Intraoperative multi-exposure speckle imaging of cerebral blood flow.

Multiple studies have demonstrated that laser speckle contrast imaging (LSCI) has high potential to be a valuable cerebral blood flow monitoring technique during neurosurgery. However, the quantitative accuracy and sensitivity of LSCI is limited, and highly dependent on the exposure time. An extension to LSCI called multi-exposure speckle imaging (MESI) overcomes these limitations, and was evaluated intraoperatively in patients undergoing brain tumor resection. This clinical study ( n = 8) recorded multiple exposure times from the same cortical tissue area spanning 0.5-20 ms, and evaluated images individually as single-exposure LSCI and jointly using the MESI model. This study demonstrated that the MESI estimates provided the broadest flow sensitivity for sampling the flow magnitude in the human brain, closely followed by the shorter exposure times. Conservation of flow analysis on vascular bifurcations was used to validate physiological accuracy, with highly conserved flow estimates (<10%) from both MESI and 1 ms LSCI ( n = 14 branches). The MESI model had high goodness-of-fit with proper image calibration and acquisition, and was used to monitor blood flow changes after tissue cautery. Results from this study demonstrate that intraoperative MESI can be performed with high quantitative accuracy and sensitivity for cerebral blood flow monitoring.

Quantitative contrast-enhanced ultrasound measurement of cerebrospinal fluid flow for the diagnosis of ventricular shunt malfunction.

OBJECT: Cerebral shunt malfunction is common but often difficult to effectively diagnose. Current methods are invasive, involve ionizing radiation, and can be costly. The authors of this study investigated the feasibility of quantitatively measuring CSF flow in a shunt catheter using contrast-enhanced ultrasound. METHODS: A syringe pump was used to push a solution of gas-filled microbubbles at specific flow rates through a shunt catheter while a high-frequency ultrasound imaging system was used to collect ultrasound images for offline processing. Displacement maps and velocity profiles were generated using a speckle-tracking method based on a cross-correlation algorithm. An additional correction factor, to account for a predictable underestimation and to adjust the measured flow rates, was calculated based on the geometry of the ultrasound imaging plane and assuming a simple model of laminar flow. RESULTS: The developed method was able to differentiate between physiologically relevant flow rates, including no flow and 0.006 to 0.09 ml/min, with reasonable certainty. The quantitative measurement of flow rates through the catheter using this method was determined to be in good agreement with the expected flow rate. CONCLUSIONS: This study demonstrated that contrast-enhanced ultrasound has the potential to be used as a minimally invasive and cost-effective alternative method for outpatient shunt malfunction diagnosis.

Intraoperative laser speckle contrast imaging with retrospective motion correction for quantitative assessment of cerebral blood flow.

Although multiple intraoperative cerebral blood flow (CBF) monitoring techniques are currently available, a quantitative method that allows for continuous monitoring and that can be easily integrated into the surgical workflow is still needed. Laser speckle contrast imaging (LSCI) is an optical imaging technique with a high spatiotemporal resolution that has been recently demonstrated as feasible and effective for intraoperative monitoring of CBF during neurosurgical procedures. This study demonstrates the impact of retrospective motion correction on the quantitative analysis of intraoperatively acquired LSCI images. LSCI images were acquired through a surgical microscope during brain tumor resection procedures from 10 patients under baseline conditions and after a cortical stimulation in three of those patients. The patient's electrocardiogram (ECG) was recorded during acquisition for postprocess correction of pulsatile artifacts. Automatic image registration was retrospectively performed to correct for tissue motion artifacts, and the performance of rigid and nonrigid transformations was compared. In baseline cases, the original images had [Formula: see text] noise across 16 regions of interest (ROIs). ECG filtering moderately reduced the noise to [Formula: see text], while image registration resulted in a further noise reduction of [Formula: see text]. Combined ECG filtering and image registration significantly reduced the noise to [Formula: see text] ([Formula: see text]). Using the combined motion correction, accuracy and sensitivity to small changes in CBF were improved in cortical stimulation cases. There was also excellent agreement between rigid and nonrigid registration methods (15/16 ROIs with [Formula: see text] difference). Results from this study demonstrate the importance of motion correction for improved visualization of CBF changes in clinical LSCI images.

Comparison of indocyanine green angiography and laser speckle contrast imaging for the assessment of vasculature perfusion.

