Optical-resolution photoacoustic microscopy (ORPAM) in theory provides lateral resolution equivalent to the optical diffraction limit. Scattering media, such as biological turbid media, attenuates the optical signal and also alters the diffraction-limited spot size of the focused beam. The ORPAM signal is generated only from a small voxel in scattering media with dimensions equivalent to the laser spot size after passing through scattering layers and is detected by an acoustic transducer, which is not affected by optical scattering. Thus, both ORPAM and confocal laser scanning microscopy (CLSM) reject scattered light. A multimodal optical microscopy platform that includes ORPAM and CLSM was constructed, and the lateral resolution of both modes was measured using patterned thin metal film with and without a scattering barrier. The effect of scattering media on the lateral resolution was studied using different scattering coefficients and was compared to computational results based on Monte Carlo simulations. It was found that degradation of lateral resolution due to optical scattering was not significant for either ORPAM or CLSM. The depth discrimination capability of ORPAM and CLSM was measured using microfiber embedded in a light scattering phantom material. ORPAM images demonstrated higher contrast compared to CLSM images partly due to reduced acoustic signal scattering.
In this study, a photoacoustic detector integrated with Fourier-transform infrared spectroscopy was used to measure
biomarkers in gas samples independently. Simulated exhaled breath samples were created by mixing varying
concentrations of acetone, ammonia and ethane. The results of these measurements demonstrate the potential of
photoacoustic spectroscopy to detect biomarkers from human breath.
PURPOSE: Needle guidance software using augmented reality image overlay was translated from the experimental phase to support preclinical and clinical studies. Major functional and structural changes were needed to meet clinical requirements. We present the process applied to fulfill these requirements, and selected features that may be applied in the translational phase of other image-guided surgical navigation systems. METHODS: We used an agile software development process for rapid adaptation to unforeseen clinical requests. The process is based on iterations of operating room test sessions, feedback discussions, and software development sprints. The open-source application framework of 3D Slicer and the NA-MIC kit provided sufficient flexibility and stable software foundations for this work. RESULTS: All requirements were addressed in a process with 19 operating room test iterations. Most features developed in this phase were related to workflow simplification and operator feedback. CONCLUSION: Efficient and affordable modifications were facilitated by an open source application framework and frequent clinical feedback sessions. Results of cadaver experiments show that software requirements were successfully solved after a limited number of operating room tests.
PURPOSE: The purpose of this study was to determine if medical trainees would benefit from augmented reality image
overlay and laser guidance in learning how to set the correct orientation of a needle for percutaneous facet joint
injection. METHODS: A total of 28 medical students were randomized into two groups: (1) The Overlay group received
a training session of four insertions with image and laser guidance followed by two insertions with laser overlay only;
(2) The Control group was trained by carrying out six freehand insertions. After the training session, needle trajectories
of two facet joint injections without any guidance were recorded by an electromagnetic tracker and were analyzed.
Number of successful needle placements, distance covered by needle tip inside the phantom and procedural time were
measured to evaluate performance. RESULTS: Number of successful placements was significantly higher in the Overlay
group compared to the Control group (85.7% vs. 57.1%, p = 0.038). Procedure time and distance covered inside
phantom have both been found to be less in the Overlay group, although not significantly. CONCLUSION: Training
with augmented reality image overlay and laser guidance improves the accuracy of facet joint injections in medical
students learning image-guided facet joint needle placement.
PURPOSE: A ground-truth validation platform was developed to provide spatial correlation between ultrasound
(US), temperature measurements and histopathology images to validate US based thermal ablation monitoring
methods. METHOD: The test-bed apparatus consists of a container box with integrated fiducial lines. Tissue
samples are suspended within the box using agar gel as the fixation medium. Following US imaging, the gel block
is sliced and pathology images are acquired. Interactive software segments the fiducials as well as structures
of interest in the pathology and US images. The software reconstructs the regions in 3D space and performs
analysis and comparison of the features identified from both imaging modalities. RESULTS: The apparatus and
software were constructed to meet technical requirements. Tissue samples were contoured, reconstructed and
registered in the common coordinate system of fiducials. There was agreement between the sample shapes, but
systematic shift of several millimeters was found between histopathology and US. This indicates that during
pathology slicing shear forces tend to dislocate the fiducial lines. Softer fiducial lines and harder gel material
can eliminate this problem. CONCLUSION: Viability of concept was presented. Despite our straightforward
approach, further experimental work is required to optimize all materials and customize software.