DMS 101 Week 5 Class 9 - Ultrasound Beam Formation and Resolution

Vocabulary flashcards covering sound beam formation, beam anatomy, and spatial resolutions (axial, lateral, and slice thickness) from DMS 101 Week 5 Class 9.

Diffraction

The spreading out of sound (or light) into a pie shape when produced by a small source.

Huygens' Principle

Principle stating that each point on the surface of the transducer is a separate and individual point of sound. Overlapping and interference of these wavelets cause the ultrasound beam to assume its typical hourglass shape.

Focus

The point at which the beam of sound is at its minimum diameter. Image quality is optimum at this focal point.

Near Field

Also known as the Near Zone or Fresnel Zone; the area or space between the transducer face and the focus.

Near Zone Length (NZL)

Also known as Focal Length; the length of space between the transducer's face and the focus.

NZL Formula

$$\text{NZL} = \frac{(\text{Transducer Diameter})^2 \times \text{Frequency}}{6}$$

Far Zone

Also known as the Fraunhofer Zone; the area or space beyond the focus where the sound beam starts to enlarge or widen.

Detail Resolution

Also known as Spatial Resolution; the ability to distinguish structures clearly from a spatial perspective.

Axial Resolution

The ability to distinguish 2 structures as separate and distinct from each other when located along the beam's path (front to back, parallel to sound travel).

Axial Resolution Synonyms

Longitudinal, Axial, Range, Radial, Depth (LARD).

Axial Resolution Formula

$$\text{Axial Resolution (mm)} = \frac{\text{SPL (mm)}}{2}$$

Lateral Resolution

The ability to distinguish 2 structures as separate and distinct from one another when located perpendicular to the beam's path.

Lateral Resolution Synonyms

Lateral, Angular, Transverse, Azimuthal (LATA).

Lateral Resolution Formula

$$\text{Lateral Resolution} = \text{Beam Diameter}$$

Slice Thickness Resolution

Also known as Elevational resolution, Out of plane focusing, Elevational axis, Section thickness, or Z axis; the resolution that is at $90^\circ$ (perpendicular) to a 2-dimensional scan.

Spatial Resolution Ranking

In diagnostic imaging, spatial resolution quality ordered from best to worst is: 1. Axial Resolution, 2. Lateral Resolution, 3. Elevational Resolution.