Scaling of transverse nuclear magnetic relaxation due to magnetic nanoparticle aggregation

The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time T2 of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between T2 and details of the aggregate. We find that in the motional averaging regime T2 scales as a power law with the number N of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension d of the aggregates. We find T2 N^{-0.44} for aggregates with d=2.2, a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, T2 is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times.Comment: 20 pages, 3 figures, submitted to Journal of Magnetism and Magnetic Material

A model based on clinical parameters to identify myocardial late gadolinium enhancement by magnetic resonance in patients with aortic stenosis: An observational study

Objective With increasing age, the prevalence of aortic stenosis grows exponentially, increasing left heart pressures and potentially leading to myocardial hypertrophy, myocardial fibrosis and adverse outcomes. To identify patients who are at greatest risk, an outpatient model for risk stratification would be of value to better direct patient imaging, frequency of monitoring and expeditious management of aortic stenosis with possible earlier surgical intervention. In this study, a relatively simple model is proposed to identify myocardial fibrosis in patients with a diagnosis of moderate or severe aortic stenosis. Design Patients with moderate to severe aortic stenosis were enrolled into the study; patient characteristics, blood work, medications as well as transthoracic echocardiography and cardiovascular magnetic resonance were used to determine potential identifiers of myocardial fibrosis. Setting The Royal Brompton Hospital, London, UK Participants One hundred and thirteen patients in derivation cohort and 26 patients in validation cohort. Main outcome measures Identification of myocardial fibrosis. Results Three blood biomarkers (serum platelets, serum urea, N-terminal pro-B-type natriuretic peptide) and left ventricular ejection fraction were shown to be capable of identifying myocardial fibrosis. The model was validated in a separate cohort of 26 patients. Conclusions Although further external validation of the model is necessary prior to its use in clinical practice, the proposed clinical model may direct patient care with respect to earlier magnetic resonance imagining, frequency of monitoring and may help in risk stratification for surgical intervention for myocardial fibrosis in patients with aortic stenosis

Magnetic resonance imaging: Physics basics for the cardiologist

Magnetic resonance imaging physics can be a complex and challenging topic for the practising cardiologist. Its evolving nature and the increasing number of novel sequences used in clinical scanning have been topics of excellent reviews; however, the basic understanding of physics underlying the creation of images remains difficult for many cardiologists. In this review, we go back to the basic physics theories underpinning magnetic resonance and explain their application and use in achieving good quality cardiac imaging, whilst describing established and novel magnetic resonance sequences. By understanding these basic principles, it is anticipated that cardiologists and other health professionals will then appreciate more advanced physics manuscripts on cardiac scanning and novel sequences

Oleic acid and peanut oil high in oleic acid reverse the inhibitory effect of insulin production of the inflammatory cytokine TNF-α both in vitro and in vivo systems

<p>Abstract</p> <p>Background</p> <p>Chronic inflammation is a key player in pathogenesis. The inflammatory cytokine, tumor necrosis factor-alpha is a well known inflammatory protein, and has been a therapeutic target for the treatment of diseases such as Rheumatoid Arthritis and Crohn's Disease. Obesity is a well known risk factor for developing non-insulin dependent diabetes melitus. Adipose tissue has been shown to produce tumor necrosis factor-alpha, which has the ability to reduce insulin secretion and induce insulin resistance. Based on these observations, we sought to investigate the impact of unsaturated fatty acids such as oleic acid in the presence of TNF-α in terms of insulin production, the molecular mechanisms involved and the in vivo effect of a diet high in oleic acid on a mouse model of type II diabetes, KKA^y.</p> <p>Methods</p> <p>The rat pancreatic beta cell line INS-1 was used as a cell biological model since it exhibits glucose dependent insulin secretion. Insulin production assessment was carried out using enzyme linked immunosorbent assay and cAMP quantification with competitive ELISA. Viability of TNF-α and oleic acid treated cells was evaluated using flow cytometry. PPAR-γ translocation was assessed using a PPRE based ELISA system. In vivo studies were carried out on adult male KKA^ymice and glucose levels were measured with a glucometer.</p> <p>Results</p> <p>Oleic acid and peanut oil high in oleic acid were able to enhance insulin production in INS-1. TNF-α inhibited insulin production but pre-treatment with oleic acid reversed this inhibitory effect. The viability status of INS-1 cells treated with TNF-α and oleic acid was not affected. Translocation of the peroxisome proliferator- activated receptor transcription factor to the nucleus was elevated in oleic acid treated cells. Finally, type II diabetic mice that were administered a high oleic acid diet derived from peanut oil, had decreased glucose levels compared to animals administered a high fat diet with no oleic acid.</p> <p>Conclusion</p> <p>Oleic acid was found to be effective in reversing the inhibitory effect in insulin production of the inflammatory cytokine TNF-α. This finding is consistent with the reported therapeutic characteristics of other monounsaturated and polyunsaturated fatty acids. Furthermore, a diet high in oleic acid, which can be easily achieved through consumption of peanuts and olive oil, can have a beneficial effect in type II diabetes and ultimately reverse the negative effects of inflammatory cytokines observed in obesity and non insulin dependent diabetes mellitus.</p

Cardiovascular magnetic resonance:Diagnostic utility and specific considerations in the pediatric population

Cardiovascular magnetic resonance is a non-invasive imaging modality which is emerging as important tool for the investigation and management of pediatric cardiovascular disease. In this review we describe the key technical and practical differences between scanning children and adults, and highlight some important considerations that must be taken into account for this patient population. Using case examples commonly seen in clinical practice, we discuss the important clinical applications of cardiovascular magnetic resonance, and briefly highlight key future developments in this field

Immediate post-operative effects of tracheotomy on respiratory function during mechanical ventilation

INTRODUCTION: Tracheotomy is widely performed in the intensive care unit after long-term oral intubation. The present study investigates the immediate influence of tracheotomy on respiratory mechanics and blood gases during mechanical ventilation. METHODS: Tracheotomy was performed in 32 orally intubated patients for 10.5 ± 4.66 days (all results are means ± standard deviations). Airway pressure, flow and arterial blood gases were recorded immediately before tracheotomy and half an hour afterwards. Respiratory system elastance (E(rs)), resistance (R(rs)) and end-expiratory pressure (EEP) were evaluated by multiple linear regression. Respiratory system reactance (X(rs)), impedance (Z(rs)) and phase angle (φ(rs)) were calculated from E(rs )and R(rs). Comparisons of the mechanical parameters, blood gases and pH were performed with the aid of the Wilcoxon signed-rank test (P = 0.05). RESULTS: E(rs )increased (7 ± 11.3%, P = 0.001), whereas R(rs )(-16 ± 18.4%, P = 0.0003), X(rs )(-6 ± 11.6%, P = 0.006) and φ (rs )(-14.3 ± 16.8%, P = <0.001) decreased immediately after tracheotomy. EEP, Z(rs), blood gases and pH did not change significantly. CONCLUSION: Lower R(rs )but also higher E(rs )were noted immediately after tracheotomy. The net effect is a non-significant change in the overall R(rs )(impedance) and the effectiveness of respiratory function. The extra dose of anaesthetics (beyond that used for sedation at the beginning of the procedure) or a higher FiO(2 )(fraction of inspired oxygen) during tracheotomy or aspiration could be related to the immediate elastance increase