Doc #: 60-00118 Rev. A
71
The System determines the Velocity Envelope from the spectrogram. The Velocity Envelope
indicates where it calculates the maximum velocity of the spectrogram. The maximum velocity
that the Velocity Envelope trace represents is typically of interest to the clinician. On the System
display it is manifested as an edge trace of the spectrogram.
Velocity Measurements:
The System determines the Velocity Measurements (Mean, Maximum and Minimum Velocity)
from the Velocity Envelope. It should be noted that the accuracy of the measurement numbers
depends upon the Velocity Envelope.
Note the following:
The System velocity calculations are generated based upon zero-degree Doppler angle.
The Velocity Envelope does not support heart rates below 30 beats per minute or above
130 beats per minute.
Verify the tracking of the Velocity Envelope to the edge of the Spectrogram before
interpreting the Velocity Measurements (Mean, Maximum and Minimum). If needed use
manual calculations to determine or verify measurement values.
Embolus Detection Feature Description and Limitations
The Lucid
™ M1 System has automatic embolus detection capabilities. However, not all emboli
moving through blood are detectable with ultrasound. Emboli traveling in blood have two
characteristics: movement and ultrasound reflection. Ultrasound reflection is important when
using the embolus detection feature. When the embolus is a weak reflector, then the signal may
not appear on the spectrogram or M-mode display. It should be noted that gaseous emboli are
easily detected due to the high reflection at the embolus-to-blood interface.
A solid embolus is difficult to detect due to the lower reflection of ultrasound signal. Likewise,
when an embolus appears in the weaker ultrasound beam areas (whether gaseous or solid), the
reflection will be weaker and the possibility of not counting in the automatic embolus detection
feature may occur. As a result, the sensitivity of the emboli detection feature is dependent upon
the type of emboli observed, in both size and composition. False positives have also been
observed when somewhere in the spectrogram or M-mode display there is a blood flow signal
that disappears during diastole.
A sharp Doppler angle may contribute to this situation. However, it is anticipated to be rare due to
the low fluidic resistance of the brain as well as the coaxial nature of the middle cerebral artery
M1 and M2 regions, thereby lowering the possibility of the situation occurring.
The scenario of detected flow signals fading and reemerging during systole in these conditions
may yield false positives for the emboli detection feature.
Envelope and TCD Measurement Uncertainties
The velocity envelope follows the maximum velocity of the spectrogram signal. The TCD
measurements are derived from the velocity envelope values. When interpreting TCD
measurements, confirm that the velocity envelope is tracking properly and follows the edge of the
