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Curve Fitting of Time-Density Data From CT Circulation Timing Scans for Estimation of Cardiac Output

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K Ogden

K Ogden*, E Scalzetti , H Rajebi , SUNY Upstate Medical Univ, Syracuse, NY


SU-E-QI-4 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To develop a robust algorithm for fitting gamma variate functions to time-density data acquired during a circulation time scan in preparation for a CT pulmonary angiogram (CTPA).

Methods: Time-density information in the main pulmonary artery (MPA), ascending aorta (AA), and descending aorta (DA) was retrospectively collected for 10 patients undergoing CTPA. Measurements prior to the arrival of contrast were used to estimate the baseline (blood) density value. The estimated contrast arrival delay time was varied over a range of values and the maximum correlation coefficient was used to estimate the delay time. In a second approach, an additional step was performed by shifting the data in time relative to the best-fit gamma variate and calculating a mean-squared difference (MSD). The minimum MSD was used to find a new estimate of the delay time, after which a new gamma variate fit was performed. This process was iterated five times. The final gamma variate fit was used to estimate the cardiac output (CO).

Results: The mean CO for all patients and all vessels was 6.8 l/min for both methods. To compare the robustness of the two methods, coefficient of variation (CV) of CO for the three vessels was computed for each patient. For method 1, the average CV was 0.054, for method 2 it was 0.023. Using method 2, the CV decreased for all but one patient, for whom it increased from 0.01 to 0.02. On average the CV was reduced by 57% using method 2.

Conclusion: Cardiac output may be estimated by using the time-dilution data collected during a circulation timing scan acquired at CTPA. Care must be taken in fitting a model to the data to ensure robust results. The method described has proven to reduce the variability in CO values estimated for different vessels in a single scan.

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