Conducting fluids flowing transversely to a magnetic field develop induced currents due to Lorentz force. The induced currents interacting with the transverse magnetic field produce body forces on the fluid resulting in an increase in pressure gradient in the direction of fluid flow [1]. Human blood is an electrically conductive liquid therefore it is reasonable to assume the existence of forces acting on it as it flows through the human vascular system, especially when exposed to a magnetic field strength of 10.5T. In a previous work [2], pressure calculations were made using a mathematical model for conducting liquids flowing in non-conducting, circular tubes with flow transverse to a magnetic field. An upper bound for the magneto-hydrodynamic vascular pressure in a human vessel exposed to a 10-T magnetic field was calculated. The experimental studies were also performed but they were limited to in-vitro measurements at 4.7 T. Other work investigated the effects of static magnetic field exposures (up to 8T) on vital signs of normal human volunteers [3]. Systolic/Diastolic blood pressures (BP) were measured non-invasively using pressure cuffs. Statistically significant but clinically insignificant change of 3.6mmHg increase was found in the Systolic BP over the 8.0 T range. In this work we present our preliminary data regarding invasive blood pressure measurement in anesthetized pigs at 10.5 T.

We measured blood pressure and heart rate in 4 pigs (3 Male,1 Female) in our experiments. We injected the pigs with Telazol (5-10 mg/kg)+Xylazine(1-3 mg/kg). Then we intubated the pigs and induced anesthesia by providing isoflurane (~1.5%) in 50% air and 50% oxygen mixture. Then we made an incision on the neck and inserted a pressure transducer (~ 30 cm) in the carotid artery, sewed and closed the tissue around the sensor securely. We used A&D Instruments Pressure Sensor System for all measurements consisting of a BP Transducer, a Quad Bridge Amplifier and Data Acquisition Hardware (Power Lab). We calibrated the sensor outside the scanner room using a pressure gauge calibration kit and a sphygmomanometer. We recorded the data using a single channel with a sampling rate of 4 kHz. We did not perform digital filtering during the acquisition. We detected the peak locations of the pressure signal and used it to calculate mean and standard deviation of the systolic/diastolic blood pressure as well as the heart rate. We collected the data from each pig in 3 sets of measurements: 1) on the procedure table 2) in the scanner room, on the table, out of the bore 3) inside the bore (land-marked on the head). We used the 10.5 T magnet in CMRR, which is a 88 cm Agilent Magnet equipped with Siemens whole body gradient and console. In two of the experiments, we performed additional measurements by land-marking the pigs at different locations (head vs chest ). Duration of data acquisition varied between 10 minutes to 30 minutes. All measurements were performed in supine position. Within-condition between-pig mean and standard deviation of the data were used to calculate the 95% confidence interval for the mean BP and the mean heart rate. T-distribution is assumed for confidence interval calculations. Figure 1 shows the waveform obtained by the data acquisition system. The waveform was later analyzed to calculate the systolic and diastolic pressures and hear rate. Figure 2 shows the mean value of the systolic/ diastolic blood pressures and the heart rate of each pig obtained during each individual experimental conditions explained above. The error bars denote the within-condition within-pig standard deviation of the data observed during each specific experiment. The mean values of the same parameters (averaged across pigs) are shown in Figure 3 . Considering set 2 and set 3 , the changes in the mean value of systolic BP, diastolic BP and the heart rate were 1.6% ,5.5% and 2.02 % respectively. Figure 4 shows the width of the confidence interval (for mean systolic BP) based on the standard deviation obtained for our 3 experimental conditions with respect to increasing the number of pigs. As expected, by increasing the number of pigs the confidence interval can be diminished. Finally Figure 5 shows the change in the blood pressure in two pigs when they are land-marked at head vs chest inside the bore.Initial data do not show any significant change in blood pressure in anesthetized pigs due to whole body 10.5 T exposure. Additional experiments may be required to reduce the confidence interval of the current results and make more definite statements about static field safety at 10.5 T.