High-pitch electrocardiogram-triggered computed tomography of the chest: initial results

Chest pain is one of the most frequent symptoms in the emergency department. A variety of different diseases, some of them acutely life threatening, can be the underlying cause. Electrocardiogram (ECG)-gated computed tomography angiography of the thorax has been proposed as a cost and time effective imaging technique for these patients. We describe a new high-pitch scan mode, which has been developed specifically for low-dose ECG-triggered computed tomography angiography using dual source computed tomography (CT).

Twenty-four patients were examined with this technique on a second generation dual source CT system. The scan mode uses a pitch of 3.2 to acquire a spiral CT data set of the complete thorax in less than 1 second with a temporal resolution of 75 ms (scan parameters: 128 x 0.6 mm collimation, 0.28 seconds gantry rotation time, 370 mAs at 100 kV [15 patients] and 320 mAs at 120 kV [9 patients], reconstructed slice thickness 0.6 mm, increment 0.4 mm). Data acquisition was prospectively triggered at 50% to 60% of the RR interval to cover the range over the heart in diastole. A triple phase contrast injection protocol (total volume: 80 mL) was used to optimize enhancement of the pulmonary and systemic arterial vessels. Image quality was evaluated using a 4-point scale (1 = absence of motion artifacts; 2 = slight motion artifacts, fully evaluable; 3 = motion artifacts, but evaluable; 4 = unevaluable) on a per-segment basis.

The patients had an average heart rate of 68 +/- 15 bpm (range: 43-111 bpm) during data acquisition. Motion artifact free visualization of the aorta and pulmonary vessels was possible in each case, of 344 coronary artery segments, 242 (70%) had an image quality score of 1, 60 segments (17%) a score of 2, 28 segments (8%) a score of 3, and 14 segments (4%) were rated as "unevaluable." In 17 patients (10 patients with a heart rate < or =60 bpm) all segments were evaluable. The average dose length product was 113 +/- 11 mGy x cm per scan (mean effective dose 1.6 +/- 0.2 mSv) at 100 kV and 229 +/- 31 mGy x cm per scan (mean effective dose 3.2 +/- 0.4 mSv) at 120 kV.

Our initial results indicate that this high-pitch scan mode allows motion artifact free and accurate visualization of the thoracic vessels, and diagnostic image quality of the coronary arteries in patients with low and stable heart rates at a very low radiation exposure.