Search

BACKGROUND Pulmonary regurgitation frequently occurs after surgical correction of tetralogy of Fallot. To date, reliable quantitation of pulmonary regurgitation has not been possible, and therefore the clinical significance of pulmonary regurgitation is controversial. Nuclear magnetic resonance (NMR) velocity mapping allows accurate measurement of volumetric flow. The feasibility and accuracy of NMR velocity mapping to quantify pulmonary regurgitation volumes are studied in patients after Fallot repair. METHODS AND RESULTS In 18 patients (mean age, 16.5 +/- 6.5 years), late (12.6 +/- 5.2 years) after Fallot surgery, forward and regurgitant volume flow was measured in the main pulmonary artery with NMR velocity mapping. To validate the measurements of pulmonary forward flow, right ventricular stroke volume was used as an internal reference standard. Pulmonary regurgitation volumes were compared with the differences between the corresponding right and left ventricular stroke volumes. Ventricular volumes were measured with a multisection gradient echo NMR method. In addition, the relation between pulmonary regurgitation and right ventricular volumes was studied. Measurements of pulmonary regurgitation volume with NMR velocity mapping closely corresponded with the tomographically determined volumes (r = .93). Forward pulmonary volume flow was nearly identical to right ventricular stroke volume (r = .98). Pulmonary regurgitation volume was significantly correlated with end-diastolic volume (r = .82, P < .0005), end-systolic volume (r = .63, P < .01), and stroke volume (r = .89, P < .0005) of the right ventricular but not with right ventricular ejection fraction (r = .41, P = NS). CONCLUSIONS NMR velocity mapping is an accurate method for the noninvasive, volumetric quantification of pulmonary regurgitation after surgical correction of tetralogy of Fallot.

BACKGROUND Currently available noninvasive techniques for measuring blood flow velocities are constrained by limited view orientations (Doppler ultrasound) or limited time resolution (magnetic resonance imaging, MRI). We describe an MRI technique for measuring flow velocities in real time at arbitrary orientations within a cylindrical volume or "beam": V-mode nuclear magnetic resonance (NMR). METHODS AND RESULTS The technique was implemented on a standard 1.5-T clinical NMR imager with no special hardware and was tested on phantoms and human volunteers. The beam can be fired at rates up to 60 times per second, allowing measurements on a time scale that is appropriate for ungated cardiac studies. In phantoms, steady flow velocities were measured with the beam aligned along the direction of flow, and the measured velocities correlated well with the actual velocities (r > 0.99). The radial distribution of velocities in phantoms under constant flow conditions was also determined. In humans, flow of blood in the descending aortas of normal and aortic insufficiency subjects was measured. Distinctive backflow of blood because of aortic insufficiency was readily apparent. CONCLUSIONS The V-mode NMR technique is capable of acquiring clinically relevant real-time blood flow information from any desired angle of view with no attenuation at bone or air-tissue interfaces.

Mitral and pulmonary venous flows are important indexes in the evaluation of left ventricular diastolic function and in the assessment of mitral valve disease. We used MR phase-shift velocity mapping to measure mitral and pulmonary venous flow velocity in 10 healthy volunteers and mitral flow velocity in 5 patients with mitral valve stenosis. Normal mitral flow shows two positive peaks: one during early ventricular diastole and the other during atrial contraction. Peak mitral flow velocity (mean +/- SD) in early diastole was 68 +/- 12 cm/s and during atrial contraction 39 +/- 10 cm/s. The ratio of peak mitral flow velocity in early diastole to that during atrial contraction was 1.9 +/- 0.6. In patients with mitral valve stenosis, the initial high flow velocity persisted through diastole. Peak mitral flow velocity of patients with mitral valve stenosis correlated well with values obtained from Doppler echocardiography. Pulmonary venous flow showed two positive peaks: one during ventricular systole and the other in ventricular diastole. A small backflow during atrial contraction was noticed. Peak systolic velocity in the right lower pulmonary vein was 47 +/- 11 cm/s, peak diastolic velocity was 40 +/- 9 cm/s, and peak backflow velocity was 14 +/- 3 cm/s. Magnetic resonance velocity mapping is a noninvasive technique for the evaluation of time-related flow velocity patterns and for quantitative measurement of mitral and pulmonary venous blood flow velocity.

A 36-year-old female patient presented with recurrent arterial emboli of both arms and a suspected transient ischemic attack. Routine thoracic contrast-enhanced, 3D magnetic resonance angiography (CE-MRA) at 3 T was performed to rule out additional arterial thrombi. The resulting CE-MRA images and consecutive, curved, multiplanar reconstructions (Figure 1B and 1C) revealed a partially obstructing thrombus (as a signal void in the otherwise-bright aortic lumen) in the aortic arch and the proximal left subclavian artery. In contrast, maximum-intensity-projection analysis (Figure 1A) did not depict these findings, which mimicked normal aortic geometry. Figure 1. A, Inconspicuous CE maximum-intensity projection of MRA at 3-T field strength. No obvious cause for the concomitant …

A case of suspected femoral arteriovenous fistula after cardiac catherization remained undiagnosed because of inability to obtain access for arteriography. Magnetic resonance imaging with phase-shift velocity mapping allowed a noninvasive diagnosis and qualitative evaluation of the lesion.

Four-dimensional (4D) velocity mapping technology is used here to evaluate blood flow patterns associated with an incidentally noted, non-hemodynamically significant pseudocoarctation of the proximal descending thoracic aorta in a healthy volunteer (Figure). The 4D phase-contrast magnetic resonance (MR) velocity mapping using time-resolved, cardiac-gated 3-dimensional (3D) velocity data allows for visualization of complex multidimensional blood flow with complete spatial and temporal registration of the region of interest. Four-dimensional velocity mapping is a reliable technique for the analysis and visualization of normal and pathological blood flow features throughout the thoracic aorta. The 4D nature of …