Performance assessment of two motion management systems for frameless stereotactic radiosurgery.

BACKGROUND/PURPOSE: Frameless stereotactic radiosurgery (SRS) requires dedicated systems to monitor patient motion in order to avoid inaccurate radiation delivery due to involuntary shifts. The purpose of this study is to assess the accuracy and sensitivity of two distinct motion monitoring systems used for frameless SRS. METHODS: A surface image-guided system known as optical surface monitoring system (OSMS), and a fiducial marker-based system known as high definition motion management (HDMM) as part of the latest Gamma Knife Icon® were compared. A 3D printer-based cranial motion phantom was developed to evaluate the accuracy and sensitivity of these two systems in terms of: (1) the capability to recognize predefined shifts up to 3 cm, and (2) the capability to recognize predefined speeds up to 3 cm/s. The performance of OSMS, in terms of different reference surfaces, was also evaluated. RESULTS: Translational motion could be accurately detected by both systems, with an accuracy of 0.3 mm for displacement up to 1 cm, and 0.5 mm for larger displacements. The reference surface selection had an impact on OSMS performance, with flat surface resulting in less accuracy. HDMM was in general more sensitive when compared with OSMS in capturing the motion, due to its faster frame rate, but a delay in response was observed with faster speeds. Both systems were less sensitive in detection of superior-inferior motion when compared to lateral or vertical displacement directions. CONCLUSION: Translational motion can be accurately and sensitively detected by OSMS and HDMM real-time monitoring systems. However, performance variations were observed along different motion directions, as well as amongst the selection of reference images. Caution is needed when using real-time monitoring systems for frameless SRS treatment.

Is It Possible to Save the Deep Brain Stimulation Hardware when Presenting with Wound Dehiscence or Hardware Infection?

INTRODUCTION: Deep brain stimulation (DBS) hardware complications have been traditionally managed by removal of the entire system. Explantation of the system results in prolonged interruption to the patient's care and potential challenges when considering reimplantation of the cranial leads. The purpose of this study was to understand whether complete explantation can be avoided for patients initially presenting with wound dehiscence and/or infection of hardware. METHODS: We performed a retrospective study that included 30 cases of wound dehiscence or infection involving the DBS system. Patients underwent reoperation without explantation of the DBS system, with partial explanation, or with complete explantation as initial management of the complication. RESULTS: A total of 17/30 cases were managed with hardware-sparing wound revisions. The majority presented with wound dehiscence (94%), with the scalp (n = 9) as the most common location. This was successful in 76.5% of patients (n = 13). Over 11/30 patients were managed with partial explantation. The complication was located at the generator (91%) or at the scalp (9%). Partial explantation was successful in 64% of patients (n = 7). In cases that underwent a lead-sparing approach, 33% of patients ultimately required removal of the intracranial lead, and 2/30 cases of hardware infection were managed initially with total explantation. DISCUSSION/CONCLUSION: Wound dehiscence can be successfully managed without complete removal of the DBS system in most cases. In cases of infection, removing the involved component(s) and sparing the intracranial leads may be considered. Wound revision without removal of the entire DBS system is safe and can improve quality of life by preventing or shortening the withdrawal of DBS treatment.

Magnetic resonance-guided laser interstitial thermal therapy for posterior fossa neoplasms.

