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A Guide to the Identification of Major Cerebral Arteries with Transcranial Color Doppler Sonography

¹ Department of Radiology, Bialystok Medical Academy, M. Sklodowskiej-Curie 24a, 15-279 Bialystok, Poland.
² Department of Neurosurgery, Bialystok Medical Academy, 15-279 Bialystok, Poland.
³ Department of Radiology, The Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD 21287-2182.
⁴ Department of Radiology, Boston Medical Center, 88 E. Newton St., Boston, MA 02118-2393.

Received June 29, 1999; accepted after revision October 4, 1999.

 
Address correspondence to J. Krejza.

Introduction

Top Introduction The Acoustic Window Identification of Bony and... Identification of Arterial... Middle Cerebral Artery Anterior Cerebral Artery Posterior Cerebral Artery References

 
By allowing the intracranial vascular velocities to be measured, conventional transcranial Doppler sonography can reveal arterial stenosis or occlusion and arteriovenous shunting and vasospasm [1, 2]. A major limitation of this method is the inability of the operator to visualize the intracranial vessel being interrogated and hence define the angle between the vessel and ultrasound beam. Variability in the angle of insonation degrades the reproducibility of velocity measurements [1, 3].

Transcranial color Doppler sonography, in contrast to the "blind" method (i.e., conventional Doppler sonography), allows outlining of parenchymal structures and visualization of the vessel examined. This improves consistency and accuracy in placing the sample volume and allows angle-corrected blood velocities to be obtained [2, 3]. In several recent publications, investigators have reported improved reliability and reproducibility of intracranial flow velocity measurements with the color Doppler technique compared with conventional Doppler sonography [2,3,4,5].

Admittedly, visualization of intracranial vascular anatomy with color Doppler sonography is inferior to that with CT and MR imaging, but color Doppler sonography can provide reliable estimations regarding cerebral hemodynamics. Furthermore, the examination is noninvasive, efficient (complete study takes on average 15 min), timely, and inexpensive and can be performed in a portable fashion.

We believe that standardization of the transcranial color Doppler examination is critical for improving reliability. However, no uniform standards have been adopted [6]. Knowledge of specific intracranial landmarks typically seen during the color Doppler examination should help standardize the examination. These landmarks should help the operator navigate through freely defined anatomy in oblique planes, identify the intracranial structures, and optimally place the sample volume.

In this essay, we share our experience in identifying the main intracranial arteries and selecting preferential sites of vessel insonation. A 2.5-MHz transducer was used to obtain the sonographic images from patients randomly selected from a population of those with cerebral aneurysms. We illustrate the trajectory of the sonographic beam and the location of the acoustic window with respect to the major cerebral arteries using data from three-dimensional time-of-flight MR images and three-dimensional helical CT angiograms as templates.

The Acoustic Window

Top Introduction The Acoustic Window Identification of Bony and... Identification of Arterial... Middle Cerebral Artery Anterior Cerebral Artery Posterior Cerebral Artery References

 
The most common approach allowing visualization of the anterior, middle, and posterior cerebral arteries is through the temporal acoustic window in the thin temporal region of the skull (Figs. 1 and 2A,2B,2C). Its exact location and size vary considerably, being broader in young people and more restricted, or even absent, in older individuals. This may cause problems with visualization of the intracranial structures [3].

View larger version (129K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —65-year-old man with subarachnoid hemorrhage. Three-dimensional CT angiogram shows relationships of middle cerebral artery (solid arrow), lesser sphenoid wing (arrowheads), temporal sonographic window (W), and ultrasound beam direction (dashed arrow). Horizontal portion of artery runs laterally to edge of sphenoid wing and bows ventrally. Origin of artery projects near medial edge of sphenoid wing.

View larger version (150K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —48-year-old man with aneurysm of right middle cerebral artery. T = transducer. Three-dimensional CT reconstruction shows course of ultrasound beam (dashed arrows) toward middle (curved arrow), anterior (long straight arrow), and posterior (short straight arrows) cerebral arteries. Note resultant sites of vessel intersection and angle of insonation as well as relationship of arteries to lesser sphenoid wing (arrowheads), acoustic window (W), and transducer.

