Aortic and valvular function — CMR phenotype documentation

Aorta

Aortic Distensibility

Arterial stiffness, defined as the resistance to deformation, serves as an early indicator of adverse functional and structural changes in the arterial system (Cavalcante et al. 2011). Aortic distensibility is a local marker of arterial elasticity and quantifies stiffness by measuring the relative change in cross-sectional area for a given pressure increment at a fixed vessel length (Groenink et al. 1998; Cavalcante et al. 2011).

Definition: The relative cross-sectional area (or diameter) change for a given pressure step at fixed vessel length (Cavalcante et al. 2011).
Calculation: Distensibility = (A<sub>max</sub>−A<sub>min</sub>)/(A<sub>min</sub>×PP) where A refers to the aortic cross-sectional area and PP is the pulse pressure, i.e., systolic blood pressure subtracted by diastolic blood pressure in unit mmHg (Groenink et al. 1998; Cavalcante et al. 2011; Singh et al. 2019).
Acquisition Type: Aortic distensibility cine

Reference Range:

Ascending aorta:

Study	Cohort Size	Gender	Age	Reference Value (10<sup>−3</sup>mmHg)	Note
(Kawel-Boehm et al. 2020)	12	male	20-29	(5.6, 1.5)
	16	male	30-39	(3.6, 1.4)
	11	male	40-49	(3.5, 1.5)
	12	male	50-59	(3.2, 1.6)
	10	male	60-69	(2.1, 1.3)
	14	female	20-29	(7.9, 3.4)
	12	female	30-39	(6.5, 3.0)
	13	female	40-49	(5.3, 1.2)
	13	female	50-59	(3.6, 1.1)
	11	female	60-69	(2.7, 1.0)
(Cecelja et al. 2022)	6492	male		(1.77, 1.15)	average age 62.6 years
	5999	female		(2.10, 1.45)	average age 61.9 years
(Rose et al. 2010)	13	male		(6.06, 2.51)	average age 35 years
	13	female		(8.55, 2.68)	average age 35 years
(Redheuil et al. 2011)	45	male		(5.07, 4.13)	average age 45 years
	55	female		(5.07, 3.60)	average age 48 years
(Rerkpattanapipat et al. 2002)	10			(4.3, 1.3)	4 males, 6 females, average age 24 years
	10			(2.2, 1.2)	5 males, 5 females, average age 71 years
(Rutz et al. 2012)	39			4.8-6.9	27 males, 12 females, average age 27 years
(Redheuil et al. 2014)	3675			(1.86, 1.31)	46% males, 54% females, average age 61 years

Descending aorta:

Study	Cohort Size	Gender	Age	Reference Value (10<sup>−3</sup>mmHg)	Note
(Kawel-Boehm et al. 2020)	12	male	20-29	(4.2, 0.9)
	16	male	30-39	(4.2, 0.9)
	11	male	40-49	(3.8, 1.3)
	12	male	50-59	(2.9, 1.1)
	10	male	60-69	(2.3, 0.9)
	14	female	20-29	(6.0, 1.4)
	12	female	30-39	(5.5, 1.9)
	13	female	40-49	(4.2, 1.2)
	13	female	50-59	(3.7, 1.3)
	11	female	60-69	(3.1, 0.9)
(Rose et al. 2010)	13	male		(5.05, 2.40)	average age 35 years
	13	female		(7.20, 1.61)	average age 35 years
(Redheuil et al. 2011)	45	male		(6.0, 3.33)	average age 45 years
	55	female		(5.86, 4.0)	average age 48 years
(Rutz et al. 2012)	39			5.5-10.0	27 males, 12 females, average age 27 years

