Abdomen

Question 1

Absorption of an X-ray beam in tissues depends on

Answer 1

• thickness of tissue
• density of tissue
• atomic number of tissue to the 4th power
  
  • also applies to contrast
  • powerful influence - changes appearance of what we see

Question 2

What can be differentiated on X-ray?

Answer 2

• air
• fat (a little bit, doesn’t absorb X-rays quite as well)
• soft tissues, muscle, liver, fluids
• bone

Question 3

What is Percutaneous Transhepatic Cholangiography?

Answer 3

• contrast directly introduced into bile ducts through a needle
• real-time X-ray

Question 4

How is intravacular contrast administered?

Answer 4

intravenous or intra-arterial

organic salts containing iodine (53)

Question 5

What is a voxel?

Answer 5

pixel + volume; 3D rendering of the data

Question 6

What are radioisotopes?

Answer 6

• emit gamma rays
  
  • need a special detector
• they are attached to an isotope (most often technicium) that targets an organ
  
  • eg taken up in bones by osteoblasts, excreted like bilirubin
• normally given intravenously - path recorded by gamma rays emitted

Question 7

What is ultrasound?

Answer 7

• high frequency sound, short wavelength
  
  • ~300m cycles per second
  • tf sound doesn’t go very far, behaves differently than the sounds we hear that project further
    
    • eg we hear low frequencies at long distances, they go further
• produce thin sectional images using echoes bounced back from tissue interfaces
  
  • position is worked out by speed of sound in tissue

Question 8

Ultrasound cannot look through

Answer 8

lung, bone

due to shadowing (all of the sound is reflected back)

Question 9

What is the Doppler effect?

Answer 9

perceived change in frequency of waves when there is relative movement between source of wave and observer of wave

Question 10

Doppler ultrasound allows us to look at

Answer 10

blood flow velocity

Question 11

How is the velocity of blood flow determined?

Answer 11

angle of flow relative to the angle of soundbeam (from transudcer)

Question 12

How does MRI work?

Answer 12

• pt placed in a strong magnetic field (0.3-3.0 Tesla, 1 Tesla = 10 000 Gauss)
• uses pulses of altered magnetic field/in a different direction to induce momentary changes in magnetism in the body
• turn off pulses
• listen for signals coming back (in the radiowave frequency)
• can display tissue as slices (similar to CT)
• based on how magnetism in the body is altered

Question 13

On the electromagnetic spectrum, X-rays are

Answer 13

short wavelength & high energy

between UV and gamma rays