View larger version (158K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —48-year-old man with aneurysm of right middle cerebral artery. T = transducer. Three-dimensional CT reconstruction shows exact site of transducer in relation to bony landmarks of outer aspect of skull, lesser sphenoid wing (solid arrowheads), and middle (curved arrow), anterior (long straight arrow), and posterior cerebral arteries (short straight arrow). Open arrowhead indicates aneurysm.

View larger version (127K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C. —48-year-old man with aneurysm of right middle cerebral artery. T = transducer. Three-dimensional CT reconstruction shows area within sonographic field of transducer, positioned at temporal acoustic window. Main structures of orientation that may by included in this oblique axial plane are lesser sphenoid wing (solid arrowheads), posterior sagittal sinus (S), and posterior (short straight arrows), middle (curved arrow), and anterior cerebral arteries (long straight arrow). Open arrowhead indicates aneurysm.

The fastest way to get the window is to turn on the color and move the probe until a vessel is imaged. A more reliable way, especially useful when arterial flow is slow or absent, is to first identify the hyperechoic outline of the bony structures at the skull base and the posterior segment of the superior sagittal sinus and then identify the hypoechoic midbrain.

Identification of Bony and Parenchymal Structures

Top Introduction The Acoustic Window Identification of Bony and... Identification of Arterial... Middle Cerebral Artery Anterior Cerebral Artery Posterior Cerebral Artery References

 
The hyperechoic lesser sphenoid wing and superior margin of the petrous pyramid are convenient landmarks for identification of the middle and posterior cerebral arteries (Figs. 1,2A,2B,2C,3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L).

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (A) and corresponding sonographic image (B) show lesser sphenoid wing (solid white arrowheads), temporal bone apex (black arrow), upper ridge of petrous pyramid (black arrowheads), posterior sagittal sinus, and squama of occipital bone (solid white arrows). Aneurysm (open arrowhead, A) shown on CT scan was not revealed by transcranial color Doppler sonography.

View larger version (142K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (A) and corresponding sonographic image (B) show lesser sphenoid wing (solid white arrowheads), temporal bone apex (black arrow), upper ridge of petrous pyramid (black arrowheads), posterior sagittal sinus, and squama of occipital bone (solid white arrows). Aneurysm (open arrowhead, A) shown on CT scan was not revealed by transcranial color Doppler sonography.

View larger version (135K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (C) and corresponding sonographic scan (D) show butterfly-shaped brainstem (BS) surrounded by ambient cistern containing posterior cerebral artery (short white arrow), and quadrigeminal plate cistern (Q). In front of brainstem, cisterna interpeduncularis (long white arrow) and tuberculum sellae (black arrow) can be identified. Solid arrowheads indicate lesser sphenoid wing; open arrowhead (C) indicates aneurysm.

View larger version (141K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3D. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (C) and corresponding sonographic scan (D) show butterfly-shaped brainstem (BS) surrounded by ambient cistern containing posterior cerebral artery (short white arrow), and quadrigeminal plate cistern (Q). In front of brainstem, cisterna interpeduncularis (long white arrow) and tuberculum sellae (black arrow) can be identified. Solid arrowheads indicate lesser sphenoid wing; open arrowhead (C) indicates aneurysm.

View larger version (140K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3E. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (E) and corresponding sonographic scan (F) show relation of distal internal carotid artery (straight black arrow), P1 segment (curved black arrow) and P2 segment (white arrow) of posterior cerebral artery to brain stem (BS), quadrigeminal plate cistern (asterisk), and lesser sphenoid wing (arrowheads).

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3F. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (E) and corresponding sonographic scan (F) show relation of distal internal carotid artery (straight black arrow), P1 segment (curved black arrow) and P2 segment (white arrow) of posterior cerebral artery to brain stem (BS), quadrigeminal plate cistern (asterisk), and lesser sphenoid wing (arrowheads).