Clinical Associations: Distensibility of the ascending aorta is reduced in individuals with hypertension (Malayeri et al. 2008), heart failure (HF) (Rerkpattanapipat et al. 2002), coronary artery disease (CAD) (Christodoulos Stefanadis et al. 1987; C. Stefanadis et al. 1990), Marfan syndrome (Groenink et al. 1998; Cavalcante et al. 2011), atherosclerosis (Siegel et al. 2013), and conotruncal defects such as Tetralogy of Fallot (TOF) and dextro-transposition (Rutz et al. 2012). Decreased distensibility is also associated with aortic regurgitation (AR), bicuspid aortic valve (BAV), and hypertrophic cardiomyopathy (HCM) (Cavalcante et al. 2011).
ICC:
- Ascending aorta: 0.57
- Descending aorta: 0.88

Pulse Wave Velocity (PWV)*

PWV is the rate of propagation of the systolic wave front down a vessel (aorta) and is a marker of vessel wall stiffness (Singh et al. 2019). PWV is the most validated method to non-invasively quantify arterial stiffness. It is considered the gold standard index of aortic stiffness, given its simplicity, accuracy, reproducibility, and strong prediction of adverse outcomes. It can be regionally determined by measuring the pulse transit time from the pressure waveforms at the 2 sites over a certain arterial length (Cavalcante et al. 2011). Alternatively, it can also be assessed locally through the Bramwell-Hill equation through the inverse relationship of aortic distensibility. The resulting PWV value is strongly associated with the gold-standard value measured from invasive measurements at consecutive locations in the aorta, as shown in the figure below (Westenberg et al. 2012).

<figure> <img src="/latex/images/aorta/PWV.png" id="fig:PWV" alt="Three methods for pulse wave velocity assessment. A: \text{PWV}{\text{through-plane}}: a CMR acquisition plane is positioned perpendicular to the ascending aorta, transecting both the ascending and descending aorta. Velocity is encoded perpendicular to the acquisition plane. Transit time is determined for the systolic velocity wave front to propagate from site 1 to site 2. The PWV can then be determined from the ratio of the distance and the transit-time. B: \text{PWV}{\text{in-plane}}: Three consecutive CMR acquisition planes capture the aortic arch in double-oblique sagittal orientation. Velocity is encoded in-plane in two directions. The velocity propagation along the centerline of the aorta determines the PWV. C: \text{PWV}_{\text{pressure}}: A pressure tip catheter is inserted in the aorta and positioned at the aortic valve. During pullback, invasive pressure is determined at positions 5.8 cm apart. The propagation of the pressure wave determines the PWV.(Westenberg et al. 2012)" /><figcaption aria-hidden="true">Three methods for pulse wave velocity assessment. <strong>A</strong>: <span class="math inline">PWV<sub>through-plane</sub></span>: a CMR acquisition plane is positioned perpendicular to the ascending aorta, transecting both the ascending and descending aorta. Velocity is encoded perpendicular to the acquisition plane. Transit time is determined for the systolic velocity wave front to propagate from site 1 to site 2. The PWV can then be determined from the ratio of the distance and the transit-time. <strong>B</strong>: <span class="math inline">PWV<sub>in-plane</sub></span>: Three consecutive CMR acquisition planes capture the aortic arch in double-oblique sagittal orientation. Velocity is encoded in-plane in two directions. The velocity propagation along the centerline of the aorta determines the PWV. <strong>C</strong>: <span class="math inline">PWV<sub>pressure</sub></span>: A pressure tip catheter is inserted in the aorta and positioned at the aortic valve. During pullback, invasive pressure is determined at positions 5.8 cm apart. The propagation of the pressure wave determines the PWV.<span>(Westenberg et al. 2012)</span></figcaption> </figure>

Definition: The rate of propagation of the systolic wave front down a vessel (aorta).
Calculation:
1. (Regionally) $\text{PWV}_{\text{regional}}=\frac{\Delta x}{\Delta t}$ where Δ**x is the distance around the aortic arch between the two sections through ascending and descending aorta, and Δ**t is the transit time delay for two volume flow curves for the descending and ascending aorta (Singh et al. 2019; Westenberg et al. 2012).
2. (Locally) PWV<sub>local</sub> = (ρ×Distensibility)<sup>1/2</sup> with ρ being the blood density 1059kg × m<sup>−3</sup> (Cavalcante et al. 2011; Westenberg et al. 2012)
Acquisition Type: Aortic distensibility cine

