Beam and Transducer Anatomy/

What is the Near Zone

Near field, fresnel zone. Between transducer & focal point. Sound beam CONVERGES.

What is the widest the near zone will get in diameter

Diameter of crystal/element. AKA aperture “D”

Relationship between frequency, diameter and NZL

when frequency and diameter increase the Near zone will be DEEPER

Focal Point

focus, end of near zone, beginning of far zone, middle of focal zone. NARROWEST part of the beam

What is the diameter of the focal point

½ D

Focal Depth

Focal length, near zone length. Length of the near zone.

Far Zone

fraunhofer. Zone deeper than the focus, beyond the near field. DIVERGE.

Diameter of the far zone

at 2NZL, it will be the same diameter as the element/crystal

For an unfocused continuous wave disc transducer what is the beam diameter at the end of the near zone

½ the transducer diameter or aperture

Focal Zone

the region surrounding the focus equally into the near zone and far zone where it is “sort of narrow” the picture is relatively good

What two factors determine focal depth

transducer diameter/aperture and frequency

What characteristics does a shallow focus have

small diameter, low frequency

What characteristics does a deep focus have

large diameter, high frequency

Between shallow and deep focus which has a lower intensity at the focus

deep focus

Sound beam divergence and what determines it

describes the spread of the sound beam in the deep far zone.

1- transducer diameter/aperture

2-frequency

Divergence in relation to a larger diameter crystal

produces higher frequency sound produce beams that diverge less in the far field

Divergence in relation to smaller diameter crystals p

producing lower frequency sound produce beams that diverge substantially in the far field.

In far field with large diameter what does the beam look like, and frequency, what is best

Narrow beam, Lateral resolution is best, large diameter, high frequency

Frequency CW is determined by

electronic frequency

Frequency Pulsed is determined by

thickness of ceramic and speed of sound in ceramic

Focal length is determined by

aperture of ceramic and frequency of sound

Divergence is determined by

aperture of ceramic and frequency of sound

Diffraction pattern

V-shaped wave, called HUYGEN’S wavelet.

Huygen’s principle

explains the hourglass shape of an imaging transducer’s sound beam.

The overall hourglass shape of a sound beam is the result of

constructive and destructive interference. (in phase in the hourglass, out of phase everywhere else)

What is the relationship of wavelength and transducer frequency

Wavelength is equal to the speed of sound in media/transducer frequency (if frequency remains the same, wavelength is unchanged)

Spatial resolution

dependent on pixels of a monitor and scan lines in an image

contrast resolution

ability to differenciate shades of gray

temporal resolution

determines the accuracy of moving objects

elevation resolution

determines if we are accurately seeing a thin slice of anatomy w/ the beam

lateral resolution

accuracy of side by side structures/perpendicular being displayed between 2 echoes

axial resolution

ability to distinguish 2 structures close to each other front to back, parallel to or along the beam’s main axis

Synonyms for Axial Resolution

LAARD

longitudinal

axial

range, radial

depth

What is axial resolution highly dependent on

SPL

spatial pulse length