Regional changes in extravascular lung water detected by positron emission tomography

Abstract

Regional measurements of extravascular lung water (rEVLW) were made with positron emission tomography (PET) and 15O-labeled radionuclides. The label used to measure the total lung water (TLW) content fully equilibrated with TLW prior to scanning in both dogs with normal and low cardiac outputs, and nearly so in areas of lung made edematous by oleic acid injury (the TLW values used were 97% of maximum values). Regional EVLW measurements made by PET (EVLW-PET) and gravimetric techniques in both normal and edematous lung were closely correlated (r = 0.93), and EVLW-PET increased from an average of 0.20 to 0.37 mlH2O/ml lung (P less than 0.05) after regional lung injury. PET measurements of regional blood volume always decreased [from an average of 0.12 to 0.09 ml blood/ml lung (P less than 0.05)] after cardiac output was lowered by hemorrhage in a separate set of animals. Total EVLW (by thermodye indicator dilution) did not change. Likewise, regional EVLW remained constant in areas below the left atrium but decreased in areas above the left atrium. We conclude that PET measurements are accurate, noninvasive, and reproducible and that regional changes may be detected even when measurements of total EVLW by other methods may fail to change significantly.

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“…In this case, a further correction is necessary for the so-called 'partial volume averaging effect' (~5-10% in humans), which occurs as a result of the limited spatial resolution of PET relative to the size of the ventricular chamber [34]. With the assumption that 84% of blood is water (a reasonable assumption at normal hematocrits), the blood water content in a lung region can be subtracted from the total lung water concentration, yielding a derived image of extravascular water concentration [36]. The total time required to measure EVLW with PET is about 45min, but repeat measurements can begin in as little as 10-15min from the previous one.…”

Measurement of extravascular lung water using the single indicator method in patients: research and potential clinical value

“…Using PET, EVLW can be measured directly. PET estimates of EVLW correlate well with gravimetric measures of lung water (50,54), although PET consistently underestimates gravimetric measures by approximately 10 -15%. PET estimates of lung water are reproducible and, more importantly, are sensitive to changes in lung water with the ability to detect a 1-ml increase in EVLW (20).…”

Response to Inhaled Nitric Oxide in Acute Lung Injury Depends on Distribution of Pulmonary Blood Flow Prior to Its Administration

“…These measurements were obtained with a "Super-PETT" 3000 system built in-house. Design features, methods for calibration, corrections for activity decay, and corrections for photon attenuation have been described previously (13)(14)(15)(16).…”

“…The methods used to measure PBF and LWC, including supporting validation studies, have also been described previously in detail (13)(14)(15)17). In general, PET is used to measure the tissue concentration and distribution of a positron-emitting radionuclide, which in the present study was simply H 2 15 O.…”