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Simple and Accurate Assessment of Forward Cardiac Output by Use of 1-¹¹C-Acetate PET Verified in a Pig Model

¹ Clinical Physiology, Department of Medical Sciences, Academic Hospital, Uppsala, Sweden
² Uppsala University PET Centre, Uppsala, Sweden
³ Thoracic Surgery, Department of Medical Sciences, Academic Hospital, Uppsala, Sweden
⁴ Cardiology, Department of Medical Sciences, Academic Hospital, Uppsala, Sweden

View larger version (15K): [in a new window]   FIGURE 1. Representative time–activity curves recorded from ROI in RV and LV cavities, respectively. Time frame where first pass of bolus ends and recirculation arrives is determined interactively by locating time frame with lowest concentration shortly after injection (arrows). In this case, 244 MBq 1-11C-acetate were injected as rapid bolus directly into superior vena cava during intravenous infusion of 25 µg/kg/min of dobutamine in pig. Irregular activity in LV is seen initially, probably due to variable flow velocity caused by respiration. Division of amount of injected activity by average concentration in cavity during first-pass transit reveals number of milliliters it takes to move entire dose through cavity, which equals CO. Estimates of CO by PET were 6.2 and 5.8 L/min for RV and LV, respectively. CO simultaneously estimated by standard thermodilution technique was 5.8 L/min.

View larger version (22K): [in a new window]   FIGURE 2. (A) Plot of estimates of COPET derived from RV ROI (RV-COPET) against standard thermodilution technique (COthermo). (B) Bland–Altman plot shows difference (Diff.) between 2 methods plotted against mean values. Slope of regression line is not significantly different from 0, but values of RV-COPET are 0.3 ± 0.4 L/min higher than COthermo (P < 0.001). Difference is probably due to partial-volume effects.

View larger version (22K): [in a new window]   FIGURE 3. (A) Plot of estimates of COPET derived from LV ROI (LV-COPET) against standard thermodilution technique (COthermo). (B) Bland–Altman plot shows difference (Diff.) between 2 methods plotted against mean values. Slope is significantly different from 0.

View larger version (15K): [in a new window]   FIGURE 4. Plot of estimates of COPET derived from LV ROI (LV-COPET) by 2 observers. Observer 2 performed all postprocessing steps but was unaware of all other data. Correlation between estimates was highly significant (r = 0.98, P < 0.001), indicating that PET method is well reproduced. Interobserver variability was calculated to be 6%.

View larger version (18K): [in a new window]   FIGURE 5. Plot of pulmonary uptake of 1-11C-acetate, normalized to baseline values, in relation to invasively derived LV input resistance, calculated as PCWP divided by CO. Linear and highly significant correlation was found (r = 0.91, P < 0.001), suggesting that alterations in pulmonary tracer uptake are primarily affected by capillary transit time and left atrial pressure.

View larger version (17K): [in a new window]   FIGURE 6. Plot of pulmonary uptake of 1-11C-acetate in relation to SV. Both variables were normalized to values obtained at initial baseline scan in each animal. Plot shows that marked elevation of pulmonary tracer uptake occurs when LV contractility is lowered. This relation was best fitted by piecewise linear regression algorithm (r = 0.95, P < 0.001).