Novel use of a modified Amplatzer Vascular Plug® to occlude a patent ductus arteriosus in two patients

We describe two cases in which a patent ductus arteriosus (PDA) was successfully occluded percutaneously, using the novel approach of prefilling an Amplatzer Vascular Plug® with embolization coils to decrease the risk of residual shunting through the device. One patient was a small premature neonate, and the other was a child with an aneurismal, tubular PDA with no aortic ampulla. These are situations in which more popular PDA devices such as the Amplatzer Duct Occluder® may be contraindicated. © 2008 Wiley‐Liss, Inc.     

电解可脱弹簧圈栓塞治疗颅内破裂动脉瘤的近期疗效及影响因素

目的总结电解可脱弹簧圈(GDC)栓塞治疗颅内破裂动脉瘤的近期疗效及其相关影响因素.方法应用GDC栓塞治疗123例,分析动脉瘤几何形态学、病情严重程度对栓塞效果及临床治疗的影响.结果Hunt＆Hess分级Ⅰ～Ⅱ级病人中,预后良好者(GOS评分4～5分)为100%,Ⅲ～V级病人中分别为95%、78%、50%,窄颈动脉瘤完全栓塞率、大部栓塞率及部分栓塞率分别为92%、6%、2%,宽颈动脉瘤中分别为81%、13%、6%,大动脉瘤的疗效明显低于小动脉瘤.结论动脉瘤的栓塞程度不仅与瘤颈有关,还受瘤体大小的影响.载瘤动脉的形态影响GDC栓塞的操作,采用双弯塑形,有利于动脉瘤的超选与致密填塞.而临床预后与Hunt&Hess分级呈负相关.     

颅内宽颈动脉瘤的介入治疗

介入治疗已成为颅内动脉瘤治疗的重要手段。电解可脱卸弹簧圈（GDC）栓塞颅内动脉瘤具有微创、安全、效果可靠的优点。但宽颈动脉瘤的致密栓塞率低，复发率高，如何提高颅内动脉瘤的致密栓塞是该技术的要点和难点。动脉瘤微导管的双弯塑型、横向成篮、篮外填塞、分部填塞及瘤颈重塑型技术可明显提高动脉瘤的致密栓塞率。常见的并发症有术中出血、血栓栓塞、血管痉挛等，迅速继续填塞动脉瘤是处理术中出血最有效的措施；实施腰蛛网膜下腔持续引流，释放血性脑脊液，辅以抗凝及“3H”治疗是防治脑血管痉挛和血栓栓塞的关键。对于特别宽颈及梭形动脉瘤，无法单纯采用GDC治疗，血管内支架结合GDC是治疗颅内梭形及宽颈动脉瘤的有效方法。正确的支架选择，防止支架移位，是手术成功的关键，但确切疗效需进一步长期随访。     

Eye-position dependence of three-dimensional ocular rotation-axis orientation during head impulses in humans

 If horizontal saccades or smooth-pursuit eye movements are made with the line-of-sight at different elevations, the three-dimensional (3D) angular rotation axis of the globe tilts by half the vertical eye eccentricity. This phenomenon is named ”half-angle rule” and is a consequence of Listing’s law. It was recently found that the ocular rotation axis during the horizontal vestibulo-ocular reflex (VOR) on a turntable also tilts in the direction of the line-of-sight by about a quarter of the eye’s vertical eccentricity. This is surprising, since, in a ”perfect” VOR, the angular rotation axis of the eye should be independent from the position of the eye to fully compensate for the 3D angular head rotation. We asked whether this quarter-angle strategy is a general property of the VOR or whether the 3D kinematics of ocular movements evoked by vestibular stimulation would be less eye-position dependent at higher stimulus frequencies. Nine healthy subjects were exposed to horizontal head impulses (peak velocity ∼250°/s). The line-of-sight was systematically changed along the vertical meridian of a tangent screen. Three-dimensional eye and head movements were monitored with dual search coils. The 3D orientation of the angular eye-in-head rotation axis was determined by calculating the average angular velocity vectors of the initial 10° displacements. Then, the difference between the tilt angles of the ocular rotation axis during upward and downward viewing was determined and divided by the difference of vertical eccentricity (”tilt angle coefficient”). Control experiments included horizontal saccades, smooth-pursuit eye movements, and eye movements evoked by slow, passive head rotations at the same vertical eye eccentricities. On average, the ocular rotation axis during horizontal head-impulse testing at different elevations of the line-of-sight was closely aligned with the rotation axis of the head (tilt angle coefficient of pooled abducting and adducting eye movements: 0.11±0.17 SD). Values for slow head impulses, however, exceeded somewhat the quarter angle (0.33±0.12), while smooth-pursuit movements (0.50±0.09) and saccades (0.44±0.11) were closest to the half angle. These results demonstrate that the 3D orientation of the ocular rotation axis during rapid head thrusts is relatively independent of the direction of the line-of-sight and that ocular rotations elicited by head impulses are kinematically different from saccades, despite similar movement dynamics. Received: 17 July 1998 / Accepted: 17 May 1999     

