Computed Radiography (CR) Bushong chapter 15 & Carter chapter 1

DR systems have a dynamic range from _______ to __________ different shades of gray.

256 to 4096 note: We cannot visualize a dynamic range of the x-ray beam as it exits the patient - a computer can.

Based on average hospital department workflow, _____ cassettes per hour is possible.

50

Typical cassette throughput is ______. 5 cassettes/min 25 cassettes/min 25 cassettes/hour 50 cassettes/hour

50 cassettes/hour

The wavelength of the CR reader laser is ______ nm. 336 636 633 366

633

This layer of the IP is called? - A soft polymer that protects the back of the cassette

Backing layer

The device that moves the laser rapidly back and forth across the imaging plate is known as ______. Beam optics Laser scanner Beam deflector Optical mirror

Beam optics (polygon or oscillating)

During laser beam formation, both ends of the laser reflect energy back and forth so that the atoms ______. Absorb each other Bombard each other Lose energy Create x-ray energy

Bombard each other

This layer of the IP is called? - newer plates may contain this layer. located between the active & support layers and absorbs the stimulating light but reflects emitted light.

Color layer

This layer of the IP is called? - A layer of material that will absorb and reduce static electricity. When the imaging plate is irradiated, stimulated electrons enter here.

Conductive layer note: if static exists because of low humidity, hair can cling to the imaging plate. important to clean IP.

The power source for the laser must be ______. Oscillating Constant Preheated Cold

Constant

______________ ____________ is any imaging acquisition process that produces an electronic image that can be viewed and manipulated on a computer.

Digital imaging note: most modern medical imaging modalities produce digital images that can be sent through a computer network to various locations.

The optical mirror in the reader ______. Directs the laser beam to the imaging plate surface Forms the laser beam into a circle Causes the laser beam to diverge Creates the laser beam

Directs the laser beam to the imaging plate surface

The range of exposures over which a detector can acquire image data. Digital image acquisition systems are capable of capturing an image across a much larger range of exposures than film-screen. This is known as?

Dynamic range note: is the range of exposures that can be captured by a detector. Typical DR systems will respond to exposures as low as 100 uR & as high as 100 mR.

___________________ is present in very small amounts. It is an activator and is responsible for the storage property of the PSL. Similar to the sensitivity center of film emulsion because without it, there would be no latent image.

Europium (Eu)

Lasers create and amplify wide, soft beams of divergent light. True False

False

Does "S" # change if the orientation of the IP is turned upside down with the green bar switched around? True or False?

False note: The S # will not change

This layer of the IP is called? - A layer that sends light in a forward direction when released in the cassette reader. May be black to reduce the spread of stimulating light and the escape of emitted light. some detail lost in this process.

Light reflective layer

The default gradient curve applied to the data set of your image determining the initial display contrast. It can be adjusted after the initial image processing has been applied. What is this?

Look-up-Table note: is basically a mathematical process used to add the desired level of brightness & contrast to the image.

_________ screen is housed in a rugged cassette and appears similar to a screen-film cassette. (imaging plate) (IP).

PSP (Photostimuable Phosphor)

This layer of the IP is called? - A layer of photostimulable phoshor the "traps" electrons during exposure.

Phosphor layer (active layer) note: Phosphors from barium fluorohalide. Contain a dye that differentially absorbs the stimulating light to prevent as much spread as possible.

Some materials such as barium fluorohalide with europium emit some light promptly in the way that scintillator does following x-ray exposure. However, they also emit light some time later when exposed to a different light source. Such a process is called _____________________ __________________.

Photostimulable luminescence (PSL)

Digital images require each pixel to be assigned a unique value, so that a unique gray shade is assigned to that pixel. This processes takes electrical signals & turns them into digital bits of information which are brightness levels. This is known as?

Quantization note: "unique value" (quantized)

This layer of the IP is called? - a semirigid material that gives the imaging sheet some strength.

Support layer

The process of scanning the moving imaging plate is known as ______. Transition Raster scanning Digitization Translation

Translation

Coherent light is formed by the laser because the photons ______. Are at right angles to each other Travel in all directions Travel in the same direction Are at varying frequencies

Travel in the same direction

The energy stored in the IP is lost over time? True or false?

True note: The latent image on the plate will lose about 25% of its energy in 8hrs, so it is important to process the cassette shortly after exposure!

