112 - Imaging of the Abdomen 1

Question 1

What does absorption of X-ray beam depend on?
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Answer 1

• Thickness of tissue
• Density of tissue
• Atomic number of tissue (to 4th power)

Question 2

Examples of low-atomic number components of a body, imaged on an X-ray

Answer 2

H, C, O

Question 3

Why can’t cartilage be seen very well on an X-ray?

Answer 3

Not much calcium in it

Question 4

How can natural differences in X-ray absorption be improved?
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Answer 4

1) Alter the absorption (introduce a radiographic contrast medium)
2) Measure the absorption by a more sensitive method (computer assisted tomography)

Question 5

How can absorption be altered for an X-ray?

Answer 5

Barium meal (can be applied as an enema after giving a powerful laxative)

Question 6

Examples of imaging of pancreatic duct and bile duct
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Answer 6

1) Endoscopic retrograde cholangio-pancreatography (ERCP).
Endoscope inserted, goes into ampulla from duodenum, injects radiodense fluid into it, which is then imaged.

2) PercutaneousTranshepaticCholangiography

Question 7

Intravascular contrast medium
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Answer 7

1) Intravenous or intraarterial
2) Organic salts containing iodine (NW 53)
3) Distributed by blood vessels then excreted by kidneys.

Question 8

Method of angiography

Answer 8

Use intravascular contrast medium, then X ray.

This can be injected, or applied using an endoscope threaded through the vasculature.

Question 9

How could an intravascular contrast medium be used to image liver excretion of bilirubin?

Answer 9

Use an intravascular agent that is metabolised by the liver, excreted in bile

Question 10

How does CT work?

Answer 10

Take several X-ray slices of part of interest, use computer software to combine these images to make a high-resolution, 3D image

Question 11

Radioisotope imaging

Answer 11

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

Question 12

Ultrasound
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Answer 12

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

Question 13

Why is gel placed on skin for an ultrasound?

Answer 13

To eliminate air, which will just reflect sound back into transducer.

Question 14

Shadowing in an ultrasound

Answer 14

If an object is very echogenic, will produce an echogenic focus, and a shadow behind it.

Question 15

More sophisticated ultrasound

Answer 15

Doppler ultrasound

Question 16

Doppler ultrasound
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Answer 16

1) Use transducer to send a sound wave of a known wavelength into area of interest.
2) Measure Doppler shift of reflected wave, angle at which reflecting moving object is positioned relative to transducer.
3) From this can work out speed, direction of movement (EG: speed and direction of blood flow)

Question 17

MRI
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Answer 17

1) Patient placed in a strong magnetic field
2) Use pulses of altered magnetic field to induce momentary change in magnetism.
3) Detect resulting signal (radiowave frequency) and differences in signal from different tissues
4) Produces sectional images in any plane

Question 18

Tesla

Answer 18

Unit of magnetic strength.

1 Tesla = 10, 000 Gauss

Question 19

Earth’s magnetic field

Answer 19

0.5 Gauss

Question 20

MRI units

Answer 20

1.5 Tesla (~30, 000 times Earth’s magnetic field)