View larger version (152K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3G. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (G) and corresponding sonographic scan (H) show middle cerebral artery (curved white arrow), anterior cerebral artery (straight white arrow), and lesser sphenoid wing (arrowheads). Middle cerebral artery appears as color mosaic because of effect of aliasing from increased flow velocity. Black arrow (H) indicates A2 segment of anterior cerebral artery.

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3H. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (G) and corresponding sonographic scan (H) show middle cerebral artery (curved white arrow), anterior cerebral artery (straight white arrow), and lesser sphenoid wing (arrowheads). Middle cerebral artery appears as color mosaic because of effect of aliasing from increased flow velocity. Black arrow (H) indicates A2 segment of anterior cerebral artery.

View larger version (141K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3I. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (I) and corresponding sonographic image (J) show relationship of middle cerebral artery (curved white arrow) and anterior cerebral artery (straight white arrow) to third ventricle (black arrow), pineal gland (PG), choroid plexus of trigonum (CP), and lesser sphenoid wing (arrowheads).

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3J. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (I) and corresponding sonographic image (J) show relationship of middle cerebral artery (curved white arrow) and anterior cerebral artery (straight white arrow) to third ventricle (black arrow), pineal gland (PG), choroid plexus of trigonum (CP), and lesser sphenoid wing (arrowheads).

View larger version (157K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3K. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (K) and corresponding sonographic image (L) show lateral ventricles (thin white arrows), choroid plexus of trigonum (CP), internal cerebral veins (thin black arrow, K), and straight sinus (thick white arrow).

View larger version (131K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3L. —48-year-old man with right middle cerebral artery aneurysm. Subsequent sonographic scans and corresponding CT images, used as templates, show intracranial structures in same oblique axial planes. T = transducer, S = sagittal sinus, A = anterior, P = posterior. Oblique axial CT scan (K) and corresponding sonographic image (L) show lateral ventricles (thin white arrows), choroid plexus of trigonum (CP), internal cerebral veins (thin black arrow, K), and straight sinus (thick white arrow).

Identification of the hyperechoic posterior part of the sagittal sinus provides anterior-to-posterior orientation of the intracranial structures (Fig. 3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L). The hypoechoic, butterfly-shaped mesencephalon, surrounded by hyperechoic subarachnoid cisterns, is the central structure for orientation in the axial sonographic plane. The anechoic lumen of the third ventricle, framed by two hyperechoic ependymal linings, is frequently visualized by directing the beam somewhat rostrally. The hyperechoic pineal gland cannot usually be discriminated from the adjacent subarachnoid cisterns (Fig. 3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L).

Identification of Arterial Trunks

Top Introduction The Acoustic Window Identification of Bony and... Identification of Arterial... Middle Cerebral Artery Anterior Cerebral Artery Posterior Cerebral Artery References

 
The beam is directed toward the circle of Willis by tilting the probe caudally 10-20° and rotating it slightly toward the occiput (Fig. 4A,4B). Thus, the "axial" plane obtained is angled caudally 10-20° from the anatomic axial plane. As a result, the image produced by the intersection of a vessel and this oblique imaging plane is different from the more familiar axial CT and MR images (Fig. 3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L).

View larger version (15K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A. —Sketch showing head and planes commonly used in transcranial color-coded Doppler sonography. Sonographic plane (dashed line) is skewed anteroposteriorly by 10-20° from anatomic axial plane (solid line) by rotating transducer slightly toward occiput. [UNK] = position of probe.

View larger version (23K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B. —Sketch showing head and planes commonly used in transcranial color-coded Doppler sonography. Sonographic plane (dashed line) is also angled in frontal projection by approximately 10-20° from standard axial plane (solid line) by tilting transducer caudally (back relative to front) approximately 10-20°.

