Parameter study of an inductively powered railgun

This article deals with the numerical simulation of an inductively powered railgun in order to determine the electrical parameters of the inductive storage of the pulsed power supply. A numerical model was set up and validated by experimental results. A parameter sweep was performed by varying the time constant of the coil, the initial current and the initially stored energy. The results show that the generated pulse shape, and thus the transfer efficiency and electromagnetic forces, strongly depend on the inductance of the storage coil. On the contrary, the dependency on the coil time constant, and thus on the coil volume for a given coil shape and conductor material, is small and can be neglected for high time constants.

The ’bendy' basilar: progressive aneurysm tilting and arterial deformation can be a delayed outcome after coiling of large basilar apex aneurysms

BackgroundMorphological changes in the basilar artery and the artery-aneurysm relationship following coiling of large basilar apex aneurysms may induce morbidity.MethodsThe basilar artery radius-of-curvature was measured along its center line on volumetrically reconstructed images formatted along the plane of curvature. The aneurysm-tilt-angle was measured between the distal basilar and the vertical long axis of the aneurysm. The measurements were compared between small (<10 mm) and large (≥10 mm) aneurysms on baseline and follow-up studies. The volume (mm3) and mass (g) of the deployed coils was also compared.ResultsAmong 94 consecutive aneurysms, 62 (66%) were <10 mm and 32 (34%) were ≥10 mm. The mean aneurysm size and volume was 9 mm (±4) and 507 mm3(±1366) respectively. The median aneurysm follow-up was 24 months (IQR 6–59). There was no difference between the groups based on age, gender, or associated comorbidities. The coil mass was 0.4 g (±0.2) for aneurysms <10 mm and 1.9 g (±1.6) for aneurysms ≥10 mm (P<0.0001). The total coil volume was 32 (±20) mm3 for aneurysms <10 mm and 187 (±172) mm3 for aneurysms ≥10 mm (P<0.0001). Aneurysms ≥10 mm tilted 13.5o (±14.4) compared with 1.1o (±2.8) for aneurysms <10 mm (P<0.0001). The basilar artery became more curved by 1.3 (±9.4) mm for aneurysms ≥10 mm and 0.25 (±2.1) mm for aneurysms <10 mm (P=0.0002). Other than size of the coiled aneurysms no other factors correlated with the geometrical changes.ConclusionLarge coiled basilar apex aneurysms may be more prone to aneurysm tilting and bending of the basilar artery. Speculative causes include the weight of the coil mass and the biomechanical forces exerted on the coiled aneurysm.

The significant impact of framing coils on long-term outcomes in endovascular coiling for intracranial aneurysms: how to select an appropriate framing coil

OBJECTIVE The importance of a framing coil (FC)—the first coil inserted into an aneurysm during endovascular coiling, also called a lead coil or a first coil—is recognized, but its impact on long-term outcomes, including recanalization and retreatment, is not well established. The purposes of this study were to test the hypothesis that the FC is a significant factor for aneurysmal recurrence and to provide some insights on appropriate FC selection. METHODS The authors retrospectively reviewed endovascular coiling for 280 unruptured intracranial aneurysms and gathered data on age, sex, aneurysm location, aneurysm morphology, maximal size, neck width, adjunctive techniques, recanalization, retreatment, follow-up periods, total volume packing density (VPD), volume packing density of the FC, and framing coil percentage (FCP; the percentage of FC volume in total coil volume) to clarify the associated factors for aneurysmal recurrence. RESULTS Of 236 aneurysms included in this study, 33 (14.0%) had recanalization, and 18 (7.6%) needed retreatment during a mean follow-up period of 37.7 ± 16.1 months. In multivariate analysis, aneurysm size (odds ratio [OR] = 1.29, p < 0.001), FCP < 32% (OR 3.54, p = 0.009), and VPD < 25% (OR 2.96, p = 0.015) were significantly associated with recanalization, while aneurysm size (OR 1.25, p < 0.001) and FCP < 32% (OR 6.91, p = 0.017) were significant predictors of retreatment. VPD as a continuous value or VPD with any cutoff value could not predict retreatment with statistical significance in multivariate analysis. CONCLUSIONS FCP, which is equal to the FC volume as a percentage of the total coil volume and is unaffected by the morphology of the aneurysm or the measurement error in aneurysm length, width, or height, is a novel predictor of recanalization and retreatment and is more significantly predictive of retreatment than VPD. To select FCs large enough to meet the condition of FCP ≥ 32% is a potential relevant factor for better long-term outcomes. These findings support our hypothesis that the FC is a significant factor for aneurysmal recurrence.

