Intra-aneurysmal high-resolution 4D MRI flow imaging for hemodynamic imaging markers in intracranial aneurysm instability.

BACKGROUND AND PURPOSE: Prediction of aneurysm instability is crucial to guide treatment decisions and to select appropriate patients with unruptured intracranial aneurysms (IAs) for preventive treatment. High resolution four-dimensional magnetic resonance (4D MRI) flow imaging and 3D quantification of aneurysm morphology could offer insights and new imaging markers for aneurysm instability. In this cross-sectional study, we aim to identify 4D MRI flow imaging markers for aneurysm instability by relating hemodynamics in the aneurysm sac to 3D morphological proxy parameters for aneurysm instability. MATERIALS AND METHODS: In 35 patients with 37 unruptured IAs, a 3T MRA and a 7T 4D flow MRI scan was performed. Five hemodynamic parameters -peak-systolic (WSSMAX) and time-averaged wall shear stress (WSSMEAN), oscillatory shear index (OSI), mean velocity, and velocity pulsatility index (vPI)-were correlated to six 3D morphology proxy parameters of aneurysm instability -major axis length, volume, surface area (all three size parameters), flatness, shape index, and curvedness -by Pearson's correlation with 95% confidence intervals (CI). Scatterplots of hemodynamic parameters that correlated with IA size (major axis length) were created. RESULTS: WSSMAX and WSSMEAN correlated negatively with all three size parameters (strongest for WSSMEAN with volume (r = -0.70, 95% CI -0.83 to -0.49)) and OSI positively (strongest with major axis length (r = 0.87, 95% CI 0.76 to 0.93)). WSSMAX and WSSMEAN correlated positively with shape index (r = 0.61, 95% CI 0.36 to 0.78 and r = 0.49, 95% CI 0.20 to 0.70, respectively) and OSI negatively (r = 0.82, 95% CI -0.9 to -0.68). WSSMEAN and mean velocity correlated negatively with flatness (r = -0.35, 95% CI -0.61 to -0.029 and r = 0.33, 95% CI -0.59 to 0.007, respectively) and OSI positively (r = 0.54, 95% CI 0.26 to 0.74). vPI did not show any statistically significant correlation. CONCLUSIONS: Out of the five included hemodynamic parameters, WSSMAX, WSSMEAN, and OSI showed the strongest correlation with morphological 3D proxy parameters of aneurysm instability. Future studies should assess these promising new imaging marker parameters for predicting aneurysm instability in longitudinal cohorts of IA patients. ABBREVIATIONS: IA = intracranial aneurysm; 3D = three dimensional; 4D MRI flow = four-dimensional Magnetic Resonance Imaging flow; TOF-MRA = Time-of-flight Magnetic Resonance Angiography; WSS = wall shear stress; WSSMAX = WSS calculated at peak systole; WSSMEAN = time averaged WSS; OSI = oscillatory shear index; vPI = velocity pulsatility index.

High Spatiotemporal Resolution 4D Flow MRI of Intracranial Aneurysms at 7T in 10 Minutes.

BACKGROUND AND PURPOSE: Patients with intracranial aneurysms may benefit from 4D flow MR imaging because the derived wall shear stress is considered a useful marker for risk assessment and growth of aneurysms. However, long scan times limit the clinical implementation of 4D flow MR imaging. Therefore, this study aimed to investigate whether highly accelerated, high resolution, 4D flow MR imaging at 7T provides reliable quantitative blood flow values in intracranial arteries and aneurysms. MATERIALS AND METHODS: We used pseudospiral Cartesian undersampling with compressed sensing reconstruction to achieve high spatiotemporal resolution (0.5 mm isotropic, ∼30 ms) in a scan time of 10 minutes. We analyzed the repeatability of accelerated 4D flow scans and compared flow rates, stroke volume, and the pulsatility index with 2D flow and conventional 4D flow MR imaging in a flow phantom and 15 healthy subjects. Additionally, accelerated 4D flow MR imaging with high spatiotemporal resolution was acquired in 5 patients with aneurysms to derive wall shear stress. RESULTS: Flow-rate bias compared with 2D flow was lower for accelerated than for conventional 4D flow MR imaging (0.31 ± 0.13, P = .22, versus 0.79 ± 0.17 mL/s, P < .01). Pulsatility index bias gave similar results. Stroke volume bias showed no difference for accelerated as well as for conventional 4D flow compared to 2D flow MR imaging. Repeatability for accelerated 4D flow was similar to that of 2D flow MR imaging. Increased temporal resolution for wall shear stress measurements in 5 intracranial aneurysms did not show a consistent effect for the wall shear stress but did show an effect for the oscillatory shear index. CONCLUSIONS: Highly accelerated high spatiotemporal resolution 4D flow MR imaging at 7T in intracranial arteries and aneurysms provides repeatable and accurate quantitative flow values. Flow rate accuracy is significantly increased compared with conventional 4D flow scans.

