Final answer:
Apodization is a technique in ultrasound imaging used to improve image contrast by reducing the strength of side lobes. This is done by applying variable damping to the edges of the ultrasound beam, which does not primarily aim at improving axial resolution, contrast visualization, or reducing lobe artifacts.
Step-by-step explanation:
Apodization is a technique used in ultrasound imaging to reduce side lobes, which are unwanted artifacts that can degrade the quality of the image. The purpose of apodization is to manipulate the acoustic pressure field created by the ultrasound transducer. By applying variable damping to the edges of the ultrasound beam, apodization reduces the strength of side lobes, thus improving the image quality and the contrast resolution of the scan. However, strengthening the central focus of the beam can also improve the axial resolution to a certain extent.
Therefore, the correct answer to what apodization is used for is D) To improve image contrast. It is technically not aimed at reducing lobe artifacts (option A) or contrast visualization directly (option B), nor is it primarily about improving axial resolution (option C), but rather it helps in enhancing the overall contrast of the ultrasound image by depressing the side lobe levels.