Chapter 21 computed radiography

transmission and processing

a digital image is one that has been converted into numerical values for?

matrix

a series of boxes in rows and columns that give form to the image is called?

High frequency grids

To avoid the Mauri effect in CR manufacturers recommend using?

Higher kVp should be used which decreases patient dose

What type of technique is better for CR?

The movie effect

The imaging plate is scanned line by line if the scan frequency and grid frequency are similar and going in the same direction, what happens?

When you see visible lines on the image from the grid

What is the morie effect

pixel

individual matrix box or also known as picture elements is called?

AEC

What exposure technique system was developed specifically for CR equipment and is used to avoid repeats and minimize radiation exposure?

-edge enhancement

-image stitching

Two examples of post processing techniques include?

-spatial resolution processing

-frequency processing

Postprocessing can be done using two approaches what are they?

Picture elements

Pixels are also known as?

shade of gray

each pixel represents wide range of different?

the grayscale bit depth

the number of shades of gray is determined by?

8-32

The grayscale bit depth can have bits that range from ____ bits

computed radiography (CR) or digital radiography (DR)

an image can be taken on either a _____________________ or _________________

PSP/IPrC

CR uses ___________ technology typically inside cassette or wall unit

-exposure field recognition

-histogram analysis

-grayscale analysis

During preprocessing the following can happen?

detector and reader, cassette

DR uses __________ and _________ as permanent part of table or wall bucky, no _________ being used and the image is sent directly to the display monitor

-direct conversion (without scintillator)

-indirect conversion (with scintillator)

what are the two DR configurations?

Maximum spatial resolution

Pixel pitch determines the?

-point processing

-local processing

-geometric processing

what are the 3 image processing operations to change the input values of the pixels to improve diagnostic quality of the image shown on the monitor

-resolution

-noise

-DQE

what 3 things help comprise digital image quality factors

the photostimulable storage phosphor imaging plate (PSP)

what is used in the bucky, similar to traditional film and is inside of the cassette?

by fuji in the 1980s

when was the photostimulable storage phosphor plate introduced?

readers

the photostimulable phosphor plate is a cassette based system that requires a _______ to process the plate and create the image

two-step process

the radiographer has a __________________ in order to see the image on display

records and enhances

the photostimulable imaging plate _________ and _______ the transmission of image from x-ray beam

6 layers

inside the photostimulable imaging plate is how many layers?

the protective layer

insulates the IP from handling trauma is called?

the phosphor layer

contains phosphors, is the active component is called?

the support layer

a base for other layers is called?

the conductor layer

grounds the plate to eliminate static and absorbs light is called?

the light-shield layer

prevents light from erasing data or leaking through backing is called?

the backing layer

what is the last layer of the 6 layers?

Barium fluorohalide bromides with equpium activators and barium fluorohalide bodies with europium activators

what is the most common type of CR phosphors?

BaFBr:Eu

barium fluorohalide bromides =

BaFl:Eu

Barium fluorohailde iodides with europium =

sensitive

IP is more __________ to scatter both before and after it is sensitized through exposure

low-energy

IP phosphors will absorb more ________________ scatter than a rare-earth phosphor found in film

IP phosphors

appropriate kVp, collimation and masking must be used to achieve optimal image when using?

fluorescence

radiation exposure from incident x-ray beam causes ______________- of the fluorohalide phosphors on the imaging plate

reading and processing

the energy stored for the latent image production is used to create an image during?

high, latent image and wider

excited electrons are trapped in the crystal structure of the phosphor at ______ energy levels creating the ______________- similar to the image on film but with much _____________ latitude

release

in the latent image production, the plate needs to be read to _____________ the stored information

europium

the latent image is formed at the ______________ phosphor sites

25% and 8

the latent image will lose about _____ of it energy in ____ hours

process

it is very important to __________ the latent image shortly after the exposure

a loss of most of the latent image

failing to process a cassette for several days will result in?

image reader, helium-neon t

the cassette is then loaded into a ____________ device (IRD) where the plate is scanned by a ________-_______ laser beam

light photons

the laser causes the phosphors to emit (or free) the stored latent image in the form of?

electrical

photosensitive receptors then convert light photons into _________ signal

digital

electrical signal the converts to a unique __________ value for that level of luminescence

a ghosting effect on the next image

once the plate is read, it is erased, grossly overexposed plates may not erase completely, this results in?

