Evaluation of augmented reality training for a navigation device used for CT-guided needle placement.

PURPOSE: Numerous navigation devices for percutaneous, CT-guided interventions exist and are, due to their advantages, increasingly integrated into the clinical workflow. However, effective training methods to ensure safe usage are still lacking. This study compares the potential of an augmented reality (AR) training application with conventional instructions for the Cube Navigation System (CNS), hypothesizing enhanced training with AR, leading to safer clinical usage. METHODS: An AR-tablet app was developed to train users puncturing with CNS. In a study, 34 medical students were divided into two groups: One trained with the AR-app, while the other used conventional instructions. After training, each participant executed 6 punctures on a phantom (204 in total) following a standardized protocol to identify and measure two potential CNS procedural user errors: (1) missing the coordinates specified and (2) altering the needle trajectory during puncture. Training performance based on train time and occurrence of procedural errors, as well as scores of User Experience Questionnaire (UEQ) for both groups, was compared. RESULTS: Training duration was similar between the groups. However, the AR-trained participants showed a 55.1% reduced frequency of the first procedural error (p > 0.05) and a 35.1% reduced extent of the second procedural error (p < 0.01) compared to the conventionally trained participants. UEQ scores favored the AR-training in five of six categories (p < 0.05). CONCLUSION: The AR-app enhanced training performance and user experience over traditional methods. This suggests the potential of AR-training for navigation devices like the CNS, potentially increasing their safety, ultimately improving outcomes in percutaneous needle placements.

NASA's Satellite Laser Ranging Systems for the 21st Century.

For over 40 years, NASA's global network of satellite laser ranging (SLR) stations has provided a significant percentage of the global orbital data used to define the International Terrestrial Reference Frame (ITRF). The current NASA legacy network is reaching its end-of-life and a new generation of systems must be ready to take its place. Scientific demands of sub-millimeter precision ranging and the ever-increasing number of tracking targets give aggressive performance requirements to this new generation of systems. Using lessons learned from the legacy systems and the successful development of a prototype station, a new network of SLR stations, called the Space Geodesy Satellite Laser Ranging (SGSLR) systems, is being developed. These will be the state-of-the-art SLR component of NASA's Space Geodesy Project (SGP). Each of SGSLR's nine subsystems has been designed to produce a robust, kilohertz laser ranging system with 24/7 operational capability and with minimal human intervention. SGSLR's data must support the aggressive goals of the Global Geodetic Observing System (GGOS), which are 1 millimeter (mm) position accuracy and 0.1 mm per year stability of the ITRF. This paper will describe the major requirements and accompanying design of the new SGSLR systems, how the systems will be tested, and the expected system performance.

Attenuation of blood flow pulsatility along the Atlas slope: a physiologic property of the distal vertebral artery?

BACKGROUND AND PURPOSE: Physiologic and pathologic arterial tortuosity may attenuate blood flow pulsatility. The aim of this prospective study was to assess a potential effect of the curved V3 segment (Atlas slope) of the vertebral artery on arterial flow pulsatility. The pulsatility index and resistance index were used to assess blood flow pulsatility. MATERIALS AND METHODS: Twenty-one healthy volunteers (17 men, 4 women; mean age, 32 years) were examined with a 3T MR imaging system. Blood velocities were measured at 2 locations below (I and II) and at 1 location above the V3 segment (III) of the vertebral artery by using a high-resolution 2D-phase-contrast sequence with multidirectional velocity-encoding. RESULTS: Pulsatility and resistance indices decreased along all measurement locations from proximal to distal. The pulsatility index decreased significantly from location II to III and from I to II. However, the decrease was more pronounced along the Atlas slope than in the straight-vessel section below. The decrease of the resistance index was highly significant along the Atlas slope (location II to III). The decrease from location I to II was small and not significant. CONCLUSIONS: The pronounced decrease in pulsatility and resistance indices along the interindividually uniformly bent V3 segment compared with a straight segment of the vertebral artery indicates a physiologic attenuating effect of the Atlas slope on arterial flow pulsatility. A similar effect has been described for the carotid siphon. A physiologic reduction of pulsatility in brain-supplying arteries would be in accordance with several recent publications reporting a correlation of increased arterial flow pulsatility with leukoencephalopathy and lacunar stroke.

