Unit 1: CR + DR Systems and Image Acquisition | Advanced Radiographic Imaging

What is a preprogrammed set of instructions for specific tasks?

Algorithm

What is a collection of algorithms that allow a user to perform a general application?

Computer program

What is the part of a computer that interprets and executes instructions?

Central processing unit (CPU)

What is the name of the small circuit chip that a CPU is contained on?

Microprocessor

Computer speed is determined by the speed of an internal clock of the microprocessor and is measured in units of?

Hertz (cycles per second)

What classification of computer has one single microprocessor, a desktop, and is considered a diagnostic x-ray machine console?

Microcomputer

What classification of computer has many microprocessors and is either cabinet size or fill a room, and is considered either a CT or MRI computer?

Minicomputer

What classification of computer has hundreds/thousands of microprocessors and fill up large rooms or entire floors of buildings?

Mainframe/Supercomputer

What is a language used by computers by using 1s and 0s?

Binary code

What assigned value does a closed circuit have?

1

What assigned value does an open circuit have?

0

What helps process binary code and may be switched on and off millions of times per second?

Transistors

For the decimal system, the value of the number’s place position to the right or left of the decimal point is based upon the exponent of the base 10. What is the place value based on for the binary system?

2

What is the term for a single unit of data?

Bit

Is a one or a 0

What is made up of 8 bits and is the amount of memory needed to store one alphanumerical character?

Byte

Computer memory is defined by the number of?

Bytes

What part of the CR cassette absorbs exit x-ray intensities and ionizes the atoms?

Phosphor plate

Some of the absorbed energy is released as light, and the remaining energy contained in the phosphor plate creates what?

Latent image

What is released to a normal energy state during beam scanning in the reader unit?

Electrons

What is viewed after an exposure is made and the CR cassette is processed in the reader?

Manifest image

What are the main unit components of a CR reader?

Drive mechanism

Optical system (laser, optical fibers)

Photodetector (photomultiplier tube)

Analog to digital converter

(T/F) Matrix size will be the same regardless of CR size.

True

(T/F) Smaller cassettes have better spatial and contrast resolution.

True

In what type of pattern does the CR reader process the plate?

Raster-like pattern

What are the two types of readout processing?

Point by point

Line by line

What inside the reader processor picks up emitted light at a different angle than the incident laser beam and channels it to the photomultiplier tube for amplication?

Optic fibers (flexible glass/plastic fibers)

What term describes the act of electrons moving through a wire?

Current

What is a layer of material (in CR systems) that releases electrons when light strikes it (through the photoelectric effect)?

Photodetector (photocathode)

What is the purpose of a photomultiplier tube?

Collects, amplifies, and converts visible light to an electrical signal

(T/F) The electrical signal is proportional to the range of energies stored in the PSP.

True

The photomultiplier tube is sensitive to what color of light?

Blue-violet

What occurs when the intensity of a light/electrical signal is measured for each pixel?

Sampling

Sampling ___ is determined by the laser beam in the CR reader?

Aperture/shape

How often the analog signal is reproduced in its digital form is called?

Sampling frequency

(T/F) A higher sampling frequency system has fewer sampling points, an increased pixel pitch, worse spatial resolution, and a shorter scan time.

False

(T/F) The neon helium laser must overlap pixels that are being recorded as the plate is readout.

True

What is the distance between adjacent pixels?

Pixel pitch (sampling pitch)

In CR systems, what is determined by the sampling frequency?

Pixel pitch

(T/F) The smaller the pixel pitch, the smaller the pixels, and the better the spatial resolution.

True

With a fixed sampling frequency, what is the same regardless of cassette size?

Spatial resolution

(T/F) A fixed matrix size always cuts the image into the same amount of pixels.

True

Where does the photomultiplier tube send the electrical signal after it amplifies and converts the light into said electrical signal?

Analog to digital converter

What takes the electrical signal and converts it into a series of 1s and 0s?

Analog to digital converter

Where does the quantization step take place?

Analog to digital converter

What is it called when the ADC assigns a discrete numerical value to each pixel from a pre-designated grayscale?

Quantization

What determines the shade of gray for each pixel?

Quantization

What is the total number of possible brightness levels that the computer is capable of showing?

Bit depth

(T/F) If there are more gray values than the system can show, the ADC will round values up or down.

True

A larger bit depth has (more/less) shades of gray and possible brightness levels

More

What is used to remove any residual image on a CR cassette?

Bright white light

Each exposure made on a CR cassette must be identified with what before the image can be read by the processor?

