Real-Time Imaging and Temporal Resolution Flashcards

These vocabulary flashcards cover the fundamental concepts of real-time imaging, frame rate, and the trade-offs involved in temporal, lateral, and spatial resolution in ultrasound physics.

Static scanning

An early process of diagnostic ultrasound where images were displayed one frame at a time, making it impossible to image moving structures.

Real-time imaging

The modern ultrasound capability where each frame is created and displayed very quickly, providing the impression of constant motion, like an ultrasound 'movie.'

Frame rate

The most important operational parameter associated with real-time imaging, describing the system's ability to create numerous frames each second, measured in hertz ($Hz$).

Temporal resolution

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

$$T_{frame}$$

The time required to make a single image; it is the reciprocal of the frame rate ($T_{frame} \times \text{frame rate} = 1$).

Imaging depth

A sonographer-controlled setting that is inversely related to frame rate; shallower imaging results in higher frame rates and superior temporal resolution.

Single focus

An imaging mode where only one sound pulse is transmitted down each scan line, resulting in higher frame rates and better temporal resolution, but poorer lateral resolution.

Multi-focus

A feature that improves lateral resolution by transmitting multiple pulses down each scan line, which increases the number of pulses per frame and diminishes temporal resolution.

Sector size

Also called field of view, this parameter is inversely related to frame rate; narrower sectors require fewer pulses and result in higher frame rates.

Line density

The spacing between sound beams; high line density improves spatial (detail) resolution but decreases frame rate and temporal resolution.

Lateral resolution

A characteristic of image accuracy that improves when multiple focal zones are activated, despite the negative effect on temporal resolution.

Spatial resolution

Also known as detail resolution, it improves with high line density because the gaps between scan lines are smaller and the image contains more detail.

Speed of sound in the medium

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

Pulse repetition period (PRP)

The round-trip time required for a pulse to travel to a maximum depth and back; the time needed to make a frame is calculated as \text{# pulses} \times PRP.

Pulse repetition frequency (PRF)

The number of pulses created per second; it is determined by multiplying the number of lines per frame by the frame rate.