Our results suggest that the COSLOF index could be used as a noninvasive quantitative marker for the preclinical stage of AD.

Wavelength effects influence radiofrequency (RF) power deposition distributions and limit magnetic resonance (MR) medical applications at very high magnetic fields. The power depositions in spherical saline gel phantoms were deduced from proton resonance shift thermal maps at both 1.5 T and 3.0 T over a range of conductivities. Phase differences before and after RF heating were measured for both a quadrature head coil and a circular surface coil. A long echo time (TE) pulse sequence with a 3D phase unwrap algorithm provided increased thermal sensitivity. The measured thermal maps agreed with a model of eddy-current heating by circularly polarized oscillating RF fields in a conducting dielectric sphere. At 3.0 T, thermal maps were acquired with a <0.32°C temperature rise at 4 W. Proton resonance shift thermal maps provided a measure of hot spots in very-high-field MR imaging (MRI), in which both the phase sensitivity and signalto-noise ratio (SNR) were increased. The method provides a means of studying the heat distribution generated by RF coils excited by clinical pulse sequences. MRI thermal mapping provides a means of estimating the radiofrequency (RF) power deposition (1). As the resonance frequency increases, effects from the finite electromagnetic wavelength increasingly influence the power distribution. Measuring the nonuniform power deposition in very-high-field magnetic resonance (MR) systems is an important step in establishing a safe operating environment for fast imaging sequences (2,3). RF fields in the head during a high-field MR exam exhibit wave phenomena (4 -11) similar to those of RF fields interacting with a dielectric sphere-a problem that has been discussed in a number of textbooks (4 -7). The distribution of heat absorbed in a conducting dielectric sphere, and the RF field pattern both depend on the diameter relative to the radiation wavelength. An oscillating magnetic field induces eddy currents that act to reduce the field inside the sphere, as well as displacement currents from the dielectric properties that enhance the field in the center (7). Early low-field MRI systems had a long wavelength compared to the head size. It was argued that eddy-current screening would limit the application of high-field systems (8); however, the first 1.5-T imaging system built in our laboratory had a uniform RF field profile that balanced conductivity screening and dielectric field focusing. At higher field strengths, finite wavelength effects become the dominant phenomenon, and the RF field is observed to peak in the center of the head (9 -11). Tissue conductivity leads to Joule heating, which imposes an imaging limitation described by the specific absorption rate (SAR) that increases with RF frequency. The RF power absorbed in tissue raises the temperature depending on both the tissue conductivity and the mean square electric field induced by the circularly polarized magnetic field. For safety reasons, it is important to establish methods to accurately predict heating during an MR examination. Numerical...

Introduction: Current volume status markers under-perform. Dynamic markers demonstrate improved outcomes in goal directed fluid therapy but maintain validity in a narrow range of clinical parameters. In addition, they assess volume responsiveness over total volume status. Repeated echo assessments may be infeasible. Hypothesis: Intravenous waveform analysis-derived F1 more closely models volume status than current markers in a rat resuscitation model. Methods: Seven Sprague Dawley rats were anesthetized and mechanically ventilated. Pressure transductions occurred via cannulation of the right femoral vein, left femoral artery and right internal jugular vein. Hemorrhage and resuscitation occurred via the left femoral vein. Heparinized rats were bled to 80% of the estimated blood volume (EBV) then resuscitated with their own whole blood in increments of 2% of the EBV until euvolemia was reached. Cardiac output (CO) and left ventricular end diastolic area (LVEDA) were calculated with echocardiography. Fast Fourier transform was performed on venous waveforms to obtain the heart rate linked F1 amplitude. Pearson’s correlation coefficients were compared using Fisher’s Z transformation. Mixed effects modeling goodness-of-fit was assessed with Akaike information criterion (AIC). Significance was set at p=.05. Results: F1 had the strongest correlation with volume status, r= .70, followed by CO, r=.55, LVEDA, r=.55, mean arterial pressure (MAP), r=.50, central venous pressure r= -.02, and pulse pressure variation (PPV), r=.01. When compared, F1 rho was significantly greater than that of all variables except CO and LVEDA, p=.09 and p=.07, respectively. In mixed effects regression, F1 displayed the most significant AIC, -274, followed by CO at -239. Conclusions: The novel marker F1 is strongly correlated with volume status during whole blood resuscitation. F1 may be superior to current markers for directing volume resuscitation therapy.