IntroductionThe assessment of activation and energetics in exercising muscle has been abundantly performed in high field magnetic environment1-3 using MR imaging (MRI) and 31P spectroscopy (31P-MRS). In order to control and measure exercise intensity, dedicated MR-compatible ergometers have been built4-6 and kinetic parameters of the movement have been assayed with specific sensors. For most of the setups reported so far, signals were transmitted with wires7,8 related to potential risks of electromagnetic interferences (EMI). More recently and with the aim of limiting EMI, a research group reported the utilization of an optical sensor9 which can be directly transmitted with an optical fiber where other used the conversion of analog signal from a conventional sensor to an optical transmission.5,10 However, these kinds of setup have never been designed for multiple sensors in order to assess multiple kinetic parameters leading to an accurate quantification of muscular work during exercise.In the present study, we report results related to an original setup allowing a multiplexed optical transmission of signals from multiple analog sensors connected to MR-compatible ergometer. We demonstrated that multiple analog signals can be simultaneously transmitted via a single optical fiber.MethodsTwo communication units connected by an optical fiber were designed to convert and transmit analog signals measured by sensors connected to a MR-compatible ergometer previously described.6 A schematic representation of the experimental design is displayed in Figure 1. Briefly, the unit in the MR scanner room digitally encodes the different analogic signals (forces, displacements and angle) and converts them into a multiplexed code using an Arduino-based microcontroller. Then the composite signal is transmitted (Steps #1 and #2) via a single optical fiber (Step #3) to the second unit located inside the control room. The second unit handles the composite signal demultiplexing and the digital-to-analog conversion, using another Arduino-based microcontroller (Steps #4).In order to assess the accuracy of our measurements, we compared the analog signals at the sensors level and those from the output transducer. The corresponding results were analyzed with a Pearson product-moment correlation (r). A linear adjustment (calibration) between the electric signal and the calibrated measures was assessed with a determination coefficient R2.Analog signals were recorded during a 31P-MRS investigation performed in a single subject in a 3T super-conducting whole-body scanner (Siemens Verio, Erlangen, Germany). A 31P-1H surface coil was positioned under the right quadriceps femoris muscle group. Fully-relaxed (TR = 15s, NEX = 1, Number of Scans = 6) 31P spectra were recorded at rest while analog signals were measured during a submaximal exercise. The signal-to-noise (SNR) of 31P spectra and the PCr/ATP ratios were quantified.ResultsThe correlations between analog signals measured on both sides of the optical transmission were very high (r > 0.99, Figure 2). The very high determination coefficients found for each channel (R² > 0.99) supported the accuracy of the corresponding measurements (Figure 2).The SNR of the 31P MR spectra was very large (93 ± 9) while the averaged of PCr/ATP value was 3.9 ± 0.5 (Figure 4).DiscussionWe designed an optical-based electronic device which allowed accurate and reliable analog measurements in a magnetic environment. Shape and amplitude of mechanical signals were similar to those obtained in previous studies.6,11 The SNR of the 31P MR spectra and the metabolic ratio were also in accordance with those previously reported.12,13 In addition, our system considerably reduced wires congestion and potential electric/magnetic signal crosstalk. No mutual influence of the electric and magnetic signals was found thereby demonstrating the ability of our system to assess mechanical parameters in exercising muscle within a magnetic environment.ConclusionOur electronic device based on a multiplexed transmission via an optical fiber allows an accurate conversion/transmission of several analog signals related to human movement kinetics and measured in a high-field magnetic environment.Read less <