Introduction to Imaging

Introduction to Imaging

  • X-Ray – first image of bones of hand. Silhouette of anatomy.
  • Silhouette sign – bony material silhouetted against air. Lost on chest X-ray with pathology
  • Age of patient important in radiology. Multiple lesions on chest X-ray – most likely secondary.
  • Only 25% of world has access to X-ray
  • First scanner developed in Wimbledon by Godfrey Hansfield – a SGUL graduate. First scan in 1976
  • CT chest = 400 chest X-rays. Particularly important to consider in children. And brain/eyes are particularly radiosensitive. Repetitive exposure give cumulative risk. Risk of cancer with CT chest 1 in 1000 (smoking doubles your risk).
  • Childrens’ doses kept low with ultrasound where possible.
  • CT scanning has evolved due to computer progress.
  • EMI record label funded 1st CT, so The Beatles indirectly helped fund CT scanning
  • Functional CT due to labelled glucose – tumours can be imaged due to glucose uptake
  • PET (functional) and CT (anatomy) scans fused together allows tumour to be staged -PETCT
  • All imaging carries risk, due to energy being imputed to patient (ultrasound and MRI heat, X-ray ionising).
  • 1/3 of admissions are for chest pain. Half don’t have heart. Computed coronary angiography is 99% effective for screening. Very high negative predictive value.
  • In fluoroscopy, user gets dose (cardiologists, interventional radiologists and some surgeons are high risk users)
  • Ultrasound – Ian Donald. Uses sonar (WWII technology) used first in 1950s, published in Lancet. High frequency bell which rings
  • Risk is tissue cavitation
  • Black on image is fluid (transmits), white (reflects), grey (partially reflects).
  • Seeing the anatomy can sometimes give you the diagnosis.
  • Doppler effect can assess patency of blood vessels
  • Moore’s law. Every 10 years, size halves. Ultrasound is now ‘point of care’, can be size of smartphone.
  • Ultrasound can image stomach – eg. Pyloric stenosis in child
  • Ultrasound – high negative predictive value, good for excluding pathology inc fractures in remote locations, due to portability
  • Ultrasound prices £40-£120,000
  • MRI – invented by Peter Mansfield in Nottingham
  • 20% of patients cannot tolerate
  • Protons align due to magnetic field, water has most protons,
  • Magnetic field strength is icreasingtarted with 1tesla, now 3tesla which improves signal to noise ratio
  • Radio frequency added (this causes the noise during the scan), which knocks protons off axis. During time they are knocked off, they emit signal, which can be measured
  • Exquisite resolution. Can see bone bruises, MS plaques, tumour inc blood vessels
  • Cannot perform with pacemaker, metal artefacts, certain heart valves
  • Can image mother in first trimester
  • Shall we image early? – eg locked knee before pt sees surgeon
  • Cost of MRI is coming down, more private providers, hence availability is going up

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