Digital Image Processing (Ch. 20)

What are the two systems of digital radiography?

• Computed radiography (CR)

• Digital radiography (DR)

Computed radiography uses?

Photostimulable storage phosphor imaging plate (PSP or IP)

Where is CR located?

Inside the cassette

Once the ____ is exposed, cassette taken to reader to process image and then it is erased

PSP

For digital radiography, image is acquired and sent ____ to display monitor for radiographer

Directly

What does DR include?

• detector and reader as permanent part of table or wall

• can be moved around

• some wireless

• very expensive

• very fragile

Indirect conversion is ___ scintillator

With

Indirect conversions two part process:

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

2) photodetector (converts light into electronic signal)

Indirect conversion is used in:

• PSP

• Charged coupled device (CCD)

• Amorphous silicon with a thin film transistor (TFT)

Direct conversion is ___ scintillator

Without

Direct conversion directly converts incoming x-ray photons to _______

electric signal

Direct conversion uses ____ and a _____

Amorphous selenium and thin film transistor (TFT)

A digital image is one that has been converted into _____ for transmission or processing

numerical values

ADC=

analog-to-digital converter

What is sampling?

Analog values measured at chosen sampling frequency

What is quantification?

Sample piece of analog data is computed and assigned a value

Analog values converted to binary digit=

Bit

8-byte word=

1 byte

What is a matrix?

Series of boxes laid out in rows and columns that gives form to the image (Ex. 4 × 4)

What is a pixel?

Each box of the matrix

A pixel has its own ___determined by its address

location

Pixel is capable of representing a wide range of different shades of gray (_____ —> ____)

pure white, total black

Each pixel represents a _____ known as a volume element a _____

3D data point, voxel

What is field of view (FOV)?

Overall matrix, determined by the size of the detector

As matrix size _____, the pixels get ____, and the ____ the image

Increases, small, sharper

The greater the matrix size for the same FOV, the ____ the spatial resolution

Better

What is spatial resolution?

Image sharpness

Spatial resolution is a critical image quality factor determined by ____

pixel size

Spatial resolution is measured in?

Line pairs per millimeter (lp/mm)

What is grayscale bit depth?

Determines that number of shades of gray in one pixel

Grayscale bit depth ranges from ____ bits to ____ bits

8-32

Grayscale bit depth of 12 produces ___ gray levels

2^12

How many different shades of gray in one pixel/voxel?

4096

What are the 3 processes a computer goes through after an exposure?

1) point processing

2) local processing

3) geometric processing

What is point processing?

Happens from when the image receptor sends its input image signal to when the output image is viewed on the monitor by you

Point processing operations is the _____ processing operations in DR

Most common

Grayscale processing allows for adjusting image ____ and _____

Brightness and contrast

Grayscale processing creates:

1) histogram

2) look up table (LUT)

3) windowing

Histogram is generated from image data, allows system to find ____

useful signal

For histograms the scanned are is divided into pixels and _____ for each pixel is determined

signal intensity

Histogram locates ____ and _____ signal within the anatomical regions of interest in the image

minimum and maximum

____ of the histogram corresponds to specific anatomy

Shape

Histogram analysis is performed within computer to determine _____

1) values of interest (VOI)

2) exposure indicator (EI)

____ is what locates min/max exposure for the body part

VOI

if the VOI are over/underexposed, the computer will correct the image on its own= ____ or histogram modification

Rescaling

What is reference histogram?

Each body part has a reference histogram that was obtained using the correct exposure factors

Wide histogram=

Higher contrast

Narrow histogram=

Lower contrast

After the histogram, the next step during point processing operation is to adjust ___ with the LUT

Contrast

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

Low

LUT is applied to the data which has the standard ___ for the exam

Contrast

LUT gives ___ image contrast on the display

Desired

Selecting proper LUT= proper ____, regardless of variations in kVp and mAs

Grayscale

Windowing changes ___ and ___ of the image on the monitor

Contrast and brightness

What is window width (WW)?

Range of densities that will be displayed

Narrow window width =

Few shades of gray, high contrast

Large window width=

Many shades of gray, low contrast

What is window level (WL)?

Center of WW and controls brightness of image

Low window level=

lighter

High window level=

darker

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

Less

What is local processing operations?

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 in computers

What is spatial frequency filtering?

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

What is high pass filtering also known as?

Edge Enhancement

Highpass filtering removed or suppresses ____ spatial frequency to produce a ___ output image

Low, sharper

Highpass filtering results in greatly ___ contrast

Increased

With highpass filtering, ____ edges are enhanced as well

Undesirable

Lowpass filtering is also known as?

Smoothing

Lowpass filtering intentionally ____ the image

Blurs

Lowpass filtering reduces ___ and the displayed brightness level of pixels

Noise

Lowpass filtering ___ image detail

Decreases

What is unsharp masking?

‘blurring’ subtracts a low-pass filtered image from the original, producing a new subtracted and sharper image

What us geometric processing operations?

Used to change position or orientation of pixels in image

Geometric processing operations allow radiographer to:

• rotate

• magnify

• flip horizontally

• flip vertically

What makes up digital image quality?

• resolution

• noise

• detective quantum efficiency (DQE)

• artifacts

Spatial resolution is controlled by the ____ and how many ____ can be displayed by the monitor

Matrix size and pixels

Matrix size ___ and pixel size goes down= ____ in spatial resolution

Increases, increase

____ is part of bit depth; the greater the bit depth= better density resolution

Density resolution

What is contrast resolution?

Ability of a detecter to resolve different energy differences striking it, and transferring this energy into signal values

Noise is classified as either:

• system noise

• ambient noise

• quantum mottle noise

System noise an ambient noise are random ____ information that is detected

background

System noise and ambient noise does ____ contribute to image quality

not

System noise and ambient noise are measured in _____

signal-to-noise-ratio (SNR)

____ SNR indicates ____ noise in the image

High, little

Increase in noise= ____ in contrast

Decrease

Decrease in noise= ____ in contrast

Increase

Quantum mottle noise results from an _____ of photons from an improperly set exposure factors (mAs and kVp)

Insufficient quantity

Quantum mottle noise produces ____ image

Grainy

Only way to correct the noise made from quantum mottle noise is to repeat with ___ technical factors

Increased

What is detective quantum efficiency (DQE)?

A 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= ____ meaning ____ of information

1, no loss

DR systems have DQEs of ___ - ___

.3-.7 (30-70%)

DQE is affected by _____

SNR, noise, detector material

DR processing systems use ____ to provide information regarding the Exposure to the IR

exposure indicators

EI indirectly determines the quantity of ____ striking the detector

photons

If number/readout is within “acceptable range” of EI value =_____

best image quality

Fuji relationship to exposure

Inverse

Konica relationship to exposure

Inverse

Philips relationship to exposure

Inverse