ch 4

Support phosphor protective

The CR imaging plate (IP) primarily consists of what 3 layers:

Detector elements (DELs).

The TFT layer is divided into squares known as:

Dose-area product (DAP) is a measure of exposure in air, followed by computation to estimate absorbed dose to the patient.

What is DAP:

DR direct conversion

What type of image receptor converts the exit radiation into electrical charges and stores them before readout and digitization?

increases

When using a fixed matrix size what happens to pixel size when increasing from 10x12 to 14x17

phosphor layer

With (CR), the photon intensities are absorbed by the________:

imaging plate

With (CR), the radiation exiting the patient interacts with the ________:

europium atoms

With CR what atoms become ionized when the x-ray photons are absorbed by the phosphor:

Lower

With CR, decreased pixel density and larger sampling pitch will result in a higher or lower sampling frequency?

larger

With a fixed matrix CR reader system, changing to a larger IP for the same FOV will result in larger or smaller pixels

A

14. A higher sampling frequency during CR latent image digitization will A. increase spatial resolution. B. decrease pixel density. C. increase pixel pitch. D. increase CNR.

D

5. Which of the following would improve the spatial resolution of the digital image for a given field of view (FOV)? A. A fixed matrix size and larger IP B. A decreased sampling frequency and larger IP C. A small matrix size and larger pixel size D. A fixed matrix size and small IP

DQE is a measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image.

Define Detective quantum efficiency (DQE):

MTF is a measure of the imaging system's ability to display the contrast of anatomic objects varying in size.

Define Modulation Transfer Function (MTF):

CNR is a method of describing the contrast resolution compared with the amount of noise apparent in a digital image.

Define contrast-to-noise ratio (CNR):

A method of describing the strength of the radiation exposure (signal) in comparison to the amount of noise apparent in the digital image.

Define signal-to-noise ratio (SNR):

Bit depth = 2^n (n=number of bits)

Bit depth is expressed as what:

D

1. Which of the following would improve spatial resolution? A. Small matrix and large pixel size B. Decreased pixel density and increased pixel pitch C. Large matrix and large pixel size D. Large matrix and increased pixel density

C

10. refers to the range of exposures that should be used to produce a diag. nostic image. A. Modulation transfer function B. Bit depth C. Exposure latitude D. Dynamic range

B

11. A lower signal-to-noise ratio (SNR) improves the quality of a digital image A. True B. False

A

12. Decreasing the displayed FOV for a given matrix size will decrease the size of the pixels and increase spatial resolution A. True B. False

C

13. Which of the following is a measurement of the efficiency of an IR in converting the x-ray exposure it receives to a quality radiographic image? A. DAP B. MTF C. DOE D. SNR

B

15. A 16-bit digital system would have a narrow dynamic range compared to a 12-bit system. A. True B. False

D

16. Which of the following provide an indication of patient radiation risk during a radiographic procedure? A. DOE B. DAP C. KAP D. B and C only

D

17. Digital detectors that require a two-stage process to acquire and digitize the latent image include A. flat-panel detectors indirect conversion. B. CCD. C. CMOS. D. all the above.

A

18. Image artifacts can be caused by 1. dirty CR IPs. 2. low sampling frequency. 3. increased pixel density. A. 1 and 2 only B. 1 and 3 only C. 2 and 3 only D. 1, 2, and 3

C

2. The type of image receptor (IR) that uses a photostimulable phosphor to acquire the latent image is A. an intensifying screen B. a flat-panel detector C. computed radiography D. direct radiography

A

3. Which of the following is used to extract the latent image from an imaging plate (IP)? A. Laser beam B. Photomultiplier tube C. Analog-to-digital converter D. Thin-film transistor

D

4. Which of the following will improve the spatial resolution of the digital image? A. Decreased sampling frequency and increased sampling pitch B. Decreased sampling frequency and decreased sampling pitch C. Increased sampling frequency and increased sampling pitch D. Increased sampling frequency and decreased sampling pitch

C

6. What is the process of assigning a numerical value to represent a brightness value? A. Dynamic range B. Signal-to-noise ratio C. Quantization D. spectral sensitivity

D

7. Which of the following pixel bit depths would display a greater range of shades of gray to represent anatomic tissues. A. 8 bit B. 10 bit C. 14 bit D. 16 bit

C

8. Small anatomic detail has A. decreased pixel density B. increased spatial resolution C. high spatial frequency D. low signal to noise ratio

A

9. Digital imaging systems have a wide dynamic range. A. True B. False

An imaging system that has a high MTF can display anatomic detail with improved visibility.

An imaging system that has high MTF means what:

increases

An increase in CNR_______the visibility of anatomic details:

A bright white light

Before the IP leaves the CR reader how is it essentially erased:

Digital image receptors have a wide dynamic range (they can accurately detect a wide range of radiation intensities)

Digital IR's have what type of dynamic range:

larger matrix size that includes a greater number of smaller pixels

Digital image quality is improved with a larger or smaller matrix:

Smaller sampling pitch

Does a decrease in pixel size and an increase in pixel resolution mean a larger or smaller sampling pitch?

