Bandwidth and Quality Factor

What are two other names for frequency bandwidth?

Bandwidth or pulse bandwidth.

What is the definition of frequency bandwidth?

The range of frequencies in the pulse surrounding the resonant frequency.

What are the units for frequency bandwidth?

MHz.

What is the typical value of the frequency bandwidth for a 3 MHz transducer?

1 MHz.

The bandwidth will always be higher or lower than the resonant frequency?

Lower.

What are the two major types of bandwidths?

• Narrow bandwidth

• Broad (wider) bandwidth

Undamped crystals produce a sound with a narrow or wide bandwidth?

Narrow. (A narrow range of frequencies around the resonant frequency).

Damped crystals produce a sound with a narrow or wide bandwidth?

Wide. (A wide range of frequencies around the resonant frequency).

In imaging, what type of pulses do we use to get good resolution?

Short pulses.

Short pulses are produced by what?

Damped crystals.

Short pulses are broad or narrow bandwidth?

Broad.

For good imaging, we like broad or narrow bandwidths?

Wide.

Why do sonographers like broad bandwidths? (5)

• Short pulses are broad bandwidths

• Using a broad bandwidth allows us to select from a range of transmit frequencies

• Broad bandwidth is good for pulsed and colour Doppler

• Broad bandwidth is good for frequency tuning the receiver

• Broad bandwidth is good for harmonics

What is the quality factor (Q)?

It describes the quality of sound.

High Q sound has what type of bandwidth?

Narrow.

Low Q sound has what type of bandwidth?

Broad (wide).

CW Doppler has what type Q?

High Q.

Pulsed wave Doppler ultrasound has what type of Q?

Low Q.

What is the calculation for Q factor?

Frequency (MHz)/Bandwidth (MHz)

Does Q factor have a unit?

No. It is unitless.

What is the typical value for low Q?

2-3 (same as # of cycles in a damped transducer).