CH 20 Digital Imaging Processing

What are the two systems of digital radiography?

1. computed radiography (CR)

2. direct radiography (DR)

Computed Radiography (CR) uses what type of imaging plate?

photostimulable storage phosphor imaging plate (PSP)

Where is the PSP located?

inside the cassette

Once the PSP is exposed what happens next?

the cassette is taken to the reader to process image and then it is erased (two steps)

How does direct radiography work?

the image is acquired and sent directly to the display monitor for the radiographer

True/False: indirect conversions are WITH scintillator

True

What is the two-step process used by the detector of indirect conversions?

1. uses scintillator (converts incoming x-ray photons to light)

2. then photodetector (converts light into electric signal)

Indirect conversions are used in Amorphous _______ w/ a TFT

silicon

True/False: direct conversions are WITHOUT scintillator

True

True/False: the detector of direct conversions directly converts incoming x-ray photons to electronic signal

True

Direct conversions are used in Amorphous ________ w/ a TFT

selenium

What is a matrix?

series of boxes laid out in rows and columns that gives form to the image

What is a pixel?

each box of the matrix

What is a pixel also known as?

picture element

How is a pixels location determined?

by its address

True/False: a pixel is capable of representing a wide range of different shades of gray

True

What does ADC stand for?

analog to digital converter

What are the two steps that ADC is done through?

1. sampling

2. quantification

'Analog values measured at chosen sampling frequency' best describes what term?

sampling

'Sampled piece of analog data is computed and assigned a value' best describes what term?

quantification

Analog values converted to a binary digit is a ___

bit

What is the 8-bit word?

byte

What is a voxel?

a three-dimensional volume of tissue

What is a voxel also known as?

volume element

Grayscale bit depth ranges from _ bits to __ bits

8; 32

What is the field of view (FOV)?

overall matrix; determined by size of the detector

If FOV remains the same, then as matrix size increases, the pixels get ____, and the resolution gets ____

smaller; sharper

True/False: the greater the matrix size for the same FOV, the better the spatial resolution

True

What is spatial resolution determined by?

pixel size

Spatial resolution is measured in what?

line pairs per millimeter (lp/mm)

What are the three processes intended to change the input values of the pixels to improve diagnostic quality of the image?

1. point processing

2. local processing

3. geometric processing

Which of the image processing systems is the most important for DR systems?

point processing

Define point processing:

performed between the receipt of the input image from the IR and the output image that is viewed on the monitor

What is a common point processing operation?

grayscale processing

What is grayscale processing?

allows for adjustments to image brightness and contrast

Grayscale processing involves the creation of (three things):

1. histogram

2. look-up-table (LUT)

3. windowing

How is a histogram generated?

the scanned area is divided into pixels and the signal intensity for each pixel is determined

Histogram, locates _______ and _______ signal within the anatomical regions of interest in the image

minimum; maximum

The shape of the histogram corresponds to what?

specific anatomy and technique used for an exam

A histogram analysis is performed to determine what two things?

1. values of interest (VOI)

2. exposure indicator (EI)

What happens if the VOI are under/overexposed?

the computer will correct the image on its own (rescaling or histogram modification)

Wide histogram indicates ______ contrast

higher

Narrow histogram indicates _____ contrast

lower

Without LUT applied, the image would display as a ___ contrast image

low

Selecting the proper LUT = proper _________

grayscale (regardless of variations in kVp and mAs)

What does windowing change?

contrast and brightness of the image on the monitor

What is window width (WW)?

range of densities that will be displayed

A narrow window width has few shades of gray and ____ contrast

high

A large window width has many shades of grays and ___ contrast

low

What is window level (WL)?

center of window width and controls brightness of image

The more the original image is changed by the Radiographer before sending to PACS, the _____ information the radiologist has to work with

less

Local processing operations is also called what?

area or group processing

What is local processing?

mathematical calculations are applied to only a small group of pixels at a time (eventually covering all pixels)

What is a kernel?

processing code that is mandatory and common to the computer system

Spatial Frequency Filtering is used to do what?

sharpen, smooth, blur, reduce noise, or pull elements of interest from image

What are the two kinds of spatial frequency filtering?

1. high-pass filtering

2. low-pass filtering

True/False: high-pass filtering is also called edge enhancement

True

What does high-pass filtering do?

- removes or suppresses low spatial frequency to produce a sharper output image

- greatly increases contrast

True/False: low-pass filtering is also called smoothing

True

What does low-pass filtering do?

- intentionally blurs the image

- reduces noise and displayed brightness

What is unsharp masking?

"blurring" subtracts a low-pass filtered image from the original

What is geometric processing used for?

to change position or orientation of pixels in the image

Digital image quality is based on what four things?

1. resolution

2. noise

3. detective quantum efficiency (DQE)

4. artifacts

Spatial resolution is controlled by what?

matrix size and how many pixels can be displayed by the monitor

If matrix size increases and pixel size decreases, what happens to spatial resolution?

it increases

Noise is classified as what (three things)?

1. system noise

2. ambient noise

3. quantum mottle noise

A high signal to noise ratio (S/N) indicates ______ noise in the image.

little

If there is an increase in noise, what happens to contrast?

decreased contrast

If there is a decrease in noise, what happens to contrast?

increased contrast

What is quantum mottle noise?

- results from an insufficient quantity of photons from an improperly set exposure factors

- produces grainy image

How do you correct quantum mottle noise?

repeat with increased technical factors

What is detective quantum efficiency the measure of?

the sensitivity and accuracy by which the IR converts the incoming data to the output viewing device

a device with 100% efficiency has DQE = 1, meaning ...

no loss of information

DR systems have a DQE between

30%, 70%

Exposure Indicators determine what?

the quantity of photons that strike the detector

What is the deviation index (DI)?

a comparison between the actual exposure and the proper exposure received by the image detector

exposure sensitivity of imaging detectors ranges from:

0.1 mR to 100 mR; or a range of 1000:1