Objectives: Novel quantitative measures of the trans-pulmonary circulation status may allow improvement of heart failure (HF) patient management. In this work, we propose a method for the assessment of the trans-pulmonary circulation using measurements from indicator time-intensity curves, derived from dynamic contrast-enhanced magnetic resonance (DCE-MRI) image series. The derived indicator dilution parameters in healthy volunteers (HV) and HF patients were compared, and repeatability was assessed. Furthermore, we compared the parameters derived using the proposed method with standard measures of cardiovascular function (such as left ventricular volumes and ejection fraction).Materials and methodsIn all, 19 HVs and 33 HF patients underwent a DCE-MRI scan on a 1.5 T MRI scanner using a T1-weigthed spoiled gradient echo sequence. Image loops with one heart-beat temporal resolution were acquired in four-chamber view during ventricular late diastole, after the injection of a 0.1 mmol gadoteriol bolus. On a subset of the patients (8 HF, 2 HV), a second injection of a 0.3 mmol gadoteriol bolus was performed with same imaging settings. The study was approved by the local institutional review board. Indicator dilution curves (IDCs) were derived averaging the MR signal within regions of interest in the right and left ventricle; parametric deconvolution was performed between right and left ventricular (LV) IDCs to identify the impulse response of the trans-pulmonary dilution system. The local density random walk model was used to parametrize the impulse response; pulmonary transit time (PTT) was defined as the mean transit time of the indicator; λ, related to the Peclet number (ratio between convection and diffusion) for the dilution process, was also estimated. Results PTT was significantly prolonged in HF patients (8.70 ± 1.87 s vs. 6.68 ± 1.89 s in HV, p<0.005), even stronger when normalized to subject heart rate (normalized PTT, 9.90 ± 2.16 vs. 7.11 ± 2.17 in HV, dimensionless, p<0.001). λ was significantly smaller in HF patients (8.59 ± 4.24 in HF vs. 12.50 ± 17.09 in HV, dimensionless, p<0.005), indicating a longer tail for the impulse response. PTT correlated well with established cardiovascular parameters (left ventricular end-diastolic volume index, r=0.61, p<0.0001; left ventricular ejection fraction r=-0.62, p<0.0001). We consider the measurement of indicator dilution parameters this way repeatable (correlation between estimates based on the two repetitions for PTT: r=0.94, p<0.001, difference between two repetitions 0.01 ± 0.60 s, for λ: r=0.74, p<0.01, difference 0.69 ± 4.39).ConclusionsCharacterization of the trans-pulmonary circulation by DCE-MRI is feasible in heart failure patients and healthy volunteers. Significant differences are observed between indicator dilution parameters measured in healthy volunteers and heart failure patients; preliminary results suggest good repeatability for the proposed parameters.
- Indicator dilution, trans-pulmonary circulation, DCE-MRI, heart failure