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# AMATH 482-582 Homework 1 An ultrasound problem solved

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You dog fluffy swallowed a marble. The vet suspects that it has now worked its way into the intestines. Using
ultrasound, data is obtained concerning the spatial variations in a small area of the intestines where the marble
is suspected to be. Unfortunately, fluffy keeps moving and the internal fluid movement through the intestines
generates highly noisy data.

Do you want your dog to live? In order to save your dog’s life you must located and compute the trajectory
of the marble. Go to the class webpage and download: Testdata.mat. This containes 20 rows of data for 20
different measurements that were taken in time.

1. Through averaging of the spectrum, determine the frequency signature (center frequency) generated by
the marble.
2. Filter the data around the center frequency determined above in order to denoise the data and determine
the path of the marble. (use plot3 to plot the path once you have it)
3. Where should an intense acoustic wave be focused to breakup the marble at the 20th data measurement.
Good luck, and I hope your dog doesn’t die.

The following code will help you get started in analyzing the data. It also tells you the spatial and spectral
resolution of your ultrasound equipment. (NOTE: the reason for the close all command before isosurface is
that isosurface doesn’t seem to clear the previous imagine before plotting a new one)
clear all; close all; clc;

L=15; % spatial domain
n=64; % Fourier modes
x2=linspace(-L,L,n+1); x=x2(1:n); y=x; z=x;
k=(2*pi/(2*L))*[0:(n/2-1) -n/2:-1]; ks=fftshift(k);
[X,Y,Z]=meshgrid(x,y,z);
[Kx,Ky,Kz]=meshgrid(ks,ks,ks);
for j=1:20

Un(:,:,:)=reshape(Undata(j,:),n,n,n);
close all, isosurface(X,Y,Z,abs(Un),0.4)
axis([-20 20 -20 20 -20 20]), grid on, drawnow
pause(1)
end