Table 2.

Summary of 4D flow-derived metrics

Category	Metric	Definition	Comment
Geometry & Stiffness	PA volume, V (ml)	Temporally averaged volume of the MPA, LPA, RPA branches over a cardiac cycle	Internal diameters potentially influenced by proximal thrombus
	PA area, A (cm2)	Centerline-based cross-sectional slice located 50% down the length of the MPA, LPA, and RPA branches
	Relative area change (Pulsatility)
	Compliance (cm2/mmHg)		Healthy PA compliance = 0.15 cm2/mmHg§
	Distensibility (%/mmHg)		Healthy PA distensibility = 3.1%/mmHg§
Velocity Flow Profile	Centerline velocity (cm/s)	Maximum velocity in the center 30% radius of a cross-sectional slice located 50% down the length of each branch.
	Flow rate (L/min)	is the velocity vector, is the surface normal vector, A is the area of the cross-sectional slice located 10% down the length of the MPA, LPA, and RPA
	Acceleration ime ratio	is the time between the end-systolic and end-diastolic timepoint
Secondary Flow Profile	Fractional area of reverse flow	Areas where velocity is perpendicular or negative to the forward flow direction. Taken at a cross-sectional slice 50% down the length of the branch	Quantifies areas of recirculation, may correspond to large visual vortices
	Vorticity, (1/s)	is the spatial gradient, is the velocity vector, V is the volume of the branch; spatially averaged over the volume of the branch	Local rotation in a fluid flow including local shearing in space
	Helicity density, Hd (m/s2)	Amount of rotation parallel to the local velocity vector	Clockwise rotation when >0, counterclockwise rotation when <0
	Volume fraction of positive helicity	V is the volume of the branch
	Helical flow index, HFI	Absolute value of the cosine of the angle between the vorticity and velocity vector, measure of helicity intensity	Limit from 0 to 1
	Dean number, De	D is the diameter of the vessel, is the mean velocity (computed at a cross-sectional slice 50% down the length of the pulmonary trunk), is the density of blood (1.06 g/cm3), is the viscosity of blood (0.04 Poise), and is the radius of curvature of the vessel defined from the centerlines in the MPA, LPA, or RPA	Non-dimensional parameter of the inertial, centripetal, and viscous forces; tendency of Dean vortices to form in a curved vessel
	Q-criterion	Defines a vortex as a connected fluid region where the norm of the vorticity tensor, , outweighs the norm of the strain rate tensor, .	May not uniquely detect visual vortical regions
RV Function§§	% Predicted RV metrics		Adjusted for differences in sex, age, weight, height
		RVEF: a = 0.0706, b=-0.00771, c=-0.0782  m = 75.19 (female), 71.52 (male)
		RVEDV: a=-0.258, b = 1.582, c = 0.382  m = 27.94 (female), 31.50 (male)
		RVESV: a=-0.417, b = 1.501, c = 0.617  m = 5.58 (female), 7.24 (male)
		RVSV: a=-0.187, b = 1.574, c = 0.304  m = 21.12 (female), 22.42 (male)

^§Healthy PA compliance and distensibility from Sanz et al. [29]

^§§RV metrics were adjusted for sex, age, weight, and height based on normalized equations from Kawut et al. [27]. RV, right ventricle, EF, ejection fraction, EDV, end-diastolic volume, ESV, end-systolic volume, SV, stroke volume, PA, pulmonary artery