Take-Home Final - What two facets of speckle imaging...

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What two facets of speckle imaging prevent measurement of absolute red blood cell velocity in practice? Light scattering from stationary tissue and difficulty in precisely measuring size/shape/spin of scattering particles are two facets of speckle imaging that prevent measurement of absolute red blood cell velocity in practice. a) What two phases of the heart are measured to determine ejection fraction? End-Diastole and End- Systole b) How could the images associated with these phases be selected from CTA data alone? To select the images for given phases, an intensity threshold can be applied to determine when the muscle in a ventricle is contracting in an image, and vice versa. c) What physiological feature of the heart makes segmentation of the left ventricle more difficult in one phase than the other? The ends of the left ventricle extend into the atrium. a) What characteristic of MR imaging renders direct application of absolute-intensity techniques not useful? Noise in the scanning process as well as asymmetry in tissue causes fluctuation in intensity during the MRI process, so a neural network is needed to take into consideration the inter-relationship between pixels of the entire image. b) What pre-processing step is commonly applied to MR images and why? Centering is a pre- processing step commonly applied to MR images because positions of an object will shift between images and the variation needs to be minimized by performing this centering. a) What common effect occurs at the borders of an object in digital images? Sharp change in pixilation values during digital quantization b) How could this be a problem for absolute pixel classifiers (i.e. pixel belongs to a single class)? Since absolute pixel classifiers absolutely must classify each pixel in one category or another, when it encounters an edge, it does not know how to classify the pixels lying on the front of a sharp change in pixilation. a) Name two factors affecting image quality with regards to bright-field microscopy cytology images. Non-homogenous background illumination from microscope light source and contrast/focus adjustment b) How could these effects be minimized? Background illumination can be corrected by finding normalized transmittance and then clipping it back into the image; image distortion can be minimized by adjusting contrast no farther than the point at which the image comes into focus.
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