despite recent advances in endovascular techniques and technology for coil embolization of intracranial aneurysms , thromboembolic complications intra- and post - procedure are not uncommon , particularly in branches originating from the dome of the aneurysm .
surgeons often face the dilemma of achieving complete coil obliteration of an arterial aneurysm while preserving blood flow to the branches .
management decisions require a precise assessment of the risks of thromboembolic events tailored to individual aneurysms .
the use of computational fluid dynamics ( cfd ) has helped to clarify patient - specific intra - aneurysmal flow patterns . here ,
we attempt to clarify the optimal coil configuration for endovascular embolization without compromising blood flow in the branching arteries , using cfd and a model based on an unruptured vertebral artery  posterior inferior cerebellar artery ( va  pica ) aneurysm .
we selected a patient with an unruptured va  pica aneurysm predicted to show impairment of flow in the pica during endovascular coil embolization .
three - dimensional ct angiography was performed using an aquilion 64 ct scanner ( toshiba medical systems , tokyo , japan ) , and a patient - specific model was built using digital imaging and communications in medicine ( dicom ) data .
next , a 3-dimensional voxel model was built ( case 0 ; figure 1 ) .
this method is less time consuming compared with the method using an unstructured body - fitted grid , and aneurysm models , with or without modifications , can be easily built .
we then built 6 models ( cases 16 ) of various idealized final coil configurations in the modeled aneurysm ( figure 2 ) .
case 5 incorporated antegrade neck remodeling with a hyper - compliant balloon , and case 6 incorporated retrograde neck remodeling with a compliant balloon entering the pica from the va . finally , the outflow to the pica in each of the models was analyzed using cfd .
. a : schema of a vertebral artery ( va)posterior inferior cerebellar artery ( pica ) aneurysm ( an ) .
schema of 6 models with various final coil configurations in the modeled aneurysm ( case 0 ) .
cfd of these models was carried out using the incompressible fluid analysis module in fujitsu -flow software ( fujitsu , tokyo , japan ) .
we assumed that a non - newtonian fluid property for blood and an elastic property of the vessel walls could be neglected .
the simulations were performed with the material constants for blood density = 1055 kg / m and blood dynamics viscosity = 0.0049 pas .
each simulation was performed for 8 s. the boundary condition " velocity - inlet " was based on data from the patient with the aneurysm selected for modeling , acquired using a 3.0-tesla mr scanner ( signa infinity twinspeed with excite [ version 12 ] ; ge healthcare , milwaukee , wi , usa ) with a commercially available 8-channel head array coil .
the grid points in the blood vessel and the aneurysm numbered about 500,000 in each simulation .
the calculations were performed with the fujitsu hpc2500 at the information technology center of nagoya university .
we selected a patient with an unruptured va  pica aneurysm predicted to show impairment of flow in the pica during endovascular coil embolization .
three - dimensional ct angiography was performed using an aquilion 64 ct scanner ( toshiba medical systems , tokyo , japan ) , and a patient - specific model was built using digital imaging and communications in medicine ( dicom ) data .
next , a 3-dimensional voxel model was built ( case 0 ; figure 1 ) .
this method is less time consuming compared with the method using an unstructured body - fitted grid , and aneurysm models , with or without modifications , can be easily built .
we then built 6 models ( cases 16 ) of various idealized final coil configurations in the modeled aneurysm ( figure 2 ) .
case 5 incorporated antegrade neck remodeling with a hyper - compliant balloon , and case 6 incorporated retrograde neck remodeling with a compliant balloon entering the pica from the va . finally , the outflow to the pica in each of the models was analyzed using cfd .
. a : schema of a vertebral artery ( va)posterior inferior cerebellar artery ( pica ) aneurysm ( an ) .
schema of 6 models with various final coil configurations in the modeled aneurysm ( case 0 ) .
cfd of these models was carried out using the incompressible fluid analysis module in fujitsu -flow software ( fujitsu , tokyo , japan ) .
we assumed that a non - newtonian fluid property for blood and an elastic property of the vessel walls could be neglected .
the simulations were performed with the material constants for blood density = 1055 kg / m and blood dynamics viscosity = 0.0049 pas .
each simulation was performed for 8 s. the boundary condition " velocity - inlet " was based on data from the patient with the aneurysm selected for modeling , acquired using a 3.0-tesla mr scanner ( signa infinity twinspeed with excite [ version 12 ] ; ge healthcare , milwaukee , wi , usa ) with a commercially available 8-channel head array coil .
the grid points in the blood vessel and the aneurysm numbered about 500,000 in each simulation .
