Sound Beams and Ultrasound Resolution

Practice flashcards covering the anatomy of sound beams, Huygens' Principle, various types of image resolution, and focusing techniques based on lecture notes.

Huygens' Principle

The principle stating sound beams are formed by small wavelets combining through constructive and destructive interference to create an hourglass-shaped diffraction pattern.

Sound Beam

The width or diameter of an ultrasound pulse as it travels away from the transducer.

Main scanning plane

The scanning plane that determines both axial and lateral resolution.

Perpendicular plane

Also known as the Z-axis or slice thickness, this plane determines elevational resolution.

Slice thickness

Another name for the perpendicular plane which contributes to the partial volume artifact.

Partial volume artifact

An imaging artifact where echoes from outside the actual structure are included in the image, often filling in anechoic structures.

Side lobes

Acoustic energy that travels outside the main beam axis, occurring primarily with single-element (mechanical) transducers.

Grating lobes

Artifacts caused by ultrasound energy traveling outside the main beam axis in array transducers due to multiple active elements.

Apodization

A reduction technique where central transducer elements receive higher electrical voltage and outer elements receive lower voltage to reduce side-lobe energy.

Subdicing

The process of dividing a crystal element into smaller sub-elements that are electrically connected to function as a single element to reduce artifacts.

Near zone

Also known as the Fresnel zone or near field, the region where the beam originates at the transducer face and narrows toward the focus.

Fresnel zone

An alternative name for the near zone or near field.

Far zone

Also known as the far field or Fraunhofer zone, the region beyond the focus where the sound beam begins to diverge.

Fraunhofer zone

An alternative name for the far zone or far field.

Near zone length (NZL)

The distance from the transducer face to the focal point, dependent on crystal diameter, frequency, and aperture.

Focal zone

 represents the region where the beam diameter is at its narrowest, specifically at the focus.

Dynamic aperture

Also known as variable aperture, it represents the number of active elements emitting ultrasound pulses to keep the beam narrow.

Aperture

The number of active elements in a transducer used to emit ultrasound pulses.

Detail resolution

A type of imaging resolution directly related to the transducer, containing axial and lateral resolution.

Contrast resolution

A type of imaging resolution that is directly related to the ultrasound instruments.

Temporal resolution

An aspect of imaging resolution that is directly related to the ultrasound instruments.

Axial resolution

The ability to distinguish two closely spaced reflectors along the direction of the ultrasound beam; calculated as $\frac{\text{Spatial pulse length (mm)}}{2}$.

Longitudinal resolution

One of the alternative names for axial resolution, part of the LARRD acronym. (L)

Radial resolution

One of the alternative names for axial resolution, part of the LARRD acronym. (Rd)

Range resolution

One of the alternative names for axial resolution, part of the LARRD acronym. (R)

Depth resolution

One of the alternative names for axial resolution, part of the LARRD acronym. (D)

LARRD

An acronym for the synonyms of axial resolution: Longitudinal, Axial, Radial, Range, and Depth.

Lateral resolution

The ability to distinguish two reflectors side-by-side, perpendicular to the beam, and is numerically equal to the beam diameter.

Angular resolution

One of the alternative names for lateral resolution, part of the LATA acronym. (an)

Transverse resolution

One of the alternative names for lateral resolution, part of the LATA acronym. (T)

Azimuth resolution

One of the alternative names for lateral resolution, part of the LATA acronym. (az)

LATA

An acronym for the synonyms of lateral resolution: Lateral, Angular, Transverse, and Azimuth.

Spatial pulse length (SPL)

The length of a pulse in space; reducing this improves axial resolution.

Damping

A process that provides short pulses to improve axial resolution.

Elevational resolution

Considered the third aspect of detail resolution, measured perpendicular to the imaging plane in the slice thickness direction.

Z-axis resolution

A term used interchangeably with elevational resolution or slice thickness resolution.

Unfocused beam

A beam that has a natural focus where the diameter is half the transducer diameter, with divergence beginning after the natural focus.

Natural focus

The focal point found in an unfocused ultrasound beam.

Mechanical focusing

Fixed or conventional focusing used with single-crystal transducers where the focal depth cannot be adjusted.

External focusing

A type of mechanical focusing achieved by applying a LENS to the transducer.

Internal focusing

A type of mechanical focusing achieved by using a curved PZT crystal.

Electronic focusing

Focusing used in array transducers that requires multiple crystal elements.

Fixed focusing

Another name for mechanical or conventional focusing because the focal depth is determined and cannot be adjusted.

Lens

A hardware component used to achieve external focusing in a single-element transducer.

Curved PZT

A crystal shape used to achieve internal focusing in a transducer.

1, and 1/2 D crystal

A type of crystal arrangement used in array transducers to improve elevational resolution.

Disc shaped crystal

Crystal design used in mechanical and annular transducers to improve elevational resolution.

Sound Intensity

A property of the sound beam that varies with diameter and is highest at the focus.

Diffraction pattern

The specific hourglass-shaped beam pattern formed when wavelets combine through interference.

Harmonics imaging

An imaging method that can be used to improve lateral and elevational resolution.