Computed/digital imaging - misc - 140

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A digital image is formed by

a matrix of pixels (picture elements) in rows and columns.

A high SNR (e.g., 1000:1) indicates that there is far more signal than

noise

A larger image matrix (1800 x 1800) offers better resolution than

a smaller image matrix (700 x 700).

A lower SNR (e.g., 200:1) indicates a

"noisy" image.

A matrix that has 512 pixels in each row and column is a

512 x 512 matrix

A narrow laser beam is required

for optimum resolution

Advantages of computed radiography (CR) over digital radiography (DR) include

1. CR is useful for mobile imaging.
2. CR is compatible with existing equipment.

AEC refers to

automatic exposure control and is unrelated to dynamic range or latitude

Aligning the tube, part, and IR so that they are parallel reduces

shape distortion

Another advantage is

the ability to perform "road-mapping."

Any images obtained in DXA/bone densitometry are strictly to evaluate:

the accuracy of the ROI (region of interest); they are not used for further diagnostic purposes—additional diagnostic examinations are done for any required further evaluation

Any images obtained using DXA bone densitometry

are used to evaluate accuracy of the ROI

As in traditional radiography, spatial resolution is measured in

line pairs per mm (lp/mm)

As in traditional radiography, spatial resolution is measured in

line pairs per mm

As intensification factor increases, radiographic density generally

increases.

As matrix size is increased, there are more and smaller pixels in the matrix, and therefore improved

resolution

As matrix size is increased

there are more and smaller pixels in the matrix therefore improved spatial resolution

As pixel size decreases, resolution

increases

As pixel size increases, resolution

decreases

As the plate is scanned in the "reader," it releases a violet light—a process referred to as

photo- (or light) stimulated luminescence.

As the plate is scanned in the CR reader, it releases

a violet light—a process referred to as photo-stimulated luminescence.

Because there is an image plate (IP), CR can be used for

mobile studies

Better resolution is obtained with

high SNR

Bone densitometry is often performed to

1. measure degree of bone (de) mineralization.
2. evaluate results of osteoporosis treatment/therapy.

Bone densitometry, DXA, can be used to evaluate

bone mineral content of the body, or part of it, to diagnose osteoporosis or to evaluate the effectiveness of treatments for osteoporosis

CD/DR affords much greater

exposure latitude; technical inaccuracies can be effectively eliminated

Change in window level affects

change in the image brightness, that is, optical density

Change in window width affects

change in the number of gray shades, that is, image contrast

Characteristics of digital radiographic imaging include

1. solid state detector receptor plates.
2. direct-capture imaging system.
3. immediate image display.

CR cassettes do not contain:

intensifying screens or film and therefore do not need to be light tight.

CR is less expensive primarily because

it is compatible with existing equipment

CR uses

traditional x-ray devices to enclose and protect the PSP image plate

digital radiographic imaging requires the use of

somewhat different equipment.

DR affords the advantage of

immediate display of the image,compared to CR's delayed image display

DR cannot be used with mobile studies because

no cassettes are used

DR does not use

cassettes or a traditional x-ray table; it is a direct-capture system of x-ray imaging

DR offers the advantage of

immediate visualization of the x-ray image; in CR, there is a short delay

DR requires existing equipment to be

modified or new equipment purchased

DR uses

solid state detector plates as the x-ray image receptor (instead of a cassette in the Bucky tray) to intercept the collimated x-ray beam and form the latent image

Dual x-ray absorptiometry (DXA) (bone densitometry) imaging is used to

evaluate bone mineral density (BMD).

DXA imaging is used to

evaluate BMD (bone mass density).

DXA is the most widely used method of

bone densitometry—it is low dose, precise, and uncomplicated to use/perform

DXA uses two photon energies

one for soft tissue and one for bone.

Factors that contribute to an increase in the intensification factor generally function to

reduce resolution.

Fewer and larger pixels result in

a poor resolution, "pixelly" image, that is, one in which you can actually see the individual pixel boxes.