Patient information

(T/F) CR phosphor plates can be re-used thousands of times.

True

What are three CR developments?

Dual-sided reading (2 sets of detectors used in the reader)

Line scan readers (lines of data read instead of point by point)

Solid-state laser diodes (reliable + consistent)

CR phosphor plates are about how much more sensitive to scatter compared to film screen?

10 times

(T/F) Radiographers should erase any cassette prior to use if there is any chance it has not been used for 2 or more days.

True

What is the typical background exposure on a CR cassette that can occur per day?

70-80 micro-Roentgen

(T/F) Multiple exposures can be placed on one CR cassette.

False

(T/F) Extra CR cassettes can be left in the exposure area with no effects.

False

(T/F) CR cassette bins should be rotated, so the same cassettes are not used for every exam.

True

What type of radiography replaced film screen and is the first filmless radiography system?

Computed Radiography (CR)

Where is the latent image captured in CR systems?

Photostimulable imaging plates (PSP)

What is the CR reader’s purpose?

To process the plate and send a digitized image to the monitors

What CR layer converts x-rays into visible light?

Phosphor layer

What CR layer is considered the active layer?

Phosphor layer

What CR layer prevents static discharge and absorbs light?

Conductive layer

The support layer of a CR cassette is usually made of what material and gives the plate strength?

Polyester

What CR layer keeps light away from the back of the plate?

Light shield layer

The back panel of CR cassettes contain a thin sheet of what to reduce backscatter radiation?

Lead foil

(T/F) CR cassettes are made up of aluminum or plastic with a high attenuation carbon fiber front.

False

Both front and back panels of a CR cassette are lined with what type of material that minimizes static electricity buildup and cushions the plate from jolts?

Felt

Photostimulable phosphor (PSP) is one of a small number of what compound?

Barium-fluor halide

What layer of the CR plate possesses the property of stimulated phosphorescence?

PSP layer

What is considered an activator as it maintains the presence of electron holes in the PSP layer?

Europium

What are the two common PSP phosphors used?

Barium fluorohalide bromides

Barium fluorohalide iodides

What is the Kedge attenuation of barium?

Best between 35-50 kev

(T/F) CR cassettes/PSP plates are more sensitive to scatter before and after exposure than film.

True

PSPs are sensitive to (high/low) levels of radiation energy?

Low

PSPs have a (wide/narrow) exposure latitude

Wide

What is the range of exposures that can produce quality images at an appropriate patient dose?

Exposure latitude

(T/F) Phosphor crystals convert x-rays into visible light.

True

(T/F) Turbid phosphor crystals are evenly distributed within the active layer.

False

What type of phosphor crystals are used in both CR and DR image receptors?

Turbid

What type of phosphor crystals are columnar within the active layer and resemble needles packed together?

Structured

What type of phosphor crystal makes a thinner layer which is better for spatial resolution?

Turbid

What metal is used as a light activator inside the phosphor layer?

Europium

Phosphor crystals and europium store and release energy through the process of what?

Photoelectric absorption

Where does photoelectric absorption happen within the CR plate?

PSP

(T/F) The number of photoelectrons produced in the phosphor layer is inversely proportional to the number of photons that interacted with it.

False

As exit radiation reaches the phosphor layer, what interacts with the atoms in the phosphor layer?

Photons

What is the process of photoelectric absorption?

Photon ejects an inner shell electron and is absorbed

Energy excites the ejected electron — is now a photoelectron

Photoelectrons excite other electrons in the phosphor layer

Excited electrons move from a low-energy valence band toward a high-energy conduction band

Which band has a low binding energy and is the outer shell?

Valence band

In which electron band do electrons undergo covalent or ionic bonding?

Valence band

What is an additional energy band between valence and conduction bands?

F center

What band is responsible for the coloration in the crystals?

F center

What contains defects created in a BaFH crystal's crystal structure when constructed by adding europium? Defects can trap and store electron energy.

F center

(T/F) Energy that is trapped within the F centers of phosphor atoms remains stored there until the imaging plate is put into the reader and is erased.

True

The latent image can be retrieved after several hours; however, only how much percent is retained of the original image 8 hours after the exposure?

75%

How long after an exposure does the latent image begin to dissipate/fade?

1 hour

How is the trapped energy released from the plate?

Crystals within the PSP layer are excited by being scanned with a helium-neon red laser beam

Energy is lost from electrons (falling back into their shells) after being released by the helium-neon laser and is emitted as what color of light?

Blue violet