Enhancement ultrasound is a specialized medical imaging technique that provides more detailed images than a standard ultrasound by improving the visualization of blood flow and organ features. The purpose is to gain clearer diagnostic information without resorting to more invasive procedures or those involving radiation. This is accomplished through the use of a special contrast agent that helps to highlight areas of interest within the body.
How Enhancement Ultrasound Works
This imaging technique relies on the intravenous (IV) injection of a contrast agent made of microbubbles. These are tiny, gas-filled spheres with a flexible outer shell, approximately the size of a red blood cell. The shell is composed of materials like lipids or proteins, while the gas inside is a harmless substance like perfluorocarbon or sulfur hexafluoride.
Once injected into the bloodstream, the microbubbles are confined to the vascular system and travel with the blood. They are too large to pass through the small gaps between the cells that line blood vessels.
When ultrasound waves from the transducer encounter these microbubbles, they are strongly reflected, which creates the enhanced contrast in the resulting image. The microbubbles resonate in response to the pressure changes of the sound waves, rapidly contracting and expanding. This vibration makes the microbubbles thousands of times more reflective than the body’s own tissues, which “lights up” blood vessels for detailed, real-time observation of blood flow. After the procedure, the body eliminates the microbubbles, with the gas being expelled through normal breathing.
Common Medical Applications
The enhanced visualization of blood flow makes this technique useful in a variety of clinical settings. One of the most common applications is in the characterization of lesions found in organs such as the liver and kidneys. By observing the pattern of blood flow within a tumor or mass, radiologists can differentiate between benign and malignant growths, which can reduce the need for more invasive procedures like biopsies.
In cardiology, the technique, often called contrast echocardiography, is used to assess heart function. It improves the delineation of the heart’s chambers, allowing for more accurate measurements of how much blood the heart is pumping with each beat. It can also help detect abnormal blood flow within the heart itself.
Another application is in monitoring the health of transplanted organs. After a transplant, it is important to ensure that the new organ is receiving adequate blood supply. Enhancement ultrasound can provide a clear picture of blood perfusion in the transplanted organ, helping to identify potential complications like vascular stenosis or thrombosis at an early stage.
The Procedure for Patients
For the patient, the procedure is straightforward and similar to a standard ultrasound. A small intravenous (IV) catheter will be placed into a vein in the arm or hand. The patient will then be asked to lie comfortably on an examination table.
Initially, the sonographer will perform a conventional ultrasound, applying a water-based gel to the skin and moving a transducer over the area of interest. After these initial images are taken, the microbubble contrast agent is injected through the IV line. The sonographer continues to scan as the contrast circulates, capturing real-time images of the blood flow. The entire process takes between 15 and 30 minutes.
The injection of the contrast agent is generally painless, though some people report a cold sensation in their arm as the fluid enters the vein. The scanning portion of the procedure is identical to a regular ultrasound and does not cause any discomfort. A second dose of the contrast agent may be given to get a clearer image.
Safety of Contrast Agents
The microbubble contrast agents used in enhancement ultrasound have a strong safety record and are well-tolerated. Serious side effects are rare. When side effects do occur, they are typically mild and short-lived, with the most common being a headache or nausea.
There is a small risk of an allergic-type reaction, estimated to occur in about 1 in 10,000 administrations. For this reason, patients may be asked to remain in the department for a short period after the scan for observation. Patients should inform their healthcare provider of any severe heart conditions or past allergic reactions before the procedure.
A benefit of these contrast agents is that they do not contain iodine, which is used in contrast agents for CT scans. This makes enhancement ultrasound a safe alternative for individuals with iodine allergies. Furthermore, the microbubbles are not known to pose a risk to kidney function, unlike contrast agents used in both CT and MRI scans, making the procedure a good option for patients with pre-existing kidney disease.