Homework #3

BME 424/BME 526 Bioimaging Homework #3 (25 points) Due Wednesday, February 15, 2017 To be completed individually, but collaboration is allowed (no copying or cheating)! (a) (b) 1. (25%) Two x-ray images of the hand are shown here. One corresponds to an x-ray beam with an effective energy of 140 keV and the other to an effective energy of 50 keV. Explain which is which and the reasons for the differences in image contrast and signal intensity. Note that the gray scale value of one image has been adjusted (because the author of the book is a jerk and wanted to confuse you); pay attention to local contrast of the hand. 2. (25%) The width of the electron beam in an x-ray tube is 6 mm, and the anode bevel angle is 10°. The patient is placed 180 cm from the x-ray tube, directly on top of the flat panel detector. Calculate the geometric unsharpness for a very small lesion at the front of the abdomen and at the back of the abdomen, assuming that the tissue thickness of the body at this point is 25 cm. 1 2 3 3. (25%) Calculate x-ray intensity, as a function of the incident intensity, I0, that reaches the detector for each of X-rays the three x-ray beams shown in the figure. The darkshaded area represents bone, and the light-shaded area 1 cm represents tissue. The linear attenuation coefficients at the -1 -1 effective x-ray energy of 68 keV are 10 cm and 1 cm for 1 cm bone and tissue, respectively. 1 cm 1 cm detector 4. (25%) Shown below are three CT images: one represents the reconstructed image with no filtering, one has been high-pass filtered, and the other has been low-pass filtered. For each image, state which form of filtering has been used. State the effects on signal to noise ratio, spatial resolution, and contrast to noise. Match each image to one of the spread functions.

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