Unit 2 Digital Image Characteristics and Processing (Midterm Radiographic Imaging)

Information from CH 20 + 23

(T/F) The latent image is stored as digital data.

True

What must be processed by the computer before viewing on a display monitor?

Latent image

What is made up of pixels and voxels?

Matrix

What is dependent on matrix size?

Spatial resolution

What is the picture element of the matrix?

Pixel

What is the volume element of the matrix?

Voxel

Digital image quality is (improved/decreased) with a larger matrix size.

Improved

There are a (smaller/greater) number of (bigger/smaller) pixels in a larger matrix.

Greater

Smaller

What is expressed as the number of pixels contained on a display?

Monitor resolution

More pixels equals a (higher/lower) image resolution and more information that can be displayed.

Higher

What describes the size of the area being imaged?

Field of view (FOV)

The FOV is expressed in what form of measurement?

Millimeters

(More/less) anatomy is imaged with a large FOV.

More

The pixel size, FOV, and fixed matrix size have a(n) (indirect/direct) relationship.

Direct

In a fixed matrix system, if the FOV is displayed on the monitor is increased, then the pixel size (increases/decreases)

Increases

In a fixed FOV system, if the matrix size is increased, then the pixel size (increases/decreases).

Decreases

Fixed FOV systems have a (direct/indirect) relationship between the matrix size and pixel size.

Indirect

What is the equation to determine the pixel size?

FOV/Matrix size = pixel size

When the matrix decreases, there will be (more/less) pixels in a fixed FOV system.

Less

When the matrix increases, there will be (more/less) pixels in a fixed FOV system.

More (but smaller)

What is described as the number of pixels packed into an area?

Pixel density

The greater the pixel density, the (better/worse) the spatial resolution.

Better

What is the distance measured from the center of a pixel to the center of an adjacent pixel?

Pixel pitch

A smaller pixel pitch results in (increased/decreased) spatial resolution.

Increased

Smaller sized pixels have an (increased/decreased) pixel pitch.

Decreased

(T/F) Sampling happens in both CR and DR systems.

True

What is dependent on matrix size and image receptor size?

Sampling frequency

What is expressed in pixels per mm or (pixels/mm)?

Sampling frequency

Pixel pitch and spatial resolution are (inversely/directly) related.

Inversely

What is the standard at which imaging systems have to meet to function?

DICOM standard

What is listed as part of the DICOM header?

Bit depth

The maximum bit depth for medical images is about __ bits.

16

What is the ability of an imaging system to differentiate between two adjacent structures as separate and distinct regardless of varying tissue densities?

Spatial resolution

What imaging characteristic is limited to the size of the pixel?

Spatial resolution

The number of details that can fit into a given amount of space describes?

Spatial frequency

What is a method of measuring spatial resolution?

Spatial frequency

Spatial frequency is expressed as what?

Line pairs per millimeter (lp/mm)

Small objects have a (lower/higher) spatial frequency?

Higher

Large objects have a (higher/lower) spatial frequency?

Lower

(T/F) Spatial frequency is the number of lines within a given length.

True

A system with an increased spatial resolution will also have (increased/decreased) spatial frequency.

Increased

What are the three pixel characteristics?

Pixel size

Pixel pitch

Pixel density

What pixel characteristics affects the spatial frequency?

Pixel size

Pixel pitch

Pixel density

The more pixels in a matrix, the (smaller/larger) the pixels are, and the (better/worse) the spatial resolution.

Smaller

Better

In DR systems, each DEL is represented as what on the image?

Pixel

The (smaller/larger) the DEL, the better the spatial resolution.

Smaller

The (smaller/larger) the DEL pitch, the better the spatial resolution.

Smaller

(T/F) DELs are further apart and there are fewer DELs able to fit into an area, with a smaller DEL pitch.

False

The larger the DEL fill factor (for DELs of the same size), the (better/worse) the spatial and contrast resolutions.

Better

(T/F) A large fill factor will have increased spatial and contrast resolution.

