Circular Scanning Pattern Research Articles

Estimating Tree Diameter at Breast Height (DBH) Using iPad Pro LiDAR Sensor in Boreal Forests

Traditional Diameter at Breast Height (DBH) mensuration is labor-intensive and costly. This scoping study explored the possibility of using the Apple iPad Pro Light Detection And Ranging (LiDAR) sensor to estimate DBH. Three plots were scanned in a research plantation near Thunder Bay, Canada. Sites consisted of either Black Spruce (Picea mariana) or Red Pine (Pinus resinosa) planted with different initial densities. DBH was manually measured for validation. Point clouds were acquired for each plot using three scanning patterns; circular, figure-8, and transect. Single and five cross sections of 4 or 10 cm in thickness were extracted from each point cloud, centered at 1.3 m above the ground. Two circle fitting algorithms (Pratt, Taubin) and two ellipse fitting algorithms (Taubin, Szpak) were applied to the extracted cross-sections to estimate DBH. Scanning pattern and curve-fitting formula significantly impacted DBH estimate accuracy (p-value ≤ 0.001), while cross-section count and thickness did not. The circular scanning pattern with a single 4 cm cross-section and a combination of circle- and ellipse-fitting formulas was the most accurate DBH estimation method (RMSE = 1.1 cm; 6.17%).

High dynamic range 3D motion tracking using circular scans with optical coherence tomography.

Motion artifacts, from such sources as heartbeats, respiration, or peristalsis, often degrade microscopic images or videos of live subjects. We have developed a method using circular optical coherence tomography (OCT) scans to track the transverse and axial motion of biological samples at speeds ranging from several micrometers per second to several centimeters per second. We achieve fast and high-precision measurements of the magnitude and direction of the sample's motion by adaptively controlling the circular scan pattern settings and applying interframe and intraframe analyses. These measurements are the basis of active motion compensation via feedback control for future in vivo microscopic and macroscopic imaging applications.

Optimization of circular scan path to produce bowl shapes in 3D laser forming process

In a three-dimensional laser forming process, laser scan path and scan path parameters are crucial to produce desired shapes. In this manuscript, the optimized perimeter laser scan pattern which results in bowl shapes is presented. Several circular scan paths in circular AISI 304 sheets are considered to produce bowl shapes. Scan path parameters are as follows: (1) continuity or discontinuity of the path; (2) the start point of the path; and (3) the direction of the scan path in each step, including clockwise (CW) and counter clockwise (CCW). Thus, three different continuous circular scan patterns consist of the CW or CCW path with a similar angular location, mixed CW and CCW paths with different start points and the CW or CCW scan paths with different start points are investigated. Besides, two discontinuous circular paths, including the same CW or CCW direction, and mixed CW and CCW directions are studied. Comparison between different proposed scan patterns is carried out based on three criteria considered, that is, the average height of the perimeter points, the edge distortion, and the standard deviation of the final product. The results show that the continuous CW or CCW scan path with different start points is the optimized circular scan pattern. In addition, further experimentations using the presented results in this manuscript illustrate the continuous circular path with the same scan direction and a 90° angular step leads to optimum desired bowl shapes.

Variability and repeatability of quantitative, Fourier-domain optical coherence tomography Doppler blood flow in young and elderly healthy subjects.

