Quantitative magnetic resonance imaging of pulmonary hypertension: a practical approach to the current state of the art

Abstract

Pulmonary hypertension is a condition of varied etiology, commonly associated with poor clinical outcome. Patients are categorized on the basis of pathophysiological, clinical, radiologic, and therapeutic similarities. Pulmonary arterial hypertension (PAH) is often diagnosed late in its disease course, with outcome dependent on etiology, disease severity, and response to treatment. Recent advances in quantitative magnetic resonance imaging (MRI) allow for better initial characterization and measurement of the morphologic and flow-related changes that accompany the response of the heart-lung axis to prolonged elevation of pulmonary arterial pressure and resistance and provide a reproducible, comprehensive, and noninvasive means of assessing the course of the disease and response to treatment. Typical features of PAH occur primarily as a result of increased pulmonary vascular resistance and the resultant increased right ventricular (RV) afterload. Several MRI-derived diagnostic markers have emerged, such as ventricular mass index, interventricular septal configuration, and average pulmonary artery velocity, with diagnostic accuracy similar to that of Doppler echocardiography. Furthermore, prognostic markers have been identified with independent predictive value for identification of treatment failure. Such markers include large RV end-diastolic volume index, low left ventricular end-diastolic volume index, low RV ejection fraction, and relative area change of the pulmonary trunk. MRI is ideally suited for longitudinal follow-up of patients with PAH because of its noninvasive nature and high reproducibility and is advantageous over other biomarkers in the study of PAH because of its sensitivity to change in morphologic, functional, and flow-related parameters. Further study on the role of MRI image based biomarkers in the clinical environment is warranted.

Figure 1

Axial black blood images from a patient without PH (A) and a patient with PH (B), showing the absence and presence of pulmonary flow artefacts, respectively and enlargement of the main pulmonary artery in PH (B).

Figure 2

Short axis images from the systolic phase of the cardiac cycle in a patient with PAH. The inter-ventricular septum is flattened and there is marked RV dilatation and hypertrophy.

Figure 3

Systolic short axis MR images from a patient found to have normal pulmonary without PH (Image A) and a patient with PH (Image B) showing normal and abnormal) systolic septal configuration respectively.

Figure 4

Pulmonary artery images for calculation of relative area change Slices acquired orthogonal to the pulmonary artery, showing the pulmonary artery at its maximal (A) and minimal area (B). Relative area change and area change area calculated from these measurements.

Figure 5

Short axis late gadolinium enhancement (LGE) image of a patients with mPAP<25mmHg (right), patient with LGE at the right ventricular insertion points (left), this is a typical feature seen in most patients with PH.

Figure 6

Magnetic resonance angiograms (MRA) and perfusion images in three patients with PH: IPAH (1a/b), PH-COPD (2a/b) and a patient with CTEPH (3a/b)). 1a and 1b, shows vessel tortuosity and patchy perfusion in a patient with IPAH. 2a shows typical vessel splaying seen in patients with COPD/emphysema and associated reduced perfusion in the upper zones (2b). Figure 3a shows vessel stenoses and occlusions typical of a patient with CTEPH and the associated segmental perfusion defects are shown in 3b.

Figure 7

Dynamic contrast enhanced images. Images show the passage of contrast through the cardiopulmonary system. Six frames are shown from the series of 48 time points. Time (t) is in seconds.