Computed Tomography Final Exa1

How many generations of CT Devices have there been? -8. What are the basic Principles of CT? -3D image of unknown object can be produced via multiple projections through the object. Which generation CT scanner is multiple source? -5th Generation. What is a Ray? -Single transmission measurement through patient made by a single detector at a given moment in time. What is a projection/view? -A series of ray that pass through patient at the same orientation. What are the two projection geometries used in CT imaging? -Parallel beam geometry: in which all rays in projection are parallel to one another. Fan beam geometry: in which the rays are at a given projection angle. What is the 1st Generation CT? -Pencil beam. rotate/translate. 2 X-Ray detectors. It has a parallel ray geometry. Translated linearly to acquire 160 rays across 24cm. Rotated slightly between translations to acquire 180 projections at 1-degree intervals. single source. What is the advantage of 1st generation CT? -There is no scatter. what is the disadvantage of 1st generation CT? -It is very slow. What is the purpose of CT scanner Hardware? -Acquire a large number of transmission measurements through the patient at different positions. How many rays are there on average in a CT image? -800. What direction is the table moved before acquisition of the next slice in a CT Scan? -Crainial-caudal direction. What is the 2nd Generation CT? -Narrow fan beam. Rotate/translate. linear array of 30 detectors. single source. What is the advantage of 2nd Generation CT? -Faster than 1st Gen. What is the disadvantage of 2nd Generation CT? -Low efficiency and more scatter detected due to the narrow fan beam. What is the 3rd Generation CT? -Rotate/Rotate. Wide fan beam. more than 800 detectors. single source. What are the benefits of 3rd Generation CT? -The need for rotation is eliminated due to the wide fan beam. X-Ray tube and detector are mechanically joined and rotate together. Faster scan times than 2G. What are the disadvantages of 3rd Generation CT? -High Cost Low Efficiency. Ring Artefacts. What are Ring artefacts? -The rotate/rotate geometry of the 3rd generation scanner which leads to a situation in which each detector is responsible for the ring in the image. Drift in singal levels of the detectors over time affect the values that are backprojected to produce a CT image, causing these artefacts. What is the 4th Generation CT? -Rotate/Stationary. It is designed to overcome ring artefacts. stationary ring of about 4800 detectors. single source. Advantage of 4th Gen CT? -High efficiency. Disadvantage of 4th Gen CT? -High scatter. What is at the apex of the 3rd generation CT fan beam geometry? -The X-Ray tube. What is at the apex of the 4th generation CT fan beam geometry? -The detector. What is 5th Generation CT used for? -cardiac tomographic imaging. What is the 5th Generation CT? -Stationary/stationary multiple source. Large arc of tungsten encircles the patient and lies opposite the detector, Electron beam is steered around the patient and strikes the annular tungsten target. can produce CT movies of the beating heart. No X-Ray tube. What is the advantage of 5th Gen CT? -Ultrafast for cardiac. What is the disadvantage of 5th Gen CT? -High Cost. What is the 6th Generation CT? -Helical They acquire data whilst the table is moving. Avoiding time required to move the patient table, total scan time is reduced. allows for use of less contrast agent.