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WorksheetsMRSC5038 - WEEK 2
Total questions: 80
Worksheet time: 52mins
This image has poor
(a)
This image has poor
(a)
This image has poor
(a)
What is contrast?
Random fluctuations in the number of x-ray photons absorbed by the detector element
Difference in signals between structures
Dynamic Range
Ability to distinguish very small objects or objects that are close together
What is considered a "signal" when referencing contrast in images?
The speed of the image receptor response
The optical density in film
The amount of scatter radiation detected
The grey level value in digital and CT
Factors affecting Contrast:
Subject Contrast = Tissue + ____ _______
(a)
Factors affecting Contrast:
Subject Contrast - Tissue = density, thickness, (a) (CA)
Factors affecting Contrast:
Subject Contrast - Beam Quality
kVp & Filtration
Body Habitus
Imaging Plate
Differential absorption of tissues
What is spatial resolution?
Random fluctuations in the number of x-ray photons absorbed by the detector element
Difference in signals between structures
Dynamic Range
Ability to distinguish very small objects or objects that are close together
The highest spatial frequency a digital system can accurately resolve.
Pixel size of the detector
Aliasing Resolution
Nyquist Frequency
X-ray Emission Frequency
What is the purpose of the Nyquist Frequency?
To measure the speed of the CR reader
To prevent motion blur in digital images
To determine the optimal kVp for an exposure
To ensure accurate sampling and avoid aliasing in digital images
Factors affecting Spatial Resolution
Geometry: Focal spot, SID
Detector: Dels, Light scatter
Monitor: Pixel size
Patient Motion: Blur
1 line pair (lp) = _______?
1 metal, 1 air
2 metal
2 metal, 2 air
2 air
What is noise?
Random fluctuations in the number of x-ray photons absorbed by the detector element
Difference in signals between structures
Dynamic range
Ability to distinguish very small objects or objects that are close together
What is signal-to-noise ratio (SNR)?
The speed at which a digital detector processes an image
The difference in brightness between two adjacent structures
The amount of scatter radiation detected by the image receptor
Strength of desired signal compared to random noise
How can we increase SNR?
Apply heavy image filtering to remove noise
Use higher kVp to reduce contrast
Increase mAs (higher x-ray photons) and optimise detector efficiency
Decrease mAs to reduce patient dose
Increasing dose will increase SNR and increase noise
True
False
What factor does NOT improve SNR?
Reducing electronic noise in the imaging system
Decreasing patient thickness
Using a higher DQE (Detective Quantum Efficiency) detector
Optimising exposure factors
Contrast resolution is the ability to
detect subtle changes in grey scale & distinguish them from noise
measure general image clarity
distinguish small objects close together
detect motion artifacts in dynamic imaging
For an obese patient, which technique best improves SNR while minimizing dose?
Reduce SID to increase photon flux
Apply edge enhancement filters post processing
Use lower kVp to increase contrast
Increase mAs and use a higher DQE detector
Quantum noise in digital radiography is primarily caused by:
Random variation in x-ray photon distribution
Heat generated by the detector’s electronics
Patient motion during exposure
Inefficient analog-to-digital conversion
(a) noise arises from detector circuitry
Why does DR typically have a higher SNR than CR?
DR requires longer exposure times
DR detectors have higher DQE and less noise
DR uses photostimulable phosphor plates
CR cassettes are immune to scatter radiation
CR uses
Fluorescence
Semiconductors
Phosphorescence
What is the primary phosphor material used in CR imaging plates?
Gadolinium Sulfide
Caesium Iodide
Amorphous Selenium
Barium-Fluoro Halide
In CR systems, what happens to electrons in the phosphor material when exposed to X-rays?
They scatter and reduce spatial resolution
Some are excited to the conduction band, while others get trapped
They convert directly into an electrical signal
They immediately emit blue light
In CR systems, X-rays give energy to the electrons in the _______ ____, which excites some electrons into the _______ band. Some electrons do not return to their low energy state but drop into _____.
(a)
Traps are created through a process known as
(a)
In CR systems, the number of trapped electrons is proportional to the amount of x-rays absorbed
True
False
Why is a RED laser used during CR image readout?
To increase spatial resolution
To stimulate trapped electrons into the conduction band
To erase residual signals on the plate
To ionize trapped electrons
When reading images out in CR systems: Laser stimulates electrons from _____ into the conduction band; electrons then give up their energy and return to the valence band. During this process ____ _____ _______ are emitted. This emission = luminescence
(a)
How is the CR plate prepared for reuse after image readout?
Heated to remove residual charge
Washed with chemical solutions
Exposed to bright white light to erase trapped electrons
Cooled to stabilise the phosphor
What are the key features of all DR detectors?
Input layer, detector elements, electrical components
Input layer, traps, output layer
Valence band, traps, conduction band
Input layer, capacity layer, detector elements
The input layer in all DR detectors Indirect DR = _______ Direct DR = __________
(a)
Array of detector elements - dels
1. Indirect = _____
2. Direct = ______
1. photodiodes
2. charge collection electrodes
1. charge collection electrodes 2.photodiodes
What is used to read out the stored charge in all DR detectors?
