What happens to image noise as the number of x-ray photons used to create an image decreases?

As the number of X-ray photons used to create an image decreases, image noise increases. This relationship is rooted in the way images are formed in radiography. When fewer photons are available to interact with the imaging receptor, the statistical variability in the signal received also increases. This variability translates into more 'random' fluctuations which manifest as noise in the image.

The signal-to-noise ratio (SNR) is crucial in imaging; it refers to the level of the desired signal compared to the background noise. With a lower photon count, the signal derived from the actual image decreases while the relative influence of noise remains significant or grows. As a result, the overall quality of the image diminishes, making it harder to interpret and leading to potential misdiagnosis. Thus, with a decrease in the number of X-ray photons, the increase in image noise detracts from the clarity and diagnostic value of the image.