112 - Imaging of the Abdomen 1 Flashcards
What does absorption of X-ray beam depend on?
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- Thickness of tissue
- Density of tissue
- Atomic number of tissue (to 4th power)
Examples of low-atomic number components of a body, imaged on an X-ray
H, C, O
Why can’t cartilage be seen very well on an X-ray?
Not much calcium in it
How can natural differences in X-ray absorption be improved?
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1) Alter the absorption (introduce a radiographic contrast medium)
2) Measure the absorption by a more sensitive method (computer assisted tomography)
How can absorption be altered for an X-ray?
Barium meal (can be applied as an enema after giving a powerful laxative)
Examples of imaging of pancreatic duct and bile duct
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1) Endoscopic retrograde cholangio-pancreatography (ERCP).
Endoscope inserted, goes into ampulla from duodenum, injects radiodense fluid into it, which is then imaged.
2) PercutaneousTranshepaticCholangiography
Intravascular contrast medium
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1) Intravenous or intraarterial
2) Organic salts containing iodine (NW 53)
3) Distributed by blood vessels then excreted by kidneys.
Method of angiography
Use intravascular contrast medium, then X ray.
This can be injected, or applied using an endoscope threaded through the vasculature.
How could an intravascular contrast medium be used to image liver excretion of bilirubin?
Use an intravascular agent that is metabolised by the liver, excreted in bile
How does CT work?
Take several X-ray slices of part of interest, use computer software to combine these images to make a high-resolution, 3D image
Radioisotope imaging
Substances that emit radiation (almost always gamma rays), attached to a molecule (that targets to a particular organ).
Introduced to the body, usually IV.
EG: To image biliary system, attach to a molecule that behaves like bilirubin
Ultrasound
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1) Produces thin, sectional images using echoes returned from tissue interfaces.
2) Position of echo display derived from known speed of sound
3) No risk of ionising radiation
Why is gel placed on skin for an ultrasound?
To eliminate air, which will just reflect sound back into transducer.
Shadowing in an ultrasound
If an object is very echogenic, will produce an echogenic focus, and a shadow behind it.
More sophisticated ultrasound
Doppler ultrasound