spatial resolution & distortion

chapter 28 & 29

another word for spatial resolution is:

detail

geometric properties are:

detail and distortion

________________ is the degree of geometric sharpness or accuracy of the structural lines actually recorded in the image

spatial resolution

good detail will still exist even when it cannot be seen. this is because of:

IR exposure

_______________ is the easiest to evaluate and adjust than other image quality factors

spatial resolution

in film unit of detail is measured in:

line pairs per millimeter (lp/mm)

_________________ is the point at which the viewer can separate the closest pair of lines from each other represents the lp/mm reading

resolution tool

spatial resolution (detail) is determined by:

pixel size, matrix size, and grayscale bit depth

spatial frequency is usually described as ________ or _________ detail

high; low

shorter wavelength signal (high frequency) represents pairs of lines that can be visualized close together = _________________

high resolution

all radiographic images have _______ (more/less) spatial resolution than the object itself

less

xrays are bringing only what percent of detail from our bodies?

30-70%

art of radiography is making sure:

body part is truly represented good

____________ is the lack of sharp definition of fine detail (not sharp)

penumbra

___________________ measures penumbra and is used to quantify digital system spatial resolution

point spread function (PSF)

PSF gives us the number of:

how unsharp an image is

_______________ is evaluated during quality control testing by a resolution test tool

spatial resolution

__________ (big/small) structures are easiest to evaluate. why?

small, bc it’s easier to see detail/evaluate (ex. hand)

________________________ describes the ability of an imaging system to accurately display objects in two dimensions

assessing resolution

spatial resolution is expressed in terms of three elements:

x-axis, y-xis, and grayscale bit depth

why do x-y grid matrix dimensions make up the spatial resolution?

bc this info is represented through various points in space

grayscale bit depth represents the:

depth to the info

digital image quality is very concerned with ____________________

grayscale bit depth

what 3 spread functions all express the boundaries of the image?

point, line, and edge spread functions

____________ is determined by complex mathematical measurement of the image from a single point

point spread function (PSF)

______________ is the same type of data as PSF but found using a slit in a sheet of lead

line spread function (LSF)

________________ uses a sharp edge instead of line or point

edge spread function (ESF)

what is high spatial resolution?

high frequency signal that is capable of imaging smaller objects

what is low spatial resolution?

lower frequency signal that can only image larger objects

_____________________ measures the accuracy of an image compared to the original object on a scale on 0-1

modulation transfer function (MTF)

the raw data for MTF measurement is the total from ________, _______, ________

PSF; LSF; ESF

MTF measures the percentage of ____________________ that is recorded

object contrast

________________________ measures percentage of object contrast that is recorded

modulation transfer function (MTF)

________ (high/low) MTF values at _________ (high/low) spatial resolution are desirable and key specification in digital detectors

high; high

MTF of 0 = _________________

no signal

MTF of 1 = ______________________

extremely high signal

as the spatial frequency of objects rises, MTF ______________

decreases

what number is the goal to have MTF close to as possible?

1

_________________ is the total noise that the imaging receptor receives

imaging noise

what are 3 types of noises?

system, ambient, and quantum noise

____________ can filter out the noise as long as the imaging noise is significantly lower than the amount of info coming in

algorithms

_____________________ is a measure of signal strength relative to total noise

signal-to-noise ratio (SNR)

signal-to-noise ratio depends on the amount of _____________________ to the detector and the detectors _______________________

radiation exposure; detective quantum efficiency

_________________________ is defined as the ratio of the difference of signal intensities of two regions of interest to the imaging noise

contrast-to-noise ratio (CNR)

CNR is dependent upon both ___________________ and _________

digital image contrast; SNR

high CNR values are not possible with ______ (high/low) SNR values

high

low contrast resolution

is a type of contrast resolution that deals with the ability to visualize subtle energy differences

