chapters 7 and 8

Time of flight

Time a pulse takes a "round trip" to and from the transducer

Time of flight is also referred to as

Go time return, round trip time

To create an anatomical image, a sound pulse must travel to a reflector located in the body and return to the

Transducer

Time of flight formula (round trip)

distance (mm)= 1.54mm/μs x go return time (μs) /2

Time of flight formula (from transducer to boundary)

distance TO boundary (mm)= time to reflector (μs) x 0.77 (mm/μs)

When one reflector is twice as deep as another reflector, what happens to the pulse's time of flight?

It's doubled or increased by a factor of two

13 microsecond rule

For every 13 μs of travel time, the object is 1 cm deeper in soft tissue

The 13 microseconds rule only applies in

Soft tissue

Pulse repetition period (PRP)

Start of one pulse to the start of the next pulse (on and off time)

When the depth of view is shallow, PRP is

Short

When depth of view is deep, the PRP is

Long

PRP and maximum imaging depth are

Directly related to

PRP imaging depth formula

PRP (μs) = Imaging depth (cm) x 13 μs/cm

Pulse repetition frequency

the number of pulses that an ultrasound system transmits into the body each second

PRF and maximum imaging depth are

Inversely related

As imaging depth increases (deeper), what happens to PRF?

It occurs less often

PRF imaging depth formula

PRF (Hz) = 77,000 cm/s / imaging depth (cm)

As imaging depth decreases (shallower), what happens to PRF?

It occurs more often

Transducer

Any device that converts one form of energy into another

U/S transducer's 2 functions are

transmit electrical energy and convert it into sound

receive the reflected sound pulse converted back into electricity

Transducers require what level of disinfection?

Low level

Endocavitary probes require what level of disinfection?

High level

When is sterile probe cover needed?

When skin or mucous membranes are penetrated

Cold germicides used to disinfect

Cidex, gluteradehyde

NEVER sterilize probes using

dry or moist heat, or chemicals

DON'T disinfect using

alcohol

Imaging Transducer Characteristics

damping is effective (backing material)

short pulse length & duration

Imaging Transducer Characteristics

decreased output power

Imaging Transducer Characteristics

low Quality Factor

Imaging Transducer Characteristics

wide bandwidth (broadband)

Imaging Transducer Characteristics

low sensitivity

Imaging Transducer Characteristics

short pulse length & duration

Transducers with damping material are

less able to convert low level sound reflections into meaningful electrical signal during reception

Backing material reduces (good things) it also reduces _ during __ (bad thing) - causes transducers to be less responsive

vibration, vibration, reception

Bandwidth (Hz, MHz)

the range of frequencies between the highest and lowest frequency emitted from the transducer

Bandwidth formula

Bandwidth (Hz)= max freq - min freq

Case

protects internal components from damage and insulates patients from electrical shock

Wire

provides electrical connection between the PZT and the ultrasound system

Electric Shield

thin metallic barrier lining the inside of the case

Acoustic Insulator

thin barrier of cork or rubber that isolates or "uncouples"

the internal components of the transducer from the case

Matching Layer

¼ wavelength thick and increases the percentage of

transmission between the active element and skin

Dampening Element/ backing material

bonded to the back of the active element and reduces the

"ringing" of the PZT and is mace of epoxy resin and impregnated with tungsten (makes shorter pulses= creates better images)

Decreasing order of impedance

PZT > matching layer > gel > skin

Curie point

the temperature above which a material loses its magnetization and becomes depolarized (360° C or 680° F)

The active element is also known as

PZT, ceramic, crystal

Piezoelectric effect

when applied pressure or deform to a material with our sound wave, it has the ability to create voltage

Time of flight and distance are

directly related

Longer distances have

longer time of flight

Since the pulse travels to and from the transducer, the total distance that a pulse travels is

twice the reflector

PRF and PFP are

indirectly related

Reverse piezoelectric effect

the material can change shape when a voltage is applied

Decreased sensitivity

during reception, transducers with damping material are less able to convert low-level sound reflections into meaningful electrical signals

Wide bandwidth

short pulse duration has wide bandwidth with many frequencies

The shorter the pulse, the greater the

range of frequencies present

Bandwidth synonyms

center, resonant, primary, natural frequency

Quality factor

unit less number that is the extent of dampening and is inversely related to bandwidth

Quality factor formula

Quality factor= main frequency/bandwidth

Quality factor and pulse length are

directly related

Non imaging transducer characteristics

creates continuous wave or pulses w a long duration and length

Non imaging transducer characteristics

no backing material

Non imaging transducer characteristics

increased sensitivity

Non imaging transducer characteristics

narrow bandwidth

Non imaging transducer characteristics

higher quality factor

Non imaging transducer characteristics

cant create images