Ultrasound: Where we're at and where we're going

Seven Dutch and German authors outlined recent technological progressions—notably in diagnosis and therapy—which are slowly transitioning to clinical use and speculated on the future of ultrasound, in a March 1 article published in the Journal of Nuclear Medicine.

Corresponding author Fabian Kiessling, MD, with the Institute for Experimental Molecular Imaging at the University Aachen in Germany, and colleagues broke down their report by ultrasound techniques.

New Ultrasound Contrasts

The contrast in ultrasound grayscale imaging is not adequate in reconstructing material outlines, and even with theoretical applications the feasibility of implementing these methods is still out of reach.

Elastography methods—which image mechanical properties of tissue—are less operator-dependent, than traditional ultrasound, and demonstrated accuracy in diagnosing liver fibrosis and characterizing breast and thyroid tumors. But, standardization and increased computing complexity is still needed, noted Kiessling et al.

Photoacoustic or optoacoustic imaging offers additional tissue contrasts that may lead to tissue characterization and improved diagnosis.

Contrast-enhanced ultrasound imaging (CEUS)

In an unrelated study, CEUS was cited as an alternative to MRI and CT for grading Crohn’s disease activity.

And in a recent first-in-human pilot study on hepatic and extrahepatic tumors, 3D CEUS beat conventional 2D techniques. The modality claimed a higher repeatability of the measurements and reduced sampling error resulting from tumor tissue heterogeneity.

“It is expected that new imaging procedures, refined post-processing techniques and new 3D transducers will further improve the acceptance of CEUS as a complementary imaging technique to MRI and CT,” wrote Kiessling et al.

Super-resolution ultrasound imaging

Currently, experts are attempting to advance ultrasound to analyze the microvasculature of tissues.

Plotting the movement of individual microbubbles over time has led to the development of super-resolution images, and subsequent studies have increased the resolution of clinical ultrasound images by a factor of 2.2 to 5.1.

While study data found it difficult to translate these higher resolution images, authors propose post-processing data from 3D matrix transducers for the job.

Radiomic ultrasound analysis

Algorithms are attempting to extract unused information contained in ultrasound images with hopes the information may help locate diagnostically relevant biomarkers which otherwise go unnoticed.

Radiomic CT and MRI studies are underway, but authors claim it “highly likely” ultrasound data can be used for radiomic analysis in the future.

A first proof-of-concept study could demonstrate the radiomic analysis of ultrasound data and help differentiate tumor models.

High-intensity focused ultrasound (HIFU)

HIFU is used for a variety of therapies—whether guided by ultrasound or MRI—and is clinically approved to treat essential tumors, uterine fibroids, pain palliation in bone metastases and prostate cancer.

These therapies allow ultrasound-focused precision down to one mm diameter, which would prove highly beneficial in treatment and therapy.

“With many drugs approved or under development for immune system stimulation (or inhibition of tumor-associated immune suppression), there is a bright future for HIFU-supported immunotherapy in oncology,” wrote Kiessling et al.

Sonoporation

Clinically, oscillating microbubbles have been used to induce stable or inertial cavitation to promote vascular perfusion, permeability and/or tissue penetration—also known as sonoporation.

Studies have shown this technique can improve drug delivery to pancreatic cancer patients. Kiessling and colleagues cited a study using focused ultrasound and sonoporation to temporarily open the blood-brain-barrier within MRI scanners.

“In such setups, imaging allows for the real-time assessment of blood-brain-barrier opening and help to maximize the efficacy of the intervention while minimizing toxicity,” wrote Kiessling et al. “It can be envisaged that new techniques, like elastography, multi-parametric and super-resolution imaging will substantially improve the robustness and diagnostic power of ultrasound. Furthermore, therapeutic applications like HIFU and sonoporation will increase the therapeutic importance of this modality not only in oncology but also in neurology and the cardiovascular field.”