Ch 3a Harmonics

Question 1

What is a harmonic frequency?

Answer 1

-Harmonic frequencies are patterns that are only created within the object/instrument at specific frequencies of vibration
-Each frequency that an object/instrument produces has its own vibrational mode or standing wave pattern

Question 2

Harmonic imaging is a form of what?

Answer 2

Signal filtering

Question 3

The transmitted/fundamental frequency echoes get filtered out in harmonic imaging, but what happens to the second harmonic frequency echoes produced?

Answer 3

They are accepted

Question 4

Explain what the bandpass filter does in harmonic imaging?

Answer 4

-The filter is centered at the 2nd harmonic frequency with an appropriate bandwidth to ensure the bandwidth of the 2nd harmonic echo signal is included in the filter

-Filters out + cancels the 1st fundamental/transmitted frequency echo

Question 5

Is the harmonic beam narrow or wide?

Answer 5

Much narrower, which improves our lateral resolution

Question 6

What does harmonic imaging do to our lateral resolution?

Answer 6

Improves lateral resolution (due to narrow beam)

Question 7

Why does harmonic imaging improve our resolution?

Answer 7

B/c harmonics are generated only in the highest intensity portion of the beam

Question 8

Are grating lob artifacts eliminated with harmonic imaging?

Answer 8

Yes, b/c the extra beams from the artifacts are not sufficiently strong enough to overcome the harmonics

Question 9

Can harmonic imaging reduce/eliminate some artifacts, how?

Answer 9

Yes! B/c the harmonic beam is generated at a depth beyond where some artifact problems occur, such as reverberation, this is how artifacts get reduced/eliminated

Question 10

What technique does harmonic imaging use to improve our axial resolution?

Answer 10

Pulse inversion

(this uses 2 pulses per scan line, rather than 1, with the second pulse being the inverse of the first)

Question 11

Do the fundamental frequency echos or the 2nd harmonic echoes get cancelled?

Answer 11

Fundamental = cancelled
2nd harmonic = remains

Question 12

If the axial + lateral resolution improves with harmonic imaging, what happens to the temporal resolution?

Answer 12

It degrades, b/c the frame rate gets reduced

Question 13

What does harmonic imaging do to our image quality overall + how does it do this?

Answer 13

-Improves it (specifically axial + lateral)
-By sending pulses of frequency into the tissue, then the imaging echos of frequency double

Question 14

2 advantages of harmonic imaging?

Answer 14

-Improved signal to noise ratio
-Artifact reduction

Question 15

List 3 scenarios where harmonic imaging will be useful?

Answer 15

-Obesity
-Hollow structures (cysts, GB, bladder)
-Deep seated major vessels (IVC, AO)

Question 16

What is the disadvantage to harmonic imaging?

Answer 16

There is a decrease in depth - b/c the frequency is too high

(can opt to turn off harmonics when imaging larger pt’s so that the frequency will go down)

Question 17

Does the fundamental frequency or 2nd harmonic frequency have a higher frequency?

Answer 17

2nd harmonic frequency has 2x higher frequency

Question 18

What is a bandpass filter?

Answer 18

-A device that passes frequencies within a certain range and rejects frequencies outside that range
-Only allows a specific range of frequencies to pass through it