Point Spread Function Analysis Research Articles

Effect of a vehicle's mobility on SNR and SINR in vehicular optical camera communication systems.

The widespread use of light-emitting diodes (LEDs) and cameras in vehicular environments provides an excellent opportunity for optical camera communication (OCC) in intelligent transport systems. OCC is a promising candidate for the Internet of Vehicles (IoV), and it uses LEDs as the transmitter and cameras as the receiver. However, the mobility of vehicles has a significant detrimental impact on the OCC system's performance in vehicular environments. In this paper, a traffic light that uses multiple-input multiple-output (MIMO) technology serves as the transmitter, and the receiver is a camera mounted on a moving vehicle. The impact of vehicle mobility on the vehicular MIMO-OCC system in the transportation environment is then examined using precise point spread function (PSF) analysis. The experimental results are used to evaluate the proposed PSF. A good agreement between the laboratory's recorded videos and this PSF model's simulations is observed. Moreover, the signal-to-noise ratio (SNR) and signal-to-interference-plus-noise ratio (SINR) values are evaluated. It is shown that they are greatly influenced by the vehicle's speed, direction of motion, and position of the camera. However, since the angular velocity in a typical transportation environment is low, it does not have a significant impact on the performance of the vehicular OCC systems.

Phasor field based photoacoustics: A virtual orthogonal wavefield model for nonnegative photoacoustic computational tomography

The phasor field technique has substantially aided the advancement of the time of flight imaging field and sparked intense scientific research interest during the past several years. Recently, phasor field approach was brought to the field of photoacoustic imaging and results in greatly enhanced image SNR and less artifact interference. This paper aims to establish the foundation for a comprehensive physical framework for phasor field based photoacoustics. To demonstrate the rigorousness of the phasor field based photoacoustics, this work gives a derivation of its virtual forward propagation and backward phasor field reconstruction. Phasor field based photoacoustic system works by creating chunks of initial orthogonal photoacoustic vibration, propagating the virtual orthogonal phasor waves, and performing backward phasor field reconstruction. We present here a formal study of phasor field framework utilizing spherical harmonic function decomposition based point spread function (PSF) analysis and provide a rigorous theoretical explanation for its nonnegative imaging capability of phasor field photoacoustic imaging. Simulation and experimental results reported in the paper support the effectiveness of the phasor field photoacoustic method for nonnegative imaging reconstruction. Moreover, the virtual nature of phasor field method enables flexibility and compatibility with different reconstructive mechanism for optimized imaging performance. Phasor field method the potential to advance the photoacoustic imaging techniques across multiple fields, benefiting various applications and enabling new avenues of research and development.

Improved image uniformity using optimized diverging-wave acquisition sequence for high frame rate pulse-echo ultrasound

Ultrafast pulse-echo ultrasound imaging uses unfocused plane-wave transmit (PWT) or diverging-wave transmit (DWT) wavefronts and coherent compounding for image reconstruction. PWT imaging is more commonly utilizedbut has a limited region of overlapping insonification. This work characterizes the tradeoffs between PWT and DWT, to determine an optimal DWT transmit scheme for given constraints on imaging field of view (depth and width), frame rate, and resolution uniformity. Using Field II, the transmit energy field of a 64-element, 2.75-MHz linear phased array (Verasonics P4-2v) was analyzed for PWT and various active apertures and relative virtual source locations for DWT. This was followed by a Field II calculation and analysis of point-spread functions (PSFs) at many locations in the field (to depth z = 35 mm and x = 20 mm laterally) for each PWT and DWT case, and several cases of PWT and DWT compounding. The amplitude and resolution of the PSF, and the uniformity (variance) of each of these metrics over the field of view, weremeasured in each case. Preliminary results suggest that a DWT scheme provides improved PSF amplitude uniformity over a broader field of view than PWT, with only a slight reduction in lateral resolution at greater depths.

