Validation of magnetic resonance phase-contrast flow measurements in the main pulmonary artery and aorta using perivascular ultrasound in a large animal model.
OBJECTIVE
Phase-contrast flow magnetic resonance imaging (pc-MRI) measurements are an established technique for noninvasive assessment of hemodynamics. However, in vivo validation data on the accuracy of pc-flow especially for nonphysiologic hemodynamic conditions are missing. The goal of our work was 1) to validate pc-flow with perivascular ultrasound in different hemodynamic conditions in the main pulmonary artery (MPA) and ascending aorta (AO) and 2) to investigate the relation between pc-MRI and invasive pressure measurements.


METHODS
Five healthy pigs with opened chest were investigated. Ultrasound measurements were performed outside the MRI unit using a detachable MR-table. Parallel to ultrasound flow measurements, invasive pressure measurements were performed. PC-MRI (1.5 T MRI) measurements were done using a FLASH 2-dimensional sequence. First the animals were examined in normotonia, followed by hypertension (infusion of Arterenol) and hypotension (infusion of Sodiumnitropussid).


RESULTS
Flow measurements acquired in normotonia were 2.7 +/- 0.6 L/min (ultrasound) and 2.8 +/- 0.6 L/min for pc-MRI (not significantly different, P = 0.17). During hypertonia, the blood flow increased to 3.1 +/- 0.7 and 2.7 +/- 0.8 L/min, respectively (P = 0.01). During hypotension, the blood flow decreased to 1.7 +/- 0.5 and 1.7 +/- 0.5 L/min, respectively (P = 0.7). An excellent linear correlation (taking all measurements together) between the ultrasound and pc-MRI measurements was found (r = 0.89). 95% Limits of intraindividual agreement correspond to relative differences of -36 to 44%. Systolic pressure measurements in the AO were 91 mm Hg (normotonic), 111 mm Hg (hypertonic), and 64 mm Hg (hypotonic) and in the MPA 23 mm Hg (normotonic), 29 mm Hg (hypertonic), and 20 mm Hg (hypotonic). Systolic pressure measurements showed good linear correlation with pc-MRI average flow per minute and peak velocity (AO: r = 0.79, MPA: r = 0.66).


CONCLUSIONS
MRI pc-flow measurements are a reliable tool for noninvasive assessment of blood flow. Hemodynamic parameters derived by MRI demonstrate good linear correlations with the pressure in the systemic and pulmonary arterial circulation.
Ley
Sebastian
S
Department of Pediatric Radiology, Children's Hospital University Heidelberg, Germany. ley@gmx.net
Unterhinninghofen
Roland
R
Ley-Zaporozhan
Julia
J
Schenk
Jens-Peter
JP
Kauczor
Hans-Ulrich
HU
Szabo
Gabor
G
D000818:Animals; D001013:Aorta, Thoracic / Q000000981:diagnostic imaging* / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D006439:Hemodynamics; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D023421:Models, Animal; D009599:Nitroprusside / Q000008:administration & dosage; D009638:Norepinephrine / Q000008:administration & dosage; D011651:Pulmonary Artery / Q000000981:diagnostic imaging* / Q000502:physiology*; D013552:Swine; D018084:Ultrasonography, Interventional
D009599:Nitroprusside; D009638:Norepinephrine