Term
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Definition
| Inappropriate (ambiguous) representation of velocities, which exceed the measuring capacity of a pulsed Doppler system. The velocity limit at which this occurs is defined by the pulsed repetition frequency, the interrogating frequency (FO), and the range. |
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Term
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Definition
| Angle between the interrogating sound beam and the velocity vector of the blood flow. An angle of incidence greater than 20 degrees, significantly lowers the measured velocity, and underestimates the actual flow velocities. |
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Term
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Definition
| Difference between highest and lowest frequencies present. If frequencies from 200 to 500 Hz are present the bandwidth is 300 Hz. On the spectral tracing, a widened bandwidth implies multiple velocities in the same sample volume or along the continuous wave beam path. |
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Term
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Definition
| By shifting the baseline up or down, it is possible to summate velocities from one direction of the spectral tracing onto the other portion. The effect is to double the maximum detectable velocity in the pulse mode which is an aid when aliasing is present. |
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Term
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Definition
| Hydraulic formula relating changes in pressure across an obstruction (gradient) to velocity change. P1-P2 = 4V2 |
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Term
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Definition
| Method of analyzing individual frequencies within a complex waveform. Chirp Z and FFT are the two commonly used analysis methods in Doppler echocardiography. |
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Term
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Definition
| Use of two transducers or sets of transducers to simultaneously send and receive ultrasound waves of constant amplitude. Continuous wave Doppler has no theoretical velocity limitations. |
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Term
| Disturbed (nonlaminar) Flow |
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Definition
| Flow characterized by multiple directions and velocities of red blood cells, usually occurring in the presence of an obstruction to flow. |
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Term
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Definition
| A change of frequency and wavelength which occurs when either the source or receiver are moving relative to one another. Doppler echocardiography uses the change in frequency or reflected sound to measure the velocity of blood within the heart and great vessels. |
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Term
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Definition
| The difference in frequency between the interrogating frequency (FO) and the received frequency. The shift frequency is proportional to the speed of the reflectors. |
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Term
| Fast Fourier Transformation (FFT) |
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Definition
| Analysis method of displaying frequencies from a complex waveform, often used in spectral analysis. |
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Term
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Definition
| Cycles per second. In ultrasound, expressed as kilo Hz (thousands of cycles per second) or mega Hz (millions). |
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Term
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Definition
| Use of increased pulsed repetition frequency to measure velocities outside the limits of pulsed Doppler. The pulse repetition frequency is increased two to four times, with parallel increases in measurable velocity. Since multiple samples are within the hear, however, range ambiguity is introduced. |
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Term
| Interrogating Frequency (Fo) |
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Definition
| Sound frequency emitted by the transducer for computation of the Doppler shift. Increasing Fo reduces the velocity limit of pulsed Doppler at any depth. |
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Term
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Definition
| Discrete area of very high velocities distal to an obstruction. The velocity is proportional to the pressure difference (gradient) across the obstruction. |
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Term
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Definition
| Characteristic blood flow in smooth structures defined by parallel direction of flow of most red blood cells, producing a narrow spectral bandwidth. |
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Term
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Definition
| Analysis of more than one sample volume along the path of a single pulse of ultrasound, used in flow mapping. |
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Term
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Definition
| Inability of pulsed Doppler to measure (resolve) frequencies of more than one half of the PRF. The Nyquist frequency is defined as PRF/2. |
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Term
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Definition
| Distance from the transducer in cm. |
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Term
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Definition
| Area from which sound is analyzed in pulsed Doppler, defined by length (range gate) and the width and depth of the interrogating beam. |
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Term
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Definition
| Breaking a complex waveform into its component frequencies by either FFT or Chirp Z methods. |
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Term
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Definition
| Display of all velocities present as a graph versus time. |
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Term
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Definition
| Eliminates low frequency Doppler shifts from the spectrum, improving the ability to ignore heart wall motion. |
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