Overview Of Image Production Flashcards
Objective of diagnostic imaging?
🔹To produce images of optimum quality for diagnosis
🔹To aid in the management/treatment of the patient
The procedure should produce images with…?
🔹Limited magnification
🔹Minimum unsharpness
🔹Radiation dose as low as reasonably practicable (ALARP)
Ideal set up for image production?
(X-Ray)
🔹Have the body part being imaged parallel to and in contact with the image detector
🔹X-Ray beam should be at right angles to the detector and not angled across it as this produces a distorted image
Factors which affect the quality of the image and/or radiation dose to the patient when using X-Rays?
(X-Ray beam characteristics)
🔹Focal spot size
🔹Filtration of the beam
🔹Exposure factors
🔹Field size
🔹Production and management/reduction of scatter
🔹Geometry of image production
Factors which affect the quality of the image and/or radiation dose to the patient when using X-Rays?
(Patient)
🔹Ability to keep still
🔹Thickness and density of the body parts
Factors which affect the quality of the image and/or radiation dose to the patient when using X-Rays?
(Detector and Imaging System)
🔹Using computed radiography (CR) and digital radiography (DR) technology
🔹Quantum Detection Efficiency (QDE)
🔹Display system
🔹Viewing conditions
Requirements of the X-ray beam for image production?
🔹The beam needs to be filtered
🔹The source of radiation (focus) from the X-ray tube is small
🔹The size of the radiation beam can be collimated to the body part
🔹Energy beam needs the be adjustable
Why does the X-ray beam need to be filtered?
🔹To preferentially remove low energy photons which will not penetrate the patient
🔹This reduces radiation dose
🔹It changes the energy range of the X-rays in the beam, which hardens the beam
🔹Makes the beam more homogenous, so there is a smaller range of intensities
Typical range for source of radiation (focus)
🔹From 0.3mm2 fine focus
🔹To 2mm2 broad focus
Why is the size of the radiation beam collimated to the body part?
🔹Reduce scatter
🔹 Reduce intensity
What is collimation?
🔹The process of limiting the area of an X-ray beam that hits a patient and detector
Why does the energy of the beam need to be adjustable?
🔹To enable a range of exposures
Range of exposures for the energy beam?
(Kilovoltage, Milliampage, Exposure Times)
🔹Kilovoltage - From 40-125
🔹Milliampage - From 50-1000
🔹Exposure Times - From 0.001-several seconds
What is scattered radiation?
🔹Scatter radiation is a type of secondary radiation that occurs when a radiation beam interacts with a substance and spreads out in multiple directions
What are the only three possibilities for the X-ray photons leaving the X-ray tube?
🔹Photons are absorbed by the patient
🔹Photons pass through the patient
🔹Photons are scattered within the patient or detector
What happens when the photons are absorbed by the patient?
🔹Photons cease to exist
🔹This may cause radiation damage
🔹Gives information about the density and thickness of the patient
🔹Helps create an image (signal)
What happens when the photons pass through the patient?
🔹Produce a point of information in the detector
🔹Helps create an image (signal)
What happens when the photons are scattered within the patient or detector?
🔹This contributes to noise if they if they interact with the detector
🔹Absorbed photons in the patient again may cause radiation damage with no benefit to the image
What is noise?
🔹Noise is a measure of the graininess or variability in an image that’s not part of the desired signal
What is attenuation?
🔹Attenuation is the reduction in intensity of an X-ray or ultrasound beam as it passes through matter.
🔹This reduction can be caused by absorption or scattering of photons from the beam.
🔹The image on the detector can be seen as an attenuation map of radiation which has passed through the patient
What is the field size and how can it be controlled?
🔹 Field size refers to the size of the X-ray field
🔹Can be controlled by the collimation of the X-ray beam
What is the maximum field size?
🔹At 100cm focus receptor distance (FRD) is 43cm2
Why is it important for the beam of radiation to be limited only to the area of interest?
🔹Can improve image quality
🔹Reduce the radiation dose to the patient and staff
🔹Minimising the amount of scattered radiation produced
