Image Quality and Practicality of Scanning Large Abdomens with Large-Low Frequency and Smaller-High Frequency Transducers

Abstract

Pulse echo imaging of deeper structures in patients with large abdomens yields very poor image quality in most cases. This is due in part to the fact that the 2.25 MHz and lower frequency transducers, which have enough sensitivity for imaging at long ranges, have been so small in diameter that the beam cannot be focused at long ranges, that is, large depths in the patient. It is a fundamental limitation of ultrasound transducers that their focal point cannot be placed at a range from the transducer greater than the near to far field transition point. As can be calculated readily, the length of the near field of commonly employed ultrasound transducers extends beyond 14 cm only on the 3.5 MHz, 19 mm diameter transducer. Unfortunately, many ultrasound systems cannot image deep structures at frequencies as high as 3.5 MHz.