True

In CR systems, the reader’s laser determines the sampling _.

Aperture/shape

What occurs when the intensity of light or the electrical signal is measured for each pixel in CR systems?

Sampling frequency

What is the measure of an imaging systems ability to display the contrast and spatial resolution of anatomic objects varying in size?

Modulation transfer function

What measures the accuracy of the image compared to the actual object?

Modulation transfer function

MTF values range between 0 and _.

1

An imaging system with a (low/high) MTF value can display anatomic detail with improved visibility.

High

What is used as a method of comparing spatial resolutions of imaging systems?

Modulation transfer function

If comparing two imaging systems, the system with the (higher/lower) MTF value will have images with improved image quality.

Higher

What is the way the imaging system can estimate the dose patient’s receive during exams called?

Dose monitoring

What provides an indication of the patient’s radiation risk?

Dose

What does DAP stand for?

Dose Area Product

What reflects the total amount of x-ray energy delivered to a patient?

DAP

What form of measurement is the DAP expressed in?

mGy-cm²

What imaging characteristics affect the image signal/exposure?

Detective quantum efficiency (DQE)

Dynamic range

Noise

Signal to noise ratio (SNR)

What is the measurement of the efficiency of an image rector in converting the x-ray exposure it receives to a quality radiographic image?

Detective quantum efficiency (DQE)

The higher the DQE is of a system, the (higher/lower) the radiation exposure to produce a quality image

Lower

(T/F) A higher DQE decreases the patient’s exposure and dose.

True

What characteristic is impacted by the type of material used in the IR to capture the exit radiation and energy of the beam?

DQE

(T/F) CR systems have a higher DQE than DR systems.

False

(T/F) Higher techniques are needed in CR systems because they have a lower DQE.

True

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

Dynamic range

The range of exposure that can be captured by an IR describes?

Dynamic range

(T/F) Digital image receptors have a wide dynamic range.

True

(T/F) Because an exposure is within the dynamic range, it does not mean the exposure will produce a quality image.

True

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

Exposure latitude

(T/F) Exposure latitude includes the exposures that result in a good image and a good dose to the patient.

True

(T/F) The exposure latitude is what the exposure should be.

True

What is everything on an image that does not represent actual patient anatomy?

Noise

What results from not using enough technique?

Quantum noise

(T/F) The technologist can control the production of quantum noise.

True

What is the random information created by electronic components in the system?

System noise

What is created from background radiation, and is only able to be controlled in CR systems by routinely erasing CR cassettes?

Ambient noise

What happens or is created when photons are not aligned to the anatomy?

Scatter

(T/F) Scatter is added exposure to the patient.

True

(T/F) Scatter can add useful information.

False

(T/F) Scatter can be controlled (lessened) by the technologist.

True

What is the method of describing the strength of radiation exposure in comparison to the amount of noise apparent in the digital image?

Signal to noise ratio (SNR)

(Increasing/decreasing) the SNR means that the strength of the signal is high compared to the amount of noise.

Increasing

(Increasing/decreasing) the SNR will improve the quality of the digital image.

Increasing

An increase in signal + a decrease in noise = (increased/decreased) SNR

Increased

(T/F) Increasing the number of photons (increase in mAs and kVp) striking the IR will increase the signal.

True

(T/F) Increasing the signal should be done with caution as it also increases patient dose.

True

Increasing which technical factor too much can result in increased scatter.

kVp

What is the smallest exposure change that can be detected and displayed by the system called?

Contrast resolution

What is the number of shades of gray the system is capable of showing?

Bit depth

(T/F) A greater bit depth has a greater range of gray shades and a better contrast resolution.

True

Increased contrast resolution (increases/decreases) the visibility of anatomic details and the ability to distinguish among small anatomic areas of interest.

Increases

A system that can display a greater number of shades of gray has a larger bit depth and therefore has better what?

Contrast resolution

What two characteristics affect the contrast resolution?

Bit depth

Scatter

What is the equation for bit depth?

2^n

n = number of bits in the system