Spatial resolution of transcranial pulsed Doppler technique in vitro evaluation of the sensitivity distribution of the sample volume.
The spatial resolution of pulsed Doppler sonography is determined by the size of the sample volume. It is known that the axial length is dependent upon the duration of the range gate interval and the lateral extension upon the beam width. In addition, the working size is also a function of the sensitivity distribution within the sample volume. All of these parameters determine the working size of the sample volume. Especially for the transcranial Doppler evaluation of the basal cerebral arteries, the site and the working size of the sample volume are essential diagnostic criteria. To measure the working size of the sample volume a flow rig with a thin tube target has been developed and used. The highest sensitivity (100% level) was registered only in a relatively small area and only if the center of the sample volume hit the target. At the 10% level the size of the sample volume increased 5 to 10 times in the lateral and axial dimension in comparison with the 90% level. Therefore, the Doppler signal from a strong reflector distant from the center of the sample volume may mask the signal of a weak reflector located within the center. This lack of spatial resolution due to sensitivity effects may result in clinical misinterpretation. The manufacturers should be urged to supply more precise information relative to the sample volume size.
Arnolds
B J
BJ
Neurologische Klinik, Universität Freiburg, West-Germany.
Kunz
D
D
von Reutern
G M
GM
D001783:Blood Flow Velocity; D002536:Cerebral Arteries / Q000033:anatomy & histology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D008961:Models, Structural; D014465:Ultrasonics; D014463:Ultrasonography / Q000379:methods*