basics principles of transcranial ultrasound procedure in patients

1. Nitish kumar
Masters
(neuroscience &
technology)
Transcranialdoppler

2. Introduced by Rune Aaslid in 1982 for detecting blood flow in the basal
intracerebral arteries.
Important and established applications now incudes:
- Detection of the right to left cardiac shunt.
- Cerebral vasomotor reactivity
- Monitoring flow velocities for stroke prevention
- Continuous monitoring during thrombolysis
- Diagnosis of brain death.

4. Basic concept of ultrasound physics
Ultrasound are the waves of frequency >20KHz and are longitudinal in nature.
Types
Duty factor: pulse emition/pulse wave interval*100
Pulsed wave USG: transducer receives
the signal for most of the time (>90%)
Continuous wave ultrasound:
requires 2 transducers where one act
as emitter and the other as receiver.
- Not optimal for diagnostic studies as
it provides low spatial resolution.

6. Ultrasound transducers
Transmitters: converts electric
signals into ultrasound
Receivers: converts ultrasounds
into electric signals
Transceivers: can perform
both the functions

7. • Frequency
- Lower frequency and higher wavelength provides better sapling size
by increasing penetration through skull bones.
- Higher frequency and lower wavelengths probes are used in colour
flow and obtains a better structural gray scale imaging.

8. • Gate: the range of soft tissue which can be sampled depending upon
the depth. It is usually ( +-5% of depth).
• Focusing: procedure to shape the ultrasound beam to increase the
resolution. It includes:-
• 1. External: Changing curvature of the probe by putting lens ahead of
it.
• 2. internal: changing the curvature of piezoelectric crystals.
• 3. Phased array: for phased array transducers in duplex imaging.

9. Piezoelectric effect is a property of materials to generate voltage if
mechanically deformed and vice versa.
• Physical parameters and their determining factors:
1. Sound source: it determines the frequency and period if ultrasound
waves.
2. Soft tissues: it determines the propagation speed of the ultrasound
waves.
-the parameters like wavelength , intensity, amplitude, power is initially
determines by the source and as it passes the soft tissues can be
altered by them.
Propagation speed ∝ stiffness ∝ 1/density

10. Hemodynamicprinciplesgoverningdopplerultrasound
The factors affecting blood flow across a vessel if determined by several
factors:-
Blood flow ∝ change in pressure ∝ 1/resistance across the vessel
the resistance therefore is determined by –
 Length of vessel
 Cross sectional area/ diameter
 Viscosity of blood

11. Winkiesel effect: it is a property of arterial blood vessels to convert
energy received from heart to pulsatile energy during systolic ejections
& thus converting it into continuous pulsating waves for propagation
through the systemic system.
∝ distensibility of arterial walls

12. Types of blood flow
Laminar flow Turbulant flow
Parabolic or pluglike movement of blood in
layers
Consists of streamline flow as well as eddy
currents
Minimal energy loss doesn’t takes place due to
vessel resistance
Energy loss occurs
Eg: parabolic flow pattern and pluglike flow
pattern.
Eg: in stenosis and bifurcation of blood vessels

14. Themajoracousticwindowsinpulsed wave ultrasound includes:
Transtemporal: can be used to measure velocities in MCA,ACA,PCA& PCOM.
Transorbital: ophthalmic artery, Internal carotid artery
Suboccipital and transforaminal: allows insonation of vertebral arteries and
basilar arteries.

16. The Doppler effect
It is the change in the observed frequency of a wave when the source
and the observer move relative to the medium.
Doppler shift is the difference between the emitted and reflected
frequency of the wave.
- It can be used to determine the velocity and direction of moving
objects, such as blood flow, by analyzing the frequency difference
between the ultrasound waves.
D.S = 2*(blood speed*transducer frequency cosθ)/propagation speed

17. For transcranial vessels, major documented parameters
1. Peak systolic velocity:
2. End diastolic velocity
3. Mean flow velocity
4. Pulsatality index
5. Resistivity index:

18. • Lindegards ratio: MFV MCA/Unilateral ICA
• Soustel ratio: MFV BA/ Unilateral VA

20. Normal flow patterns at different levels

21. Abnormal findings in
transcranial doppler

22. Cerebral circulatory arrest (brain death)
• Brain death is seen on TCD as variying
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.

23. Methodology
1. Clinical examination followed by NCCT to obtain desired relevant history and side
of weakness.
2. The procedure should be started to the contralateral side of the infract, in order to
obtain a baseline and normative values for the patient. It also establishes a
indication of the affected side.
3. The probe to be placed angulated anterio-superior axis for examining th MCA.
4. Depth and other settings to be adjusted depending upon the patient.
5. For PCA, probe to be tilted medially/posteriorly.
6. USG gel to be used adequately to ensure proper contact b/w the skin and probes.

24. Thank you