At present, the cardiovascular magnetic resonance imaging (MRI) is an important imaging technique used for investigation of heart structure and function. On the other hand, in this type of a non-invasive examining device, the pulsating current in the gradient coil system generates mechanical vibration and acoustic noise. Such a vibration is often accompanied by a local heating effect which can be measured by a contactless method using a thermal imaging camera. The shape of the peripheral pulse wave of the photoplethysmography (PPG) signal reflects the current state of a human cardiovascular system including changes in the arterial stiffness, the arterial blood pressure, and the heart rate. These parameters can be also used for detection of the stress effect during examination in the MRI device.

The quality of the sensed PPG signals and the determined PPG wave features depend also on the actual state of the skin at the position of the optical sensor. Human age and gender as well as the skin color and the temperature of the skin surface can have influence on the PPG signal, too. For precise determination of PPG wave parameters, the current temperature should be measured at the same time as the PPG signal is sensed.

This paper describes the process of design, realization, and testing of a special prototype of a wearable PPG sensor with the contact thermometer to carry out a detailed measurement of the skin temperature in the place where the optical part of the PPG sensor touches a finger/wrist. To enable proper and safe function in the weak magnetic field environment of the MRI device, the whole wearable PPG sensor must consist of non-ferromagnetic materials and all parts must be fully shielded by aluminum boxes against the radiofrequency disturbance.