Final answer:
Noise is the determinant of CT image quality responsible for the grainy or speckled appearance of an image, adversely affecting the visibility of details.
Step-by-step explanation:
The determinant of CT image quality responsible for how grainy or speckled an image appears is d) Noise. Noise in a CT image refers to the random variations in pixel intensity that are not part of the actual image, often perceived as a grainy or speckled appearance that can obscure small details. The factors influencing noise include patient size, radiation dose, and the technical settings of the CT scanner. To reduce noise and improve image quality, adjustments to the scanner settings, such as increasing the radiation dose or using advanced image reconstruction algorithms, can be made. However, it's important to balance the need for clearer images with the patients' safety and minimize their exposure to radiation.