Term
| What are the two modes of ultrasound sent from the probe? |
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Definition
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Term
| For ultrasound, what type of wave is used and why? |
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Definition
| - For ultrasound pulsed wave is used. Continuous wave is not used because there should be some "listening time" when getting an image with ultrasound. |
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Term
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Definition
Also known as temporal pulse length, or "talking time". It is the time the machine takes sending the signal.
___M___M___M___
^
PD |
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Term
| What is the Pulse Repetition Period (PRP)? |
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Definition
| The PRP is the time it takes for the machine to send the signal and receive the echoes. The units are any unit of time. |
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Term
| How much listening time should be allowed for echo returns from deep structures? |
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Definition
| Adequate listening time should be allowed for echo returns from deep structures. |
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Term
| What is Duty Factor (DF)? |
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Definition
| The fraction or percentage of time the machine is "on". |
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Term
| What is the DF ranges for imaging? |
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Definition
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Term
| What does an increase in DF mean as far as patient exposure? |
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Definition
| An increase in DF means an increase in patient exposure. |
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Term
| What is spatial pulse length (SPL)? |
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Definition
| The amount of space that a pulse takes up. The units are a unit of length. Similar to pulse duration except instead of measuring the pulse in time it measures it in length. |
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Term
| What can the technologist adjust? |
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Definition
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Term
| What is the purpose of the matching layer of a transducer? |
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Definition
| To increase %T from crystal to soft tissue. |
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Term
| What is the acoustic impedance of the matching layer? |
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Definition
| Somewhat between the crystals and soft tissue. |
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Term
| What is done to ensure constructive interference? |
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Definition
| The thickness of the matching layer is set to be 1/4 of the wavelength. |
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Term
| What is the purpose of crystals? |
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Definition
| The job of the crystals is to convert electrical impulses into sound waves and returning echoes (sound waves) into electrical impulses. |
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Term
| What are crystals made out of? |
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Definition
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Term
| Where does piezoelectric material naturally occur? |
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Definition
- Quartz
- Rochelle salt
- Tourmaline |
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Term
| How is piezoelectric material man made? |
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Definition
with:
- Lead
- Zirconate
- Titanate
(PZT) |
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Term
| Explain the steps in Crystal production. |
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Definition
1) In a natural state, dipoles are scattered chaotically.
2) Then once heated up to Curie temperature it allows them to move freely.
3) A magnetic field is then put across the crystal and makes the dipoles line up so that the positive side of the dipole faces the negative plate, and the negative side of the dipole faces the positive plate (this means they are PZT polarized).
4) The PZT is then cooled down below Curie temperature in the magnetic field. The dipoles then keep their arrangement. |
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Term
| How should the transducer be cleaned? |
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Definition
- It should never be autoclaved (form of sterilization requiring heat), because this will cause a depolarization of the dipoles.
- Only chemical disinfection should be used. |
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Term
| What is the converse piezoelectric effect? |
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Definition
The conversion of an electrical impulse into a mechanical wave.
- Converse piezoelectric effect: Electrical to mechanical waves (Cats Eat Mice) |
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Term
| What is the piezoelectric effect and briefly explain how it works. |
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Definition
- Piezoelectric effect is when a mechanical wave is converted into an electrical impulse.
- It happens when the crystals in the probe are hit with a high frequency pressure wave causing them to vibrate, which in turn produces voltage. |
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Term
| What should the thickness of the crystal be to ensure constructive interference in the piezoelectric effect? |
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Definition
| - It should be 1/2 the wavelength. |
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Term
| Each crystal produces a sound of a... |
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Definition
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Term
| What does the frequency of a continuous wave transducer depend on? |
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Definition
| - The voltage applied to the crystal. |
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Term
| What does the frequency of a pulsed wave (pw) transducer depend on? |
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Definition
- the speed of sound in the crystal (density, elasticity, compressibility, bulk modulus)
- the thickness of the crystal |
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Term
| ** What does the frequency of the crystal depend on? |
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Definition
| It depends on the thickness of the crystal, therefore it is constant for each crystal. |
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Term
| What are the possible names for the frequency of a crystal? |
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Definition
- Resonance frequency
- Natural frequency
- Central frequency |
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Term
| What happens to the frequency and velocity of the sound wave as it enters a tissue? |
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Definition
- The frequency stays the same.
- The velocity changes though since it's dependent on the properties of the medium, and because w.l. = v/f, wavelength must change also. |
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Term
| What is the frequency in a continuous wave? |
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Definition
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Term
| What is the frequency in a pulse wave? |
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Definition
| - The frequency in a pulse wave varies. |
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Term
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Definition
| - The range of frequencies in a pulse. |
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Term
| What does short pulse mean in relation to band width? |
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Definition
| A short pulse (small PD 1-5 cycles) generates a wide band width, this is used in imaging because it has a higher sensitivity. |
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Term
| What does a long pulse generate in terms of band width? |
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Definition
| - A long pulse (high PD 5-10 cycles) generates a narrow band width which is used in doppler. This has decreased sensitization. |
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Term
| What is frequency fusion? |
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Definition
- Frequency fusion is when a technologist chooses a frequency out of possible frequencies in a band width.
> Same number and variations of frequency is still sent out.
> Echoes are received.
> Machine filters out the unwanted frequencies. |
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Term
| What is the mechanical coefficient's relation to axial resolution? |
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Definition
| - More Q the worse axial resolution is, that's why Mcvay calls it the "unquality factor". |
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Term
What will a low Q transducer have for the following:
- Band width:
- Pulse Duration:
- Cycles/Pulse:
- Sensitivity (Axial Resolution):
- Uses: |
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Definition
- Band width: Wide
- Pulse Duration: Short
- Cycles/Pulse: 1-5
- Sensitivity (Axial Resolution): High
- Uses: Imaging |
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Term
What will a high Q transducer have for the following:
- Band width:
- Pulse Duration:
- Cycles/Pulse:
- Sensitivity (Axial Resolution):
- Uses: |
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Definition
- Band width: Narrow
- Pulse Duration: Long
- Cycles/Pulse: 5-10
- Sensitivity (Axial Resolution): Poor
- Uses: Doppler |
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Term
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Definition
| When the backing material reduces crystal ringing which in turn generates a shorter pulse which improves axial resolution. |
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