CR cassettes eliminate the need for: a. a film processor b. proper patient positioning c. techniques that minimize dose d. a darkroom e. computers

a darkroom

The x-ray capture element of a CR imaging plate is the: a. BaFlBr b. cassette c. CCD d. laser beam e. light-collecting optics

a. BaFlBr (barium fluorobromide crystals)

What is the principal difference between screen-film radiography and computed radiography? a. analog vs digital b. involves light c. requires processing d. the cassette e. uses an imaging plate

a. analog vs digital

How does the CR reader maintain the laser beam as a circle? a. beam-shaping optics b. fast-scan regulation c. intensity control d. light-collecting optics e. slow-scan regulation

a. beam-shaping optics

Scan is nearly always located at right angles to the direction of any grid lines; in this way, ______________ __________ are reduced.

aliasing artifacts

The output of the photodetector is a time-varying __________ signal that is transmitted to a computer system that has multiple functions.

analog

The analog signal must be converted to a digital signal for computer to be able to work with the image info. The __________ ____ _________ ____________ does the conversion.

analog to digital converter (ADC)

Europium is an activator in the PSP. An activator is responsible for: a. contrast resolution b. emitted light intensity c. reduced patient dose d. spatial resolution e. x-ray absorption

b. emitted light intensity

The activator in PSP is there to: a. define laser wavelength b. enhance electron metastability c. increase x-ray absorption d. select the proper wavelength e. shape the wavelength of stimulable emission

b. enhance electron metastability note: Europium is the activator & is added with the barium fluorohalide to make the photostimulable go faster

To remove the image of background radiation or a previous image, one should: a. clear the image receptor with a cleaning solution b. expose the image receptor to intense light c. expose the image receptor to intense x-ray exposure d. store the image receptor for 3 days e. transfer the image receptor signal to digital storage.

b. expose the image receptor to intense light note: White light "Fluorescent lamps"

The photostimulable emission in CR: a. has longer wavelength than the laser-stimulating light. b. has shorter wavelength than the laser-stimulating light c. is discrete, as is the laser-stimulating light d. is in the far infrared region of the spectrum e. is monochromatic, as is the laser-stimulating light

b. has shorter wavelength than the laser-stimulating light

The slow-scan portion of the CR reader: a. has a speed that is determined by the emission rate b. is under mechanical control c. is under optical control d. relies on a photometric response e. requires mirrors and prisms

b. is under mechanical control

Which of the following is monochromatic? a. Infrared light b. laser light c. stimulated emission d. visible light e. x-ray beam

b. laser light

The source of the stimulating light is: a. emitted light b. the laser c. the optical path d. the photometer e. x-radiation

b. the laser

Motor drive must be constant to avoid ____________ _________.

banding artifacts

The laser beam (infrared light) causes metastable electrons to return to the ground state with emission of a shorter wavelength light in the ____________ region of visible spectrum. Through this process the ____________ image is made visible.

blue latent

About how much time can pass between exposing a CR cassette and reading a CR cassette before image quality declines? a. 1 hour b. 10 minutes c. 8 hours d. 3 weeks e. 6 days

c. 8 hours

The luminescent light emitted by the PSP is transformed into the image seen on the CRT by the: a. PSP b. scanner reader c. ADC d. helium neon laser

c. ADC (analog to digital converter)

PSP image receptors: a. are relatively insensitive to x-rays b. become radiation fatigued c. can be fogged by background radiation d. have better spatial resolution than screen-film e. require higher patient dose

c. can be fogged by background radiation

Spatial resolution in CR is principally determined by: a. fast-scan rate b. field of view c. laser beam diameter d. phosphor size e. slow-scan rate

c. laser beam diameter note: diameter is 50 to 100 micro meters

The component of the CR image plate (IP) that records the radiologic image is the: a. emulsion b. helium neon laser c. photostimulable phosphor d. scanner reader

c. photostimulable phosphor

With CR, no _____________ processor or _______________ is necessary.

chemical darkroom

The laser light used in CR: a. is in the ultraviolet light region b. is more energetic than the stimulated light c. is pulsed across the PSP d. has longer wavelength than the stimulated light e. produces light of intense fluorescence

d. has longer wavelength than the stimulated light

Which of the following steps can be eliminated during switching from screen-film radiography to CR? a. positioning patient b. perform examination c. process image d. reload cassette e. repeat examination

d. reload cassette

CR is the first example of ____________ radiography

digital

Computed radiography is a form of ____________ radiography

digital

An electron that is described as being metastable: a. is outside the atom b. is present in positive and negative form c. is the transformation of an x-ray d. has been captured by the nucleus e. has higher energy than it should have

e. has higher energy than it should have "excited"

Doping of a PSP with europium results in: a. better contrast resolution b. better spatial resolution c. higher x-ray absorption d. lower patient dose e. more stimulable light emission

e. more stimulable light emission

The latent image in the PSP, barium fluorohalide occurs in the form of metastable _______________.

electrons

While the IP is being transported in the slow scan direction (along the long axis of the IP), a deflection device such as a rotating polygon or oscillating mirror deflects the laser beam back & forth across the IP. This is the _________ scan mode.

fast note: the IP barely leaves the cassette so it is not subject to roller damage. (banding artifact)

Systems automatically erase the IP by flooding it with __________________ light to remove any electrons still trapped after the initial plate reading. plates should be run at least:___________ under an erase cycle to remove background radiation and scatter. a. twice a week b. once a week c. everyday d. once a month

fluorescent (intense light) b. once a week note: IP should be used soon after the erase cycle has been completed.