Middle Cerebral Artery

Top Introduction The Acoustic Window Identification of Bony and... Identification of Arterial... Middle Cerebral Artery Anterior Cerebral Artery Posterior Cerebral Artery References

 
Although blood in the middle cerebral artery flows almost directly toward the probe, in cases of high flow velocity, the vessel often appears as a mosaic of color rather than entirely red (Fig. 3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L). This results primarily from aliasing, when the peak arterial velocity exceeds the upper limit of the color scale [7]. This effect can be avoided by maximally extending the color scale at the expense of reducing both sensitivity to Doppler signals and size of the displayed velocity spectrum.

The origin of the middle cerebral artery projects near the medial aspect of the lesser sphenoid wing (Figs. 1,2A,2B,2C,3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L). In young patients, the horizontal portion of the middle cerebral artery runs laterally, somewhat rostrally, and bows dorsally. In older patients, it is usually straight or bows ventrally, coursing even closer to the edge of the sphenoid wing and almost in the aforementioned oblique axial plane [8] (Fig. 5A,5B,5C,5D,5E). Nevertheless, the artery may be tortuous and often escapes this favorable plane (Figs. 1 and 5A,5B,5C,5D,5E). In this situation, our solution is to build up a mental map of the M1 course from several oblique slices of the vessel obtained by smoothly tilting the probe. The sample volume is then placed within the initial segment of the artery, and angle correction is accomplished by aiming at this imagined dummy vessel.

View larger version (50K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A. —Diagrams based on three-dimensional time-of-flight coronal images show variations of course of middle cerebral artery (MCA) in relation to sonographic oblique axial plane, marked with dashed lines. (Reprinted with persmission from [8] Images typical for older adults (>50 years old) show that horizontal segment of MCA is either straight or bows ventrally.

View larger version (50K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B. —Diagrams based on three-dimensional time-of-flight coronal images show variations of course of middle cerebral artery (MCA) in relation to sonographic oblique axial plane, marked with dashed lines. (Reprinted with permission from [8]) Images typical for older adults (>50 years old) show that horizontal segment of MCA is either straight or bows ventrally.

View larger version (50K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C. —Diagrams based on three-dimensional time-of-flight coronal images show variations of course of middle cerebral artery (MCA) in relation to sonographic oblique axial plane, marked with dashed lines. (Reprinted with persmission from [8]) Images typical for children and young adults show that horizontal segment of MCA tends to run laterally and somewhat rostrally (C and D), bows dorsally (E), or both.

View larger version (50K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5D. —Diagrams based on three-dimensional time-of-flight coronal images show variations of course of middle cerebral artery (MCA) in relation to sonographic oblique axial plane, marked with dashed lines. (Reprinted with permission from [8]) Images typical for children and young adults show that horizontal segment of MCA tends to run laterally and somewhat rostrally (C and D), bows dorsally (E), or both.

View larger version (49K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5E. —Diagrams based on three-dimensional time-of-flight coronal images show variations of course of middle cerebral artery (MCA) in relation to sonographic oblique axial plane, marked with dashed lines. (Reprinted with permission from [8]) Images typical for children and young adults show that horizontal segment of MCA tends to run laterally and somewhat rostrally (C and D), bows dorsally (E), or both.

The standard site of insonation of the M1 segment remains to be established [3, 6]. In our opinion, the most accurate measurement can be obtained if one is able to place a 3-mm-wide sample volume within a straight segment of the artery 10 mm from the carotid bifurcation (Fig. 6A,6B,6C,6D,6E,6F,6G,6H). Disturbed flow near the bifurcation may prevent reliable determination of the angle of insonation, whereas sampling farther from the bifurcation provides a less favorable angle and carries the risk of sampling a branch of the middle cerebral artery [3] (Fig. 3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L). Despite these pitfalls, the middle cerebral artery is usually localized with better accuracy than the posterior and anterior cerebral arteries.

