Difference and relationship between density resolution and spatial resolution in medical imaging

Spatial resolution is sometimes called geometric resolution or high contrast resolution in CT equipment, which refers to the ability to distinguish fine structures under high contrast, that is, the ability to display the smallest volume lesions or structures. When evaluating the quality of CT images, spatial resolution is often considered first. Because the detector of CT image has a certain size and the sampling distance is also certain, the spatial resolution of CT image is determined by the geometric size of the focus of X-ray tube, and basically has nothing to do with X-ray dose. In the case of a certain X-ray dose, there is a certain restriction between spatial resolution and density resolution, so it is impossible to improve spatial resolution and contrast resolution at the same time.

The density resolution represents the minimum density difference that can be displayed in an image. The density resolution of CT is limited by noise and display size. The smaller the noise, the larger the display and the better the density resolution. The density resolution of CT images is much higher than that of X-rays.

The degree of density difference that can be distinguished by density resolution is expressed in%. Computed tomography (CT) imaging performance and one of the indexes to explain image quality. If the density resolution of computed tomography is 0.5%, it means that the density difference between the two substances is equal to or greater than 0.5%. When the density difference is less than 0.5%, it is impossible to distinguish because of the interference of noise.