Interaction of Sound and Media
Rank the four media of the body according to their propagation speed in increasing order.
Lung
Fat
Soft Tissue
Bone
What is the piezoelectric effect?
The process by which ultrasound transducer crystals produce images. Pressure energy is converted into electrical energy
The image on the monitor is too dark. What is the first function the sonographer should adjust?
receiver gain before output power for ALARA
Assume that during a clinical doppler study the transducer is positioned so that the red blood cells within the vessel are traveling from left to right at a 90-degree angle to the sound beam. What kind of Doppler shift will be produced and measured?
No doppler shift occurs at a 90-degree angle between the RBCs and the sound beam
Which is more likely to cause thermal bioeffects a focused beam or an unfocused beam?
Unfocused bc a larger area of tissue is being heated and rapid transfer of the heat to neighboring tissue is not possible.
SPTA intensity limit for focused beams is 100 mw/cm squared and for unfocused beams it is much lower: 100 mw/cm squared.
Which three parameters are used to describe the magnitude of a sound beam?
Amplitude, power, and intensity
What kind of crystal will produce poor lateral resolution?
Larger crystal diameter
While performing an exam a sonographer is using a 3 MHz transducer. Due to poor image quality, she activates the harmonic mode. What is the fundamental frequency during the harmonic mode operation?
6 MHz- harmonic frequency is always twice that of fundamental frequency.
If a pulsed doppler system produces 6000 pulses per second, what is the Nyquist limit of this system?
3000 Hz Nyquist Limit
What is the most relevant intensity measurement for pulsed ultrasound?
Ispta- spatial peak, temporal average intensity
If the Ispta is less than 100 mW/cm squared he risk is considered negligible
Rank the media of the body in order from most attenuating to least attenuating.
Air
Lung
Bone
muscle
Soft Tissue
bodily fluids
Water
What does a damping material do to a system's longitudinal resolution?
Improves it!
What tool can we use to remove clutter from our display?
Wall filter
The greatest Doppler shifted frequency in a higher direction would be
A. Away from the observer
b. Towards the observer
Towards!
What are the two mechanisms that can occur as a result of interaction between sound waves and biological tissues causing bioeffects?
Thermal and cavitation.
What determines the PRF of a diagnostic imaging system?
The sonographer determines the PRF by adjusting depth. Shallow depths = high PRF Deeper depths= low PRF
What are the 5 functions of the ultrasound receiver?
Amplification
Compensation
Compression
Demodulation
Rejection
An analog converter with a dielectric matrix of 1000 x 1000 processes an image. The same image is processed by a digital converter has a 256 x 256-pixel matrix. Which converter will produce the image with the greatest detail.
The analog converter bc it is made of more pixels or picture elements.
What is the primary advantages and disadvantages of pulsed wave doppler and continuous wave doppler?
Advantage of Pulsed wave Doppler= Range specificity which means we can choose what depth to sample from. Disadvantage =aliasing
Advantage of CW doppler= no limit on maximum velocities which means no aliasing. Disadvatage= range ambiguity which means we can't choose our depth and we get a sample of all depths along the path of the beam
Should an in vitro study be regarded as a real study?
Yes, but any in vitro bioeffect studies that claim to have direct clinical experience should be viewed with caution.
How is attenuation related to frequency the of a sound wave?
Higher frequency is attenuated more than a lower frequency.
What is the Curie point?
if the temperature of a transducer rises above the curie point heat damage to the transducer will occur and it will lose it piezoelectric properties.
The Curie point is in the range of 300-400 C.
System X has a maximum imaging depth of 10 cm, a field of view of 8 cm, and a line density of 9 lines per cm.
System Y has a maximum imaging depth of 10 cm, a field of view of 8 cm, and a line density of 15 lines per cm.
Which system will produce a higher quality image? And which will produce better temporal resolution.
System Y will have higher quality images bc of the higher line density
System X Will have better temporal bc fewer pulses mean a higher frame rate= better temporal resolution
Which is more accurate Fast Fourier Transform or Autocorrelation?
FFT is more accurate.
Autocorrelation can be performed more rapidly though.
These are both methods of identifying various frequencies combined to form a complex doppler waveform
What does a hydrophone measure?
Output power