Distortion/ Recorded detail (spatial resolution)

Question 1

Shape distortion

Answer 1

unequal magnification of structure
Elongation (tube an IR not aligned)
foreshortening (body part not properly aligned)

Question 2

Factors Affecting Size Distortion

digital systems

Answer 2

Magnification – post processing

Minification – post processing

Question 3

2 geometric properties

Answer 3

-recorder detail (definition, sharpness, spatial
resolution)
-distortion

Question 4

Spatial resolution/recorder detail is determined by

in digital

Answer 4

degree of geometric sharpness, structure lines.
easy to adjust (detail)
Dependent on matrix size, pixel size, and grayscale bit depth
Correspond to to the x and y axes of the digital image

Question 5

Unit of resolution

Answer 5

line pairs per millimeter
(lp/mm) or cycles per mm
measure by resolution test tool

Question 6

Resolution test tool

Answer 6

how many lines you see it in image

human eye = 5 lp/mm

Question 7

clinical evaluation

Answer 7

trabecular pattern

how sharp patters of bone look

Question 8

Unsharpness

Answer 8

penumbra (outline of shadow)

point spread function (PSF) measures penumbra

Question 9

Spatial Resolution definition

Answer 9

-Ability of an imaging system to accurately display
objects in two dimensions
-smallest object that can be detected in an image
-film-screen system have better spatial resolution than
digital

Question 10

Good detail/resolution may exist even if

Answer 10

you can’t see it due to poor visibility.

Question 11

Spatial Frequency

Answer 11

-High or low frequency signal
-Determined by measuring distance between pairs of
lines distinct from one another

Question 12

High frequency would represent an image with

Answer 12

better resolution/detail

Question 13

point spread function (PSF)

Answer 13

complex mathematical measurement of the image produced from a single point

Question 14

line spread function (LSF)

Answer 14

would be measured using a narrow slit in a sheet of lead

Question 15

edge spread function (ESF)

Answer 15

uses a sharp edge instead of a line or point

Question 16

Modulation transfer function (MTF)

Answer 16

Measures accuracy of image compared to actual object
Measures the percentage of object contrast that is absorbed

scale 0 to 1
0=no signal, therefore no image;
1=records image perfectly

Question 17

noise

Answer 17

Background information received by image receptor

cause by Quantum noise, Quantum mottle (not properly exposed image) noise affects spatial resolution.

Question 18

Imaging Noise

Answer 18

total noise the IR receives. Includes quantum noise, system noise, and ambient noise

Question 19

Signal-to-Noise Ratio(SNR)

Answer 19

measures strength of the signal to noise. Depends on amount of radiation exposure(signal) to the detector and detector’s quantum efficiency.

Question 20

digital sampling

Answer 20

not as much info as film

Question 21

Spatial resolution of a digital system is equal to

Answer 21

½ the Nyquist frequency.

Question 22

Nyquist frequency or criterion is the

Answer 22

highest spatial frequency that a digital detector can record and is determined by the sampling frequency of a CR system and the spacing of the DELs of DR systems

Question 23

Aliasing (Moire Pattern)

Answer 23

-Occurs when Nyquist Criterion not met
-Low-frequency image wraps around high-frequency
image
-Visual appearance of two images slightly out of
alignment, scan lines an grid lines in same direction

Question 24

Primary factors affecting spatial resolution in digital systems are

Answer 24

the detector geometric properties and the processing system

Question 25

Primary limitation: | digital

Answer 25

Size of detector element (system can only show objects the size of the DEL)

Question 26

CR imaging plates limitations

Answer 26

similar to intensifying screens | Also affected by image reader device (IRD

Question 27

Indirect DR (flat panel systems)

Answer 27

``` -2 types: TFT and charge couple device (CCD) both need a scintillator to change x-rays to light TFT uses amorphous Silicon (photodetector), amorphous requires scintillator such as cesium iodine or gadolinium oxysulfide Fill factor(number of photons that can be registered within a single detector) High fill factor=high resolution and vice versa ```

Question 28

Direct DR

Answer 28

direct converting photons to electronic signal uses amorphous Selenium (photoconductor) and TFT NO scintillator (no light conversion process so they have better spatial resolution)

Question 29

Images lacking fine detail Appear blurry Assessment of motion Factors Affecting Recorded Detail:

Answer 29

-Eliminate motion -Reduce OID -Reduce focal spot size (wires) -Reduce intensifying screen phosphor size(the larger the faster speed in intensifying screen=loss of detail) hhand concentration, means we can use less radiation for same density -Increase SID

Question 30

Geometry

Answer 30

``` -Distance SID= tube to IR OID= object to IR SOD= source to IR -Focal spot size ```

Question 31

Voluntary motion

Answer 31

under patient control | control with Communication

Question 32

Involuntary motion

Answer 32

unable to control (heartbeat, Parkinson, etc.) Exposure time reduction (manipulate mA, time relation or 15% rule) Immobilization devices

Question 33

grayscale bit depth

Answer 33

of shades of gray each pixel in that matrix is capable of recording

Question 34

only things that have an impact in recorded detail

Answer 34

OID SID focal spot size maybe also intensifying screen

Question 35

the lower the speed of the intensifying screen ...

Answer 35

the better the recorded detail

Question 36

digital systems image processing system limits on spatial res/recorded detail

Answer 36

Acquisition and display matrix Pixel size Grayscale bit depth (how many shades of gray) larger matrix=smaller pixels=better spatial resolution

Question 37

umbra

Answer 37

distinctly sharp area of shadow or the region of complete shadow

Question 38

distortion

Answer 38

misrepresentation of the size and shape .

Question 39

magnification

Answer 39

equal shape distortion only possible with size distortion, controlled by distances SID,OID reducing magnification increases spatial resolution

Question 40

minification

Answer 40

divergent property of x-rays photons

Question 41

when OID is increase and cannot compensate u need to..

Answer 41

increase SID

Question 42

to find magnification factor

Answer 42

(always come up to 1.something) M=SID/SOD to find SOD = SID-OID

Question 43

to find object size

Answer 43

O= I/M

Question 44

factors affecting shape distortion

Answer 44

``` Alignment Central ray Anatomical part Image receptor Angulation Degree Direction ```

Question 45

angulation

Answer 45

Angling tube is designed to cause a controlled or expected amount of shape distortion, usually to avoid superimposition. Angulation also changes SID which needs to be compensated for. In general, decrease SID 1 inch for every 5 degrees of tube angle or increase exposure factors to compensate for new SID.