Ultrasound Axial Resolution — FRCA Primary MCQ

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HardPhysics & Clinical MeasurementUltrasound Axial ResolutionFRCA Primary

A 7.5 MHz transducer emits two-cycle pulses in soft tissue, where sound speed is 1540 m s−1. What is the approximate axial resolution?

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Correct answer: E — 0.21 mm

The best answer is “0.21 mm”. Wavelength equals c/f: 1540/(7.5×10^6)=0.205 mm. A two-cycle pulse has a spatial pulse length of about 0.41 mm, and axial resolution is half the spatial pulse length, about 0.21 mm. Higher frequency improves axial resolution but reduces penetration through tissue.

Reference: Gupta et al., Potential role of ultrasound in anesthesia and intensive care: https://pmc.ncbi.nlm.nih.gov/articles/PMC4173359/