Table of contents

Philosophy of vascular ultrasound service

Vascular ultrasound is a subspeciality of diagnostic ultrasound imaging and should only be performed by specifically trained vascular ultrasound practitioners including vascular sonographers, ultrasound-skilled vascular surgeons or interventional radiologists. These vascular ultrasound practitioners will henceforth referred to as "specialist vascular sonographer”.

The recommended setting for vascular ultrasound is that of a dedicated vascular laboratory allowing for an integrated team approach to solve clinical problems. The speciliast vascular sonographer must have direct access to and regular contact with the clinicians treating the patient. Performing vascular ultrasound in the setting of a general radiology department is discouraged. Duplex ultrasound should not be performed by sonographers not specifically trained in a vascular setting and should not be interpreted by general radiologists.

The primary aim of a vascular ultrasound examination is:

1. clinical review of the patient,

2. skilful and detailed application of diagnostic instruments including duplex ultrasound, pressure testing, exercise testing, etc,

3. careful examination of all relevant anatomy and pathology,

4. accurate description of the ultrasound findings, and most importantly,

5. formulation of an accurate diagnostic opinion on the basis of sound clinical judgement and production of a clinically-focused report.

The secondary aim is documentation of the findings for archiving. In this regard, simple completion of a scanning protocol without placing it in the context of the patient’s clinical presentation and medical background is insufficient.

The role of the specialist vascular sonographer is that of an independent expert diagnostitian. The specialist vascular sonographer may use, at their discretion and in line with current best practice, any diagnostic tools including: B-mode ultrasound, colour Doppler ultrasound, spectral Doppler ultrasound, combination of imaging modes (duplex, triplex), contrast-enhanced ultrasound (CEUS), 3D ultrasound, pressure plethysmography testing using pulsed wave (PW), continuous wave (CW) instruments, pulse plethysmography (PPG) and other validated and evidence-based tools. The specialist vascular sonographer is responsible for the performance, interpretation and provision of the final report.

Vascular ultrasound examination overview

Determination of the appropriateness of vascular laboratory investigations

All vascular laboratory investigations (such as US) should be performed on the basis of sound clinical justificaiton. Specifially, the decision to perform a test should based on the decision to intervene is disease is present.

Pre-encounter and encounter review

Prior to commencing the ultrasound examination, the specialist vascular sonographer should:

1. Review the referral letter,

2. Review all relevant medical records including:

• laboratory findings,

• previous imaging findings and PACS image records,

• clinic letters,

• admissions and discharge summaries, and,

• any other relevant medical records available including relevant surgical records,

3. elicit relevant history from the patient, and,

4. clinically examine the area of interest if required.

Performing the vascular duplex examination

Duplex ultrasound examination should be sufficiently comprehensive to encompass all the relevant anatomical regions. For instance, the examination of the lower limb arteries should commence at the aorta and end at the ankle. Occasionally, targeted examinations can be performed in segments of the anatomy have already been examined recently with duplex ultrasound or other imaging such as contrast CT or MRI. This may include reassessment of areas of intervention, or targeted scanning to answer a specific clinical question.

Extending and limiting the examination

Vascular sonographers have considerable professional independence and decisional latitude in the performance of the ultrasound examination and are encouraged to use their clinical judgement to extend the examination wherever appropriate. Sonographers may also limit the scope of the examination or cancel a requested examination if the examination is not clinically justified.

Ultrasound examination techniques

Because of the variability of approaches to clinical problem-solving, we do not advocate establishing protocols in a manner of a "picture-by-picture" imaging procedure. We believe that rigid protocols promote a culture of "compliant picture-taking", rather than a culture of clinical problem solving. Therefore, the protocols suggested in these standards of practice focus on the overarching principles and minimum recommended documentation. It is the responsibility of the specialist vascular sonographer to examine each patient appropriately.

Doppler angle

Colour and spectral Doppler examination should be performed at favourable Doppler angle 0-60 degrees.

Angle-correction

Spectral Doppler angle-correction should be aligned with the flow vector in the vessel as visualised on colour Doppler. We do not support the use of fixed angle correction.

Assessment of blood vessels

The assessment of vessels is performed in real-time with continuous ultrasound visualisation using a combination of B-mode and colour Doppler. Skipping vessel segments or preforming a picture-by-picture imaging protocol is discouraged.