Effect of hyperbaric oxygen therapy and corticosteroid therapy in military personnel with acute acoustic trauma.

INTRODUCTION: Acute acoustic trauma (AAT) is a sensorineural hearing impairment due to exposure to an intense impulse noise which causes cochlear hypoxia. Hyperbaric oxygen therapy (HBO) could provide an adequate oxygen supply. The aim was to investigate the effectiveness of early treatment with combined HBO and corticosteroid therapy in patients with AAT compared with corticosteroid monotherapy. METHODS: A retrospective study was performed on military personnel diagnosed with AAT between November 2012 and December 2017. Inclusion criteria for HBO therapy were hearing loss of 30 dB or greater on at least one, 25 dB or more on at least two, or 20 dB or more on three or more frequencies as compared with the contralateral ear. RESULTS: Absolute hearing improvements showed significant differences (independent t-test) between patients receiving HBO and the control group at 500 Hz (p=0.014), 3000 Hz (p=0.023), 4000 Hz (p=0.001) and 6000 Hz (p=0.01) and at the mean of all frequencies (p=0.002). Relative hearing improvements were significantly different (independent t-test) at 4000 Hz (p=0.046) and 6000 Hz (p=0.013) and at all frequencies combined (p=0.005). Furthermore, the percentage of patients with recovery to the functional level required by the Dutch Armed Forces (clinical outcome score) was higher in the HBO group. CONCLUSIONS: Early-stage combination therapy for patients with AAT was associated with better audiometric results at higher frequencies and better clinical outcome score.

Markers of Pulmonary Oxygen Toxicity in Hyperbaric Oxygen Therapy Using Exhaled Breath Analysis.

INTRODUCTION: Although hyperbaric oxygen therapy (HBOT) has beneficial effects, some patients experience fatigue and pulmonary complaints after several sessions. The current limits of hyperbaric oxygen exposure to prevent pulmonary oxygen toxicity (POT) are based on pulmonary function tests (PFT), but the limitations of PFT are recognized worldwide. However, no newer modalities to detect POT have been established. Exhaled breath analysis in divers have shown volatile organic compounds (VOCs) of inflammation and methyl alkanes. This study hypothesized that similar VOCs might be detected after HBOT. METHODS: Ten healthy volunteers of the Royal Netherlands Navy underwent six HBOT sessions (95 min at 253 kPa, including three 5-min "air breaks"), i.e., on five consecutive days followed by another session after 2 days of rest. At 30 min before the dive, and at 30 min, 2 and 4 h post-dive, exhaled breath was collected and followed by PFT. Exhaled breath samples were analyzed using gas chromatography-mass spectrometry (GC-MS). After univariate tests and correlation of retention times, ion fragments could be identified using a reference database. Using these fragments VOCs could be reconstructed, which were clustered using principal component analysis. These clusters were tested longitudinally with ANOVA. RESULTS: After GC-MS analysis, eleven relevant VOCs were identified which could be clustered into two principal components (PC). PC1 consisted of VOCs associated with inflammation and showed no significant change over time. The intensities of PC2, consisting of methyl alkanes, showed a significant decrease (p = 0.001) after the first HBOT session to 50.8%, remained decreased during the subsequent days (mean 82%), and decreased even further after 2 days of rest to 58% (compared to baseline). PFT remained virtually unchanged. DISCUSSION: Although similar VOCs were found when compared to diving, the decrease of methyl alkanes (PC2) is in contrast to the increase seen in divers. It is unknown why emission of methyl alkanes (which could originate from the phosphatidylcholine membrane in the alveoli) are reduced after HBOT. This suggests that HBOT might not be as damaging to the pulmonary tract as previously assumed. Future research on POT should focus on the identified VOCs (inflammation and methyl alkanes).

