ECE380_Midterm1_Solution

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University of Illinois, Urbana Champaign *

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380

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Electrical Engineering

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Dec 6, 2023

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I/' ECE/BIOE 380 (Fall 2023) Biomedical Imaging Midterm Exam October 19, 2021 7:00 - 10:00 pm Closed book, closed notes, no formula sheets, conventional calculators allowed (not on a smart P.hone/tablet/comP.u~ ~~u:e_nt_N_am_e=~~ ~S::==o=~L::~u~~ = T:=1::0:,:~=: / ===- Problem 1 (40 points): Problem 2 (30 points): Problem 3 (20 points): Problem 4 (10 points): Problem 5 (10 points): Problem 6 (10 points): Problem 7 (12 points): Problem 8 (18 points): Total ( 150 points): I '

1. Circle the b t 1 ) (T e ~~ swer._ (2pts each question, 40 pts total) . ~e or~ A high k 0 _ 1 value indicates a wide point-spread-function and hence poorer spatial resolution. 2 ) (True o@ Fine details of an image tend to cluster near the center of the 2-D Fourier transform of the image. 3) ~ or False) In an x-ray tube , if the applied voltage is less than the k-shell binding energy of the target, then ka characteristic x-rays would not be generated. 4) ~ or False) Deeper tissues (with respect t_o x-ray source) are more susceptible to Comp ton scattering because of the beam hardenmg. 5) S or False) We inject iodine-based contrast for coro~ary arte~ exams because iodine increases x-ray attenuation and thus decrease the x-ray signal received by the detector. 6) Which of the following processes (select all that apply) involve ejection of electrons from the target atoms? a. Bremsstrahlung radiation @= haracteristic radiation c. Rayleigh scattering @): ompton scattering ("E)Photoelectric effect Y Pair production 7) (True or~ The overall system spatial resolution (or point spread function) 1s determine~e system component that has the narrowest/best PSF. 8) ~ or False) Increasing source x-ray energy is helpful for obese patients in the context of signal-to-noise-ratio because it compensates for the increased x-ray attenuation and casts more photons on the detector. 9) (True o~ To properly capture an image object with sinusoidal patterns (e.g., sine or cosine waves) and the smallest wavelength being 1 mm, the pixel or detector size of the imaging system should be at least I mm to avoid aliasing. 10) Which of the following factors influence the photoelectric effect? (select all that apply) @ Atomic number of tissue {3) X-ray energy c. Tissue density d. Electron density e. Mass attenuation coefficient 11) (True o~ Characteristic radiation only occurs when the K-shell electrons are ejected. 12) (True _or Q A higher density_ material or tissue always produces more Compton scattermg ~ hat of a lower density material. 13) fr~ r False) The reason why bone appears brighter than air in x-ray imaging is because ~ s higher x-ray attenuation. 2

14 ) O. r False) s ft · . . . ~ 0 tissue trans1t1ons from predominantly photoelectric effect to Compton hi h enng fa st er than does the bone with increased x-ray energy because soft tissue has g er electron density than bone. lS) ~ r False) The lower the HVL (half-layer value) of an x-ray source, the lower the x- ray energy. 16 ) (True o~ For screen film-based x-ray imaging systems, a thicker screen provides better spatial resolution because it converts more x-ray photons into visible ones. 17) The following factors result in a slower helical CT scan (select all that apply): (i) Low pitch number b. Large number of detector arrays (in z-axis) c. Large slice thickness ( or detector size in z-axis) d. Small field-of-view (FOV) in z-axis e. None of the above 18) (True ~ The fan-beam geometry requires less projections to be collected than does the par~m geometry because each projection angle encompasses a range of angles instead of only one. 19) (True o@ In CT, to avoid aliasing, one needs to reduce the step angle ti0 and increase the number of projections. 20) G r False) Backprojection generates blurred CT images because it under-samples the high-frequency range of the Fourier k-space. 2. Short answers (10 pts each, 30 pts total) 1) In two to three sentences, describe the tradeoff between x-ray energy and x-ray imaging quality. X-Y~ <?A'<?tr9~ t --;?.> qt. pJwio,._J A~eo( 1-> SNR. t x-~ (?,f\~~ t ~ Cr..r1n,. ~ieri"J 1 ➔ kb~ t J,es"~~ \I; , __ ifAj ~IK9'J t -> pl,-6,elec, t>.c. ~~~ ~ i 3

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