If residual latent image remained after erasing, ______________ could appear.

ghosting

Purpose of the barcode label is to identify the?

imaging plate. note: label enables the technologist to match the image information with the patient-identifying barcode on the exam request.

Compton & photoelectric effects most interact with the outer shell electrons and excite them to a metastable state. when the electrons return to the ground they emit light. The stimulated luminesced phosphors are also able to store some of the light energy (latent image). The return to the ground state can be accelerated or stimulated by exposing the phosphor to intense ______________ _________ from a laser in a left to right scan called a raster pattern.

infrared light

Before reuse of the CR imaging plate, any residual metastable electrons are moved to the ground state by _____________ light from a bank of specially designed fluorescent lamps. (Erasing the image)

intense (white) note: If the residual latent image remained, ghosting could appear on the next use of the IP...

In screen-film radiography, the radiographic ________________ ___________ is a scintillator that emits light in response to an x-ray interaction.

intensifying screen note: in CR, the response to x-ray interaction is seen as trapped electrons in a higher energy metastable state.

Both CR and screen-film carry a ___________ image, but processed differently. Both CR and screen-film use as the image receptor an x-ray sensitive plate that is encased in a protective ________________.

latent cassette

When irradiated the phosphors fluoresce similar to x-ray screens but more importantly, capture a ___________ _________.

latent image note: electrons are trapped & their energy stored as the latent image.

The IP has a __________ backing that reduces backscatter x-rays. This improves the contrast resolution of the image receptor.

lead note: backscatter created by x-ray photons transmitted through the back of the cassette can cause dark line artifacts.

The _________ _______________ optics direct the released phosphor energy to an optical filter and then to a photodetector.

light collecting

Solid-state lasers produce ____________ wavelength light and therefore are less likely to interfere with emitted light.

longer

The CR reader represents the marriage of _____________ , ___________ & _______________ _________.

mechanical optical computer modules

The laser light used to stimulate the photostimulable phosphor (PSP) is ____________________. Resultant emitted light is _________________.

monochromatic polychromatic (of two or more colors; multicolored) note: A solid state laser is the stimulating source of choice over the HeNe gas laser.

Components like the laser, beam-shaping optics, light-collecting optics, optical filters & photodetector in the CR reader are known as the _____________ features.

optical

The _____________________ converts phobostimuble luminescence into an electric current. (converts light into electrons)

photodetector

The ________________ converts photostimuble luminescence into an electric current

photodetector or PMT (photomultiplier tube)

The light collecting optics direct the light up the light guide to the ____________________ _______ which are only sensitive to blue light. Convert light to an electrical signal which is in an ____________ form.

photomultiplier tube (PMT) analog note: then goes to the ADC

The diameter of the laser beam and scan motion determine the size of each ____________.

pixel

The intensity of the laser-stimulated light is ________________ to the x-ray intensity at the image receptor.

proportional

This layer of the IP is called? -a very thin, tough, clear plastic for protection of the phosphor layer.

protective layer

What are the names of the layers of the Imaging plate? 1. 2. 3. 4. 5. 6. 7.

protective layer phosphor layer or "active layer" light reflective layer conductive layer support layer light shielding layer backing layer. note: newer plates may contain a "color layer" located between the active & support layers and absorbs the stimulating light but reflects emitted light.

The laser scans the imaging plate in a ______ pattern. Raster Horizontal Circular Random

raster

The reader scans the plate with _____ light in a zig zag, or _________ __________.

red raster pattern

Appropriate image plate selection for the exam eliminates ______________ outside the initial collimation & increases image resolution.

scatter.

emitted light is the _____________ & stimulating light is the ____________.

signal noise

___________ laser beam diameter is critical for ensuring high spatial resolution.

small note: beam shaping optics keep the beam size, shape, speed, & intensity constant.. The lens system keeps the beam small.

A 2000 x 2000 matrix on an 8x10 cassette results in much ______________ pixel size, thereby increasing resolution.

smaller note: If, for example, a hand were imaged on a 14x17 cassette, the entire cassette would be read according to a 14x17 matrix size with much larger pixels, and the resultant image would be very large.

use the ________________ imaging plate possible for each exam results in the highest sampling rate.

smallest note: when the smallest possible imaging plate is selected, a corresponding matrix is used by the computer algorithm to process the image.

The diameter of the stimulating laser beam determines the ___________ ________________ of the CR imaging system.

spatial resolution. note: beam diameter is between 50 to 100 micro meters.

The laser is the source of stimulating light; however, it ____________ as it travels to the rotating/oscillating reflector.

spreads

Advantage of CR is that it can be _______________ for screen-film radiography and used with any x-ray imaging system.

substituted.

When metastable electrons return to their ground state, ___________ light is emitted.

visible (blue-violet)