Reference Range:


Study	Cohort Size	Gender	Age	Reference Value (m/s)	Note
(Kim et al. 2013)	26		20-29	3.4-4.0	12 males, 14 females
	28		30-39	3.5-6.0	16 males, 12 females
	24		40-49	3.7-5.0	11 males, 13 females
	25		50-59	5.4-7.2	12 males, 13 females
	21		60-69	7.4-12.4	10 males, 11 females
(Eikendal et al. 2016)	57	male	25-35	3.9-5.6
	61	female	25-35	3.6-6.0
(Mehmood et al. 2024)	10			(4, 2)	9 males, 1 female, average age 22.9 years
	10			(11, 8)	4 males, 6 females, average age 60.5 years

Clinical Associations: PWV is elevated in patients with Marfan syndrome and atherosclerosis (Groenink et al. 1998; Blacher et al. 1999). An increase of aortic PWV of 1m/s also raises cardiovascular risk by more than 10% (Cavalcante et al. 2011).

Heart Valves

The assessment of blood flow parameters is important to the study of cardiovascular function and to the clinical evaluation of cardiovascular disease. Evaluation of the heart valves requires identification and quantification of stenoses and regurgitation, and congenital cardiac abnormalities require identification and quantification of shunt flow. Consider a single slice acquired at a single cardiac phase. To obtain the velocity map (i.e., an image where pixel intensity is proportional to v<sub> ⊥ i</sub>), a flow-encoding gradient is applied along the slice-selection direction of the imaging pulse sequence, after the excitation but before the readout. Spins that flow along the direction of the flow-encoding gradient accumulate phase ϕ<sub>i</sub>. Two complete sets of raw image data are acquired. A phase difference reconstruction is then applied to two raw data sets to obtain an image where the intensity of the ith pixel is proportional to the measured, perpendicular component of the fluid velocity v<sub> ⊥ i</sub> (Nayak et al. 2015).

As v<sub> ⊥ i</sub> provides an excellent approximation to the true, average velocity component within the voxel, unless flow-related aliasing occurs. The aliasing velocity is an operator-selected parameter of the phase contrast pulse sequence, often denoted by VENC, which is the maximum encoded velocity and is measured in units of cm/s. Provided the average perpendicular component of velocity within a voxel lies within the range, − VENC < |v<sub>⊥</sub>| < VENC, the pixel intensity in the phase difference image remains linearly proportional to v<sub> ⊥ i</sub> through $v_{\perp i}=\text{VENC}\frac{\Delta \phi_i}{\pi}$ . When |v<sub> ⊥ i</sub>| exceeds VENC, velocity aliasing will occur, meaning that velocities in excess of ± VENC will be aliased erroneously to velocities within the range of ± VENC (Nayak et al. 2015).

Peak Velocity

Velocity is a measure of how fast blood flows past a point (Silverthorn et al. 2013). The peak velocity v<sub>peak</sub> is determined when the heart is in peak contraction (Biederman et al. 2008). One heuristic approach to reduce spuriously high peak velocity values is to identify the 99th percentile velocity for all pixels at each time point, and retain the maximum value at any time point during systole (Kany et al. 2023).

Definition: The maximum velocity of blood flow measured within the aorta during a specific phase of the cardiac cycle, typically at systole.
Acquisition Type: Phase contrast (PC) imaging

Reference Range:

Study	Cohort Size	Gender	Age	Reference Value (cm/s)	Note
(Garcia et al. 2018)	9		9-15	(132, 11)
	13		16-20	(127, 16)
	27		21-39	(107, 18)
	40		40-59	(128, 23)
	9		>60	(142, 33)
	57	male		(128, 25)
	41	female		(118, 21)
(Kany et al. 2023)	22807	male		81-155	average age 65.8 years
	24416	female		83-153	average age 64.5 years
(Cotella et al. 2023)	977	male		86-159	average age 48 years
	926	female		88-165	average age 47 years
(Defrance et al. 2012)	21			108-137	10 males, 11 females, average age 50 years
(Garcia et al. 2021)	22			(117, 27)	average age 37 years, measured using 4D flow MRI
(Guala et al. 2019)	48			(120, 20)	31 males, 17 females, average age 39 years

