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what is spatial resolution
the sharpness or accuracy of an anatomical structure lines
what are other words for spatial resolution
sharpness, definition, recorded detail, detail
what does visibility of SR refer to
brightness or density of the image with image contrast
how is accuracy of structural lines achieves
high SR while minimizing distortion
what is the film-screen unit for resolution
line pairs per mm (Ip/mm) or cycles per mm
how are resolution test tools arranged
pairs of lines set at a distance from one another
how are resolution test tools read
based on the viewer can differ the close line pairs from each other represents the Ip/mm reading
what is Ip/mm most people can read up to
5 Ip/mm
what is the relationship between Ip/mm and resolution
the higher the Ip/mm, closer the line pairs, the higher the resolution (direct relationship)
what determines spatial resolution
matrix size, pixel size, and grayscale bit depth
spatial resolution is commonly described in terms of
spatial frequency
what is the relationship between SR and spatial frequency
when SR is high, there is a shorter wavelength signal, so SF is also high for fine details only (direct relationship)
what is the relationship between line pairs and spatial frequency
higher the SF the closer the line pairs
what is lack of sharp definitions of fine details caused by
penumbra
regarding information from images,
some information is always lost
what also increases unsharpness of an image regarding a patient
patient movement
how is SR for digital radiographic images described
x-axis, y-axis, and z-axis (grayscale bit depth)
what does the z-axis represent
the different shade of gray represent the added depth of the image or the info by each pixel
what is a matrix
a combo of rows and columns of pixels
what are pixels
small squares that makes up the matrix
what does each pixel represent
a number representing the amount of brightness
what does the pixel location on the matrix represent
the area within the patient or the volume of tissue
what is field of view (FOV)
the dimensions of an anatomical area
what is the relationship bw matrix size, pixels, and resolution
the greater the matrix size, the greater amount of pixels, and the better the resolution (direct relationships)
what is the equation for pixel size
pixel size = FOV/matrix size
what is the relationship between the matrix side and the pixel size w/ fixed FOV size
when matrix size increase, the pixel size decreases (inverse relationship)
what is the relationship between the FOV and the pixel size w/ fixed matrix size
the greater the FOV, the greater the pixel size (direct relationship)
what does each pixel have
bit depth
what is the relationship between bit depth and resolution
the larger the bit depth, the greater number of shades of gray, the better the resolution
what is point spread function (PSF)
measuring penumbra by using a single point from an extended line
what is the relationship between PSF, penumbra, and resolution
when PSF increases, penumbra increases, and resolution decreases
what was line spread function (LSF)
a narrow slit in a sheet of lead to measure penumbra
what is edge spread function (ESF)
uses a sharp edge instead of a line or point to measure penumbra
how is PSF measured in other modalities (xray, NM< CT, US, MRI)
X-ray: tiny hole in lead sheet then producing x-ray image of the hole
NM: point source of radioactivity
CT: a thin metal wire
US: a monofilament
MRI: water filled hole in a phantom
what does a PSF graph look like it
the narrow part of the graph has better resolution
what is modulation transfer function (MTF)
the ability of the system to record spatial frequencies
what does MTF measure
the accuracy of an image compared to the original object
what is the desired relationship between MTF and SR
high MTF at high SR
what is the relationship between MTF and spatial frequency
when MTF increases, spatial freq decreases
what is system noise
noise from the digital equipment
what is ambient noise
noise from background radiation
what is quantum noise
noise caused my insufficient photons hitting the IR due to improper kVp and mAs (quantum mottle)
what is signal to noise ratio (SNR)
the amount of radiation exposed to the detector (signal) compared to the noise
what is the relationship between the SNR and noise
high SNR means stronger signal than noise and vice versa
what is the relationship between SNR and SR
higher the SNR the better the SR
what is contrast to noise ratio (CNR)
how big of a difference bw the contrast ad the noise
what is the relationship between CNR and noise
when CNR is high, the contrast is better than the noise and vice versa
what is the nyquist criterion
the requirement for systems to sample spatial frequency signals twice per cycle
why is sampling twice required
the more sampling during a cycle taken, the more information will be taken and the more detail of the image will be seen
making up for the spaces between the pixels
what is aliasing
when there was not enough sampling causing the data to be misinterpreted
often due to the spacing between the pixels
what factors affect spatial resolution
motion
SID
OID
focal spot size
intensifying screens
phosphor size
phosphor concentration
