Evaluation of tumor microvasculature with 3D ultrasound localization microscopy based on 2D matrix array

Objective

Evaluation of tumor microvascular morphology is of great significance in tumor diagnosis, therapeutic effect prediction, and surgical planning. Recently, two-dimensional ultrasound localization microscopy (2DULM) has demonstrated its superiority in the field of microvascular imaging. However, it suffers from planar dependence and is unintuitive. We propose a novel three-dimensional ultrasound localization microscopy (3DULM) to avoid these limitations.

Methods

We investigated 3DULM based on a 2D array for tumor microvascular imaging. After intravenous injection of contrast agents, all elements of the 2D array transmit and receive signals to ensure a high and stable frame rate. Microbubble signal extraction, filtering, positioning, tracking, and other processing were used to obtain a 3D vascular map, flow velocity, and flow direction. To verify the effectiveness of 3DULM, it was validated on double helix tubes and rabbit VX2 tumors. Cisplatin was used to verify the ability of 3DULM to detect microvascular changes during tumor treatment.

Results

In vitro, the sizes measured by 3DULM at 3 mm and 13 mm were 178 \(\mathrm{\mu m}\) $\mu \mathrm{m}$ and 182 \(\mathrm{\mu m}\) $\mu \mathrm{m}$ , respectively. In the rabbit tumors, we acquired 9000 volumes to reveal vessels about 30 \(\mathrm{\mu m}\) $\mu \mathrm{m}$ in diameter, which surpasses the diffraction limit of ultrasound in traditional ultrasound imaging, and the results matched with micro-angiography. In addition, there were significant changes in vascular density and curvature between the treatment and control groups.

Conclusions

The effectiveness of 3DULM was verified in vitro and in vivo. Hence, 3DULM may have potential applications in tumor diagnosis, tumor treatment evaluation, surgical protocol guidance, and cardiovascular disease.

Clinical relevance statement

3D ultrasound localization microscopy is highly sensitive to microvascular changes; thus, it has clinical potential for tumor diagnosis and treatment evaluation.

Key Points

• 3D ultrasound localization microscopy is demonstrated on double helix tubes and rabbit VX2 tumors.

• 3D ultrasound localization microscopy can reveal vessels about 30 \(\mu m\) $\mu m$ in diameter—far smaller than traditional ultrasound.

• This form of imaging has potential applications in tumor diagnosis, tumor treatment evaluation, surgical protocol guidance, and cardiovascular disease.