Final answer:
The pulse duration of an ultrasound system remains unchanged if system components are not altered, which is true. Echo times in ultrasound scanning are used to resolve details within the body, with smaller time differences needed to see finer details. The period of ultrasound waves must be smaller than the time resolution required for imaging, dictating the minimum frequency necessary for diagnostic purposes.
Step-by-step explanation:
The statement that the pulse duration of an ultrasound and transducer system remains unchanged as long as the system components remain unchanged is true. Pulse duration is an inherent property of the system determined by the transducer's physical characteristics and the electronics of the ultrasound machine. The pulse speed depends on the properties of the medium and is not influenced by the amplitude or pulse length.
Regarding echo times for a diagnostic ultrasound scanner, these are used to measure the distance to reflecting surfaces within the body. If we are to find the difference in echo times for tissues at 3.50 cm and 3.60 cm beneath the surface, we need to use the speed of sound in the tissue and calculate the time it takes for the ultrasound to travel to that depth and back. The differences in echo times are critical in resolving details as small as 0.100 cm.
For the period T of an ultrasound wave, it must be smaller than the minimum time resolution to resolve small details within the body. The minimum frequency is the reciprocal of the period (f=1/T), which must be high enough to allow for the necessary time resolution. Typically, diagnostic ultrasound frequency ranges from about 2 to 15 MHz, which is well above the human hearing range and suitable for medical imaging.