PURPOSE: Magnetic resonance-guided laser interstitial thermal therapy (LITT) has been increasingly used to treat a number of intracranial pathologies, though its use in the posterior fossa has been limited to a few small series. We performed a multi-institutional review of targets in the posterior fossa, reporting the efficacy and safety profile associated with laser ablation in this region of the brain. METHODS: A retrospective review of patients undergoing LITT in the posterior fossa was performed from August 2010 to March 2020. Patient demographic information was collected alongside the operative parameters and patient outcomes. Reported outcomes included local control of the lesion, postoperative complications, hospital length of stay, and steroid requirements. RESULTS: 58 patients across four institutions underwent LITT in the posterior fossa for 60 tumors. The median pre-ablation tumor volume was 2.24 cm3. 48 patients (50 tumors) were available for follow-up. An 84% (42/50) overall local control rate was achieved at 9.5 months median follow up. There were two procedural complications, including insertional hemorrhage and laser misplacement and 12/58 (21%) patients developed new neurological deficits. There was one procedure related death. The median length of hospital stay was 1 day, with 20.7% of patients requiring discharge to a rehabilitation facility. CONCLUSIONS: LITT is an effective approach for treating pathology in the posterior fossa. The average target size is smaller than what has been reported in the supratentorial space. Care must be taken to prevent injury to surrounding structures given the close proximity of critical structures in this region.

Magnetic resonance-guided laser interstitial thermal therapy for brain tumors in geriatric patients.

OBJECTIVE: There is a paucity of studies assessing the use of MR-guided laser interstitial thermal therapy (LITT), specifically in the elderly population. The aim of this study was to evaluate the safety of LITT for brain tumors in geriatric patients. METHODS: Geriatric patients (≥ 65 years of age) treated with LITT for intracranial tumors at a single institution between January 2011 and November 2019 were retrospectively identified. The authors grouped patients into two distinct age cohorts: 65-74 years (group 1) and 75 years or older (group 2). Baseline characteristics, operative parameters, postoperative course, and morbidity were recorded for each patient. RESULTS: Fifty-five geriatric patients underwent 64 distinct LITT procedures for brain tumors. The majority of lesions (40 [62.5%]) treated were recurrent brain metastases or radiation necrosis. The median modified frailty index was 0.1 (low frailty; range 0-0.4) for patients in group 1 and 0.2 (intermediate frailty; range 0-0.4) for patients in group 2 (p > 0.05). The median hospital length of stay (LOS) was 1 day (IQR 1-2 days); there was no significant difference in LOS between the age groups. The hospital stay was significantly longer in patients who presented with a neurological symptom and in those who experienced a postoperative complication. The majority of patients (43 [68.3%] of 63 cases) were fit for discharge to their preoperative accommodation following LITT. The rate of discharge to home was not significantly different between the age groups. Those discharged to rehabilitation facilities were more likely to have presented with a neurological symptom. Nine patients (14.1% of cases) were found to have acute neurological complications following LITT, with nearly all patients showing complete or partial recovery at follow-up. The 30-day postoperative mortality rate was 1.6% (1 case). The complication and 30-day postoperative mortality rates were not significantly different between the two age groups. CONCLUSIONS: LITT can be considered a minimally invasive and safe neurosurgical procedure for the treatment of intracranial tumors in geriatric patients. Careful preoperative preparation and postoperative care is essential as LITT is not without risk. Appropriate patient selection for cranial surgery is essential, because neurosurgeons are treating an increasing number of elderly patients, but advanced age alone should not exclude patients from LITT without considering frailty and comorbidities.

Risk of leptomeningeal carcinomatosis in patients with brain metastases treated with stereotactic radiosurgery.

There is limited available literature examining factors that predispose patients to the development of LMC after stereotactic radiosurgery (SRS) for brain metastases. We sought to evaluate risk factors that may predispose patients to LMC after SRS treatment in this case-control study of patients with brain metastases who underwent single-fraction SRS between 2011 and 2016. Demographic and clinical information were collected retrospectively for 19 LMC cases and 30 controls out of 413 screened patients with brain metastases. Risk factors of interest were evaluated by univariate and multivariate logistic regression analyses and overall survival rates were evaluated by Kaplan-Meier survival analysis. About 5% of patients with brain metastases treated with SRS developed LMC. Patients with LMC (median 154 days, 95% CI 33-203 days) demonstrated a poorer overall survival than matched controls (median 417 days, 95% CI 121-512 days, p = 0.002). The most common primary tumor histologies  that lead to the development of LMC were non-small cell lung cancer (36.8%), breast cancer (26.3%), and melanoma (21.1%). No association was found between the risk of LMC and the location of the brain lesion or total volume of brain metastases. Prior surgical resection of brain metastases before SRS was associated with a 6.5 times higher odds (95% CI 1.45-29.35, p = 0.01) of developing LMC post-radiosurgery compared to those with no prior resections of brain metastases. Additionally, adjuvant WBRT may help to reduce the risk of LMC and can be considered in decision-making for patients who have had brain metastasectomy.

