Electrical Impedance Myography is a none or minimally invasive technique for assessing muscle condition. It provides a quantitative index of muscle health serving as a diagnostic tool or biomarker. So technique is quantitative, rapid, and does not require detailed image analysis so it can serve as a convenient biomarker of disease status in a therapeutic study.
Another useful aspect of Electrical Impedance Myography is that it is sensitive to most types of skeletal muscle pathology. Abnormal Electrical Impedance Myography values can reveal underlying histological alterations. For surface measurements, the skin needs to be prepared well.
One has to become familiar with the appearance of contact impedance artifacts and remeasure if needed. To begin, place the mouse on the bench in a prone position after confirming the absence of response during the toe pinching test. Place the animal's leg to be analyzed at a 45 degree angle with the knee extended and secure the foot with medical tape.
Trim the fur overlaying the gastrocnemius muscle using a hair clipper, and apply a thick layer of depilatory cream over the animal's skin for one minute. Remove the depilatory agent using the saline saturated gauze and repeat this process up to three times until all the fur overlaying the gastrocnemius muscle is removed. Connect the surface array to the Electrical Impedance Myography device and let the electrodes rest on a piece of gauze soaked in saline solution.
Place the surface array directly on the skin, over the gastrocnemius muscle oriented longitudinally to the muscle fibers. Check for appropriate contact by checking that all the bars appear green on the software with the stability of the 50 kilohertz resistance, reactance, and phase values. Then acquire the Electrical Impedance Myography measurements.
Rotate the surface array by 90 degrees and reposition it on the skin over the gastrocnemius to obtain the transverse measurements. Connect the needle array to the Electrical Impedance Myography device and let the electrode array rest in a weighing boat containing saline solution. Then check for connectivity and signal stability.
Place the needle array in a longitudinal position compared to the my fibers, and press it firmly into the skin until all the needles penetrate the skin and the underlying muscle up to the plastic guard on the array. Acquire the data. Gently remove the array and reinsert it through the skin and into the muscle at a 90 degree angle relative to the first measurement in the transverse direction.
Then acquire this data. For Ex Vivo Electrical Impedance Myography, prepare the ex vivo dielectric cell, add saline solution to the chamber and connect the cell to the Electrical Impedance Myography device to obtain the reference values. Place the gastrocnemius muscle on a sheet of dental wax and section it using a razor blade in a ruler to obtain a 10 millimeter by 10 millimeter section for rats.
And five millimeter by five millimeter section for mice from the center of the gastrocnemius muscle. Gently place the gastrocnemius in the dialectric cells using tweezers, making sure the fibers are oriented longitudinally and the muscle is entirely in contact with the metal electrodes. Attach the top part of the dialectric cell and insert two monopolar needles of 26 gauge into the two holes.
Connect the wires from the Electrical Impedance Myography device to the ex vivo cell in the order mentioned in the manuscript. Then acquire the longitudinal measurement. Open the dialectric cell and reorient the muscle in the transverse direction by rotating it 90 degrees.
Reattach the top of the dialectric cell and acquire the transverse measurement. Electrical Impedance Myography can be obtained in many conditions with surface in vivo arrays, needle in vivo arrays, and ex vivo dialectric cells. Representative curves for surface E I M are shown for phase, reactance and resistance for longitudinal in transverse measurements.
Some irregularities, which are typically related to contact issues can result in extreme values observed at low frequencies. A graph showing the reactance as a resistance function and longitudinal and transverse directions is displayed. Good skin preparation is crucial for surface measurements.
There can be no fur remaining. Repeat fur removal, saline application and measurement if contact artifact is identified. Electrical Impedance Myography allows enhanced assessment of disease status and therapy effects in rodent models helping to speed the identification of promising new therapies for the treatment of neuromuscular diseases.
