RT 304 Final Exam Study Guide: Digital Radiography (DR) PDF

RT 304 Final Exam Study Guide: Digital Radiography (DR) Pixel Size and Spatial Resolution: o Smaller pixel size increases spatial resolution but may increase patient dose. Matrix Size and Pixel Count: o How to calculate the number of pixels in a matrix...

RT 304 Final Exam Study Guide: Digital Radiography (DR) Pixel Size and Spatial Resolution: o Smaller pixel size increases spatial resolution but may increase patient dose. Matrix Size and Pixel Count: o How to calculate the number of pixels in a matrix Spatial Resolution Limitation: o Limited by size of the Detector Element (DEL) in digital systems. Capture Systems: o Indirect DR uses amorphous silicon; direct DR uses amorphous selenium. Pre and Post Processing o Window width vs Window level o Histogram o Flatfielding o Interpolation Image Characteristics: o Improved spatial resolution with higher matrix size and smaller pixel size. o Signal processing in DR often involves reusable receptors. Radiographic Physics and Image Quality Imaging System o Small vs. Large Filament o Filament Material o Parts of the Anode side of the x-ray tube o Parts of the Cathode side of the x-ray tube o Comparing single phase, three phase, and high frequency systems Heat Units Calculation:  o Formula: HU=kVp×mA×s×generator factor o For a high-frequency generator, factor = 1.4. Radiation Safety: o Leakage radiation from lead-lined housing should not exceed 100 mR/hr at 1 meter. Beam Characteristics: o Increased kVp increases beam penetrability and decreases image contrast. o mAs impacts beam intensity but not quality. o Off focus radiation o MTF (Modulation Transfer Function) o DQE (Detective Quantum Efficiency) o Foreshortening vs elongation Contrast and Spatial Resolution Definitions: o Contrast Resolution: Ability to differentiate objects of similar density. o Spatial Resolution: Ability to distinguish between objects close together. Factors Influencing Image Quality: o Tight collimation, patient compression, and lower kVp improve contrast resolution. o Lowering kVp increases patient dose but improves contrast. X-Ray Production and Interaction X-Ray Interactions: o Bremsstrahlung: Produced when electrons are decelerated near the nucleus.  o Characteristic X-Rays: Produced when an inner-shell electron is ejected, creating a vacancy. o Most x-rays in diagnostic imaging are bremsstrahlung. Filtration: o Increases beam quality (hardening) and reduces patient dose How do changes in the following affect the emission spectrum of the x-ray beam? o mAs o kVp o filtration Grids and Scatter Control Grid Use: o Grid ratio = height of the grid strips/interspace width. o Higher grid ratios reduce scatter but require increased exposure (mAs). Scatter Factors: o Influenced by kVp, field size, and patient thickness. Artifacts in Digital Imaging Common Causes: o Pixel failure, dust, scratches, or incomplete erasure. Corrections: o Dead pixels are corrected using interpolation. Image Artifacts: o Can result from improper collimation, patient positioning, or incorrect histogram selection. Radiation Dose and Intensity  Inverse Square Law: o Intensity is inversely proportional to the square of the distance from the source. o I1/I2 = (D2/D1)2 Dose Reduction Strategies: o Use higher kVp with lower mAs to reduce patient dose without compromising image quality. Mathematical Problems Magnification Factor: o MF=SID/SOD or MF= Image size/ Object size Grid Conversion: o mAs adjustments are proportional to grid ratio changes.