Effects of variable power on tissue ablation dynamics during magnetic resonance-guided laser-induced thermal therapy with the Visualase system.

PURPOSE: Magnetic resonance-guided laser-induced thermal therapy (MRgLITT) is a minimally invasive procedure used to treat various intracranial pathologies. This study investigated the effects of variable power on maximal estimated thermal damage during ablation and duration required to reach maximal ablation. MATERIALS/METHODS: All ablations were performed using the Visualase Thermal Therapy System (Medtronic Inc., Minneapolis, Minnesota), which uses a 980 nm diffusing tip diode laser. Cases were stratified into low, medium and high power. Maximal thermal damage estimate (TDEmax) achieved in a single plane and time to reach maximal damage (ttdemax) were measured and compared between groups using a 2×3 Fixed Factor Analysis of Covariance. Ablation area change for cases in which an initial thermal dose was followed by a subsequent dose, with increased power, was also assessed. RESULTS: We used real-time ablation data from 93 patients across various intracranial pathologies. ttdemax (mean ± SEM) decreased linearly as power increased (low: 139.2 ± 10.4 s, medium: 127.5 ± 4.3 s, high: 103.7 ± 5.8 s). In cases where a second thermal dose was delivered at higher power, the TDE expanded an average of 51.4 mm2 beyond the initial TDE generated by the first ablation, with the second ablation approaching TDEmax at a higher rate than the initial ablation. CONCLUSION: Increased power results in a larger TDEmax and an increased ablation rate. In cases where an initial thermal dose does not fully ablate the target lesion, a second ablation at higher power can increase the area of ablation with an increased ablation rate.

Theoretical model for laser ablation outcome predictions in brain: calibration and validation on clinical MR thermometry images.

PURPOSE: Neurosurgical laser ablation is experiencing a renaissance. Computational tools for ablation planning aim to further improve the intervention. Here, global optimisation and inverse problems are demonstrated to train a model that predicts maximum laser ablation extent. METHODS: A closed-form steady state model is trained on and then subsequently compared to N = 20 retrospective clinical MR thermometry datasets. Dice similarity coefficient (DSC) is calculated to provide a measure of region overlap between the 57 °C isotherms of the thermometry data and the model-predicted ablation regions; 57 °C is a tissue death surrogate at thermal steady state. A global optimisation scheme samples the dominant model parameter sensitivities, blood perfusion (ω) and optical parameter (µeff) values, throughout a parameter space totalling 11 440 value-pairs. This represents a lookup table of µeff-ω pairs with the corresponding DSC value for each patient dataset. The µeff-ω pair with the maximum DSC calibrates the model parameters, maximising predictive value for each patient. Finally, leave-one-out cross-validation with global optimisation information trains the model on the entire clinical dataset, and compares against the model naïvely using literature values for ω and µeff. RESULTS: When using naïve literature values, the model's mean DSC is 0.67 whereas the calibrated model produces 0.82 during cross-validation, an improvement of 0.15 in overlap with the patient data. The 95% confidence interval of the mean difference is 0.083-0.23 (p < 0.001). CONCLUSIONS: During cross-validation, the calibrated model is superior to the naïve model as measured by DSC, with +22% mean prediction accuracy. Calibration empowers a relatively simple model to become more predictive.

A newly diagnosed case of polymorphous low-grade neuroepithelial tumor of the young.

