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Understanding Ultrasound Physics Ch.3
Ultrasound Physics Ch. 3 Chapter Questions
20
Physics
Not Applicable
05/04/2016

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Term

How did ultrasound get its name?

 

Definition
Sound is classified based on the ability of humans to hear it.  Sound with frequencies so high that humans cannot hear it is called ultrasonic or ultrasound.
Term
Why is frequency important in diagnostic sonography?
Definition

It affects penetration & image quality.

 

Term

 What is the relationship between frequency & period?

 

Definition

 Inversely related. 

↑ F = ↓ P    &    ↑ P = ↓ F

Term

 What is the difference between amplitude & peak-to-peak amplitude?

 

Definition

Amplitude is measured from the midline to the max or min of the wavelength. 

 

      Peak-to-peak is measured from the top of the wavelength to the bottom.  It is twice the value of the amplitude.       

 

Term
How are amplitude & power related?
Definition

Directly related. 

↑ Power = ↑ Amplitude. 


Both are parameters that describe the size or magnitude of a wave. 

Power is ȣ to Amplitude2.

 

 

 

Term

How is intensity related to power & amplitude?

 

Definition

Intensity ȣ Power ȣ Amplitude 2. 

They are all proportional to each other.

Term
What is the difference between wavelength & period?
Definition

Both are a single cycle in a sound wave, but a period is the time it takes to complete a single cycle & a wavelength is the length of a single cycle.

 

Term
What is the relationship between wavelength and frequency?
Definition

 Inversely related. 

↓ F = ↑ λ


The lower the frequency the longer the wavelength. 

 

Term

What is the wavelength of 1 MHz sound in soft tissue?

 

Definition
1.54mm
Term

What is the wavelength of other frequency sound waves in soft tissue?

 

Definition

 Sound with a frequency of 2 MHz has a wavelength of 0.77mm in soft tissue.

 

                                    1.54mm = 0.77mm 

                                    2

 

Term

What is the rule that defines the relationship btween frequency & wavelength of sound in soft tissue?

 

Definition

Divide 1.54mm by the frequency in MHz.

 

                                  λ  (mm) = 1.54mm/us

                                                 F (MHz)         

 

 

 

Term
Why is wavelength important in diagnostic ultrasound?
Definition
Short wave = high frequency = better picture.
Term
What is the speed of sound in soft tissue?
Definition

1,540 m/s  (or 1.54 mm/us)

 

Term

What is the speed of sound in biologic tissues other than soft tissue?

 

Definition

             Lung = 500 m/s

            Fat = 1,450 m/s

            Liver = 1,560 m/s

            Blood = 1,560 m/s

            Muscle = 1,600 m/s

            Tendon = 1,700 m/s

            Bone = 3,500 m/s

 

Term
What is the speed of sound in other media?
Definition

             Air = 330 m/s 

            Water = 1,480 m/s 

            Metals = 2,000 – 7,000 m/s 

 

                                    C (m/s) = F (Hz) x λ (m)

 

Term

What characteristics of a medium determine the speed of sound in that medium?

 

Definition

 Density & Stiffness

 

Term
How does stiffness affect speed?
Definition

Directly related.

↑ Stiffness = ↑ Speed


The stiffer the media, the faster the sound.

 

Term
How does density affect speed?
Definition

Inversely related. 

↑ Density = ↓ Speed


The denser the media, the slower the sound.  If 2 media are equally stiff, the denser medium will have a lower speed.

 

 

 

Term
What other terms describe stiffness?
Definition

Elasticity & Compressibility

 

Term
Which has the greater influence on speed, density or stiffness?
Definition
Stiffness.
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