Transcatheter aortic valve replacement alters ascending aortic blood flow and wall shear stress patterns: A 4D flow MRI comparison with age-matched, elderly controls.

BACKGROUND: With the implementation of transcatheter aortic valve replacement (TAVR) in lower-risk patients, evaluation of blood flow characteristics and the effect of TAVR on aortic dilatation becomes of considerable interest. We employed 4D flow MRI in the ascending aorta of patients after TAVR to assess wall shear stress (WSS) and compare blood flow patterns with surgical aortic valve replacement (SAVR) and age- and gender-matched controls. METHODS: Fourteen post-TAVR patients and ten age- and gender-matched controls underwent kt-PCA accelerated 4D flow MRI of the thoracic aorta at 3.0 Tesla. Velocity and wall shear stress was compared between the two groups. In addition, aortic flow eccentricity and displacement was assessed and compared between TAVR patients, controls and 14 SAVR patients recruited as part of an earlier study. RESULTS: Compared to controls, abnormally elevated WSS was present in 30±10% of the ascending aortic wall in TAVR patients. Increased WSS was present along the posterior mid-ascending aorta and the anterior distal-ascending aorta in all TAVR patients. TAVR results in eccentric and displaced flow in the mid- and distal-ascending aorta, whereas blood flow displacement in SAVR patients occurs only in the distal-ascending aorta. CONCLUSION: This study shows that TAVR results in increased blood flow velocity and WSS in the ascending aorta compared to age- and gender-matched elderly controls. This finding warrants longitudinal assessment of aortic dilatation after TAVR in the era of potential TAVR in lower-risk patients. Additionally, TAVR results in altered blood flow eccentricity and displacement in the mid- and distal-ascending aorta, whereas SAVR only results in altered blood flow eccentricity and displacement in the distal-ascending aorta. KEY POINTS: • TAVR results in increased blood flow velocity and WSS in the ascending aorta. • Longitudinal assessment of aortic dilatation after TAVR is warranted in the era of potential TAVR in lower-risk patients. • Both TAVR and SAVR result in altered blood flow patterns in the ascending aorta when compared to age-matched controls.

Aneurysmal Parent Artery-Specific Inflow Conditions for Complete and Incomplete Circle of Willis Configurations.

BACKGROUND AND PURPOSE: Hemodynamics are thought to play a role in intracranial aneurysm growth and rupture. Computational fluid dynamics is frequently performed to assess intra-aneurysmal hemodynamics, using generalized flow waveforms of healthy volunteers as inflow boundary conditions. The purpose of this study was to assess differences in inflow conditions for different aneurysmal parent artery locations and variations of circle of Willis configurations. MATERIALS AND METHODS: In a series of 96 patients with 103 aneurysms, velocity measurements were acquired using 2D phase-contrast MR imaging perpendicular to the aneurysmal parent arteries in the circle of Willis. Circle of Willis configurations were inspected for variations using multiple overlapping thin-slab-acquisition MRAs. Flow rates, velocity magnitudes, and pulsatility indices were calculated for each parent artery location in subgroups of complete and incomplete circle of Willis configurations. RESULTS: Flow rates, velocity magnitudes, and pulsatility indices were significantly different among aneurysmal parent arteries. Incomplete circle of Willis configurations were observed in 24% of the cases. Significantly lower basilar artery flow rates were observed in configurations with hypoplastic P1 segments. Significantly higher A1 flow rates were observed in configurations with a hypoplastic contralateral A1 segment. CONCLUSIONS: Inflow conditions vary substantially between aneurysmal parent arteries and circle of Willis configurations. We have created a collection of parent artery-specific inflow conditions tailored to the patient-specific circle of Willis configuration that can be used in future computational fluid dynamics studies analyzing intra-aneurysmal hemodynamics.