High-resolution monitors (2-4 MP, megapixels) are required for

high-quality, high-resolution image display

How effectively the phosphors make this energy conversion is termed

conversion efficiency

How efficiently the phosphors detect and interact with the x-ray photons is termed

quantum detection efficiency

If fluorescent light from one intensifying screen passes through the film to the opposite emulsion and intensifying screen, the associated diffusion creates a type of distortion called

crossover

If FOV increases, pixel size

increases.

If FOV increases, pixel size

increases.

If single-emulsion film is placed in a dual-screen cassette:

the emulsion will receive only one-half of the intended exposure, and the resulting image will exhibit decreased density

if the matrix size is increased, pixel size

decreases.

if the matrix size is increased, pixel size

decreases

Image matrix has a great deal to do with

resolution

In CR, there is a linear relationship between

the exposure, given the PSP (photostimulable phosphor, or image plate) and its resulting luminescence, as it is scanned by the laser

In CR/DR, there is a linear relationship between the exposure, given the PSP and

its resulting luminescence, as it is scanned by the laser

In digital imaging, as the size of the image matrix increases:

1. pixel size decreases
2. spatial resolution increases

In digital imaging, pixel size is determined by

dividing the field of view (FOV) by the matrix; the FOV and matrix size are independent of one another, that is, either can be changed and the other will remain unaffected.

In general, as the intensification factor increases

radiographic density increases

In this procedure

the most recent fluoroscopic image is retained on the screen/monitor

Increasing the SID and decreasing the OID decreases

size distortion.

Inside the IP (CR cassette) is the

photostimulable phosphor (PSP) image storage plate.

Intensifying screens used in screen-film x-ray imaging tend to produce high

contrast

Intensifying-screen phosphors

have a high atomic number are more likely to absorb a high percentage of the incident x-ray photons and convert x-ray photon energy to fluorescent light energy.

Matrix and pixel sizes are related to

(spatial) resolution of digital images

Most laser film is loaded into a film magazine in

total darkness.

Most laser film is sensitive to both the

Wratten 6B and the GBX (green, blue, x-ray) safelight filters. Laser film will fog if it is handled under these safelight conditions.

Most laser film must be handled

in total darkness

ntensifying screens do need a degree of

reflectance to enhance their speed.

Once the IP is placed into the CR processor (reader/scanner), the PSP plate is automatically

removed

One advantage of digital imaging in fluoroscopy is the ability to perform "road-mapping." Road-mapping

1. keeps the most recent fluoroscopic image on the screen.
2. aids in the placement of guidewires and catheters.
3. reduces the need for continuous x-ray exposure to the patient.

One of the biggest advantages of CR is

the dynamic range, or latitude, it offers.

One of the biggest advantages of CR/DR is

the latitude it offers.

Other factors contributing to image resolution are

the size of the laser beam and the size of the PSP/IP phosphors

Overexposure of up to

500% and underexposure of up to 80% are reported as recoverable, thus eliminating most retakes.

pixel size is affected by changes in either the

FOV or matrix size

pixel size is affected by

changes in either the FOV or matrix size

Pixel size is inversely related to

resolution

Pixel size is inversely related to

resolution

Processing temperatures for laser film are the same as

those for regular x-ray film.

Resolution in computed radiography increases as

1. laser beam size decreases
2. PSP crystal size decreases

Road-mapping is particularly useful in procedures that require

guidewire/catheter placement

Scatter and filtration are unrelated to

intensifying screens.

Since bone is more dense and attenuates x-ray photons more readily, their attenuation is calculated to represent

the degree of bone density.

Size distortion (magnification)

is inversely proportional to SID and directly proportional to OID.

Slow-speed (detail or "extremity") screens resolve more

line pairs per millimeter (lp/mm) than much faster screens

Smaller image matrices look

"pixelly."

Smaller phosphor size improves resolution in ways similar to that of intensifying screens

anything that causes an increase in light diffusion will result in a decrease in resolution

Smaller phosphors in the PSP plate allow

less light diffusion

Soft tissue attenuation information is not used to measure

bone density

Spatial resolution in CR is impacted by

the size of the PSP, the size of the scanning laser beam, and monitor matrix size.

