Medical Imaging

Question 1

Main difference between X-ray and fluoroscopy

Answer 1

X-ray: single pulse of X-rays with one imagine created
Fluoroscopy : continuous/pulsed X-rays with real time moving images created

Question 2

Explain how you produce an image using X-rays (4)

Answer 2

1. Electrons accelerated towards a metal target and interaction with the metal produces photons (x-rays)
2. Some X-rays pass through the patient to a detector
3. Some are attenuated (absorbed,scattered,lose energy) as they pass through - appear brighter on an X-ray e.g bone, metal
4. Detected imagine digitised and process then uploaded to PACS

Question 3

What does the attenuation in X-rays depend on? (2)

Answer 3

Density and atomic number of tissue/material - e.g. bone attenuates X-rays more than soft tissues
Energy of the X-ray beam

Question 4

View of materials on an X-ray

Answer 4

Air = black = no attenuation
Fat = dark grey = some attenuation
Soft tissue = grey
Bone = very light grey = less X-rays are hitting detector
Metal = white = most X-rays attenuated

Question 5

Systematic analysis to approach a chest X-ray

Answer 5

A - airways, is everything in the right place?
B - breathing - left and right lung same size?
C - circulation - normal size heart, correct border between heart and lungs?
D - disability - any bone fractures or metastasis?
E - everything else - breast shadow, gastric bubble

Question 6

Systemic analysis approach to interpret an AXR (abdominal x-ray)

Answer 6

A- air - normal bowel gas pattern, no loops or air outside of bowel
B - bowel - small and large bowel
D - densities - bones, strones, tubes
O - organs - liver, spleen, kidneys, bladder

Question 7

Clinical use of X-rays

Answer 7

Chest - shortness of breath, infection, tube positioning, cancer
Abdomen - pain, bowels not opening, obstruction ]
MSK - trauma, pain, swelling, fracture, dislocation, infection

Question 8

4 advantages of X-rays

Answer 8

Quick
Portable
Cheap
Simple

Question 9

4 disadvantages of X-rays

Answer 9

Radiation (relatively low)
One plane, 2D
Cannot see all pathology
Poor soft tissue imaging

Question 10

Process of fluoroscopy X-rays

Answer 10

Process similar to normal X-rays but pulsed or continuous X-ray used, creating moving images

Question 11

How are fluoroscopy images enhanced?

Answer 11

Using contrast - usually barium/iodine
High atomic number = good X-ray absorber = dense on image

Question 12

4 clinical uses of fluoroscopy

Answer 12

Vascular/angiography
GI
GU
MSK - joint injections, orthopaedic surgery ( surgeons can see where placing metal work)

Question 13

2 advantages of fluoroscopy

Answer 13

Dynamic studies in real time - assess function or carry out intervention
Quick (using X-rays)

Question 14

5 disadvantages of fluoroscopy

Answer 14

Higher radiation dose than single X-ray
Radiation exposure to clinical e.g. hand is close to area of patient, X-rays reflect and hit
One plane, 2D
Cannot see all pathology
Poor soft tissue imaging

Question 15

How do computed tomography (CT) scans work?

Answer 15

X-rays produced as described earlier
X-ray tube on one side of a rotating gantry, and detectors on the opposite side
Patient table moves through gantry
Same principle of X-ray attenuation
Cross sectional slices of patient imaged and detected signal processed by computer to make cross sectional images

Question 16

3 clinical uses of CT

Answer 16

Diagnosis/ guiding further investigation/ management
Directly guiding and intervention - radiotherapy
Monitor conditions - cancer treatments, intestinal lung disease

Question 17

3 advantages of CT scan

Answer 17

Quick
Good spatial resolution
Can scan most part of the body well

Question 18

8 disadvantages of CT scan

Answer 18

Radiation
Lower contrast resolution
Not best for some areas e.g. Gynae
Affected by artefact e.g. patient moves, has metal in them
Requires holding breath
Overuse
Incidental findings
Contrast reactions

Question 19

Explain how PET works

Answer 19

1. Radionucleotide emit positrons during decay (positron emission)
2. Emitted positrons collide with nearby electrons in patient (annihilation)
3. two annihilation gamma photons are produced, which are detected by gamma camera

Question 20

How are radionucleotides administered?