________________ is determined by the imaging system’s ability to visualize small objects of low contrast

low contrast resolution

____________________ is the relationship between the duration of data acquisition and motion of structures under study

temporal resolution

___________ (bigger/shorter) acquisition time will demonstrate better temporal resolution because it _______________ motion

shorter; minimizes

as temporal resolution increases, spatial resolution ______________

decreases

digital imaging requires that the spatial resolution frequency be samples how many times from each cycle?

twice

_________________ is the processing algorithm that averages the incoming analog data by using the distance between the imaging detector elements

nyquist criterion

______________ is the misrepresentation of signal frequencies

alasing

______________ occurs when the spatial frequency exceeds the nyquist frequency and the incoming data is sampled less than twice per cycle

aliasing

aliasing looks identical to what effect that happens in CR?

Murray effect

________________ affects the image appearance by demonstrating fine detail structures

spatial resolution

when fine detail is lacking, the image will often appear _____________

blurred

4 factors that affect spatial resolution:

1. distance

2. focal spot size

3. image receptor

4. motion

resolution problems should be approached in what order:

reduce OID

increase SID

if film: reduce phosphor size, concentration

elimination of motion

reduce focal spot size

elimination of motion

reduce OID

reduce focal spot size

in film: reduce phosphor size, concentration

increase SID

______________ is the most important factor in establishing the level of resolution desired for spatial resolution

geometry

x-ray beam is created at a _______________

small FSS

the further a photon travels, the __________ (more/less) it diverges

more

_____, ______, _________ are critical in establishing sufficient detail

SID; OID; SOD

detail is improved when OID is ______________

decreased

why is part of interest usually closest to IR?

there will be less time for the photons to diverge when closer to IR = less penumbra

decrease OID, ____________ penumbra

decrease

resolution is improved when SID is ______________

increased

why do we want increased SID?

bc there will be less time for the photons to diverge = less penumbra

___________ distance, to _____________ OID, for _____________ detail

increase; decrease; increase

increase SID, ______________ penumbra

decrease

why is PA chest preferred over AP chest?

bc it puts the heart closer to the IR, so it gives better detail

______________ is controlled by the line focus principle

focal spot size

focal spot size is controlled by:

line focus principle

__________ is a sharp area of a shadow - sharp edge of anatomy

umbra

___________ is the imperfect, unsharp shadow surrounding part

penumbra

why is FSS a major controller of spatial resolution?

bc it controls penumbra

FSS decreases, penumbra ____________, detail _____________

decreases; increases

what exams will have a large FSS?

chest and abdomen bc it’s bigger anatomy

what is the mathematical equation to calculate penumbra?

P = focal spot size x OID / SOD

penumbra is also increased by:

attenuation or absorption unsharpness

T/F: an xray image will always have penumbra.

true, our bodies aren’t trapezoidal, we just want to lower penumbra as much as possible

primary factors that affect spatial resolution are:

detector geometric properties and image processing system

___________ depends on the phosphors in detector to acquire incoming photon data

detector

3 factors of phosphors:

1. size

2. layer thickness

3. concentration

2 issues for the IR detecotrs:

1. intensifying screens

2. scanning systems

DR systems are either _________ or _________ detectors

silicon; selenium

_____________ are limited bc of the amount of photons that can be registered within a single detector

silicon detectors

high fill factor = _________ (high/low) resolution

high

___________ and ___________ detectors are both limited bc of the size of the detector elementt

silicon; selenium

________________ has limits set based on detail

processing system

processing system depends on acquisition and _______________, ______________, ________________

display matrix size, pixel size, grayscale bit depth

___________ is most commonly classified by speed

film

___________ relationship between speed and resolution

inverse

intensifying screen depends on phosphor _________, ________________, _________________

size; layer thickness; concentration

quantum mottle may drastically affect detail when _______ (high/low) speed intensifying screens are used with extremely _______ (high/low) mAs

high; low

with digital imaging, ___________________ is more pronounced

quantum mottle

how do we fix quantum mottle?

increase mAs

image will look like a blurred series of exposures:

motion

3 types of moiton:

1. voluntary - coughing

2. involuntary - heart beat

3. equipment - cassette moves