A compartmental model for alveolar clearance of pertechnegas.
The washout of an inhaled water soluble radiotracer from the lungs is a measure of alveolar integrity. Data evaluation of 99mTc-DTPA studies were previously performed mainly with monoexponential fitting with or without background subtraction. The introduction of 99mTc-pertechnegas for the assessment of alveolar permeability necessitates the investigation of adequate data evaluation schemes for this radiotracer.


METHODS
We developed a three-compartmental model to describe 99mTc-pertechnegas kinetics after inhalation. Monoexponential fitting of the first 5 min was investigated as simplification for clinical use. Different background corrections based on blood samples or representative regions of interest were compared.


RESULTS
Correction of intra- and extravascular background by subtraction of calibrated curves, which are derived from blood or background areas, resulted in monoexponential washout curves. Clearance rates based on the three-compartmental model were nearly the same as those derived from a monoexponential fit after blood-activity subtraction (r = 0.96). A monoexponential analysis of the first 5 min without any background correction correlates well with the first component of the biexponential analysis (r = 0.97).


CONCLUSIONS
A dynamic study of more than 45 min allows quantitative determination of the transfer rate of 99mTc-pertechnegas from the alveoli into the blood using compartmental analysis. A simplified monoexponential analysis of the first 5 min allows assessment of lung clearance without any background correction.
Kotzerke
J
J
Department of Nuclear Medicine, Center for Internal Medicine Medical School Hannover, Germany.
van den Hoff
J
J
Burchert
W
W
Wagner
T F
TF
Emter
M
M
Hundeshagen
H
H
D000280:Administration, Inhalation; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D010539:Permeability; D011650:Pulmonary Alveoli / Q000378:metabolism*; D011877:Radionuclide Imaging; D013670:Sodium Pertechnetate Tc 99m / Q000008:administration & dosage / Q000493:pharmacokinetics*
C056708:Technegas; D013670:Sodium Pertechnetate Tc 99m