Final answer:
In a CTA of the neck, the patient is instructed not to swallow to prevent artifacts from creating poor image quality, which obscures true anatomy and can interfere with accurate diagnosis.
Step-by-step explanation:
During a CTA (computed tomography angiography) of the neck, the patient is instructed not to swallow to avoid artifacts on the images, which can lead to poor image quality. Artifacts are distortions or errors in medical imaging that may obscure the true anatomy or pathology, making accurate diagnosis more difficult. Instructions to remain still, including not swallowing, are crucial because movement can cause blurring and degrade the quality of the images.
Furthermore, the area of interest in a neck CTA is very close to structures that move during swallowing, so stability in this region is especially important to obtain clear images for assessment of the blood vessels.