View larger version (123K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6A. —35-year-old healthy man. Three-dimensional time-of-flight coronal and axial MR images of major cerebral arteries compared with their sonographic images and flow velocity spectra. Sonograms show blood flow velocity spectra of right anterior cerebral artery (ACA R), right middle cerebral artery, and right posterior cerebral artery adjacent to color image of arteries superimposed on gray-scale images of intracranial structures. Note lack of color image of left anterior cerebral artery in typical location (open arrow, B), but with preserved velocity spectrum. Solid arrow (A) indicates A1 segment of anterior cerebral artery.

View larger version (101K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6B. —35-year-old healthy man. Three-dimensional time-of-flight coronal and axial MR images of major cerebral arteries compared with their sonographic images and flow velocity spectra. Sonograms show blood flow velocity spectra of right anterior cerebral artery (ACA R), right middle cerebral artery, and right posterior cerebral artery adjacent to color image of arteries superimposed on gray-scale images of intracranial structures. Note lack of color image of left anterior cerebral artery in typical location (open arrow, B), but with preserved velocity spectrum. Solid arrow (A) indicates A1 segment of anterior cerebral artery.

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6C. —35-year-old healthy man. Three-dimensional time-of-flight coronal and axial MR images of major cerebral arteries compared with their sonographic images and flow velocity spectra. Sonograms show blood velocity spectra of right and left middle cerebral arteries (MCA R and MCA L, respectively) with adjacent color image of arteries (arrow) superimposed on gray-scale image of intracranial structures.

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6D. —35-year-old healthy man. Three-dimensional time-of-flight coronal and axial MR images of major cerebral arteries compared with their sonographic images and flow velocity spectra. Sonograms show blood velocity spectra of right and left middle cerebral arteries (MCA R and MCA L, respectively) with adjacent color image of arteries (arrow) superimposed on gray-scale image of intracranial structures.

View larger version (99K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6E. —35-year-old healthy man. Three-dimensional time-of-flight coronal and axial MR images of major cerebral arteries compared with their sonographic images and flow velocity spectra. Sonograms show blood velocity spectra of right and left posterior cerebral arteries (PCA R and PCA L, respectively) with their adjacent color images (arrow).

View larger version (84K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6F. —35-year-old healthy man. Three-dimensional time-of-flight coronal and axial MR images of major cerebral arteries compared with their sonographic images and flow velocity spectra. Sonograms show blood velocity spectra of right and left posterior cerebral arteries (PCA R and PCA L, respectively) with their adjacent color images (arrow).

View larger version (108K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6G. —35-year-old healthy man. Three-dimensional time-of-flight coronal and axial MR images of major cerebral arteries compared with their sonographic images and flow velocity spectra. Three-dimensional time-of-flight coronal MR image shows major cerebral arteries in relation to ultrasound beam (dashed lines) and transducer (T). Anterior cerebral artery on left side is hypoplastic (open arrow). Solid arrow indicates A1 segment of anterior cerebral artery; R = right, L = left.

View larger version (113K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6H. —35-year-old healthy man. Three-dimensional time-of-flight coronal and axial MR images of major cerebral arteries compared with their sonographic images and flow velocity spectra. Three-dimensional time-of-flight axial MR image shows anterior (long thick straight arrows), middle (curved arrows), and posterior (short straight arrows) cerebral arteries in relation to ultrasound beams (long thin arrows) emerging from rectangular phased array 2.5-MHz transducers (T) positioned at temporal acoustic windows. Note asymmetries in angle of insonation of cerebral arteries on both sides, which are most prominent at posterior cerebral arteries. R = right, L = left.

