Objectives: VT ablations could benefit from dynamic 3D (i.e. 4D) visualisation of the left ventricle (LV) as roadmap for anatomy-guided procedures, e.g. by means of rotational angiography (3DRA). To limit radiation burden, low-dose, noisy 3DRA image datasets have to be used. Our aim was to develop an algorithm combining information of several cardiac phases to filter out noise, enabling accurate semi-automatic segmentation (SAS) and generation of multi-phase segmentation surfaces.

Methods and Results: We explored non-rigid interphase registration (IPR) using image warping and subsequent image averaging of 4 cardiac phases in low-dose 3DRA images from 5 porcine experiments, acquired with a novel protocol of slow atrial pacing. IPR parameter settings were optimized against manual delineations of the LVs using a score (Q) composed of standardised similarity measures. SAS was done for varying voxel intensity thresholds (ISO). Figure A shows a 4D posterior view sequence of 4 LV phases constructed with and without IPR, after SAS at ISO = 0 relative to optimal ISO. Relevant structures are the apex (1), LV inflow (2), LV outflow tract (3) and posterior papillary muscle (4). Distances to the manual delineations were reduced to 3 mm for 95.6 ± 2,7% of model surfaces (d3mm) at optimal ISO with IPR. Post-SAS IPR and non-IPR models were compared using 3 quality measures (Q; d3mm and Hausdorff Distance [HD, reflecting maximum error]). Improved quality was proven by significant increases in d3mm (illustrated in Figure B for the experiment of Figure A) and Q irrespective of ISO (mean increase at optimal ISO was 7.75% (95%CI 4.60-10.90, p<0.0001) for d3mm and 7.57% (95%CI 4.65-10.50, p < 0.0001) for Q). HD decreased significantly (-21.35%; 95%CI -18.61—24.10, p<0.0001). 4D model generating time was ±11.5min with IPR vs. ±22min without.

Conclusions: Generating 4D LV models is feasible, with clinically useful accuracy, using a novel image acquisition protocol and non-rigid IPR to reduce image noise and speed up 4D image generation. Due to the use of low dose acquisition protocols, radiation dose can be kept at a clinically acceptable low level. By using slow atrial pacing, the risk of inducing unwanted ventricular tachy-arrhythmias is minimised. These findings open the perspective of realising a 4D image sequence for more accurate integration with electro- anatomical mapping systems or per-procedural fluoroscopy to facilitate ablation in locations with high degrees of movement (like the LV). (1-3) (Figure A, Figure B)