Imaging Processing and Characteristics

Digital Imaging I

What kind of signal does an analog produce?

continuous

Bit

binary number

Byte

8 bits

What does 0 and 1 equal on an analog?

0 = off

1 = on

Matrix

rows and columns of pixels

Pixel

picture element

Voxel

volume element (had depth)

When does a pixel become a bit?

When it is assigned a number

What controls the numbers of shades of grey?

Bit depth

What is the equation for shades of grey?

2^n n= bit depth

Spatial Resolution

ability to distinguish adjacent structures as separate, distinct structures

How is spatial resolution expressed?

lp/mm

Does film screen or DR have better spatial resolution?

FILM SCREEN

Is smaller or larger focal spot preferred for better resolution?

small

What pixel size is preferred for better resolution?

small

Is small or large pixel pitch better for resolution?

low

Do we want a thin or thick phosphor layer?

thin

What laser size is preferred for better resolution?

thin

Contrast Resolution

ability of an imaging system to distinguish and display a range of attenuation coefficients from different tissues within the body

Does digital or film have better contract resolution?

digital

Histogram

graphic representation of the frequency of each pixel intensity

Where are histograms stored?

Look-up table

VOI (values of Interest)

data to be included in an image

Dynamic Range

range of exposure intensities that IR can respond to and use to acquire image data "possibility"

What type of dynamic range does digital have?

WIDE/LINEAR

Exposure Latitude

Range of exposure values an IR is able to produce. "it can"

Deviation Index

difference between actual and ideal exposure for specific body parts

What is a result of sever under exposure?

Quantum Mottle

Exposure Indicator

the amount of exposure recienved by imaging plate

If the S-value is very high is the image under or over exposed?

under

How many times must a pixel be sampled?

twice

Pixel Pitch

Distance between two pixels

Aliasing

Occurs when a frequencies not sampled enough

Detective Quantum Efficiency (DQE)

overall efficiency of with which a detector converts incoming xray exposure to useful output image

In best to worst what is the order of DQE?

1. indirect capture

2. direct

3. CR

4. film screen

Modulation Transfer Function (MTF)

-ability of a system to record available spatial frequencies

-quantifies the gain or loss of resolution between anatomy of interest and IR

Diagnostic Yield

images are assumed to be taken using established department procedures and protocols in accordance with standards of care

Diagnostic Efficacy

faithful representation of the patient on the radiograph

Image Fidelity

all information on image should clearly represent patient

What are the 2 types of image quality factors?

-geometric quality

-visibility quality

Can image quality ever be better than the quality of the viewing monitor?

NO

QC and Diagnostic Reading Monitor levels?

QC- 1K

Reading Monitor- 2K

What are the 2 types of preprocessing?

1. Flat fielding\

2. Signal Interpolation

Flatfielding

makes a uniform response

-gain: every few months

-offset: many times a day

Signal Interpolation

averaging defective pixels, results in removal of artifacts

Window Width

controls shades of grey/contrast

Window Level

sets center point (brightness)

Edge Enhancement (High pass filtering?

increases contrast, edges are enhanced

Smoothing (low pass filtering)

used to visualize small structures, "smooth out" details

Shuttering

blacken white boarders of images

What are some examples of post processing?

• Stitching

• annotating

• magnifying

• inversion

• subtraction

Pixel shift

misregistration of image

ROI (region of interest)

area of anatomical structure on a reconstructed digital image

Dead pixels

non functioning or poor connections between pixels can cause artifact

Image Lag

detector does not clear signal from previous image

Data drop

extreme over exposure, data points are dropped

Detector Saturation

involves areas or regions

Photon Starvation

inadequate exposure

How do you calculate pixel size?

FOV/matrix (mm)

What is the mathematical formula used by the computer to preform functions?

Algorithm

Spatial Resolution is a term used to describe image…

sharpness of detail

A digital systems ability to demonstrate subtle differences in shades of grey is…

contrast resolution

What describes the ratio of recorded contrast to the real contrast of an object..

MTF

Image _ is caused by electronic interference?

snow

When the computer adjust pixel intensities to match those of the average on the histogram is….

rescaling

Are digital systems more or less sensitive to scatter?

More

What IR types has higher patient dose?

Indirect Capture

with digital imaging, the analogue x ray singal is sampled and coverted to

digital

the exposure intensities that will be included in the image construction

value of interest

what is the word used for picture element 

pixel 

the smaller the ______ the better the image _______

pixel, resolution

what controls the number of shades of gray available to the image

bit depth

the number of shades of gray available to an image controls image

contrast resolution

the larger the matrix, the ________ the resolution 

better 

how to calculate pixel size 

FOV/matrix (in MM) 

term is used to describe the amount of exposure received by the image receptor 

exposure index/indicator 

mathematical formula used by computer to perform functions

algorithms

under exposed image will have an excessive amount of

noise

what controls brightness

window level

what controls image contrast

window width

image resolution is very dependent on

pixel size

spatial resolution is a term used to describe image

sharpness of detail

digital systems ability to demonstrate subtle differences in shades of grey describes

contrast resolution

sampling frequency is too low

aliasing

high pass filtering

edge enhancement

low pass filtering

smoothing

describes ratio of recorded contrast to real contrast of object

modulation transfer function

amount of signal vs noise in digital image expressed by

signal to noise ratio

term used when not enough photons are available in image (kVp)

quantom mottle

dynamic range 

range of exposure intensities that an IR can respond to and use to acquire digital image date