Influence of System Variables on the Heating Characteristics of Water during Continuous Flow Microwave Heating

A domestic microwave oven (1000 W) was modified to permit the continuous flow of liquids run through a helical coil centrally located inside the oven cavity. Heating characteristics were evaluated by measuring inlet and outlet temperatures of coil as a function of system variables. The influence of number of turns, coil diameter, tube diameter, pitch and initial temperature were evaluated at different flow rates. The average residence time of water was computed by dividing the coil volume by the volumetric flow rate. The influence of Dean number was evaluated. Results from this study showed that (1) higher number of turns resulted in lower heating rate, lower temperature fluctuations, higher exit temperature and longer time to achieve temperature equilibrium; (2) larger tube or coil diameter gave larger coil volume causing the heating rate to decrease; (3) faster flow rates resulted in lower exit temperatures, lower temperature fluctuation, higher Dean number and slightly higher heating rate; (4) higher initial temperatures resulted in higher exit temperatures; (5) higher Dean number resulted in more uniform heating and slightly higher heating rate. Overall, the coil volume was the more dominant factor affecting heating rate as compared with flow rate and Dean number.

Early Ceasing of Intra-aneurysmal Contrast Opacification During Coil Embolization in Ruptured Aneurysms Compared With Unruptured Aneurysms

BACKGROUND: The difference between coil-embolized ruptured and unruptured aneurysms with respect to intra-aneurysmal thrombus formation remains to be determined. OBJECTIVE: We examined whether there was a difference between ruptured and unruptured coil-embolized aneurysms in the rate and timing of thrombus formation in the aneurysmal sac and discuss the effect of thrombus on the treatment outcome. METHODS: We evaluated 209 aneurysms with an aneurysmal dome smaller than 10 mm and a neck size less than 4 mm. Of these, 91 (43.5%) were ruptured. We assessed intra-aneurysmal thrombus formation by the coil-packing ratio (CPR): the percentage of coil volume occupying the aneurysmal sac. The initial CPR was defined as the CPR at which contrast influx into the sac ceased and the final CPR as that at the end of the procedure. ΔCPR was calculated as the difference between initial and final CPRs. Embolized aneurysms were evaluated on follow-up angiograms. RESULTS: The initial CPR was significantly lower in ruptured aneurysms (P &lt; .01), and there was not a significant difference in the final CPR between ruptured and unruptured aneurysms (P = .05). ΔCPR was significantly higher in ruptured aneurysms (P &lt; .01). The rate of aneurysmal recanalization was significantly higher in ruptured aneurysms (P &lt; .05). The incidence of recanalization was high in ruptured aneurysms with low initial CPR and ΔCPR values. CONCLUSION: In ruptured aneurysms, intra-aneurysmal thrombus formation tends to occur in the earlier stages of coil embolization. In some cases, thrombus formation may inhibit dense coil packing and result in recanalization.

Cranial nerve palsy following transvenous embolization for a cavernous sinus dural arteriovenous fistula: association with the volume and location of detachable coils

Object Transvenous embolization (TVE) for the treatment of a cavernous sinus (CS) dural arteriovenous fistula (DAVF) occasionally causes cranial nerve palsy (CNP). Overpacking of coils is considered to result in CNP. The purpose of this study was to analyze the association of TVE-induced CNP with the volume and location of coils activated in the CS. Methods Thirty-one patients with CS DAVFs (33 lesions) underwent TVE. Results Cranial nerve palsy occurred or was aggravated in 13 cases (39.4%; CNP group). The cumulative volume of activated coils was significantly greater in the CNP group (0.241 ± 0.172 cm3) than in the non-CNP group (0.119 ± 0.075 cm3; p < 0.05). Of those lesions with > 0.2 cm3 of coil volume, 77.8% showed immediate aggravation or a new occurrence of CNP after TVE. Five lesions treated with a smaller volume of coils showed a delayed worsening or occurrence of CNP. In cases with induced oculomotor nerve palsy, coils had been densely packed in the superolateral part of the anterior CS. Dense packing in the lateral portion of the posterior CS frequently induced abducent nerve palsy. Although patients harboring lesions with a greater coil volume required a longer recovery time, newly developed or aggravated CNP, related to 84.6% of the lesions, resolved completely. Conclusions The cumulative volume and specific locations of coils in the CS correlated with TVE-induced CNP. Overpacking appeared to be the predominant cause of CNP; however, for CNP in cases involving smaller coil volumes, an alternative mechanism may be involved.