This document provides an overview of Doppler ultrasound, including:
- The physics of the Doppler effect as it relates to ultrasound imaging. Changes in frequency due to relative motion between a sound source and receiver.
- Two main types of Doppler imaging - pulsed wave Doppler which allows measurement of velocity and depth, and continuous wave Doppler which is better for measuring fast flow.
- Additional Doppler modes like color Doppler, power Doppler, and spectral Doppler which display Doppler information in different ways.
- Applications of Doppler ultrasound include evaluating blood flow, detecting fetal heartbeats, and more.
Learn from our Slideshare about the differences between ultrasound transducers. We also cover tips on how to treat your probes and how to select the right one.
Learn from our Slideshare about the differences between ultrasound transducers. We also cover tips on how to treat your probes and how to select the right one.
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History of ultrasound, Principle of Ultrasound.
Ultrasound wave and its interactions
Ultrasound machine and its parts, Image display, Artifacts and their clinical importance
what is Doppler ultrasound, Elastography and Recent advances in field of ultrasound.
Safety issues in ultrasound.
Definition of Side lobes and the principle behind its production during ultrasound imaging. Side lobes artifact and its result on image. Explanation of harmonic imaging, its production and the techniques use to eliminate fundamental frequency to produce optimal harmonic images.
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what is Doppler ultrasound, Elastography and Recent advances in field of ultrasound.
Safety issues in ultrasound.
Definition of Side lobes and the principle behind its production during ultrasound imaging. Side lobes artifact and its result on image. Explanation of harmonic imaging, its production and the techniques use to eliminate fundamental frequency to produce optimal harmonic images.
SELDINGER TECHNIQUE & INTERVENTIONAL RADIOLOGYRiyas M K
its a basic introduction about Seldinger technique and Intervetional radiology.In interventional radiology, procedures generally start with the Seldinger technique to access the vasculature, using a needle through which a guidewire is inserted, followed by navigation of catheters within the vessels.
This slide contain application of ultrasound and biological effects of ultrasound , ppt contains many GIF files and notes , which may not be accessible here ,,
Doppler Effect ultrasound is a non invasive procedure by which high frequency sound sound waves are used to visualize the blood vessels where by the red indicate as the arteries and blue indicates as veins.
Doppler Effect is the apparent change in frequency and wavelength when the observer and source are in relative motion
This concepts of Doppler physics contents are introduction, history, on which principle it works, applications of this physics Doppler angle types of flow types of Doppler advantages disadvantages and summary
Electromagnetic Flow meters
Blood flow helps to understand basic physiological processes and e.g. the dissolution of a medicine into the body.
Blood flow and changes in blood volume, are usually correlated with concentration of nutrients and other substance in the blood.
Also, Blood Flow measurement reflects the concentration of O2.
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Craniospinal Irradiation (CSI) is often implemented for treatment of childhood medulloblastoma. For adults, the use of CSI is more complicated because of the very long field length (>54 cm). This case report shows the implementation of a CSI plan using IMRT with Three-Isocentre Overlap Junction (TIOJ).
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Phyllodes tumour of the breast is a rare fibroepithelial tumour, composed of an epithelial and a cellular stromal component.
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The research raises the need for optimization in radiotherapy of children. It compares IMRT, Proton Therapy, Electron Beam Therapy and Conventional Radiotherapy.
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IORT uses a high single-fraction radiation dose (10-30 Gy) is delivered during surgery to a surgically-exposed tumour bed, immediately after a chunk of the tumour has been surgically excised. This slide includes topics like APBI, IOERT, IOHDR.
An overview of Renography - the medical imaging of kidneys using Nuclear Medicine - including its advantages and disadvantages over other Radiographic imaging modalities.
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Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
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Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
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Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
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Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
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the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
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NVBDCP was launched in 2003-2004 . Vector-Borne Disease: Disease that results from an infection transmitted to humans and other animals by blood-feeding arthropods, such as mosquitoes, ticks, and fleas. Examples of vector-borne diseases include Dengue fever, West Nile Virus, Lyme disease, and malaria.
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2. OUTLINE
• Introduction
• Physics of Doppler Effect
• Conditions for Doppler Effect
• Classifications
• Types
• Modes
• Applications
• Artifacts in Doppler Imaging
• Conclusion
2
3. INTRODUCTION
• Ultrasound is sound waves with frequency greater than
20kHz (Medical Ultrasound range: >2MHz)
• Sound waves travelling through a medium can be
reflected, refracted, absorbed or transmitted.
