Instrumentation, Optimization, & Contrast (Physics) Flashcards
In color flow Doppler imaging, what is a pulse packet?
To accurately determine the direction and velocity of blood flow, a group of ultrasound pulses is transmitted, received, and compared with respect to phase shift. This group of pulses is called a pulse packet.
What is the color flow Doppler technique?
The color flow Doppler technique is a pulsed method for recording and displaying flow information, superimposed on anatomic images (M-mode or two-dimensional).
Color flow displays usually involve two-dimensional images; by convention, flow toward the probe appears red, and flow away from the probe appears blue. The display indicates the flow velocity and direction by changing the hues of these two colors
Why are color Doppler pulse packets important?
The larger the pulse packet, the more accurate the flow-related information. The bad news is, large packet size takes longer to transmit and receive so image frame-rate decreases.
Note: For satisfactory blood-flow sensitivity, it is generally best to use a larger packet size and to gain back an acceptable frame rate by decreasing the depth or narrowing the color sector
If the primary flow direction through a shunt is left-to-right, why are contrast echocardiographic studies so sensitive in detecting atrial shunts?
Even when shunt flow is primarily left-to-right, a small right-to-left component is usually present at end-diastole.
If the contrast study yields a negative result, performing another injection during the release phase of the Valsalva maneuver may produce a positive result, because the right-sided pressures will undergo a transient increase.
What is the continuous wave Doppler mode?
In the continuous wave Doppler mode, two transducer elements (or sets of elements) are used to record flow. One element continuously transmits ultrasound signals, and the other element continuously receives such signals.
The received signals are analyzed for Doppler frequency shifts and the resulting information is displayed on the screen.
What are the main advantages and disadvantages of the continuous wave Doppler mode, compared to the pulsed wave Doppler mode?
The main advantage of the continuous wave Doppler mode is its ability to record high velocity flow without aliasing. The disadvantage of this mode is that, although flow along the ultrasound beam is recorded, the location of this flow is not known.
What is the most important part of the Doppler equation?
The most important part of the Doppler equation is the cosine of the angle theta.
Theta denotes the angle between the ultrasound beam and the moving target (blood). As long as this angle is less than 20 degrees, the calculated velocity is accurate.
When the angle is greater than 20 degrees, the velocity is underestimated by the Doppler equation
What causes side-lobe artifacts?
Side-lobe artifacts are caused by strong reflectors outside the main ultrasound beam. These off-axis targets create reflections from weaker extra ultrasound beams alongside the main beam.
What is the best way to minimize side-lobe artifacts?
The best way to minimize side-lobe artifacts is to decrease the overall gain, increase the reject level, or decrease the time gain compensation (TGC) in the area of strong reflectors (such as the pericardium.)
What cardiac lesion is detected by injecting agitated saline contrast material into the right side of the heart?
Saline contrast material is injected to detect atrial shunts. It may also be used to document abnormal venous return and to detect right-sided intracardiac masses.
Why does saline contrast material rarely appear on the left side of the heart?
After being injected into a peripheral vein, saline contrast material advances into the right atrium. The mixed bubbles are too large to pass through the pulmonary bed. If bubbles are seen in the left atrium and the left ventricle within three to five heartbeats after injection, an atrial level communication should be suspected.
When performing a two-dimensional echocardiographic exam, you notice that the image has very little gray scale. Which controls could you adjust to increase the gray scale?
To increase the gray scale quality, you would change the post processing curve or the compress/reject control on most ultrasound machines. Also, you could check the monitor controls (brightness and contrast) and make sure that the transmit gain is set properly.
You also notice that the structures in the far field are very hard to see. Which controls could you adjust in order to see them better?
Increasing the TGC (Time Gain Compensation) control for the far field will brighten the structures in that area. Also switching to a lower frequency transducer will help with penetration and increase structures in the far field.
In the apical four-chamber view, you have trouble differentiating an apical thrombus from an artifact.
Name three things that can help you differentiate these two entities
Ways of differentiating an apical thrombus from an artifact might include:
- change the depth settings, because range artifacts may move with changes in depth.
- switch to a higher-frequency transducer, preferably one with a short focal zone.
- decrease the transmit gain and time gain compensation controls in the near field to
- minimize chest wall reverberations.
- turn off tissue harmonics
- use echo contrast
What is the easiest way to adjust the color Doppler gain?
With color flow Doppler turned on, increase the color gain until background Doppler noise appears on the color display. Then decrease the color gain until the background noise disappears. Normal and abnormal flow should now be displayed in an optimal manner. If the Doppler display still appears weak, switch to a lower frequency transducer, decrease the depth of field, or narrow the color sector to increase the frame rate.
