Medical Signal Analysis

Definition

  • Biosignals are those signals that are generated and transduced from a biological or medical source, and that at any level: molecular, cellular, tissular, organic level. They are primarily acquired for monitoring (detecting or estimating) specific pathological/physiological states for diagnosis and evaluating therapies. Those signals are encountered in the clinic environment, research laboratory, etc. 

Some examples 

  • ECG (or EKG),  ElectroCardioGrams (1D) :                                                                                                                    

A diagnostic test that evaluates heart rhythm and function through a record of the electrical activity of the heart.

The heartbeats because electrical signals are emitted from the right atrium (in a structure called the sinus node) and are transmitted through specific pathways that are distributed throughout the heart, leading to a heartbeat.

This electrical activity can be collected through electrodes that stick to the skin, specifically in the front of the chest and in the arms and legs.                                                                                                                                                                                                                           

The electrical impulses are recorded in the form of lines or curves on graph paper, which translate into the contraction or relaxation of both the atria and the ventricles. This paper record is what is called an electrocardiogram. 

  • EMG, ElectroMioGrams (1D ) :                                                                                                                                                        An electromyogram is a test used to study the function of the peripheral nervous system and the muscles it supplies. Thanks to it, congenital or acquired neuromuscular diseases can be accurately diagnosed and allows to be classified according to their intensity and origin.

The test consists essentially of registering to utilize special electrodes the electrical currents that form in the nerves and muscles when contractions occur. 

  • EOG, ElectroOculoGrams (1D):                                                                                                                                                          The mean transepithelial voltage of bovine Retinal pigment epithelium is 6 millivolts (mV).The electrooculogram (EOG) is an electrophysiological test that measures the existing resting electrical potential between the cornea and Bruch's membrane.

The EOG was described and named by Elwin Marg in 1951. Clinical applications were described first by Geoffrey Arden in 1962, who realized that the most valuable information was the comparison of the amplitudes under light and dark-adapted states (the Arden ratio).

The Arden ratio, the ratio of the Light peak (Lp) to dark trough (Dt) is used to determine the normalcy of the results.  An Arden ratio of 1.80 or greater is normal, 1.65 to 1.80 is subnormal, and < 1.65 is significantly subnormal. 

The analysis

The main idea is to quantify physiologically meaningful interactions among those signals. Current technology allows also the acquisition of multiple channels for a signal, which brings up additional information as well as challenges.

We can use decoding and modeling of specific biological systems among other possibilities of analysis.

We need to convert analog signals to digital numbers, otherwise we cannot display them on digital screens, store them on servers/computers, apply digital filters on them (to remove noise), or make automatic calculations on them, and in general, we cannot evaluate or use them easily.

Personal apreciation

I particularly do not enjoy signal analysis a lot, as it is very centered on the electronic part, although I understand and appreciate the valuable information and knowledge it brings to biomedicine. Same for Medical Image Analysis.