Carotid Duplex Ultrasound The neil mclean seminar

The demonstration of appropriate workflow competency 1 The demonstration of appropriate workflow

B-Mode Imaging Transverse sweep CCA, carotid bulb, bifurcation  ICA + ECA Identify plaques and intimal thickening Assess approach required for Doppler imaging Identify incidental pathology In B-mode I sweep the transducer in transverse orientation through the common carotid, carotid bulb, internal carotid and external carotid arteries. During this sweep I am looking for plaques and intimal thickening and noting the position of them on the patients neck or distance from nearby structures e.g. that big solid echogenic shadowing plaque there near the superior pole of the thyroid. This is also a good opportunity to look at surrounding structures for incidental findings. I am also assessing the approach required for the rest of the examination i.e. how high is the bifurcation, how tortuous are the vessels etc. If I find plaque during this sweep I make an assessment in B-mode, power Doppler and B-flow imaging (see below: Plaque Morphology).

Colour Flow Imaging Longitudinal survey Identify aliasing For each of the three main vessels of the study (CCA, ICA and ECA) I survey the vessel longitudinally with colour flow Doppler to determine any points of aliasing (see ICA Stenosis). A longitudinal image of each vessel representing my findings is recorded.

Doppler Velocity Measurement Four main vessels of interest: Common carotid artery (CCA) Internal carotid artery (ICA) External carotid artery (ECA) Vertebral artery Once the morphological assessment is complete, I turn my attention toward measuring the velocity through each of the four main arteries of interest – CCA, ICA, ECA and vertebral.

CCA Two or three traces Determine optimal point of signal strength Assess for waveform changes I will perform a few traces of the CCA in order to not only determine where the optimal signal strength is to be had but also to assess the waveforms for indications of changes distally (see below: CCA Changes). Once the best signal strength is found I record the peak systolic and end diastolic velocities to the worksheet. Same vessel, better signal

ECA Waveform recorded is representative Representative Colour flow image carries equal diagnostic weight An ECA waveform is then recorded. The peak systolic velocity and waveform changes are secondary in my mind to the demonstration of the length of the artery in B-mode, B-flow and power Doppler. This is discussed below (see: ECA Stenosis).

ICA Primary focus for carotid duplex examination Highest clinical impact for stenosis NASCET criteria equivalent to PSV The ICA is the primary focus of the carotid duplex examination, the vessel for which the most evidence exists as to the utility of ultrasound in investigating stenosis. I examine the vessel carefully during the morphological assessment and provide at least three recorded waveforms – proximal, mid and distal. The proximal measurement I take from a couple of centimetres downstream of the bulb. Turbulence in that region contributes to the degradation of the ICA waveform giving the potential for misunderstanding about changes to the waveform i.e. a high resistance component may sneak and misdirect you into thinking unnecessarily there is a stenosis distally. The mid measurement is taken at the last point before the ICA dives down deeper into the neck. I avoid taking the trace too close to the turn to again avoid artefactual waveform changes.

Distal ICA Drop depth of image Straighten colour box Lower Doppler transmit frequency Once the ICA dives down I perform a series of manoeuvres designed to eke a good signal from the deepest part of the vessel possible: Straighten the beam steering on the colour flow box, reduce its width and increase its depth Lower the depth of the B-mode image Drop the Doppler transmit frequency The most distal measurement of velocity for the ICA is usually the most diagnostic in terms of waveform changes and peak systolic velocity. Changes at this point should be correlated to the previous two waveforms and differences should be accounted for (see discussion below: ICA Stenosis)

Vertebral Artery Antegrade vs Retrograde Try to demonstrate CCA and vertebral flowing in same direction The vertebral artery waveform is recorded to demonstrate antegrade flow in that vessel. Where possible I try to demonstrate the vertebral artery and CCA flowing in the same direction on the same image (or where not possible I will sometimes do a split screen image with the same technical factors showing the CCA on one side and the vertebral on the other). I usually reserve the extra attention to the vertebral where there is a stenosis demonstrated in the ICA.

competency 2 Investigate pathology found and conclude based on sonographic and clinical evidence

Plaque Morphology Transverse b-mode to investigate degree of lumen narrowing Longitudinal b-mode to demonstrate contour ‘capped’ Ruptured Old / chronic Morphology: soft (hypoechoic) vs hard (echogenic) plaque How do I investigate plaque morphology if found? In B-mode I scan the plaque in transverse to estimate the degree of vessel stenosis caused. Turning the probe longitudinally I sweep through to determine the B-mode characteristics of the plaque in order to describe its composition. Echogenic and shadowing components of the plaque denotes old / chronic and calcified. Hypoechoic components suggest newer thrombus deposition / plaque formation. Where hypoechoic components have been identified the plaque must be analysed for the possibility of thrombus rupture and subsequent embolus formation. I use power Doppler to demonstrate the degree of maximal stenosis evident in the transverse view (making sure that the colour gain is as high as possible without introducing noise). Turning longitudinally I investigate the flow around a soft plaque. Where the plaque has a smooth contour and a slightly echogenic ‘cap’ – this suggests the plaque is on its way to becoming an old echogenic chronic plaque with little chance of embolus formation. Where the plaque has an irregular contour, especially where flow can be demonstrated within an ‘ulcerated’ section of the plaque – this is a significant finding that increases the risk of transient ischaemic attack due to embolus formation from the plaque. I use B-flow in the same way as power Doppler to investigate a plaque. It produces much the same information as power Doppler but provides an image of particulate flow across the plaque surface, which can be handy for visualising very small plaque ulcerations.