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a recently described variant of low-grade neuroepithelial tumors that exhibits infiltrative growth, histopathological variability with frequently prominent oligodendroglioma-like components, intense labeling for CD34, absence of 1P/19Q codeletion, a distinct DNA methylation signature and genetic alterations involving MAP kinase pathway constituents of either the B-Raf proto-oncogene BRAF or fibroblast growth factor receptors 2 or 3 (FGFR2 and FGFR3). We here report a newly diagnosed case of PLNTY involving the temporal lobe in a 31-year-old man with chronic focal epilepsy. This tumor had histologic and immunophenotypic features similar to the recently described PLNTY and proved BRAF V600E mutant. Biomolecular profiling is becoming increasingly important in characterizing neuroepithelial tumors. Furthermore, biomolecular features such as CD34 expression and BRAF mutation have been reported to be significantly associated with the clinical behavior of these tumors. Like other low-grade neuroepithelial tumors, PLNTYs appear to be generally indolent with excellent seizure relief after total surgical resection. It is important to recognize cases of PLNTY in order to guide clinical management including the indication for surgery.
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Assessing Cerebral Hemodynamic Stability After Brain Injury.

OBJECTIVE: Following brain injury, unstable cerebral hemodynamics can be characterized by abnormal rises in intracranial pressure (ICP). This behavior has been quantified by the RAP index: the correlation (R) between ICP pulse amplitude (A) and mean (P). While RAP could be a valuable indicator of autoregulatory processes, its prognostic ability is not well established and its validity has been questioned due to potential errors in measurement. Here, we test (1) whether RAP is a consistent measure of intracranial hemodynamics and (2) whether RAP has prognostic value in predicting hemodynamic instability following brain injury. MATERIALS AND METHODS: RAP was tested in seven brain injured patients treated in a surgical intensive care unit. A sample of ICP data was randomly chosen and segmented into 1 hour periods. Hours were then categorized as either stable, which contained no sharp rises in ICP, or unstable, which contained ≥1 sharp rise-where a sharp rise is defined as ICP exceeding a mean slope of 0.15 mmHg/s. Equal numbers of stable and unstable segments were then selected for each patient. RAP was calculated as the Pearson's correlation coefficient between ICP pulse amplitude (AMP) and mean (mICP), determined in 6 second windows, according to established methods. RESULTS: Results showed that (1) average AMP and ICP levels were similar between stable and unstable periods and (2) unstable periods were identified by RAP values exceeding 0.6 with an average positive predictive value of 74%. CONCLUSIONS: We conclude that RAP can provide a valid measure of ICP dynamics, is not affected by sensor drift, and can better distinguish periods of instability than ICP or AMP alone.

Trending autoregulatory indices during treatment for traumatic brain injury.

Our goal is to use automatic data monitoring for reliable prediction of episodes of intracranial hypertension in patients with traumatic brain injury. Here we test the validity of our method on retrospective patient data. We developed the Continuous Hemodynamic Autoregulatory Monitor (CHARM), that siphons and stores signals from existing monitors in the surgical intensive care unit (SICU), efficiently compresses them, and standardizes the search for statistical relationships between any proposed index and adverse events. CHARM uses an automated event detector to reliably locate episodes of elevated intracranial pressure (ICP), while eliminating artifacts within retrospective patient data. A graphical user interface allowed data scanning, selection of criteria for events, and calculating indices. The pressure reactivity index (PRx), defined as the least square linear regression slope of intracranial pressure versus arterial BP, was calculated for a single case that spanned 259 h. CHARM collected continuous records of ABP, ICP, ECG, SpO2, and ventilation from 29 patients with TBI over an 18-month period. Analysis of a single patient showed that PRx data distribution in the single hours immediately prior to all 16 intracranial hypertensive events, significantly differed from that in the 243 h that did not precede such events (p < 0.0001). The PRx index, however, lacked sufficient resolution as a real-time predictor of IH in this patient. CHARM streamlines the search for reliable predictors of intracranial hypertension. We report statistical evidence supporting the predictive potential of the pressure reactivity index.

