Final answer:
To improve lateral resolution, the sonographer should increase the number of focal zones and decrease scanning depth. Maximizing output power and using a lower frequency do not improve resolution. Higher ultrasound frequencies provide greater resolution but have less penetration depth.
Step-by-step explanation:
To improve lateral resolution in ultrasound imaging, the sonographer should perform certain operations. Of the given options, increasing the number of focal zones generally improves lateral resolution because it sharpens the beam and enhances the image quality at the focal points. This is because with multiple focal zones, the ultrasound beam is more tightly focused at different depths, which allows for finer differentiation of structures located side by side.
Decreasing the scanning depth can also improve lateral resolution since the ultrasound beams spread less when the depth is shallower. However, maximizing the output power does not directly improve lateral resolution and could have implications for patient safety due to increased exposure to ultrasound energy. Using a lower frequency probe also does not improve lateral resolution; in fact, higher frequencies yield better resolution but with lower penetration depth. For example, a 7 MHz abdominal scan can achieve 1-mm detail which is usually sufficient, but higher frequencies up to the penetration limit, like 500×0.22 mm for 7 MHz, enable even finer details to be seen.
Regarding echo times and frequencies used in diagnostic ultrasound, the period (T) of the sound wave must be less than the minimum time resolution to resolve details. If the tissues are at 3.50 and 3.60 cm depths, the echo times will be different by a correspondingly small amount, and only ultrasound frequencies that produce periods shorter than this time difference will be able to distinguish between the two. Knowing that the speed of sound is approximately 1540 m/s in tissue, the minimum frequency can be calculated based on the desired resolution (such as 0.250 mm), which would be in the MHz range usually within the normal range for diagnostic ultrasound.