ECG-correlated imaging of the heart with subsecond multislice spiral CT

The new spiral multislice computed tomography (CT) scanners and the significant increase in rotation speed offer great potential for cardiac imaging with X-ray CT. The authors have therefore developed the dedicated cardiac reconstruction algorithms 180° multislice cardio interpolation (MCI) and 180° multislice cardio delta (MCD) and here offer further details and validation. The algorithm 180° MCI is an electrocardiogram (ECG)-correlated filtering (or weighting) algorithm in both the cardiac phase and in the z-position. Effective scan times (absolute temporal resolution) of as low as t_eff=56 ms are possible, assuming M=4 simultaneously measured slices at a rotation time of t_r0t=0.5 s and S≤d≤3S for the table feed d per rotation, where S denotes the collimated slice thickness. The relative temporal resolution w (fraction of the heart cycle depicted in the image), which is the more important parameter in cardiac imaging, will then be as low as w=12.5% of the heart cycle. The second approach, 180°MCD, is an ECG-correlated partial scan reconstruction of 180°+δ data with δ≪Φ (fan-angle). Its absolute temporal resolution lies in the order of 250 ms (for the central ray, i.e., for the center of rotation), and the relative temporal resolution w increases with increasing heart rate, e.g., from typically w=25% at f_H=60 min^-1 to w=50% at f_H=120 min^-1, assuming again t_r0t=0.5 s. For validation purposes, the authors have done simulations of a virtual cardiac motion phantom, measurements of a dedicated cardiac calibration and motion phantom, and they have reconstructed patient data with simultaneously acquired ECG. Both algorithms significantly improve the image quality compared with the standard reconstruction algorithms 180° multislice linear interpolation (MLI) and 180° multislice filtered interpolation (MFI). However, 180° MCI is clearly superior to 180°MCD for all heart rates. This is best illustrated by multiplanar reformations (MPR) or other three-dimensional (3-D) displays of the volume, 180° MCI, due to its higher temporal resolution, is best for spatial and temporal four-dimensional (4-D) trac- king of the anatomy. A tunable scanner rotation time to avoid resonance behavior of the heart rate and the scanner´s rotation and shorter rotation times would be of further benefit.