Hyperbaric oxygen therapy for sudden sensorineural hearing loss in divers.

OBJECTIVE: Sudden sensorineural hearing loss in divers may be caused by either inner-ear barotrauma or inner-ear decompression sickness. There is no consensus on the best treatment option. This study aimed to evaluate the therapeutic value of hyperbaric oxygen therapy for sudden sensorineural hearing loss in divers. METHOD: A literature review and three cases of divers with sudden sensorineural hearing loss treated with hyperbaric oxygen therapy are presented. RESULTS: Hyperbaric oxygen therapy resulted in hearing improvement in 80 per cent of patients: 39 per cent had hearing improvement and 41 per cent had full recovery. CONCLUSION: Hyperbaric oxygen therapy improved hearing in divers with sudden sensorineural hearing loss.

Thinner Regions of Intracranial Aneurysm Wall Correlate with Regions of Higher Wall Shear Stress: A 7T MRI Study.

BACKGROUND AND PURPOSE: Both hemodynamics and aneurysm wall thickness are important parameters in aneurysm pathophysiology. Our aim was to develop a method for semi-quantitative wall thickness assessment on in vivo 7T MR images of intracranial aneurysms for studying the relation between apparent aneurysm wall thickness and wall shear stress. MATERIALS AND METHODS: Wall thickness was analyzed in 11 unruptured aneurysms in 9 patients who underwent 7T MR imaging with a TSE-based vessel wall sequence (0.8-mm isotropic resolution). A custom analysis program determined the in vivo aneurysm wall intensities, which were normalized to the signal of nearby brain tissue and were used as measures of apparent wall thickness. Spatial wall thickness variation was determined as the interquartile range in apparent wall thickness (the middle 50% of the apparent wall thickness range). Wall shear stress was determined by using phase-contrast MR imaging (0.5-mm isotropic resolution). We performed visual and statistical comparisons (Pearson correlation) to study the relation between wall thickness and wall shear stress. RESULTS: 3D colored apparent wall thickness maps of the aneurysms showed spatial apparent wall thickness variation, which ranged from 0.07 to 0.53, with a mean variation of 0.22 (a variation of 1.0 roughly means a wall thickness variation of 1 voxel [0.8 mm]). In all aneurysms, apparent wall thickness was inversely related to wall shear stress (mean correlation coefficient, -0.35; P < .05). CONCLUSIONS: A method was developed to measure the wall thickness semi-quantitatively, by using 7T MR imaging. An inverse correlation between wall shear stress and apparent wall thickness was determined. In future studies, this noninvasive method can be used to assess spatial wall thickness variation in relation to pathophysiologic processes such as aneurysm growth and rupture.

Additional Value of Intra-Aneurysmal Hemodynamics in Discriminating Ruptured versus Unruptured Intracranial Aneurysms.

BACKGROUND AND PURPOSE: Hemodynamics are thought to play an important role in the rupture of intracranial aneurysms. We tested whether hemodynamics, determined from computational fluid dynamics models, have additional value in discriminating ruptured and unruptured aneurysms. Such discriminative power could provide better prediction models for rupture. MATERIALS AND METHODS: A cross-sectional study was performed on patients eligible for endovascular treatment, including 55 ruptured and 62 unruptured aneurysms. Association with rupture status was tested for location, aneurysm type, and 4 geometric and 10 hemodynamic parameters. Patient-specific spatiotemporal velocities measured with phase-contrast MR imaging were used as inflow conditions for computational fluid dynamics. To assess the additional value of hemodynamic parameters, we performed 1 univariate and 2 multivariate analyses: 1 traditional model including only location and geometry and 1 advanced model that included patient-specific hemodynamic parameters. RESULTS: In the univariate analysis, high-risk locations (anterior cerebral arteries, posterior communicating artery, and posterior circulation), daughter sacs, unstable inflow jets, impingements at the aneurysm body, and unstable complex flow patterns were significantly present more often in ruptured aneurysms. In both multivariate analyses, only the high-risk location (OR, 3.92; 95% CI, 1.77-8.68) and the presence of daughter sacs (OR, 2.79; 95% CI, 1.25-6.25) remained as significant independent determinants. CONCLUSIONS: In this study population of patients eligible for endovascular treatment, we found no independent additional value of aneurysmal hemodynamics in discriminating rupture status, despite high univariate associations. Only traditional parameters (high-risk location and the presence of daughter sacs) were independently associated with ruptured aneurysms.

