Medical Imaging

Question 1

How do X-Ray provide an image?

Answer 1

Focused beam of high energy electrons, pass through body Onto receiver. Some are absorbed or scattered (attenuation), this depends upon material density and atomic number.

More dense/higher number=more attenuation=lighter appearance

Question 2

What are the advantages and disadvantages of X-Rays?

Answer 2

Advantage =quick, cheap, portable, simple, digital can zoom+measure distance+change density etc

Disadvantage=radiation (low), one plane so 2D image, cant see all pathology, cant visualise all areas, poor soft tissue imaging

Question 3

What are the uses of X-Rays?

Answer 3

Chest-infection, pneumothorax, trauma, effusion,oedema

Bowel-dilation, perforation

Orthopaedic-fracture, trauma

Post-procedure-positioning of tubes, pacemakers

Dentists

Question 4

What is Fluoroscopy?

Answer 4

Examination of anatomy and motion
Uses a constant stream of X-Rays often enhanced by a contrast/dye

Contrast=Barium or Iodine
They strongly absorb X-Rays so appear dense white, can be used anywhere its swallowed, inserted or injected

Question 5

What are the uses of fluoroscopy?

Answer 5

Angiography

Contrast GI studies

Therapeutic Joint Injections

Arthrograms

Screening in theatre

Question 6

What are the advantages and disadvantages of Fluoroscopy?

Answer 6

Advantages=dynamics studies, cheap, interventional procedures (stents etc)

Disadvantages=Clinicians exposure must be limited, gives of radiation

Question 7

What is a CT?

Answer 7

Computed Tomography

Patient on rotating gantry, X-Ray tube on one side, detector on other
Images put together by computer
Same principle of attenuation as an x-RAY

Question 8

What are Hounsfield Units?

Answer 8

Tissues have a designated unit, helps distinguish different tissues on a CT scan.

Less dense tissue=negative unit=dark colour (fat, air)
Water = 0 HU
More dense tissue=positive unit=light colour (bone. Metal)

Question 9

What is notable about the view of a CT scan?

Answer 9

Look from feet up 
Transverse imaging
Left side image= right side body
Right side image = left side body
Spine is posterior (at bottom)

Question 10

What are CT scans used for?

Answer 10

Diagnosis-cancer, stroke, bone injury, blood flow

Guide further test/treatment-radiotherapy, biopsy

Monster conditions=cancer treatments

Question 11

What are advantages and disadvantages of CT scans?

Answer 11

Advantages=quick, good spatial resolution (distinguish between tissues), can scan most areas (not all)

Disadvantages=radiation, lower contrast resolution, affected by artefacts, requires breath hold (patient dependant), overuse (diagnosis fishing), incidental findings (find non dangerous tumours etc and create more unneeded work)

Question 12

What is an MRI?

Answer 12

Strong magnetic field turned on,
Aligns hydrogen atoms in body
Some towards head, some to feet, not 50:50 split some ions remain unmatched,
A radio frequency pulse is applied
Unmatched ions absorb energy and spin in diff direction
Pulse turns off and atom spins return, emitting energy
Computer processes energy release into an image

Question 13

What are the 2 different MRI weighting?

Answer 13

Different relaxations produce different Weighting’s from tissues

T1 = fat is white, water is black 
T2= fat is black, water is white (T2=H2O white)

White=high signal
Black=low signal

Question 14

What are the uses of MRI?

Answer 14

CNS-brain and spinal cord

Bones an joins

Heart and blood vessels

Internal organs

Question 15

What are the advantages and disadvantages of MRI?

Answer 15

Advantages=no radiation, good contrast resolution

Disadvantages=expensive, time consuming, availability, claustrophobic, some patient wont fit, loud, need to lay still, metalwork ripped out

Question 16

What is Scintigraphy?

Answer 16

Injection of radio pharmaceuticals
Emit gamma rays
Highly sensitive as target structures
Functional and anatomical info

Question 17

What is PET?

Answer 17

Position Emission Tomography
Radionucleotides decay by positron emission
Bound to glucose
PET camera detects annihilations (gamma rays) more annihilations=bigger signals, tend to be combined with CT/MRI

Hot spot=area high glucose metabolism
Heavy use in oncology-tumour staging, asses treatments, differentiate Benign and malignant, detect tumour recurrence

Question 18

What is ultrasound?

Answer 18

High freq sound waves from transducer probe
Wave reflected back by tissues where density differs (impedance)
Probe detects reflected waves
Creates electrical signal (distance=time taken to come back, impedance=proportion of reflected waves)

Great density diff means sound completely reflected so cant see behind bone, air and stone

Question 19

What is Doppler ultrasound?

Answer 19

Moving objects influence sound waves
Therefore flowing blood can effect ultrasound signals, coming towards-increased frequency, going away-decreased frequency

Duplex ultrasound=2D image + Doppler

Question 20

What is Ultrasound used for?

Answer 20

Solid organs-liver, kidney, spleen, pancreas, thyroid, testes

Urinary tract-stones, dilation, volume

Obs+Gynea-Pregnancy, uterus

Musculoskeletal

Use in body cavities-transvaginal, transrectal, transoesophageal

Question 21

What are the advantages and disadvantages of ultrasound?

Answer 21

Advantages=lack ionising radiation, low cost, portable, insertable, baby safe, dynamic (blood flow)

Disadvantages=Operator dependant (skill needed), no bone/gas penetration, body habitus (fat hard to see throug)