Ultrasound for Blood Clots: Finding Clots and Breaking Up Microclots
By Tim Ottowitz ยท Updated October 30, 2026
Short answer
Ultrasound is how doctors look for a large blood clot in a deep vein, but microclots are far too small to show up on a scan. Separately, lab studies in 2025 and 2026 found low-frequency ultrasound broke up amyloid microclots on a chip. As of October 2026 that's research, not a treatment you can get.
- An ultrasound can show a large clot that blocks a deep vein; doctors pair it with D-dimer and sometimes CT.
- Microclots measure roughly 1 to 200 micrometres and show up only under a microscope with a Thioflavin T stain.
- In a 2025 lab-on-chip study, 150 kHz ultrasound cut microclot size and large-clot counts up to three-fold.
- In a 2026 study, ultrasound shrank clots by over 60%, and adding enzymes made no significant difference at 150 kHz.
- No study in people has tested ultrasound for microclots as of October 2026.
Can an ultrasound detect a blood clot?
An ultrasound can show a large blood clot in a deep vein, because a deep vein clot is big enough to block the vein, unlike a microclot of 1 to 200 micrometres. When a large clot is suspected, a clinician usually starts with a history and examination, then orders a D-dimer blood test and imaging such as ultrasound or CT where it's indicated.
D-dimer measures fragments released when clots break down. A normal D-dimer helps rule out an acute clot, and a high or rising one needs medical review. Our partner site explains the difference in D-dimer vs microclot testing.
Can an ultrasound see microclots?
An ultrasound can't see microclots, which measure roughly 1 to 200 micrometres and show up only under a microscope with a Thioflavin T stain. The fibrin amyloid microclots studied in Long COVID have folded into an amyloid-like shape that resists the body's normal clot breakdown.
| Large clot (DVT, pulmonary embolism) | Fibrin amyloid microclot | |
|---|---|---|
| Size | Big enough to block a named vein or artery | Roughly 1 to 200 micrometres |
| Found with | Ultrasound, CT, D-dimer | Thioflavin T fluorescence microscopy |
| Urgency | Can be an emergency | Not an emergency on its own; effects on small-vessel blood flow are still being studied |
For the background, see what microclots are and whether microclots are dangerous.
Can ultrasound break up microclots?
Low-frequency ultrasound at 150 kHz broke up amyloid microclots in a 2025 lab-on-chip study, shrinking clots and cutting large ones up to three-fold (Rasouli et al., 2025). The team tested 150, 300 and 500 kHz and 1 MHz, with and without microbubbles and the clot-busting drug rtPA. Adding microbubbles and rtPA broke the clots up further.
A follow-up by the same group formed amyloid microclots from blood plasma, by freezing and thawing it 12 times, and treated them in a chip built to mimic a 6 mm leg vein (Rasouli et al., 2026). At 150 kHz, mean clot diameter fell by over 60% and the number of clots larger than 30 micrometres fell by more than 80%.
| Rasouli et al., 2025 | Rasouli et al., 2026 | |
|---|---|---|
| Journal | Frontiers in Bioengineering and Biotechnology | Journal of Thrombosis and Thrombolysis |
| Frequencies | 150, 300, 500 kHz and 1 MHz | 150, 300 and 500 kHz |
| Added to ultrasound | Microbubbles, rtPA | Microbubbles plus rtPA, lumbrokinase or nattokinase |
| Best result | Up to three-fold smaller clots and fewer large clots at 150 kHz | Over 60% smaller clots, over 80% fewer large clots at 150 kHz |
| Where tested | Lab chip | Lab chip |
Why would ultrasound work when enzymes struggle?
Ultrasound breaks microclots up mechanically, and the 2026 study concluded that mechanical forces were the dominant cause of clot disruption. Clot-dissolving enzymes rely on cutting fibrin, and the 2025 study notes they "struggle to address amyloid-rich microclots due to their structural resistance to enzymatic breakdown".
That resistance shows up elsewhere too. Long COVID microclots survived a full digestion with trypsin, a strong protein-cutting enzyme, and dissolved only after a second round (Pretorius et al., 2021; Kruger et al., 2022).
In the 2026 study, adding rtPA, lumbrokinase or nattokinase made no significant difference at 150 or 300 kHz. At 500 kHz, where ultrasound alone was weaker, rtPA and lumbrokinase helped significantly and nattokinase didn't. The full enzyme picture is in our partner site's comparison of 8 nattokinase studies.
Is ultrasound treatment for microclots available?
Ultrasound treatment for microclots isn't available as an established therapy: as of October 2026 it has only been tested on lab chips, and we found no published study in people. Nobody yet knows the right frequency, dose or safety in the body.
The studies used specific frequencies, microbubbles and a sealed chip. They didn't test the ultrasound therapy devices sold for pain or physiotherapy, so those devices aren't evidence of anything for microclots.
What can you do now?
Emergency symptoms come first; after that, work with a clinician on standard tests, and if you want microclot data, an at-home amyloid test reports within 1 day of the lab receiving your sample. The at-home amyloid test from our partner site stains a finger-prick dried blood sample with Thioflavin T, the same staining principle as the published research.
The report is informational data for you and your clinician, not a diagnosis, and it doesn't measure your risk of a large clot. Other approaches being studied are listed under treatments for blood clots and microclots.
Ultrasound and blood clots: frequently asked questions
Ultrasound and blood clot questions below are answered from the 2021 to 2026 studies cited on this page.
- Can an ultrasound detect a blood clot in the leg?
- An ultrasound can show a large clot in a deep vein of the leg, because a deep vein clot is big enough to block the vein. Doctors use it, along with a D-dimer blood test and sometimes a CT scan, when they suspect a deep vein thrombosis. A swollen, painful or warm leg needs to be checked promptly.
- Can an ultrasound see microclots?
- No. Microclots are microscopic particles, roughly 1 to 200 micrometres across, and they're seen only under a microscope with a stain such as Thioflavin T. A normal ultrasound scan doesn't rule microclots in or out, and a normal D-dimer doesn't either.
- Does ultrasound dissolve microclots?
- In lab studies, it broke them up. A 2025 lab-on-chip study found 150 kHz ultrasound cut microclot size and the number of large microclots up to three-fold, and a 2026 study found over 60% smaller clots and more than 80% fewer large clots. Both used microclots in a sealed chip, not in a person.
- Can I get ultrasound treatment for microclots?
- Not as an established treatment. As of October 2026, ultrasound for amyloid microclots has only been tested on lab chips, and we found no published study in people. The studies used specific frequencies and microbubbles, not the ultrasound therapy devices sold for pain or physiotherapy.
Sources
- Low-intensity ultrasound lysis of amyloid microclots in a lab-on-chip model. Frontiers in Bioengineering and Biotechnology, 2025.
- Investigation of the synergistic effect of enzymatic and ultrasound-induced amyloid microclot degradation. Journal of Thrombosis and Thrombolysis, 2026.
- Persistent clotting protein pathology in Long COVID/Post-Acute Sequelae of COVID-19 (PASC) is accompanied by increased levels of antiplasmin. Cardiovascular Diabetology, 2021.
- Proteomics of fibrin amyloid microclots in long COVID/post-acute sequelae of COVID-19 (PASC) shows many entrapped pro-inflammatory molecules. Cardiovascular Diabetology, 2022.