Photoacoustic tomography has great potential; however, limited detector coverage is a key issue that results in artifacts. While analytical and simulation studies regarding this issue are extensive, experimental setups are lacking. A ring-shaped detector array was rotated and translated to achieve near-full view angle coverage. Following system optimization, phantom imaging of star shape, synthetic breast tumor specimen, and vascular phantoms was performed. Approximately 4000 detectors were needed for high quality images, and phantoms were clearly imaged with minimal artifacts. A near full-view spherical system has been developed, allowing for future work validating experimentally the theoretical advantages of using a full-view setup.
Approximately 19% of breast cancer patients undergoing breast conserving surgery (BCS) must return for a secondary surgery due to incomplete tumour removal. We propose a single sensor, low-frequency hand-held photoacoustic imaging (PAI) probe for detection of residual cancer tissue during BCS within the surgical cavity and on the excised specimen based on lipid content differences. The probe incorporated a single polyvinylidene fluoride acoustic sensor, a 1-to-4 optical fibre bundle and a polycarbonate axicon lens for light delivery. A phantom consisting of nylon strings was imaged to find an optimal scanning geometry and resolution of the probe. The effect of limited angular coverage was evaluated by comparing the PAI results of a phantom mimicking an ex-vivo breast cancer specimen obtained with the hand-held probe and near-full view PAI system. Translation of the probe with 4 mm steps and rotation over 6° steps resulted in lateral and axial resolution of 1.8 mm and 1 mm, respectively. Experiments with the prototype hand-held PAI probe at 930 nm resulted in excellent image contrast exclusively from lipids. Lipid-free gaps mimicking positive margins were clearly visible in the images. Compared to images from the near full-view PAI system, the hand-held PAI probe had a higher signal-to-noise ratio but suffered from more negativity image artefacts. Taken together, the results show that PAI with the hand-held probe has the potential for detection of residual breast cancer tissue during BCS.
KEYWORDS: Sensors, Spherical lenses, Acquisition tracking and pointing, Photoacoustic tomography, Optical spheres, Signal detection, Tumors, Imaging systems, Stars, Signal to noise ratio
Significance: Photoacoustic tomography (PAT) is a widely explored imaging modality and has excellent potential for clinical applications. On the acoustic detection side, limited-view angle and limited-bandwidth are common key issues in PAT systems that result in unwanted artifacts. While analytical and simulation studies of limited-view artifacts are fairly extensive, experimental setups capable of comparing limited-view to an ideal full-view case are lacking.Aims: A custom ring-shaped detector array was assembled and mounted to a 6-axis robot, then rotated and translated to achieve up to 3.8π steradian view angle coverage of an imaged object.Approach: Minimization of negativity artifacts and phantom imaging were used to optimize the system, followed by demonstrative imaging of a star contrast phantom, a synthetic breast tumor specimen phantom, and a vascular phantom.Results: Optimization of the angular/rotation scans found ≈212 effective detectors were needed for high-quality images, while 15-mm steps were used to increase the field of view as required depending on the size of the imaged object. Example phantoms were clearly imaged with all discerning features visible and minimal artifacts.Conclusions: A near full-view closed spherical system has been developed, paving the way for future work demonstrating experimentally the significant advantages of using a full-view PAT setup.
KEYWORDS: Near infrared spectroscopy, Spectroscopy, In vivo imaging, Brain, Oxygen, Blood circulation, Surgery, Spectrometers, Single photon, Semiconductor lasers
Phenylephrine is commonly used in cardiac surgery is common to increase mean arterial pressure without affecting cardiac output; however, its effects on the microcirculation of the brain and in skeletal muscle are unclear. The objective of this study is to use hyperspectral near infrared spectroscopy (h-NIRS) and diffuse correlation spectroscopy (DCS) to monitor the microcirculation during a phenylephrine bolus would be able to discern the timing and effects of a phenylephrine bolus on brain and skeletal muscle microvasculature. The h-NIRS subsystem uses two spectrometers and a halogen light source, and the DCS subsystem uses a long coherence diode laser (785 nm) and a single photon counting module. Probes were positioned on the left hind limb and the top of the skull, with a source-detector distance of 10mm. Data were collected from Sprague Dawley rats (n = 1, 158 g). Nine microvascular challenges were monitored by recording a two-minute baseline, then injecting 0.1mL of phenylephrine (0.1 ug/mL) intravenously, followed by collecting data for 4 additional minutes. Oxygen saturation increased by 9% in the brain and 2% in the muscle. Blood flow increased by 60% in the brain, and 17% in the muscle. This study is the first report on the use of h-NIRS and DCS to investigate the effects of phenylephrine in the microvasculature. Dissimilitude in flow response may be due to differences in regulation mechanisms. Future work will include acquiring data from both subsystems simultaneously to provide further insight into the relationship between oxygen saturation and blood flow.
