Tremendous advances have been made in technological development of whole body molecular imaging, including PET, SPECT, MRI, bioluminescence, and ultrasound. However, a great unmet need still exists for high resolution imaging of biological processes that occur in the epithelium, the thin layer of tissue where many important cancers originate. Confocal endomicroscopes designed with a fiber bundle are used in the clinic, but they can only create images in the horizontal plane. Imaging in the plane perpendicular to the tissue surface is also important because epithelial cells differentiate in the vertical direction. Subtle changes in normal tissue differentiation patterns can reveal the early expression of cancer biomarkers.
In this work, we present a side-viewing confocal endomicroscope that can collect images in either horizontal or oblique plane using an integrated monolithic electrostatic 3D MEMS scanner. The endomicroscope can perform sub-cellular resolution imaging in both the horizontal plane and the oblique plane with FOVs of 500 x 700 µm2 and 500 x 200 µm2. A side-viewing probe will allow optimal contact between the imaging window and the luminal wall, which makes it easy to navigate in the hollow organ. The endomicroscope is packaged into a stainless steel tube with outer diameter of 4.2 mm, which can be used for both small animal and human GI tract imaging. We demonstrate in vivo imaging of colonic dysplasia in mice, showing the endomicroscope can potentially be used for early detection and staging of colon cancer.
We demonstrate a dual axes confocal architecture, which can be used to collect horizontal(XY-plane) or vertical cross-sectional(XZ-plane) images for tissue. This scanner head is 5.5mm in outer diameter(OD), and integrates a 3D MEMS scanner with a compact chip size of 3.2×2.9mm2. To realize the miniaturization, there are some obstacles of the small size of 3D MEMS scanner, MEMS wire bundle, the air pressure effect for MEMS motion, the processing of parabolic mirror, and optical alignment to come over. In our probe, separation mechanical structure for optical alignment was adopted and a step shape MEMS holder was designed to deal with the difficult of MEMS wire bundle. Peptides have been demonstrated tremendous potential for in vivo use to detect colonic dysplasia. This class of in vivo molecular probe can be labeled with near-infrared (NIR) dyes for visualizing the full depth of the epithelium in small animals. To confirm our probe performance, we take use of USAF 1951 resolution target to test its lateral and axial resolution. It has lateral and axial resolution of 2.49um and 4.98um, respectively. When we collect the fluorescence imaging of colon, it shows that the field of view are 1000um×1000um (horizontal) and 1000um×430um (vertical). The horizontal and vertical cross-sectional images of fresh mouse colonic mucosa demonstrate imaging performance with this miniature instrument.
A piezoelectric microactuator previously proposed by the authors for laser scanning in dual axes confocal endomicroscopy meets two primary challenges for dual axes confocal imaging: large out-of-plane actuation (~500μm) and a relatively high bandwidth (>100Hz). In order to further reach stage positioning error better than desired imaging resolution of 5 μm and to improve the robustness of actuator performance, a closed-loop controller and thus on-chip sensing, are being incorporated and integrated with system modeling.
This work presents these thin-film PZT based microstages where piezoelectric unimorphs are used not only to actuate its central platform but also to estimate its vertical motion. Initial results from on-chip piezoelectric sensing are presented. Although sensing output shows some feed-through from the actuation signal, testing shows detection of AC motion from various vibration modes of the stage. Meanwhile, 3D profiles of the entire actuator structure at different DC voltage levels were obtained and used to form a nonlinear optimization problem to estimate all forces and moments that each component of the device experiences for the prediction of its deflection. A comparison between modeled and experimental deflection of the actuation beams is included. These results will be used to describe the dynamic behavior of the actuation beams, where the sensors are embedded, and to estimate sensing outputs in order to implement a close-loop controller. Prototype stages are currently being assembled into a handheld dual axes confocal imaging system.
Both piezoresistive and piezoelectric materials are commonly used to detect strain caused by structural vibrations
in macro-scale structures. With the increasing complexity and miniaturization of modern mechanical systems
such as hard disk drive suspensions, it is imperative to explore the performance of these strain sensors when their
dimensions must shrink along with those of the host structures. The miniaturized strain sensors must remain as
small as possible so as to minimum their effect on structure dynamics, yet still have acceptable sensing resolution.
The performances of two types of novel micro-scale strain gage for installation on stainless steel parts are
compared in this paper. Micro-fabrication processes have been developed to build polycrystalline silicon piezoresistive
strain sensors on a silicon substrate, which are later bonded to a steel substrate for testing. Piezoresistor
geometries are optimized to effectively increase the gage factor of piezoresistive sensors while reducing sensor
size. The advantage and disadvantage of these piezoresistors are compared to those of piezoelectric sensors.
Experimental results reveal that the MEMS piezoelectric sensors are able to achieve a better resolution than
piezoresistors, while piezoresistors can be built in much smaller areas. Both types of the MEMS strain sensors
are capable of high sensitivity measurements, subject to differing constraints.
As data densities in computer hard disk drives increase, airflow-induced vibration of the disk drive suspension becomes a major barrier to positioning the read-write head with sufficient precision. One component in reducing these vibrations is a dedicated sensor system for detecting vibration on the sensor arm directly, which enables high-frequency sampling and modal selectivity. In this paper, an efficient method for identifying optimal position and shape of piezoelectric strain gages on a flexible structure is presented, and applied to the steel suspension of a hard disk drive. Zinc oxide deposition processes are adapted to steel substrates, and used to fabricate miniature zinc oxide strain gages at the optimal strain gage location. Substrates with sensors installed were assembled into full disk drive suspensions and tested in a commercial disk drive.