MR‐based measurements and simulations of the magnetic field created by a realistic transcranial magnetic stimulation (TMS) coil and stimulator

Transcranial magnetic stimulation (TMS) is an emerging technique that allows non‐invasive neurostimulation. However, the correct validation of electromagnetic models of typical TMS coils and the correct assessment of the incident TMS field (B_TMS) produced by standard TMS stimulators are still lacking. Such a validation can be performed by mapping B_TMS produced by a realistic TMS setup. In this study, we show that MRI can provide precise quantification of the magnetic field produced by a realistic TMS coil and a clinically used TMS stimulator in the region in which neurostimulation occurs. Measurements of the phase accumulation created by TMS pulses applied during a tailored MR sequence were performed in a phantom. Dedicated hardware was developed to synchronize a typical, clinically used, TMS setup with a 3‐T MR scanner. For comparison purposes, electromagnetic simulations of B_TMS were performed. MR‐based measurements allow the mapping and quantification of B_TMS starting 2.5 cm from the TMS coil. For closer regions, the intra‐voxel dephasing induced by B_TMS prohibits TMS field measurements. For 1% TMS output, the maximum measured value was ~0.1 mT. Simulations reflect quantitatively the experimental data. These measurements can be used to validate electromagnetic models of TMS coils, to guide TMS coil positioning, and for dosimetry and quality assessment of concurrent TMS‐MRI studies without the need for crude methods, such as motor threshold, for stimulation dose determination.     

A low‐cost,mechanically simple apparatus for measuring eddy current‐induced magnetic fields in MRI

The fidelity of gradient waveforms in MRI pulse sequences is essential to the acquisition of images and spectra with minimal distortion artefacts. Gradient waveforms can become nonideal when eddy currents are created in nearby conducting structures; however, the resultant magnetic fields can be characterised and compensated for by measuring the spatial and temporal field response following a gradient impulse. This can be accomplished using a grid of radiofrequency (RF) coils. The RF coils must adhere to strict performance requirements: they must achieve a high sensitivity and signal‐to‐noise ratio (SNR), have minimal susceptibility field gradients between the sample and surrounding material interfaces and be highly decoupled from each other. In this study, an apparatus is presented that accomplishes these tasks with a low‐cost, mechanically simple solution. The coil system consists of six transmit/receive RF coils immersed in a high‐molarity saline solution. The sensitivity and SNR following an excitation pulse are sufficiently high to allow accurate phase measurements during free‐induction decays; the intrinsic susceptibility matching of the materials, because of the unique design of the coil system, results in sufficiently narrow spectral line widths (mean of 19 Hz), and adjacent RF coils are highly decoupled (mean S₁₂ of ?47 dB). The temporal and spatial distributions of eddy currents following a gradient pulse are measured to validate the efficacy of the design, and the resultant amplitudes and time constants required for zeroth‐ and first‐order compensation are provided. Copyright © 2013 John Wiley & Sons, Ltd.     

High‐permittivity solid ceramic resonators for high‐field human MRI

The properties of a ceramic‐based annular dielectric resonator designed for 7 T MRI have been examined. Electromagnetic simulations and experimentally determined modal frequencies agree to within ~1%. The dependence of the resonance frequency of the degenerate quadrature HEM₁₁ modes on hole diameter and shield diameter was also investigated. The constructed coil, with a 2.5 cm diameter hole, had an unloaded Q value of 400, which was reduced to 150 when loaded with a human finger. Simulated and experimental B₁⁺ maps show a high degree of homogeneity with a sensitivity of ~11.5 μT/√W at the centre. A comparison with a loop gap resonator showed an approximately 25% higher sensitivity for the dielectric resonator. High‐resolution images of the digital interphalangeal (DIP) and proximal interphalangeal (PIP) joints of volunteers were acquired in imaging times of less than 2 min. Finally, novel methods of double tuning such ceramic resonators to two relatively close frequencies, e.g. proton and fluorine, have been shown. Copyright © 2013 John Wiley & Sons, Ltd.     

可膨胀水凝胶弹簧圈栓塞颅内动脉瘤的临床应用

目的探讨可膨胀水凝胶弹簧圈栓塞治疗颅内动脉瘤的安全性及临床价值。方法对24例28个动脉瘤进行了栓塞治疗，其中23个动脉瘤使用水凝胶弹簧圈栓塞。21例为破裂出血动脉瘤，其中Hunt-Hess分级I级6例，Ⅱ级9例，Ⅲ级4例，Ⅳ级2例。动脉瘤最大径3．6-17mm，平均（8．3±3．4）mm。结果完全致密栓塞20个，瘤颈残留6个，部分栓塞2个。栓塞密度为39％～124％，平均（67．6±32．3）％。暂时性对侧肢体轻偏瘫4例，脑室引流术致严重血管痉挛、颅内感染及多器官功能衰竭死亡各1例。结论可膨胀水凝胶弹簧圈栓塞治疗颅内动脉瘤安全有效，其栓塞的致密程度令人满意，其临床应用效果值得进一步研究。