Chapter 5 RADR 1313

What is the relationship between display field of view (FOV) and pixel size for a fixed matrix size?

Direct

A combination of rows and columns of pixels is called a what?

Matrix

What unit is used to measure pixel size?

Microns

Digital image quality is improved with what?

All options are correct

What happens to pixel size when matrix size increases for a fixed field of view (FOV)?

Pixel size decreases

What happens to spatial resolution when matrix size increases for an exposure FOV?

Spatial resolution increases

If display FOV is 500 mm and matrix size is 1024, what is the pixel size?

0.49 mm

What determines digitizing precision and the number of gray shades?

Bit depth

What happens to the number of gray shades when bit depth increases?

The number of shades of gray increases

What happens to contrast resolution when bit depth increases?

Contrast resolution increases

What does pixel bit depth determine in an image?

Contrast resolution

How many shades of gray can a 10-bit pixel display?

1024

What happens to contrast resolution when a system can digitize and display more gray shades?

Contrast resolution increases

What does greater pixel bit depth provide?

More precise digitization and more shades of gray

What is the number of pixels per unit area called?

Pixel density

What is the center-to-center distance between adjacent pixels called?

Pixel pitch

What improves spatial resolution?

Increased pixel density and decreased pixel pitch

What happens to spatial resolution when the number of line pairs per millimeter resolved increases?

Spatial resolution increases

What measures an imaging system’s ability to display contrast of objects varying in size?

Modulation transfer function (MTF)

What MTF value represents the maximum difference in brightness levels?

1.0

What is the range of exposures that should be used to produce a diagnostic image called?

Exposure latitude

What dose monitoring value measures exposure in air and estimated absorbed dose?

KAP (kerma-area product)

What measures the efficiency of an image receptor in converting X-ray exposure into a quality image?

Detective quantum efficiency (DQE)

What is the relationship between DQE and MTF?

Directly proportional

Which statement is true concerning computed radiography (CR) imaging plates?

All options are correct

What is the emission of light from a substance following stimulation by radiation called?

Luminescence

What is the CR phosphor layer composed of?

Barium fluorohalide with europium

What does the CR latent image consist of?

Electrons trapped in the phosphor layer

What is the emission of light when stimulated by a high-intensity laser beam called?

Photostimulable luminescence

What is the primary barium fluorohalide material in a CR imaging plate called?

Photostimulable phosphor

Which is NOT a component of a CR imaging plate?

Thin-film transistor (TFT) layer

In CR, which atoms become ionized when X-ray photons are absorbed by the phosphor?

Europium

In CR, what happens to trapped electrons?

Their number is proportional to exit exposure intensity, and they are released during readout

Which is NOT part of a CR reader unit?

Capacitor

What collects, amplifies, and converts visible light into an electrical signal?

Photomultiplier tube (PMT)

What scans the imaging plate in a CR reader unit?

Helium-neon laser beam

What is the sequence of events in a CR reader unit?

Stored energy is released as light → PMT converts light into an electrical signal → sampling and digitization

What happens when sampling frequency increases in CR?

Pixel density increases and sampling pitch decreases

What happens when sampling pitch increases in CR?

Pixel size increases and pixel resolution decreases

What determines how often an analog signal is reproduced in discrete digitized form?

Sampling frequency

What is the distance between analog points being sampled called?

Sampling pitch

With a fixed-matrix CR reader, what happens when a larger imaging plate is used?

Pixel size increases

What determines pixel bit depth?

Analog-to-digital converter (ADC)

Immediately before leaving the CR reader, what is the imaging plate exposed to?

Intense white light

Which digital imaging system converts exit radiation into electrical charges and stores them before readout?

Digital radiography (DR)

In DR imaging systems, where is electrical charge briefly stored?

Thin-film transistor (TFT)

Which array is divided into square detector elements (DELs)?

Thin-film transistor (TFT) array

What is the percentage of X-rays reaching a detector that are captured called?

Fill factor

Which is NOT a component of a direct flat-panel detector?

Phosphor layer

What does an indirect conversion detector use?

A scintillator and a photodetector

What are examples of scintillators used in indirect conversion DR?

Gadolinium oxysulfide and cesium iodide

What happens to X-rays in an indirect conversion DR system?

X-rays are converted to light, then to electrical charges

What is the sequence of direct conversion DR image production?

Exit radiation → electrical charge → TFT storage → ADC

What describes a detector’s ability to capture a variety of photon intensities in remnant radiation?

Dynamic range

What measures the efficiency of an image receptor in converting X-ray exposure into a quality image?

Detective quantum efficiency (DQE)

What happens to the exposure required for a quality image when DQE increases?

Required exposure decreases

What may result from overexposing a digital image receptor?

High signal-to-noise ratio (SNR) and increased patient exposure

What compares radiation exposure signal strength with image noise?

Signal-to-noise ratio (SNR)

What does a high SNR indicate?

High signal strength relative to noise

What happens to the visibility of anatomic details when SNR increases?

Visibility of anatomic details increases

What compares image contrast with image noise?

Contrast-to-noise ratio (CNR)

What happens to the visibility of anatomic details when CNR increases?

Visibility of anatomic details increases

What must be applied to the photoconductive detector element (DEL) surface for a DR detector to capture incoming radiation exposure?

A small electrical charge

According to the course answer key, what is the key distinction between CR and DR receptor technology?

DR detectors must have electrical communication with the X-ray generator (course answer; not universal)

What must DR detector panels be protected from?

All of the above

What does the size of a detector element (DEL) principally determine in DR?

Spatial resolution

Once data is digital, are CR and DR image processing and display the same?

True

Is no light produced with CR when radiation interacts with the imaging plate?

False

Does CR raw image data quality remain the same for up to 6 hours after exposure?

False

Do both CR and DR combine image capture and readout?

False

Does a DR system require a separate reader unit?

False — a DR system does not require a separate reader unit

With a flat-panel detector (FPD), are charges from each detector element (DEL) read out separately?

True

Is exit radiation converted to visible light in a direct conversion detector?

False

Do small anatomic objects have higher spatial frequency?

True

Does digital imaging’s large dynamic range mean significantly low exposure still produces a quality image?

False

Does an image with high SNR have decreased detail visibility?

False

Is bit depth determined by matrix size?

False

Is the spatial resolution of flat-panel receptors generally superior to CR?

True

Is DQE higher for DR compared with CR?

True

According to the course answer key, do all DR detectors require communication with the X-ray generator to enable data transfer following exposure?

True — course-marked answer; technically not universal

Is fading over time due to sensitive material the principal concern with DR images?

False