Digital Imaging Characteristics

This set of flashcards covers the technical factors of digital image acquisition, matrix characteristics, bit depth, spatial resolution factors, and image noise (quantum mottle).

In digital imaging, what is the square chain of boxes called that gives shape to an image?

A matrix

What is the specific name for each individual box or pixel within an image matrix?

A detector element (DEL)

How does the matrix size relate to pixel size and image resolution?

A greater matrix size provides smaller pixels, which results in greater detail and resolution.

Unlike screen/film systems, what is the correlation between exposure level and spatial resolution in digital imaging?

There is no correlation between exposure level and spatial resolution.

What term describes the available grayscale for image acquisition and display?

Bit depth

What mathematical formula is used to calculate the number of shades of gray in a digital image?

$2^n$, where $n$ is the number of bits.

According to the bit depth formula, how many shades of gray are represented by $10 \text{ bits}$?

$1,024$ shades of gray

What is the definition of spatial resolution in digital imaging?

The degree of geometric sharpness or accuracy of structural lines actually recorded in the image.

Besides matrix size, what factor known as the frequency response of the incoming signal affects spatial resolution?

Bandwidth

What is the difference between pixel size and pixel pitch?

Pixel size is measured from side to side of the pixel, while pixel pitch is measured from the center of one pixel to the center of an adjacent one.

What are the three characteristics that affect spatial resolution for cassette-based systems?

1. Sampling frequency, 2. Receptor size, and 3. Phosphor thickness layer.

What is the range of sampling frequencies for data acquired from an exposed detector?

$5\text{ pixels/mm}$ to $20\text{ pixels/mm}$

How does a high sampling frequency affect pixel size and spatial resolution?

A higher sampling frequency makes the pixel size smaller and increases spatial resolution.

According to the Photostimulable Phosphor sampling chart, what is the spatial equivalent of a $5\text{ pixels/mm}$ sampling frequency?

$$200\text{ micron}$$

What is the spatial resolution in $lp/mm$ for a system with a $10\text{ pixels/mm}$ sampling frequency?

$$4.0\text{ lp/mm}$$

In cassette-less (flat-panel) systems, what does the spatial resolution depend on?

The detector element size (DEL)

What happens to spatial resolution if the DEL size is increased in a cassette-less system?

The spatial resolution decreases.

True or False: The technologist can change the detector element size (DEL) in flat-panel systems.

False

What are the three factors that cause quantum mottle (noise) on a receptor?

1. Insufficient signal strength, 2. Excessive scatter, and 3. Excessive fog.

Specifically, what causes quantum noise in digital images?

Insufficient signal strength, meaning there are not enough x-ray photons striking the receptor.

What does a high Signal-to-noise Ratio (SNR) indicate about an image?

It indicates little noise on the image.

What is the relationship between image noise and image contrast?

Image noise has an inverse relationship to contrast; increased noise decreases image contrast.

What percentage of underexposure results in a mottled image or the appearance of noise?

50\text{\\%} or greater

What occurs when there is overexposure greater than 100\text{\\%} to 200\text{\\%} in a digital image?

It results in a loss of image contrast.

What is the name of the device used to assess noise and low contrast resolution?

Leeds TO.12 Low Contrast Resolution Phantom