[Neuroradiological focus on stroke imaging]. / Fokussierte neuroradiologische Diagnostik beim akuten Hirnschlag.

Stroke is heterogenous in its symptoms, which are also caused by various pathologies. Clinically the causing mechanism (bleeding or ischemia) of a new onset of neurological deficits can not reliably be distinguished. However, ischemia is four times more frequent than a bleeding causing neurological symptoms. Modern imaging technologies (computed assisted tomography or magnetic resonace imaging) and interventional techniques are a mainstay in diagnostics and management of acute onset of neurological symptoms. They can reliably distinguish between bleeding and stroke, especially taking newest technologies, such as perfusion studies and angiographies, into account. Neuroradiology with its interventional options has nowadays furthermore become an important tool in strokes and offers a local maneuver to retrieve the clotting pathology and even opens the therapeutic window for a delayed start of the therapy since symptom's onset beyong the conventional 4.5 hours window. Also risks of a therapy and which therapy option should be used can immediately be assessed.

[Implementation of the laryngeal tube for prehospital airway management: training of 1,069 emergency physicians and paramedics]. / Implementierung des Larynxtubus im präklinischen Atemwegsmanagement: Ausbildung von 1069 Notärzten und Rettungsassistenten.

OBJECTIVE: The European Resuscitation Council recommends that only rescuers experienced and well-trained in airway management should perform endotracheal intubation. Less trained rescuers should use alternative airway devices instead. Therefore, a concept to train almost 1,100 emergency physicians (EP) and emergency medical technicians (EMT) in prehospital airway management using the disposable laryngeal tube suction (LTS-D) is presented. METHODS: In five operational areas of emergency medicine services in Germany and Switzerland all EPs and EMTs were trained in the use of the LTS-D by means of a standardized curriculum in the years 2006 and 2007. The main focus of the training was on different insertion techniques and LTS-D use in children and infants. Subsequently, all prehospital LTS-D applications from 2008 to 2010'were prospectively recorded. RESULTS: None of the 762 participating EMTs and less than 20% of the EPs had previous clinical experience with the LTS-D. After the theoretical (practical) part of the training, the participants self-assessed their personal familiarity in using the LTS-D with a median value of 8 (8) and a range of 2-10 (range 1-10) of 10 points (1: worst, 10: best). Within the 3-year follow-up period the LTS-D was used in 303 prehospital cases of which 296 were successfully managed with the device. During the first year the LTS-D was used as primary airway in more than half of the cases, i.e. without previous attempts of endotracheal intubation. In the following years such cases decreased to 40% without reaching statistical significance. However, the mean number of intubation attempts which failed before the LTS-D was used as a rescue device decreased significantly during the study period (2008: 2.2 ± 0.3; 2009: 1.6 ± 0.4; 2010: 1.7 ± 0.3). CONCLUSION: A standardized training concept enabled almost 1,100 rescuers to be trained in the use of an alternative airway device and to successfully implement the LTS-D into the prehospital airway management algorithm. Because the LTS-D recently became an accepted alternative to endotracheal intubation in difficult airway scenarios, the number of intubation attempts before considering an alternative airway device is steadily decreasing.

Optimizing the risk estimation after a transient ischaemic attack - the ABCDE⊕ score.