Answer 20

Taken into the tissue by the pharmaceutical and the radionuclide creates the image. Radionuclide decays in tissues and emits gamma radiation,detected by gamma camera

Question 21

What does the gamma camera do in PET?

Answer 21

Contains a scintillator which converts signal into light, then this light is amplified and processed by computers to produce images

Question 22

Common pharmaceutical used in PET

Answer 22

Flurorodeoxyglucose - glucose analogue so taken up by areas of high glucose metabolism e.g tumours

Question 23

4 clinical uses of PET

Answer 23

Oncology - detection, staging, response to treatment
Neurological
Cardiac
Infection/inflammation

Question 24

2 advantages of PET

Answer 24

Good contrast and spatial resolution
Can analyse anatomy and function

Question 25

5 disadvantages of PET

Answer 25

Physiological uptake of radiopharmaceutical - some tissues take up glucose anyway
Radiation dose to patient
Risk of radiation to others e.g. no public transport after PET
Radioactive waste produced
Very expensive and time consuming`

Question 26

Explain how magnetic resonance imaging works (MRI)

Answer 26

1. Patient placed in strong magnetic field which aligns the hydrogen ions longitudinally
2. Radio frequency pulse applied to patient, ‘tipping’ hydrogen atoms
3. This creates a detectable magnetic field perpendicular to main MRI magnetic field, which induces electric current in nearby coils
4. Signal processed to create images

Question 27

How is the contrast in MRI images produced?

Answer 27

Hydrogen atoms relax back into alignment with the longitudinal magnetic field of MRI magnet
Contrast is due to different relaxation times of hydrogen atoms in different tissues as there is a difference in signal strength

Question 28

Clinical uses of MRI

Answer 28

Good for imaging of: CNS, bones and joins, soft tissue lesions , heart and blood vessels, gynaecological tumours
In paediatrics/pregnancy to avoid radiation from CT

Question 29

2 advantages of MRI

Answer 29

No radiation
Good contrast resolution, especially of soft tissues

Question 30

6 disadvantages of MRI

Answer 30

Expensive
Time consuming
Fewer machines, fewer radiographers
Contradictions : claustrophobia, lack of mental capacity
Contrast reaction

Question 31

How does ultrasound work?

Answer 31

Crystal in transducer oscillates, creating high frequency sound waves
Sound waves travel through tissues and are reflected back at boundaries between tissues of different densities (acoustic impedance mismatch)
Probe detects reflected sound waves and converts them into electrical signal, creating images

Question 32

How do you calculate how deep a tissue is in ultrasound?

Answer 32

Time taken for echo to return

Question 33

Hyperechoic and hypoechoic in ultrasound

Answer 33

Hyperechoic = more reflection = white on image
Hypoechoic = less reflection = dark on image

Question 34

What is acoustic shadowing?

Answer 34

Sound waves completely reflected back so none pass through to tissue below, creating a shadow and leaving behind a dark area

Question 35

What is Doppler ultrasound?

Answer 35

If something is moving towards or away from sound wave e.g. blood flow in vessels
Moving towards sound waves : increased frequency of echo wave
Moving away from sound waves : decreased frequency of echo wave

Question 36

5 clinical uses of ultrasound

Answer 36

Solid organs - tissue, masses, bleeding
Hollow structures - tubes, ducts, bladders, chambers
Obstetrics
Musculoskeletal
Interventional - guided injections and biopsies

Question 37

4 advantages of ultrasound

Answer 37

Lack of radiation
Low cost
Portable
Dynamic (can see movement)

Question 38

4 disadvantages of ultrasound

Answer 38

Operator dependent
No bone or gas penetration
Difficult with obese/frail/unwell patients
Theoretical risk of overheating foetus