Exam 2 Image Production II

What is the imaging process for CR?

Acquisition, Processing, Display

What kind of imaging plate does CR use?

Photostimulable phosphor

How is the image acquired?

The plate is processed through a reader

How are cassette-based systems different from film/screen radiography?

Casette-based systems use a light-proof container that protects the imaging plate from light and handling.

What are cassettes made of?

Durable, lightweight plastic

What are cassettes backed with?

Aluminum or lead to absorb backscatter X-Ray photons

What is anti-static (felt) material used for in cassettes?

Protects against static electricity buildup, dust collection, and mechanical damage

What is the imaging plate and what does it do?

It is a thin piece of plastic and it records the image

How many layers does the imaging plate have?

7

What is the protective layer?

Thin, tough clear plastic that protects the phosphor layer

What is the phosphor/active layer?

It contains a photostimulable phosphor that “traps” electrons during exposure

What is the most common type of phosphor layer?

Barium fluorohalide family

What is the reflective layer?

It sends light in a forward direction, reduces the light spread and escape (if black), and decreases resolution

What is the conductive layer?

Absorbs and reduces static electricity

What is the color layer?

Located between the active and support layers, the color layer absorbs the stimulating light but reflects the emitted light

What is the support layer?

The support layer is the semi-rigid material that provides strength

What is the backing layer?

Soft polymer that protects the back of the cassette

Why is the bar code important?

Before each new examination, the barcode label that identifies the patient and the barcode label on the cassette must be scanned and registered to the examination.

How is the image acquired/formed?

In PSP, the remnant beam interats with electrons in the barium fluorohalide crystals within the imaging plate. This interactions gives the electrons within the crystals energy, trapping them in an area of the crystal known as the phosphor center.

Important facts about image acquisition in PSP

The trapped signal can remain for hours, even days, and is never completely lost; deterioration begins almost immediately; imaging plates are never completely erased (however, residual trapped electrons are so few that they do not interfere with subsequent exposures).

How is the imaging plate read?

It is placed into a reader, where the plate is extracted and scanned with either a helium laser beam or solid-state laser diodes

What are the two types of PSP readers?

Point scan and line scan

What do point scan readers have?

Optical stage, scanning laser beam, translation mechanics, light pick-up guides, a photomultiplier, signal transformer/amplifier, ANALOG-TO-DIGITAL CONVERTER

What is important about the laser in point scan readers?

Only a single laser point radiates the imaging plate at any point in time

The PSP (CR) cassette is backed by ________ or lead that _________

aluminum; absorbs backscatter x-rays

What is the **optimum** kVp exposure range with PSP systems

60 to 110

In the PSP imaging plate, which layer is also known as the “active layer”?

Phosphor layer

When the imaging plate is exposed, electrons are trapped in this layer

Phosphor

Quantum mottle is caused by

Too little mAs

Barium fluorohalide crystals in the imaging plate release light energy, which is then stored in the ______ layer

Conductive

The imaging plate uses a _______ to scan the imaging plate, releasing the energy stored

laser

A _________ collects the light and sends it to a signal detector

Photodetector

What does “laser” stand for?

Light amplification of stimulated emission of radiation

Line scan readers based on the acquisition of PSL occurs with

CCD

The imaging plate is scanned using a _______ pattern

raster

The _________ assigns a numerical value to each pixel in a matrix according to the intensity of the detected light

ADC

What is a photoconductor made of?

Amorphous selenium

What are the two types of conversion methods in TFT?

Indirect and direct

________ absorbs x-ray photons and immediately converts them to an electrical signal

Photoconductors

Indirect conversion detectors use a _______ that converts x-rays into visible light, which is then converted into an electrical charge

Scintillator

Based on simultaneous stimulation of the imaging plate, line scan readers scan _________

one line at a time

Acquisition of the photostimulated luminescence (PSL) occurs with a ________________

**charge-coupled device (CCD)** line array photodetector

What are the two scan directions within the reader?

