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Attenuation of the gamma rays within the patient can lead to significant underestimation of activity in deep tissues, compared to superficial tissues. Approximate correction is possible, based on relative position of the activity, and optimal correction is obtained with measured attenuation values.
Time gain compensation (TGC) is a setting applied in diagnostic ultrasound imaging to account for tissue attenuation. [1] By increasing the received signal intensity with depth, the artifacts in the uniformity of a B-mode image intensity are reduced.
Attenuation decreases the intensity of electromagnetic radiation due to absorption or scattering of photons. Attenuation does not include the decrease in intensity due to inverse-square law geometric spreading. Therefore, calculation of the total change in intensity involves both the inverse-square law and an estimation of attenuation over the ...
When various barriers and restricting factors such as cell membranes and microtubules interfere with the free diffusion, we are measuring an "apparent diffusion coefficient", or ADC, because the measurement misses all the local effects and treats the attenuation as if all the movement rates were solely due to Brownian motion. The ADC in ...
Cadmium telluride and cadmium zinc telluride detectors have the advantage of high attenuation and relatively high photoelectric-to-Compton ratio for X-ray energies used in CT imaging. This means the detectors can be made thinner and lose less spectral information due to Compton scattering. (Although they still lose spectral information due to K ...
An MRI artifact is a visual artifact (an anomaly seen during visual representation) in magnetic resonance imaging (MRI). It is a feature appearing in an image that is not present in the original object. [1] Many different artifacts can occur during MRI, some affecting the diagnostic quality, while others may be confused with pathology.
Water has an attenuation of 0 Hounsfield units (HU), while air is −1,000 HU, cancellous bone is typically +400 HU, and cranial bone can reach 2,000 HU or more (os temporale) and can cause artifacts. The attenuation of metallic implants depends on the atomic number of the element used: Titanium usually has an amount of +1000 HU, iron steel can ...
The lungs have a very low attenuation value because they are air-filled and show up as dark areas on radiographs, while the thoracic spine is bony with higher attenuation and displays as white or grey. The vast differences in density make it difficult to acquire a high quality, detailed x-ray unless a compensating filter is applied. [1]