Assessment of arterial stenoses

The suspicion of a stenosis on colour Doppler examination should prompt spectral Doppler assessment with the main focus to detect the highest flow velocity. High PRF should be used to isolate the highest flow velocities and to determine the flow vector/geometry. A velocity ratio (V2/V1) should be obtained to assist in the categorisation of stenosis severity. This includes a spectral Doppler sample pre-stenosis (V1) and at the point of maximum velocity (V2). Specific circumstances may allow for B-mode assessment of stenosis diameter, such as stenoses in haemodialysis grafts and stenoses within a large ICA bulb. Velocity ratios are only useful for focal stenoses and may not perform well with long stenoses, gradually funnelling stenoses or diffusely diseased vessels.

Measurement of aneurysm diameter

All fusiform aneurysms should be measured in true transverse axis to the vessel from adventitia to adventitia (external diameter) in the the axial dimension.

Measurement of venous diameter

Venous diameters should be measured in true transverse axis to the vessel from intima to intima (internal diameter) in the axial dimension.

Assessment of venous reflux

Venous reflux is defined as retrograde flow in a lower extremity vein lasting >0.5 seconds. It is important to exaggerate the venous pressure and create favourable conditions for reflux to occur. In proximal vessels (such as the sapheno-femoral junction and upper thigh vessels), vigorous Valsalva or simulated Valsalva manoeuvre may be used. Further peripherally, prolonged augmentation with release is preferred. Augmentation can be performed manually or with the use of an automated pneumatic cuff.

Carotid duplex ultrasound

Typical examination includes both carotid artery systems from proximal CCA to distal-most intracranial ICA and vertebral arteries bilaterally. At minimum, the following images should be recorded:

1. B-mode CCA.

2. Colour Doppler CCA.

3. Spectral Doppler in the distal CCA with measurement of PSV and EDV.

4. B-mode Bifurcation.

5. B-mode proximal ICA.

6. Colour Doppler proximal ICA.

7. Spectral Doppler proximal ICA with measurement of PSV and EDV.

8. Spectral Doppler distal ICA.

9. Spectral Doppler of the vertebral artery.

Note: velocity and ratio criteria provide a luminal diameter reduction estimation according to the NASCET method (smallest diameter compared to normal distal diameter). However, we recognise that large plaques in large bulbs may still post a risk for an embolic event. We suggest in cases where there is a large carotid bulb, direct measurement of the bulb diameter and plaque thickness is made (ECST method) and reported with a note that measurements were obtained using the ECST method, and that a reasonable residual patent lumen remains.

If abnormal waveforms are identified in the vertebral artery the examination should be extended to include bilateral blood pressure measurements.

Reference: Oates CP, Naylor AR, Hartshorne T, Charles SM, Fail T, Humphries K, et al. Joint Recommendations for Reporting Carotid Ultrasound Investigations in the United Kingdom. European Journal of Vascular and Endovascular Surgery. 2009 Mar;37(3):251–61.

Reference: Cossman DV, Ellison JE, Wagner WH et al. Journal of Vascular Surgery 1989;10:522

Upper extremity arterial examination

Typical examination includes assessment of brachial systolic pressure and a continuous duplex examination of the entire arterial tree from the proximal-most visualisable point to the wrist.

Criteria for upper limb arterial stenosis are not well established. They are generally assumed to be the same as for lower limb arteries.

Lower extremity venous examination for deep vein thrombosis (DVT)

A typical examination includes the following:

1. A spectral Doppler waveform at the CFV under normal respiration to determine the presence or absence of phasicity and pulsatility. Absence of venous respiratory phasicity at the CFV prompts an investigation of the proximal veins for the presence of venous obstruction or compression.

2. Transverse compression of the lower limb deep veins is performed every 2-3 cm from the groin to the ankle. At minimum, an image in B-mode should be obtained in each vessel segment.

3. Colour Doppler examination from the groin to ankle to detect flow changes associated with chronic fibrin webs/strands that may escape detection on compression ultrasound

4. Examination of the area of pain

Lower extremity venous examination in chronic venous insufficiency (CVI)

A typical examination includes the following:

1. Visual examination for the location and distribution of the varicose veins and associated clincial features

2. Duplex assessment of the deep veins for patency and competence

3. Determination of the source, path and ouflow of venous reflux

4. Assessment of junctions and major trunkal veins

5. Determination whether endovascular interventions are feasible

In female patients with non-truncal varices or clinical features of pelvic venous congestion, transabdominal examination of the pelvic veins (ovarian, internal iliac and parametrial veins) should be performed.