BACKGROUND: Assessment of the vasculature is critical for overall success in cranial vascular neurological surgery procedures. Although several methods of monitoring cortical perfusion intraoperatively are available, not all are appropriate or convenient in a surgical environment. Recently, 2 optical methods of care have emerged that are able to obtain high spatial resolution images with easily implemented instrumentation: indocyanine green (ICG) angiography and laser speckle contrast imaging (LSCI). OBJECTIVE: To evaluate the usefulness of ICG and LSCI in measuring vessel perfusion. METHODS: An experimental setup was developed that simultaneously collects measurements of ICG fluorescence and LSCI in a rodent model. A 785-nm laser diode was used for both excitation of the ICG dye and the LSCI illumination. A photothrombotic clot model was used to occlude specific vessels within the field of view to enable comparison of the 2 methods for monitoring vessel perfusion. RESULTS: The induced blood flow change demonstrated that ICG is an excellent method for visualizing the volume and type of vessel at a single point in time; however, it is not always an accurate representation of blood flow. In contrast, LSCI provides a continuous and accurate measurement of blood flow changes without the need of an external contrast agent. CONCLUSION: These 2 methods should be used together to obtain a complete understanding of tissue perfusion.

Thoracoscopic resection of symptomatic herniated thoracic discs: clinical results in 121 patients.

STUDY DESIGN: Retrospective review of a prospectively maintained surgical database. OBJECTIVE: To report the indications, surgical procedures performed, and outcomes from the largest series of thoracoscopically treated herniated thoracic discs (HTDs). We also compared approach-related complications with an unmatched cohort undergoing thoracotomy for HTD. SUMMARY OF BACKGROUND DATA: Symptomatic HTDs are rare, and their surgical management is technically challenging. METHODS: A prospectively maintained surgical database of all patients undergoing surgery for symptomatic HTDs by the senior author (blinded for review) was reviewed. As needed, the database was supplemented with hospital and clinic charts and telephone conversations with patients. A triportal method of thoracoscopic discectomy was performed in all cases. RESULTS: Between 1994 and 2008, 121 patients underwent 125 thoracoscopic-assisted operations for 139 HTDs. Their mean age at surgery was 46.6 years. Indications for thoracoscopic resection currently include small symptomatic disc, anterior location, nonmorbidly obese patient, favorable chest anatomy, and T4-T11 location. Symptom duration averaged 32 months. Radiculopathy was the most common presentation, followed by myelopathy and pain (radiculopathic or back). The mean hospital stay was 4.8 days. Chest tubes remained in place for a mean of 3.2 days. At a mean follow-up of 2.4 years, myelopathy, radiculopathy, and back pain had resolved or improved at a rate of 91.1%, 97.6%, and 86.5%, respectively. Patients reported worsening in 0%, 1.2%, and 0% of cases, respectively. Most patients (97.4%) would be willing to undergo the operation again. The complication rate was acceptable. Patients undergoing thoracoscopic excision had less approach-related morbidity than an unmatched cohort undergoing excision using thoracotomy. CONCLUSION: Thoracoscopic-assisted microsurgical resection is a safe, effective, and minimally invasive method of treating symptomatic HTDs in appropriately selected patients. The symptoms of most patients improve or resolve with minimal morbidity.

Dysphagia after anterior cervical spine surgery: incidence and risk factors.

OBJECTIVE: To evaluate risk factors for the development of dysphagia after anterior cervical surgery. METHODS: The records of 249 patients who underwent anterior cervical surgery were reviewed. The presence and severity of dysphagia were assessed with the Dysphagia Disability Index 6 weeks and 3, 6, and 12 months after surgery. Age; sex; ethnicity; cigarette smoking; previous cervical surgeries; reoperation for same pathology; type of procedure, incision, and instrumentation; number and levels involved; side of procedure, length of surgery; and use of postoperative bracing were analyzed. RESULTS: During the first 6 months after surgery, 27 (10.8%) patients developed dysphagia. From these patients the presence of dysphagia at 6 weeks and at 3 and 6 months was 88.8%, 29.6%, and 7.4%, respectively. By 12 months, dysphagia had resolved in all cases. The mean age of patients with dysphagia was 55 years (SD 12.98) and 50 years (SD 12.07) in patients without dysphagia (P = 0.05). Dysphagic patients had an average of 2.2 (SD 1.15) levels operated compared with 1.84 (SD 0.950) in nondysphagic patients (P = 0.05). Patients who developed dysphagia were most often treated at C4-5 (67%) and C5-6 (81%: P < 0.001). Although mean operative time was slightly longer in patients with dysphagia (186 minutes) compared with those without (169 minutes), the difference was not significant. CONCLUSIONS: In our patients, the incidence of dysphagia was low, and it had completely resolved at 12 months in all cases. Risk factors for dysphagia were multilevel procedures, involvement of C4-5 and C5-6, and age.

