Trans-cranial Doppler (TCD) ultrasonography is used to evaluate blood flow velocities in the basal intracerebral arteries. It was introduced in 1982 and has since been used for applications like detecting vasospasm after subarachnoid hemorrhage, monitoring stroke risk in sickle cell disease, and as a supplementary test for confirming brain death. TCD uses acoustic windows to insonate arteries like the middle cerebral artery, assessing flow parameters like peak systolic velocity to evaluate stenosis or vasomotor reactivity. It can also detect embolic signals and changes in flow patterns associated with conditions like atrial fibrillation or cerebral circulatory arrest.

1. Dr. Nishtha Jain
Senior Resident
Department of Neurology
GMC, Kota.

2.  called as the doctor’s stethoscope of the brain.
 Introduced by Rune Aaslid in 1982 for detecting blood
flow in the basal intracerebral arteries.
 Mark Moehring in 2002 invented the transcranial
power-motion mode Doppler (PMD).
 initially introduced for detecting the vasospasm following
subarachnoid hemorrhage.

3.  Important and established applications of TCD include
-detection of the right-to-left shunt.
-cerebral vasomotor reactivity.
-monitoring flow velocities for stroke prevention in sickle cell
disease.
-as a supplementary diagnostic test for the confirmation of brain
death.
-continuous TCD monitoring during systemic thrombolysis.

4.  based on the pulse-echo technique.
 The four commonly employed acoustic windows in adults
are —
 1. Temporal - the flow velocities in MCA, ACA, PCA, and
PCOM can be obtained.
 2. Orbital - ophthalmic artery (OA) and internal carotid
artery (ICA) siphons are insonated .
 3. Suboccipital - allows insonation of the vertebral (VA)
and basilar (BA) arteries.
 4. Submandibular - evaluate the distal cervical ICA.

5.  The BA can also be evaluated through the transforaminal
approach (direct insonation through the foramen
magnum).

7. Trans-temporal insonation
 A red color signal (toward the probe) between 40 and
65mm - ipsilateral MCA.
 A blue signal between 65 and 80 mm - ipsilateral ACA.
 A red signal beyond 80 mm - contralateral A1 ACA
 A bidirectional signal obtained at 60-70 mm represents
ICA bifurcation.

8.  The ultrasound probe is slowly oriented posteriorly by 10
to 30 degrees.
 Usually there is a flow gap followed by flow signals from
the PCA.
 Flow signals directed toward the probe - P1 PCA
 Away from the flow - P2 segment of the PCA
 Both segments are visualized at depths of 55-70 mm.
 An absence of the flow gap while moving the transducer
posteriorly after MCA/ ACA evaluation - PCOM.

11. Transorbital insonation
 The transducer placed over the eyelid and angled slightly
medial and upward.
 Flow signals at a depth of less than 60 mm toward the
probe - ophthalmic artery.
 ICA siphon is a curved artery - the flow signals may be
directed toward or away from the probe.

12. Suboccipital insonation
 Place the transducer just below and medial to the
mastoid process.
 Directed slightly medially and more horizontally toward
the bridge of the nose or contralateral eye.
 Ipsilateral VA between the depths of 50 to 75 mm -
signals always away from the probe.

13.  By turning the probe slightly upward and medially from
the depths of 75 to 110 mm - BA may be insonated.
 May also be obtained through the transforaminal window
- transducer just below the occipital protuberance and
toward the nasal bridge.
 The flow from the BA is away from the probe.

14.  The normal spectral waveform - A sharp systolic upstroke
and stepwise deceleration with positive end-diastolic flow.
 Peak systolic velocity-This is the first peak on a TCD
waveform from each cardiac cycle.
 A rapid upstroke represents the absence of a severe
stenotic lesion between the insonated intracranial arterial
segment and heart.

15.  End-diastolic velocity - lies between 20 and 50% of the
peak systolic velocity (PSV) values, indicating a low
resistance intracranial arterial flow pattern.
 Mean flow velocity - calculated as EDV plus one-third of
the difference between PSV and EDV.
 MCA should have the highest MFV among all major
intracranial arteries.

16. Pulsatility index
 Flow resistance is usually assessed by PI, calculated by
subtracting EDV from PSV and dividing the value by
MFV.
 Most frequently used TCD parameter to determine the
flow resistance.
 A value more than 1.2 represents high resistance blood
flow.

17. Resistance index (RI)
 Used to assess the flow resistance.
 It represents flow resistance distal to the site of
insonation.
 RI is calculated by subtracting EDV from PSV and
dividing the value by PSV.
 Any value below 0.75 is normal.

19. Spectrum with abnormal systolic
flow acceleration
 Seen distal to a proximal
steno-occlusive lesion.
 The waveform shows delayed
systolic flow acceleration,
flattened systolic upstroke, and
slow diastolic deceleration.
 EDV is usually more than 50%
of PSV, due to compensatory
distal vasodilatation.
 Also called a blunted flow
signal.