Capacitors
Caesium Iodide
Thin Film Transistors
Semiconductors
The most common scintillator material in Indirect DR systems is
Caesium Iodide
Amorphous Selenium
Barium-Fluoro Halide
Amorphous Silicon
Why is Caesium Iodide used for Indirect DR detectors?
Its columnar structure minimises light scatter
It does not require TFTs for read out
It emits x-rays when stimulated
It increases light scatter, making the spatial resolution better
How does a thicker scintillator layer affect image quality?
Decreases patient dose and improves resolution
Converts x-rays directly to charge
Increases absorption efficiency but may reduce spatial resolution
Eliminates the need for photodiodes
The most common photodiode material in Indirect DR systems is
Caesium Iodide
Amorphous Selenium
Barium-Fluoro Halide
Amorphous Silicon
Reorder the following to the correct summary of process in Indirect DR systems
X-rays are converted to light in the phosphor layer
Light from the input phosphor strikes photodiode
Photodiode converts light to electronic charge
Charge is stored by capacitors
TFT converts charge to digital image
Which DR type is most commonly used in mammography?
Direct DR with amorphous selenium
Indirect DR with Csl
CR with barium fluoro halide
Indirect DR with gadolinium oxysulfide
What limits the minimum achievable del size in DR detectors?
Patient dose requirements
Scintillator thickness
Fill factor reduction due to electronics
X-ray tube focal spot size
The Nyquist frequency for a detector with 50μm del size is _____ lp/mm
10
5
20
2
How does Direct DR achieve better spatial resolution than Indirect DR
By eliminating light scatter through direct charge conversion
Via higher Kip settings
By using thicker scintillator layers
Through larger del sizes
X-rays —> Electronic —> Image
Direct
Indirect
What is the typical del size range for mammography Direct DR detectors?
85-100μm
140-200μm
50-85μm
10-40μm
A resolution test object image showing 1 line pair per 2 (a) demonstrates the Nyquist Frequency
Direct DR detector elements (dels) are
photodiodes
charge collection electrodes
Why is a voltage applied across the a-Se layer in Direct DR?
To attract charge to the collection electrodes
To erase residual images
To stimulate light emission
To generate x-rays
Reorder the following process steps for Direct DR systems
X-rays converted to electrical charge in a-Se layer
Charge captured by charge collection electrodes
Charge is stored by capacitors
TFT converts charge to digital image
What is meant by the term ‘fill factor’?
Electron capture area in mm2
Total del area
Percentage of useful area
Area taken up by electronics
Fill factor = Useful area / _____ ___ area
(a)
Which factor does NOT affect spatial resolution in DR?
Del size
Fill factor
Patient BMI
Input layer material
Typical del size for general radiography and fluoroscopy
500μm
100μm
140-200μm
50-85μm
Small dels = 🔺spatial resolution, 🔻fill factor, 🔻SNR
True
False
We want greater/wider Line Spread Function (LSF)
True
False
X-rays --> Light --> Electronic --> Image
Direct
Indirect
Image Acquisition --> Image processing --> Image (a) --> Image storage
Advantages of DR
Wide dynamic range
Ability to post process
Cheaper storage
Lower dose without image quality compromise
What is a potential issue in digital photography?
(a)
What does "grey level" represent in digital radiography?
Exposure Index
Optical Density
Mean Pixel Value
Dose Area Product
Which of the following is an advantage of a wide dynamic range in digital radiography?
Increased Patient Dose
Better Collimation
Consistent Image Quality
Reduced Exposure Index
Where do the sensors to detect radiation typically sit in AEC systems for general radiography?
Behind the collimator
Between the anti-scatter grid and the detector
Inside the generator
Within the image processing algorithm
Which parameter is most ideal for assessing image quality in DR?
Exposure Time
Signal-to-Noise Ratio (SNR)
Entrance Skin Dose (ESD)
Dose Area Product (DAP)
What should the EI deviation be during routine QC testing?
±5%
±10%
±15%
±20%
What does Dose Area Product (DAP) represent?
Product of dose and exposed area
Detector efficiency
Dose to the patient only
Field size only
Cropping an image will change the Dose Area Product
True
False
What statistical measure is used to set the National DRL?
Mean
Median
75th Percentile
50th Percentile
Proper collimation is amazing because it
reduces scatter
reduces patient effective dose
improves image quality
increases DAP
AEC systems adjust exposure time (mAs) based on patient thickness, (a) , and the preset kV.
Radiology Department - Service
QA
QC
X-ray equipment or DR Detector - Product
QA
QC
________ _____ is related to the dose received by the DR detector
(a)
EI gives us an indication that the image has been correctly exposed without the need to draw ROIs and calculate the SNR
True
False
Which test ensures the exposure index remains stable over time?
Patient dose audit
QC test using 1mm copper
Repeat analysis
Entrance Skin Dose test
Why are AEC sensors placed behind the image receptor in mammography?
To avoid noise artifacts
Lower kV used
Detector is sensitive to scatter
Higher kV used
The National Diagnostic Reference Level (DRL) sets a mandatory maximum dose limit for patient examinations, and exceeding it indicates a breach of radiation safety regulations.
True
False
I am a measure of entrance skin dose at a given point multiplied by the area of the field of view
(a)
A QA program must include tests to ensure optimisation. Therefore, it is important to keep checks on:
EI
ESD
DAP
Storage
