Recoded detail
�Geometric property of image quality
�Detail/recorded detail/resolution/spatial resolution
�Use synonymously
�Image sharpness
umbra
�distinctly sharp area of a shadow
�complete shadow
�Sharp borders
Penumbra
�Imperfect, unsharp shadow surrounding the image
�Image unsharpness
�Fuzzy border around the image
�Pairs of lines that are different distances apart
�Tool is imaged by the system
�Viewer determines the smallest pair of lines that can be visualized
�Pairs of lines are measured
�Lp/mm
Resolution test tool
�Line pairs per millimeter
�Lp/mm
�Small structures are the easiest to examine for detail/resolution
�Trabecular pattern
Unit of resolution
Spatial resolution is high when:
�Object size - small
�Object distance - close
�High number of lp/mm
�High MTF (Modulation Transfer Function)
�Closest to 1.0
�Low PSF (Point Spread Function)
point spread function (PSF)
�Expresses the boundaries of an image
�Image produced from a single point
�Describes the blurring properties of an imaging system
PSF is the same as
penumbra or blur (used in film/screen)
MTF (modulation transfer function)
measure of the ability of the detector to transfer its spatial resolution characteristic to the image
MTF 0
represents no signal & no image
MTF 1
represents a perfect image (not normal)
As spatial frequency of objects _________, the MTF ________
Increase, decrease
MTF closest to 1 will
give you the best spatial resolution
Image noise
background information that the image receptor receives.
Quantum Noise
Lack of sufficient data
Quantum Mottle
�Insufficient photons reaching the IR
�Photon starvation
�Not enough mAs
�How do we fix it?
SNR (Signal to Noise Ratio)
�Signal is good information
�Noise is the bad information
�We want a higher SNR (1000:1)
Digital Sampling
�Digital does not collect as much information as analog.
�Spatial resolution frequency must be sampled twice per cycle in order to achieve a good spatial resolution.
Nyquist criterion
�Averages the incoming analog data
�Signal averaging
Aliasing
�Occurs when nyquist criterion is not performed
�Data is not sampled at least twice per cycle
�Can mimic a moire pattern
�Not a grid problem
How does motion affect recorded detail?
�Eliminate/reduce motion
How does OID affect recorded detail?
�Reduce OID
How does SID affect recorded detail?
�Increase SID
How does focal spot size affect recorded detail?
�Reduce FSS
focal spot size
�Controlled by line focus principle
Major controller of image resolution because it controls
Penumbra
As focal spot ________ in size, penumbra ___________
Decrease
As focal spot ______________ in size, recorded detail/resolution __________
Decrease, increase
Penumbra
� increased also by attenuation or absorption unsharpness.
�Because of the divergence of the x-ray beam, an trapezoid would be the only perfectly sharp image.
�Tissue/parts of the body are not trapezoid in shape.
�When radiated and attenuation occurs, abs
Motion
�Reduces recorded detail/spatial resolution
�Doesn't allow enough time for a well-defined image to be formed.
�Appears blurred.
�Two types of motion
�Voluntary
�involuntary
voluntary motion
�Under direct control of patient
�Communication is number one way to reduce voluntary motion.
�Effective communication is key.
�Immobilization devices can help.
�Sandbags
�Tape
�Sponges
�Sheets
�velcro
involuntary motion
�Not under conscious control of the patient.
�Heartbeat
�Peristalsis
�Reduced by decreasing exposure time