Visual and refractive outcomes of new intraocular lens implantation after cataract surgery

To report the visual and refractive outcomes of new aspheric hydrophobic acrylic monofocal intraocular lens (IOL). Retrospective case series. This study included eyes of patients who underwent routine cataract surgery for uncomplicated age-related cataract with implantation of a Aktis SP (NS-60YG; Nidek Co. Ltd., Japan) IOL and attended regular follow ups at 1 week, 1 month, 3 months, and 12 months. At each post-operative visit, ophthalmological evaluation included measurement Uncorrected (UCVA) and Best corrected visual acuity (BCVA), contrast sensitivity, posterior capsular opacification (PCO), optical aberrations, analysis of point spread function (PSF) and modulation transfer function (MTF). The study included 2102 eyes of 1358 patients aged 45 to 75 years (mean age 62.6 years ± 5.6 SD). The mean preoperative BCVA was 0.56 ± 0.26 logMAR. At 1 year follow up, the mean postoperative UCVA and BCVA were 0.11 ± 0.09 and 0.02 ± 0.03 logMAR, respectively. At the end of 6 months, around 1487 (93%) eyes had BCVA of 20/20 and better than 20/30 in 100% of the eyes. Mild posterior capsule opacification (PCO) was observed in 56 patients, but none required Nd YAG laser capsulotomy. There was reduction in ocular spherical aberration and Higher order aberrations (HOAs) as compared to pre operative. This explains better contrast sensitivity obtained by MTF and PSF values. The study shows that the Aktis SP IOL is safe, effective, and stable lens that could be inserted through 2.2 mm incision with satisfactory visual and refractive outcomes, even in late post-operative period.

Searching for Binary Asteroids in Pan-STARRS1 Archival Images

We developed two different point-spread function (PSF) analysis techniques for discovering wide separation binary asteroids in wide-field surveys. We then applied these techniques to images of main belt asteroids in the 4–60 km size range captured by Pan-STARRS1. Johnston lists fewer than 10 known binaries in this size range with separations greater than 10% of the primary’s Hill radius, so discovering more wide binary asteroids is crucial for understanding the limits of binary stability and improving our knowledge of asteroid masses. We analyzed each image by (i) comparing the major axis orientation of the asteroid’s elliptical PSF to its nonsidereal rate on the sky and (ii) comparing the one-dimensional median profile created by collapsing the image along the asteroid’s direction of motion to that of nearby field stars. For both methods, we flagged any results that deviated significantly from the expected measurements of single asteroids, and those targets with the most flags were identified as binary candidates for confirmation with high-acuity imaging.

Ultrafast B1 mapping with RF-prepared 3D FLASH acquisition: Correcting the bias due to T1 -induced k-space filtering effect.

PurposeThe traditional radiofrequency (RF)‐prepared B1 mapping technique consists of one scan with an RF preparation module for flip angle‐encoding and a second scan without this module for normalizing. To reduce the T1‐induced k‐space filtering effect, this method is limited to 2D FLASH acquisition with a two‐parameter method. A novel 3D RF‐prepared three‐parameter method for ultrafast B1‐mapping is proposed to correct the T1‐induced quantification bias.TheoryThe point spread function analysis of FLASH shows that the prepared longitudinal magnetization before the FLASH acquisition and the image signal obeys a linear (not proportional) relationship. The intercept of the linear function causes the quantification bias and can be captured by a third saturated scan.MethodsUsing the 2D double‐angle method (DAM) as the reference, a 3D RF‐prepared three‐parameter protocol with 9 s duration was compared with the two‐parameter method, as well as the saturated DAM (SDAM) method, the dual refocusing echo acquisition mode (DREAM) method, and the actual flip‐angle imaging (AFI) method, for B1 mapping of brain, breast, and abdomen with different orientations and shim settings at 3T.ResultsThe 3D RF‐prepared three‐parameter method with complex‐subtraction delivered consistently lower RMS error, error mean, error standard deviation, and higher concordance correlation coefficients values than the two‐parameter method, the three‐parameter method with magnitude‐subtraction, the multi‐slice DREAM and the 3D AFI, and were close to the results of 2D or multi‐slice SDAM.ConclusionThe proposed ultrafast 3D RF‐prepared three‐parameter method with complex‐subtraction was demonstrated with high accuracy for B1 mapping of brain, breast, and abdomen.

