Contrast-enhanced ultrasound of the kidneys

The development of ultrasound contrast agents and dedicated software for the detection of microbubbles has improved the potential contrast resolution of ultrasound and this, added to the already excellent spatial and temporal resolution, makes contrast-enhanced ultrasound (CEUS) well suited for the study of many organs, not only the liver. The contrast agents in clinical use today are so called blood pool agents meaning that, contrary to X-ray contrast media, they do not leave the blood vessels. This provides us with an excellent tool for delineating tissues with perfusion differences and for following the dynamic phases of contrast enhancement, in both large vessels and the microcirculation in parenchymatous organs. For vascular applications, CEUS improves detection of the renal arteries as well as strengthening Doppler signals. Emboli, posttraumatic rupture and other conditions impairing perfusion are readily detected and it may be possible to estimate blood flow by quantifying the contrast enhancement. The CEUS changes in diffuse renal disease are little explored but regional perfusion differences, such as in pyelonephritis, may be seen and quantified. In focal lesions, CEUS helps in the evaluation of atypical cysts and indeterminate masses detected on CT or MR. Many solid lesions may have a perfusion similar to the renal parenchyma but since many tumours are hypovascular, they tend to become echopoor relative to the enhanced renal parenchyma. The detection of a necrotic centre may further help both detection and characterization.