A model evaluation study for treatment planning of laser-induced thermal therapy.

A cross-validation analysis evaluating computer model prediction accuracy for a priori planning magnetic resonance-guided laser-induced thermal therapy (MRgLITT) procedures in treating focal diseased brain tissue is presented. Two mathematical models are considered. (1) A spectral element discretisation of the transient Pennes bioheat transfer equation is implemented to predict the laser-induced heating in perfused tissue. (2) A closed-form algorithm for predicting the steady-state heat transfer from a linear superposition of analytic point source heating functions is also considered. Prediction accuracy is retrospectively evaluated via leave-one-out cross-validation (LOOCV). Modelling predictions are quantitatively evaluated in terms of a Dice similarity coefficient (DSC) between the simulated thermal dose and thermal dose information contained within N = 22 MR thermometry datasets. During LOOCV analysis, the transient model's DSC mean and median are 0.7323 and 0.8001 respectively, with 15 of 22 DSC values exceeding the success criterion of DSC ≥ 0.7. The steady-state model's DSC mean and median are 0.6431 and 0.6770 respectively, with 10 of 22 passing. A one-sample, one-sided Wilcoxon signed-rank test indicates that the transient finite element method model achieves the prediction success criteria, DSC ≥ 0.7, at a statistically significant level.

Assessment of irrigation dynamics in magnetic-resonance guided laser induced thermal therapy (MRgLITT).

BACKGROUND AND OBJECTIVES: Magnetic-Resonance Guided Laser-Induced Thermal Therapy (MRgLITT) is a minimally-invasive ablation procedure for treating intracranial pathology using laser energy delivered through a fiber-optic. Saline irrigation is used to cool the fiber-optic, but factors affecting irrigation efficacy are not well studied, and quantitative information regarding irrigation speed and volume during MRgLITT procedures have not been reported. Here, we aimed to characterize variables affecting irrigation efficacy in MRgLITT. METHODS: We investigated the irrigation setup of the Visualase thermal therapy system during MRgLITT procedures (Visualase Inc., Houston, TX). Using the system's peristaltic pump, irrigation flow rate was quantitated by measuring volume over five one-minute intervals. Pump settings 1-10 were assessed with and without the position-locking, resistance-imparting bone anchor in both single and double-catheter setups. Multiple tightness settings of the bone anchor were tested, and flow rates were analyzed. RESULTS: Rate of flow increased non-linearly with pump setting (F(1,4) = 2168.86; P < 0.001) in both single and double catheter setups. The lowest pump setting had a flow rate of 24 cc/min, while the highest setting was 36 cc/min. The rate of change in flow successively decreased without plateau. Tightness setting of the bone anchor affected flow in a reverse sigmoid pattern, with no impact on rate until after two quarter-turns, which produced a marked decrease in flow up to one-half of the initial rate (F(1,4) = 12818.96; P < 0.001). CONCLUSION: Flow rate through the cooling catheter in MRgLITT follows a non-linear pattern with increasing peristaltic pump speed. This rate is subject to significant changes when the bone anchor is tightened more than two quarter-turns. These findings serve as a foundation for future studies aimed at understanding the effect of irrigation speeds in achieving optimal ablation volumes.

A Learning Based Fiducial-driven Registration Scheme for Evaluating Laser Ablation Changes in Neurological Disorders.

