Doppler Ultrasound Sample Volume Size: Increasing or decreasing the size of the sample volume.
©Walter Rasmussen, R.D.C.S.
In PW Doppler the size of the sample volume is adjustable however, this only affects the length of the sample volume. The width of the sample volume is determined by the ultrasound beam width and this dimension widens the farther it is moved from the transducer. The area of the sample volume is therefore not accurately represented on the sample volume cursor.
The sample volume length is usually set at about 5mm. Most sonographers do not make frequent adjustments to the sample volume size however, this adjustment can aid in producing a dramatically stronger spectral Doppler recording, when needed. If the pulsed Doppler recording is faint or the spectral envelope is rough, increasing the sample volume size can improve the recording. Experimentation with the sample volume size adjustment will give the sonographer more options for obtaining difficult to obtain blood flow assessment.
Making the sample volume size larger or smaller affects the range of velocities displayed and is not suitable to make it so large that there is uncertainty that its positioning will accurately pinpoint the desired blood flow.
On some machines, changing the sample volume size can change the scale, allowing higher velocities to be recorded when elevating or lowering baseline is not sufficiently effective.