Harmonics - Ch 14

Question 1

what is fundamental frequency and harmonic frequency?

Answer 1

fundamental = transducer frequ
harmonic = 2x the transducer frequ aka the second harmonic. **harmonics are multiples of the transducer frequency

Question 2

what is harmonic imaging?

Answer 2

harmonic imaging creates US images by using reflections that are 2x the transmitted frequency. The harmonic reflections are processed to make an image.

Question 3

when is harmonic imaging used?

Answer 3

in situations where the fundamental image is suboptimal, the second harmonic data may produce higher quality images.

Question 4

where are harmonics created?

Answer 4

harmonics are created in the tissues, not in the transducer or receiver.

Question 5

how are harmonics created?

Answer 5

non-linear behavior creates this

Question 6

what is non-linear behavior (describe how it’s created)

Answer 6

non-linear = uneven. Sound moves slightly faster in regions of compression (high press), and slightly slower in regions of rarefaction (low pressure). this small difference in speeds (nonlinear behavior) distorts the sound wave and creates harmonics

Question 7

what is pulse inversion harmonic imaging?

Answer 7

a form of harmonic imaging where a positive pulse then a negative pulse is transmitted down each scan line. The neg pulse is the inverse of the pos pulse creating destructive interference, thereby cancelling out the funda reflections. Only the harmonic reflections remain to create harmonic images.

Question 8

what is the disadvantage of using pulse inversion harmonic imaging?

Answer 8

the frame rate is half that of fundamental imaging. Thus, pulsed inversion imaging degrades temporal resolution (lower frame rate), while improving spatial resolution (image detail).

Question 9

transducer bandwidth must include what? (in regards to harmonics)

Answer 9

must include transmit and harmonic frequencies