Clinical Associations: Peak velocity is useful for accurately diagnosing the stages of valvular AS (Nishimura et al. 2014). Elevated peak velocity is also associated with CAD (Kany et al. 2023).
ICC: Note: 0.45

Mean Gradient

Liquids and gases flow down pressure gradients from regions of high pressure to regions of low pressure. The pressure gradient is analogous to the difference in pressure between two ends of a tube through which fluid flows (Silverthorn et al. 2013).

<figure> <img src="/latex/images/aorta/Bernoulli%20Principle.png" id="fig:Bernoulli" alt="The Bernoulli principle is based on the law of conservation of energy, which states that the total energy of an isolated system remains constant over time. Blood flowing through the heart and vessels obey the law of conservation of energy. It follows that the sum of kinetic energy K and pressure energy P of blood must be equal in two separate points in the system (“The Bernoulli Principle and Estimation of Pressure Gradients” n.d.)." /><figcaption aria-hidden="true">The Bernoulli principle is based on the law of conservation of energy, which states that the total energy of an isolated system remains constant over time. Blood flowing through the heart and vessels obey the law of conservation of energy. It follows that the sum of kinetic energy <span class="math inline"><em>K</em></span> and pressure energy <span class="math inline"><em>P</em></span> of blood must be equal in two separate points in the system <span>(<span>“The <span>Bernoulli</span> Principle and Estimation of Pressure Gradients”</span> n.d.)</span>.</figcaption> </figure>

Definition: Average pressure gradient across a segment of the aorta.
Calculation: The peak velocity v<sub>peak</sub> is used to compute the gradient using the simplified Bernoulli equation: Δ**P = 4v<sub>peak</sub><sup>2</sup> (Caruthers et al. 2003; Biederman et al. 2008; Nishimura et al. 2014; Kany et al. 2023). Then the mean value of the gradient at all time points during systole is taken as the mean gradient (Kany et al. 2023).
Acquisition Type: PC

Reference Range:

Study	Cohort Size	Gender	Reference Value (mmHg)	Note
(Kany et al. 2023)	22807	male	1.5-4.6	average age 65.8 years
	24416	female	1.5-4.5	average age 64.5 years
(Cotella et al. 2023)	977	male	1.55-4.90	average age 48 years
	926	female	1.58-5.50	average age 47 years
(Defrance et al. 2012)	21		2.0-3.8	10 males, 11 females, average age 50 years

Clinical Associations: Similar to peak velocity, mean gradient can be used for determine the stage of AS. Specifically, mild stenosis is defined as smaller than 20 mmHg, moderate 20 to 40 and severe over 40 (Nishimura et al. 2014). Elevated mean gradient is also associated with CAD (Kany et al. 2023).
ICC: 0.65

Regurgitant Fraction (RF)

As the vessel lumen is covered by a set of pixels, the flow Q<sub>i</sub> through pixel i can be formed through the product Q<sub>i</sub> = a<sub>i</sub> × v<sub>⊥</sub>i where a<sub>i</sub> is the area of ith pixel and is usually identical. The total flow Q is then calculated by summing over the N pixels that cover the desired vessel lumen in the image $Q_{tot}=\sum_{i=1}^N Q_i=\sum_{i=1}^N a_iv_{\perp i}=A\langle v_\perp \rangle$ for average velocity ⟨v<sub>⊥</sub>⟩ over the vessel lumen (Nayak et al. 2015). The aortic valve regurgitant fraction can be determined using the aortic valve regurgitant volume and the forward left ventricular stroke volume, where the regurgitant volume is the blood volume returning from the aorta to the left ventricle in diastole; and the forward left ventricular stroke volume is the blood volume that is pumped from the left ventricle to the aorta during systole (Gomes et al. 2022).

