the basic principals related to image reconstruction?
Algorithms
Fourier transform
Convolution
Interpolation
What is an algorithm? Which are applicable in CT?
An algorithm is a set of rules or directions for getting a specific outcome / result, from a specific input.
Back Projection
Iterative Methods
Analytic Methods
What is the Fourier Transform?
The Fourier Transform was developed by Baron Jean-Baptiste-Joeseph Fourier, used to reconstruct images of a patients anatomy in CT and MRI. It transforms a matematical function that converts signals, it divides waveform into a series of sine and cosine functions.
What is Convolution?
Convolution is a digital image processing technique to modify images through a filter function.
What is Interpolation?
Interpolation is a mathmatical technique used in CT to reconstruct and determine slices in helical / spiral CT imaging.
What is meant by a projection?
How are they obtained?
A set of rays is referred to as a projection. They can be obtained through both parallel and fan beam geometry.
What is Back Projection?
Back Projection is a simple procedure also referred to as "summation method" and "linear superimposition mehtod" explained best by a graphic or numeric approach.
It does not produce a sharp image. Star pattern artifact. Not used in clinical CT.
What causes the Star pattern artifact?
the Star pattern artifact occurs because points outside a high-density object recieve some of the back projected intensity of that object.
What are Iterative Methods?
Iterative Methods starts with an assumption, and the uses actual measuments to average to the two together to find a acceptable medium.
Different types include:
simultaneous iterative recon., interative least-squares tech.,alegebraic recon. tech.
What are Analytic Methods?
Analytic Methods help overcome the limitations of back projection and iterative algorithms. Ex.Fourier Transform algo. and filtered back-projection.
What is Filtered Back-Projection?
Filtered back-projection also referred to as the convolution method is used to remove/filter typical star like blurring seen on simple back projection
What is the Fourier Reconstruction Process?
Fourier Reconstruction Process is used in MRI, but not modern CT, it is easier to use simple back projected algorithms.
What are the four types of measurement data?
1. raw data
2. filtered raw data / convolved data
3. image data
4. reconstructed data
What is Measurement Data?
measurement data, or scan data, come from the detectors. subject to preprocessing to correct it before the reconstruction algorithm is applied. Errors need to be corrected, otherwise image quality is poor.
What is Raw Data?
Raw data is the result of preprocessed scan data and are subjected to reconstruction algorithms.
What is Convolved data?
The data that comes after the raw data is filtered through the conolution technique, which inproves image quality by reducing blur.
What is Image data?
Image data or reconstructed data are convolved data that have been back projected onto the image matrix to create CT images.
Of the analytic methods, which is used in modern CT?
Filtered Back Projection Algorithm