Laser speckle contrast imaging of cerebral blood flow in humans during neurosurgery: a pilot clinical study.

Monitoring cerebral blood flow (CBF) during neurosurgery can provide important physiological information for a variety of surgical procedures. CBF measurements are important for assessing whether blood flow has returned to presurgical baseline levels and for assessing postsurgical tissue viability. Existing techniques for intraoperative monitoring of CBF based on magnetic resonance imaging are expensive and often impractical, while techniques such as indocyanine green angiography cannot produce quantitative measures of blood flow. Laser speckle contrast imaging (LSCI) is an optical technique that has been widely used to quantitatively image relative CBF in animal models in vivo. In a pilot clinical study, we adapted an existing neurosurgical operating microscope to obtain LSCI images in humans in real time during neurosurgery under baseline conditions and after bipolar cautery. Simultaneously recorded ECG waveforms from the patient were used to develop a filter that helped reduce measurement variabilities due to motion artifacts. Results from this study demonstrate the feasibility of using LSCI to obtain blood flow images during neurosurgeries and its capability to produce full field CBF image maps with excellent spatial resolution in real-time with minimal disruption to the surgical procedure.

Update on evidence for a genetic predisposition to cerebral vasospasm.

Considerable evidence links cerebral vasospasm to the decreased bioavailability of endothelial nitric oxide synthase (eNOS) after aneurysmal subarachnoid hemorrhage (SAH). In recent studies from the cardiology literature, researchers have suggested that a genetic predisposition to coronary vasospasm might develop as the result of a T-786C single nucleotide polymorphism (SNP) in the eNOS gene. The authors of this study attempted to determine if there may be a similar genetic predisposition toward cerebral vasospasm. The authors prospectively identified 28 patients with Fisher Grade 3 SAH from a group of 51 consecutive patients with ruptured intracranial saccular aneurysms. Genomic DNA was isolated from a peripheral blood sample obtained with permission from each patient. Gene microarray technology was used to assay the samples for the presence and distribution of certain key eNOS gene polymorphisms. Clinical, radiological, and genomic data were analyzed. The finding of eNOS T-786C SNP could be used to significantly differentiate between the presence and severity of cerebral vasospasm (p = 0.04). The findings from this preliminary study support similar findings in the coronary vasospasm literature as well as the hypothesis that a predisposition toward cerebral vasospasm may be related partially to genetic factors, which needs to be confirmed in a larger study. Such gene-based information may be important in rapidly identifying patients at increased risk of vasospasm after SAH, independent of their Fisher grade. In this article, the authors review key studies in this area.

Computational hyperspectral interferometry for studies of brain function: proof of concept.

Hyperspectral interferometric microscopy uses a unique combination of optics and algorithm design to extract information. Local brain activity rapidly changes local blood flow and red blood cell concentration (absorption) and oxygenation (color). We demonstrate that brain activity evoked during whisker stimulation can be detected with hyperspectral interferometric microscopy to identify the active whisker-barrel cortex in the rat brain. Information about constituent components is extracted across the entire spectral band. Algorithms can be flexibly optimized to discover, detect, quantify, and visualize a wide range of significant biological events, including changes relevant to the diagnosis and treatment of disease.

Moyamoya disease in adults: the role of cerebral revascularization.