20. Intracranial stenosis
 Focal stenosis increases the
flow velocities represented
by the ‘bruit’, seen as a
symmetrical artifact on either
side of the baseline.

21.  Compared with computed tomography angiography
(CTA) TCD demonstrate 79% sensitivity and 94%
specificity in detecting intracranial stenosis.

23. Spectrum with irregular rhythm
 Identify cardiac rhythm
abnormalities like atrial
fibrillation by TCD as
variable Doppler spectra and
velocities.
 The cardiac cycle with the
highest flow velocities is
used for measurement of
various parameters.

24. Cerebral-circulatory arrest (brain
death)
 Cerebral circulatory arrest is
seen on TCD as varying
from high-resistance to
diastolic flow reversal
(reverberating) to absent
flow.
 TCD is often used as a
supplementary test for the
confirmation of brain death.

25. TCD monitoring for spontaneous
emboli
 Extended monitoring of an intracranial artery distal to the
steno-occlusive site can detect spontaneous
microembolic signals (MES) and quantify the
embologenic potential of the atherosclerotic plaque.
 Detection of even a single MES during 40 min of
monitoring is considered as clinically significant.

26.  The International Cerebral Hemodynamics Society
describes MES as:
 a. Random occurrence during the cardiac cycle.
 b. Brief duration (usually <0.1 s).
 c. High intensity (>3 dB over background).
 d. Primarily unidirectional signal.
 e. Audible component (chirp, whistle, or pop).

27.  The presence of MES on TCD distal to a high-grade
asymptomatic stenosis of internal carotid artery identifies
patients at a higher risk of stroke.

29. Right-to-left shunt (RLS) detection
 TCD “bubble” test to detect RLS.
 More sensitive and specific than transesophageal
echocardiography for RLS detection as well as for
quantifying its “functional-potential.”

30. International Consensus Criteria (ICC)
 Grade 0: No MES.
 Grade 1: MES count 1-10.
 Grade 2: MES count 11-30, and
 Grade 3: MES count more than 30 with “shower” or “curtain”
appearance.
Spencer’s Logarithmic Scale
 Grade 0: No MES.
 Grade 1: MES count 1-10.
 Grade 2: MES count 11-30.
 Grade 3: MES count 31-100.
 Grade 4: MES count 101-300.
 Grade 5: MES count more than 300.

32. Vasomotor reactivity (VMR)
 VMR represents the response of cerebral circulation to
various vasomotor stimuli for maintaining a near-constant
blood flow.
 The subject is asked to hold his/her breath for a minimum
of 30 s while MCAs were being monitored with TCD.
 MCA flow velocities are noted 4 s after breathing is
restarted.

33.  BHI of <0.69 is
considered to represent
an impaired cerebral
vasodilatory reserve
(CVR) regulated by the
parasympathetic nervous
system.

34.  A decreased BHI - failure of the collateral flow to maintain
adequate cerebral perfusion in response to the
hypercapnic challenge.
 Used to identify patients at a higher risk of stroke among
the cohort of asymptomatic carotid stenosis or previously
symptomatic carotid occlusion.

35.  The sympathetic nervous system control of intracranial
flow can also be tested.
 The patient is asked to hyperventilate and MCA flow is
continuously monitored.
 Hyperventilation induces hypocapnea that results in
cerebral vasoconstriction, leading to a reduction of flow
velocities.

36.  VMR= MFVhypercapnea -MFVhypocapnea/MFVat rest ×
100
 A value more than 65% indicates normal VMR while the
value of less than 33% reflects an exhausted VMR.
 VMR between 33% and 65% represents borderline
impaired autonomic control.

38. TCD in sickle cell disease
 Children with sickle-cell disease (SCD) carry a significant
stroke risk.
 11% of all homozygous sickle cell (HbSS) patients
develop ischemic stroke before the age of 20 years.
 Primarily result from stenosis or occlusion of the distal
intracranial internal carotid arteries and/or proximal MCA.

39.  TCD can identify children with the highest risk of the first-
ever stroke and those in need of blood transfusion.
 In a trial,TCD detection of time averaged maximum mean
flow velocity of 200 cm/s on two separate examinations
was used to determine the need for blood transfusion
that resulted in about 90% relative risk reduction of first-
ever stroke.

43.  TCD is performed according to stroke prevention in
sickle-cell disease (STOP) trial protocol.
 STOP protocol uses time-averaged mean of the
maximum (TAMM) velocities of the MCA, and/or TICA
recorded on two separate occasions separated by at
least 2 weeks.

44. STOP classification for risk stratification and treatment
strategy:
 Normal: TAMM velocity <170 cm/s — a repeat assessment is
indicated.
 Conditional: TAMM 170-200 cm/s in the MCA and/or terminal
ICA — in children with no previous records, a repeat TCD is
planned in about 2 weeks
 Abnormal: TAMM >200 cm/s in the MCA and/or terminal ICA
— urgent blood transfusion is arranged.