Spatial resolution increases as

SNR (signal-to-noise ratio) increases.

That portion of a CR cassette that records the radiologic image is the

photostimulable phosphor

The characteristic curve of typical film emulsion has a "range of correct exposure," limited by

the toe and shoulder of the curve.

The digital image's scale of contrast, or contrast resolution, can be changed electronically through

leveling and windowing of the image

The digitized images can also be

manipulated in postprocessing, electronically transmitted, and stored/archived

The electrical energy is sent to an analog-to-digital converter (ADC) where

it is digitized and becomes the digital image that is eventually displayed (after a short delay) on a high-resolution monitor and/or printed out by a laser printer.

The exposed CR cassette is placed into the CR scanner reader

where the PSP/imaging plate is automatically removed.

The faster the screens, the higher the

contrast; higher contrast is often associated with decreased latitude

the following statements regarding dual x-ray absorptiometry are true

1. two x-ray photon energies are used.
2. photon attenuation by bone is calculated.

The FOV and matrix size are

independent of one another, that is, either can be changed and the other will remain unaffected.

The frame-hold function eliminates the need for

continuous fluoroscopy, thereby reducing patient exposure

The larger the matrix size, the better the

image resolution

The latent image appears as the PSP is scanned by

a narrow high-intensity helium-neon laser to obtain the pixel data.

The latent image on the PSP is changed to a manifest image as :

it is scanned by a narrow high-intensity helium-neon (or solid state) laser to obtain the pixel data

The level control determines the

central or mid density of the scale of contrast, while the window control determines the total number of densities/grays (to the right and left of the central/mid density)

The luminescent light is converted to

electrical energy representing the analog image

the main function of a CR cassette is to

support and protect the IP that lies within the CR cassettes.

The matrix and the field of view can be changed independently, without one affecting the other, but changes in either will change

pixel size

The photostimulable IP is not affected by

light.

The process of "leveling and windowing" of digital images determines the image

contrast

The PSP can store the latent image for:

several hours; after about 8 hours, noticable image fading will occur

The radiographer can manipulate (change, enhance) digital images displayed on the CRT through postprocessing. One way to alter image contrast and/or density is through

windowing

The same exposure factors as screen-film systems, or less, are generally recommended for

CR/DR

the scanning laser light must be the correct

intensity and size.

The solid state detector plates are made of

barium fluorohalide compounds similar to that used in CR's PSP image plates

The term field of view is used to describe

how much of the patient (eg, 150-mm diameter) is included in the matrix.

The term windowing refers to

some change made to window width and/or window level

The use of fast screens results in some loss of

recorded detail

The violet light emited by the photostimulable phosphor (PSP) is transformed into the image seen on the CRT by the

ADC

There are several advantages of electronic/digital fluoroscopy

1. Electronic/digital fluoroscopic images are produced with less patient exposure and can be postprocessed (windowed to improve/enhance the image).
2. The fluoroscopic still-frame images can be stored and/or transmitted to a TV monitor.

There are two types of shape distortion

IR results in foreshortening of the object.

This affords much greater

exposure latitude and technical inaccuracies can be effectively eliminated

This PSP with its layer of europium-activated barium fluorohalide serves as the:

image receptor as it is exposed in the traditional manner and receives the latent image

To be suitable for use in intensifying screens, a phosphor should have which of the following characteristics?

1. High conversion efficiency
2. High x-ray absorption
3. High atomic number

Tube angulation causes

elongation of the object.

Types of shape distortion include

1. elongation.
2. foreshortening.

Typical image matrix size (rows and columns) used in chest radiography is

2048 x 2048

What will result from using single-emulsion film in an image receptor having two intensifying screens?

Decreased density

Which of the following terms refers to light being reflected from one intensifying screen, through the film, to the opposite emulsion and screen?

Crossover

Which possesses the widest dynamic range?

CR

Windowing allows for

contrast and density post-processing manipulation

Windowing and other postprocessing mechanisms permit the radiographer to affect changes in the image and to produce "special effects" such as

edge enhancement, image stitching (useful in scoliosis examinations), image inversion, rotation, and reversal.

