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Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis
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Computerised axial tomography
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis What does CAT stand for? Computerised axial tomography Basically, X-ray machines are used to take images from various viewpoints to build up a slice of the body
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Case 1 - Normal CT Scan:
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Case 2 - Acute Subdural Haematoma Demonstrating Midline Shift:
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Invented by Godfrey Hounsfield
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis Invented by Godfrey Hounsfield Tested it on a fresh cow brain in the late 1960s First used medically in 1971 Won 1979 Nobel prize for physiology or medicine
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Be able to describe how an image is constructed by a CAT scan
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis
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Early scanners took 10-15 minutes to image each slice
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis Early scanners took minutes to image each slice Modern machines can collect the data in a few seconds
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Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis In action…
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Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis How is the image formed?
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The fan is very thin so that a small slice is imaged each time
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis cross-section of patient detector X-rays X-ray tube collimator Produces a fan-shaped beam of X-rays The fan is very thin so that a small slice is imaged each time
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Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis The dark and light patches are due to the amount of X-ray attenuation occurring The detectors in CT scanners are much more sensitive to changes in the amount of attenuation than photographic film
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For CT scanners the amount of attenuation is measured in Hounsfield Units
The Hounsfield Scale
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CT Image Construction Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis The numbers represent how much attenuation is occurring (units arbitrary) a d b e c f 5 7 11
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Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis a d b e c f 3 4 9 7
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Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis Another way to look at this is to consider the amount of energy being absorbed Input energy of 50 units 15 25 10 Have a go at question 2, page 208
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Doctors are able to rotate the images and view from different angles
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis 3-D images A computer is able to take all of the images of the slices for a scan and construct a 3D image. Doctors are able to rotate the images and view from different angles
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Be able to describe how an image is constructed by a CAT scan
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis
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Be able to describe how an image is constructed by a CAT scan
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis
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Be able to describe how an image is constructed by a CAT scan
Learning Objectives By the end of this lesson you should… Be able to describe the operation of a CAT scanner Be able to describe how an image is constructed by a CAT scan Know the advantages of using CAT scans for diagnosis
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