• Reflection occurs at the point of acoustic impedance
mismatch.
3
4. MOVING SOUND
• One or both the sound source and receiver may be
stationary or moving.
• If the sound source moves towards the listener, the
sound is perceived to have a higher frequency/pitch, and
a lower frequency as it moves away from the
listener.
4
5. DOPPLER EFFECT
Doppler effect is the change in frequency of
sound (or any wave) due to the relative motion* of
the source and receiver.
Doppler Shift (Δf) = Reflected Frequency – Transmitted frequency
Doppler angle ( θ ) = Angle between the direction of source – direction of sound
5
6. CONDITIONS FOR DOPPLER SHIFT
The Doppler effect will NOT occur:
• If the source and observer both move in the same direction at the
same speed.
• Where one source/listener is at the centre of a circle while the
other is moving on it with uniform speed.
• If the source/receiver is at 900 to the receiver/source.
6
8. 8
Sound waves reflected from a moving object are compressed
(higher frequency) when moving towards the listener/
transducer,
…and expanded (lower frequency) when moving away from
the listener/transducer compared to the incident sound
wave frequency.
10. The velocity of sound (c) is given by the equation,
Speed, c =
𝑊𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ (λ)
𝑃𝑒𝑟𝑖𝑜𝑑 (𝑇)
= Wavelength (λ) * frequency (f)
λo =
𝑐
𝑓 𝑜
Consider a sound source travelling at a velocity 𝒗 𝒔 towards a detector.
After time t, the new wavelength,
λ1 =
𝑐 − 𝒗 𝒔
𝑓 𝑜
10
PHYSICS OF DOPPLER EFFECT
𝒗 𝒔
c
11. With a shortened wavelength, the new frequency f1 is given by:
f1 =
𝑐
λ1
=
𝑐
(c−vs) / fo
f1 = fo
𝑐
( 𝑐 − 𝒗 𝒔
)
Δf = f1 - fo = fo
𝑐
( 𝑐 − 𝒗 𝒔
) - fo
= fo
𝑐
( 𝑐 − 𝒗 𝒔
) - 1
= fo
𝑐 −( 𝑐 −𝑣𝑠 )
( 𝑐 − 𝒗 𝒔
)
Δf = fo
𝑣 𝑠
( 𝑐 − 𝒗 𝒔
)
If c >> vs , then
Δf = fo
𝑣 𝑠
𝑐
11
12. A similar equation can be written for a detector moving towards a source,
Δf = fo
𝑣 𝑑
𝑐
It can be shown that for a source moving away,
λ1 =
𝑐 + 𝒗 𝒔
𝑓 𝑜
Δf = fo
−𝑣 𝑠
𝑐
OR fo
−𝑣𝑑
𝑐
For a 2-way motion where a transducer emits ultrasound of frequency f,
and it gets reflected back by moving blood of velocity v (and c>>v), then:
Δf = 2f
𝑣
𝑐
12
13. If direction of motion is oblique, then:
Δf = (2vf Cos θ) /c
where:
Δf = Doppler shift
f = transducer frequency
v = velocity of source/receiver
c = velocity of sound
θ = Doppler angle 13
PHYSICS OF DOPPLER EFFECT (contd.)
14. • Doppler shift, Δf increases with:
• increasing source velocity v, and
• increasing transducer frequency, f
• Δf is maximum at θ = 0o and minimum at θ = 90o.
• To experience Doppler effect, θ ≠ 90o
14
Δf = (2vfCos θ) /c
Doppler Shift = 2 x Velocity of Blood x Transducer Freq x Cos θ
Propagation Velocity of Sound
FACTORS AFFECTING DOPPLER SHIFT
15. If the object is moving perpendicular (θ=90o) to the ultrasound beam, there is no change
in frequency or wavelength.
By measuring the frequency shift, Doppler Ultrasonography can be used to determine
any or all of these 4:
• Speed
• Direction
• Flow (Laminar or Turbulent)
• Location
15
Δf = (2vfCos θ) /c
16. USES OF DOPPLER METHOD
With Doppler, US can be used for static and dynamic imaging.
The Doppler method can be used for:
• detection and characterization of blood flow,
• detection of foetal heartbeat,
• detection of air emboli,
• blood pressure monitoring, and
• localization of blood vessel occlusions.
