The ERC funded project “3-D Super resolution Ultrasound Real time imaging of Erythrocytes” - SURE develops ultrasound methods for visualizing the flow in the smallest vessel in the human body. Current experimental super resolution imaging uses small micro bubbles injected into a vein to visualize the flow in the human body. The method is invasive and takes several minutes for yielding satisfactory images. This can be avoided using our newly developed SURE method, which employs the red blood cells for imaging. Here a ultrasound research scanner is used for acquiring data for only 3 seconds to yield images with a resolution of 25 micrometers without any preparation of the patient. This has recently been demonstrated on the kidney of a Sprague-Dawley rat, which was scanned using a Verasonics research scanner, and the SURE processing program. It shows that super resolution imaging with a resolution of 25-40 micrometers can be attained in 3 seconds, orders of magnitude faster than current super resolution imaging with contrast agents, which takes 3-10 minutes to acquire. The SURE images need no contrast agents, and the patients can be directly scanned by a conventional ultrasound probe. This makes translation into the clinic easy. The images were compared to micro-CT scans acquired over 11 hours, and the vasculature of the SURE images were compared to the micro-CT scans. Selected vessels with a size between 55 to 85 micrometers agreed within 10 micrometers. Tracking can now also be used in the SURE processing, making it possible to quantify the flow velocity in the micro-vasculature and characterize arterioles and venules. Mice with an implanted tumor has also be scanned and the micro-vasculature of the tumor can be seen. Early studies indicate a radically different flow pattern than for healthy tissue. Further studies with be conducted to reveal the growth of tumors and their characterization.
The SURE method has now been translated to human clinical use and several clinical protocols have been submitted and approved by the authorities. Trials on the lymph nodes, tendons, kidney, and the breast are on-going. Early indications are that previously unseen flow in tendons and their vasculature can be revealed with SURE. This has also been seen for selected lymph nodes.
A study on non-invasive pressure gradient estimations in the carotid artery has also been initiated using the same ultrasound sequence as for SURE imaging. It has been shown that the method can measure gradients with a ten times higher precision than current invasive pressure catheters. This makes it possible to make screening of the carotid artery for a much wider patient group. A clinical study has been approved and is now on-going on both volunteers and patients.
A major results is three-dimensional ultrasound imaging using specialized row-column probes. The project has demonstrated that our row-column technology can be used for both super resolution imaging, normal high quality anatomic imaging, and blood velocity imaging, where the blood velocity vector is found in all three directions within the full volume and with a high time resolution. The row-column array only need 128 measurement channels, whereas a similar matrix probe used in current commercial scanners would need 16,384 channels, yielding 128 times more data. The processing is, thus, 128 times faster with our approach. The new method makes it possible to fabricate probes that are larger, which can see deeper into the tissue, and use higher frequencies for a corresponding higher resolution. This has the potential to introduce very high quality 3-D imaging in medical ultrasound using current scanner hardware. A new beamfoming method has been developed where only a single plane is needed for each emission for extrapolating to the the full volume. This further reduces the calculation demand by a factor of 100 for a combined reduction of 12,000 times compared to full matrix probes. This has been implemented on a standard research scanner and GPU card . Real time full volumetric imaging can now be attained for hundred of volumes a second, making it possible to implement 3-D ultrasound imaging using standard, commercial hardware.
CMUT probes are also being fabricated in the project. They avoid the use of lead in ultrasound probes and are therefore more environmentally friendly. It has also been shown that CMUT probes can be used in combination with coded excitation for increased penetration depth or resolution to further increase imaging quality.
