# Ultrafast power Doppler imaging for RV myocardial perfusion assessment: histopathologic correlation and in vivo comparison—a pilot study

## TL;DR

A new imaging technique called acFMBV using ultrafast power Doppler was tested to non-invasively measure blood volume in the right ventricle of rats and humans, showing promise for assessing heart conditions.

## Contribution

The study introduces and validates a novel non-invasive method (acFMBV) for quantifying right ventricular myocardial blood volume using ultrafast power Doppler.

## Key findings

- Mid-diastolic acFMBV was significantly lower in rats with pulmonary artery banding compared to controls.
- acFMBV correlated strongly with capillary density in rat models (r = 0.78).
- Human patients with RV pressure overload had lower acFMBV than healthy volunteers.

## Abstract

Myocardial vascular remodeling is a key feature in various diseases associated with right ventricular (RV) pressure overload but its non-invasive assessment remains challenging. The new technique attenuation-compensated fractional moving blood volume (acFMBV) based on ultrafast power Doppler (UPD) was developed for myocardial blood volume quantification, linked to RV remodeling and capillary density, but not validated in vivo.

To quantify RV myocardial blood volume across the cardiac cycle using UPD in rodent models, with histopathological validation, and assess its feasibility in human patients.

Twelve rats (sex ratio 1/1) were randomized to pulmonary artery banding (PAB) (n = 6) or sham controls (n = 6). After 6 weeks, UPD-derived acFMBV was measured in the RV lateral wall, representing myocardial blood volume. Capillary density was quantified via CD31 immunostaining, and its correlation with mid-diastolic acFMBV was evaluated. UPD was also applied in seven healthy human volunteers and seven age-matched patients with RV pressure overload. Mid-diastolic acFMBV in PAB rats was significantly lower than in controls (5.3% ± 0.9% vs. 7.8% ± 1.2%, P < 0.05), correlating with reduced capillary density (r = 0.78, P < 0.01). In humans, mid-diastolic acFMBV was also lower in RV pressure overload patients compared with healthy volunteers (4.8% ± 0.7% vs. 3.1% ± 2.3%, respectively, P = 0.03).

In this pilot study, UPD-based acFMBV correlates with histological capillary density, supporting its potential as a reliable, non-invasive tool for quantifying RV myocardial blood volume in clinical settings. These observations will need to be confirmed in studies with larger sample sizes.

Myocardial vascular remodeling in right ventricle (RV) pressure overload is difficult to assess non-invasively. This study validated attenuation-compensated fractional moving blood volume (acFMBV) using ultrafast power Doppler (UPD) to quantify RV myocardial blood volume. Twelve rats underwent pulmonary artery banding (PAB) or sham surgery, with acFMBV measured and correlated with capillary density. PAB rats had lower mid-diastolic acFMBV and capillary density (r = 0.78, P < 0.01). In humans, RV pressure-overload patients showed reduced acFMBV compared with healthy volunteers (P = 0.03). UPD-based acFMBV correlates with histology, supporting its use as a non-invasive tool for assessing RV perfusion.

Graphical AbstractEstimation of blood volume by UPD and histology method. (a) Estimate blood volume by UPD-based acFMBV in RV middle endocardium. Post-processing was applied in ROIs for PD values that contain blood signals. The acFMBV was calculated as the ratio of PD values in ROIs, representing the percentage of blood volume in ROI in RV myocardium. (b) Estimate capillary density by histology, as defined by the ratio of pixel numbers between stained capillaries and the whole myocardium area. acFMBV: attenuation compensated fractional moving blood volume; LV: left ventricle; PD: power Doppler; ROI: region of interest; RV: right ventricle; SVD: singular value decomposition; UPD: ultrafast power Doppler.For image description, please refer to the figure legend and surrounding text.

Estimation of blood volume by UPD and histology method. (a) Estimate blood volume by UPD-based acFMBV in RV middle endocardium. Post-processing was applied in ROIs for PD values that contain blood signals. The acFMBV was calculated as the ratio of PD values in ROIs, representing the percentage of blood volume in ROI in RV myocardium. (b) Estimate capillary density by histology, as defined by the ratio of pixel numbers between stained capillaries and the whole myocardium area. acFMBV: attenuation compensated fractional moving blood volume; LV: left ventricle; PD: power Doppler; ROI: region of interest; RV: right ventricle; SVD: singular value decomposition; UPD: ultrafast power Doppler.