Reduction of radiation exposure using low pulse rate fluoroscopy during neuroendovascular surgery.

INTRODUCTION: Endovascular surgery is minimally invasive, but the radiation exposure can be problematic. There is no report assessing whether radiation exposure can be reduced by using a low pulse rate during carotid artery stenting (CAS). The aim of this study was to evaluate whether reducing the pulse rate from 7.5 to 4 frames per second (f/s) can reduce the radiation exposure while maintaining safety during CAS procedure. METHODS: We retrospectively reviewed the radiation data and clinical features of all 100 patients who underwent CAS between 2014 and 2019. We changed the pulse rate from 7.5 to 4 f/s in 2017. The fluoroscopic time (FT), dose area product (DAP), and total air kerma (AK) were collected. Statistical analyses were performed between the pulse rate and clinical outcomes, including radiation exposure.

Feasibility of Smart Metal Artifact Reduction Algorithm on Computed Tomography Angiography for Clipping of Recurrent Aneurysms After Coil Embolization.

BACKGROUND: The number of patients with a history of clipping of recurrent aneurysms after coil embolization has increased. The aim of this article was to report the feasibility of CT angiography using a commercial metal artifact reduction algorithm (Smart Metal Artifact Reduction [MAR]) for patients who underwent clipping of recurrent aneurysms after coil embolization. METHODS: Six cases of clipping of recurrent aneurysms after coil embolization were examined with CT angiography using MAR between 2015 and 2018 at a single institution. Conventional CT angiography and three-dimensional digital subtraction angiography data were compared, and depiction of the status of treated aneurysms using MAR was estimated. RESULTS: Conventional CT angiography was unable to depict the status of treated aneurysms in the patients with a history of clipping of recurrent aneurysms after coil embolization because of metal artifacts. With MAR, metal artifacts were greatly reduced, and the status of treated aneurysms was able to be depicted, although depiction was inferior to three-dimensional digital subtraction angiography. CONCLUSIONS: For patients with a history of clipping of recurrent aneurysms after coil embolization, CT angiography using MAR is feasible, although further development of imaging techniques is needed.

Clipping of Recurrent Cerebral Aneurysms After Coil Embolization.

BACKGROUND AND AIMS: To assess the technical points of surgical clipping for recurrent aneurysms after coiling, we examine a consecutive series of 14 patients who underwent re-treatment. MATERIALS AND METHODS: From 2009 to 2016, 27 recurrent aneurysms after coiling were re-treated with endovascular treatment or surgical clipping. Of these, 14 were re-treated surgically. In cases where the remnant neck was sufficiently large, neck clipping was chosen. Where the remnant neck was too small and the border between the thrombosed and non-thrombosed portion was distinct, partial clipping was chosen. Surgical clipping was attempted without removing the coils when technically feasible. RESULTS: Among the 14 cases, neck clipping was performed in 11, partial clipping in 2, and trapping with bypass in 1 case. Clipping without removal of coils was accomplished in all cases. No neurological deterioration occurred after surgical clipping in any case. CONCLUSION: Clipping of recurrent aneurysms after coiling can compensate for the failure of initial endovascular therapy. For clipping without removal of coils, precise evaluation of the remnant neck is required. Bypass surgery is key to treatment in the case of aneurysm trapping.

Freehand Technique of an Electromagnetic Navigation System Emitter to Avoid Interference Caused by Metal Neurosurgical Instruments.

BACKGROUND: Electromagnetic (EM) navigation has been reported to be a noninvasive and easy-to-use technique. However, the use of metal neurosurgical instruments (e.g., skin hooks, head frames, brain retractors systems) can interfere with the magnetic fields of such systems. We present the freehand technique, a new technique involving the manual manipulation of the emitter of an EM navigation system, which helps to prevent interference caused by metal instruments during surgery. METHODS: The AxiEM Electromagnetic StealthStation Navigation System (Medtronic) was used in this study. The emitter was placed in the sterilized surgical field, which allowed it to be moved freely during surgery. When navigation was necessary during the procedure, the assistant held the emitter at an appropriate angle to the sterile surgical field to avoid interference caused by the metal neurosurgical instruments. RESULTS: During surgery involving metal surgical instruments, all of the functions of the EM navigation system were available throughout the procedure. The accuracy of the navigation system was sufficient to allow craniotomy and intradural manipulation to be conducted. CONCLUSIONS: During the use of EM navigation systems, the freehand technique with the emitter can prevent interference caused by metal instruments.

Utility of the Lone Star Retractor System in Microsurgical Carotid Endarterectomy.