16
19. CONTINUOUS WAVE DOPPLER
• It is a continuous wave of ultrasound being sent into
the body.
• Measures mainly the velocity of moving blood.
19
20. CW: TRANSDUCER PROPERTIES
• CW uses a relatively narrow-band high-Q transducer, to
preserve velocity information.
20
21. CW: TRANSDUCER PROPERTIES
• The piezoelectric elements of the transducer are divided into 2:
• Transmitter: continuously transmitting US, and
• Receiver: detecting reflected echoes.
Doppler Shift = Received Freq – Transmitted Freq
21
22. 22
Transmitter and Receiver are angled
against each other.
The Transmitter produces sinuosoidal US
waves of the form Cos 2πfot.
The received signal is of form:
Cos [ 2π (fo + fD) t ]
The Doppler signal is thus of form:
Cos 2πfDt , and can be recovered via
frequency demodulation of the
received signal.
Fig: CW Doppler Scan Geometry (angled Tx and Rx)
23. WALL FILTER: CW DOPPLER
• The Doppler signal contains very low frequency signals
(clutter) from moving specular reflectors, such as blood vessel
walls.
• A "Wall Filter" selectively removes these other low
frequencies.
23
24. BEAT: CW DOPPLER (contd.)
• The Doppler ultrasound signal is amplified to an audible
sound level (called Beat).
• Doppler Beat can be heard through a speaker or a
headphone.
24
25. CW DOPPLER (contd.)
• The audio indicates the spread of velocities involved in a
heart beat.
• It forms the basis of the ultrasound stethoscope for
foetal heartbeat monitoring.
25
26. Fig: Foetal Heart Rate (FHR) Doppler Detector
Some also display the Heart Rate in Beats Per Minute (BPM)
Uses the principle of Continuous Wave Doppler. 26
27. BEATS: CW DOPPLER (contd.)
• The higher the pitch, the greater the velocity.
• The harsher the sound, the greater the turbulence.
27
Δf = (2vfCos θ) /c
29. CW DOPPLER (contd.)
• Output can also be displayed on a Spectrum analyser,
constructing a pixel grayscale.
• Quadrature Detection (type of signal processing) permits
determination of the direction of flow of blood in CWD, if
used.
29
30. CW DOPPLER SPECTRAL DISPLAY
• The pixel greyscale represents the magnitude of the short
time Fourier Transform of the Doppler signal.
• A pixel in a Doppler spectrum represents the proportion
of red blood cells (RBCs) in the field of view that was
moving at a particular velocity at a particular time.
30
31. LIMITATIONS OF CW DOPPLER
• Poor Spatial Resolution: resulting from the large area of overlap
between the transmitter and receiver beams.
• Range Ambiguity: Measures velocity, but not location.
• CW cannot be used to distinguish the flow of overlapping vessels
at different depths.
• Lack of TGC (time gain compensation).
31
32. ADVANTAGES OF CW DOPPLER
• For measuring fast flow (high velocities) without aliasing.
• Good for assessing deep-lying vessels.
• It is inexpensive.
32
33. PULSED WAVE DOPPLER
• It transmits a sequence of short pulses, rather than a
continuous sinusoidal wave.
• PW allows both velocity and depth information to be
obtained.
33
34. PW DOPPLER (contd.)
• One single group of array elements is used for both receiving and
transmitting.
• PW Doppler allows measurement from a small, specific blood volume
(region of interest), which is defined by a sample volume.
• After the pulse has traveled forth and back (travel time T), an electronic
range gate is opened for a short period of time to receive the echoes.
34
35. OPTIMIZING PW
• Doppler Shift measurement: Achieved using longer
spatial pulse length (SPL)/high Q-factor transducer.*
• Depth Selection: Achieved with an electronic time gate
circuit (or range gate) to reject all echo signals, except
those falling within the determined gate window.
35
36. SAMPLE AND HOLD OPERATION
As the echo from each successive transmission is received, a
single sample at the expected arrival time of echoes from the
range gate is acquired and held until the echo from the next
pulse is received.
36
37. Fig: Sample-and-
Hold Operation of
PW Doppler
37
If the reflectors are moving, the signal received from the range gate will
change with each subsequent pulse, and the sample-and-hold operation will
construct a staircase signal (as above).
38. PW DOPPLER (contd.)
• The second pulse should be transmitted no sooner than the
expected arrival time of the echoes from the range gate that arise
from the first pulse*.
