Contrast Resolution

  • Contrast resolution-the ability of the scanner to differentiate small differences in attenuation between closely spaced objects.
    • Being able to differentiate between two tissues with similar attenuation is a crucial aspect of a CT scanner. This ability is often what allows for the diagnosis of certain pathologies.
    • The contrast resolution of a CT scanner can be measured through the use of a phantom that contains objects of different densities. The varying densities represent a certain level of attenuation and a representative HU that is able to be displayed for that scanner.
    • Factors that impact contrast resolution include:
      • Object Contrast-the natural contrast of an object being imaged can impact the level of contrast resolution. In these instances, contrast media may be given to the patient to assist with differentiation of tissues.
      • Scatter-reducing the radiation beam will also reduce the scatter radiation, which will improve contrast resolution.
      • Image reconstruction– use of reconstruction algorithms similar to a soft tissue kernel, will help to improve contrast resolution.
      • Detector size-smaller detectors improve contrast resolution as thinner slices reduce the variation of attenuation within each pixel.
      • Noise-the level of noise in an image directly impacts the contrast resolution. Decreasing the noise in an image will improve the contrast resolution. Increasing the noise will worsen the contrast resolution.