Anterior Cerebral Artery

Top Introduction The Acoustic Window Identification of Bony and... Identification of Arterial... Middle Cerebral Artery Anterior Cerebral Artery Posterior Cerebral Artery References

 
The A1 segment curves medially and forward from the carotid bifurcation (Figs. 2A,2B,2C, 3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L, and 6A,6B,6C,6D,6E,6F,6G,6H). The artery is usually imaged in blue because the blood flows away from the probe. With higher blood velocities aliasing may occur. The proximal A1 segment curves upward, which places it entirely within the oblique axial section, whereas the distal A1 segment often leaves this plane and escapes visualization [3]. Erroneous A1 aplasia may be diagnosed in elderly subjects because of the difficulty in color imaging of this segment, which results from the increased sonographic attenuation produced by the lesser sphenoid wing. Thus, the question of how to obtain an accurate spectral trace is raised. Our answer is to first localize the carotid bifurcation, then locate the origin of the A2 segment at the midline. The sample is then placed midway between these two points where the vessel is expected to run, which produces the spectral trace and allows angle correction (Fig. 6A,6B,6C,6D,6E,6F,6G,6H).

Posterior Cerebral Artery

Top Introduction The Acoustic Window Identification of Bony and... Identification of Arterial... Middle Cerebral Artery Anterior Cerebral Artery Posterior Cerebral Artery References

 
It is better to begin the artery localization from the P2 segment because the P1 segment is frequently hypoplastic [3]. The origin of P1, if present, can be found as a red trail in the interpeduncular cistern. Outlining the cerebral peduncle helps in P2 identification, because the artery encircles this structure. The P2 segment is usually found as a red strand at the ventrolateral aspect of the peduncle, within the ambient cistern (Figs. 2A,2B,2C, 3A,3B,3C,3D,3E,3F,3G,3H,3I,3J,3K,3L, and 6A,6B,6C,6D,6E,6F,6G,6H). Placement of the sample volume within the P1 segment, whenever possible, is advantageous, because of the more favorable angle of insonation.

References

Top Introduction The Acoustic Window Identification of Bony and... Identification of Arterial... Middle Cerebral Artery Anterior Cerebral Artery Posterior Cerebral Artery References

 

1. Lupetin AR, Davis DA, Beckman I, Dash N. Transcranial Doppler sonography. 1. Principles, technique, and normal appearances. RadioGraphics 1995;15:179 -191[Abstract]
2. Bazzocchi M, Quaia E, Zuiani C, Moroldo ML. Transcranial Doppler: state of the art. Eur J Radiol 1998;27[suppl 2]:S141 -S148
3. Baumgartner RW, Mattle PH, Aaslid R. Transcranial color-coded duplex sonography, magnetic resonance angiography, and computed tomography angiography: methods, applications, advantages, and limitations. J Clin Ultrasound 1995;23:89 -111[Medline]
4. Baumgartner RW, Mattle HP, Schroth G. Assessment of 50% and <50% intracranial stenoses by transcranial color-coded duplex sonography. Stroke 1999;30:87 -92[Abstract/Free Full Text]
5. Maurer M, Shambal S, Berg D, et al. Differentiation between intracerebral hemorrhage and ischemic stroke by transcranial color-coded duplex-sonography. Stroke 1998;29:2563 -2567[Abstract/Free Full Text]
6. Krejza J, Mariak Z, Walecki J. Usefulness of transcranial color-coded sonography in the diagnosis of cerebral vasospasm. Stroke 1999;30:2240 -2241
7. Nelson TR, Pretorius DH. The Doppler signal: where does it come from and what does it mean? AJR 1988;151:439 -447[Abstract/Free Full Text]
8. Ring BA. The middle cerebral artery. In: Newton TH, Potts GD, eds. Radiology of the skull and brain. Great Neck, NY: Mosby, 1974:1442 -1526

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				J. Krejza, Z. Mariak, and J. Lewko Standardization of Flow Velocities with Respect to Age and Sex Improves the Accuracy of Transcranial Color Doppler Sonography of Middle Cerebral Artery Spasm Am. J. Roentgenol., July 1, 2003; 181(1): 245 - 252. [Abstract] [Full Text] [PDF]

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				J. Krejza, Z. Mariak, and V. L. Babikian Importance of Angle Correction in the Measurement of Blood Flow Velocity with Transcranial Doppler Sonography AJNR Am. J. Neuroradiol., October 1, 2001; 22(9): 1743 - 1747. [Abstract] [Full Text] [PDF]

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