45. TCD as supplementary test for
confirmation of brain
death
 TCD can be used to help in diagnosing cerebral
circulatory arrest in adults and children (older than 6
months).
 Once a reverberating signal is found, it should be
monitored for at least 30 min in the both MCAs and the
basilar artery (BA) to avoid false-positive findings.

46.  Scanning protocol and algorithm if cerebral circulatory arrest is
suspected:
 a. Document arterial blood pressure at the time of TCD
examination.
 b. Assess both MCAs (starting depth 50 mm) and BA (80 mm).
 c. Positive MCA or BA end-diastolic flow is found = No cerebral
circulatory arrest.
 d. Absent end-diastolic flow = Uncertain cerebral circulatory
arrest (too early or too late).
 e. Reversed minimal end-diastolic flow = Possible cerebral
circulatory arrest [continue monitoring, document diastolic
blood pressure (BP) ≥50 mmHg].
 f. Reverberating flow = Probable cerebral circulatory arrest
(confirm in both MCAs at 50-60 mm and BA at 80-90 mm).

48. TCD monitoring of vasospasm in
subarachnoid hemorrhage
TCD can be used
 to detect asymptomatic vasospasm onset,
 follow spasm progression
 facilitate triple-H-therapy
 identify patients with severe vasospasm,
 monitor the effect of therapies and interventions
 and detect spasm resolution.

49.  In patients with subarachnoid hemorrhage and signs of
vasospasm, a submandibular approach can be used.
 Sample the distal ICA in the neck to calculate mean flow
velocity ratios between the MCA and ICA -- hemispheric
or Lindegaard index.

51. TCD monitoring of intracranial
pressure (ICP)
 TCD-derived pulsatility
index (PI) provides useful
information about ICP.

52. Fast-track ultrasound in acute
cerebral
ischemia
 A high yield and accuracy in diagnosing lesions
amenable to interventional treatment (LAIT), both in
patients eligible as well as ineligible for thrombolysis.
 LAIT is defined as an occlusion or near-occlusion or ≥
50% stenosis or thrombi in an artery (or arteries)
supplying brain area(s) affected by ischemia.

53.  The diagnostic yieid is particularly high when performed
early after the symptom onset.
 More than 70% of patients who have significant and fixed
neurological deficits show an arterial occlusion if
examined within the first 6 h of symptom onset.
 Up to 90% of patients who receive intravenous TPA
within the first 3 h after stroke onset demonstrate an
acute occlusion on TCD, particularly if the pretreatment
National Institute of Health Stroke Scale (NIHSS) is >10
points.

56. TCD Monitoring
The beginning, speed, timing, and amount of recanalization
represent important parameters of thrombolytic therapy for stroke
and are measured by following five parameters:
 1. Waveform change by > 1 TIBI residual flow grade
 2. Appearance of embolic signals (transient high intensity signals
of variable duration)
 3. Flow velocity improvement by > 30% at a constant angle of
insonation
 4. Signal intensity and velocity improvement of variable duration
at constant skull/probe interface and gain/ sample volume/scale
settings
 5. Appearance of flow signals with variable (> 30%) pulsatility
indexes and amplitude of systolic peaks.

57. Arterial recanalization can be classified as:
 1) sudden (abrupt appearance of a normal or stenotic
low-resistance signal),
 2) stepwise (flow improvement over 1 to 29 min), and
 3) slow (> 30 min).
 Rapid arterial recanalization is associated with better
short-term improvement.
 Slow flow improvement and dampened TIBI flow signals
are less favorable prognostic signs.

59.  Experimental evidence suggests that ultrasound
substantially increases the thrombolytic effect of TPA,
particularly if used in the low MHz-kHz frequency range.
 Ultrasound exposure causes various changes
-- reversible disaggregation of uncrosslinked fibrin fibers;
-- microcavity formation in the shallow layers of thrombus;
-- increase in the enzymatic transport of TPA,
-- improving its uptake and penetration of TPA into clots;
-- residual flow enhancement with microstreaming and
vessel dilation.

60. LIMITATIONS
 Operator-dependent technique requiring detailed three-
dimensional knowledge of the intracranial arterial
anatomy.
 Secondly, TCD is hampered by the 10-15% rate of
inadequate temporal windows most commonly seen in
Blacks, Asians, and elderly female patients.
 However, the temporal resolution and convenience of
TCD make it a vital asset to observing the evolution of
blood flow changes in the critically ill patient.

61. Thank you

62. Referrences
 Transcranial doppler: Technique and common findings(Part 1).
Bathala et al. Ann Indian Acad Neurol 2013;16:174-9.
 Transcranial Doppler: Techniques and advanced applications:
Part 2. Sharma et al. Ann Indian Acad Neurol 2016;19:102-
107.
 Role of transcranial Doppler ultrasonography in acute stroke.
Sharma et al. Ann Indian Acad Neurol 2008;11:S39-S51.
 AIUM Practice parameter—Transcranial Doppler Ultrasound
for Adults and Children. 2012
 Stroke Prevention Trial in Sickle Cell Anemia (STOP):
extended follow-up and final results. Lee et al. Blood, 1 august
2006 volume 108, number 3.