BACKGROUND: The retractor system is an important device in carotid endarterectomy (CEA). We applied the Lone Star (LS) Retractor System, which is a self-retaining retractor originally designed for improved visualization in many other surgical fields, in microsurgical CEA. METHODS: The LS disposal retractor (14.1 cm × 14.1 cm) and LS elastic stays (5-mm sharp hook) were used as a retractor system in 38 consecutive CEAs. RESULTS: Using the LS retractor system, a shallow operative field could be obtained by lifting up the connective tissue surrounding the deep structures hooked by the LS elastic stays. The LS elastic stays were quick and easy to handle in the microsurgical operative field. There were no complications using the LS retractor system. CONCLUSIONS: The application of the LS retractor system in microsurgical CEA is feasible. An additional merit is that it is single use.

Direct Surgery of Previously Coiled Large Internal Carotid Ophthalmic Aneurysm for the Purpose of Optic Nerve Decompression.

Background Progressive visual loss after coil embolization of a large internal carotid ophthalmic aneurysm has been widely reported. It is generally accepted that the primary strategy for this complication should be conservative, including steroid therapy; however, it is not well known as to what approach to take when the conservative therapy is not effective. Case Presentation We report a case of a 55-year-old female presenting with progressive visual loss after the coiling of a ruptured large internal carotid ophthalmic aneurysm. As the conservative therapy had not been effective, we performed neck clipping of the aneurysm with optic canal unroofing, anterior clinoidectomy, and partial removal of the embolized coils for the purpose of optic nerve decompression. After the surgery, the visual symptom was improved markedly. Conclusions It is suggested that direct surgery for the purpose of optic nerve decompression may be one of the options when conservative therapy is not effective for progressive visual disturbance after coil embolization.

Regulation of cerebral metabolism during cortical spreading depression.

We analyzed the metabolic response to cortical spreading depression that drastically increases local energy demand to restore ion homeostasis. During single and multiple cortical spreading depressions in the rat cortex, we simultaneously monitored extracellular levels of glucose and lactate using rapid sampling microdialysis and glucose influx using 18 F-fluorodeoxyglucose positron emission tomography while tracking cortical spreading depression using laser speckle imaging. Combining the acquired data with steady-state requirements we developed a mass-conserving compartment model including neurons and glia that was consistent with the observed data. In summary, our findings are: (1) Early breakdown of glial glycogen provides a major source of energy during increased energy demand and leaves 80% of blood-borne glucose to neurons. (2) Lactate is used solely by neurons and only if extracellular lactate levels are >80% above normal. (3) Although the ratio of oxygen and glucose consumption transiently reaches levels <3, the major part (>90%) of the overall energy supply is from oxidative metabolism. (4) During cortical spreading depression, brain release of lactate exceeds its consumption suggesting that lactate is only a circumstantial energy substrate. Our findings provide a general scenario for the metabolic response to increased cerebral energy demand.

Isoflurane suppresses cortical spreading depolarizations compared to propofol--implications for sedation of neurocritical care patients.

Sedatives in the neurointensive care unit can strongly influence patients' risks of developing secondary brain damage. In particular, isoflurane, a volatile anesthetic, has been recently re-introduced to the neurointensive care unit, and first clinical studies suggest beneficial effects due to elevation of cerebral blood flow and reduction of metabolism. In contrast, propofol is a commonly used intravenous sedative that reduces cerebral blood flow and intra-cranial pressure. We have here studied the influence of these two sedatives on the occurrence of cortical spreading depolarizations (CSDs), which have emerged over the last decade as a major mechanism of delayed brain injury in stroke and brain trauma, constituting a substantial vascular and metabolic threat to peri-infarct tissue and being associated with poor patient outcome. Two experimental models were tested in Wistar rats anesthetized either with isoflurane or with propofol: KCl-evoked CSDs (n=10) and spontaneous CSDs after occlusion of the middle cerebral artery (n=14). Spatiotemporal patterns of CSD waves were observed by real-time laser speckle imaging of regional cerebral blood flow changes associated with the CSDs. During 30 min of cortical KCl application, 5.2±0.7 CSDs were induced under isoflurane compared to 10.2±1.8 CSDs under propofol (p<0.001). After focal ischemia, 2.43±1.0 CSDs/h emerged spontaneously under isoflurane versus 6.83±2.5 CSDs/h under propofol (p<0.001). Furthermore, baseline blood flow and glycemia were much higher under isoflurane compared to propofol, which may set the tissue in better metabolic conditions to recover from the occurrence of CSD waves. We conclude that isoflurane, in comparison to propofol, decreases the occurrence of CSDs and may improve recovery from these metabolically demanding waves. To reduce CSD induced secondary tissue damage, we suggest isoflurane to be favored over propofol to sedate acute stroke and trauma patients in the neurointensive care unit.

