Physics transducers

what determines the frequency of a transducer?

speed of sound in the PZT, and thickness of the PZT

what is the advantage of using a wide-bandwidth transducer vs. a narrow bandwidth transducer?

improves axial resolution

wider bandwidths have

shorter pulse lengths

what improves lateral resolution?

smaller beam diameter;

narrower beam, higher frequency

Focal point:

focus, or focal point

narrowest part of the sound beam

width of the sound beam at the focus is one-half the width of the beam as it leaves the transducer.

Focal zone (focal region)

area around the focus where the beam is narrow. it contains half the NZ and half the FZ

Fresnel zone-

near zone, or near field.

area from the transducer to the focus. @ the end of the near zone

beam gradually narrows (converges) within the near zone.

at the end of the near zone to only ½ the width

Fraunhofer zone-

far field, or far zone

area that starts at the focus and extends deeper

from the focus out

within the far zone the beam diverges (spreads out)

when the beam is 2 nzl from the transducer, the beam is again the same size as the active element.

focal length-

focal depth, or near zone length (nzl)

the distance from the transducer to the focus.

Do phased array and annular arrays have the same image shape?

YES- fan or sector- shaped

which type of focusing is used in the elevational plane?

fixed focusing

what trandsucer produces a beam that is symmetrical about the beams axis?

annular phased arrray

lateral resolution (degrades or improves) at a shallower depth with a smaller transducer.

degrades

what are 4 things that axial resolution is improved by?

shorter SPL, shorter PD, wide bandwidth and low Q factor

______ refers to constructive and destructive interference of sound waves from each individual sound source.

Huygen’s Principle

increasing transducer diameter will ____ the NZL

increase

using 4 transmit focal zones will need ____ pulse sequences

4

using ______ reduces frame rate

multifocal zones

which transducer is focused electronically but mechanically steered?

Annular phased array

which transducer has the same elevational and lateral resolution?

annular phased array

what is the method used to reduce side lobes?

Apodization

when a voltage is applied to the PZT element, what happens to that element?

Piezoelectric effect

T/ F: Lateral resolution remains constant at any depth?

FALSE

what transducer will decrease slice thickness of the beam?

1 ½ dimensional array

what is the purpose of the matching layer?

to match the impedance between the skin and the transducer.

what thickness is the matching layer?

¼ wavelength thick

Dynamic receive focusing uses delay lines ____ the echoes are detected in the array elements.

after

what characterizes the frequency bandwidth of the transmitted ultrasound wave?

Q factor

varying voltages to each crystal in the group is called?

apodization

T/F: Phases array TRX are electronically focused along the beam path, mechanically focused along the elevational plane and electronically steered?

TRUE

resolution of two structures parallel to the path of the sound beam is called?

Axial Resolution

Which transducer has the same line density in both the near and far fields?

Linear array

for a single transducer to offer multiple frequency scanning selections, it must have ____.

a wide bandwidth

the conversion of an incident pressure wave to an electrical signal is called?

piezoelectric effect

how is electronic focusing accomplished?

phased delay; time delays

what is the purpose of subdicing?

reduces grating lobes.

the crystal is divided into groups of small crystals

what part of the TRX controls ringing?

damping element/ backing material

an internal method of focusing is:

curved crystal fixed.

T/F: Many active elements fire at almost the same time in a mechanical TRX?

FALSE

What resolution is affected by pulse duration?

axial resolution

what resolution would be affected by aperture size?

Lateral

the spectrum of frequencies emitted by a pulsed wave trx is known as?

bandwidth

what is the optimal thickness for a matching layer?

¼ wavelength thick

the type of resolution that is characterized by the f number?

lateral

what TRX would have the largest field of view in both the near field and at depth?

Linear sequential, convex array, or phased array

convex array

what element is commonly used in modern TRX elements?

PZT

Modern day TRX use how many cycles in a pulse (B mode)?

2-3

what is the minimum beam diameter for an unfocused disk transducer?

½ the initial beam

what probe is the most helpful for intercostal scanning?

Linear Phased Array

what defines the best axial resolution that can be obtained with a given TRX?

SPL / 2

what term describes the ability of sound to separate closely spaced objects?

Resolution

how is the beam focused in a single element TRX?

mechanical/ fixed focusing

when using a trx with a poor elevation resolution, what problem may occur when imaging a small cyst in the liver?

slice thickness artifact; fill in of sm cystic spaces

increasing which of the following will improve axial resolution?

PD, Pulse length, frequency, period, focusing

Frequency

which type of transducers produce side lobes?

Single- mechanical

which transducer is best for cardiac imaging?

Phased Array ( Linear Phased Array)

Focal point is the region having te best _____ resolution?

Lateral

Man made properties receive the piezoelectric property through a process called?

Polarization

The point at which an ultrasound trx gives up its piezoelectric property is called the ____

Curie Point

Lead Zirconate titanate loses its piezoelectric property at what temperature?

680 degrees F 350 degrees C

the center frequency for a pulsed wave transducer is determined primarily by its?

PZT thickness

the optimal impedance value for matching layer is

an impedance that is b/w the PZT and the sking

what improves with damping?

axial resolution

the most effective way to increase the NZL:

increase in diameter or frequency

NZL = D² x F / (heart)

Name a disadvantage of using a trx with a small footprint?

lateral resolution will degrade at a shallower depth w/ a smaller diameter trx

a type of focusing that is characterized by a value known as the f-number is:

aperture focusing

T/F the diameter of the trx helps determine the operating frequency of the trx?

FALSE

T/F Transducer frequency and NZL are inversely related?

FALSE

T/F Trx frequency and beam divergence are inversely related?

TRUE

High or Low frequency transducers have the best range resolution?

HIGH

T/F Many active elements fire at almost the same time (delays) in a mechanical trx?

FALSE

Why would the use of multifocal zones decrease frame rate?

for every focus that is sent out, a pulse must be sent down that scan line. This decreased the rate b/c it takes longer to build the frame.