With all other factors constant, as digital image matrix size increases,

1. pixel size decreases.
2. resolution increases.

Which of the following possesses the widest dynamic range? 1)high speed screen, 2)slow speed screen, 3)AEC, 4)CR

4) CR --
One of the biggest advantages of CR is the dynamic range, or latitude, it offers. The characteristic curve of x-ray film emulsion has a certain "range of correct exposure," limited by the toe and shoulder of the curve. In CR, there is a linear relationship between the exposure, given the PSP (photostimulable phosphor, or image plate) and its resulting luminescence, as it is scanned by the laser. This affords much greater exposure latitude and technical inaccuracies can be effectively eliminated. Overexposure of up to 500% and underexposure of up to 80% are reported as recoverable, thus eliminating most retakes. This surely affords increased efficiency; however, this does not mean that images can be exposed arbitrarily. The radiographer must keep dose reduction in mind. The same exposure factors as screen-film systems, or less, are generally recommended for CR.
Intensifying screens used in screen-film x-ray imaging tend to produce high contrast. The faster the screens, the higher the contrast; higher contrast is often associated with decreased latitude. AEC refers to automatic exposure control and is unrelated to dynamic range or latitude.

Any images obtained using DXA bone densitometry
1. are used to evaluate accuracy of the ROI.
2. are used as evaluation for various bone/joint disorders.
3. reflect the similar attenuation properties of soft tissue and bone.

1 only -- are used to evaluate accuracy of the ROI. --
DXA imaging is used to evaluate BMD (bone mass density). It is the most widely used method of bone densitometry (it is low dose, precise, and uncomplicated to use/perform). DXA uses two photon energies, one for soft tissue and one for bone. Since bone is more dense and attenuates x-ray photons more readily, their attenuation is calculated to represent the degree of bone density. Soft tissue attenuation information is not used to measure bone density. Any images obtained in DXA/bone densitometry are strictly to evaluate the accuracy of the ROI (region of interest); they are not used for further diagnostic purposes—additional diagnostic examinations are done for any required further evaluation. Bone densitometry, DXA, can be used to evaluate bone mineral content of the body, or part of it, to diagnosis osteoporosis or to evaluate the effectiveness of treatments for osteoporosis.

Focal spot blur is greatest
A. directly along the course of the central ray.
B. toward the cathode end of the x-ray beam.
C. toward the anode end of the x-ray beam.
D. as the SID is increased.

B - toward the Cathode end of the beam --
Focal spot blur, or geometric blur, is caused by photons emerging from a large focal spot. The actual focal spot is always larger than the effective (or projected) focal spot, as illustrated by the line focus principle. In addition, the effective focal spot size varies along the longitudinal tube axis, being greatest in size at the cathode end of the beam and smallest at the anode end of the beam. Because the projected focal spot is greatest at the cathode end of the x-ray tube, geometric blur is also greatest at the corresponding part (cathode end) of the radiograph.

High-kilovoltage exposure factors are usually required for radiographic examinations using
1. water-soluble, iodinated media.
2. a negative contrast agent.
3. barium sulfate.

3 only - Barium sulfate --
Positive-contrast medium is radiopaque; negative-contrast material is radioparent. Barium sulfate (radiopaque, positive-contrast material) is most frequently used for examinations of the intestinal tract, and high-kVp exposure factors are used to penetrate (to see through and behind) the barium. Water-based iodinated contrast media (Conray, Amipaque) are also positive-contrast agents. However, the K-edge binding energy of iodine prohibits the use of much greater than 70 kVp with these materials. Higher kVp values will obviate the effect of the contrast agent. Air is an example of a negative-contrast agent, and high-kVp factors are clearly not indicated.

An increase in kVp will have which of the following effects?
1. More scattered radiation will be produced.
2. The exposure rate will increase.
3. Radiographic contrast will increase.

1 & 2 only --
An increase in kilovoltage (photon energy) will result in a greater number (ie, exposure rate) of scattered photons (Compton interaction). These scattered photons carry no useful information and contribute to radiation fog, thus decreasing radiographic contrast.

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