When confirming graft function during vascular surgery, many surgeons still rely on Doppler ultrasound. It’s familiar. It’s fast. It’s non-invasive.

But there’s one problem: Doppler doesn’t measure flow. It measures velocity. 

That distinction matters, especially when you’re trying to determine whether the graft actually delivers adequate blood flow after an infrainguinal bypass. When the goal is limb salvage, good velocity might not be good enough.

Transit-time flow measurement (TTFM) is also fast and non-invasive, but it goes further by giving you what Doppler can’t: true, quantitative volume flow in real-time.

What Doppler Measures and What It Doesn’t

Doppler ultrasound uses the Doppler effect to measure how fast blood is moving through a vessel. It can also help identify the direction of flow, which can be useful in many contexts. 

But it does not measure volume flow. In bypass cases, that's a critical limitation.

You can have high velocity in a vessel that’s significantly narrowed, twisted or kinked. In those cases, Doppler might sound strong, but the actual volume of blood moving through the graft may be inadequate to perfuse tissue effectively. That means a graft that sounds good can still fail.

What TTFM Measures and Why It Matters

TTFM doesn’t just confirm that blood is moving. It tells you exactly how much is moving through the graft, measured in mL/min. This quantitative data helps you assess not just the presence of flow, but the functional performance of your bypass.

It works by sending ultrasound waves both upstream and downstream across the graft. The difference in signal transit time is used to calculate true volume flow, beat by beat. This provides a level of accuracy in the moments that matter most.

With TTFM, you can:

• Confirm graft patency in real time
• Compare flow rates to clinical benchmarks
• Make on-the-spot revisions if necessary

Doppler Tells You Something Is Moving. TTFM Tells You If It’s Enough.

By itself, Doppler can’t tell you how much blood is reaching the tissue. That’s a problem, especially for patients with a high risk of graft failure.

With TTFM, you have numbers. Data. Clarity. And when you’re deciding whether to close the case or make a revision, that can make all the difference. Confirm graft success with confidence.

Learn more about the TTFM difference during infrainguinal bypasses.