Week 13: IR Exposure Flashcards
(10 cards)
How does kV affect scatter?
As kV increases more photons are created with greater penetrability so more photons enter the patient which increases scatter. Higher kV means more scatter will leave the patient so it is good for the patient dose but bad form image detail.
How does atomic number affect scatter?
As the atomic number increases, scatter decreases. This is because higher atomic number materials have more electrons within each atom and therefore a higher number of PE absorption and lower Compton scatter.
Image Contrast
The imaging systems ability to differentiate between adjacent IR exposures and then display them. Limited by the bit depth of each pixel.
Bit Depth
How many shades of grey can each pixel display. As the bit depth goes up the system has a greater dynamic range and therefore greater contrast resolution.
Dynamic Range
How many shades of grey can the system display.
Subject Contrast
The range of the difference in the intensity of the x-ray beam after it has passed through the subject. Created with proper kV selection and based on the difference in composition of anatomical structures in the patient.
Differential Attenuation
The x-ray beam changes as it passes through the patient due to differential attenuation of the beam by different part of the patients body (why we have an image at all). Lower kV = higher differential attenuation so subject contrast is also high.
Atomic Packing Density
Refers to how tightly the atoms of a substance are packed. Higher atomic packing density = increased attenuation.
Physical Contrast
The total range of attenuation data recorded by the image receptor at one time. Proper IR exposure is important to ensure high quality physical contrast data to create the histogram.
Visible Contrast
Controlled by the LUT and can also be manipulated in post processing by changing WW.
