Differences in Doppler Techniques Used in Echocardiography

Lauren Nichols

03/10/2010

Doppler Effect

• Was first introduced in 1842 by Johann Christian Doppler.

• Is the change in wavelength and frequency of a wave that is perceived by an observer relative to the source of the wave.

• For example: • When a police car is moving towards

you the wavelength decreases and its frequency increases causing the sirens to become louder and when it moves away from you the wavelength increases and its frequency decreases causing the sirens to become softer.

Doppler Shift

• positive Doppler Shift= blood flow moving away from the transducer and the received frequency is greater than transmitted frequency

• negative Doppler shift= blood flow moving away from the transducer and the received frequency is less than transmitted frequency

• zero Doppler shift = blood flow stationary compared to the transducer and the received frequency and transmitted frequency are equal.

Doppler Echocardiography

• Is a method used to determine the presence or absence of blood flow, flow velocities, flow direction and flow characteristics within the heart.

• Provides quantitative information that is essential in clinical diagnosis.

• It depends entirely on the measurement of the relative changes in the returned ultrasound frequency when compared to the transmitted frequency.

Different modalities of Doppler

• continuous wave Doppler

• pulsed wave Doppler

• color flow Doppler

Continuous Wave Doppler

• Is the older and most electronically simple of three types of Doppler.

• Continuous wave refers to the “continuous” transmission of the Doppler signal toward the moving RBCs (red blood cells) and the “continuous” reception of the returning signals reflected from the moving RBCs .

• Uses one transducer that acts as both the transmitter and receiver of sound waves.

Continuous wave Doppler

• Advantages• Has the ability to measure high blood velocities

accurately and record the highest velocities in any valvular or congenital heart disease

• No limitations to the pulse repetition frequency which allows high-frequency shifts or velocities to be detected and displayed.

Continuous wave Doppler

• Disadvantages• The primary disadvantage is a lack of range resolution.

Range resolution is an indication of the depth from which the signals are being generated. This lack of range resolution makes interpretation of flow signals confusing.

• Is unable to determine the specific location of velocities within the beam and cannot be used to produce color flow images.

Clinical Applications of Continuous wave Doppler

• Used in adult cardiac scanners to investigate the high velocities in the aorta.

• Used to measure peak velocities in valvular stenosis or regurgitation, coarctation of the aorta, and ventricular septal defect.

Pulsed Wave Doppler

• Is used to detect the specific location of turbulent jets, which are representative of, increased blood flow velocities .

• Uses one transducer which requires the transmitted signals to be timed so that they do not interfere with the received signals.

Pulsed wave Doppler

• Advantages• Is able to pinpoint a specific area of interest and provide

specific information regarding the blood flow.• This modality has the ability to use Doppler information from

a particular location with the heart or great vessels by using a sample volume. The depth of interest is called the sample volume because signals from a small volume of blood are sampled using beam geometry by measuring the width and height of this volume.

Pulsed wave Doppler

• Disadvantages• Has limitations in measuring velocities in regions with

high velocities such as stenotic (narrowed) valves, regurgitation or shunts.

• This limitation is known as “aliasing”. Aliasing occurs when the abnormal velocity exceeds the rate at which the pulsed wave system can record it properly

Clinical Applications of pulsed wave Doppler

• Is used to assess for aortic stenosis, diastolic measurements, and pulmonary vein flow.

• Best used for investigating specific areas

Color Flow Doppler

• Uses color that helps physicians identify the direction and speed of blood flow within a vessel or a chamber of the heart .

• Displays turbulent flow and allows the operator to differentiate between normal and abnormal patterns.

• Evaluates laminar (smooth appearance) flow velocities within a vessel for diagnostic purposes without the use of pulsed wave or continuous wave Doppler.

Meaning of color

• Main colors used are red and blue.

• Red is blood flow toward the transducer.

• Blue is blood flow away from the transducer.

• These two colors were chosen because they are the primary colors of light.

• The color black always represents the absence of flow.

Color flow Doppler

• Advantages• Able to obtain real time information on valvular

regurgitation, obstructions and intra-cardiac defects.

• Evaluates laminar flow velocities within a vessel for diagnostic purposes without the use of pulsed wave or continuous wave Doppler.

• More readily identifies blood flow patterns within the heart.

• Frequently uses aliasing to its advantage since it may dramatically highlight the presence of high velocities.

Color flow Doppler

• Disadvantages• The pulse repetition of the system can affect the

display of the color signals.

• The ability to obtain an optimal Doppler signal is dependant on a proper flow angle.

Clinical Applications of color flow Doppler

• Easy identification of valvular regurgitation and the direction and pattern of flow of the lesion; stenotic valves usually produce a turbulent color pattern, and easier identification of shunts.

• Defects across the ventricular and atrial septa can be more readily identified.

Conclusion

• Doppler is used in echocardiography to determine the presence or absence of blood flow, flow velocities, flow direction, and flow characteristics within the heart and provides quantitative information that is essential in clinical diagnosis.

• Each modality of Doppler has its advantages and disadvantages.

• However, each modality is necessary in the use of echocardiography. When used together each modality provides clinical information to correctly diagnosis cardiac defects.