01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Imaging before lower-limb revascularisation is a planning step, not a substitute for diagnosis, physiological assessment or shared treatment selection. First establish the clinical syndrome: stable intermittent claudication, chronic limb-threatening ischaemia, or acute limb ischaemia. Confirm PAD with examination and appropriate haemodynamic testing, judge functional or tissue threat, deliver best medical treatment, and decide whether revascularisation is realistically under consideration. ESVS 2024 explicitly states that medical imaging is not indicated for diagnosing or conservatively treating intermittent claudication; it becomes useful when a procedure is being planned. This prevents a visually striking stenosis from driving an intervention that has no patient-centred indication.
NICE CG147 provides a clear UK sequence. Offer duplex ultrasound first to every person with PAD for whom revascularisation is being considered. If further imaging is needed after duplex, offer contrast-enhanced MRA; offer CTA when contrast-enhanced MRA is contraindicated or not tolerated. This is a sequence rather than a claim that one modality is universally superior. Duplex is safe and haemodynamic but operator dependent. CTA is fast and shows calcification and the whole arterial tree, but uses ionising radiation and iodinated contrast and can overstate lumen loss in heavy calcium. MRA avoids radiation and may provide excellent mapping, but device compatibility, claustrophobia, acquisition time, metal artefact and gadolinium considerations matter.
Catheter digital subtraction angiography is invasive and usually belongs where non-invasive studies are equivocal, very distal detail is essential, or diagnosis and endovascular treatment can occur in the same session. It carries access-site, embolic, contrast and radiation risks. The chosen map must show the anatomy required for the proposed operation: inflow, common femoral bifurcation, target arterial path, distal runoff, ankle and foot vessels for tissue loss, and potential landing or anastomotic zones. A report that merely lists percentage stenoses without answering these questions is incomplete.
Interpret imaging with symptoms, haemodynamics, tissue condition, comorbidity, conduit and goals. Stable claudication generally earns intervention only after risk-factor advice and supervised exercise have failed to give satisfactory improvement and disability remains meaningful. In CLTI, the Global Vascular Guidelines structure decisions around Patient risk, Limb severity and ANatomic complexity (PLAN); WIfI grades wound, ischaemia and foot infection, while GLASS describes the arterial target path. Anatomy contributes to feasibility and durability, but it never replaces the clinical indication.
Key points
- Order anatomical imaging when revascularisation is genuinely being considered, not merely because peripheral arterial disease has been diagnosed.
- NICE recommends duplex ultrasound first for people being considered for peripheral arterial revascularisation.
- If duplex is insufficient, NICE next recommends contrast-enhanced magnetic resonance angiography when it is suitable.
- Use computed tomography angiography after duplex when contrast-enhanced magnetic resonance angiography is contraindicated or not tolerated.
- Choose each study to map inflow, target lesions, outflow and access while documenting the exact treatment question.
- Review renal function, contrast history, implanted devices, pregnancy possibility, calcification and prior stents before cross-sectional or catheter angiography.
- For chronic limb-threatening ischaemia, obtain imaging through the ankle and foot when revascularisation remains an option.
- An anatomical stenosis does not by itself prove symptom causation or establish an indication to intervene.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
Reproducible exertional muscle pain remains disabling after appropriate non-invasive therapy, and the person would consider a procedure if benefits justify risk.
Rest pain, ulceration or gangrene with objective PAD requires a complete distal map if limb-salvage revascularisation is feasible.
Abrupt sensory or motor change, severe pain and a cold mottled foot require emergency vascular care rather than the elective imaging sequence.
A severe-looking lesion may be incidental when symptom distribution, exercise limitation and physiological testing do not align with its vascular territory.
Kidney impairment, severe previous contrast reaction, pregnancy possibility, ferromagnetic material, claustrophobia or heavy calcification changes modality choice and preparation.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Duplex arterial ultrasoundFirst stepFirst line - Why
- Provide first-line anatomical and haemodynamic mapping when revascularisation is being considered.
- Interpretation and limitations
- Velocity change, waveform disturbance and colour imaging localise significant disease and flow consequences. Results depend on operator skill and may be limited by obesity, bowel gas, calcification, wounds and deeply placed vessels.
- 02
Contrast-enhanced magnetic resonance angiography - Why
- Extend the arterial map after duplex when further pre-procedural imaging is required.
- Interpretation and limitations
- MRA maps multilevel disease without ionising radiation, but review MRI compatibility, claustrophobia, metal artefact and kidney-related gadolinium considerations with radiology; absence of calcium information can affect procedural planning.
- 03
Computed tomography angiography - Why
- Map the arterial tree when further imaging is needed and contrast MRA cannot be used or tolerated.
- Interpretation and limitations
- CTA is rapid and displays calcification, access and surrounding anatomy, but iodinated contrast, radiation and blooming from heavy calcium can limit safety or overestimate stenosis.
