Pulse oximetry for hypoxemia: a warning to users and manufacturers.

Pulse oximetry represents a major advance in patient monitoring, but measurement below 70 to 80% saturation has important limitations. Several authors have tested pulse oximetry at low saturations with conflicting results. A review of these data indicates that every patient with a pulse oximeter value below 75 to 80% SaO2 should have one or more invasive measurements of the arterial SaO2 in order to avoid undetected severe hypoxemia.

Post-mortem cardiac 3-T magnetic resonance imaging: visualization of sudden cardiac death?

OBJECTIVES: This study aimed to investigate post-mortem magnetic resonance imaging (pmMRI) for the assessment of myocardial infarction and hypointensities on post-mortem T2-weighted images as a possible method for visualizing the myocardial origin of arrhythmic sudden cardiac death. BACKGROUND: Sudden cardiac death has challenged clinical and forensic pathologists for decades because verification on post-mortem autopsy is not possible. pmMRI as an autopsy-supporting examination technique has been shown to visualize different stages of myocardial infarction. METHODS: In 136 human forensic corpses, a post-mortem cardiac MR examination was carried out prior to forensic autopsy. Short-axis and horizontal long-axis images were acquired in situ on a 3-T system. RESULTS: In 76 cases, myocardial findings could be documented and correlated to the autopsy findings. Within these 76 study cases, a total of 124 myocardial lesions were detected on pmMRI (chronic: 25; subacute: 16; acute: 30; and peracute: 53). Chronic, subacute, and acute infarction cases correlated excellently to the myocardial findings on autopsy. Peracute infarctions (age range: minutes to approximately 1 h) were not visible on macroscopic autopsy or histological examination. Peracute infarction areas detected on pmMRI could be verified in targeted histological investigations in 62.3% of cases and could be related to a matching coronary finding in 84.9%. A total of 15.1% of peracute lesions on pmMRI lacked a matching coronary finding but presented with severe myocardial hypertrophy or cocaine intoxication facilitating a cardiac death without verifiable coronary stenosis. CONCLUSIONS: 3-T pmMRI visualizes chronic, subacute, and acute myocardial infarction in situ. In peracute infarction as a possible cause of sudden cardiac death, it demonstrates affected myocardial areas not visible on autopsy. pmMRI should be considered as a feasible post-mortem investigation technique for the deceased patient if no consent for a clinical autopsy is obtained.

Automatic quality assessment in structural brain magnetic resonance imaging

MRI has evolved into an important diagnostic technique in medical imaging. However, reliability of the derived diagnosis can be degraded by artifacts, which challenge both radiologists and automatic computer-aided diagnosis. This work proposes a fully-automatic method for measuring image quality of three-dimensional (3D) structural MRI. Quality measures are derived by analyzing the air background of magnitude images and are capable of detecting image degradation from several sources, including bulk motion, residual magnetization from incomplete spoiling, blurring, and ghosting. The method has been validated on 749 3D T(1)-weighted 1.5T and 3T head scans acquired at 36 Alzheimer's Disease Neuroimaging Initiative (ADNI) study sites operating with various software and hardware combinations. Results are compared against qualitative grades assigned by the ADNI quality control center (taken as the reference standard). The derived quality indices are independent of the MRI system used and agree with the reference standard quality ratings with high sensitivity and specificity (>85%). The proposed procedures for quality assessment could be of great value for both research and routine clinical imaging. It could greatly improve workflow through its ability to rule out the need for a repeat scan while the patient is still in the magnet bore.

The effect of workplace smoking bans on heart rate variability and pulse wave velocity of non-smoking hospitality workers

OBJECTIVES: To investigate the effect of a change in second-hand smoke (SHS) exposure on heart rate variability (HRV) and pulse wave velocity (PWV), this study utilized a quasi-experimental setting when a smoking ban was introduced. METHODS: HRV, a quantitative marker of autonomic activity of the nervous system, and PWV, a marker of arterial stiffness, were measured in 55 non-smoking hospitality workers before and 3-12 months after a smoking ban and compared to a control group that did not experience an exposure change. SHS exposure was determined with a nicotine-specific badge and expressed as inhaled cigarette equivalents per day (CE/d). RESULTS: PWV and HRV parameters significantly changed in a dose-dependent manner in the intervention group as compared to the control group. A one CE/d decrease was associated with a 2.3 % (95 % CI 0.2-4.4; p = 0.031) higher root mean square of successive differences (RMSSD), a 5.7 % (95 % CI 0.9-10.2; p = 0.02) higher high-frequency component and a 0.72 % (95 % CI 0.40-1.05; p < 0.001) lower PWV. CONCLUSIONS: PWV and HRV significantly improved after introducing smoke-free workplaces indicating a decreased cardiovascular risk.

Magnetic resonance imaging overestimates ferumoxide-labeled stem cell survival after transplantation in the heart.

BACKGROUND: Stem cell labeling with iron oxide (ferumoxide) particles allows labeled cells to be detected by magnetic resonance imaging (MRI) and is commonly used to track stem cell engraftment. However, the validity of MRI for distinguishing surviving ferumoxide-labeled cells from other sources of MRI signal, for example, macrophages containing ferumoxides released from nonsurviving cells, has not been thoroughly investigated. We sought to determine the relationship between the persistence of iron-dependent MRI signals and cell survival 3 weeks after injection of syngeneic or xenogeneic ferumoxides-labeled stem cells (cardiac-derived stem cells) in rats. METHODS AND RESULTS: We studied nonimmunoprivileged human and rat cardiac-derived stem cells and human mesenchymal stem cells doubly labeled with ferumoxides and beta-galactosidase and injected intramyocardially into immunocompetent Wistar-Kyoto rats. Animals were imaged at 2 days and 3 weeks after stem cell injection in a clinical 3-T MRI scanner. At 2 days, injection sites of xenogeneic and syngeneic cells (cardiac-derived stem cells and mesenchymal stem cells) were identified by MRI as large intramyocardial signal voids that persisted at 3 weeks (50% to 90% of initial signal). Histology (at 3 weeks) revealed the presence of iron-containing macrophages at the injection site, identified by CD68 staining, but very few or no beta-galactosidase-positive stem cells in the animals transplanted with syngeneic or xenogeneic cells, respectively. CONCLUSIONS: The persistence of significant iron-dependent MRI signal derived from ferumoxide-containing macrophages despite few or no viable stem cells 3 weeks after transplantation indicates that MRI of ferumoxide-labeled cells does not reliably report long-term stem cell engraftment in the heart.

Magnetism of isolated Mn12 single-molecule magnets detected by magnetic circular dichroism: Observation of spin tunneling with a magneto-optical technique

We report magnetic and magneto-optical measurements of two Mn12 single-molecule magnet derivatives isolated in organic glasses. Field-dependent magnetic circular dichroism (MCD) intensity curves (hysteresis cycles) are found to be essentially identical to superconducting quantum interference device magnetization results and provide experimental evidence for the potential of the optical technique for magnetic characterization. Optical observation of magnetic tunneling has been achieved by studying the decay of the MCD signal at weak applied magnetic field

Impact of the Advisa MRI pacing system on the diagnostic quality of cardiac MR images and contraction patterns of cardiac muscle during scans: Advisa MRI randomized clinical multicenter study results.

