EM Notes – Ultrasound

Introduction

Advantages:

  1. Does not involve ionising radiation
  2. Used quite freely for antenatal scanning, children
  3. Safe for repeated examinations
  4. No evidence that it break chromosomes, damages tissues or predisposes to malignancy
  5. Non-invasive
  6. Painless
  7. Equipment much cheaper than MRI scanners and more portable
  8. Possibly the best imaging modality for soft tissues.
  9. Has some therapeutic uses too – soft tissue injury etc

Background

  1. Ultrasound relies on reflection of very high frequency sound waves by tissue interfaces.
  2. This frequency is typically 2.5 to 10MHz. Higher freq resolution but penetration.
  3. At interfaces sound waves may be absorbed, reflected to varying degrees back to the probe, or transmitted through the tissue at different velocities.
  4. Displayed image depends on detecting the variously attenuated reflected sound waves.
  5. Uniform substances such as water or urine, produce no echoes (black)
  6. A gel or oil is employed to give a non-reflective acoustic interface between probe & skin.
  7. A full bladder for transabdominal pelvic scans.
  8. Acoustic shadowing if very reflective interface (tissue/bone, caluli) or scattering (gas).
  9. Scans performed at other sites: transrectal (prostate), trans-vaginal (gynae), and TOE.
  10. Technical advances include: resolution, realtime scanning, colour Doppler, ‘3D’ imaging.

Many uses (including):

  1. Abdominal organs (Liver, Kidney, Spleen, Pancreas)
  2. Biliary tree (ED)
  3. Renal tract calculi (ED)
  4. Appendicitis
  5. Bladder filling (ED)
  6. Gynaecological
  7. Pregnancy/ectopic (ED)
  8. FAST (ED)
  9. DVT (Doppler)
  10. Echocardiology (ED)
  11. Abdominal aorta (ED)
  12. Subcutaneous FB (ED)
  13. Central line placement (ED)

ED – Increasingly performed by ED physicians

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