• The pulse travel time T determines the shortest possible time
interval between two successive transmit pulses.
38
39. Pulse repetition Frequency (PRF) is the number of pulses that an ultrasound
system transmits into the body each second.
The PRF of the transmitted pulses is the effective sampling frequency.
PRF = 1/T
The maximum detectable frequency shift (Nyquist Limit) is determined by
the value of one-half PRF.
fmax = ½ PRF
39
NYQUIST LIMIT
40. CONDITION TO AVOID ALIASING:
The PRF must be at least twice the Nyquist Limit.
PRF ≥ 2 fmax
40
NYQUIST LIMIT
fmax = ½ PRF
PRF = 2 fmax
Otherwise, at high blood velocities, aliasing will occur.
41. Fig A: Aliasing as shown in spectral Doppler effect
41
Aliased signals wrap around to negative amplitude,
masquerading as reversed flow and underestimating velocity.
A
42. PW MAX. VELOCITY
• Recall Doppler frequency is given by:
Substituting Maximum PW Doppler Frequency fmax for Δf, we get:
fmax = (2 vmax f Cosθ ) /c
PRF/2 = (2 vmax f Cosθ ) /c
42
Δf = (2vfCos θ) /c
vmax = cPRF
4fCosθ
43. PW MAX VELOCITY
• vmax represents the maximum velocity of reflector (e.g.
RBCs) that can be measured without aliasing.
• For a range gate positioned at depth z,
z = ½ λ
PRF = c/2z
43
vmax = ___c2____
8 z f Cosθ
vmax = cPRF
4fCosθ
44. PW MAX. VELOCITY
• The maximum velocity that can be accurately
determined by Pulsed Doppler increases with PRF,
lower operating frequency, and increasing angle.
44
vmax = ___c2____
8 z f Cosθ
vmax = c PRF
4 f Cosθ
45. DISADVANTAGES OF PW DOPPLER
PW cannot accurately measure fast blood velocities due to aliasing.
To avoid aliasing:
• increase the PRF
• increase Doppler angle
• reduce the depth
• reduce the transducer frequency
• change the baseline
• use CW instead.
45
vmax = ___c2____
8 z f Cosθ
47. MULTIGATED (MG) PULSED WAVE DOPPLER
• This is a variation of Pulsed Wave Doppler.
• Whereas PW Doppler system can only provide information from a particular
sample, MG PW Doppler obtains information from several depths
simultaneously using multiple gates.
• After demodulation, the received signal is directed to a number of parallel
processing chains - each with slightly different range of gate settings. 47
48. MG PW DOPPLER (CONTD.)
• Velocity distribution profile across the vessel cross-section can be
determined.
• It is a useful diagnostic tool for presence of plaques and stenosis.
• Orientation and location of a desired vessel still remain a problem, which
can be solved by Duplex Scanning.
48
49. MODES OF DOPPLER IMAGING
To display Doppler information, one of 3 modes may be chosen:
• Color Doppler
• Power Doppler
• Spectral Doppler
49
51. COLOUR DOPPLER (CD or CCD)
• Color (flow) scanning involves displaying Colour Doppler data
on real time (B-mode) grayscale images.
• The superimposition is such that tissue volumes containing
• no detectable flow are displayed in greyscale,
• while those in motion are in colour (usually red and blue).
51
52. COLOUR DOPPLER
Colours are assigned, depending on:
• DIRECTION : motion towards (Positive Doppler shift) or
(Velocity Mode) away (Negative Doppler shift) from the transducer.
• FLOW (Variance Mode): Laminar or Turbulent flow
• VELOCITY MAGNITUDE: mapped to the colour intensity
52
54. LIMITATIONS OF COLOUR DOPPLER
• Clutter of slow-moving solid structures and noise can
overwhelm the smaller echoes from moving blood.
• Spatial resolution of the colour image is lower than
grayscale.
54
55. USES OF COLOUR DOPPLER
• Imaging the heart and major blood vessels in
applications for which mean flow velocity is a
diagnostically useful parameter.
• To recognize and localize vessels and vascular blockage.
55
56. POWER DOPPLER
• Power Doppler represents the total power in the
Doppler spectrum at each sample volume.
• Unlike colour Doppler, Power Doppler usually
uses a single colour.
56
57. POWER DOPPLER
1. Power Doppler uses the magnitude of return Doppler
signal strength / power /intensity / amplitude alone.