During surgery with cardiopulmonary bypass (CPB), maintaining adequate cerebral blood flow (CBF) is paramount to prevent adverse neurological outcome; tissue damage can occur if CBF reduction is sufficient to impair energy metabolism. Ten adult patients undergoing cardiothoracic surgery with CPB received perfusion and metabolic neuromonitoring using a novel optical system combining diffuse correlation spectroscopy and broadband near-infrared spectroscopy. CPB onset resulted in large increases in CBF and significant drops in mean arterial pressure and metabolism. No changes were observed transitioning off CPB. Real-time assessment of cerebral perfusion and metabolism could alert clinicians to relevant hemodynamic events before brain injury occurs.
The premature brain embodies an underdeveloped vascular system, which can lead to poor cerebral blood flow (CBF), impaired metabolism, and subsequent brain injury. NNeMo (Neonatal NeuroMonitor) is an in-house built brain monitor that provides continuous and simultaneous measurements of CBF, tissue saturation (StO2), and metabolism. Nine premature infants were monitored for 6 h on day 1 and 3 of life. An oscillatory signal was observed in CBF and StO2 which diminished by day 3; metabolic response was not impacted by minor fluctuations in perfusion. Hemodynamic neuromonitoring could aid in predicting the onset of cerebral hemorrhaging or gauging brain injury severity.
Photoacoustic tomography (PAT) has excellent sensitivity for hemoglobin and lipids, which make up much of human breast tissue. Our group has focused on intraoperative PAT applied to tissues obtained during breast-conserving surgery (BCS). In BCS, the tumor is excised with a margin of healthy tissue to ensure tumor removal. Margin detection can be difficult and re-excision surgeries are required in 10 to 25% of cases. Our first-generation intraoperative PAT system was capable of 3D imaging specimens up to 11 cm in diameter and several centimeters thick. The system used a semi-circular ring of low frequency transducers, resulting in a 2.5 mm spatial resolution. The current objective is to improve spatial resolution using higher frequency transducers. An array was constructed with 41 circular transducers positioned on two concentric circular rungs with a single point of focus. An optical window at the center allowed illumination. The array was tested with imaging phantoms consisting of written words on a clear plastic bag, 108 µm polyester monofilament arranged as parallel lines with spacing varying from 1 mm to 8 mm, and finally with porcine tissues. The array was positioned above and perpendicular to the imaging area and raster scanned. Signal averaging was implemented, and images were reconstructed with universal back projection. Image analysis demonstrated a 400 μm spatial resolution, but with low penetration depth and low sensitivity. Results suggest the transducers could improve spatial resolution of the first-generation intraoperative PAT system by 6-fold.
Objective and accurate surface measurements of the human breast are important for surgical planning. Traditionally, surgeons plan their procedures using radiographic images, but these images do not illustrate the breast in the surgical position (i.e. supine position). As a result, surgeons need to account for differences in breast size and shape, and surgical outcome is largely dependent on the surgeon’s experience. Previous studies have shown that scanning large-breasted patients in the standing position resulted in breast ptosis and high variability. A system capable of accurately scanning patients in the supine position is therefore desirable. The aim of this work was to develop a non-contact imaging system that can provide 3D information of each breast surface from patients in the supine position. Two structured-light surface scanners were combined using separate colour optical filters to minimize cross-talk between scanners. Test scans were collected from a 3D printed breast phantom in both the supine and standing positions. Scanning with blue and green filters simultaneously at two different angles eliminated shadowing artifacts compared to a single scanner reconstruction. The mean error distance between the phantom CAD model and point cloud measurements was 0.1 ± 0.1 mm for both standing and supine positions. Our system performed better than currently available commercial systems, which have accuracy of 0.5 - 1 mm.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.