The result of the DB test was expressed as the mean value for the ratio of maximal interval between two consecutive R waves on the ECG (RR) during breathing out, over minimal RR during breathing in at each respiratory cycle.
After a 15-minute rest lying down, each subject underwent a 5-minute, single ECG lead recordingduring controlled breathing (15 breaths per minute, 0.25 Hz).
The recorded parameters are the EEG, eye movements, muscle tone, different cardiorespiratory parameters (nasal air flow, breathing effort, ECG, oxygen saturation, etc)., body position, snoring and limb movements.
For each pacing site, at least six consecutive pacing stimuli were analysed in order to average the influence of random factors such as patient breathing or ECG signal noise.
After a 10-minute rest lying down, each subject underwent a 5-minute, single ECG lead recording during controlled breathing (15 breaths per minute, 0.25 Hz).
CT scans were acquired during free breathing without ECG-gating, at spiral mode with pitch 1.4, tube voltage of 130 kV, 30 mAs, scan time 14.67 s, CTDI (computed tomography dose index) of approximately 3.2, and DLP (dose-length product) of 55.
However, the images obtained without ECG-gating and/or free breathing are still applicable for 3D printing if it is not aimed to show small structures such as coronary arteries.
If breathing and ECG-gating artifacts appeared at the same time in one patient, the artifact with the worst impact on image quality was noted.
All the subjects of this study were in sinus rhythm during the ECG recordings, furthermore, the mean breathing frequency for all was <img src="http://journals.plos.org/plosone/article/asset?id=info?doi/10.1371/journal.pone.0017060.e001.PNG" class= inline-graphic"/> breaths/min.
A score of 2 indicated decreased image quality of thoracic vascular structures with severe impairment of diagnostic value (non-diagnostic) due to breathing, motion, or ECG-gating artifacts.
