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TCD 101:
An Introduction to Transcranial Doppler Examinations [continued] |
|
| ICAVL DIVISION NEWS | Winter 2009
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<<BACK | 1 | 2 | 3 | 4 |
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Pointing in the Right Direction
| Arterial Segment |
Insonation Depth |
Normal Adult Flow Velocity |
Identification of the Vessel Segment |
| Middle Cerebral Artery (M2) |
30-40 mm |
30-80 cm/sec |
Bidirectional Flow |
| Middle Cerebral Artery (M1) |
40-65 mm |
30-80 cm/sec |
Flow toward the probe |
| Anterior Cerebral Artery (A1) |
60-75 mm |
30-80 cm/sec |
Flow away from the probe |
| A1-A2 Anterior Cerebral Artery |
45-70 mm |
20-80 cm/sec |
Flow toward the probe |
| Carotid Siphon (C1) |
58-65 mm |
20-70 cm/sec |
Bidirectional Flow |
| Opthalmic Artery |
40-50 mm |
Variable |
Flow toward the probe |
| Posterior Cerebral Artery (P1) |
55-75 mm |
20-60 cm/sec |
Bidirectional Flow |
| Basilar Artery |
80-105 mm |
20-60 cm/sec |
Flow away from the probe |
| Vertebral Artery |
40-75 mm |
20-50 cm/sec |
Flow away from the probe |
Notes for The Sonographer
The sonographer must be sufficiently skilled in the exam technique and have good understanding of the anatomy. Space occupying lesions and anatomic variables can lead the sonographer to misidentification of the vessels. Proper attention must be paid to the depth and angulation of the ultrasound beam to avoid mislabeling the spectral Doppler waveforms. Caution should be used to avoid misrepresenting a stenotic artery for a hyperdynamic collateral. Stenosis and vasospasm can easily be confusing to the less experienced technologist. Finally, the easiest solution to some technical issues may be simply proper patient positioning.
New Tools for Old Jobs: Duplex imaging with color coded Doppler and Power Motion mode Doppler (PMD) are rapidly becoming popular among transcranial Doppler sonographers. Duplex imaging allows the technologist to have a visual landscape of the anatomy. This technique, in experienced hands, enables rapid and accurate vessel identification with exact placement of the Doppler sample volume, therefore enabling a shorter exam time. Similarly, PMD for non-imaging TCD instruments is a convenient window-finding tool that extends vessel interrogation and may also yield specific flow signatures of diagnostic significance.
Conclusion
Currently, there are 74 laboratories accredited by the ICAVL in Intracranial Cerebrovascular testing. In light of the extreme technical difficulty associated with TCD examinations, all laboratories performing these studies are encouraged to document the level of patient care they are providing by seeking ICAVL accreditation.
***
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REFERENCES
Practice Standards for Transcranial Doppler Ultrasound: Part I – Test Performance. Alexandrov, A. Et al. American Society of Neuroimaging, 2007.
Intracranial Cerebrovascular Evaluation. Transcranial Doppler (Non-Imaging). Society of Vascular Ultrasound, 2006.
Assessment: Transcranial Doppler Ultrasonography. Report of the Therapeutics and Technology Assessment Subcommittee of the American College of Neurology. Sloan, MA, et al. American Academy of Neurology, 2007.
Yield and Accuracy of Urgent Combined Carotid/Transcranial Ultrasound Testing in Acute Cerebral Ischemia. Journal of the American Heart Association – Stroke, 2004.
Vascular Diagnosis. Fourth Edition 1993. Bernstein, EF.
Introduction to Vascular Ultrasonography. Fifth Edition 2005. Zweibel, WJ. Pellerito, JS. |
