Final answer:
Grayscale imaging is the technique that creates the least exposure for the patient as it does not use electromagnetic radiation and relies on high-frequency sound waves for imaging.
Step-by-step explanation:
The technique that will generate the LEAST amount of exposure to the patient among the options listed - Spectral Doppler, Color flow Doppler, Grayscale, and M-mode - is Grayscale imaging. This is because Grayscale, also known as B-mode ultrasound, uses the transmission of high-frequency sound waves into the body to produce images based on the echoes received, and does not use electromagnetic radiation. In contrast, Spectral Doppler and Color flow Doppler techniques are used to visualize and measure the flow and speed of blood using the Doppler effect, which may require higher power and possibly more exposure if used for extended periods. Meanwhile, M-mode or motion mode ultrasound is also safe but is more specific for assessing moving structures within the body and may not be the technique of choice for minimal exposure scenarios.