Using ultrasounds to measure blood flow velocity
- Dashboard
- Using ultrasounds to measure blood flow velocity
Most Recent Score Report
| Questions Correct | Questions Answered | Time Spent | Status | Attempt Date | |
|---|---|---|---|---|---|
| -- | -- | -- | -- | -- |
Previous Score Reports
| Questions Correct | Questions Answered | Time Spent | Status | Attempt Date | |
|---|---|---|---|---|---|
| -- | -- | -- | -- | -- |
Using ultrasounds to measure blood flow velocity
Array
(
[passage] => WP_Post Object
(
[ID] => 559622
[post_author] => 12815
[post_date] => 2025-01-09 08:31:03
[post_date_gmt] => 2025-01-09 13:31:03
[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Using the Doppler Effect, it is possible to measure motions within the body. The ultrasonic flow meter is a medical device that can approximate the velocity of blood flow in a particular vessel. The transducer of ultrasonic flow meter is composed of both a transmitter and a receiver component. Ultrasonic waves of a set frequency (f0) are emitted by the transmitter, which are then scattered by the moving red blood cells (RBCs) that they come in contact with. These scattered waves return to the receiver with a frequency altered by the Doppler Effect (f'). Figure 1 depicts how an ultrasonic flow meter functions.
Figure 1: Ultrasonic Flow Meter Measuring Blood Flow Velocity
The Doppler frequency, fDoppler, the difference between the received frequency, f', and transmitted frequency, f0, can be estimated from the following equation:
where vrbc is velocity of the red blood cells, ϴ is the angle between the transmitted ultrasonic wave and the motion of RBCs, and c is the speed of sound moving through soft tissues which is approximately 1.5105 cm/s. Blood flow can be characterized as either laminar, plug, disturbed or turbulent. Laminar blood flow follows a parabolic pattern with the greatest flow velocities being greatest at the center of the vessel. Plug flow is seen in vessels with large diameter such as the aorta where the velocity of the flow is relatively uniform throughout the vessel. In a disturbed flow, RBCs no longer travels in straight lines; however, in general they continue to move in the forward direction. Turbulent flow is chaotic and random with RBCs flowing in all directions at varying velocities.
[post_title] => Using ultrasounds to measure blood flow velocity
[post_excerpt] =>
[post_status] => publish
[comment_status] => closed
[ping_status] => closed
[post_password] =>
[post_name] => using-ultrasounds-to-measure-blood-flow-velocity
[to_ping] =>
[pinged] =>
[post_modified] => 2025-01-09 08:32:11
[post_modified_gmt] => 2025-01-09 13:32:11
[post_content_filtered] =>
[post_parent] => 0
[guid] => https://medlifemastery.com/?post_type=passage&p=559622
[menu_order] => 0
[post_type] => passage
[post_mime_type] =>
[comment_count] => 0
[filter] => raw
)
[questions] => Array
(
[0] => Array
(
[quiz_unique_key] => 578908434
[question] => According to Figure 1, which of the following is a true statement regarding f0 and f‘ when the angle ϴ is between 0 and 90 degrees (0 < ϴ < 90)?
[value] => Array
(
[answer] => 2
[description] => Reason for the Correct Answer:
Cosine of any angle between 0 and 90 degrees will yield a positive number.
This implies that the Doppler Frequency will also e positive. f‘– f0 > 0
Rearranging the this inequality gives us f0
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. f0 ≤ f’
)
[1] => Array
(
[each_answer] => B. f0 < f‘
)
[2] => Array
(
[each_answer] => C. f0 ≥ f‘
)
[3] => Array
(
[each_answer] => D. f0 > f‘
)
)
)
[1] => Array
(
[quiz_unique_key] => 3873426850
[question] => What additional information is needed to determine the time it takes for an emitted ultrasonic wave to return back to the ultrasonic flow meter?