BACKGROUND AND PURPOSE: The risk of stroke after a transient ischaemic attack (TIA) can be predicted by scores incorporating age, blood pressure, clinical features, duration (ABCD-score), and diabetes (ABCD2-score). However, some patients have strokes despite a low predicted risk according to these scores. We designed the ABCDE+ score by adding the variables 'etiology' and ischaemic lesion visible on diffusion-weighted imaging (DWI) -'DWI-positivity'- to the ABCD-score. We hypothesized that this refinement increases the predictability of recurrent ischaemic events. METHODS: We performed a prospective cohort study amongst all consecutive TIA patients in a university hospital emergency department. Area under the computed receiver-operating curves (AUCs) were used to compare the predictive values of the scores with regard to the outcome stroke or recurrent TIA within 90 days. RESULTS: Amongst 248 patients, 33 (13.3%, 95%-CI 9.3-18.2%) had a stroke (n = 13) or a recurrent TIA (n = 20). Patients with recurrent ischaemic events more often had large-artery atherosclerosis as the cause for TIA (46% vs. 14%, P < 0.001) and positive DWI (61% vs. 35%; P = 0.01) compared with patients without recurrent events. Patients with and those without events did not differ with regard to age, clinical symptoms, duration, blood pressure, risk factors, and stroke preventive treatment. The comparison of AUCs [95%CI] showed superiority of the ABCDE+ score (0.67[0.55-0.75]) compared to the ABCD(2) -score (0.48[0.37-0.58]; P = 0.04) and a trend toward superiority compared to the ABCD-score (0.50[0.40-0.61]; P = 0.07). CONCLUSION: In TIA patients, the addition of the variables 'etiology' and 'DWI-positivity' to the ABCD-score seems to enhance the predictability of subsequent cerebral ischaemic events.

Significance of microbleeds in patients with transient ischaemic attack.

BACKGROUND AND PURPOSE: The aim of this study was to determine the prognostic significance of microbleeds in TIA-patients. In patients with a transient ischaemic attack (TIA), the prognostic value of microbleeds is unknown. METHODS: In 176 consecutive TIA patients, the number, size, and location of microbleeds with or without acute ischaemic lesions were assessed. We compared microbleed-positive and microbleed-negative patients with regard to the end-point stroke within 3 months. RESULTS: Four of the seven patients with subsequent stroke had microbleeds. Microbleed-positive patients had a higher risk for stroke [odds ratios (OR) 8.91, 95% CI 1.87-42.51, P<0.01] than those without microbleeds. Microbleed-positive patients with accompanying acute ischaemic lesions had a higher stroke risk than those with neither an acute ischaemia nor a microbleed (OR 6.20, 95% CI 1.10-35.12; P=0.04). CONCLUSION: Microbleeds alone or in combination with acute ischaemic lesions may increase the risk for subsequent ischaemic stroke after TIA within 3 months.

Fast high-resolution brain imaging with balanced SSFP: Interpretation of quantitative magnetization transfer towards simple MTR.

Magnetization transfer (MT) reflects the exchange of magnetization between protons bound to macromolecules, such as lipids and proteins, and protons in free liquid, and thus might be an early marker for subtle and undetermined pathologic changes in tissue. Detailed analysis of the entire MT phenomenon, however, commonly requires extensive data acquisition and scanning time, and hence is only of limited clinical interest. Therefore, in practice, magnetization transfer effects are commonly confined into a simple ratio measure, the so-called magnetization transfer ratio (MTR), calculated from a MT-weighted and a non-MT-weighted image. However, subtle physiologic and pathologic changes in tissue, invaluable for specific diagnostic imaging, may be lost since MTR-values depend not only on quantitative magnetization transfer (qMT) parameters but also on sequence parameters and relaxation properties. In order to evaluate and assess the diagnostic specificity of MTR versus qMT, high-resolution whole brain MT data was collected from twelve healthy volunteers using balanced steady-state free precession (bSSFP). In contrast to common MT imaging based on spoiled gradient echo (SPGR) sequences, whole brain qMT imaging can be performed with MT-sensitized bSSFP within a clinically feasible acquisition time. Hence, MT-sensitized bSSFP provides access to both MTR and qMT parameters within a clinical setting. The reliability and possible diagnostic value of MTR are analyzed for twelve white matter (WM) and eleven gray matter (GM) structures of the normal appearing brain. Strong correlations were found within and between longitudinal and transverse relaxation times (T1, T2) and MT parameters (ratio between macromolecular and water protons, F, and magnetization exchange rate, kf), whereas weaker correlations were observed between MTR-values and relaxation times or MT parameters. Structures with highly similar MTR-values, such as the crus cerebri and the anterior commissure in the WM, or the pallidum and the amygdala in the GM, however, were also found that showed significant differences in most quantitative parameters. This observation was confirmed from simulations revealing that the overall effect on MTR from an increase (decrease) in relaxation times may be counterbalanced with a decrease (increase) in MT parameters. These findings corroborate the expectation that qMT is superior to MTR imaging, especially for the evaluation and assessment of pathologic or physiological changes in healthy and pathologic brain tissue.

