Within tissue lies a strongly reflecting boundary which back

Within tissue lies a strongly reflecting boundary, which backscatters 70% of the intensity of the ultrasound beam. Given a 100 dB receiver dynamic range, and an operating frequency of 3 MHz, what is the maximum depth within tissue at which this boundary can be detected?

Solution

ANSWER:

   Given,

Receiver Dynamic Range = 100dB

Operating frequency = 3 MHz

The energy of ultrasound decreases (attenuation) as it travels through tissue. The stronger the initial intensity or amplitude of the beam, the faster it attenuates. Standard instrument output is ~ 100 dB. So for a 3 MHz transducer, the maximum penetration would be as follows,

1 dB/cm/MHz x 3 MHz x (2 x max depth) = 100 dB

Therefore ,   Max depth = 100/6 = 16,66 cm

Attenuation of ultrasound in soft tissue depends on the initial frequency of the ultrasound and the distance it has to travel.

In soft tissue the greater the frequency the higher is the attenuation. So we can image deeper with lower frequency transducer. The further into the tissue the ultrasound travels, the higher the attenuation is, so it is ultimately the limiting factor as to how deep we can image clinically relevant structures.