2. It ignores the angle and direction of flow (phase).
3. It adopts slower frame rates and thus has greater
sensitivity to motion of the patient, tissues, and
transducer. 57
Power α Intensity α Amplitude2
61. ADVANTAGES OF POWER DOPPLER
• PW’s greater sensitivity to motion allows detection and interpretation of
very subtle and slow blood flow.
• Power Doppler provides a more continuous display of tortuous vessels.
• Helps to rule out vascular occlusions,
• Helps to differentiate between blood carrying vessels and other fluid
occurrences
• It is not prone to aliasing.
61
62. DISADVANTAGES OF POWER DOPPLER
• It is susceptible to flash artifacts, which are colour signals due to its greater
sensitivity to motion.
• No information on flow velocity and direction of flow.
• Evaluation of hemodynamic properties such as the pulsation of flow, is
limited, since, most often, the image frame rate is too low.
62
63. USES OF POWER DOPPLER
• Used for tumour imaging, where moving blood volume is a
diagnostically useful parameter.
63
64. SPECTRAL DOPPLER
• The Spectral Doppler uses the Doppler frequency shift of the
echo signal as a measure of flow velocity and direction of flow.
• The Doppler spectrum ascertains the distribution of flow
velocities and their frequencies of occurrence at a defined
sampling site as a function of time.
64
65. SAMPLING SITE: SPECTRAL DOPPLER
• The sampling site is determined by using B-mode, Color Doppler
or Power Doppler image display (Duplex imaging).
65
SPECTRAL DOPPLER
66. The spectra from within or directly behind a stenosis (numbers 2 to 4) show increased
velocities, turbulence and reverse flow.
These changes in spectrum provide information on flow in the blood vessels.
66
67. FLOW
• Laminar flow normally exists at the centre of large
smooth vessels.
• Turbulent flow occurs when the vessel is disrupted by
plaque and stenosis.
67
68. USES OF SPECTRAL DOPPLER
68
SPECTRAL DOPPLER
• Spectral Doppler provides a detailed qualitative, semi-
quantitative or quantitative evaluation of hemodynamic
changes in tissues.
69. DUPLEX SCANNING
• Duplex scanning combines 2D B-mode imaging and a Doppler
type (e.g. Colour Doppler).
• The duplex system allows estimation of the flow velocity directly
from the Doppler shift frequency.
69
72. (SOFT) TISSUE DOPPLER IMAGING
• Used to image soft tissue using a low pass filter.
• A conventional Doppler system assumes blood flow is concentrated at
intermediate and high velocities, while scatterers moving at low
velocities correspond to soft tissue.
• Therefore to eliminate such low velocities, a high pass wall filter is
usually used.
72
73. (SOFT) TISSUE DOPPLER IMAGING
• Tissue Doppler Imaging replaces the high pass wall filter with a
low pass filter, thus allowing only low Doppler frequency signal,
corresponding to low velocity movements.
• Can be done in Pulsed Wave Doppler mode or Colour Doppler mode.
• Used in diagnosing regional abnormalities in ventricular wall motion.
73
74. TRANSCRANIAL DOPPLER ULTRASONOGRAPHY (TCD)
• TCD is a non-imaging Pulsed Wave Doppler technique measuring
local blood flow velocity and direction in the proximal portions
of large intracranial arteries.
• Used for evaluation and management of patients with risk of
cerebrovascular disease.
74
75. TCD: Stroke Prevention for Children with SCD
• In 2017, Dr. M. Adekunle and Prof. O. Akinyanju (of Sickle Cell
Foundation Nigeria) recommended annual screening of children
with Sickle Cell Disorder (SCD to assess risk of stroke.
• Children aged 2-16 years with Sickle Cell Disorder (SCD) have a
high risk of stroke, esp. children aged 2-8 years.
75
76. TCD: Stroke Prevention for Children with SCD
• Stroke occurs when part of the brain is damaged by inadequate
blood supply.
• Inadequate blood supply occurs due to cerebral bleeding
(bleeding from arteries) or thrombosis (blood clots), which
impede flow of blood in the arteries of the brain.
76
77. If the velocity in an artery exceeds 250cm/s, that area is at a higher risk of stroke
[Adams]. 77
Fig: Transcranial Doppler Ultrasound of blood vessels in the Circle of Willis of the brain
78. TCD: Stroke Prevention (contd.)
• Stroke can cause paralysis, seizures, loss of speech or reduced
intellectual capacity.
