Improving coronary ultrafast Doppler angiography using fractional moving blood volume and motion-adaptive ensemble length.

Coronary microperfusion assessment is a key parameter for understanding cardiac function. Currently, coronary ultrafast Doppler angiography is the only non-invasive clinical imaging technique able to assess coronary microcirculation quantitatively in humans. In this study, we propose to use fractional moving blood volume (FMBV), proportional to the red blood cell concentration, as a metric for perfusion. FMBV compares the power Doppler in a region of interest (ROI) inside the myocardium to the power Doppler of a reference area in the heart chamber, fully filled with blood. This normalization gives then relative values of the ROI blood filling. However, due to the impact of ultrasound attenuation and elevation focus on power Doppler values, the reference area and the ROI need to be at the same depth to allow this normalization. This condition is rarely satisfiedin vivodue to the cardiac anatomy. Hereby, we propose to locally compensate the attenuation between the ROI and the reference, by measuring the attenuation law on a phantom. We quantified the efficiency of this approach by comparing FMBV with and without compensation on a flow phantom. Compensated FMBV was able to estimate the ground-truth FMBV with less than 5% variation. This method was then adapted to thein vivocase of myocardial perfusion imaging during heart surgery on human neonates. The translation fromin vitrotoin vivorequired an additional clutter filtering step to ensure that blood signals could be correctly identified in the fast-moving myocardium. We applied the singular value decomposition filter on temporal sliding windows whose lengths were a function of myocardium motion. This motion-adaptive temporal sliding window approach was able to improve blood and tissue separation in terms of contrast-to-noise ratio, as compared to well-established constant-length sliding window approaches. Therefore, compensated FMBV and singular value decomposition assisted with motion-adaptive temporal sliding windows improves the quantification of blood volume in coronary ultrafast Doppler angiography.

Quantitative imaging of coronary flows using 3D ultrafast Doppler coronary angiography.

Coronary flow rate remains complex to assess in clinical practice using non-invasive, non-ionizing imaging tools. In this study, we introduce 3D ultrafast Doppler coronary angiography (3D UDCA), an ultrasound-based method to assess coronary blood flows in three-dimensions at high volume-rate and in one single heartbeat. We demonstrate that 3D UDCA can visualize the coronary vasculature with high temporal and spatial resolution and quantify the absolute flow. The feasibility of the technique was demonstrated in an open-chest swine model. The flow rate of the left-anterior descending artery (LAD) assessed by 3D UDCA was reconstructed successfully at the early diastolic and late diastolic phases and was in good agreement with an invasive gold-standard flowmeter during baseline, reactive hyperemia and coronary stenosis (r2 = 0.84). Finally, we demonstrate that a coronary stenosis on the LAD can be visualized as well as its associated flow acceleration.

4D simultaneous tissue and blood flow Doppler imaging: revisiting cardiac Doppler index with single heart beat 4D ultrafast echocardiography.

The goal of this study was to demonstrate the feasibility of semi-automatic evaluation of cardiac Doppler indices in a single heartbeat in human hearts by performing 4D ultrafast echocardiography with a dedicated sequence of 4D simultaneous tissue and blood flow Doppler imaging. 4D echocardiography has the potential to improve the quantification of major cardiac indices by providing more reproducible and less user dependent measurements such as the quantification of left ventricle (LV) volume. The evaluation of Doppler indices, however, did not benefit yet from 4D echocardiography because of limited volume rates achieved in conventional volumetric color Doppler imaging but also because spectral Doppler estimation is still restricted to a single location. High volume rate (5200 volume s-1) transthoracic simultaneous tissue and blood flow Doppler acquisitions of three human LV were performed using a 4D ultrafast echocardiography scanner prototype during a single heartbeat. 4D color flow, 4D tissue Doppler cineloops and spectral Doppler at each voxel were computed. LV outflow tract, mitral inflow and basal inferoseptal locations were automatically detected. Doppler indices were derived at these locations and were compared against clinical 2D echocardiography. Blood flow Doppler indices E (early filling), A (atrial filling), E/A ratio, S (systolic ejection) and cardiac output were assessed on the three volunteers. Simultaneous tissue Doppler indices e' (mitral annular velocity peak), a' (late velocity peak), e'/a' ratio, s' (systolic annular velocity peak), E/e' ratio were also estimated. Standard deviations on three independent acquisitions were averaged over the indices and was found to be inferior to 4% and 8.5% for Doppler flow and tissue Doppler indices, respectively. Comparison against clinical 2D echocardiography gave a p  value larger than 0.05 in average indicating no significant differences. 4D ultrafast echocardiography can quantify the major cardiac Doppler indices in a single heart beat acquisition.