Role of Contrast-Enhanced Ultrasound (CEUS) in Native Kidney Pathology: Limits and Fields of Action

Abstract

Gray scale ultrasound has an important diagnostic role in native kidney disease. Low cost, absence of ionizing radiation and nephrotoxicity, short performance time, and repeatability even at the bedside, are the major advantages of this technique. The introduction of contrast enhancement ultrasound (CEUS) in daily clinical practice has significantly reduced the use of contrast enhancement computed tomography (CECT) and contrast enhancement magnetic resonance (CEMR), especially in patients with renal disease. Although there are many situations in which CECT and CEMRI are primarily indicated, their use may be limited by the administration of the contrast medium, which may involve a risk of renal function impairment, especially in the elderly, and in patients with acute kidney injury (AKI) and moderate to severe chronic kidney disease (CKD). In these cases, CEUS can be a valid diagnostic choice. To date, numerous publications have highlighted the role of CEUS in the study of parenchymal micro-vascularization and renal pathology by full integration with second level imaging methods (CECT and CEMRI) both in patients with normal renal function and with diseased kidneys. The aim of this review is to offer an updated overview of the limitations and potential applications of CEUS in native kidney disease.

Renal Contrast-enhanced Ultrasound: Clinical Applications and Emerging Researc

“…Microbubbles (MBs) contain a core gas (generally sulfur hexafluoride or octafluoropropane) that has low diffusibility and solubility in water, as well as high vapor pressure, resulting in UCAs persisting inside the intravascular space. In response to ultrasound waves MBs contract and expand, reflecting the transducer with improved acoustic energy than passive reflectors and enabling increased backscattering signals (up to 30 dB) [1,2]. The non-linear oscillation pattern of MBs generates harmonic signals that help differentiate contrast signals from background tissues [3].…”

“…Microbubbles are cleared from the vascular space approximately five to fifteen minutes following the injection of UCA. The internal gas is exhaled through the lungs, and the shell particles are metabolized by the liver [1,2]. A dual-image system is traditionally employed by CEUS, where half the screen displays a low mechanical index (MI) B-mode image for anatomical guidance while the other displays the image of the nonlinear MBs signal.…”

“…CEUS provides realtime imaging evaluation in addition to a video recording from the time the UCA permeates vascular structures (wash-in) to the time when the MB enhancement pattern is no longer evident (wash-out) [4]. As CEUS commonly relies on phase/pulse inversion to suppress the background signals (artifacts and tissue) while maintaining a low MI to prevent microbubble disruption, nonlinear signal processing is usually required for proper imaging characterization [1,2,5]. Finally, the interpretation of CEUS is based on qualitative (degree and timing of the enhancement) and quantitative analyses (time-intensity curves from regions of interest are used to quantify blood flow speed and relative volume indirectly) [6,7].…”

“…The use of CEUS can be an effective method of evaluating kidney pathology [8]. Approximately 21% of the cardiac output is directed to the kidney, which implies that the contrast agent rapidly enhances the renal parenchyma and vascular structures [2]. Compared to power and color Doppler, CEUS is more sensitive in detecting microvascular architecture with very slow blood flow [1].…”

“…Currently, hypersensitivity to any agent contents is the only absolute contraindication for UCAs [9]. However, severe allergic reactions have only been reported in a small number of patients (0.006-0.009%) [1,2]. In a few cases, severe cardiopulmonary reactions have been reported following the administration of MBs, and they should be administered with caution to patients with these conditions [10].…”