<figure> <img src="/latex/images/aorta/RF.png" id="fig:RF" alt="Illustration of different types of stroke volume and regurgitation volume. Net left ventricular stroke volume is the forward left ventricular stroke volume minus valve regurgitant volume (Gomes et al. 2022)." /><figcaption aria-hidden="true">Illustration of different types of stroke volume and regurgitation volume. Net left ventricular stroke volume is the forward left ventricular stroke volume minus valve regurgitant volume <span>(Gomes et al. 2022)</span>.</figcaption> </figure>

Definition: The ratio of regurgitant volume and the forward left ventricular stroke volume.
Acquisition Type: PC
Reference Range:
Study Cohort Size Reference Value (%) Note
(Garcia et al. 2021) 22 (0.3, 0.4) average age 37 years, measured using 4D flow MRI
(Gomes et al. 2022) 40077 (7.7, 6.5) average age 64.5 years
Clinical Associations:
According to AHA guidelines, mild regurgitation is defined as RF < 30%, moderate 30% to 49% and severe is ≥ 50%. (Biederman et al. 2008; Nishimura et al. 2014).
ICC: 0.53

Study	Cohort Size	Reference Value (%)	Note
(Garcia et al. 2021)	22	(0.3, 0.4)	average age 37 years, measured using 4D flow MRI
(Gomes et al. 2022)	40077	(7.7, 6.5)	average age 64.5 years

Systolic Flow Reversal Ratio (sFRR)

The systolic forward and backward flows can be defined in a similar manner, but only during systole instead of the entire cardiac cycle.

<figure> <img src="/latex/images/aorta/sFFR.png" id="fig:sFFR" alt="Minimal flow reversal during systolic phases in healthy individual (Mehmood et al. 2024)" /><figcaption aria-hidden="true">Minimal flow reversal during systolic phases in healthy individual <span>(Mehmood et al. 2024)</span></figcaption> </figure>

Definition: The ratio of systolic regurgitant volume and the systolic forward volume (Zhao et al. 2023; Mehmood et al. 2024).
Acquisition Type: PC

Reference Range:

Study	Cohort Size	Reference Value (%)	Note
(Assadi et al. 2023)	169	(4.3, 5.5)	96 males, 73 females
(Mehmood et al. 2024)	10	(2.0, 2.0)	9 males, 1 female, average age 22.9 years
	10	(7.0, 6.0)	4 males, 6 females, average age 60.5 years
(Zhao et al. 2023)	58	(2.3, 1.7)	35 males, 23 females, age ranges: 21-36 years
	56	(5.2, 3.4)	30 males, 26 females, age ranges: 37-50 years
	55	(10.5, 5.4)	31 males, 24 females, age ranges: 51-76 years

Clinical Associations: Patients with HFpEF have increased sFFR when compared with healthy controls (Mehmood et al. 2024).
ICC: 0.79

Flow Displacement

Flow displacement provides an approach to assess the degree of eccentric blood flow. The flow displacement can be averaged during systole, late systole and diastole (Zhao et al. 2023).

<figure> <img src="/latex/images/aorta/flow_displacement1.png" id="fig:flow_displacement1" alt="The left panel is the schematic representation of the displacement of flow (Disp), the center with respect to centerline of aorta (AoC). The right panel displays the flow displacement from the center of the aorta for normal, midly and markedly eccentric peak systolic flow patterns (Sigovan et al. 2011)." /><figcaption aria-hidden="true">The left panel is the schematic representation of the displacement of flow (Disp), the center with respect to centerline of aorta (AoC). The right panel displays the flow displacement from the center of the aorta for normal, midly and markedly eccentric peak systolic flow patterns <span>(Sigovan et al. 2011)</span>.</figcaption> </figure>

<figure> <img src="/latex/images/aorta/flow_displacement2.png" id="fig:flow_displacement2" alt="Curve of flow displacement. Late systole is defined as the interval between peak systole and end systole (Zhao et al. 2023)." /><figcaption aria-hidden="true">Curve of flow displacement. Late systole is defined as the interval between peak systole and end systole <span>(Zhao et al. 2023)</span>.</figcaption> </figure>

