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10 Transcranial Doppler (TCD/TCCS) Approaches: Acoustic Windows
183
a
Fig. 10.7 (a) Transforaminal insonation at vertebral arteries plane. The blue circle is magnied to
better understanding of the insonated structures. See how both vertebral arteries nd each other to
follow as the basilar artery. Red dots with shades area demarcate the foramen magnum (hypoechoic),
the black triangle indicates the location of the clivus (hyperechoic). (b) Complete insonation of the
basilar artery in depth range between 70 and 100 millimeters (area between orange dotted lines),
and spectral Doppler showing basilar ow velocity. (Author: Jorge Carrizosa)
Table 10.3 Targets of visualization: transorbital Window
Targets of visualization
B-mode: retrobulbar space
Color Doppler and pulsed wave Doppler modes: ophthalmic artery, carotid siphon, central
retinal artery, central retinal vein, posterior ciliary artery
b
and measured in different segments at 80–90–100 millimeters [5]. Vertebral arteries
and basilar arteries are coded blue as their ow direction goes away from the transducer. The posterior inferior cerebellar artery can also be visualized through this
window emerging from the distal segment of the vertebral artery with red colorcoding as its ow goes toward the transducer.
10.2.3 Transorbital Acoustic Window (Table10.3)
10.2.3.1 Technique
Adjust power output and decrease 10% before placing the 2.0–3.5MHz phased
array transducer in B-mode image on the closed upper eyelid. Remember the as low
as reasonably achievable (ALARA) principle (“as low as reasonably achievable”),
in order to decrease thermal and mechanical effects [6]. Lightest pressure possible
184
J. Ca rr izosa
must be applied to minimize the risk of injuries to eyeball and retina. Set depth to
10 centimeters: eyeball and retrobulbar structures (intraconal and extraconal) are
seen. Activate the color mode box right behind the eyeball and place the color box
between 3 and 6 centimeters in order to identify the ophthalmic artery (red colorcoded with peripheral vessel morphology in spectral Doppler mode). Tilt the transducer downward and medial to identify the ipsilateral carotid siphon. This structure
is usually found between 55 and 75 millimeters. Flow direction varies according to
the insonated segment of the carotid siphon (Figs.10.8 and 10.9).
Fig. 10.8 Insonation of
the transorbital window. A
chart of the internal carotid
artery has been drawn on
the picture for educational
purposes. The ultrasound
beam is represented with
the shaded gray box. Note
that tilting exploration with
the transducer must be
done to nally insonate the
different segments of the
carotid syphon and the
ophthalmic artery (OA)
(number 1 to 5). 1: C4
segment; 2: C3 segment; 3:
ophthalmic artery; 4: C2
segment; 5: C1 segment.
(Author: Jorge Carrizosa)
a
Fig. 10.9 Transorbital window examination. (a) B-mode image identifying the hyperechoic line
in the retrobulbar space, separating intraconal and extraconal structures (orange dashed line). (b)
Color-coded Doppler at the same level illustrated above with a chart of the path of the carotid
syphon for clarity (red shaded area). Three different segments of the carotid syphon can be identied as C4-C3-C2. CRA central retinal artery, OA ophthalmic artery, PCom posterior communicating artery. (Author: Jorge Carrizosa)
b
10 Transcranial Doppler (TCD/TCCS) Approaches: Acoustic Windows
185
Examination of specic structures requires a switch to a linear-array transducer
emitting 7.5–12MHz in order to achieve better resolution. Ophthalmic or neuroorbital preset is available in many ultrasound machines, and it is strongly recommended to keep safety aspects. Place the linear-array transducer on the closed upper
eyelid. B-mode image will allow examining optical nerve, optic nerve sheath,
papilla [7]. Color Doppler mode box placed right behind the papilla will allow to
insonate ophthalmic artery, central retinal artery, central retinal vein, and posterior
ciliary artery.
10.2.4 Submandibular Acoustic Window (Table10.4)
10.2.4.1 Technique
Place the 2.0–3.5 MHz phased array transducer in B-mode image at the submandibular level. The objective of this approach is to insonate and measure blood ow
velocity of the distal internal carotid artery right before the entrance of the artery to
the skull (40 to 60 millimeters) (Figs.10.10 and 10.11). Data from these measurements are required to calculate the MCA/internal carotid artery (ICA) mean ow
velocity ratio or Lindegaard ratio. Lindegaard ratio is useful in the differentiation
process between vasospasm and hyperemia [8]. A review of carotid protocol and
examination of neck vascular structures is detailed in another chapter in this book.