the calculations were performed with the fujitsu hpc2500 at the information technology center of nagoya university .
imaging and analysis of flow dynamics were successfully obtained for all models ( e.g. , case 0 ; figure 3 ) .
the results of the outflow to the pica for each model are shown in the figure 4 and 5 .
the average outflow to the pica was highest in case 0 and lowest in case 2 ( in descending order , case 0 , 5 , 4 , 6 , 1 , 3 , and 2 ) .
there was better preservation of outflow to the pica in the balloon neck remodeling models than in the neck remnant models .
therefore , a linear coil configuration did not necessarily improve preservation of outflow to the pica compared with a round coil configuration .
the horizontal and vertical axis shows time ( second ) and the outflow velocity ( m / sec ) , respectively .
this study reveals that the risk of thromboembolic complications in endovascular - treated aneurysms may be affected by subtle differences in the coil configuration around the aneurysmal neck .
the geometry of some pica aneurysms precludes selective endovascular occlusion of the aneurysm with preservation of flow to the branch .
however , direct surgery for these aneurysms is also challenging because of their location and close proximity to the medulla and lower cranial nerves .
we used cfd in a modeled va  pica aneurysm to determine outflow to the pica under a number of conditions .
we have previously reported a successful method to make patient - specific aneurysmal models using dicom data in the rectangular coordinate system . in the present study ,
this aneurysm model was modified and various coil - embolized aneurysms were built . before running the models , we expected that cases 2 and 3 would have higher outflow than case 1 .
moreover , we expected that case 2 would have higher flow than the pretreatment condition ( case 0 ) because of adjusted flow to the pica . however , it appears that when the branch originates at a sharp angle , as was the case with this aneurysm , the outflow is highest under the pretreatment condition .
the finding of better preservation of outflow in the balloon neck remodeling models compared with the neck remnant models suggests that the use of a balloon to lift the coil mass around the aneurysmal neck was effective .
in particular , balloon herniation with a hyper - compliant balloon ( case 5 ) preserved the highest amount of outflow to the pica .
because surgical closure lines are generally linear , surgeons have to pay careful attention to preserve arterial branches . despite recent advances in computational flow analysis ,
the pulsating motion of vessels , peripheral vascular resistance , and differences among individual patients are also important factors in the accurate evaluation of flow patterns .
previous reports have suggested that the effects of vessel wall elasticity and pulsation are not significant in relation to intra - aneurysmal flow .
the present study shows a tendency towards different flow patterns in models with subtle changes in coil configuration in the neck of the aneurysm . further research , using patient - specific cfd , is needed to properly analyze the relationship between coil configuration in the neck of an arterial aneurysm and the outflow to the branches . in the future
, cfd could be used to assess safety and to determine appropriate coil configurations for individual aneurysms .
we identified considerable differences in the outflow to the branching artery with small changes in coil configuration for endovascular coil embolization .
careful preoperative planning is important to minimize the risk of thromboembolic events during and after endovascular coil embolization . in the future
, cfd could be applied to individual cases to determine a safe and adequate coil configuration for endovascular coil embolization .
 abstractendovascular coil embolization of arterial aneurysms is often complicated by reduced blood flow to branching arteries . to determine the optimal coil configuration for safe embolization of endovascular aneurysms without compromising blood flow in branching arteries . 
 a 3-dimensional voxel model , built based on an unruptured vertebral artery  posterior inferior cerebellar artery ( va  pica ) aneurysm , predicted to show impairment of flow in the pica during endovascular coil embolization ( case 0 ) . six different models of final coil configuration were generated and applied to this aneurysm . 
 case 1 was a round coil mass . 
 case 2 was designed with a stent assist . 
 cases 3 , and 4 were designed with a neck remnant and cases 5 and 6 incorporated a balloon neck remodeling technique . 
 computational fluid dynamics was used to analyze the flow in the pica in each model . 
 the average outflow to the pica was highest in case 0 and lowest in case 2 ( in descending order , case 0 , 5 , 4 , 6 , 1 , 3 , and 2 ) . 
 there was better preservation of outflow to the pica in the balloon neck remodeling models than in the neck remnant models . in a model of endovascular coil embolization , we found considerable differences in outflow to the branching artery with small changes in coil configuration . 
 careful preoperative planning is important to minimize the risk of thromboembolic events during and after endovascular coil embolization . 
INTRODUCTION
MATERIAL AND METHODS
Computational Models
Computational Simulation
RESULTS
DISCUSSION
CONCLUSIONS
ACKNOWLEDGEMENTS