[value] => Array
(
[answer] => 4
[description] => Reason for the Correct Answer:
Time = Distance divided by Velocity
Velocity of the ultrasonic wave is provided in the passage.
Distance between the transducer and the blood vessel is the only missing variable needed to determine the time it takes for an emitted ultrasonic wave to return back to the ultrasonic flow meter.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. The velocity of the blood flow
)
[1] => Array
(
[each_answer] => B. The frequency of the ultrasonic wave
)
[2] => Array
(
[each_answer] => C. The angle between the transmitted ultrasonic wave and the motion of the red blood cells
)
[3] => Array
(
[each_answer] => D. The distance between the transducer and the blood vessel
)
)
)
[2] => Array
(
[quiz_unique_key] => 83407773
[question] => If a 1MHz ultrasonic flow meter is used to measure the blood velocity in the aorta, what will be the received frequency if the transducer is oriented perpendicular to the aorta?
[value] => Array
(
[answer] => 2
[description] => Reason for the Correct Answer:
From the equation provided in the passage, when the transducer is perpendicular to the aorta, cosine of 90 degrees equals zero and so does the Doppler Frequency.
This implies that f‘– f0 > 0 and therefore f‘= f0.
f0 is provided in the question stem: 1 MHz.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. 0 MHz
)
[1] => Array
(
[each_answer] => B. 1 MHz
)
[2] => Array
(
[each_answer] => C. 2 MHz
)
[3] => Array
(
[each_answer] => D. 4 MHz
)
)
)
[3] => Array
(
[quiz_unique_key] => 2261298308
[question] => Spectral broadening occurs when Doppler shifted frequencies exist over a wide range of frequencies, rather than at a single frequency. Which of the following types of flow is most likely to exhibit the greatest amount of spectral broadening?
[value] => Array
(
[answer] => 4
[description] => Reason for the Correct Answer:
Spectral broadening occurs when Doppler shifted frequencies exist over a wide range of frequencies, rather than at a single frequency. From the equation provided in the passage, it can be reasoned that this occurs when flow produces a wide range of values for vrbc and .
Read carefully on the four major types of blood flow to determine which will mostly likely to have RBCs moving at varying speeds and directions.
Turbulent flow moves in random directions at varying velocities, hence it will cause the greatest amount of spectral broadening.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. Disturbed flow
)
[1] => Array
(
[each_answer] => B. Plug Flow
)
[2] => Array
(
[each_answer] => C. Laminar Flow
)
[3] => Array
(
[each_answer] => D. Turbulent Flow
)
)
)
[4] => Array
(
[quiz_unique_key] => 2377279144
[question] => Ultrasonic flowmeter are useful for measuring blood flow velocity, but not blood flow volume. Which following statement best explains why this is so?
[value] => Array
(
[answer] => 2
[description] => Reason for the Correct Answer:
Ultrasonic flow meter measure blood flow velocity using the Doppler Effect.
According to the continuity equation, Q = Av , cross sectional area is needed to determine blood flow volume.
The pulsatile nature of blood flow causes the cross sectional area of the blood vessels to vary with the cardiac cycle making it difficult to calculate Q from the continuity equation.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. Flows in most vessels are of the plug type which leads to intense spectral broadening.
)
[1] => Array
(
[each_answer] => B. Cross-sectional area of blood vessels changes with the pulsatile nature of blood flow.
)
[2] => Array
(
[each_answer] => C. The Doppler frequency is difficult to calculate because the speed of sound is much greater than the speed of moving RBCs.
)
[3] => Array
(
[each_answer] => D. Cell to cell interactions of RBCs cause the viscosity of blood to vary with blood flow velocity.
)
)
)
)
[total_question] => 5
[correct_answers] => Array
(
[559622|1] => B
[559622|2] => D
[559622|3] => B
[559622|4] => D
[559622|5] => B
)
[hide_display_feedback_settings] =>
[hide_solutions] =>
)
