Exam 4 Flashcards
What are the TWO major functions of the ultrasound system
- Preparation and transmission - electrical signals to the transducer, to create a sound beam. 2. Reception - receives electrical signals from the transducer, processes these signals into critically meaningful images and sounds.
PULSER When does the PULSER generate voltage that is delivered to the PZT crystals in the transducer?
During transmission
The PULSER is also known as;
Power Acoustic power Pulser power Output power
What is the job of the pulser and Beam former?
To create and control the electrical signals sent to the transducer.
When the pulser is set to LOW VOLTAGE, how will it affect the following; 1. PZT vibrations 2.The Patient 3. Image brightness 4. Signal-to-noise ratio
- PZT crystals vibrate gently and a weak sound Beam will be transmitted 2. Better for reducing bio effects on the patient 3. Darker- due to gentle vibrations creating a weak sound beam. 4. Produces an image with a large amount of contamination and less diagnostic value. A lot of noise.
When the pulser is set to HIGH VOLTAGE, how will it affect the following; 1. PZT vibrations 2.The Patient 3. Image brightness 4. Signal-to-noise ratio
- PZT Crystals vibrate forcefully and they strong sound Beam will be transmitted. 2. Increasing the power provides the pulser with increased voltage and increased strength of the echo entering the patient, therefore there is A higher risk of bioaffects to the patient. *ALARA* 3. Brighter- because the PZT crystals are vibrating forcefully and creating a stronger beam The reflected echoes are strong and the entire image is bright. 4. The signal is stronger than the noise so this creates a high-quality image.
When imaging a shallow/deeper image the PULSER determines HOW OFTEN The transducer sends out a sound Pulse. (PRP&PRF) Changing the image depth will change the time between omitted pulse or voltage to the PZT crystals. How are the PRP & PRF affected with shallow imaging and deeper imaging?
Shallow Imaging - Short PRP & High PRF Deeper imaging - Longer PRP & Lower PRF
When does the beam former function?
Transmission and reception
Beam former during TRANSMISSION
Controls apodization Apodization- reduce side lobe artifact
Beam former during RECEPTION
DynaMic receive focusing & dynamic aperture.
RECEIVER
Transforms the electrical signals from the transducer for display on the systems monitor.
5 functions/operations of the Receiver that must be performed in order.
- Amplification 2. Compensation 3. Compression 4. Demodulation 5. Reject
Receiver Function #1
Amplification (AKA Gain, Receiver gain)- * Each signal undergoes an equal amount of amplification. * Needed because retuning signals are too low to be displayed on the monitor. ** CAN be adjusted by adjusting GAIN. — Does NOT improve signal-to-noise ratio because signal and noise are both amplified.— > Makes entire image brighter or darker when the sonographer adjusts the gain.
Receiver function #2
Compensation - (AKA TGC, Time Gain Compensation, DGC) - ability to adjust echo amplitudes affected by attention as sound travels into body (depth). Without Compensation, your image becomes increasingly dark with depth. **creates image that is uniformly bright from top to bottom. — Sonographer can adjust the compensation on the ultrasound machine using TGC.— **Does NOT effect Signal-to-noise ratio**
Receiver function #3
Compression (AKA Dynamic Range) - Reduces the total range of signals, from the smallest to largest, changes gray scale mapping. **smallest stays the smallest and largest stays the largest ** Sonographer can change compression by adjusting DYNAMIC RANGE. >NARROW DYNAMIC RANGE- Few gray shades, black & white, high contrast/highly compressed. - vessels >WIDE DYNAMIC RANGE- Many shades of gray, low contrast. - liver **Does NOT effect Signal-to-noise ratio**