The purpose of this study was to determine the within-session variability and between-session repeatability of spectral Fourier-domain optical coherence tomography (Doppler FD-OCT) Doppler retinal blood flow measurements in young and elderly subjects. Doppler FD-OCT blood flow was measured using the RTVue system. One eye of each of 20 healthy young (24.7 ± 2.7 years) and 16 healthy elderly (64.6 ± 5.1 years) subjects was randomly selected, and the pupil was dilated. The double circular scanning pattern of the RTVue was employed. Six Doppler FD-OCT measurements (i.e., each separate measurement comprising an upper and a lower nasal pupil scan) were acquired at each session. Measurements were repeated approximately 2 weeks later. Total retinal blood flow was calculated by summing flow from all detectable venules surrounding the optic nerve head. The coefficient of variation (COV) and coefficient of repeatability (COR) were calculated for each individual. The individual COVs for retinal blood flow for young subjects ranged from 0.4% to 20.4% (median 7.5%) and for the elderly subjects ranged from 0.6% to 34.6% (median 9.2%). The group mean CORs for retinal blood flow for young participants were 6.4 μL/min (median 5.91 μL/min, relative to a mean effect 39.8 μL/min) and for elderly subjects were 10.5 μL/min (median 9.2 μL/min, relative to a mean effect 46.4 μL/min). Doppler FD-OCT gave consistent and repeatable blood flow measurements within retinal venules in normal subjects. Considering the individual variation in blood flow measurements, confidence limits for retinal hemodynamics need to be determined on an individual basis.

Gold Nanorods as a Contrast Agent for Doppler Optical Coherence Tomography

PurposeTo investigate gold nanorods (GNRs) as a contrast agent to enhance Doppler optical coherence tomography (OCT) imaging of the intrascleral aqueous humor outflow.MethodsA serial dilution of GNRs was scanned with a spectral-domain OCT device (Bioptigen, Durham, NC) to visualize Doppler signal. Doppler measurements using GNRs were validated using a controlled flow system. To demonstrate an application of GNR enhanced Doppler, porcine eyes were perfused at constant pressure with mock aqueous alone or 1.0×1012 GNR/mL mixed with mock aqueous. Twelve Doppler and volumetric SD-OCT scans were obtained from the limbus in a radial fashion incremented by 30°, forming a circular scan pattern. Volumetric flow was computed by integrating flow inside non-connected vessels throughout all 12 scans around the limbus.ResultsAt the GNR concentration of 0.7×1012 GNRs/mL, Doppler signal was present through the entire depth of the testing tube without substantial attenuation. A well-defined laminar flow profile was observed for Doppler images of GNRs flowing through the glass capillary tube. The Doppler OCT measured flow profile was not statistically different from the expected flow profile based upon an autoregressive moving average model, with an error of −0.025 to 0.037 mm/s (p = 0.6435). Cross-sectional slices demonstrated the ability to view anterior chamber outflow ex-vivo using GNR-enhanced Doppler OCT. Doppler volumetric flow measurements were comparable to flow recorded by the perfusion system.ConclusionsGNRs created a measureable Doppler signal within otherwise silent flow fields in OCT Doppler scans. Practical application of this technique was confirmed in a constant pressure ex-vivo aqueous humor outflow model in porcine eyes.

Harmonic Transfer Function to Measure Translational and Rotational Velocities With Continuous-Scan Laser Doppler Vibrometry

A laser Doppler vibrometer measures the translational velocity at a point along the direction of incident light. It has been shown that rotational velocities can also be recovered when the laser scans continuously along a short line or small circular path around that point. This work uses the harmonic transfer function to relate the measured translational and rotational velocities to the input force. With this concept, the continuous-scan approach can be combined with the conventional point-by-point scheme, acquiring three dimensional velocities under various types of excitation conditions in the same amount of time that is required for obtaining only the translational velocity. The proposed approach is validated on a downhill ski under free-free boundary conditions with a circular scan pattern. The influence of the circle size, the scan rate and the surface quality on the noise level is evaluated. It is found that the circular-scan approach provides smoother and more reliable mode shapes than the conventional point-by-point approach given appropriate parameters. Local slopes at the measurement locations are then computed from the identified rotational velocities, providing additional information for model validation and damage detection.

