transcranial doppler

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.