Medical Imaging

Question 1

How do x rays work?

Answer 1

Single pulse of x rays which pass through the patient to the detectors, some are absorbed by the patient or scattered

Question 2

What is attenuation and what does it depend on?

Answer 2

• the reduction of intensity of the X-ray due to it being absorbed or scattered as it passes through matter
• depends on density + atomic number of tissue + energy of the x ray beam

Question 3

List materials on x rays from least to most dense

Answer 3

Air
Fat
Soft tissue
Bone
Metal

Question 4

What is the ABCDE approach of chest x rays?

Answer 4

Airways - trachea
Breathing - lungs
Circulation - heart, cardiothroacic ratio
Disability - bones
Everything else

Question 5

What is the ABDO X approach of an abdominal x ray?

Answer 5

Air
Bowel
Densitites
Organs
eXternal objects

Question 6

Outline the systematic interpretation of MSK X rays

Answer 6

• fractures: bone, part of bone, comminution, displacement, angulation
• bony abnormality: bone quality

Question 7

Advantages and disadvantages of x rays

Answer 7

Advantages:
- quick
- portable
- cheap
- simple
- good for bones

Disadvantages
- radiation (low)
- one plane, 2D
- cannot see all pathology
- poor soft tissue imaging

Question 8

What is fluoroscopy + what is it used to examine?

Answer 8

• Continuous/pulsed x rays which creates real time moving images (X-ray video)
• to examine anatomy, pathology, motion and function

Question 9

What contrasts are used for x rays and why?

Answer 9

• Barium + iodine
• high atomic number = good absorber of X rays = dense on image

Question 10

Advantages and disadvantages of fluoroscopy

Answer 10

Advantages
- real time > can assess function + carry out intervention
- quick

Disadvantages
- higher radiation dose than single x ray (pulsing continuous ray)
- radiation exposure to clinician
- one plane, 2D
- cannot see all pathology
- poor soft tissue imaging

Question 11

What is a CT scan?

Answer 11

• computed tomography
• multiple cross sections x ray snapshots of the patient taken in the axial plane to generate 3D images using detectors

Question 12

What does more positive vs more negative Hounsfield units HU tell you?

Answer 12

• more positive HU = more attenuating e.g. bones + metal
• more negative HU = less attenuating e.g. air + fat

Question 13

Advantages and disadvantages of CT scans

Answer 13

Advantages
- quick
- good resolution
- can scan most part of the body well

Disadvantages
- radiation
- not good for soft tissue
- affcted by artefact
- requires breath holding
- overuse
- contrast reactions

Question 14

Hypo- vs hyper dense structures in CT

Answer 14

• Hypo: dark > less dense e.g. oedema
• Hyper: bright > dense e.g. haemorrhage, calcifications

Question 15

Distinguish between acute vs chronic blood on a CT

Answer 15

• Acute: hyperdense due to clotting
• Chronic: hypodense due to clotting cleared > less dense + darker

Question 16

T1 v T2 weighting

Answer 16

T1: fat is bright, water is dark
T2: fat is bright, water is VERY bright

Question 17

Advantages and disadvantages of MRI

Answer 17

Advantages
- no radiation
- good contrast resolution especially with soft tissues

Disadvantages
- expensive
- time consuming
- contraindications e.g. pacemakers, claustrophobia
- contrast reactions
- fewer machines

Question 18

What is an MRI?

Answer 18

• magnetic resonance imaging
• uses a strong magnetic field + radio frequency pulse to generate signals > castes high resolution images

Question 19

What is an ultrasound?

Answer 19

High frequency sound waves are reflected off boundaries where different densities lie between tissue to create real time low resolution images

Question 20

What is a Doppler ultrasound used for?
Outline how

Answer 20

To assess blood flow in vessels
.
- if something is moving towards or way from the sound waves the frequency of echo waves if affected:
- towards soundwaves > increased frequency
- away from soundwaves > decreased frequency

Question 21

Advantages and disadvantages of an ultrasound

Answer 21

Advantages:
- lack of radiation
- low cost
- portable
- dynamic - movement

Disadvantages:
- operator dependant
- no bone or gas penetration
- difficult with obese or frail patients
- risk of overheating if misused

Question 22

What is a PET scan?
How does it work?

Answer 22

Positron emission tomography
- administration of radiopharmaceutical
- radionuclides (fluorine-18) emit positrons during decay
- emitted positrons collide with electrons
- annihilation gamma photons produced
- these are detected by gamma camera

Question 23

What radionuclide is typically used in PET scans?

Answer 23

Fluorine-18

Question 24

Advantages vs disadvantages to PET scans

Answer 24

Advantages
- early detection (before signs + symptoms present)
- early diagnosis
- lower radiation than CT

Disadvantages
- radiation
- false results in patients with chemical imbalance e.g diabetes, just eaten

Question 25

Clinical use of PET scan

Answer 25

• detection, staging + response of cancer
• early diagnosis of Alzheimer’s
• identification of poorly perfused myocardium

Question 26

What are the part of the radiopharmaceutical used in PET scans?
Function of each
What is most commonly used?

Answer 26

• pharmaceutical part: takes compound to tissue
• radionuclide part: sends signal from tissue
• 18F-Fluorodeoxyglucose