Fast scan and slow scan

The movement of the laser across the imaging plate is known as ___________

fast scan direction

The movement of the imaging plate through the reader is known as ___________

slow scan directionS

Slow scan direction is also known as ______________

translation or subscan direction

A _______ creates and amplifies a narrow, intense beam of coherent light

laser

The laser requires a constant power source to

prevent output fluctuations

The laser beam passes through ________ to an _________, which directs the laser beam to the surface of the imaging plate

beam-shaping optics; optical mirror

The laser gives energy to the ____________

trapped electrons

The typical throughput for reading cassettes is

50 cassettes per hour

Some manufactures claim up to ______ cassettes per hour

150

The ____________ direct the released phosphor energy to an _______ and then to the __________

light collection optics; optical filter; photodetector

Represents changing values as continuously variable physical quantities

Analog

The assignment of a numeric value to each light photon

Digitizing a signal

The scanning process results in the conversion of the light emitted from the _________ into an _____________

storage phosphor; electrical signal

_____________ and ____________ determine resolution in PSP

Phosphor layer thickness; pixel size

The electrical signal is sampled and digitized to represent a specific location within the __________ and displays as a specific _________

image matrix; brightness

The ______ the phosphor layer, the ______ the resolution

thinner; higher

The best resolution in F/S radiography is

10 lp/mm

PSP resolution is lower, at ________

2\.55-5 lp/mm

Factors affecting PSP resolution include (4)

laser beam spot size, translation speed, sampling frequency, and the laser beam sweep (IN POINT BEAM READERS)

The difference in resolution is difficult to discern because of the

greater number of available gray shade (bit depth)

More ___________ are seen on the digital radiograph, giving the appearance of more detail

tissue densities

Imaging plates are ___________ to scatter radiation

extremely sensity

The image reading process returns most of the electrons to a ________, effectively removing the image from the plater

lower energy state

How often should plates be run under an erase cycle to remove built-up background radiation and scatter?

Once a week

Erasure mode allows the plate surface to be scanned ______________

without recoding the generated signal

Systems erase the plate by _________ to remove any trapped electrons left after the initial plate reading

flooding it with light

If the last erasure time is unknown, when should cassettes be erased?

Before use

After the imaging plate has been read, where is the signal sent?

To the computer, where it is preprocessed

Where does the data go after it is sent to the computer?

To a monitor that displays the image

Improper menu selections for body parts may lead to

Overexposure of the patient and repeated exams

kVp is selected for

penetration and tissue typem

mAs is selected for

the number of photons required for the body part being imaged

_________ of the x-ray beam is the same as in F/S radiography

Attenuation

The proper balance between _______ and _________ is vital

patient dose; part penetration

kVp values now range from

45-120

The k-edge of phosphor imaging plates ranges from ___ to ____ keV so that **exposure ranges of _____ to _______ kVp are optimum**

30 to 50; 60 to 110

Digital image contrast is ____________ on kVp

No longer dependent

In digital imaging, _______ is determined by computer processing

Contrast

What are the two important factors that should be considered when selecting the PSP imaging cassette?

type and size

What is much more critical in PSP systems than it was in F/S radiography?

The use of grids

Why is the use of grids more critical in PSP systems?

PSP systems are more sensitive to low levels of radiation

Grid selection factors include (3)

frequency, ratio, and focus

What are the two typical types of imaging plates?

Standard and high resolution

High-resolution imaging plates contain a _______ phosphor level

thinner

The thinner layer ____ light spread, yielding greater image ________

reduces; sharpness

The ___ _______ _____ is important in establishing the parameters that determine __________________

Image recognition phase; collimation borders and edges

What are the three different names for image recognition?

Collimation, segmentation, exposure data recognition

All systems use a region of interest to define the _______________________ and the exposure outside the region of interest is subtracted

area where the part to be examined is recognized

Any undesirable objects on the processed image other than those caused by scatter and fog

Artifacts

What are the four common types of artifacts, aside from operator errors?

Imaging plate, plate reader, image processing, printer

What is backscatter?

Dark line artifacts

How does backscatter occur?

Worn, cracked areas of the cassette’s lead coating allows scatter in

As the imaging plate ages, it can crack. What do the cracks appear as on an image?

Lucent areas

What is an example of what a plate reader artifact looks like?

Intermittent horizontal line patterns

Horizontal white line plate reader artifacts are caused by

Dirt on the light guide in the reader

What happens when multiple imaging plates are in a single cassette?

Only 1 plate tends to get extracted, leaving the other plate to be exposed multiple times before being read

Overexposure reduces

Contrast