Final answer:
The term that refers to the scanner's ability to detect small differences in attenuation between closely spaced objects is contrast resolution, which is vital for distinguishing tissues in medical imaging.
Step-by-step explanation:
The ability of the scanner to differentiate small differences in attenuation between closely spaced objects refers to contrast resolution. Contrast resolution is crucial in medical imaging as it determines the capability of the imaging system to distinguish between variations in tissue densities. Spatial resolution refers to the detail in an image and is the ability to resolve structures that are close to each other as separate entities. Temporal resolution pertains to the ability of a system to resolve events in time. Signal to noise ratio measures the amount of signal present in an image relative to the amount of noise.