Medical Imaging Flashcards
How do X-Ray provide an image?
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
What are the advantages and disadvantages of X-Rays?
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
What are the uses of X-Rays?
Chest-infection, pneumothorax, trauma, effusion,oedema
Bowel-dilation, perforation
Orthopaedic-fracture, trauma
Post-procedure-positioning of tubes, pacemakers
Dentists
What is Fluoroscopy?
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
What are the uses of fluoroscopy?
Angiography
Contrast GI studies
Therapeutic Joint Injections
Arthrograms
Screening in theatre
What are the advantages and disadvantages of Fluoroscopy?
Advantages=dynamics studies, cheap, interventional procedures (stents etc)
Disadvantages=Clinicians exposure must be limited, gives of radiation
What is a CT?
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
What are Hounsfield Units?
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)
What is notable about the view of a CT scan?
Look from feet up Transverse imaging Left side image= right side body Right side image = left side body Spine is posterior (at bottom)
What are CT scans used for?
Diagnosis-cancer, stroke, bone injury, blood flow
Guide further test/treatment-radiotherapy, biopsy
Monster conditions=cancer treatments
What are advantages and disadvantages of CT scans?
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)
What is an MRI?
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
What are the 2 different MRI weighting?
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
What are the uses of MRI?
CNS-brain and spinal cord
Bones an joins
Heart and blood vessels
Internal organs
What are the advantages and disadvantages of MRI?
Advantages=no radiation, good contrast resolution
Disadvantages=expensive, time consuming, availability, claustrophobic, some patient wont fit, loud, need to lay still, metalwork ripped out
What is Scintigraphy?
Injection of radio pharmaceuticals
Emit gamma rays
Highly sensitive as target structures
Functional and anatomical info
What is PET?
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
What is ultrasound?
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
What is Doppler ultrasound?
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
What is Ultrasound used for?
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
What are the advantages and disadvantages of ultrasound?
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)