Cutis marmorata in decompression illness may be cerebrally mediated: a novel hypothesis on the aetiology of cutis marmorata.

INTRODUCTION: Cutaneous decompression sickness (DCS) is often considered to be a mild entity that may be explained by either vascular occlusion of skin vessels by bubbles entering the arterial circulation through a right-to-left shunt or bubble formation due to saturated subcutaneous tissue during decompression. We propose an alternative hypothesis. METHODS: The case is presented of a 30-year-old female diver with skin DCS on three separate occasions following relatively low decompression stress dives. Also presented are the findings of cutaneous appearances in previously reported studies on cerebral arterial air embolism in pigs. RESULTS: There was a close similarity in appearance between the skin lesions in this woman (and in other divers) and those in the pigs, suggesting a common pathway. CONCLUSIONS: From this, we hypothesize that the cutaneous lesions are cerebrally mediated. Therefore, cutaneous DCS might be a more serious event that should be treated accordingly. This hypothesis may be supported by the fact that cutis marmorata is also found in other fields of medicine in a non-diving context, where the rash is referred to as livedo reticularis or livedo racemosa. These are associated with a wide number of conditions but of particular interest is Sneddon's syndrome, which describes the association of livedo racemosa with cerebrovascular events or vascular brain abnormalities. Finally, there is a need for further research on the immunocytochemical pathway of cutaneous DCS.

Hyperbaric oxygen diving affects exhaled molecular profiles in men.

Exhaled breath contains volatile organic compounds (VOCs) that are associated with respiratory pathophysiology. We hypothesized that hyperbaric oxygen exposure (hyperoxia) generates a distinguishable VOC pattern. This study aimed to test this hypothesis in oxygen-breathing divers. VOCs in exhaled breath were measured in 10 male divers before and 4h after diving to 9msw (190kPa) for 1h. During the dive they breathed 100% oxygen or air in randomized order. VOCs were determined using two-dimensional gas chromatography with time-of-flight mass spectrometry. Compared to air dives, after oxygen dives there was a significant increase in five VOCs (predominately methyl alkanes). Furthermore, a strong, positive correlation was found between increments in 2,4-dimethyl-hexane and those of 4-ethyl-5-methyl-nonane. Although non-submerged hyperoxia studies on VOCs have been performed, the present study is the first to demonstrate changes in exhaled molecular profiles after submerged oxygen diving. The pathophysiological background might be attributed to either a lipid peroxidation-induced pathway, an inflammatory pathway, or to both.

Generalized versus patient-specific inflow boundary conditions in computational fluid dynamics simulations of cerebral aneurysmal hemodynamics.