Focused laser beam when applied to the phosphors, PSL

Reading the image plate involves a finely?

Photostimulated Luminescence

PSL =

Electrons, lower, light

when the laser beam frees trapped ____________, releasing blue-purple _________ photons in proportion to the absorbed radiation

Raster

Plate is fed through the processor and scanned line by line in a _________ pattern

All directions and photodetectors

Light liberated from laser is emitted in ______________ and collected by optical system which directs us to one or more ________________

-photomultiplier tubes

-linear CCD array

the light that is liberated from the laser and emitted in all directions and is directed to the photodetector, what are the 2 types of photodetectors called?

A photodetector

Converts visible light to electronic analog signal is called?

digital and ADC

Analog signal is then converted to _________ signal through and _____ or analog to digital converter in order for the computer to work with it

Computer

Signal sent to the _____________ for processing

Single

Scanners can either be _________ units or allow loading of multiple cassettes

Workload

_____________ and costs determines which unit will best serve the department requirements

Multiple PSP plates

Some tables or upright buckets have __________________ and have readers within the unit, so no cassette handling required for these

Pixel pitch

The finely focused laser beam that scans each line of the imaging plate correlates to one line spacing or ___________

The pixel pitch

The physical distance between pixels and is generally measured from center to center is?

Sampling frequency (nyquist frequency)

Pixel pitch in CR is dependent on?

More signals sampled, the more the information is obtained and the smaller the pixels can be

longer scan time =

Higher spatial resolution

Smaller pixel pitch =

Pixels/mm

In CR pixel pitch is expressed by the sampling frequency =

Detector element (DEL)

In DR, pixel pitch is expressed by the ___________________ size

Location and size

In order for the ADC data to be manipulated digitally, the analog signal is sampled to find __________ and __________ of the signal and must then be quantified to determine the average value of the signal in the sample

Quantification

The process that will determine the brightness levels or grayscale for the pixels

Greater accuracy and truer representation of the signals

Higher sampling rates of the analog signal (nyquist sampling) =

Density and contrast

The number of bits/pixels in I’ll determine how many density values can be present, which will affect the ___________ and __________ of an imaging system

Sampling frequency

In CR, the matrix size is dependent on the __________________ and sometimes the IR size as well

-preprocessing

-postprocessing

The image processing has a two step operation

-recognition

-histogram analysis

-grayscale analysis

Processing = Computer will determine 3 things

Preprocessing

the raw image data is prepared according to the proprietary algorithms of the manufacturer

Postprocessing

The manipulation of data of an image that has been preprocessed

Exposure field recognition

Used to recognize the clinically useful area on the IP so that it’s the only data that’s will be manipulated and it eliminates signals from outside of the collimated field

Orientation

The CR must then determine the _______________ of the part on the plate as well as the number of projections present per plate

Exposure data recognition (EDR)

FUJI =

Segmentation

Carestream =

Parallel and two

The best image will result when the part is __________ to the sides of the cassette and collocation is used on wt least _____ sides!!!!

Equidistant

If placing more than one image per plate the beam and part should be centers within each pattern and collocation should be parallel and _____________ from the edges of the IP

IR

Most CR systems do not send all data acquired by?

Diagnostic

Algorithm is programmed to recognize exposures above and below____________ range

Data clipping

Eliminates data that is clinically irrelevant to a particular exam

VOI or values of interest

The important information on the histogram is determined by the?

Contrast

The algorithm also have an LUT that has the appropriate __________ for each body part therefore each algorithm will vary depending on the part

Anatomical

Appropriate ______________ is selected by body part when IP is loaded into the reader

Histogram

The _____________ is also used to eliminate unnecessary information outside the collimated field (such as scatter)

Collimated

Each image will generate its own particular histogram using the data from within the ____________ edges

Workstation

“Raw” data (prehistogram) is stored at the ____________

Re-processed

The workstation allowed for images that were processed with incorrect anatomical menu to be ___________ using the correct menu with no loss of quality

CANNOT BE RE-PROCESSED

Once the image is sent to PACS _______________________ only original data on workstation can be re-processed

LUT

Once the patients image data is identified, that information is rescaled and the ______ is applied to stabilize the image density and contrast