Computed/digital imaging

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

"noisy" image.

Smaller image matrices look

"pixelly."

Matrix and pixel sizes are related to

(spatial) resolution of digital images

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

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

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.

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

Types of shape distortion include

1. elongation. 2. foreshortening.

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.

Resolution in computed radiography increases as

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

Bone densitometry is often performed to

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

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

1. pixel size decreases 2. spatial resolution increases

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

1. pixel size decreases. 2. resolution increases.

Characteristics of digital radiographic imaging include

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

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.

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

2048 x 2048

Overexposure of up to

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

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

512 x 512 matrix

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

ADC

Which possesses the widest dynamic range?

CR

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

CR/DR

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

Crossover

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

Decreased density

pixel size is affected by changes in either the

FOV or matrix size

There are two types of shape distortion

IR results in foreshortening of the object.

Spatial resolution increases as

SNR (signal-to-noise ratio) increases.

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.

A digital image is formed by

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

The latent image appears as the PSP is scanned by

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

Fewer and larger pixels result in

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

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

a smaller image matrix (700 x 700).

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

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

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

Any images obtained using DXA bone densitometry

are used to evaluate accuracy of the ROI

AEC refers to

automatic exposure control and is unrelated to dynamic range or latitude

The solid state detector plates are made of

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

DXA is the most widely used method of

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

Soft tissue attenuation information is not used to measure

bone density

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

DR does not use

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

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)

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

pixel size is affected by

changes in either the FOV or matrix size

The frame-hold function eliminates the need for

continuous fluoroscopy, thereby reducing patient exposure

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

contrast

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

contrast

Windowing allows for

contrast and density post-processing manipulation

The faster the screens, the higher the

contrast; higher contrast is often associated with decreased latitude

How effectively the phosphors make this energy conversion is termed

conversion 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

As pixel size increases, resolution

decreases

if the matrix size is increased, pixel size

decreases

if the matrix size is increased, pixel size

decreases.

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.

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.

The luminescent light is converted to

electrical energy representing the analog image

Tube angulation causes

elongation of the object.

DXA imaging is used to

evaluate BMD (bone mass density).

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

evaluate bone mineral density (BMD).

This affords much greater

exposure latitude and technical inaccuracies can be effectively eliminated

CD/DR affords much greater

exposure latitude; technical inaccuracies can be effectively eliminated

A narrow laser beam is required

for optimum resolution

Road-mapping is particularly useful in procedures that require

guidewire/catheter placement

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.

Better resolution is obtained with

high SNR

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

high-quality, high-resolution image display

The term field of view is used to describe

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

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

The larger the matrix size, the better the

image resolution

DR affords the advantage of

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

DR offers the advantage of

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

Most laser film must be handled

in total darkness

As pixel size decreases, resolution

increases

As intensification factor increases, radiographic density generally

increases.

If FOV increases, pixel size

increases.

The FOV and matrix size are

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

CR cassettes do not contain:

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

Scatter and filtration are unrelated to

intensifying screens.

the scanning laser light must be the correct

intensity and size.

Size distortion (magnification)

is inversely proportional to SID and directly proportional to OID.

CR is less expensive primarily because

it is compatible with existing equipment

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 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

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

Smaller phosphors in the PSP plate allow

less light diffusion

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

leveling and windowing of the image

The photostimulable IP is not affected by

light.

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

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

As in traditional radiography, spatial resolution is measured in

line pairs per mm

As in traditional radiography, spatial resolution is measured in

line pairs per mm (lp/mm)

The digitized images can also be

manipulated in postprocessing, electronically transmitted, and stored/archived

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

mobile studies

DR requires existing equipment to be

modified or new equipment purchased

DR cannot be used with mobile studies because

no cassettes are used

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

noise

DXA uses two photon energies

one for soft tissue and one for bone.

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

photo- (or light) stimulated luminescence.

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

photostimulable phosphor

Inside the IP (CR cassette) is the

photostimulable phosphor (PSP) image storage plate.

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

pixel size

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

quantum detection efficiency

In general, as the intensification factor increases

radiographic density increases

The use of fast screens results in some loss of

recorded detail

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

reduce resolution.

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

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

resolution

Image matrix has a great deal to do with

resolution

Pixel size is inversely related to

resolution

The PSP can store the latent image for:

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

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

shape distortion

Increasing the SID and decreasing the OID decreases

size distortion.

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

The term windowing refers to

some change made to window width and/or window level

digital radiographic imaging requires the use of

somewhat different equipment.

the main function of a CR cassette is to

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

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

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

the degree of bone density.

One of the biggest advantages of CR is

the dynamic range, or latitude, it offers.

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

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

One of the biggest advantages of CR/DR is

the latitude it offers.

In this procedure

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

Spatial resolution in CR is impacted by

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

Other factors contributing to image resolution are

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

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

the toe and shoulder of the curve.

As matrix size is increased

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

Processing temperatures for laser film are the same as

those for regular x-ray film.

Most laser film is loaded into a film magazine in

total darkness.

CR uses

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

The exposed CR cassette is placed into the CR scanner reader

where the PSP/imaging plate is automatically removed.

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