BACKGROUND AND PURPOSE: Attempts have been made to associate intracranial aneurysmal hemodynamics with aneurysm growth and rupture status. Hemodynamics in aneurysms is traditionally determined with computational fluid dynamics by using generalized inflow boundary conditions in a parent artery. Recently, patient-specific inflow boundary conditions are being implemented more frequently. Our purpose was to compare intracranial aneurysm hemodynamics based on generalized versus patient-specific inflow boundary conditions. MATERIALS AND METHODS: For 36 patients, geometric models of aneurysms were determined by using 3D rotational angiography. 2D phase-contrast MR imaging velocity measurements of the parent artery were performed. Computational fluid dynamics simulations were performed twice: once by using patient-specific phase-contrast MR imaging velocity profiles and once by using generalized Womersley profiles as inflow boundary conditions. Resulting mean and maximum wall shear stress and oscillatory shear index values were analyzed, and hemodynamic characteristics were qualitatively compared. RESULTS: Quantitative analysis showed statistically significant differences for mean and maximum wall shear stress values between both inflow boundary conditions (P < .001). Qualitative assessment of hemodynamic characteristics showed differences in 21 cases: high wall shear stress location (n = 8), deflection location (n = 3), lobulation wall shear stress (n = 12), and/or vortex and inflow jet stability (n = 9). The latter showed more instability for the generalized inflow boundary conditions in 7 of 9 patients. CONCLUSIONS: Using generalized and patient-specific inflow boundary conditions for computational fluid dynamics results in different wall shear stress magnitudes and hemodynamic characteristics. Generalized inflow boundary conditions result in more vortices and inflow jet instabilities. This study emphasizes the necessity of patient-specific inflow boundary conditions for calculation of hemodynamics in cerebral aneurysms by using computational fluid dynamics techniques.

Nitric oxide and carbon monoxide diffusing capacity after a 1-h oxygen dive to 9 m of sea water.

INTRODUCTION: To prevent extensive pulmonary lesions in submerged oxygen divers lung function like the forced vital capacity (FVC) or the diffusing capacity for carbon monoxide (DL,co) are used to monitor pulmonary oxygen toxicity (POT). As the diffusing capacity for nitric oxide (DL,no) measures more accurately the membrane diffusing capacity compared to DL,co we hypothesized that DL,no is superior in monitoring the onset of physiological changes indicative of POT as compared to DL,co or FVC. METHOD: 26 healthy divers (mean age 30.7 ± 6.2 years) made two submerged dives to 190 kPa for 1 h on two randomized separate days, whilst breathing 100% oxygen or compressed air. FVC, DL,no, DL,co and alveolar volume (VA ) were measured 6 times during a 26-h period. RESULTS: Up to 8 h no significant differences in outcomes were found between the oxygen and air dives. However, at 8 h after the oxygen dives there was a significant reduction in DL,no, DL,co and VA as compared with air dives. In contrast, the reduction in FVC was significantly greater after the air dive. At 22 h there were no longer differences in outcomes between the dives. CONCLUSIONS: These data show that DL,no and DL,co are significantly reduced 8 h after submerged oxygen dives as compared to similar air dives. Together with the reduction in VA this may be indicative of interstitial edema as an early sign of POT. Our data warrant validation of the superiority of DL,no and DL,co over FVC in the practical monitoring of divers.

Assessment of pulmonary oxygen toxicity: relevance to professional diving; a review.

When breathing oxygen with partial oxygen pressures PO2 of between 50 and 300 kPa pathological pulmonary changes develop after 3-24h depending on the PO2. This kind of injury (known as pulmonary oxygen toxicity) is not only observed in ventilated patients but is also considered an occupational hazard in oxygen divers or mixed gas divers. To prevent these latter groups from sustaining irreversible lesions adequate prevention is required. This review summarizes the pathophysiological effects on the respiratory tract when breathing oxygen with PO2 of 50-300 kPa (hyperoxia). We discuss to what extent the most commonly used lung function parameters change after exposure to hyperoxia and its role in monitoring the onset and development of pulmonary oxygen toxicity in daily practice. Finally, new techniques in respiratory medicine are discussed with regard to their usefulness in monitoring pulmonary oxygen toxicity in divers.

Severe spinal cord decompression illness after an uneventful North Sea dive.

The aim of this case report is to illustrate that, even under moderate conditions, a dive can result in spinal cord decompression illness (DCI). The diver in question completed five dives with the same profile. The first four included substantial physical strain, while the final dive was for observation only, without physical strain. The spinal cord was the target organ for DCI. We discuss the roles of various diver-related risk factors and of factors related to the dive itself. Older divers have a higher risk for decompression incidents. The nature of the dive profile is a major factor in the uptake and release of inert gas. Physical exertion during pressure-exposure boosts the inert gas load, increases bubbling in tissues and raises the risk of DCI in the decompression phase of the dive. We discuss the causal involvement of such risk factors in this case, given the characteristics of the diver and the circumstances of the dive. Finally, we want to express our concern for physical fitness and smoking habits, especially for divers over the age of 40.