10.2.5 Frontal Bone Window (Table10.5)
10.2.5.1 Technique
Place the 2.0–3.5MHz phased array transducer in B-mode image above the lateral
aspect of the eyebrow (Fig.10.12). The Sylvian ssure and the mesencephalon are
the reference structures. Frontal horns of the lateral ventricles, orbital roof, and
hypophyseal groove can also be identied (Fig.10.13) [9].
Activate the color Doppler mode box and adjust pulse repetition frequency to
medium range (20cm/s). The anterior cerebral artery is identied with ow direction toward the probe in A2 segment and away from the probe in A1 segment [10]
(Fig.10.14). Other structures of the Circle of Willis could be determined according
to the depth of insonation. However, blood ow velocity measurement is not
Table 10.4 Targets of visualization: submandibular window
Targets of visualization
B-mode: jugular vein, common carotid artery, external carotid artery, internal carotid artery
Color Doppler and pulsed wave Doppler modes: the terminal segment of the extracranial
internal carotid artery
186
Fig. 10.10 Submandibular
window insonation. An
internal carotid artery chart
has been drawn for clarity.
Note the color ow
direction away the probe as
the transducer position is
pointing in cranial
direction. Red circle is
indicating the target depth
of insonation between 40
and 60 millimeters.
(Author: Jorge Carrizosa)
J. Ca rr izosa
recommended routinely at this level in order to avoid misinterpretation of the brain
blood ow dynamics. Proper selection of a suitable window for every specic vessel
in a protocolized way is recommended.
Placing the transducer slightly lateral of the midline of the forehead and positioned vertically allows identifying the choroid plexus of the third ventricle (hyperechogenic), the corpus callosum (hypoechogenic), and the orbital roof
(hyperechogenic). Activate the color Doppler mode box and adjust pulse repetition
frequency to a low range. A3 segment of the anterior cerebral artery is identied
with ow direction away from the probe as it surrounds the corpus callosum
(Fig.10.15). Change the depth of insonation to identify the internal cerebral vein at
9 to 10 centimeters, slightly above the choroid plexus of the third ventricle
(Fig.10.16) [11].
10.3 Ethnicity, Age, andGender: TCD/TCCS
Special Considerations
There are some considerations regarding ethnicity described as initial reports that
estimate an inadequate acoustical temporal bone window of about 9% in Caucasian
people [12]. However, higher rates of an inadequate acoustical temporal bone
10 Transcranial Doppler (TCD/TCCS) Approaches: Acoustic Windows
187
a
b
Fig. 10.11 Submandibular window in B-mode and color-coded Doppler ultrasound. (a) B-mode
image at submandibular level indicating the hypoechoic area (red dotted line) corresponding with
the carotid artery. (b) Color-coded Doppler and pulsed-Doppler ultrasound at the same level above.
As the direction of the transducer is pointing in cranial direction, carotid artery ow direction is
away the probe. Small red area at the carotid bifurcation level corresponds to the jugular vein (ow
direction toward the transducer). Different spectral-Doppler waves are shown in order to identify
the vascular structures. 1: jugular vein; 2: common carotid artery; 3: external carotid artery; 4:
internal carotid artery. Orange dashed lines were sketched between 40 and 60 millimeters to prove
the correct depth of insonation to proper measurement of the internal carotid artery. (Author: Jorge
Carrizosa)
Table 10.5 Targets of visualization: frontal bone window
Targets of visualization
B-mode: third ventricle and choroid plexus of the third ventricle, Sylvian ssure, corpus
callosum, orbital roof
Color Doppler and pulsed wave Doppler modes: anterior cerebral artery[ACA],internal
cerebral vein
window have been reported in Hispanic and Asian people [13, 14]. Also, age and
gender are related to a high proportion of suboptimal windows in older women,
especially those older than 80years old, in whom an optimal temporal window has
been seen in less than 50%. It is well known that the rate of successful insonation of
brain circulation through transcranial Doppler decreases with age [15–17]. This
probability of unsuccessful insonation is related to the thickness of temporal bone
advancing with age [13].
