These transducers are typically labeled with frequencies between 5 and 10 MHz, though the actual imaging frequencies tend to be centered around 7.5 MHz. This makes them among the fastest growing applications of ultrasound. High frequency transducers are ideally suited to imaging superficial organs such as these. As good as these transducers are, however, the diagnostic information provided by the ultrasound instrument could be further enhanced by extending spatial resolution beyond the current state of the art. Though ultrasound resolution is affected by several factors1, imaging frequency has the most direct impact.
Ultrasound resolution improves in direct proportion to imaging frequency.
In a typical 5 - 1O MHz system, the resolution cell measures roughly 0.7 x 0.35 mm. The result is that anatomical structures smaller than 1 mm are likely to be missed. This limits the maximum imaging frequency to 10 MHz according to the Nyquist sampling theorem. The situation is even more difficult for analog systems since adequate focusing precision becomes more difficult as the frequency increases. Moreover, as the imaging frequencies increase, transducer design and fabrication become increasingly difficult.