3D cine phase-contrast MRI at 3T in intracranial aneurysms compared with patient-specific computational fluid dynamics.

BACKGROUND AND PURPOSE: CFD has been proved valuable for simulating blood flow in intracranial aneurysms, which may add to better rupture risk assessment. However, CFD has drawbacks such as the sensitivity to assumptions needed for the model, which may hinder its clinical implementation. 3D PC-MR imaging is a technique that enables measurements of blood flow. The purpose of this study was to compare flow patterns on the basis of 3D PC-MR imaging with CFD estimates. MATERIALS AND METHODS: 3D PC-MR imaging was performed in 8 intracranial aneurysms. Two sets of patient-specific inflow boundaries for CFD were obtained from a separate 2D PC-MR imaging sequence (2D CFD) and from the 3D PC-MR imaging (3D CFD) data. 3D PC-MR imaging and CFD were compared by calculation of the differences between velocity vector magnitudes and angles. Differences in flow patterns expressed as the presence and strengths of vortices were determined by calculation of singular flow energy. RESULTS: In systole, flow features such as vortex patterns were similar. In diastole, 3D PC-MR imaging measurements appeared inconsistent due to low velocity-to-noise ratios. The relative difference in velocity magnitude was 67.6 ± 51.4% and 27.1 ± 24.9% in systole and 33.7 ± 21.5% and 17.7 ± 10.2% in diastole for 2D CFD and 3D CFD, respectively. For singular energy, this was reduced to 15.5 ± 13.9% at systole and 19.4 ± 17.6% at diastole (2D CFD). CONCLUSIONS: In systole, good agreement between 3D PC-MR imaging and CFD on flow-pattern visualization and singular-energy calculation was found. In diastole, flow patterns of 3D PC-MR imaging differed from those obtained from CFD due to low velocity-to-noise ratios.

Quantification and visualization of flow in the Circle of Willis: time-resolved three-dimensional phase contrast MRI at 7 T compared with 3 T.

The assessment of both geometry and hemodynamics of the intracranial arteries has important diagnostic value in internal carotid occlusion, sickle cell disease, and aneurysm development. Provided that signal to noise ratio (SNR) and resolution are high, these factors can be measured with time-resolved three-dimensional phase contrast MRI. However, within a given scan time duration, an increase in resolution causes a decrease in SNR and vice versa, hampering flow quantification and visualization. To study the benefits of higher SNR at 7 T, three-dimensional phase contrast MRI in the Circle of Willis was performed at 3 T and 7 T in five volunteers. Results showed that the SNR at 7 T was roughly 2.6 times higher than at 3 T. Therefore, segmentation of small vessels such as the anterior and posterior communicating arteries succeeded more frequently at 7 T. Direction of flow and smoothness of streamlines in the anterior and posterior communicating arteries were more pronounced at 7 T. Mean velocity magnitude values in the vessels of the Circle of Willis were higher at 3 T due to noise compared to 7 T. Likewise, areas of the vessels were lower at 3 T. In conclusion, the gain in SNR at 7 T compared to 3 T allows for improved flow visualization and quantification in intracranial arteries.

Lung function before and after oxygen diving: a randomized crossover study.

RATIONALE: Breathing oxygen with a partial pressure of > 50 kPa can cause pulmonary oxygen toxicity (POT). Diffusing capacity for carbon monoxide (DL(CO)) is thought to be a more sensitive indicator of POT than vital capacity (VC). Because diffusing capacity can be measured more specifically using nitric oxide (DL(NO)), we hypothesized that DL(NO) is better able to monitor and exclude POT than DL(CO). OBJECTIVE: To compare changes in lung function after oxygen and air dives which include measurement of DL(NO) and DL(CO). METHOD: Eleven healthy male divers (mean age 27.5 +/- 3.1 years) made two immersed dives to 150 kPa for three hours on two separate days, during which they randomly breathed 100% oxygen or air. VC, DL(NO) and DL(CO) were measured six times during a 26-hour period on both days and on a third non-diving day. RESULTS: There were no significant changes in DL(CO), DL(NO) or other diffusing capacity or spirometric parameters after either type of dive. CONCLUSION: Lung function after a single three-hour oxygen dive at a pO2 of approximately 150 kPa is comparable to that after an air dive at the same depth and duration. This suggests that such an oxygen dive does not induce detectable signs of POT. Our hypothesis that DL(NO) is more sensitive than DL(CO) for detection of POT could not be tested because the oxygen exposure did not affect either parameter.