Decrease

Does a larger sampling pitch increase or decrease the pixel size:

8

Does an 8-bit depth or a 10-bit depth have decreased number of shades of gray

10

Does an 8-bit depth or a 10-bit depth have increased contrast resolution

increases

Does higher sampling frequency increase or decrease pixel density:

Increasing the sampling frequency will decrease the sampling pitch, which improves the spatial resolution of the digital image.

Does higher sampling frequency increase or decrease the sampling pitch:

Increasing pixel density and decreasing pixel pitch increases spatial resolution. Decreasing pixel density and increasing pixel pitch decreases spatial resolution.

Explain spatial resolution as it pertains to pixel density and pixel pitch:

The higher the DQE of a system, the lower the radiation exposure to produce a quality image, thereby decreasing patient exposure.

Explain the relationship between DQE and x-ray exposure:

amorphous selenium-coated detector converts exit radiation directly into electrical charges/signals then the electrical signals are sent to the ADC for digitization

Explain the relationship between direct conversion detectors in DR:

A scintillator detector converts exit radiation into visible light the photodetector converts the visible light to electrical charges/signals then electrical signals are sent to the ADC for digitization

Explain the relationship between indirect conversion detectors in DR:

Laser scanning of the exposed IP converts the released energy (visible light) into an electrical signal (voltage).

Explain the sequence of events that happens in the CR reader unit:

Increasing the SNR means that the strength of the signal is high compared to the amount of noise.

High SNR means what:

scintillators

Indirect conversion detectors use________to convert exit radiation into visible light:

Using a smaller IP for a given FOV results in improved spatial resolution. Using a larger IP for a given FOV results in decreased spatial resolution.

In CR explain the relationship between IP size and fixed matrix size:

The ADC

In CR pixel bit depth is determined by what:

The photostimulable phosphor plate (PMT)

In CR what collects, amplifies, and converts visible light to an electrical signal:

PMT

In CR what converts the visible light into an electrical single

The thin-film transistor (TFT) array.

In DR imaging systems what stores the electrical charge:

helium-neon laser beam

In the CR reader the IP is removed from the cassette and scanned with a_______:

Maximum difference in brightness levels.

MTF of 1 means what in terms of brightness levels:

Sampling frequency determines how often the analog signal is reproduced in its discrete digitized form.

Sampling frequency:

higher spatial frequency (large objects have lower spatial frequency)

Smaller objects have higher/lower spatial frequency:

true, only contrast

T or F. pixel bit depth doesn't affect spatial resolution

Increasing the number of lp/mm results in improved spatial resolution

The greater number of line pairs per millimeter resolved in the imaging system affects spatial resolution in what way:

increases

The lower the DQE of a system, the radiation exposure required to produce a quality image

MTF

The measure of the imaging system's ability to display the contrast of anatomic details varying in size is the

fill factor

The percentage of xrays that have reached the detector and have been captured

"picture elements"; are the smallest component of the matrix.

What are pixels

CsI or gadolinium oxysulfide

What are two types of scintillator philosophies used in an indirect conversion detector

A photodetector

What converts visible light to electrical charges in indirect conversion detectors:

Bit depth determines the amount of precision, therefore the number of shades of gray.

What determines the images contrast resolution:

The PSP (photostimulable phosphor) when the exit xray intensities are absorbed by the phosphor and the europium atoms become ionized by the photoelectric effect.

What forms the CR latent image:

Electrons trapped in the phosphor layer

What forms the CR latent image?

The cassette

What houses the imaging plate in computed radiography (CR):

Pixel size = FOV/Matrix size

What is the formula for pixel size:

Increasing the SNR will improve the quality of the digital image.

What is the relationship between SNR and image quality:

If the FOV displayed on the monitor is increased for a fixed matrix size, then the pixel size is also increased (direct relationship)

What is the relationship between display field of view and pixel size for a fixed matrix:

If the matrix size is increased for a fixed FOV, then the pixel size is decreased (inverse relationship).

What is the relationship between matrix size and pixel size for fixed FOV:

direct

What is the relationship between matrix size and spatial resolution

A larger matrix size has more pixels that are small. This improves image quality (spatial resolution).

What is the relationship between matrix size and spatial resolution:

A larger bit depth results in more shades of gray. A smaller bit depth results in less shades of gray.

What is the relationship between pixel bit depth and contrast resolution:

Xray converter thin-film transistor (TFT) glass substrate

What three layers make up the flat-panel detectors (FPDs).

Number of bits; determines the amount of precision, therefore the number of shades of gray

bit depth:

The ability to accurately capture the range of photon intensities that exit the patient.

dynamic range:

The range of exposures that should be used to produce a diagnostic image

exposure latitude:

in microns

how are pixels measured

The emission of light when stimulated by radiation

luminescence:

Combination of rows and columns (array) of pixels

matrix:

Emission of light when stimulated by a high-intensity laser

photostimulable luminescence:

Number of pixels per unit area.

pixel density:

The distance between the center of one pixel and the center of another.

pixel pitch

The distance between the sampling points.

sampling pitch:

Unit of line pairs per millimeter (lp/mm).

spatial frequency: