Portable NMR-Based Sensors in Medical Diagnosis

Nuclear magnetic resonance (NMR) is a well-established analytical method used for qualitative and quantitative analyses in various areas and applications. It utilizes a phenomenon where nuclei of a certain atom is resonating at a specific secondary oscillating magnetic field under a strong static magnetic field. The energy absorbed during resonance is highly specific and governed by the micro magnetic environment of the nuclei. During the early stage of development, NMR analyses were performed in laboratory by placing the sample of interest inside a strong stationary magnet. Then it followed by monitoring the absorption frequency occurred on the secondary radio-wave directed to the sample. In order to obtain high resolution in the absorption frequency, high magnetic field is required and often generated using superconductor wire surrounded with cooling coils. Although the configuration produces accurate results, the instrument is rather large, heavy, and non-portable. This has made the practical utilization less possible for on-site applications or for samples having sizes larger that the core of the permanent magnet. Continuous development based on the fundamental principle of NMR has resulted in great advancement in hardware and the detection sensitivity. One of the most remarkable achievements will be the development of portable NMR-based sensors. This class of sensor is far more flexible due to its smaller size and suits on-site in situ measurements. Furthermore, such sensors are cheaper to develop and less costly to maintain as compared to the conventional instruments. However, the sensors have lower resolution as due the weaker magnetic field generated from smaller permanent magnets. Despite this, the results recorded are still significantly useful. Data analysis and optimization of the sensor configuration can be employed to achieve better resolution. For instance, the NMR-MOUSE is one of the portable NMR-based sensor types that can be used for bio-imaging and characterization of polymers. This chapter discusses some fundamental developments of the portable NMR-based sensors and its practical application in the field of medical diagnosis. Future prospects and challenges faced in this area are highlighted.

Keywords: Cancer, drug delivery, echo, implant, in situ monitoring, magnet, magnet field, medical diagnosis, miniature NMR, NMR imaging, NMR-MOUSE, nuclear magnetic resonance, pathogen, portable, relaxation, sensor, skin, tendon, tissue, tumour.