Page 132 - Libro 2

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PART 2 — CEREBROVASCULAR
100
Velocity [cm/sec] 50
A2 EDV
100
Velocity [cm/sec] 50
v EDV
Time
PSV A1
PSV
Velocity Parameters
v = 70 cm/sec
Pulsatility
100
Velocity [cm/sec] 50
100
Velocity [cm/sec] 50
00 Time
Systolic Upstroke
Spectral Distribution
00 Time
Time
Figure 7-24 Diagnostic features of spectral waveforms for interpretation of TCD studies: mean velocity, pulsatility index, systolic upstroke, and distribution of the amplitude within the waveform.
Crossover Collateral through the Anterior Communicating Artery
• Direct evidence of carotid artery disease.
• Retrograde flow in the ACA, A1 segment ipsilat-
eral to the carotid disease.
• Increased flow velocities in the contralateral
ACA (ACA mean velocity/ipsilateral MCA mean velocity 􏰀150%). The increase in velocity is re- lated to the increase in volume flow as well as the diameter of the vessel carrying that increased
volume. In individual cases, there can be cross- over collateral with normal ACA velocities due to the large diameter of the ACA.
• There are usually very high velocities detected at midline in the small ACOA.
The accuracy of TCD in the identification of in- tracranial crossover collateralization through the ACOA in experienced laboratories has a sensitivity
of 93%, a specificity of 100%, and an accuracy of 98%.23,24
PI = PSV - EDV v
PATHOLOGY BOX 7-1
Common Pathology Observed on TCD or TCDI Examinations
Pathology ExaminationFindings
Stenosis
Occlusion (acute, total) Vasospasm (severe)
Emboli
• Focal increase in velocity
• Poststenotic turbulence
• Greater than 30 cm/s hemispheric difference • Refer to Table 7-3 for complete criteria
• Absent flow on color imaging and Doppler
• High resistance signal proximal to occlusion • MCA velocity 􏰀200 cm/s
• Can be present in more than one artery
• Temporal changes
• Brief signal lasting 􏰄300 ms
• Amplitude at least 3 dB above background
• Unidirectional signal
• Signal has snap, chirp, or moan sound