1. Necas M. Duplex ultrasound in the assessment of lower extremity venous insufficiency. Australas J Ultrasound Med. 2010 Nov;13(4):37–45.
2. Coleridge-Smith P, Labropoulos N, Partsch H, Myers K, Nicolaides A, Cavezzi A, et al. Duplex ultrasound investigation of the veins in chronic venous disease of the lower limbs--UIP consensus document. Part I. Basic principles. Vasa. 2007 Feb;36(1):53–61.
3. Cavezzi A, Labropoulos N, Partsch H, Ricci S, Caggiati A, Myers K, et al. Duplex ultrasound investigation of the veins in chronic venous disease of the lower limbs--UIP consensus document. Part II. Anatomy. Vasa. 2007 Feb;36(1):62–71.

EVAR surveillance

The entire visible length of the EVAR shoudl be interrogated using B-mode and colour Doppler. A spectral Doppler waveform should be obtained in the distal external iliac artery bilaterally.

B-mode imaging is utilised to ascertain the maximum aortic sac size diameter. This is used to determine a change in aortic sac size over time.

Colour Doppler is utilised to evaluate the presence or absence of endoleaks, and EVAR integrity or kinking . When interrogating for endoleak, low flow settings (low PRF, high gain, high ensemble length) must be applied, with special attention paid to the proximal and distal attachment sites, and to the origin of the inferior mesenteric and lumbar arteries.

• If an endoleak is identified:

  • Special attention should be paid to determine its origin and direction of flow for classification.

  • A spectral Doppler waveform should be captured at the origin of the endoleak to determine if a to-and-fro waveform is present.

  • A video capture of the endoleak is recommended.

We recommend a low threshold to utilise contrast-enhanced ultrasound (CEUS) in cases of aortic sac size expansion, with no clear cause identified on conventional colour Doppler imaging.

Renal artery examination

Renal artery duplex is typically indicated in individuals with a high level of suspicion of renovascular hypertension including: multidrug resistant hypertension (with poor or no resopnse to 3 agents), malignant hypertension, flash pulmonary oedema, decline in renal function on ACE inhibitor. Renal artery duplex should not be used in the routine work-up of hypertension.

Reliable diagnosis of renal artery stenosis relies on direct visualisation of the lesion. When patient factors prevent adequate visualisation of the renal artery, indirect parameters may be used to identify patients with advanced renal artery disease.

Haemodialysis fistula examination

1. Detailed examination of a fistula includes the continuous examination all of the following:

a) proximal in-flow arteries

b) proximal anastomosis

c) the entire length of the fistula

d) distal anastomosis (if present, for instance if this is a prosthetic fistula or if skip grafts are present)

e) all distal outflow veins

2. All all levels, the vessels are assessed in B-mode, colour Doppler and Spectral Doppler.

3. Examine areas of pain, or suspected abnormalities.
   

For example, a comprehensive assessment of left brachiocephalic fistula would require continuous assessment in B-mode and colour Doppler commencing at the level of the BCA and finishing with the BCV. Typical Doppler sampling sites would include the left:

• BCA

• SCA

• AXA

• BRA

• proximal anastomosis

• proximal, mid, and, distal fistula

• outflow veins

• SCV

• BCV

We recognise that scanning the whole circuit may be unrealistic. If the patient has had prior imaging of the proximal inflow arteries (BCA, SCA, axillary artery), with no abnormalities detected, this may be omitted from future scans unless there is clinical concern for arterial inflow.

Reference: Wolfgang A Schmidt, Ultrasound in the diagnosis and management of giant cell arteritis, Rheumatology, Volume 57, Issue suppl_2, February 2018, Pages ii22–ii31, https://doi.org/10.1093/rheumatology/kex461

Reporting of findings

The specialist vascular sonographer is responsible for the communication of the ultrasound findings in a manner that is clear, concise and easily understood by members of the health care team and referring doctors from non-vascular specialties and primary care doctors. In case of simple examinations with normal or trivial findings, a standardised brief report may be sufficient:

"Duplex examination of the carotid and vertebral arteries was performed. All vessels are widely patent with no evidence of atheromatous disease. Color and spectral Doppler parameters are normal."

or

"Lower extremity venous duplex was performed from the groin to the ankle including all major deep veins. All vessels are widely patent with no evidence of deep vein thrombosis."

Abnormal results are usually best reported with the aid of graphical diagrams in order to depict the precise anatomical location and severity of disease. This is particularly helpful in patients requiring cross-modality imaging correlation and intervention. For further information, please refer to the following guideline:

Reference: Necas M. The clinical ultrasound report: Guideline for sonographers. Australasian Journal of Ultrasound in Medicine. 2017 Nov 17;(21):9–23.