Mismatch responses in the awake rat: evidence from epidural recordings of auditory cortical fields.

Detecting sudden environmental changes is crucial for the survival of humans and animals. In the human auditory system the mismatch negativity (MMN), a component of auditory evoked potentials (AEPs), reflects the violation of predictable stimulus regularities, established by the previous auditory sequence. Given the considerable potentiality of the MMN for clinical applications, establishing valid animal models that allow for detailed investigation of its neurophysiological mechanisms is important. Rodent studies, so far almost exclusively under anesthesia, have not provided decisive evidence whether an MMN analogue exists in rats. This may be due to several factors, including the effect of anesthesia. We therefore used epidural recordings in awake black hooded rats, from two auditory cortical areas in both hemispheres, and with bandpass filtered noise stimuli that were optimized in frequency and duration for eliciting MMN in rats. Using a classical oddball paradigm with frequency deviants, we detected mismatch responses at all four electrodes in primary and secondary auditory cortex, with morphological and functional properties similar to those known in humans, i.e., large amplitude biphasic differences that increased in amplitude with decreasing deviant probability. These mismatch responses significantly diminished in a control condition that removed the predictive context while controlling for presentation rate of the deviants. While our present study does not allow for disambiguating precisely the relative contribution of adaptation and prediction error processing to the observed mismatch responses, it demonstrates that MMN-like potentials can be obtained in awake and unrestrained rats.

Dynamic causal models and physiological inference: a validation study using isoflurane anaesthesia in rodents.

Generative models of neuroimaging and electrophysiological data present new opportunities for accessing hidden or latent brain states. Dynamic causal modeling (DCM) uses Bayesian model inversion and selection to infer the synaptic mechanisms underlying empirically observed brain responses. DCM for electrophysiological data, in particular, aims to estimate the relative strength of synaptic transmission at different cell types and via specific neurotransmitters. Here, we report a DCM validation study concerning inference on excitatory and inhibitory synaptic transmission, using different doses of a volatile anaesthetic agent (isoflurane) to parametrically modify excitatory and inhibitory synaptic processing while recording local field potentials (LFPs) from primary auditory cortex (A1) and the posterior auditory field (PAF) in the auditory belt region in rodents. We test whether DCM can infer, from the LFP measurements, the expected drug-induced changes in synaptic transmission mediated via fast ionotropic receptors; i.e., excitatory (glutamatergic) AMPA and inhibitory GABA(A) receptors. Cross- and auto-spectra from the two regions were used to optimise three DCMs based on biologically plausible neural mass models and specific network architectures. Consistent with known extrinsic connectivity patterns in sensory hierarchies, we found that a model comprising forward connections from A1 to PAF and backward connections from PAF to A1 outperformed a model with forward connections from PAF to A1 and backward connections from A1 to PAF and a model with reciprocal lateral connections. The parameter estimates from the most plausible model indicated that the amplitude of fast glutamatergic excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) behaved as predicted by previous neurophysiological studies. Specifically, with increasing levels of anaesthesia, glutamatergic EPSPs decreased linearly, whereas fast GABAergic IPSPs displayed a nonlinear (saturating) increase. The consistency of our model-based in vivo results with experimental in vitro results lends further validity to the capacity of DCM to infer on synaptic processes using macroscopic neurophysiological data.

Distinct spatiotemporal patterns of spreading depolarizations during early infarct evolution: evidence from real-time imaging.

Experimental and clinical studies indicate that waves of cortical spreading depolarization (CSD) appearing in the ischemic penumbra contribute to secondary lesion growth. We used an embolic stroke model that enabled us to investigate inverse coupling of blood flow by laser speckle imaging (CBF(LSF)) to CSD as a contributing factor to lesion growth already in the early phase after arterial occlusion. Embolization by macrospheres injected into the left carotid artery of anesthetized rats reduced CBF(LSF) in the territories of the middle cerebral artery (MCA) (8/14 animals), the posterior cerebral artery (PCA) (2/14) or in less clearly defined regions (4/14). Analysis of MCA occlusions (MCAOs) revealed a first CSD wave starting off during ischemic decline at the emerging core region, propagating concentrically over large portions of left cortex. Subsequent recurrent waves of CSD did not propagate concentrically but preferentially circled around the ischemic core. In the vicinity of the core region, CSDs were coupled to waves of predominantly vasoconstrictive CBF(LSF) responses, resulting in further decline of CBF in the entire inner penumbra and in expansion of the ischemic core. We conclude that CSDs and corresponding CBF responses follow a defined spatiotemporal order, and contribute to early evolution of ischemic territories.