Dampening of blood-flow pulsatility along the carotid siphon: does form follow function?

BACKGROUND AND PURPOSE: The tortuous distal part of the ICA may have an attenuating effect on pulsatile arterial flow. We investigated local arterial blood flow patterns in the ICA proximal and distal to the carotid siphon to detect quantitative waveform changes. MATERIALS AND METHODS: Arterial flow patterns were analyzed by using flow-sensitized 4D PC MR imaging (time-resolved 3D PCMR) at 3T in 17 healthy volunteers. Time-resolved blood flow velocities were extracted from the source data at the C4 and C7 segments of the ICA. PI, RI, and PA were calculated by using time-resolved flow volume. A linear mixed-effects model was applied to compare values at C4 and C7. Furthermore, 3D blood flow visualization was performed for all 34 ICAs. RESULTS: PI, RI, and PA were significantly lower at the distal C7 segment compared with the proximal C4 segment of the ICA (P < .0001). Helical flow patterns were observed in 5 ICAs of 4 subjects. CONCLUSIONS: Arterial flow patterns showed a significant reduction in PI, RI, and PA when compared distal to proximal to the carotid siphon. The observed attenuation of flow pulsatility is most likely related to the contorted shape of the distal ICA and may bear a protective effect for downstream cerebral vasculature.

The pipeline embolization device for the intracranial treatment of aneurysms trial.

BACKGROUND AND PURPOSE: Endoluminal reconstruction with flow diverting devices represents a novel constructive technique for the treatment of cerebral aneurysms. We present the results of the first prospective multicenter trial of a flow-diverting construct for the treatment of intracranial aneurysms. MATERIALS AND METHODS: Patients with unruptured aneurysms that were wide-necked (> 4 mm), had unfavorable dome/neck ratios (<1.5), or had failed previous therapy were enrolled in the PITA trial between January and May 2007 at 4 (3 European and 1 South American) centers. Aneurysms were treated with the PED with or without adjunctive coil embolization. All patients underwent clinical evaluation at 30 and 180 days and conventional angiography 180 days after treatment. Angiographic results were adjudicated by an experienced neuroradiologist at a nonparticipating site. RESULTS: Thirty-one patients with 31 intracranial aneurysms (6 men; 42-76 years of age; average age, 54.6 years) were treated during the study period. Twenty-eight aneurysms arose from the ICA (5 cavernous, 15 parophthalmic, 4 superior hypophyseal, and 4 posterior communicating segments), 1 from the MCA, 1 from the vertebral artery, and 1 from the vertebrobasilar junction. Mean aneurysm size was 11.5 mm, and mean neck size was 5.8 mm. Twelve (38.7%) aneurysms had failed (or recurred after) a previous endovascular treatment. PED placement was technically successful in 30 of 31 patients (96.8%). Most aneurysms were treated with either 1 (n = 18) or 2 (n = 11) PEDs. Fifteen aneurysms (48.4%) were treated with a PED alone, while 16 were treated with both PED and embolization coils. Two patients experienced major periprocedural stroke. Follow-up angiography demonstrated complete aneurysm occlusion in 28 (93.3%) of the 30 patients who underwent angiographic follow-up. No significant in-construct stenosis (≥ 50%) was identified at follow-up angiography. CONCLUSIONS: Intracranial aneurysm treatment with the PED is technically feasible and can be achieved with a safety profile analogous to that reported for stent-supported coil embolization. PED treatment elicited a very high rate (93%) of complete angiographic occlusion at 6 months in a population of the most challenging anatomic subtypes of cerebral aneurysms.

Characterization of normal appearing brain structures using high-resolution quantitative magnetization transfer steady-state free precession imaging.

