Flow Rate Estimation Based on Magnetic Particle Detection Using a Miniatured High-Sensitivity OPM

The efficacy of magnetic particles (MPs) in cancer treatments prompts the investigation into MP detection methods. However, due to their microsize, MPs produce weak magnetic field signals that necessitate highly sensitive measurements to extract useful information. In this study, we introduce a technique for detecting individual MPs using a compact optically pumped magnetometer (OPM). A noninvasive and radiation-free flow rate estimation method based on the OPM is further proposed, demonstrating its clinical potential. A miniaturized dual-beam spin-exchange relaxation-free (SERF) OPM is fabricated for the system, achieving a remarkable sensitivity of 8.6 fT/Hz ${}^{\text {1/2}}$ in a compact volume of 7.7 cm3. The magnetometer accurately measures the dynamic magnetic fields, enabling the detection of translational and rotational motions of MPs in fluid flow. The particle rotation frequencies are extracted from magnetometer responses using the continuous wavelet transform (CWT), revealing a positive correlation between the flow rate and rotation frequency. Besides, CWT effectively mitigates the cardiac magnetic interference that may arise during in vivo measurements, showcasing its high applicability in processing MP signals. Finally, 90.2% of the flow rates are correctly predicted by a regression tree trained with mean and standard deviation as predictors. Overall, this highly sensitive system facilitates noninvasive and rapid flow estimation, validating promising potential for biomedical research and clinical practice.