CCA Waveform Changes Is there stenosis upstream? CCA waveform is mixture of high and low resistance ECA stenosis = ↑ PSV and spectral broadening of CCA trace ICA stenosis = ↓ EDV and spectral broadening of CCA trace CCA Changes What changes would be apparent in the CCA if there were stenosis upstream in ICA or ECA? The waveform for a normal CCA is a mixture of both high and low resistance waveforms. It will therefore demonstrate a quick rise to peak systolic but also a persistent end diastolic flow. Given its proximity to the heart (and also due to the high resistance component) the CCA will also usually demonstrate a pronounced dicrotic notch. Where a significant stenosis has occurred in the ECA the CCA waveform will demonstrate a particularly high resistance component and widespread spectral broadening – particularly nearer to the carotid bulb. If the ICA is the vessel affected then the CCA waveform will demonstrate a loss of the persistent end diastolic flow characteristic of the low resistance ICA waveform. Again spectral broadening will be a feature particularly nearer to the bulb.

ECA Analysis Stenosis criteria more similar to renal artery or peripheral artery criteria Compare to CCA as a ratio Absolute PSV approximately 15 – 200cm/s Spectral broadening Slow to peak systolic, increased diastolic (tardus / parvus) Exclude as source of clinically noted bruit ECA Stenosis What criteria do I use to assess the ECA? The criteria for stenosis at the ECA is more akin to the renal artery / peripheral artery criteria where the peak systolic velocity is compared to the CCA PSV to give a ratio. An absolute value of between 150 and 200 cm/s (depending on your source) is also a rough guide for stenosis velocity at the ECA. The indirect assessment of waveform changes are also useful as guides to stenosis in the ECA: changes such as spectral broadening, slow to peak systolic and increased diastolic flow (tardus and parvus). Given that most referrals for carotid Doppler examinations come from vascular surgeons and that very few of them are interested surgically in the ECA, the investigation of this vessel is mostly in an effort to answer the question where a clinically noted bruit may be emanating from.

ICA Stenosis Aliasing on colour flow imaging Waveform changes: Spectral broadening ↑ pulsatility proximal to stenosis ‘dampened’ flow distal to stenosis ICA Stenosis What are the sonographic signs of ICA stenosis? Colour Doppler – the use of colour flow Doppler during the initial morphology scan will be the first sign of stenosis. Aliasing due to focal velocity increases is the sonographic sign being sought in this mode. The colour settings I use include: Colour gain up as high as possible without background noise destroying the image Beam steering set so that the incident beam produces the maximum Doppler shift in the received echoes i.e. incident beam angle to direction of flow should be 0 – 60° Colour scale (PRF) set low enough to show aliasing throughout vessel then raised one notch at a time until only focal aliasing is present – this setting is the one most varied throughout the examination in order to retain the best possible sensitivity to focal aliasing Waveform – changes to the ICA waveform when a stenosis occurs include Spectral broadening due to turbulence Proximal to the stenosis the ICA waveform will become more resistive than normal, displaying a quicker acceleration to peak systolic velocity, a sharper upstroke toward PSV, loss of pan diastolic flow and as a result a greater pulsatility Distal to the stenosis the ICA will show a ‘dampened’ version of a normal waveform shape – lower and broader peak systolic and end diastolic components

ICA Stenosis – ASUM Criteria Peak systolic and end diastolic velocity changes as a sign of ICA stenosis are those defined by studies correlating ultrasound findings to angiographic or surgical findings. The accepted criteria by ASUM are: PSV < 125cm/s = 0 - 49% stenosis depending on extent of spectral broadening PSV > 125cm/s but EDV < 110cm/s = 50 – 69% stenosis PSV > 270cm/s but EDV < 140cm/s = 70 – 79% stenosis PSV > 270cm/s and EDV > 140cm/s = 80 – 99% stenosis ICA:CCA ratio is another marker accepted by ASUM as assisting in the classification of stenosis: Ratio < 2 = <50% stenosis Ratio >2 = 50 – 69% stenosis Ratio >4 = >70% stenosis

competency 3 Demonstration of appropriate patient communication, management and duty of care

Care of Elderly Patients Comfortable patient = easier scan Hearing aids Stop and assess patient regularly for signs of: Vertigo Faintness Laboured breathing Ensure elderly patients are comfortable = less movement, add pillows under head and knees as needed for comfort Hearing aids are not a contraindication but they can produce a buzzing when the probe gets near – might be better to ask patient to remove them Have patient immediately report any signs of vertigo, dizziness, faint feeling or heart arrhythmia (carotid sinus massage) – don’t push too hard

Communicating Results Check destination of report “So what does it show?” Have a plan in place Ask about patient doctor relationship – often referred by vascular surgeon so the patient may not be seeing them for results – CC report to GP? Do not offer an opinion on the findings – carotid disease more than most other scans is mainly a clinical diagnosis and takes account of the patient’s full clinical history, pathology results and medication list – many facts a sonographer will not be in command of In the case where a critical stenosis or big soft ulcerated flapping plaque has been discovered, make sure you have a plan in place to present to the patient: Finish the scan and go to discuss with radiologist Have radiologist notify referring doctor Organise transport for patient based on instructions from referring doctor