Subject Code : EBME-410
Country : India
Assignment Task:

Task:

The report should consist of a text file containing answers to questions and images, as well as an electronic copy of your Matlab program suitable for execution by a course leader. We will spot check computer codes. If your program does not work, please tell us why you think it does not work. In this project you will generate simulated x-ray images and investigate the use of different energy spectra for medical imaging. Topics include x-ray energy imaging, pre-filtration effects, tube voltage (kVp) effect on image contrast and absorption dose calculation. We suggest that you use Matlab to create these images. A template Matlab program (TemplateProj1.m) is provided that contains useful functions with detailed descriptions. This Matlab routine reads data from the file signalImage.mat and displays two images. You should study and execute this program to learn some helpful Matlab commands. We have provided five ‘.mat’ data files. The files Spectrum_80KVp.mat and Spectrum_100KVp.mat contain the x-ray spectrum for 80KVp and 100KVp as a function of energy at 1.0 meter in photons/mAs-mm2 . The files muAl.mat, muBone.mat, and muTissue.mat contain the linear attenuation coefficients for aluminum, bone and soft tissue as a function of energy in mm-1 . Other data used in this problem are given below. Tube mAs: 10 mAs Filter thickness: 3 mm Aluminum filter Bone thickness: 5 cm Bone density: 0.16g/cm3 Tissue thickness: 20 cm Tissue density: 1.06g/cm3 Source to object distance: 100 cm Detector pixel size: 0.6 mm x 0.6 mm 1) Use the 80 KVp energy spectrum (Spectrum_80KVp.mat) for the items below.

a) Plot the unfiltered X-ray spectrum as a function of energy.

b) Filter the spectrum with a 3-mm aluminum spectral filter (muAl.mat) and plot the output spectrum. Compute the mean energy. Compare results to those in (a).

c) Pass the unfiltered spectrum through 20 cm of soft tissue (muTissue.mat) and plot the output spectrum. Compute the mean energy.

d) Pass the filtered spectrum through 20 cm of soft tissue (muTissue.mat) and plot the output spectrum. Compute the mean energy. Compare results to (c).

e) What is the effect of the aluminum filter? How does this relate to the role of beam hardening on patient dose?

2) Assume an ideal photon counting detector that detects regardless of energy and assume parallel xrays to avoid having to consider 1/R2 fall-off. Use the 80 KVp spectrum (Spectrum_80KVp.mat), aluminum filter, and a fluoroscopic imaging exposure (0.1 mAs per image frame).

a) Filter the spectrum with the aluminum filter. Pass the filtered spectrum through the imaging phantom (see below). Plot the spectrum after passing through a path consisting of soft tissue only. Plot the same spectrum after passing through a path consisting of soft tissue and bone. How do they compare?

b) Compute the intensities detected by the ideal detector by integrating the spectrum. Create an image without noise that will represent the mean x-ray intensity in photons per pixel. (Note that pixel size comes into play, per units above.) For display purposes, x-ray images are typically scaled to have a constant gray level. Scale the image to convert from photons per pixel to gray level so that the soft tissue has a pixel gray level of 128. Submit the image and a plot of a row of pixels through the center of the image.

3) Repeat problem 3 with a spectrum at 100 KVp and spectral filtration. Report results of all parts from problem 3, but in this case using 100 KVp. How do the results compare to those from question 3?

4) Calculate and compare the signal contrast in problems 3 and 4. Use the definition for contrast given below, where N is the pixel value calculated in questions 3c and 4c. Explain why the contrast for one is greater than the other.

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  • Posted on : October 05th, 2019

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