Estimation of lung oedema in humans by transmission-emission scintigraphy with 99Tcm

We have used a combination of transmission and emission gamma camera techniques to scan the thorax in the anteroposterior plane in 21 patients with partially treated cardiogenic pulmonary oedema and have compared their results with those from 20 age-matched normal subjects who were scanned previously. For transmission scanning, an external 99Tcm flood source was used; for emission scanning we labelled sequentially the vascular compartment with 99Tcm autologous erythrocytes and the interstitium with 99Tcm diethylenetriaminepentaacetic acid (99Tcm-DTPA). From the transmission scans we derived the transthoracic tissue thickness (Tt) and from the emission scans, after correction for attenuation, the regional blood and interstitial volumes. In the lower zone of the right lung, mean (S.D.) Tt in normal subjects was 10.9 (S.D. 3.1) cm and in subjects with lung oedema was 12.5 (S.D. 3.1) cm (P = 0.07). There was a weak correlation between Tt and a radiographic numerical score of oedema severity (r = 0.47, P less than 0.05). In eight subjects with lung oedema, lung tissue thickness (T1) was estimated (by subtraction from Tt of radiographically estimated chest wall thickness). The T1 correlated closely with the radiographic score (r = 0.78, P less than 0.01). There was no significant change in blood or interstitial volumes in oedema.

(1) transmission scanning gives an indication of oedema severity if an allowance is made for chest wall thickness; (2) 99Tcm-DTPA fails to equilibrate fully with oedema liquid during an equilibration period of 5 min.