What is the term for the ability to detect an object with a small difference in attenuation from surrounding tissue?

The ability to detect an object with a small difference in attenuation from surrounding tissue is referred to as contrast resolution. This term specifically describes the system's capability to distinguish between varying levels of x-ray absorption in different tissues, which is crucial for identifying subtle differences in structure and pathology on a CT image. High contrast resolution means that even slight differences in density can be visualized, enabling radiologists to detect lesions, differentiate tissue types, and make more accurate diagnoses.

In the context of the other choices, spatial resolution pertains to the sharpness and clarity of structures in the image, indicating how well fine detail can be distinguished in an image. Temporal resolution refers to the ability to capture rapid movements in the subject being scanned, which is particularly relevant in dynamic imaging scenarios such as cardiac CT. Image quality encompasses a broader perspective, including factors like contrast resolution, spatial resolution, noise, and artifact presence, but does not specifically define the detection of small differences in attenuation alone. Thus, "contrast resolution" is the appropriate term for describing the described ability.