Ultrasound Real-Time Imaging and Temporal Resolution

These flashcards cover the vocabulary and core concepts of real-time imaging, temporal resolution, and the physical parameters affecting ultrasound frame rates.

Static scanning

A process used in the early days of diagnostic ultrasound where images were displayed one frame at a time, like a "photograph," making it impossible to image moving structures.

Real-time imaging

A modern ultrasound technique where each frame is created and displayed very quickly, providing the impression of constant motion, similar to an ultrasound "movie."

Frame rate

The most important operational parameter of real-time imaging, measured in hertz ($Hz$) or "images per second," representing the system's ability to create numerous frames each second.

Temporal resolution

Pertaining to "accuracy in time," it describes the ability to precisely position moving structures from instant to instant and is determined by the frame rate.

Relationship between Frame Rate and $T_{frame}$

These parameters are inversely related and are reciprocals; when multiplied together, the result is 1 ($T_{frame} \times \text{frame rate} = 1$).

Imaging depth

One of two sonographer-controlled settings that determine frame rate; it is inversely related to frame rate and temporal resolution.

Shallow imaging

Associated with short go-return times, shorter $T_{frame}$, higher frame rates, and superior temporal resolution.

Deep imaging

Associated with long go-return times, longer $T_{frame}$, lower frame rates, and inferior temporal resolution.

Multi-focus

A setting where multiple pulses are transmitted down each scan line, which improves lateral resolution but decreases frame rate and temporal resolution.

Sector size

Also called field of view; expanding this requires more pulses to create an image, resulting in a lower frame rate and decreased temporal resolution.

Line density

The spacing between sound beams; high line density uses closely packed lines and more pulses per image, improving spatial resolution while decreasing temporal resolution.

Spatial resolution

Also known as detail resolution; it improves with high line density because the smaller gaps between lines provide more detail in the image.

Lateral resolution

A form of resolution that improves with multi-focusing because the beam is narrow over a wide range of depths.

Speed of sound in the medium

The fundamental limitation of temporal resolution; in soft tissue, it is considered constant at $1.54\,km/s$.

Factors determining Number of Pulses per Frame

The three factors are: 1. number of focal points (multi-focus vs. single focus), 2. sector size, and 3. line density (lines per angle of sector).