ULTRASOUND


✅ What is Ultrasound?

Ultrasound is a non-invasive imaging technique that uses high-frequency sound waves (typically 2–15 MHz) to produce images of internal body structures.

✅ Principle of Ultrasound

Ultrasound imaging is based on the principle of sound wave reflection (echolocation):

  • Sound waves are emitted by a transducer.
  • These waves travel through tissues and reflect back when they hit a boundary between different tissue types.
  • The returning echoes are received by the transducer and converted into electrical signals.
  • A computer processes these signals to create an image.

✅ Mechanism

  1. Generation of ultrasound waves via piezoelectric crystals in the transducer.
  2. Propagation through tissues with varying acoustic impedances.
  3. Reflection/Refraction/Absorption at tissue interfaces.
  4. Echo detection and conversion into electrical signals.
  5. Image formation through signal processing and display.

✅ Transducer (Probe)

A transducer is a hand-held device that sends and receives sound waves.

🔹 Types of Transducers & Their Uses

Type Shape Frequency Range Use
Linear array Flat, rectangular 7–15 MHz Vascular, musculoskeletal, small parts (e.g., thyroid)
Curvilinear (Convex) Curved 2–5 MHz Abdominal, obstetric scans
Phased array Small footprint 2–7 MHz Cardiac imaging (echocardiography)
Endocavitary Thin, long 5–9 MHz Transvaginal or transrectal scans
3D/4D Transducer Varies Multiple Obstetrics and gynecology (real-time fetal imaging)

✅ Indications for Ultrasound

Ultrasound is widely used in many specialties:

🔹 General indications:

  • Abdominal imaging: liver, gallbladder, kidneys, pancreas
  • Obstetrics & gynecology: fetal monitoring, ovarian cysts
  • Cardiology: echocardiography
  • Vascular: DVT evaluation, carotid Doppler
  • Urology: bladder, prostate, renal imaging
  • Musculoskeletal: joint effusions, tendon tears
  • Emergency: FAST exam for trauma, POCUS (Point-of-Care US)

✅ Contraindications of Ultrasound

There are very few absolute contraindications since US is safe (non-ionizing).

🔹 Relative contraindications:

  • Open wounds or burns at the probe site
  • Inability to access the required area due to severe obesity or overlying gas
  • Deep structures where US penetration is insufficient (e.g., lungs, brain)

✅ Common Ultrasound Artifacts

Artifact Description
Acoustic Shadowing Dark shadow behind dense structures (e.g., gallstones, bone)
Posterior Enhancement Increased brightness behind fluid-filled structures
Reverberation Multiple equally spaced echoes (e.g., needle or catheter)
Mirror Image Artifact Duplication of structures across a strong reflector
Edge Artifact Shadowing at the edges of curved structures
Ring Down Artifact Continuous echo from gas bubbles
Comet Tail Artifact Short, dense echoes due to small metal or cholesterol crystals


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