REGIONAL VENTILATORY CLEARANCE BY XENON SCINTIGRAPHY - CRITICAL-EVALUATION OF 2 ESTIMATION PROCEDURES

  • 1 January 1979
    • journal article
    • research article
    • Vol. 20  (7) , 703-710
Abstract
Ventilatory clearance estimates are usually made by inspecting Xe washout images. Quantitative computer procedures that produce regional clearance rates were described, yet their accuracy is questionable. A mathematical model for scintigraphic ventilation data based on 96 human clinical studies was defined, and this model the accuracy of 2 procedures used to estimate ventilatory clearance was tested. The least-squares curve-fitting technique for washin and washout data has the same accuracy as a modified Stewart-Hamilton method (A/H) that uses washut data alone. Both procedures demonstrate relative errors of less than 5% and coefficients of variation of 10-20% when regions with equilibrium count rates of 3 cps [counts per s] and clearance times between 10 and 90 s were examined. Because the A/H procedure is preferred for its simplicity and speed, 2 of its main sources of error, early washin/washout termination and background activity, were analyzed. To measure regional ventilation by the A/H procedure, the following criteria were recommended: washin and washout periods at least 3 .times. the largest clearance of clinical interest; a regional equilibrium count rate of at least 3 cps; a 25-50 s equilibrium count rate average.