The dynamics of extracellular gadolinium-based contrast agent excretion into pleural and pericardial effusions quantified by T1 mapping cardiovascular magnetic resonance

Abstract

Introduction: Excretion of cardiovascular magnetic resonance (CMR) extracellular gadolinium-based contrast agents (GBCA) into pleural and pericardial effusions, sometimes referred to as vicarious excretion, has been described as a rare occurrence using T1-weighted imaging. However, the T1 mapping characteristics as well as presence, magnitude and dynamics of contrast excretion into these effusions is not known.

Aims: To investigate and compare the differences in T1 mapping characteristics and extracellular GBCA excretion dynamics in pleural and pericardial effusions.

Methods: Clinically referred patients with a pericardial and/or pleural effusion underwent CMR T1 mapping at 1.5 T before, and at 3 (early) and at 27 (late) minutes after administration of an extracellular GBCA (0.2 mmol/kg, gadoteric acid). Analyzed effusion characteristics were native T1, ΔR1 early and late after contrast injection, and the effusion-volume-independent early-to-late contrast concentration ratio ΔR1early/ΔR1late, where ΔR1 = 1/T1post-contrast - 1/T1native.

Results: Native T1 was lower in pericardial effusions (n = 69) than in pleural effusions (n = 54) (median [interquartile range], 2912 [2567-3152] vs 3148 [2692-3494] ms, p = 0.005). Pericardial and pleural effusions did not differ with regards to ΔR1early (0.05 [0.03-0.10] vs 0.07 [0.03-0.12] s^{- 1}, p = 0.38). Compared to pleural effusions, pericardial effusions had a higher ΔR1late (0.8 [0.6-1.2] vs 0.4 [0.2-0.6] s^{- 1}, p < 0.001) and ΔR1early/ΔR1late (0.19 [0.08-0.30] vs 0.12 [0.04-0.19], p < 0.001).

Conclusions: T1 mapping shows that extracellular GBCA is excreted into pericardial and pleural effusions. Consequently, the previously used term vicarious excretion is misleading. Compared to pleural effusions, pericardial effusions had both a lower native T1, consistent with lesser relative fluid content in relation to other components such as proteins, and more prominent early excretion dynamics, which could be related to inflammation. The clinical diagnostic utility of T1 mapping to determine quantitative contrast dynamics in pericardial and pleural effusions merits further investigation.

Keywords: Cardiovascular magnetic resonance; Gadolinium based contrast; Pericardial effusion; Pleural effusion; T1 mapping; Vicarious excretion.

Fig. 1

Flow chart of patient selection. GBCA, gadolinium based contrast agent

Fig. 2

Example T1 maps taken before, early and late after GBCA administration. The white and black regions of interest illustrate how measurements were delineated in the pericardial and pleural effusions, respectively

Fig. 3

Boxplot of native T1 for pericardial and pleural effusions. The boxes indicate median and interquartile range, and whiskers the full range

Fig. 4

T1 measurements before, early and late after extracellular GBCA injection for each individual pericardial and pleural effusion subject, respectively. Note that all effusions had a reduction in T1 at least late after contrast injection, indicating that extracellular GBCA is excreted into all pericardial and pleural effusions

Fig. 5

Plot of ΔR1 for the blood, myocardium, pleural effusion and pericardial effusion both early and late after contrast administration. Symbols denote the median, and whiskers the interquartile range. The red lines indicate change in ΔR1. ΔR1 is proportional to contrast agent concentration. Note how blood and myocardium have a relatively high contrast agent concentration early after contrast administration, which then decreases over time at the late time point. By comparison, both the pleural and pericardial effusions have measurable but low relative contrast agent concentrations early after contrast administration, which increase over time at the late time point, to a level that is lower than for blood and myocardium. These magnitudes and dynamics of relative contrast agent concentration suggest that the effusions do not establish a dynamic equilibrium with the blood. Thus, it would be misleading to calculate the extracellular volume fraction for the effusions

Fig. 6

Boxplot of the ratio formed by ΔR1early and ΔR1late for pericardial and pleural effusions. This ratio is independent of the volume of the effusion. The boxes indicate median and interquartile range, and whiskers –the full range

Fig. 7

Linear correlations between the size of effusion (mm) and ΔR1early (s⁻¹), ΔR1late (s⁻¹), unitless volume-independent ratio ΔR1early/ΔR1late for the pericardial (left) and pleural effusion groups (right)