In standard B-mode imaging of the thyroid using a linear array, the transmitted pulses typically consist of how many cycles?

• A. One to three
• B. Three to six
• C. Six to nine
• D. Nine to twelve

Answer: (A)

Short, few-cycle pulses are used in B-mode thyroid imaging with a linear array to maximize axial resolution and frame rate. The axial resolution depends on the spatial pulse length, which is the product of the number of cycles and the wavelength. For high-frequency, superficial structures like the thyroid, using one to three cycles keeps the spatial pulse length small, so closely spaced interfaces (tiny nodules, boundary details) appear more distinct. It also allows the system to emit pulses and listen for echoes more quickly, boosting frame rate for real-time imaging. If you used more cycles, the spatial pulse length would increase, blurring fine detail and decreasing frame rate, which is undesirable for precise thyroid assessment.