In this work, we present a novel learning based fiducial driven registration (LeFiR) scheme which utilizes a point matching technique to identify the optimal configuration of landmarks to better recover deformation between a target and a moving image. Moreover, we employ the LeFiR scheme to model the localized nature of deformation introduced by a new treatment modality - laser induced interstitial thermal therapy (LITT) for treating neurological disorders. Magnetic resonance (MR) guided LITT has recently emerged as a minimally invasive alternative to craniotomy for local treatment of brain diseases (such as glioblastoma multiforme (GBM), epilepsy). However, LITT is currently only practised as an investigational procedure world-wide due to lack of data on longer term patient outcome following LITT. There is thus a need to quantitatively evaluate treatment related changes between post- and pre-LITT in terms of MR imaging markers. In order to validate LeFiR, we tested the scheme on a synthetic brain dataset (SBD) and in two real clinical scenarios for treating GBM and epilepsy with LITT. Four experiments under different deformation profiles simulating localized ablation effects of LITT on MRI were conducted on 286 pairs of SBD images. The training landmark configurations were obtained through 2000 iterations of registration where the points with consistently best registration performance were selected. The estimated landmarks greatly improved the quality metrics compared to a uniform grid (UniG) placement scheme, a speeded-up robust features (SURF) based method, and a scale-invariant feature transform (SIFT) based method as well as a generic free-form deformation (FFD) approach. The LeFiR method achieved average 90% improvement in recovering the local deformation compared to 82% for the uniform grid placement, 62% for the SURF based approach, and 16% for the generic FFD approach. On the real GBM and epilepsy data, the quantitative results showed that LeFiR outperformed UniG by 28% improvement in average.

Can Publicly Available Artificial Intelligence Successfully Identify Current Procedural Terminology Codes for Common Procedures in Neurosurgery?

OBJECTIVE: Coding for neurosurgical procedures is a complex process that is dynamically changing year to year, through the annual introduction and removal of codes and modifiers. The authors hoped to elucidate if publicly available artificial intelligence (AI) could offer solutions for neurosurgeons with regard to coding. METHODS: Multiple publicly available AI platforms were asked to provide Current Procedural Terminology (CPT) codes and Revenue Value Units (RVU) values for common neurosurgical procedures of the brain and spine with a given indication for the procedure. The responses of platforms were recorded and compared to the currently valid CPT codes used for the procedure and the amount of RVUs that would be gained. RESULTS: Six platforms and Google were asked for the appropriate CPT codes for 10 endovascular, spinal, and cranial procedures each. The highest performing platforms were as follows: Perplexity.AI identified 70% of endovascular, BingAI identified 55% of spinal, and ChatGPT 4.0 with Bing identified 75% of cranial CPT codes. With regard to RVUs, the top performer gained 78% of endovascular, 42% of spinal, and 70% of cranial possible RVUs. With regard to accuracy, AI platforms on average outperformed Google (45% vs. 25%, P = 0.04236). CONCLUSIONS: The ability of publicly available AIs to successfully code for neurosurgical procedures holds great promise in the future. Future development of AI should focus on improving accuracy with regard to CPT codes and providing supporting documentation for its decisions. Improvement on the existing capabilities of AI platforms can allow for increased operational efficiency and cost savings for practices.

Volumetric trends associated with MRI-guided laser-induced thermal therapy (LITT) for intracranial tumors.

