A Review of Clinical Applications for Super-resolution Ultrasound Localization Microscopy

Renal Contrast-enhanced Ultrasound: Clinical Applications and Emerging Researc

“…It has been demonstrated that increasing the CEUS imaging frequency (e.g., to 15 MHz) can enhance spatial resolution (~100 μm). However, this leads to significantly reduced image penetration, which may be suitable only for evaluating superficial tissues [82]. To potentially address this limitation, a new CEUS imaging technology known as super-resolution ultrasound localization microscopy (ULM) has emerged [79,81].…”

“…To potentially address this limitation, a new CEUS imaging technology known as super-resolution ultrasound localization microscopy (ULM) has emerged [79,81]. While CEUS creates images using the signal intensity of MBs, ULM uses the localization of spatially isolated MBs to project super-resolved images of vascular structures using high frame rates [80,81,82]. Furthermore, by tracking the movement and location of MBs, UML can measure blood flow velocities over a wide range (1 mm/s to several cm/s), providing direct and quantitative measurements as opposed to CEUS (indirect and semi-quantitative) [82].…”

“…While CEUS creates images using the signal intensity of MBs, ULM uses the localization of spatially isolated MBs to project super-resolved images of vascular structures using high frame rates [80,81,82]. Furthermore, by tracking the movement and location of MBs, UML can measure blood flow velocities over a wide range (1 mm/s to several cm/s), providing direct and quantitative measurements as opposed to CEUS (indirect and semi-quantitative) [82]. This emerging technology provides a substantial advancement in hemodynamic quantification and evaluation of the microcirculation, demonstrating a 10fold improvement in spatial resolution using low imaging frequencies and without compromising the imaging depth of conventional CEUS [79,81,83,84].…”

“…Within renal CEUS applications, there are several clinical scenarios where the addition of ULM could provide considerable benefit [80,82]. In patients with renal malignancy, detailed visualization of the microvasculature network can provide critical information for differentiating between malignant and benign tumors, evaluating early post-therapeutic response for treatment adjustment, and distinguishing residual tumors from the inflammatory reaction band (IRB) after thermal ablation procedures [82]. In patients at risk of kidney disorders or those with established disease (i.e., CKD), early and reliable quantification of renal microvascular perfusion is an essential factor for the course and prognosis of the disease [87].…”

“…While ULM has excellent diagnostic potential, its disadvantages and technical difficulties make its clinical application challenging and favor the continued use of conventional CEUS [79,88]. Since super-resolution ultrasound requires long acquisition times (100 -200 seconds), it is impossible to visualize wash-in/out enhancement patterns in real-time [79,82]. It is also important to note that due to the lack of a gold standard with which to measure ULM's in vivo accuracy, its conclusive investigation is limited [82].…”