Definition: The distance between the vessel’s central point and the center-of-velocity, normalized to the lumen diameter. The center of velocity is calculated as the average position of lumen pixels, weighted by the velocity information $C_{vel}=\frac{\sum_i r_i|v_i|}{\sum_i |v_i|}$ , where i is the lumen pixel (Sigovan et al. 2011; Zhao et al. 2023; Mehmood et al. 2024).
Acquisition Type: PC

Reference Range:

Average during systole:

Study	Cohort Size	Reference Value (%)	Note
(Assadi et al. 2023)	169	(16, 8)	96 males, 73 females
(Mehmood et al. 2024)	10	(8, 4)	9 males, 1 female, average age 22.9 years
	10	(16, 5)	4 males, 6 females, average age 60.5 years
(Zhao et al. 2023)	58	(12, 4)	35 males, 23 females, age ranges: 21-36 years
	56	(17, 4)	30 males, 26 females, age ranges: 37-50 years
	55	(21, 6)	31 males, 24 females, age ranges: 51-76 years

Average during late systole:

Study	Cohort Size	Reference Value (%)	Note
(Zhao et al. 2023)	58	(13, 6)	35 males, 23 females, age ranges: 21-36 years
	56	(19, 6)	30 males, 26 females, age ranges: 37-50 years
	55	(26, 8)	31 males, 24 females, age ranges: 51-76 years

Average during diastole:

Study	Cohort Size	Reference Value (%)	Note
(Zhao et al. 2023)	58	(27, 7)	35 males, 23 females, age ranges: 21-36 years
	56	(28, 6)	30 males, 26 females, age ranges: 37-50 years
	55	(33, 8)	31 males, 24 females, age ranges: 51-76 years

Note: The obtained range is lower than the reference range

Clinical Associations: A higher value of flow displacement indicates more pronounced eccentric flow, which is investigated as a risk factor for ascending aorta aneurysm (Sigovan et al. 2011). The metric is elevated in patients with HFpEF (Mehmood et al. 2024).
ICC:
1. Average during systole: Note: 0.37
2. Average during late systole: <span style="color: red">0.39</span>
3. Average during diastole: Note: 0.23

Rotation Angle*

The flow displacement rotational angle (RA) refers to the angle formed by the anterior-pointing radius (12 o’clock position) and the line segment connecting the vessel center point and the center-of-velocity of the forward flow (Zhao et al. 2023). Such definition is sensitive to errors in negligible flow displacement as the position of the center-of-velocity and vessel are at a close proximity. Therefore, just a slight modification of the aortic contour can displace the location of the center-of-velocity flow and significantly alter RA. Therefore, a FD=12% threshold is usually chosen to circumvent such effect (Mehmood et al. 2024).

<figure> <img src="/latex/images/aorta/rotation_angle.png" id="fig:rotation_angle" alt="Illustration of how to calculate the rotation angle change \Delta RA. Only phases with FD>12% are considered (Zhao et al. 2023)" /><figcaption aria-hidden="true">Illustration of how to calculate the rotation angle change <span class="math inline"><em>Δ</em><em>R</em><em>A</em></span>. Only phases with FD>12% are considered <span>(Zhao et al. 2023)</span></figcaption> </figure>

Definition: The difference between the rotation angle at end systole and that at the point where the flow angle stabilized after peak systole from the rotation angle curve (Zhao et al. 2023).
Acquisition Type: PC

Reference Range:

Study	Cohort Size	Reference Value ()	Note
(Assadi et al. 2023)	169	(0, 3)	96 males, 73 females
(Mehmood et al. 2024)	10	(0, 0)	9 males, 1 female, average age 22.9 years
	10	(-3, 16)	4 males, 6 females, average age 60.5 years
(Zhao et al. 2023)	58	(-3.2, 25.1)	35 males, 23 females, age ranges: 21-36 years
	56	(10.2, 47.6)	30 males, 26 females, age ranges: 37-50 years
	55	(-9.4, 49.8)	31 males, 24 females, age ranges: 51-76 years

Assadi, Hosamadin, Gareth Matthews, Xiaodan Zhao, Rui Li, Samer Alabed, Ciaran Grafton-Clarke, Zia Mehmood, et al. 2023. “Cardiac MR Modelling of Systolic and Diastolic Blood Pressure.” Open Heart 10 (2): e002484.