BACKGROUND: MR-guided Laser Induced Thermal Therapy (LITT) is a procedure for intracranial tumors. Minimal data exists regarding post-procedure lesion volume changes. OBJECTIVES: We aim to analyze changes in lesion volume during the post-LITT period using polygonal tracing with fusion. Additionally, we investigated the role of lesion histopathology on LITT parameters and volume dynamics. METHODS: Sixteen patients with intracranial neoplasms received LITT. Using OsiriX DICOM Viewer, three raters computed lesion volumes at the following: pre-ablation (PreA), immediate post-ablation (IPA), 24 hours post-ablation (24PA), and first follow-up post-ablation (FPA), which ranged from 4 to 11 weeks post-ablation. Statistical analyses for volume changes between time points and inter-rater reliability were performed. Additionally, comparisons were made between metastatic versus non-metastatic and small versus large lesions in terms of operative parameters and volume changes. RESULTS: There was an acute increase in volume at IPA with a decrease in size by 24PA. ANOVA among inter-rater datasets showed no significant difference at any time point (highest F(1,15) = 0.225, P > 0.80, for IPA). GLM repeated measures, for Intra-Rater analysis, demonstrated statistically significant differences across time points (lowest F(1,15) = 13.297, P = 0.003). IPA volumes were larger than those at PreA, 24PA, and FPA (average volume increase [95% CI]: 281% [157-404%], 167% [134-201%], 187% [154-219%], respectively; all P < 0.004). Correlation analysis showed lower inter-rater reliability at IPA versus other time points (all P < 0.03). Larger lesions (>2.5 cm³ ) versus smaller (<2.5 cm³ ) did not demonstrate a difference in percent volume increase. Operative parameters and volume dynamics were not different between metastatic and non-metastatic groups. CONCLUSIONS: The response of intracranial lesions to LITT demonstrates a peak in volume at the IPA time point with decreased IPA inter-rater reliability. We recommend that conclusions about intracranial lesion size post-LITT be made at least 24 hours post-LITT rather than immediately after LITT.

The Evolution of Laser-Induced Thermal Therapy for the Treatment of Gliomas.

Laser-induced thermal therapy (LITT) has evolved over the past two decades to treat a number of intracranial pathologies. Although it initially emerged as a salvage treatment of surgically inoperable tumors or recurrent lesions that had exhausted more conventional treatments, it is now being used as a primary, first-line treatment in certain instances with outcomes comparable to traditional surgical resection. The authors discuss the evolution of LITT in the treatment of gliomas and future directions, which may further enhance the efficacy of this procedure.

Appearance and modeling of bubble artifacts in intracranial magnetic resonance-guided laser interstitial thermal therapy (MRg-LITT) temperature images.

PURPOSE: To understand if unexplained signal artifacts in MRg-LITT proton resonance frequency- (PRF-) shift thermometry images are caused by air bubbles or hemorrhages, and to characterize their effects on temperature measurements. METHODS: Retrospective image data from an IRB-approved clinical trial of intracranial MRg-LITT were inspected for asymmetric distortions observed in phase data during ablations, which have been previously reported as likely hemorrhages. A total of eight patient cases were selected: seven with artifact occurrence and one without. Mathematical image models for air bubbles or hemorrhages were implemented to estimate the size of the air bubble or hemorrhage needed to explain the clinically observed phase artifacts. Correlations and Bland-Altman analyses were used to determine if an air bubble model or a hemorrhage model was better correlated to the clinical data. The model was used to inject bubbles into clean PRF phase data without artifacts to examine how temperature profile distortions change with slice orientation. The simulated air-bubble injected data were compared to clinical data containing artifacts to examine the bubbles' effects on temperature and thermal damage estimates. RESULTS: The model demonstrated that air bubbles up to approximately 1 cm in diameter could explain the clinically observed phase artifacts. The bubble model predicts that a hemorrhage would have to be 2.2 times as large as an air bubble in order to explain the same extent of phase distortion observed in clinical data. Air bubbles had 16% percent higher correlations to the clinical PRF phase data than hemorrhages, even after rescaling the hemorrhage phases to better match the data. The air bubble model also explains how the phase artifacts lead to both large positive and large negative temperature errors, up to ±100 °C, which could cascade to damage estimate errors of several millimeters. CONCLUSION: Results showed that the artifacts are likely caused by air bubbles rather than hemorrhages, which may be introduced before heating or appear during heating. Manufacturers and users of devices that rely upon PRF-shift thermometry should be aware these phase distortions from bubble artifacts can result in large temperature errors.

The effect of intraventricular trajectory on brain shift in deep brain stimulation.

