Diagnostic Imaging

• Diagnostic imaging is tests performed to create images of the inside of the body to diagnose disease
• radiography

  x-ray

  electromagnetic radiation

  ionising radiation - separates electrons from ions
• how an x-ray works

  produced in an x-ray tune by the rapid deceleration of fast moving electrons

  radiographic image is created by the pattern of x-rays that reach the film

  x-rays pass or absorb depending on the density of the structure
• x-ray colours

  black = radiolucent

  white = radiopaque

  air, fat, soft tissue, bone, metal
• x-rays are 2D images of 3D structures
• CT scans

  rotating x-ray machine and detector

  uses x-rays

  2D cross sectional imaging

  3D reconstruction is possible

  avoids superimposition that occurs on x-rays
• CT scan colours

  black = hypoattenuating

  white = hyperattenuating
• CT scans

  advantages

  • detailed anatomical reconstructions
  • increasing availability

  disadvantages

  • higher dose of radiation
  • time consuming
• Ultrasound

  cross sectional imaging

  high frequency sound waves

  movement is in real time
• ultrasound how it works

  transducer emits ultrasound waves

  waves are reflected back to transducer when boundary between tissues is hit

  returning echoes become electrical signals

  computer analyses data and displays it as an image
• an ultrasound image is a series of dots

  the brightness is dependent on the echo strength

  the position is dependent on the time it takes for each echo to reach the transducer
• ultrasound allows differentiation of fluid from soft tissue, and can assess the internal architecture of soft tissue organs

  this is less useful for a bone or gas as waves are immediately absorbed (bone) or immediately bounce back (gas)
• ultrasound colours

  black Anechoic, e.g. fluid

  white = echogenic, e.g. fat

  hypoechoic and hyperechoic are used as comparative terms
• ultrasound

  Advantages

  • cheap
  • non-invasive
  • can see movement in real time

  disadvantages

  • gas or bone hinders examination
  • expensive
• MRI - magnetic resonance imaging

  use of strong magnet

  radiowaves are pulsed through patient

  detection and analysis of returned signals provide information on tissue composition
• MRI colours

  black = hypointense

  white = hyperintense
• MRI

  advantages

  • 2D cross sectional images can be stacked
  • different sequences can be run based on tissue type
  • no ionising radiation

  disadvantages

  • expensive
  • not widely available
  • lengthy process
• nuclear scintigraphy

  small amounts of radioactive isotope are administered to a patient

  isotope collects in tissue of interest

  emits gamma rays, detected by a gamma camera

  safety issue, ionising radiation