BACKGROUND: The Advisa MRI system is designed to safely undergo magnetic resonance imaging (MRI). Its influence on image quality is not well known. OBJECTIVE: To evaluate cardiac magnetic resonance (CMR) image quality and to characterize myocardial contraction patterns by using the Advisa MRI system. METHODS: In this international trial with 35 participating centers, an Advisa MRI system was implanted in 263 patients. Of those, 177 were randomized to the MRI group and 150 underwent MRI scans at the 9-12-week visit. Left ventricular (LV) and right ventricular (RV) cine long-axis steady-state free precession MR images were graded for quality. Signal loss along the implantable pulse generator and leads was measured. The tagging CMR data quality was assessed as the percentage of trackable tagging points on complementary spatial modulation of magnetization acquisitions (n=16) and segmental circumferential fiber shortening was quantified. RESULTS: Of all cine long-axis steady-state free precession acquisitions, 95% of LV and 98% of RV acquisitions were of diagnostic quality, with 84% and 93%, respectively, being of good or excellent quality. Tagging points were trackable from systole into early diastole (360-648 ms after the R-wave) in all segments. During RV pacing, tagging demonstrated a dyssynchronous contraction pattern, which was not observed in nonpaced (n = 4) and right atrial-paced (n = 8) patients. CONCLUSIONS: In the Advisa MRI study, high-quality CMR images for the assessment of cardiac anatomy and function were obtained in most patients with an implantable pacing system. In addition, this study demonstrated the feasibility of acquiring tagging data to study the LV function during pacing.

14.1T magnetic resonance spectroscopic evaluation of metabolic changes in the mouse striatum following transient middle cerebral artery occlusion

Magnetic resonance imaging (MRI) and spectroscopy (MRS) allow establishing theanatomical evolution and neurochemical profiles of ischemic lesions. However onlylimited MRS studies have been reported to-date in mice due to the challenges ofMRS in small organs. The aim of the current work was to study the neurochemicaland imaging sequelae of ischemic stroke in a mouse model in a horizontal bore14.1 Tesla system.ICR-CD1 mice were subjected to 30 minute transient middle cerebral artery occlusion.The extent of the lesion was determined by MRI. The neurochemical profileconsisting of the concentrations of 22 metabolites was measured longitudinallyfollowing the recovery from ischemia at 3, 8 and 24h in the striatum.Our model produced very reproducible striatal lesions which began to appear onT2-weighted images 8h after ischemia. At 24h, they were well established andtheir size correlated with lesions measured by histology. Profound changes couldbe observed in the neurochemical profiles of the core of the striatal lesions as earlyas 3h post-ischemia, in particular, we observed elevated lactate levels, decreases inthe putative neuronal marker N-acetyl-aspartate and in glutamate, and a transienttwo-fold glutamine increase, likely linked to excitotoxic release of glutamate andconversion to glutamine. With further ischemia evolution, other changes appearedat later time-points, mainly decreases of metabolites, consistent with disruption ofcellular function. It is interesting to note that glutamine tended to return to basallevels at 24h.We conclude that early changes in markers of energy metabolism, glutamate excitotoxicityand neuronal viability can be detected with high precision non-invasively inmice following stroke. Such investigations should lead to a better understanding andinsight into the sequential early changes in the brain parenchyma after ischemia,which could be used e.g. for identifying new targets for neuroprotection.

Gadolinium-enhanced pulmonary magnetic resonance angiography in the diagnosis of acute pulmonary embolism: a prospective study on 48 patients.

OBJECTIVE: Gadolinium-enhanced pulmonary magnetic resonance angiography (MRA) can be an option in patients with a history of previous adverse reaction to iodinated contrast material and renal insufficiency. Radiation is also avoided. The aim of this study is to prospectively compare the diagnostic value of MRA with that of a diagnostic strategy, taking into account catheter angiography, computed tomography angiography (CTA), and lung scintigraphy [ventilation-perfusion (VQ)]. MATERIAL AND METHODS: Magnetic resonance angiography was done in 48 patients with clinically suspected pulmonary embolism (PE) using fast gradient echo coronal acquisition with gadolinium. Interpretation was done with native coronal images and multiplanar maximum intensity projection reconstructions. Results were compared to catheter angiography (n=15), CTA (n=34), VQ (n=45), as well as 6-12 months clinical follow-ups, according to a sequenced reference tree. RESULTS: The final diagnosis of PE was retained in 11 patients (23%). There were two false negatives and no false positive results with MRA. Computed tomography angiography resulted in no false negatives or false positives. Magnetic resonance angiography had a sensitivity of 82% and a specificity of 100%. CONCLUSION: In our study, pulmonary MRA had a sensitivity of 82% and a specificity of 100% for the diagnosis of PE, with slightly less sensitivity than CTA. In the diagnostic algorithm of PE, pulmonary MRA should be considered as an alternative to CTA when iodine contrast injection or radiation is a significant matter.

