TITLEVascular Tutorial (SET XXX)

INSERT DATE

Principles of UltrasoundVascular Tutorial (SET 1 and 2)

20 July 2020

Clinical Scenario 2• You are doing your ultrasound lab morning and scan a patient with

increasing claudication symptoms.

• The patient has had a right SFA angioplasty in the past.

• You obtain the following images...

Imaging

Learning Objectives 2• Interpret the ultrasound findings and describe the salient features

that you will include in the report. • Describe the concept of beam steering and why that is important in

this instance including methods to alter the beam (including arrays and electronic focusing).

• Discuss factors that influence image quality and accuracy with reference to principle image artefacts.

Ultrasound report preamble• An arterial duplex ultrasound was performed of the left lower limb in

a patient with increasing left leg claudication symptoms and a history of right SFA angioplasty.

SFA proximal

SFA mid

Lower extremity spectral waveforms

Normal

1-19% diameter reduction

20-49% diameter reduction

50-99% diameter reduction

Waveform features

University of Washington Duplex Criteria for Classification of Lower Extremity Arterial Stenosis

PSV Ratio PSV at stenotic segment / normal segment

Degree of stenosis

<150 cm/s <1.5 Normal

150-200 cm/s 1.5-2.0 30-49%

200-400 cm/s 2.0-4.0 50-75%

>400 cm/s >4.0 >75%

No colour flow - Occlusion

Grading via velocity shift

Cossman DV, Ellison JE, Wagner WH, et al. Comparison of contrast arteriography to arterial mapping with color-flow duplex imaging in the lower extremities. J Vasc Surg. 1989;10(5):522-529

SFA• The left superficial femoral artery is patent with triphasic flow. There

is calcified but non-haemodynamically significant disease along its imaged length. There is a moderate (30-49%) stenosis in the mid-SFA (PSV 131.9 cm/s).

Popliteal• The popliteal artery appears patent with significant calcific disease.• In the proximal popliteal artery, there is dampened monophasic flow

with a delayed systolic upstroke suggestive of a high-grade proximal popliteal stenosis.

• The mid-popliteal artery is patent with a severe (>75%) stenosis (PSV 495 .5 cm/s).

• The distal popliteal artery is patent with dampened monophasic flow and reduced systolic velocity.

Linear array transducer

Courtesy of Dr Rachael Nightingale https://radiopaedia.org/cases/54644

From FW Kremkau. 2 - Principles and Instruments of Ultrasonography, Introduction to Vascular Ultrasonography (Seventh Edition), edited by JS Pellerito & JF Polak.

Beam steering• Directs (additional) ultrasound

beams at angles from transducer footprint

• Delays added to transmit and receive timing of beam

• Allows one point to be insonated from multiple angles

• Broadens imaging field at depth• Reduce speckle (compound

scanning)

Courtesy of Dr Hamish Smithhttps://radiopaedia.org/cases/68392

From FW Kremkau. 2 - Principles and Instruments of Ultrasonography, Introduction to Vascular Ultrasonography (Seventh Edition), edited by JS Pellerito & JF Polak.

Beam focusing• Similar principle• Time delays to “transmit focus”

• Fire outer elements first• Central element last

• Composite pulse converges at a focal point at depth

Courtesy of Dr Hamish Smithhttps://radiopaedia.org/cases/68386

Beam steering in Doppler

From FW Kremkau. 2 - Principles and Instruments of Ultrasonography, Introduction to Vascular Ultrasonography (Seventh Edition), edited by JS Pellerito & JF Polak.

• Use beam steering to indicate the Doppler angle

Optimising colour flow

Velocity range (PRF): decrease for slow flowTransducer frequency: are you using the correct transducer for the study?

Doppler angle: be sure to angle correct to the vessel, 60 degrees or less

Field of view: optimize your scanning window

Color box size: use a small color box when possible

Color gain: adjust your color gain to boost signal and avoid noiseSpectral Doppler gain: be sure to increase gain until noise appears

Power Doppler: always helpful for slow flow states

Color priority: check to be sure priority is not set too low

Wall filter: keep as low as possible in low flow states

Acoustic shadowing

• Signal void behind structure that strongly absorbs or reflects ultrasound

• Calcified plaque• Air

• Difficult to sample these areas

Aliasing in pulsed Doppler

• Aliasing caused by intermittent Doppler sampling

• Cannot record direction and velocity accurately

• Nyquist limit: PRF needs to be x2 Doppler frequency

• Below this = aliasing• Incorrect spectral display

From FW Kremkau. 2 - Principles and Instruments of Ultrasonography, Introduction to Vascular Ultrasonography (Seventh Edition), edited by JS Pellerito & JF Polak.

Aliasing in pulsed Doppler

From FW Kremkau. 2 - Principles and Instruments of Ultrasonography, Introduction to Vascular Ultrasonography (Seventh Edition), edited by JS Pellerito & JF Polak.

Aliasing in colour Doppler

From FW Kremkau. 2 - Principles and Instruments of Ultrasonography, Introduction to Vascular Ultrasonography (Seventh Edition), edited by JS Pellerito & JF Polak.

Sample volume

• 3D volume• “Thickness” not displayed• Only get information from

positioned sample volume• Can sample flow from adjacent

branch!

From JS Pellerito & JF Polak, 3 - Doppler Flow Imaging and Spectral Analysis, Introduction to Vascular Ultrasonography (Seventh Edition), edited by JS Pellerito & JF Polak.

References• Introduction to Vascular Ultrasonography (Seventh Edition), edited by

JS Pellerito & JF Polak.• Radiopaedia• Cossman DV, Ellison JE, Wagner WH, et al. Comparison of contrast

arteriography to arterial mapping with color-flow duplex imaging in the lower extremities. J Vasc Surg. 1989;10(5):522-529