• Stroke prevention therapy can be carried out for affected children.
• Adekunle and Akinyanju recommend establishment of more TCD
centres across Nigeria.
78
81. ALIASING
• Aliasing is error due to insufficient sampling rate PRF
• It causes high velocity forward flow to appear as reverse flow.
• Occurs in Colour Doppler, but not Power Doppler.
81
83. Due to reverberations and mirroring at strong reflectors, images in Color or
Power Doppler show artifacts, similar to those observed in B-mode.
e.g. mirroring of hepatic vessels at the diaphragm.
83
84. Caused by tissue vibrations at the site of an arterial-venous fistula, occlusion or
stenosis. pulsating blood pressure is transmitted to adjacent tissue causing tissue
vibration.
This is due to pulsating blood pressure at occlusions transmitted to adjacent
tissue, recognized as a colour mosaic. 84
85. • Due to changing Doppler angle
and transducer type used.
• Occurs only in Colour Doppler
(Doppler angle does not affect
Power Doppler)
• It can lead to Reverse-Flow and
Flow Acceleration artifacts.
85
• Convex/Sector Transducer & Linear Vessels: Curved transducer aperture
introduces Doppler angles, causing inaccurate depiction of blood vessel velocities.
• Linear Transducer & Curved Vessels: Produces similar effect as the above.
86. In the display of blood flow in the verterbral column in the Power Doppler mode,
due to strong reflectors (bones), a shadow is cast on the blood vessels, making
them look interrupted.
86
87. OTHER FORMS OF ANGIOGRAPHY (DSA vs CT vs MR)
• Digital Subtracted Angiography is the ‘gold standard’ in arterial
imaging.
• It uses X-ray based fluoroscopy.
• It produces its image by subtracting a pre-contrast image with an image
taken after injection of a contrast medium.
• It is considered invasive, as it involves use of catheter.
• It requires the patient to be still, and thus not favoured for heart
imaging.
87
88. OTHER FORMS OF ANGIOGRAPHY (DSA vs CT vs MR)
CT Angiography (CTA) has the advantage of producing 3D
images. It is less invasive and stressful for the patient.
MR Angiography (MRA) avoids ionizing radiation and
nephrotoxic contrast agents.
88
89. CTA vs MRA
Advantages of CTA over MRA include:
• Visualization of calcified plaques and
• Insusceptibility to metallic vascular clips.
• Lower cost: Iodinated contrast material for CT angiography is
less expensive than the dose of gadolinium required for MR
angiography.
89
90. CTA vs MRA
• Coronary Artery Disease: CTA offers better sensitivity and
specificity better than MRA.
• Arterial Stenosis of the Aortoiliac and Renal Arteries: No
statistically significant difference between CTA and MRA.
90
91. CTA vs MRA
• Aorto-iliac Arterial Disease: CTA shows higher sensitivity
(98.7%) than CCD (96.2%) in the assessment of aorto-iliac
arterial disease [A. Osama et al, 2012 ].
• Agreement between DSA and CCD was 96.1%
91
92. • Doppler Ultrasonography has a relatively high sensitivity in
comparison with digital subtraction angiography.
• It is cheaper, less-invasive, non-ionizing and offers minimal risk
of bio-effects.
92
CONCLUSION
93. REFERENCES
D. R. Dance, et al. Diagnostic Radiology, Physics. IAEA. 2014: Vienna.
M. A. Aweda. Principles of Doppler Imaging. Lagos University Teaching Hospital. Lagos. 2012.
K. O. Soyebi. An Introduction to Transcranial Doppler Imaging. Lagos University Teaching Hospital. Lagos.
2012.
J. T. Bushberg, et al. The Essential Physics of Medical Imaging. 2nd Ed. Philadelphia: Lippincott Williams &
Wilkins. 2002.
W. Huda, R. Sloan. Review of Radiologic Physics. 3rd ed. Philadelphia: Lippincott Williams & Wilkins. 2009.
M. Adekunle, O. Akinyanju. Prevention of Stroke in Children with Sickle Cell Anaemia. Sickle Cell Bulletin.
Vol 8. No. 1. Sickle Cell Foundation Nigeria. 2017.
