Non-invasive characterization of pleural and pericardial effusions using T1 mapping by magnetic resonance imaging

Abstract

Aims Differentiating exudative from transudative effusions is clinically important and is currently performed via biochemical analysis of invasively obtained samples using Light’s criteria. Diagnostic performance is however limited. Biochemical composition can be measured with T1 mapping using cardiovascular magnetic resonance (CMR) and hence may offer diagnostic utility for assessment of effusions. Methods and results A phantom consisting of serially diluted human albumin solutions (25–200 g/L) was constructed and scanned at 1.5 T to derive the relationship between fluid T1 values and fluid albumin concentration. Native T1 values of pleural and pericardial effusions from 86 patients undergoing clinical CMR studies retrospectively analysed at four tertiary centres. Effusions were classified using Light’s criteria where biochemical data was available (n = 55) or clinically in decompensated heart failure patients with presumed transudative effusions (n = 31). Fluid T1 and protein values were inversely correlated both in the phantom (r = −0.992) and clinical samples (r = −0.663, P < 0.0001). T1 values were lower in exudative compared to transudative pleural (3252 ± 207 ms vs. 3596 ± 213 ms, P < 0.0001) and pericardial (2749 ± 373 ms vs. 3337 ± 245 ms, P < 0.0001) effusions. The diagnostic accuracy of T1 mapping for detecting transudates was very good for pleural and excellent for pericardial effusions, respectively [area under the curve 0.88, (95% CI 0.764–0.996), P = 0.001, 79% sensitivity, 89% specificity, and 0.93, (95% CI 0.855–1.000), P < 0.0001, 95% sensitivity; 81% specificity]. Conclusion Native T1 values of effusions measured using CMR correlate well with protein concentrations and may be helpful for discriminating between transudates and exudates. This may help focus the requirement for invasive diagnostic sampling, avoiding unnecessary intervention in patients with unequivocal transudative effusions.

Normal values for native T1 at 1.5T in the pericardial fluid of healthy volunteers

“…Estimated GBCA concentration in pericardial fluid at the early timepoint, [Gd]early was (20±9 mmol/mL) and at the late timepoint [Gd]late was (70±28 mmol/mL). ROI size in the volume of pericardial fluid in short-axis and perpendicular slice orientations did not differ (18 [14-27] vs 16 [12][13][14][15][16][17][18][19][20][21][22][23] mm 2 , p=0.49). Resulting normal reference ranges are shown in Table 2.…”

“…Light´s criteria misclassifies 25% of pleural transudates as exudates [2], and doubts have been raised on whether it is at all feasible to use Light´s criteria for pericardial effusions, as the cut off values were validated for pleural effusions. In a recent study involving native T1 measurements of pleural and pericardial effusions, biochemical data enabling the use of Light´s criteria were available mostly for exudates and the cohort was therefore supplemented with presumed transudates by including patients with pericardial and/or pleural effusions and chronic severe left ventricular systolic dysfunction [13]. The validity of this approach is questionable as several studies have shown that most pericardial effusions are misclassified as exudate by Light's criteria, and most if not all normal pericardial fluid is classified as exudate [24][25][26].…”

“…This discrepancy could be due to the fact that diuretics, mainstay in the treatment of heart failure, have been found to increase the concentration of protein, or rather, lower the water content of effusion fluid leading to false positive classification as exudate using Light criteria [23]. As a negative correlation between protein levels and native T1 has been found in phantoms as well as in vitro [13] and ex vivo [14] effusion fluids, it is reasonable to assume that effusions in patients treated with diuretics are at risk of false positive classification as exudates by T1 mapping.…”

“…Non-contrast (native) T1 mapping has successfully been used to classify pericardial and pleural effusions as transudate or exudate [13], and has further been used to successfully differentiate between malignant and non-malignant pleural and ascitic effusions ex vivo [14]. The rationale for these approaches is that proteins and cells leaking through a permeable inflamed pericardium and into the pericardial fluid have paramagnetic properties that lower the T1 value of the effusion fluid.…”

“…Non-contrast (native) T1 mapping has successfully been used to classify pericardial and pleural effusions as transudate or exudate [13], and has further been used to successfully differentiate between malignant and non-malignant pleural and ascitic effusions ex vivo [14].…”