Improvement of algorithm for quantification of regional myocardial blood flow using 15O-water with PET

(15)O-Water and dynamic PET allow noninvasive quantification of myocardial blood flow (MBF). However, complicated image analyzing procedures are required, which may limit the practicality of this approach. We have designed a new practical algorithm, which allows stable, rapid, and automated quantification of regional MBF (rMBF) using (15)O-water PET. We designed an algorithm for setting the 3-dimensional (3D) region of interest (ROI) of the whole myocardium semiautomatically. Subsequently, a uniform input function was calculated for each subject using a time-activity curve in the 3D whole myocardial ROI. The uniform input function allows the mathematically simple and robust algorithm to estimate rMBF.

Thirty-six volunteers were used in the static (15)O-CO and dynamic (15)O-water PET studies. To evaluate the reproducibility of the estimates, a repeated (15)O-water scan was obtained under resting condition. In addition, to evaluate the stability of the new algorithm in the hyperemic state, a (15)O-water scan was obtained with adenosine triphosphate. This algorithm includes a procedure for positioning a 3D ROI of the whole myocardium from 3D images and dividing it into 16 segments. Subsequently, the uniform input function was calculated using time-activity curves in the whole myocardial ROI and in the LV ROI. The uniform input function allowed this simple and robust algorithm to estimate the rMBF, perfusable tissue fraction (PTF), and spillover fraction (Va) according to a single tissue compartment model. These estimates were compared with those calculated using the original method. A simulation study was performed to compare the effects of errors in PTF or Va on the MBF using the 2 methods.

The average operating time for positioning a whole myocardial ROI and 16 regional myocardial ROIs was <5 min. The new method yielded less deviation in rMBF (0.876 +/- 0.177 mL/min/g, coefficient of variation [CV] = 20.2%, n = 576) than those with the traditional method (0.898 +/- 0.271 mL/min/g, CV = 30.1%, n = 576) (P < 0.01). In the hyperemic state, the new method yielded less deviation in rMBF (3.890 +/- 1.250 mL/min/g, CV = 32.1%) than those with the traditional method (3.962 +/- 1.762 mL/min/g, CV = 44.4%) (P < 0.05). This method yielded significantly higher reproducibility of rMBF (r = 0.806, n = 576) than the original method (r = 0.756, n = 576) (P < 0.05). Our new method yielded a better correlation in the repeated measurement values of rMBF and less variability among the regions in the myocardium than with the original theory of the (15)O-water technique. The simulation study demonstrated fewer effects of error in the PTF or Va on the MBF value with the new method.

We have developed a technique for an automated, simplified, and stable algorithm to quantify rMBF. This software is considered to be practical for clinical use in myocardial PET studies using (15)O-water with a high reproducibility and a short processing time.