Siemens AG. Principles of Ultrasound Imaging. 1999: Med USSE
J. M. Adams. Ultrasound’s Transcranial Doppler Imaging Checks for Risk of Stroke. 2016. Cincinnati
Children’s Hospital. http://www.blog.cincinnatichildrens.org/radiology/
W. R. Hendee, E. R. Ritenour. Medical Imaging Physics. 4th Ed. New York: Wiley-Liss. 2002.
A. Osama, et al. Role of Multi-Slice CT Angiography versus Doppler Ultrasonography and Conventional
Angiography in assessment of aorto-iliac arterial disease. Egyptian Journal of Radiology and Nuclear Medicine.
2012.
R. Herzig, et al. Comparison Of Ultrasonography, CT Angiography, and Digital Subtraction Angiography In Severe
Carotid Stenoses. European Journal of Neurology. 2004.
93
NEWTON’S 1ST LAW OF MOTION & ITS RELATION
Doppler effect will not occur if both the source and receiver are both static, or both moving at the same speed in the same direction.
Doppler effect can happen in light and aby other wave.
This is explained in Slide 12.
Moving is in acircle is same distance. Source/Receiver has to move away or towards.
Sound emitted is continuous sound. So subsequent waves take longer/shorter to reach , thus appearing as a frequency change.
Frequency of sound is determined by the source (and now detector) only.
Speed is determined by the medium only.
Wavelength is det. by both source and medium.
Emboli: (sing. Embolus) : a mass, most commonly a blood clot, that becomes lodged in a blood vessel and obstructs it.
Air embolus is air that escapes from lungs to blood vessels, blocking some artieries. Usually if divers emerge from a depth too quickly.
But with quadrature detection, direction of flow is also possible.
where fo is the centre frequency and the bandwidth is the width of the frequency distribution.
The Doppler signal from the clutter is much greater than that from blood.
Beats can be recorded to track spectral changes as a function of time to assess transient pulsatile flow.
These are becoming very popular in the developed world, and cost just over $100.
SEE FORMULA.
Resolution is very low, due to use of high Q transducer.
Fourier Transform is used to construct an image.
Lack of TGC: Reflections created from RBC located at deeper depth will have a low amplitude than reflections from shallower depth.
Uses the same crystals to send and receive the signal.
Longer spatial pulse length give poorer axial resolution. Axial Resolution = SPL/2. Lower numerical values of axial resolution give better image quality.
PW Doppler works with samples.
This is determined by the depth of the range gate. The pulse travel time T determines the shortest possible time interval between two successive transmit pulses.
Using Shannon’s sampling theorem, the maximum unaliased frequency is as given above.
The PRF must be at least twice the sampling max Doppler freq shift.
Using Shannon’s sampling theorem, the maximum unaliased frequency is as given above.
The PRF must be at least twice the sampling max Doppler freq shift.
Aliasing is an an error caused by an insufficient sampling rate
(PRF) relative to the high-frequency Doppler signals generated by fast moving
Corrected here by adjusting the baseline.
V(max) represents maximum velocity that can be measured by PW Doppler effect
Just like in CW Doppler, demodulation is used to obtain velocity information from the echo signal by separating the Doppler signal of frequency f from the received signal.
Main diff is that PW includes a Sample and Hold & Range Delay
This allows for a number of adjacent sample volumes to be positioned across a vessel
Thus the problem of locating the vessel is greatly reduced
Acquisition of image information is interleaved with that of flow information.
Red and blue are used. But any colour scheme can be chosen.
What are flash artifacts?
Fluid occurences may be static. Blood vessels carry dynamic blood.
What are flash artifacts?
Since Doppler power is proportional to the concentration of moving blood cells in the sample volume, it is typically used for tumour imaging, where blood volume is a diagnostically useful parameter.
Systolic: heart contractions – during which blood is pumped into arteries
Diastolic: expansion of each heartbeat
The duplex system allows estimation of the flow velocity directly from the Doppler shift frequency.
, since the velocity of sound and the transducer frequency are known,
while the Doppler angle can be estimated from the B-mode image by the user and input into the scanner computer for calculation.
The duplex system allows estimation of the flow velocity directly from the Doppler shift frequency.
, since the velocity of sound and the transducer frequency are known,
while the Doppler angle can be estimated from the B-mode image by the user and input into the scanner computer for calculation.
Fistula is an opening caused by disease. Stenosis and occlusions are obstructions or constrictions.
Fistula is an opening caused by disease. Stenosis and occlusions are obstructions or constrictions.
Sensitivity: True positive rate. Ability to correctly identify those with disease
Specificity: Tue negative rate. Ability to correctly identify those without disease.