Comparison of phase-contrast MR imaging and endovascular sonography for intracranial blood flow velocity measurements.

BACKGROUND AND PURPOSE: Local hemodynamic information may help to stratify rupture risk of cerebral aneurysms. Patient-specific modeling of cerebral hemodynamics requires accurate data on BFV in perianeurysmal arteries as boundary conditions for CFD. The aim was to compare the BFV measured with PC-MR imaging with that obtained by using intra-arterial Doppler sonography and to determine interpatient variation in intracranial BFV. MATERIALS AND METHODS: In 10 patients with unruptured intracranial aneurysms, BFV was measured in the cavernous ICA with PC-MR imaging in conscious patients before treatment, and measured by using an intra-arterial Doppler sonography wire when the patient was anesthetized with either propofol (6 patients) or sevoflurane (4 patients). RESULTS: Both techniques identified a pulsatile blood flow pattern in cerebral arteries. PSV differed >50 cm/s between patients. A mean velocity of 41.3 cm/s (95% CI, 39.3-43.3) was measured with PC-MR imaging. With intra-arterial Doppler sonography, a mean velocity of 29.3 cm/s (95% CI, 25.8-32.8) was measured with the patient under propofol-based intravenous anesthesia. In patients under sevoflurane-based inhaled anesthesia, a mean velocity of 44.9 cm/s (95% CI, 40.6-49.3) was measured. CONCLUSIONS: We showed large differences in BFV between patients, emphasizing the importance of using patient-specific hemodynamic boundary conditions in CFD. PC-MR imaging measurements of BFV in conscious patients were comparable with those obtained with the intra-arterial Doppler sonography when the patient was anesthetized with a sevoflurane-based inhaled anesthetic.

Complex flow patterns in a real-size intracranial aneurysm phantom: phase contrast MRI compared with particle image velocimetry and computational fluid dynamics.

The aim of this study was to validate the flow patterns measured by high-resolution, time-resolved, three-dimensional phase contrast MRI in a real-size intracranial aneurysm phantom. Retrospectively gated three-dimensional phase contrast MRI was performed in an intracranial aneurysm phantom at a resolution of 0.2 × 0.2 × 0.3 mm(3) in a solenoid rat coil. Both steady and pulsatile flows were applied. The phase contrast MRI measurements were compared with particle image velocimetry measurements and computational fluid dynamics simulations. A quantitative comparison was performed by calculating the differences between the magnitude of the velocity vectors and angles between the velocity vectors in corresponding voxels. Qualitative analysis of the results was executed by visual inspection and comparison of the flow patterns. The root-mean-square errors of the velocity magnitude in the comparison between phase contrast MRI and computational fluid dynamics were 5% and 4% of the maximum phase contrast MRI velocity, and the medians of the angle distribution between corresponding velocity vectors were 16° and 14° for the steady and pulsatile measurements, respectively. In the phase contrast MRI and particle image velocimetry comparison, the root-mean-square errors were 12% and 10% of the maximum phase contrast MRI velocity, and the medians of the angle distribution between corresponding velocity vectors were 19° and 15° for the steady and pulsatile measurements, respectively. Good agreement was found in the qualitative comparison of flow patterns between the phase contrast MRI measurements and both particle image velocimetry measurements and computational fluid dynamics simulations. High-resolution, time-resolved, three-dimensional phase contrast MRI can accurately measure complex flow patterns in an intracranial aneurysm phantom.