what happens to photons coming out of the focal spot
diverge from the source like a cone shape
what is the relationship between SID and SR
as SID increases, SR increases
what is the relationship between OID and SR
as OID increase, SR decrease
what is the relationship between focal spot size and SR
when focal spot size increase, penumbra increase, SR decrease
what is the formula for finding the width of penumbra
P= (focal spot size x OID)/ SOD
what is penumbra
the unsharp edges around an image
what is umbra
the sharp area of the image often surrounded by the penumbra
what is attenuation absorption unsharpness
when the beam diverges due to the the object being attenuated causing penumbra
what are DR detectors made of
silicone or selenium
what limits DR detectors
the size of the detector elements
what does DR image processing system also limited by
matrix size, pixel pitch, and grayscale bit depth
what are CR systems limited by
phosphor size, layer thickness, concentration, and IRD
what is the relationship between film screen speed and SR
as speed increases SR decreases (inverse)
what are the part of a film
the base and the emulsion
what is the base of the film
a polyester sheet that is between the emulsions
its able to keep its size and shape through any processing condition and can be tinted blue to help with images
what is the emulsion of the film
gelatin substance that contains bromine crystals
the gelatin is colloid and amphoteric
what is the relationship between density and SR
when density increases, sensitivity increases and SR decreases (inverse)
what are intensifying screens made up of
a base and active layer
what happens when the xray beam hits the phosphor crystals
the phosphor emits light which creates the image
what are some problems of intensifying screens
light diffusion, screen speed, and poor screen contact
what is the relationship between light diffusion and SR and why
when light diffusion increases, SR decreases bc the space between the film and the phosphor cause the light to spread out on the film surface
what is the relationship between the crystal size and SR
when phosphor crystal size increase, light diffusion increase, and SR decrease
what is the relationship between intensifying screen speed and SR and why
when speed increases, more light emits causing SR to decrease
fast screens also have bigger crystals or more crystal layers making SR decrease
how does poor screen contact decrease SR
poor screen contact cause more light diffusion which decreases SR
what is the relationship of phosphor size and resolution, pt dose, and film density/IR expo
when phosphor size increase
resolution decrease, pt dose decrease, density increase
what is the relationship of phosphor layer thickness and resolution, pt dose, and film density/IR expo
when phosphor layer thickness increase
resolution decrease, pt dose decrease, density increase
what is the relationship of phosphor concentration and resolution, pt dose, and film density/IR expo
when phosphor concentration increase
resolution increases, pt dose decrease, density increase
what types of motion affect SR
voluntary, involuntary, equipment
what is voluntary movement and what is the best way to minimize it
patient has direct control over movements
communication is key or sometimes immobilization is required
what is involuntary movement and how can it be minimized
movement that’s out of the patient’s control
lowering mAs and increasing kVP (15% rule)
what is equipment motion
vibrations in the machine or xray tube suspension system
unable to use machine till fixed
what is distortion
misinterpretation of the true size and shape of the anatomy being examined
what is magnification
when the object being radiographed is bigger than the object itself
what is the only size distortion possible
magnification
what controls magnification
SID or OID
what is the relationship between size distortion and SID
when SID increases, size distortion decreases
what is the relationship between OID and size distortion
when OID increases, size distortion increases
what is ideal for the least amount of magnification
short OID with long SID
calculating magnification (formula)
M= SID/SOD
tells you how much longer and wider the image is compared to the original object
calculating actual object size (formula)
O= I/M
I: image size
M: magnification factor
O: object size
calculating % of magnification from original
M% = ((I-O)/O) x 100
what is size distortion
misrepresentation of the true size of the anatomical part on the image
what is shape distortion
misinterpretation of the true shape of the anatomical part on an image
what can be considered shape distortion
elongation or foreshorten
when does elongation occur
when the CR and the IR aren’t properly aligned while the object and the IR are parallel
i.e CR is angled or IR w/ object isn’t perpendicular with CR
how does elongated images look like
long and thin (stretched out)
what causes foreshortening
when the object isn’t properly aligned as the CR is perpendicular to the IR
how does foreshortening look
anatomical part squash together with unequal magnification
what factors affect shape distortion
when an anatomical part isn’t at the same level entirely (think as if it was diagonal rather than horizontal) causing beam divergence