BACKGROUND: Brain shift during deep brain stimulation (DBS) surgery may compromise target localization. Loss of cerebrospinal fluid is believed to be the underlying mechanism, thus an intraventricular trajectory during DBS surgery may be associated with increased shift, in addition to other complications, such as intraventricular hemorrhage. OBJECTIVE: We set out to assess the effect of traversing the lateral ventricle on brain shift during DBS surgery. METHODS: We performed a retrospective review of 65 pre- and postoperative MR images of patients who underwent bilateral subthalamic nucleus deep brain stimulator placement to treat advanced Parkinson's disease. Patients were separated into two groups: Group A (intraventricular trajectory, n = 46) and Group B (no intraventricular trajectory, n = 19). In these patients, we compared pre- and postoperative frame coordinates of the red nucleus (RN). RESULTS: Group B demonstrated significantly more posterior shift of the center of the RN (1.40 ± 1.32 mm) than Group A (0.64 ± 1.76 mm; p < 0.02). We found no increase in incidence of intraventricular hemorrhage or the number of microelectrode trajectory attempts. CONCLUSIONS: Intraventricular trajectories during DBS surgery do not appear to compromise safety or targeting accuracy.

Depth-time interpolation of feature trends extracted from mobile microelectrode data with kernel functions.

BACKGROUND/AIMS: Microelectrode recording (MER) is necessary for precision localization of target structures such as the subthalamic nucleus during deep brain stimulation (DBS) surgery. Attempts to automate this process have produced quantitative temporal trends (feature activity vs. time) extracted from mobile MER data. Our goal was to evaluate computational methods of generating spatial profiles (feature activity vs. depth) from temporal trends that would decouple automated MER localization from the clinical procedure and enhance functional localization in DBS surgery. METHODS: We evaluated two methods of interpolation (standard vs. kernel) that generated spatial profiles from temporal trends. We compared interpolated spatial profiles to true spatial profiles that were calculated with depth windows, using correlation coefficient analysis. RESULTS: Excellent approximation of true spatial profiles is achieved by interpolation. Kernel-interpolated spatial profiles produced superior correlation coefficient values at optimal kernel widths (r = 0.932-0.940) compared to standard interpolation (r = 0.891). The choice of kernel function and kernel width resulted in trade-offs in smoothing and resolution. CONCLUSIONS: Interpolation of feature activity to create spatial profiles from temporal trends is accurate and can standardize and facilitate MER functional localization of subcortical structures. The methods are computationally efficient, enhancing localization without imposing additional constraints on the MER clinical procedure during DBS surgery.

Diffuse astrocytoma with mosaic IDH1-R132H-mutant immuno-phenotype and low subclonal allele frequency.

Molecular alterations found in gliomas are now considered entity-defining features. The World Health Organization (WHO) classification system currently classifies the vast majority of gliomas utilizing an integrated genotype-phenotype approach. We present a case of diffuse astrocytoma with a mosaic isocitrate dehydrogenase (IDH)1-R132H-mutant immunophenotype and low subclonal allele frequency. A 35-year-old patient with a history of IDH1-R132H mutated diffuse astrocytoma in 20014 presented to the hospital again in 2019. MRI examination showed a non-enhancing abnormal signal in the periphery of her previous surgical cavity. Histopathological examination revealed that the tumor was hypercellular and without high grade histopathological features. The neoplastic cells were immunohistologically positive for GFAP, Olig2, and ATRX. However, only some scattered tumor cells were positive for IDH1-R132H. Cytogenetic studies revealed a lack of chromosomal 1p/19q co-deletion. Further next-generation sequencing (NGS) demonstrated a low-level IDH1-R132H mutation and allele frequency. Based on these findings, the diagnosis of diffuse astrocytoma with mosaic IDH1- R132H-mutant immunophenotype and low subclonal allele frequency (WHO grade II) was generated. This case indicates that gliomas may have heterogeneous molecular profile and the intra-tumoral molecular heterogeneity highlights the need to further characterize the molecular profile for glioma classification and clinical management.