Wavelength equation

λ = c /

Wavelength (mm) = Propagation Speed / Frequency (MHz) Ultrasound wavelength

The wavelength is basically just the distance that it takes for a single cycle to occur. Because it is a distance our units will be those of distance, i.e. mm, cm, um.

As we see in the formula the wavelength is dependent on the frequency of the beam as well as the propagation speed of the medium. Generally these are not things we can change as the user unless we use a different transducer or image through structures with a different propagation speed.

  • High frequency  : short wavelength
  • Low frequency : long wavelength

An easy way to calculate the wavelength in soft tissue is to just divide 1.54mm (the propagation speed of soft tissue) by the frequency in MHz.

Example. In soft tissue, a pulse with a frequency of 2.5MHz has a wavelength of 0.61mm.

λ = c / 

1.54 mm/us / 2.5MHz = 0.61 mm

 

Ultrasound Wavelength

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Question 1
Which of the following is false?
A
Wavelength times frequency equals propagation speed
B
Propagation speed divided by wavelength equals frequency.
C
Propagation speed divided by frequency equals wavelength.
D
Propagation speed times wavelength equals frequency.
Question 1 Explanation: 
Propagation speed is the product of multiplying wavelength and frequency. If you do not know wavelength, simply divide the propagation speed by frequency. If you do not know frequency, simply divide the propagation speed by wavelength.
Question 2
Two structures that lie at different depths within the body will be imaged as a single structure when
A
the frequency is too high.
B
the Doppler effect is accounted for.
C
they are in 2 different wavelengths.
D
they both lie within the same wave.
Question 2 Explanation: 
When two structures fall within the same wavelength they appear to be one structure. If structures at different depths are within 2 different wavelengths you will get 2 separate images.
Question 3
Frequency is
A
the number of cycles per second.
B
usually determined by the on-duty physician.
C
the number of cycles on the screen at a given time.
D
the settings which produce the best image resolution.
Question 3 Explanation: 
Frequency is the number of cycles that occur in 1 second.
Question 4
A propagation speed of 1.54 mm and a frequency of 4MHz means the wavelength is
A
6.16 mm
B
0.51 MHz
C
0.385 MHz
D
0.385 mm
Question 5
The distance from the baseline to the top of the wave is called
A
amplitude
B
the crest
C
element
D
beam frequency
Question 5 Explanation: 
Amplitude is the distance from the baseline to the top (crest) of the wave.
Question 6
The formula for wavelength is
A
propagation speed divided by frequency.
B
frequency minus wavelength times propagation speed.
C
frequency divided by propagation speed.
D
propagation speed times frequency (in MHz).
Question 6 Explanation: 
The formula for wavelength is propagation speed divided by frequency.
Question 7
The actual length of the wave is determined by
A
adjusting the transducer settings
B
both the medium and the source.
C
the ultrasound technician
D
the density of the medium
Question 8
Wavelength is
A
the measurement of a wave in millimeters.
B
the distance over which a single cycle occurs.
C
the distance between the bottom and peak of a wave cycle.
D
propagation speed multiplied by frequency,
Question 8 Explanation: 
The wavelength is basically just the distance that it takes for a single cycle to occur.
Question 9
The relationship between frequency and wavelength is inverse meaning,
A
that wavelength and frequency are an unrelated ratio.
B
there are limitless options once frequency drops below 1.0.
C
when frequency increases or decreases wavelength does the opposite.
D
when frequency goes up so does wavelength.
Question 9 Explanation: 
Wavelength and frequency always move in opposite directions from each other. Frequency down = Wavelength up Frequency up = Wavelength down Wavelength down = Frequency up Wavelength up = Frequency down
Question 10
As wavelength gets shorter what happens to frequency?
A
It remains constant.
B
The two measurements are unrelated.
C
It increases.
D
It decreases.
Question 10 Explanation: 
The shorter the waves, the more fit into a one second time span.
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I am the founder and lead Instructor here at ExamRefresh.com. I strive to help those that are entering the field of Ultrasound to be the best that they can be. Ultrasound is my passion.

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