Absolute Retinal Blood Flow Measurement With a Dual-Beam Doppler Optical Coherence Tomography

To test the capability of a novel dual-beam Doppler optical coherence tomography (OCT) technique for simultaneous in vivo measurement of the Doppler angle and, thus, the absolute retinal blood velocity and the retinal flow rate, without the influence of motion artifacts. A novel dual-beam Doppler spectral domain OCT (SD-OCT) was developed. The two probing beams are separated with a controllable distance along an arbitrary direction, both of which are controlled by two independent 2D optical scanners. Two sets of optical Doppler tomography (ODT) images are acquired simultaneously. The Doppler angle of each blood vessel segment is calculated from the relative coordinates of the centers of the blood vessel in the two corresponding ODT images. The absolute blood flow velocity and the volumetric blood flow rate can then be calculated. To measure the total retinal blood flow, we used a circular scan pattern centered at the optic disc to obtain two sets of concentric OCT/ODT images simultaneously. We imaged two normal human subjects at ages of 48 and 34 years. The total retinal blood flow rates of the two human subjects were calculated to be 47.01 μL/min (older subject) and 51.37 μL/min (younger subject), respectively. Results showed that the performance of this imaging system is immune to eye movement, since the two sets of ODT images were acquired simultaneously. The dual-beam OCT/ODT system is successful in measuring the absolute retinal blood velocity and the volumetric flow rate. The advantage of the technique is that the two sets of ODT images used for the calculation are acquired simultaneously, which eliminates the influence of eye motion and ensures the accuracy of the calculated hemodynamic parameters.

Investigation on the microstructure and mechanical properties of Ti–6Al–4V alloy joints with electron beam welding

Titanium and its alloys have excellent combination of properties, and they are extensively used in many industrial fields. However, due to their special weldability, the welding of titanium alloys is always of concern to many researchers. This work is aiming at investigation of the effect of different beam scanning patterns on the microstructure and mechanical properties of Ti–6Al–4V alloy joints by electron beam welding. The circular scanning pattern and linear scanning pattern are employed respectively during welding. Results show that the weld metal is full of cross–cross acicular α′ martensitic structure, while the base metal is of equiaxed structure. Mechanical property tests indicate that the hardness of weldment is higher than that of heat-affected zone (HAZ) and base metal. The tensile strength of joint is almost equal to that of base metal, and it is well in accordance with the relationship between microstructure and mechanical properties of welded joints. The tensile fracture morphology of joint presents obviously the characteristic of ductile fracture, which is related to the bigger and deeper dimples distributed on the surface of joint. The circular scanning pattern makes the joint microstructure coarse, while the linear scanning pattern meets the requirement of fining grains by uniform distribution of alloy elements or big grains being broken.

SU-FF-T-462: Treatment of Retinoblastoma Using Different Proton Delivery Methods: Scattering, Rectangular Scanning, and Circular Scanning

Purpose: The high risk of radiation induced malignancy in retinoblastoma with conventional radiotherapy makes treatment with proton beams advantageous since it minimizes exposure of normal tissue in brain and orbit. Until recently, only scattered proton beams were used. In this study we compare contaminating neutron dose from three different beam delivery methods: passive scattering, uniform scanning with a rectangular scan pattern, and uniform scanning with a circular scan pattern adjusted to the target size. In all three scenarios the same brass aperture was used. Methods: CT scans of three patients with retinoblastoma were selected for treatment planning. Patients were treated under anesthesia using an ocular suction cup. Two patients had bilateral, one had unilateral treatment. The plans were reproduced in a phantom using the three delivery methods described above. Dose distributions were measured with MAGIC gel placed inside the phantom with readout performed using MRI. Neutron doses to the phantom were measured using Bubble detectors (Bubble Technology Industries™) and a SWENDI-II (Thermo Electron Corporation™) detector. Results: In all three patients dose to the ethmoid bone and the frontal lobe was minimized by protons. When the optimized circular beam scanning pattern was used, secondary neutron dose was lower compared to both the rectangular scanning pattern and the passively scattered beam. For a 3 cm circular aperture, the secondary neutron component was 0.23 mSv/Gy for a 12×12 cm rectangular pattern. It was 80% lower for a 4cm optimized circular scan pattern and 15% higher for a 12cm diameter double scattered field. Conclusions: Delivery of proton beams using a scan pattern adjusted to the shape of the treatment field yields comparable dose distributions to conventional proton beam delivery but has the advantage of delivering less contaminating neutron dose to the patient.

