Unit 4 Radiographic Exposure

Exposed CR imaging plates should be processed within __________ hour(s) to avoid any loss of image quality because of fading.

1

Increasing the number of line pairs per millimeter resolved in the imaging system results in:

increased spatial resolution

With CR, a higher sampling pitch results in _____________ pixel size and ____________ spatial resolution.

increased; decreased

With CR, a higher sampling frequency results in _____________ pixel density and ____________ spatial resolution.

increased; increased

Immediately before leaving the CR reader unit, the IP is exposed to:

intense white light

Determine the bit depth:

ADC (analog-to-digital converter)

Overexposing a digital image receptor may result in a quality image, but:

ALARA has not been followed

_______ __________ specifies the intensity of x-rays at a given point in air at a known distance from the focal spot or source of x-rays.

Air Kerma

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

CNR (contrast to noise ratio)

________ is a measure of exposure in air, followed by computation to estimate absorbed dose to the patient.

DAP (Dose area product, same as KAP)

_________ is a measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image. The ________ , the patient does is decreased.

DQE (Detective Quantum Efficiency); higher DQE

With CR, a higher sampling frequency results in _____________ pixel size and ____________ spatial resolution.

Decreased; increased

What term refers to the range of exposures that should be used to produce a diagnostic image?

Exposure latitude

T/F. Bit depth is determined by the matrix size.

False

T/F. Exit radiation is converted to visible light with the direct conversion detector.

False

The quality of the CR latent image will remain the same for up to 6 hours after exposure.

False (only 1 hour)

T/F. An image with high SNR (sound to Noise Ratio) will have decreased detail visibility.

False.

In the CR reader unit, the IP is scanned with a(n):

Helium-neon laser beam

A larger bit depth:

Increases the number of shades of gray

_________ the SNR increases the visibility of anatomic details.

Increasing

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

Modulation transfer function

The ________ collects, amplifies, and converts the visible light to an electrical signal proportional to the range of energies stored in the IP.

PMT (photomultiplier tube)

The pixel spacing, or distance measured from the center of a pixel to an adjacent pixel is called the:

Pixel pitch

Layers of a CR plate in order from top to bottom:

Protective, Phosphor, Reflective, Conductive, Support

The distance between the analog points being sampled is the:

Sampling pitch

___________ _____________ is defined by the unit of line pairs per millimeter (lp/mm).

Spatial frequency (Small objects= high sf, Big objects= low sf)

DR imaging systems briefly store the electrical charge in the:

TFT (thin-film transistor)

T/F. Once the data is in digital format, there is no difference between image processing and display between CR and DR.

True

T/F. The DR system does not require a separate reader unit.

True

T/F. The spatial resolution of flat-panel receptors is generally superior to that of CR.

True

Which of the following will improve the quality of the digital image? Select one: a. Increased sampling frequency and decreased sampling pitch b. Increased sampling frequency and increased sampling pitch c. Decreased sampling frequency and decreased sampling pitch d. Decreased sampling frequency and increased sampling pitch

a. Increased sampling frequency and decreased sampling pitch

Which of the following results in improved spatial resolution? Select one: a. increased pixel density and decreased pixel pitch b. increased pixel bit depth and increased pixel density c. All options are correct. d. increased pixel bit depth and decreased pixel pitch

a. increased pixel density and decreased pixel pitch (pixel bit depth does NOT affect spatial resolution)

The CR phosphor layer is composed of:

barium fluorohalide with europium

A system that can digitize and display a greater number of shades of gray (higher bit depth) has ___________ contrast resolution.

better

Which of the following pixel bit depths would display a greater range of shades of gray to represent the anatomic tissues? Select one: a.8-bit b.10-bit c.14-bit d.16-bit

d. 16-bit (bit depth is 2^n)

The indirect conversion detector uses: Select one: a. A scintillator b. A photodetector c. Amorphous selenium d. A and B

d. A. and B.

With CR, trapped electrons are: Select one: a. Proportional in number to the tissue's x-ray absorption b. In a lower energy state c. Released during the readout stage d. A and C

d. A. and C.

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

direct

Amorphous selenium-coated detector converts exit radiation directly into electrical charges is a process used by:

direct conversion detectors

The pixel size is __________ related to FOV and ____________ related to matrix size.

directly; inversely Pixel size= FOV/Matrix size

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

dynamic range

Both types of DR flat panel detector digital imaging systems convert x-ray energy into

electrical charges

With CR, when the x-ray photons are absorbed by the phosphor, the ___________ atoms become ionized.

europium

The percentage of x-rays that have reached the detector and have been captured is the:

fill factor

A system that can digitize and display a greater number of shades of gray will have ____________ contrast resolution.

increased

Digital image quality is improved with a __________ matrix size that includes a greater number of smaller pixels.

larger

The ___________ is stored as digital data and must be processed by the computer for viewing on a display monitor.

latent image

The emission of light when stimulated by a high intensity laser beam is:

photostimulable luminescence

This material is composed of barium fluorohalide and makes up the primary component of the CR IP.

photostimulable phosphor

The CR system's ability to display a range of shades of gray is determined by its:

pixel depth

If the matrix size is increased for a fixed field of view (FOV):

pixel size is decreased

What is the process of assigning a numeric value to represent a brightness value?

quantization

CR imaging plates that have not been used for 48 hours:

should be run through an erasure cycle

If the matrix size is increased for a given FOV:

spatial resolution is increased