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Study Stack Exam Rev

Study Stack Exam Review

QuestionAnswer
An artifact any false visual feature on a medical image that simulates tissue or obscures tissue
Preprocessing Interpolation is the process of assigning a value to a dead pixel based on the recorded values of adjacent pixels Flatfielding is a preprocessing software correction that is performed to equalize the response of each pixel to a uniform x- ray beam.
Image compression Lossless compression up to 3:1 generally is considered acceptable and helpful in digital radiographic image management.  Lossy compression is greater than 10:1 compressio
Image histogram Graph of frequency of occurrence versus digital value intervals
Collimation and partition Automatic radiation field recognition is essential for artifact-free images.  Proper collimation and centering prevent histogram errors that can lead to artifacts.
X-rays that exit from the patient are remnant x-rays and those that exit and interact with the image receptor are called image-forming x-rays
Collimation reduces patient radiation dose and improves image contrast
Patient Thickness  Thicker parts produce more scatter than thin parts  Compression of anatomy improves spatial resolution and image contrast and lowers the patient radiation dos
Effect of scatter radiation on image contrast Reduced image contrast results from Compton scattered x-rays.
Beam restrictors Aperture diaphragm  Cones and cylinders  Variable-aperture collimator  Collimation reduces the patient radiation dose and improves image contrast.  Positive-beam-limiting (PBL) devices
 Grid ratio h/D
Grid frequency 10,000 μm/cm/(T+D)μm/line pair
Contrast improvement factor image contrast with a grid/image contrast without a grid  The contrast improvement factor is higher for high-ratio grids.
Bucky factor incident remnant x-rays/transmitted image-forming x-rays  As the Bucky factor increases, radiographic technique and patient radiation dose increase proportionately.
Grid Types Parallel  Grid cutoff  Distance to Grid Cutoff = SID/Grid Ratio  Crossed  Grid cutoff  Focused  High-ratio grids have less positioning latitude than low- ratio grids.  Moving  Grid lines  Virtual
Grid Problems Off-level grid  Off-center grid  Off-focus grid  Upside-down grid
Grid selection factors  Patient radiation dose increases with increasing grid ratio.  High-ratio grids are used for high-kVp examinations.  The patient radiation dose at high kVp is less than that at low kVp.
Air-gap technique Disadvantage of the air-gap technique is image magnification with associated focal-spot b
Created by: robertye12
 

 



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