Peripapillary Retinal Nerve Fiber Layer Thickness in a Population of 6-Year-Old Children: Findings by Optical Coherence Tomography

To study the distribution of retinal nerve fiber layer (RNFL) thickness by ocular and demographic variables in a population-based study of young children. Population-based cross-sectional study. One thousand seven hundred sixty-five of 2238 (78.9%) eligible 6-year-old children participated in the Sydney Childhood Eye Study between 2003 and 2004. Mean age was 6.7 years (50.9% boys). Detailed examination included cycloplegic autorefraction and measurement of axial length. Retinal nerve fiber layer scans using an optical coherence tomographer were performed with a circular scan pattern of 3.4-mm diameter. Multivariate analyses were performed to examine the distribution of RNFL parameters with gender, ethnicity, axial length, and refraction. Peripapillary RNFL thickness and RNFL(estimated integral) (RNFL(EI)), which measures the total cross-sectional area of ganglion cell axons converging onto the optic nerve head. Peripapillary RNFL thickness and RNFL(EI) were normally distributed. The mean+/-standard deviation RNFL average thickness was 103.7+/-11.4 microm and RNFL(EI) was 1.05+/-0.12 mm2. Retinal nerve fiber layer thickness was least for the temporal quadrant (75.7+/-14.7 microm), followed by the nasal (81.7+/-19.6 microm), inferior (127.8+/-20.5 microm), and superior (129.5+/-20.6 microm) quadrants. Multivariate adjusted RNFL average thickness was marginally greater in boys than in girls (104.7 microm vs. 103.2 microm; P = 0.007) and in East Asian than in white children (107.7 microm vs. 102.7 microm; P<0.0001). The RNFL was thinner with greater axial length (P(trend)<0.0001) and less positive spherical equivalent refractions (P(trend) = 0.004). Retinal nerve fiber layer average thickness and RNFL(EI) followed a normal distribution. Retinal nerve fiber layer thickness varied marginally with gender, but differences were more marked between white and East Asian children. Retinal nerve fiber layer thinning was associated with increasing axial length and less positive refractions.

The significance of orbital anatomy and periocular wrinkling when performing laser skin resurfacing.

Knowledge of orbital anatomy and the interaction of muscle contractions, gravitational forces and photoagingis fundamental in understanding the limitations of carbon dioxide (CO2) laser skin resurfacing when rejuvenating the skin of the periocular area. Laser resurfacing does not change the mimetic behavior of the facial muscles nor does it influence gravitational forces. When resurfacing periocular tissue, the creation of scleral show and ectropion are a potential consequence when there is an over zealous attempt at improving the sagging malar fat pad and eyelid laxity by performing an excess amount of laser passes at the lateral portion of the lower eyelid. This results in an inadvertent widening of the palpebral fissure due to the lateral pull of the Orbicularis oculi. Retrospectively, 85 patients were studied, who had undergone periorbital resurfacing with a CO2 laser using anew treatment approach. The Sharplan 40C CO2 Feather Touchlaser was programmed with a circular scanning pattern and used just for the shoulders of the wrinkles. A final laser pass was performed with the same program over the entire lower eyelid skin surface, excluding the outer lateral portion (e.g. a truncated triangle-like area),corresponding to the lateral canthus. Only a single laser pass was delivered to the lateral canthal triangle to avoid widening the lateral opening of the eyelid, which might lead to the potential complications of scleral show and ectropion. When the area of the crows' feet is to be treated, three passes on the skin of this entire lateral orbital surface are completed by moving laterally and upward toward the hairline. Patients examined on days 1, 7, 15, 30, 60, and one year after laser resurfacing showed good results. At two months after treatment, the clinical improvement was rated by the patient and physician as being "very good" in 81 of the 85 patients reviewed. These patients underwent laser resurfacing without complications. The proposed technique of periocular resurfacing prevents complications of scleral show and laxity in the lateral eyelid opening and even ectropion, because treatment conforms to the osseo-muscular anatomical relationship of eyelid structures.