Pulse oximetry and transcutaneous oxygen tension for detection of hypoxemia in critically ill infants and children.

We tested the performance of transcutaneous oxygen monitoring (TcPO2) and pulse oximetry (tcSaO2) in detecting hypoxia in critically ill neonatal and pediatric patients. In 54 patients (178 data sets) with a mean age of 2.4 years (range 1 to 19 years), arterial saturation (SaO2) ranged from 9.5 to 100%, and arterial oxygen tension (PaO2) from 16.4 to 128 mmHg. Linear correlation analysis of pulse oximetry vs measured SaO2 revealed an r value of 0.95 (p less than 0.001) with an equation of y = 21.1 + 0.749x, while PaO2 vs tcPO2 showed a correlation coefficient of r = 0.95 (p less than 0.001) with an equation of y = -1.04 + 0.876x. The mean difference between measured SaO2 and tcSaO2 was -2.74 +/- 7.69% (range +14 to - 29%) and the mean difference between PaO2 and tcPO2 was +7.43 +/- 8.57 mmHg (range -14 to +49 mmHg). Pulse oximetry was reliable at values above 65%, but was inaccurate and overestimated the arterial SaO2 at lower values. TcPO2 tended to underestimate the arterial value with increasing PaO2. Pulse oximetry had the best sensitivity to specificity ratio for hypoxia between 65 and 90% SaO2; for tcPO2 the best results were obtained between 35 and 55 mmHg PaO2.

Avalanche-like vortex penetration driven by pulsed microwave fields in an epitaxial LaSrCuO thin film

Different vortex penetration regimes have been registered in the output voltage signal of a magnetometer when single microwave pulses are applied to an epitaxial overdoped La2− x Sr x CuO4 thin film in a perpendicular dc magnetic field. The onset of a significant variation in the sample magnetization which exists below threshold values of temperature, dc magnetic field, and pulse duration is interpreted as an avalanche-type flux penetration. The microwave contribution to the background electric field suggests that the nucleation of this fast vortex motion is of electric origin, which also guarantees the occurrence of vortex instabilities under adiabatic conditions via the enhancement of the flux flow resistivity. Flux creep phenomena and heat transfer effects act as stabilizing factors against the microwave-pulse-induced fast flux diffusion.

Direct Observation of Magnetic Metastability in Individual Iron Nanoparticles

X-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism is used to study the magnetic properties of individual iron nanoparticles with sizes ranging from 20 down to 8 nm. While the magnetocrystalline anisotropy of bulk iron suggests superparamagnetic behavior in this size range, ferromagnetically blocked particles are also found at all sizes. Spontaneous transitions from the blocked state to the superparamagnetic state are observed in single particles and suggest that the enhanced magnetic energy barriers in the ferromagnetic particles are due to metastable, structurally excited states with unexpected life times

Direct Observation of Magnetic Metastability in Individual Iron Nanoparticles

X-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism is used to study the magnetic properties of individual iron nanoparticles with sizes ranging from 20 down to 8 nm. While the magnetocrystalline anisotropy of bulk iron suggests superparamagnetic behavior in this size range, ferromagnetically blocked particles are also found at all sizes. Spontaneous transitions from the blocked state to the superparamagnetic state are observed in single particles and suggest that the enhanced magnetic energy barriers in the ferromagnetic particles are due to metastable, structurally excited states with unexpected life times