Abstract
Magnetic microrobots offer promising potential for minimally invasive medical procedures, enabling targeted drug delivery, microsurgery, and precise diagnostics in previously inaccessible body regions. However, their clinical translation faces a critical challenge: real-time visualization and tracking in biological environments. The integration of ultrasound and photoacoustic imaging presents a potential solution, but significant innovation is required to address challenges in electromagnetic compatibility, light delivery, and system miniaturization.This thesis presents the systematic development of advanced imaging systems addressing these challenges through multiple generations of innovation. The initial system successfully integrated ultrasound and photoacoustic imaging with electromagnetic actuation, incorporating gold nanostars as contrast agents to enhance the photoacoustic signal intensity in blood-rich environments three times, achieving maximum lateral resolutions of 362.8 and 573.3 μm for photoacoustic and ultrasound imaging, respectively, while maintaining electromagnetic compatibility.
Building upon this foundation, an advanced 3D autofocusing system was developed that integrates a servo-controlled platform with precise electromagnetic interference management to maintain 10 Hz imaging performance. This system introduced optimized microrobot clusters with enhanced dual-modality visibility. A novel automated tracking algorithm that leverages the complementary strengths of ultrasound and photoacoustic imaging is implemented for robust 3D navigation.
Further advancements were realized using an illumination-adjustable imaging system incorporating a novel pushrod mechanism for real-time laser focus adjustment. This innovation provided precise control over light delivery across an 8–35 mm focusing range while achieving a minimum lateral resolution of 436.3 μm for harmonic ultrasound. The system effectively addressed critical limitations in photoacoustic excitation and artifact management during in vivo tracking.
System miniaturization was explored using flexible printed circuit board technology, developing a novel transducer design that achieved 80.7% bandwidth at a 7.8 MHz center frequency by using optimized acoustic matching layers with a PI + 18 μm copper structure. Integrating medical-grade adhesive coupling achieved transmission rates of up to 85.96%, eliminating the need for conventional coupling gel. Although manufacturing constraints affect spatial resolution, implementing a dual-row array design enables simultaneous multiplane imaging, offering unique capabilities for complex navigation tasks.
On the basis of these four major system developments (i.e., initial dual-modality integration, a 3D autofocusing system, an illumination-adjustable design, and a flexible PCB-based transducer), this thesis presents comprehensive solutions to fundamental challenges in microrobot imaging and navigation. Each generation addressed specific limitations while advancing toward clinical viability: enhanced visibility in blood-rich environments, automated 3D tracking capabilities, optimized light delivery for deep tissue imaging, and system miniaturization. These innovations collectively establish a robust foundation for translating magnetic microrobot technology into practical medical applications, particularly for minimally invasive procedures requiring precise navigation in complex biological environments.
| Date of Award | 13 Jan 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Dong SUN (Supervisor) & Gang Gary FENG (Supervisor) |
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