- 04
Catheter digital subtraction angiography - Why
- Resolve selected anatomical questions or combine definitive angiography with endovascular treatment.
- Interpretation and limitations
- It provides high spatial and temporal detail but is invasive; weigh puncture-site bleeding, embolisation, radiation and contrast harm, and avoid using it as routine diagnostic first-line imaging.
- 05
Renal function and contrast safety assessment - Why
- Identify modifiable hazards before iodinated or gadolinium-based contrast is administered.
- Interpretation and limitations
- Use current kidney function, acute illness, medicines, hydration status and previous reaction to agree a radiology protocol; one eGFR value does not by itself choose the modality.
- 06
Vein mapping when bypass is plausible - Why
- Assess autologous conduit alongside the arterial reconstruction plan.
- Interpretation and limitations
- Map ipsilateral great and small saphenous vein and alternatives when appropriate; an adequate vein can materially change the open-versus-endovascular decision in CLTI.
04Clinical next stepsHow the result changes management or prompts escalation.
01Management sequenceStage imaging around treatment intentFirst stepPAD is established and the team is deciding whether anatomical intervention should be offered.+
- 1Define the syndrome, functional or tissue threat, physiological evidence, previous therapy, procedural fitness and the patient’s goals before ordering a map.
- 2Use duplex first under NICE CG147 and state whether the question concerns inflow, a target lesion, distal runoff, access or conduit.
- 3If duplex is insufficient, use contrast-enhanced MRA when suitable or CTA when MRA is contraindicated or not tolerated.
- 4Reconcile the final map with symptoms and haemodynamics in a vascular multidisciplinary discussion, then choose treatment or continued non-invasive care.
02CLTI planningMap a threatened foot completelyObjective PAD accompanies rest pain, a non-healing ulcer or gangrene and limb salvage remains plausible.+
- 1Arrange urgent vascular review and grade wound, ischaemia and infection rather than waiting for routine outpatient imaging.
- 2PreferredObtain high-quality imaging that includes inflow, the preferred target arterial path, ankle and foot vessels, and usable distal targets.
- 3Combine patient risk, WIfI limb severity, GLASS anatomical complexity and vein availability to select an evidence-based revascularisation strategy.
- 4If deep infection or wet gangrene is present, drain and debride urgently with antibiotics, then restage before the next major reconstruction decision.
03Safety checkChoose contrast and access safelyCross-sectional or catheter angiography is proposed after the clinical indication has been established.+
- 1Check current renal function, acute kidney injury, contrast history, relevant medicines, pregnancy possibility, implants and ability to tolerate positioning.
- 2Discuss protocol modification or a different modality with radiology when contrast load, calcification, artefact or MRI compatibility threatens usefulness or safety.
- 3Record the final modality rationale and ensure post-contrast or access-site observation follows the agreed departmental pathway.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Track the referral and ensure the imaging report answers the stated revascularisation question rather than simply cataloguing disease.
- Reassess symptoms, pulses, tissue loss and infection while imaging is awaited; a worsening limb moves to an urgent or emergency pathway.
- After contrast, follow the radiology service plan for kidney or hypersensitivity risk and document any reaction for future studies.
- After catheter angiography, monitor puncture site, limb perfusion, bleeding and systemic observations according to the procedural protocol.
- Review unexpected discordance between duplex and cross-sectional imaging with vascular radiology before committing to irreversible treatment.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Intent before anatomy
A treatment-worthy clinical syndrome and informed procedural intent should precede detailed mapping, because anatomical disease is common and may not explain the disability.
Duplex adds physiology
Duplex does more than draw the lumen: velocities and waveforms show haemodynamic consequences, but thresholds remain laboratory and segment dependent.
Calcification distorts tests
Medial calcification can make ankle pressures falsely high and can cause CT blooming, so toe pressures, waveforms and another imaging modality may be needed.
Foot views matter
A groin-to-knee map is inadequate for tissue loss when distal target selection and restoration of in-line flow to the foot determine healing potential.
DSA is a procedure
Catheter angiography should carry a clear diagnostic or therapeutic purpose because arterial puncture, contrast, embolisation and radiation are real harms.
07Common pitfallsFrequent interpretation and management errors.
- 01
Ordering CTA because a pulse is weak before deciding whether revascularisation would be appropriate or acceptable.
- 02
Treating a reported percentage stenosis as proof that it causes symptoms or requires intervention.
- 03
Using a normal or high ankle brachial index to exclude PAD in diabetes or incompressible calcified vessels.
- 04
Stopping the arterial map above the ankle in a patient with tissue loss who may need distal reconstruction.
- 05
Ignoring previous severe contrast reaction, acute kidney injury, implants or stent artefact when choosing the modality.
- 06
Letting elective imaging delay emergency referral for acute limb ischaemia, wet gangrene, deep infection or sepsis.