Compared to standard spoiled gradient echo (SPGR)-methods, balanced steady-state free precession (bSSFP) provides quantitative magnetization transfer (qMT) images with increased resolution and high signal-to-noise ratio (SNR) in clinically feasible acquisition times. The aim of this study was to acquire 3D high-resolution qMT-data to create standardized qMT-values of many single brain structures that might serve as a baseline for the future characterization of pathologies of the brain. QMT parameters, such as the fractional pool size (F), exchange rate (kf) and relaxation times of the free pool (T1, T2) were assessed in a total of 12 white matter (WM) and 11 grey matter (GM) structures in 12 healthy volunteers with MT-sensitized bSSFP. Our results were compared with qMT-data from previous studies obtained with SPGR-methods using MT-sensitizing preparation pulses with significantly lower resolution. In general, qMT-values were in good accordance with prior studies. As expected, higher F and kf and lower relaxation times were observed in WM as compared to GM structures. However, many significant differences were observed within WM and GM regions and also between different regions of the same structure like in the internal capsule where the posterior limb showed significant higher kf than the anterior limb. Significant differences for all parameters were observed between subjects. In contrast to previous studies, bSSFP allowed assessment of even small brain structures due to its high resolution. The observed differences from previous studies can partly be explained by the reduced partial volume effects. MT-sensitized bSSFP is an ideal candidate for qMT-analysis in the clinical routine as it provides high-resolution 3D qMT-data of even small brain structures in clinically feasible acquisition times. The present qMT-data can serve as a reference for the characterization of cerebral diseases.

Evaporation and condensation of SiO and SiO2 studied by infrared spectroscopy.

Physical evaporation of SiO and SiO(2) under ultra-high vacuum conditions was monitored in situ with infrared spectroscopy at frequencies between 450 cm(-1) and 5000 cm(-1). The measured vibrational spectra of the condensed films are identical in both cases, for SiO and SiO(2) evaporation, and can be described with four Brendel oscillators located at 380 cm(-1), 713 cm(-1), 982 cm(-1), and 1101 cm(-1), corresponding to typical vibration modes in SiO.

Diffusion-weighted imaging findings differ between stroke attributable to spontaneous cervical artery dissection and patent foramen ovale.

BACKGROUND AND PURPOSE: Spontaneous cervical arterial dissection and patent foramen ovale (PFO) are important causes of stroke in younger patients. We tested whether characteristics of cerebral ischaemia visible on diffusion-weighted imaging (DWI) aid in differentiating between these two aetiologies. METHODS: Diffusion-weighted imaging was performed after a median of 2 days [interquartile range (IQR) 1-3 days] in 94 consecutive patients with an acute ischaemic stroke caused either by carotid or vertebral artery dissection (n = 33) or PFO (n = 61). We compared number, size, location and predefined patterns of DWI lesions between both aetiologies. RESULTS: Ninety-three out of 94 patients had acute DWI lesions and were included in the analysis. Multiple DWI lesions occurred more frequently in patients with dissection (23/33, 70%) than in those with PFO (26/60, 43%, P = 0.02). Lesions were larger in the dissection group [median diameter of largest lesion, 50 mm (IQR 19-68 mm)] than in the PFO group [23 (9-48) mm; P = 0.02]. The distribution of lesion patterns differed between the two aetiologies (P < 0.001): single, non-territorial infarcts were more frequent in PFO (25/60, 42%) than in dissection (2/33, 6%); large territorial infarcts with or without additional smaller lesions in the same territory occurred in 20/33 (61%) patients with dissection and in 16/60 (27%) patients with PFO. CONCLUSIONS: Diffusion-weighted imaging characteristics differ between PFO and dissection, suggesting differences in the pathogenesis of brain infarction between these aetiologies. A single non-territorial infarct seems to favour PFO as stroke aetiology. Whether this or other features are distinctive enough to diagnose PFO or dissection in individual patients requires further testing.

Cerebral venous thrombosis: diagnostic accuracy of combined, dynamic and static, contrast-enhanced 4D MR venography.

