13.6 Kidney and Liver Transplant Vascular Duplex

Start with the operative anatomy

Transplant duplex assesses perfusion and vascular complications in a surgically reconstructed organ. The vessels may not follow native anatomy. Review the transplant type and date, operative notes, known vascular variants, symptoms, laboratory trends, and prior ultrasound. Identify which artery and vein supply the graft before applying any velocity criterion. An examination of a native renal artery is not a substitute for a transplant protocol.

Use grayscale, color or power Doppler, and spectral Doppler together. Image the organ, adjacent collections, accessible anastomoses, inflow, outflow, and intraparenchymal vessels. Optimize settings for slow flow before diagnosing absent perfusion. Record whether a segment was truly evaluated or merely not visualized. Unexpected absent arterial or venous flow requires immediate attention and prompt communication to the transplant team.

Kidney transplant examination

A transplant kidney is commonly placed in an iliac fossa. Its artery usually joins an iliac artery and its vein joins an iliac vein, but multiple renal arteries and alternative reconstructions occur. Follow the vessels rather than assuming a single anastomosis. The superficial graft may permit a higher-frequency transducer than a native retroperitoneal kidney; choose the frequency that provides adequate penetration and resolution.

Grayscale and perfusion checklist

• Measure graft length and evaluate cortical appearance and collecting-system dilation.
• Look for perinephric fluid, hematoma, lymphocele, or other collections that might compress the graft, ureter, or vessels.
• Demonstrate global perfusion with color or power Doppler.
• Sample the feeding iliac artery, arterial anastomosis, accessible transplant renal artery, and intrarenal branches at several poles.
• Evaluate the transplant renal vein, venous anastomosis, and accessible iliac venous outflow.
• Compare with the baseline and document timing after surgery.

Transplant renal artery stenosis may show focal narrowing, color aliasing, focal acceleration, and downstream tardus-parvus waveforms. A tortuous artery, acute bend, angle error, or early postoperative flow state can produce elevated velocity without a fixed stenosis. Use validated transplant-specific criteria and the complete pattern rather than transferring native renal-aortic ratio thresholds. The reference inflow vessel is generally an iliac artery, not the suprarenal aorta.

Arterial thrombosis is concerning when adequate optimization fails to demonstrate arterial perfusion. Check several windows and avoid mistaking shadowing or very low output for occlusion. Renal vein thrombosis can cause absent venous flow, graft swelling, and high-resistance arterial flow with reversed diastole. These findings require urgent correlation; reversed arterial diastole alone is not uniquely diagnostic because severe parenchymal dysfunction or external compression can also increase resistance.

Resistive index: useful measurement, limited diagnosis

The resistive index (RI) is (PSV − EDV)/PSV. For PSV 80 cm/s and EDV 24 cm/s, RI = 56/80 = 0.70. Use representative waveforms at consistent intrarenal sites and report the values and distribution. Heart rate, pulse pressure, systemic vascular properties, venous pressure, obstruction, and parenchymal processes can influence RI.

An elevated RI does not diagnose rejection, acute tubular injury, or another specific histologic process. These conditions can overlap sonographically. Clinical evaluation, laboratory data, additional imaging, and sometimes biopsy are needed. A normal RI also does not exclude every graft complication. The correct examination answer often identifies the limitation of the measurement rather than assigning a disease from one ratio.

After a biopsy, look for an arteriovenous fistula or pseudoaneurysm when indicated. An AVF can produce focal color disturbance, high-flow low-resistance arterial supply, and arterialized venous flow. A pseudoaneurysm is a communicating sac with characteristic neck flow. Describe location and hemodynamics and let the treating team determine significance and management.

Liver transplant examination

Confirm whether the graft is whole or partial and review arterial, portal, hepatic venous, and caval reconstruction. Image the parenchyma, bile ducts where appropriate, and adjacent collections. Evaluate hepatic arterial flow from the accessible inflow and anastomosis into the right and left intrahepatic branches, portal vein inflow and branches, and hepatic venous/caval outflow.

Early postoperative edema and hemodynamic changes can transiently alter waveforms, so timing and trend matter. Persistently abnormal or worsening findings require clinical review rather than dismissal as “postoperative.” Conversely, a single abnormal ratio does not prove a lesion that is not visible and lacks supporting downstream evidence.

Worked transplant scenarios

A new renal transplant has normal color perfusion and a focal anastomotic PSV of 260 cm/s, but the vessel bends sharply at that point and intrarenal upstrokes remain brisk. Reassess the angle and course, compare with baseline, and apply the transplant laboratory's criteria. The PSV alone cannot establish a precise stenosis category.

A liver transplant patient develops rising liver tests and no reproducible hepatic arterial signal despite optimization and several windows. Preserve representative images and notify the transplant team immediately while documenting the limitations. Further imaging or intervention may be urgent. Do not diagnose “rejection” from the absent signal or delay communication while waiting for a routine report.

Correlation and preliminary findings

CT angiography, MR angiography, contrast-enhanced ultrasound, or catheter angiography may clarify a suspected complication when selected by the clinical team. Each answers a different anatomic or perfusion question and has patient-specific constraints. Report the graft and reconstruction, accessible extent, patency, measurements, comparison, and uncertainty. Label preliminary findings and document urgent communication.

AIUM solid-organ transplant practice parameter, 2024 revision and ACR solid-organ transplant parameter — checked October 18, 2026.