Real-time determination of the optimal reconstruction phase to control ECG pulsing in spiral cardiac CT.

The reconstruction phase providing optimal image quality in coronary CT angiography is dependent on the heart rate but additionally displays substantial patient-dependent variation. The purpose of this study was to provide online identification of the patient-specific optimal reconstruction phase during CT coronary angiography data acquisition and to allow adaptation of tube current modulation for the individual patient. A raw data-based cardiac motion signal (kymogram) was used for the detection of the optimal reconstruction phase. The individual motion curve of each patient was correlated with dedicated template curves to reduce signal noise. Data sets of 90 consecutive patients were used for validation purposes. The reliability of our approach increased with scan time and provided highest correlation with the visually identified optimal reconstruction phase already after half of the total scan time indicated by a difference value of 13.2% and 8.2%, respectively. A high correlation of the computed and the visually identified optimal reconstruction phase was assured in most cases providing a dose reduction of 36% compared to conventional TCM application for a confidence interval of 80%. Our method is a fully automatic computer-assisted approach identifying the optimal reconstruction phase with high reliability while online capability can be ensured. We conclude that our method can identify cardiac phases providing highest image quality already during CT scanning. Reduction of the tube current by a patient-specific optimization providing a minimal dose level is the major benefit for the patients.