BACKGROUND AND PURPOSE: MR including MRV is an established method to diagnose CVT. However, it remains unsettled which MR imaging modalities offer the highest diagnostic accuracy. We evaluated the accuracy of a combined, dynamic (1.5 seconds per dataset) and static (voxel size, 1.1 x 0.9 x 1.5 mm), contrast-enhanced MRV method (combo-4D MRV) relative to other established MR/MRV modalities. MATERIALS AND METHODS: A total of 39 patients with CVT (n = 20) and control subjects (n = 19) underwent combo-4D MRV, 2D TOF MRV, GRE imaging, and T2W imaging. For these modalities, diagnostic accuracy (ROCs) for CVT affecting 53 out of 234 predefined venous segments was determined. Sensitivity and specificity were separately calculated for different stages of CVT (acute/subacute/chronic). RESULTS: Combo-4D MRV showed the highest accuracy (AUC, 0.99 [95% CI, 0.97-1.0]; sensitivity, 97% [84%-100%]) for thrombosed dural sinuses. For all thrombosed segments including cortical veins, its sensitivity was best (76% [64%-84%]; AUC, 0.92 [0.88-0.96]), followed by TOF MRV (72% [59%-81%]; AUC, 0.93 [0.88-0.97]). Even for chronic CVT, it showed a relatively high sensitivity of 67% (30%-90%). For thrombosed cortical veins alone, GRE images achieved the highest sensitivity (66% [46%-81%]; AUC, 0.88 [0.78-0.97]). Specificities of all modalities ranged from 96% to 99%. CONCLUSIONS: Combo-4D MRV showed an excellent accuracy for the diagnosis of dural sinus thrombosis. The analysis of dynamic patterns of contrast enhancement in dural sinuses appeared useful to identify chronic thrombosis. To diagnose thrombosed cortical veins, GRE images should primarily be analyzed.

Biology-inspired synthesis of compound libraries.

Biologically active small molecules represent the basis for chemical biology applications in which small molecules are used as chemical tools to probe biological processes. In this report, we review two approaches to design and synthesize compound libraries for biological screenings, i.e., diversity-oriented synthesis (DOS) and biology-oriented synthesis (BIOS).

MR angiography of dural arteriovenous fistulas: diagnosis and follow-up after treatment using a time-resolved 3D contrast-enhanced technique.

BACKGROUND AND PURPOSE: Digital subtraction angiography (DSA) is the method of reference for imaging of dural arteriovenous fistula (DAVF). The goal of this study was to analyze the value of different MR images including 3D contrast-enhanced MR angiography (MRA) with a high temporal resolution in diagnostic and follow-up imaging of DAVFs. MATERIALS AND METHODS: A total of 18 MR/MRA examinations from 14 patients with untreated (n=9) and/or treated (n=9) DAVFs were evaluated. Two observers assessed all MR and MRA investigations for signs indicating the presence of a DAVF, for fistula characteristics such as fistula grading, location of fistulous point, and fistula obliteration after treatment. All results were compared with DSA findings. RESULTS: On time-resolved 3D contrast-enhanced (TR 3D) MRA, the side and presence of all patent fistulas (n=13) were correctly indicated, and no false-positive findings were observed in occluded DAVFs (n=5). Grading of fistulas with this imaging technique was correct in 77% and 85% of patent fistulas for both readers, respectively. On T2-weighted images, signs indicative of a DAVF were encountered only in fistulas with cortical venous reflux (56%), whereas on 3D time-of-flight (TOF) MRA, most fistulas (88%) were correctly detected. In complete fistula occlusion, false-positive findings were encountered on both T2-weighted images and on TOF MRA images. CONCLUSION: In this study, TR 3D MRA proved reliable in detecting DAVFs and suitable for follow-up imaging. The technique allowed--within limitations--to grade DAVFs. Although 3D TOF MRA can depict signs of DAVFs, its value for follow-up imaging is limited.

In vivo assessment and visualization of intracranial arterial hemodynamics with flow-sensitized 4D MR imaging at 3T.

SUMMARY: We evaluated electrocardiogram-synchronized flow-sensitized 4-dimensional MR imaging at 3T in combination with advanced 3D visualization strategies to ascertain its feasibility for the assessment of local intracranial blood-flow patterns in vivo. In large arteries of healthy volunteers, the temporal and spatial evolution of blood flow was successfully visualized and revealed--for example, a helical flow pattern in the carotid siphon. In a patient with steno-occlusive neurovascular disease, stagnant and retrograde flow patterns were readily visible.