Chapter 28 – Spatial Resolution

Flashcards covering the definitions and technical factors related to spatial resolution in radiography, including digital imaging properties, noise measurements, and geometric factors.

Spatial Resolution

Geometric sharpness OR accuracy of structural lines in an image; also known as definition, sharpness, or recorded detail.

Matrix Size

Determined by the IR size; a larger matrix provides more available pixels.

Pixel Size

Determines resolution in digital imaging where smaller pixels result in better spatial resolution and detail.

Grayscale Bit-depth

Represents the depth of the image and the number of shades of gray available, calculated as $2^n$ where $n$ is the bit depth.

Byte

A unit of digital information where $8$ bits is equal to $1$ byte.

High Spatial Frequency

A signal that can image smaller objects, characterized by line pairs close together and short wavelengths.

Low Spatial Frequency

A signal characterized by pairs of lines visualized farther apart and long wavelengths, resulting in less detail.

Penumbra

The blur or lack of sharpness at the edges of an image.

Umbra

The shadows expected on the image representing the anatomy being viewed.

Point Spread Function (PSF)

A method of measuring recorded detail using a tiny hole made in a sheet of lead.

Line Spread Function (LSF)

A method of measuring recorded detail using a tiny slit in a sheet of lead.

Edge Spread Function (ESF)

A method of measuring recorded detail using a sharp edge to obtain an x-ray image.

Modulation Transfer Function (MTF)

Measures the accuracy of the image to the actual object using a ratio from $0$ to $1$.

Fidelity

The trueness of the image, calculated when MTF measurement represents the percentage of object contrast that is recorded.

System Noise

Background information received by the image receptor caused by electronics in the system.

Ambient Noise

Background information received by the image receptor caused by background radiation.

Quantum Mottle

A type of noise caused by a lack of IR exposure or insufficient photons reaching the IR.

Signal to Noise Ratio (SNR)

A measurement of the amount of signal relative to the total amount of noise, dependent on IR exposure and DQE.

Detective Quantum Efficiency (DQE)

A measurement of the sensitivity and accuracy with which the IR converts incoming data to the output viewing device; ideal range is $0.3 - 0.7$ ($30\% - 70\%$).

Contrast to Noise Ratio (CNR)

The difference of signal intensities between two regions of interest (Noise vs. Signal intensity).

Low-Contrast Resolution (LCR)

The ability to capture and display subtle energy differences in an area of interest, such as the difference between fat and muscle.

Temporal Resolution (TR)

Resolution as a function of exposure time and dynamic motion of a body part; shorter acquisition times result in better temporal resolution.

Nyquist Criterion

A digital sampling processing algorithm ensuring data is sampled twice ($2\times$) to prevent missing information or double sampling.

Aliasing

A misrepresentation of signal frequencies that occurs when the Nyquist Criterion is not met.

Focal Spot

The site where the beam starts; a smaller effective focal spot reduces penumbra and increases spatial resolution.

Fill Factor

Regarding DR, it is how much of the detector element (Del) is taken up by the sensing area; higher fill factors result in higher resolution.

Spatial Frequency Formula

Mathematically defined as half of the pixel size of the image: $SF = \frac{1}{2 \times \text{pixel size}}$.