Final answer:
The correct option to add more levels of grey to an ultrasound image is A) Decrease compression, which allows more variation in the grayscale display, enhancing image detail.
Step-by-step explanation:
To add more levels of grey to the ultrasound image, thereby increasing the grayscale gradient and making the image more detailed and subtle, the correct option is A) Decrease compression. By lowering the compression, you allow more variation in the greyscale display, which means the image will show more gradients between black and white. Essentially, compression in ultrasound refers to the range of amplitudes in the image; decreasing it allows for a greater range of grey levels to be displayed. Option B) Reduce the dynamic range, would actually have the opposite effect, leading to higher contrast and fewer grey levels. Decreasing rejection levels (option C) or increasing threshold levels (option D) can also affect image quality, but they do not directly add more grey levels to the image.