188
Fig. 10.12 Frontal bone
window insonation. 1:
transducer position above
the eyebrow (supraorbital
zone) with probe indicator
(green dot) pointing to the
right side in horizontal
position. 2: transducer
position in paramedial
zone with probe indicator
(green dot) pointing in
cephalic direction in
vertical position. (Author:
Jorge Carrizosa)
J. Ca rr izosa
Fig. 10.13 B-mode image
in frontal window
insonation at supraorbital
zone. Typical anatomy is
showed: third ventricle in
the red box; frontal horns
of lateral ventricles in
orange lines. (Author:
Jorge Carrizosa)
10 Transcranial Doppler (TCD/TCCS) Approaches: Acoustic Windows
Fig. 10.14 Color-coded
Doppler image at frontal
window insonation through
supraorbital zone. Path of
the ipsilateral anterior
cerebral artery is shown.
AComA (ACom) anterior
communicating artery;
ACA1 anterior cerebral
artery segment A1; ACA2
anterior cerebral artery
segment A2. (Author:
Jorge Carrizosa)
189
a
Fig. 10.15 Frontal window insonation at the paramedian frontal zone. (a) B-mode image delimiting the corpus callosum (light blue dashed line) and the choroid plexus of the third ventricle (yellow rectangle). (b) Color Doppler image at the same level in the image above. Path of the anterior
cerebral artery segment A3 (pericallosal artery) is seen in the color scale surrounding the corpus
callosum. (Author: Jorge Carrizosa)
Fig. 10.16 Color-coded
Doppler image at the
paramedial frontal bone
window with depth
adjustment showing the
internal cerebral vein
(ICV) with ow direction
away from the probe.
(Author: Jorge Carrizosa)
b
190
J. Ca rr izosa
10.4 TCD/TCCS: Special Clinical Situations inICU
10.4.1 Decompressive Craniectomy
Nowadays, patients with decompressive craniectomy are not infrequent in neurocritical care units. The procedure is performed on patients with refractory intracranial hypertension, malignant brain edema in middle cerebral artery infarction, or to
manage expansive focal injury in traumatic brain injury. One of the most relevant
publications to date is the decompressive craniectomy in diffuse traumatic brain
injury (DECRA) trial [18]. Fronto-temporoparietal decompressive craniectomy,
bifrontal decompressive craniectomy, and occipital decompressive craniectomy,
among others, have been described.
As part of the skull has been removed surgically, images are easier to get, but the
sonographer/physician must take care of the pressure applied to the tissues. Lightest
pressure possible should be enough to achieve the insonation of interesting structures. By applying excessive pressure, increased intracranial pressure, direct injuries to the brain parenchyma, and wrong measurements can occur. Changes in blood
ow velocities have been described before and after a decompressive craniectomy.
The most common difference after decompressive craniectomy is an asymmetrical
increase in cerebral blood ow velocities with a higher increase in the decompressed
side than the opposite side. A decrease in the pulsatility index has also been reported
[19–21]. Monitoring the decompressed patient with transcranial Doppler ultrasound
is remarkably important as different hemodynamic patterns have been described
after the procedure.
10.4.2 Patient’s Position
Access to some windows in critical care patients could be challenging. Due to the
inability to ex the neck, risk of secondary injury removing the cervical collar, or
prone position as a complement of mechanical ventilation strategy for severe acute
respiratory distress syndrome, a complete evaluation of brain circulation is sometimes limited. No diagnostic approach should generate a risk of injury to the patient.
As a primary goal in transcranial Doppler evaluation is to identify and measure
blood ow velocities in the middle cerebral artery, transtemporal window usually
remains accessible even in conditions mentioned before [22, 23]. Identifying proper
time to perform the evaluation is recommended in synchronous work with the nurse
10 Transcranial Doppler (TCD/TCCS) Approaches: Acoustic Windows
team as the schedule for patient’s position change must be taken advantage of for
the insonation. In very extreme conditions in which it is impossible to insonate
every window, the sonographer/physician should try to take information from the
transtemporal window, transorbital window, submandibular window, transforaminal
window, and the transfrontal window in that priority order.
