Dynamic contrast-enhanced magnetic resonance imaging in patients with pulmonary arterial hypertension

Abstract

Dynamic contrast-enhanced (DCE) time-resolved magnetic resonance (MR) imaging is a technique whereby the passage of an intravenous contrast bolus can be tracked through the pulmonary vascular system. The aim of this study was to investigate the prognostic significance of DCE-MR pulmonary blood transit times in patients with pulmonary arterial hypertension (PAH). Seventy-nine patients diagnosed with PAH underwent pulmonary DCE imaging at 1.5 T using a time-resolved three-dimensional spoiled gradient echo sequence. The prognostic significance of two DCE parameters, full width at half maximum (FWHM) of the first-pass clearance curve and pulmonary transit time (PTT), along with demographic and invasive catheter measurements, was evaluated by univariate and bivariate Cox proportional hazards regression and Kaplan-Meier analysis. DCE-MR transit times were most closely correlated with cardiac index (CI) and pulmonary vascular resistance index (PVRI) and were both found to be accurate for detecting reduced CI (FWHM area under the curve [AUC] at receiver operating characteristic analysis = 0.91 and PTT AUC = 0.92, respectively) and for detecting elevated PVRI (FWHM AUC = 0.88 and PTT AUC = 0.84, respectively). During the follow-up period, 25 patients died. Patients with longer measurements of FWHM (P = 0.0014) and PTT (P = 0.004) were associated with poor outcome at Kaplan-Meier analysis, and both parameters were strong predictors of adverse outcome from Cox proportional hazards analysis (P = 0.013 and 0.010, respectively). At bivariate analysis, DCE measurements predicted mortality independent of age, gender, and World Health Organization functional class; however, invasive hemodynamic indexes CI, PVRI, and DCE measurements were not independent of one another. In conclusion, DCE-MR transit times predict mortality in patients with PAH and are closely associated with clinical gold standards CI and PVRI.

Keywords: cardiac output; dynamic contrast enhanced; magnetic resonance imaging; prognosis; pulmonary arterial hypertension; pulmonary vascular resistance.

Figure 1

Dynamic contrast–enhanced subtracted time-resolved images showing the passage of contrast through the cardiopulmonary system. Coronal images with region of interests placed in the pulmonary artery (A) and in the left atrium (B) are shown.

Figure 2

Signal-time curves are generated from regions of interest (ROIs) placed in the pulmonary artery and the left atrium. Pulmonary transit time (PTT) is calculated by subtracting the time of peak signal intensity on the pulmonary artery curve from the time of peak signal intensity on the left atrium. Full width at half maximum (FWHM) of the pulmonary artery is calculated by measuring the width of the pulmonary artery signal-time curve at half its maximum signal intensity.

Figure 3

Scatterplots showing the relationship of 1/full width at half maximum (FWHM) versus cardiac index (CI; a) and FWHM versus pulmonary vascular resistance index (PVRI; c). Receiver operating characteristic curves: showing the accuracy of FWHM for the detection of CI ≤ median values (b) and PVRI ≥ median values (d). AUC: area under the curve; WU: Wood units.

Figure 4

Scatterplots showing the relationship of 1/pulmonary transit time (PTT) versus cardiac index (CI; a) and PTT versus pulmonary vascular resistance index (PVRI; c). Receiver operating characteristic curves: showing the accuracy of PTT for the detection of CI ≤ median values (b) and PVRI ≥ median values (d). AUC: area under the curve; WU: Wood units.

Figure 5

Kaplan-Meier plots for pulmonary transit time (PTT) and full width at half maximum (FWHM) above and below median values. MRI: magnetic resonance imaging.

Figure 6

Time intensity curves from a patient with severe pulmonary hypertension (right) showing prolonged transit of contrast through both the pulmonary artery and the left atrium. The left-hand image shows signal-time curves from a patient without pulmonary hypertension with relatively rapid contrast transit (mean pulmonary arterial pressure <25 mmHg). ROI: region of interest.