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Cavalcante, João L., João A. C. Lima, Alban Redheuil, and Mouaz H. Al-Mallah. 2011. “Aortic Stiffness.” Journal of the American College of Cardiology 57 (14): 1511–22.

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Cecelja, Marina, Bram Ruijsink, Esther Puyol-Antón, Ye Li, Harriet Godwin, Andrew P. King, Reza Razavi, and Phil Chowienczyk. 2022. “Aortic Distensibility Measured by Automated Analysis of Magnetic Resonance Imaging Predicts Adverse Cardiovascular Events in UK Biobank.” Journal of the American Heart Association 11 (23): e026361.

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Cotella, Juan I, Tatsuya Miyoshi, Victor Mor-Avi, Karima Addetia, Marcus Schreckenberg, Deyu Sun, Jeremy A Slivnick, et al. 2023. “Normative Values of the Aortic Valve Area and Doppler Measurements Using Two-Dimensional Transthoracic Echocardiography: Results from the Multicentre World Alliance of Societies of Echocardiography Study.” European Heart Journal - Cardiovascular Imaging 24 (4): 415–23.

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Defrance, Carine, Emilie Bollache, Nadjia Kachenoura, Ludivine Perdrix, Nataliya Hrynchyshyn, Eric Bruguière, Alban Redheuil, Benoit Diebold, and Elie Mousseaux. 2012. “Evaluation of Aortic Valve Stenosis Using Cardiovascular Magnetic Resonance: Comparison of an Original Semiautomated Analysis of Phase-Contrast Cardiovascular Magnetic Resonance With Doppler Echocardiography.” Circulation: Cardiovascular Imaging 5 (5): 604–12.

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Eikendal, Anouk L. M., Michiel L. Bots, Cees Haaring, Tobias Saam, Rob J. Van Der Geest, Jos J. M. Westenberg, Hester M. Den Ruijter, Imo E. Hoefer, and Tim Leiner. 2016. “Reference Values for Cardiac and Aortic Magnetic Resonance Imaging in Healthy, Young Caucasian Adults.” Edited by John Lynn Jefferies. PLOS ONE 11 (10): e0164480. https://doi.org/10.1371/journal.pone.0164480.

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Garcia, Julio, Kailey Beckie, Ali F Hassanabad, Alireza Sojoudi, and James A White. 2021. “Aortic and Mitral Flow Quantification Using Dynamic Valve Tracking and Machine Learning: Prospective Study Assessing Static and Dynamic Plane Repeatability, Variability and Agreement.” JRSM Cardiovascular Disease 10 (January): 2048004021999900. https://doi.org/10.1177/2048004021999900.

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Garcia, Julio, Roel L. F. van der Palen, Emilie Bollache, Kelly Jarvis, Michael J. Rose, Alex J. Barker, Jeremy D. Collins, et al. 2018. “Distribution of Blood Flow Velocity in the Normal Aorta: Effect of Age and Gender.” Journal of Magnetic Resonance Imaging : JMRI 47 (2): 487–98. https://doi.org/10.1002/jmri.25773.

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Gomes, Bruna, Aditya Singh, Jack W O’Sullivan, David Amar, Mykhailo Kostur, Francois Haddad, Michael Salerno, Victoria N. Parikh, Benjamin Meder, and Euan A. Ashley. 2022. “Genetic Architecture of Cardiac Dynamic Flow Volumes.” Cardiovascular Medicine. https://doi.org/10.1101/2022.10.05.22280733.

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