191
10.5 TCD/TCCS: Contrast-Enhanced
The quality of the acoustic window has been related to the thickness of the temporal
squama. Insufcient temporal bone window using transcranial color-coded sonography has been described between 10% and 38% [12, 14–16, 24]. To date, there are
two agents currently approved for use in neuro sonography: Levovist® and
SonoVue®. For patients with inadequate acoustical temporal bone window, absent
or insufcient to perform an accurate diagnosis, use of echo contrast agents may be
useful to achieve better images where available. Echo contrast agents are comprised
of stabilized microbubbles with a diameter lesser than 8μm. The physical effect is
through enhancement of the scattering phenomenon related to the size of the microbubbles [25, 26]. This contrast-enhanced strategy has been described for different
conditions in addition to an insufcient window like brain death determination,
stroke, dural arteriovenous stulae, and intracranial collaterals examinations [17,
25, 27].
10.6 Conclusion
Transcranial Doppler ultrasound has become the stethoscope for the brain to evaluate the critical care patient’s brain parenchyma and cerebral hemodynamics. To
achieve a proper evaluation of the patient’s central nervous system with ultrasound,
accessible windows, and their target structures to be identied must be part of the
knowledge of the sonographer/physician. Standardization of the routine of evaluation is recommended. In some specic groups of patients, a hard-to-nd acoustic
window could represent a challenge for the sonographer/physician. Echo contrast
agents can be intravenously applied to achieve adequate insonation of targeted brain
vascular structures.
192
PcomA / PCA BA Carotid Siphon ECA AcomA
Algorithm
EMERGENCY DEPARTMENT (ED)
INTENSIVE CARE UNIT (ICU)
Clinical Status of Patient
ABCD
Level of consciousness (GCS)
Bilateral Pupillary reactivity
Hemodynamic stability?
SPECIAL SITUATIONS CONTRAST ENHANCED
Primum Non Nocere Transtemporal Window (TTW)
Decompressive Craniectomy
Light Pressure
Applied to the tissue
Prevent high ICP
Caution with the
BFV interpretation
Patient Position
Team work with
Nurse ICU staff
Neck : Ability to Flex?
Cervical Collar?
Oxigenation?
DIAGNOSIS
CRITICAL ILL PATIENT
Acute Neurological Injury
Non Acute Neurological Injury
When?
Inadequate TTW (10-38%)
Absent TTW (10-38%)
J. Ca rr izosa
Transcranial Doppler (TCD) / Transcranial Color
TRANSTEMPORAL
WINDOW (1)
B-MODE B-MODE B-MODE B-MODE B-MODE
Anatomical Reference
Structure
Midbrain
(Mesencephalon)
COLOR-CODED
ULTRASOUND
MCA / ACA / ICA (C1) VA (V4) OA / CRA ICA ACA(A2)
TRANSFORAMINAL
WINDOW (2)
Anatomical Reference
Structure
Foramen
Magnum
COLOR-CODED
ULTRASOUND
duplex Sonography (TCCS)
TRANS-ORBITAL
WINDOW (3)
Anatomical Reference
Structure
Eyeball Carotid Artery
Optic Nerve Frontal Horns of LV
COLOR-CODED
ULTRASOUND
-Coded
SUBMANDIBULAR
WINDOW (4)
Anatomical Reference
Structure
Shadow
COLOR-CODED
ULTRASOUND
FRONTAL BONE
WINDOW (5)
Anatomical Reference
Structure
3th Ventricle
COLOR-CODED
ULTRASOUND
ABCD Airway-Breathing-Circulation-Disability, MCA Middle cerebral artery, ICA Internal carotid
artery, C1 C1 segment of ICA, PcomA Posterior communicating artery, PCA Posterior cerebral
artery, BA Basilar artery, VA Vertebral artery, V4 V4 segment of VA, OA Ophthalmic artery, CRA
Central retinal artery, ECA External carotid artery, ACA Anterior cerebral artery, A2 A2 segment of
ACA,ICP Intracranial pressure, GCS Glasgow coma scale., 1-2-3-4-5 Sequence of Insonation
Protocol, TTW Transtemporal window, ICP intracranial pressure, LV Lateral ventricle
References
1. Aaslid R, Markwalder T-M, Nornes H.Noninvasive transcranial Doppler ultrasound recording
of ow velocity in basal cerebral arteries. J Neurosurg. 1982;57(6):769.
2. Lau VI, Arnteld RT. Point-of-care transcranial Doppler by intensivists. Crit Ultrasound
J. 2017;9(1):21.