Moyamoya disease is a disorder characterized by bilateral progressive steno-occlusion of the terminal internal carotid arteries with associated development of a fragile network of basal collateral vessels. It most commonly presents in children, but is also frequently seen in adults, especially in the third or fourth decade of life. Adults afflicted with this disease have very different clinical characteristics as compared with children. For example, adults more commonly present with hemorrhage than cerebral ischemia, while children present with cerebral ischemia nearly 75% of the time and very rarely present with hemorrhage. This significantly impacts treatment considerations for the adult-onset moyamoya patient, as cerebral revascularization, though well accepted in the context of cerebral ischemia, is relatively controversial for the prevention of rehemorrhage. The purpose of this article is to review the pertinent general features of moyamoya disease, examine the clinical characteristics associated with the adult-onset form of this disease, and provide a detailed discussion regarding the indications, operative techniques, and outcomes of direct and indirect revascularization surgical procedures.

Long-term outcome after angioplasty for symptomatic extracranial carotid stenosis in poor surgical candidates.

BACKGROUND AND PURPOSE: The optimal treatment of patients with symptomatic carotid stenosis who are poor surgical candidates is uncertain. The purposes of this study were to report the long-term outcome after angioplasty in a series of these patients and to compare these data with historical control data from the North American Symptomatic Carotid Endarterectomy Trial (NASCET). METHODS: We identified 42 consecutive patients with >70% carotid stenosis and ipsilateral ischemic symptoms within 120 days of treatment with angioplasty. All were considered poor surgical candidates by experienced surgeons. Baseline epidemiological stroke risk factors were obtained from review of medical records. Follow-up was from clinic records and by telephone. RESULTS: Baseline epidemiological stroke risk factors were similar to those of medically treated NASCET patients. Angioplasty patients tended to have higher degrees of stenosis (45% with >90% stenosis versus 24% in NASCET) and more frequent contralateral stenosis or occlusion (30% versus 9%) than NASCET patients. Three patients suffered procedural strokes; 2 of the 3 made nearly complete recoveries. One additional patient suffered a central retinal occlusion 48 hours after angioplasty. No ipsilateral strokes occurred during the mean follow-up period of 1.7 years. Three patients were lost to follow-up. The cumulative risk of stroke was 9.5% (4 of 42) compared with 26% at 2 years for medically treated patients in NASCET. CONCLUSIONS: These pilot data suggest a beneficial effect of angioplasty for patients with high-grade symptomatic carotid stenosis who are not good surgical candidates.

Decreased Cyclosporin A requirement with anti-ICAM-1 and anti-LFA-1 in a peripheral nerve allotransplantation model.

OBJECT: This study evaluated the dose related effects of Cyclosporin A (CsA) alone and in combination with monoclonal antibodies (mAbs) directed against intercellular adhesion molecule-1 (ICAM-1) and the alpha subunit of leukocyte function-associated antigen (LFA-1 ) on peripheral nerve allograft rejection in a rat model. METHODS: Nerve regeneration was assessed using gait analysis of returning hind limb function, histology, and morphometry. RESULTS: Regeneration comparable to isograft controls and high dose CsA treatment groups was observed when mAbs were used in combi-nation with intermediate dose CsA. Intermediate dose CsA therapy without additional mAbs was insufficient to support this level of regeneration. Nerve allografts treated with high and low dose CsA demonstrated no increased benefit with the addition of mAb therapy. CONCLUSIONS: Thus, mAbs seem to have a dose dependent effect on immunosuppression when used in combination with CsA, and may have therapeutic promise as a rescue therapy when CsA levels fall or issues of toxicity become important.

Distinguishing the transition to chaos in a spherical pendulum.

Complex responses are studied for a spherical pendulum whose support is excited with a translational periodic motion. Governing equations are studied analytically to allow prediction of responses under various excitation conditions. Stability for certain cases of damping is predicted by means of existing analysis and compared with experimental data. Numerical time-step integration of the governing equations is developed to predict responses for various types of excitation and damping conditions. Predicted results are compared with corresponding motions measured in an experimental spherical pendulum system. A data acquisition system is included whereby detailed digitized time histories of the pendulum motion can be established and various parameters can be computed to characterize the type of motion present. Two new vector spaces are defined for describing complex responses which occur for certain specified excitation conditions. It is shown in these parameter spaces that the transition from quasiperiodic to chaotic motions can be carefully quantified in systems with very light damping. This discovery provides a convenient means for comparison of complex motions in the numerical and experimental air pendulum systems. The implications of the results are important for dynamic response in various applications, including fluid motions in satellite tanks and other nonlinear time-dependent physical processes which include very light damping. (c) 1995 American Institute of Physics.