Extended focal depth Fourier domain optical coherence microscopy with a Bessel-beam - LP02 mode - from a higher order mode fiber.

We present a robust fiber-based setup for Bessel-like beam extended depth-of-focus Fourier-domain optical coherence microscopy, where the Bessel-like beam is generated in a higher order mode fiber module. In this module a stable guided LP02 core mode is selectively excited by a long period grating written in the higher order mode fiber. Imaging performance of this system in terms of lateral resolution and depth of focus was analyzed using samples of suspended microbeads and compared to the case where illumination is provided by the fundamental LP01 mode of a single mode fiber. Illumination with the LP02 mode allowed for a lateral resolution down to 2.5 µm as compared to 4.5 µm achieved with the LP01 mode of the single mode fiber. A three-fold enhancement of the depth of focus compared to a Gaussian beam with equally tight focus is achieved with the LP02 mode. Analysis of the theoretical lateral point spread functions for the case of LP01 and LP02 illumination agrees well with the experimental data. As the design space of waveguides and long-period gratings allows for further optimization of the beam parameters of the generated Bessel-like beams in an all-fiber module, this approach offers a robust and yet flexible alternative to free-space optics approaches or the use of conical fiber tips.

Probe Standoff Optimization Method for Phased Array Ultrasonic TFM Imaging of Curved Parts.

The reliability of the ultrasonic phased array total focusing method (TFM) imaging of parts with curved geometries depends on many factors, one being the probe standoff. Strong artifacts and resolution loss are introduced by some surface profile and standoff combinations, making it impossible to identify defects. This paper, therefore, introduces a probe standoff optimization method (PSOM) to mitigate such effects. Based on a point spread function analysis, the PSOM algorithm finds the standoff with the lowest main lobe width and side lobe level values. Validation experiments were conducted and the TFM imaging performance compared with the PSOM predictions. The experiments consisted of the inspection of concave and convex parts with amplitudes of 0, 5 and 15 λAl, at 12 standoffs varying from 20 to 130 mm. Three internal side-drilled holes at different depths were used as targets. To investigate how the optimal probe standoff improves the TFM, two metrics were used: the signal-to-artifact ratio (SAR) and the array performance indicator (API). The PSF characteristics predicted by the PSOM agreed with the quality of TFM images. A considerable TFM improvement was demonstrated at the optimal standoff calculated by the PSOM. The API of a convex specimen’s TFM was minimized, and the SAR gained up to 13 dB, while the image of a concave specimen gained up to 33 dB in SAR.

A spatial resolution evaluation method of endoscopic optical coherence tomography system using the annular phantom.

As an important biomedical imaging method, endoscopic optical coherence tomography (OCT) is necessary to check its performance regularly. The ordinary plane phantoms are only able to evaluate part of image tangent to the probe. In this research, a spatial resolution estimate method of the endoscope OCT system is proposed. The annular phantom, made by uniformly distributing golden scattered microparticles in polydimethylsiloxane (PDMS), can provide dynamic scanning imaging evaluation of endoscopic OCT system, closer to its actual working status. The point spread function analysis method is used to analyze the imaging results of the annular phantom with the endoscopic OCT system. And many scattered particles are statistically analyzed to determine the spatial resolution of the endoscope OCT system. The method is low in cost, simple and convenient. It is valuable for the development of test standards for endoscope OCT systems.

Spatial coherence in 2D holography.

Holography is a long-established technique to encode an object's spatial information into a lower-dimensional representation. We investigate the role of the illumination's spatial coherence properties in the success of such an imaging system through point spread function and Fourier domain analysis. Incoherent illumination is shown to result in more robust imaging performance free of diffraction artifacts at the cost of incurring background noise and sacrificing phase retrieval. Numerical studies confirm that this background noise reduces image sensitivity as the image size increases, in agreement with other similar systems. Following this analysis, we demonstrate a 2D holographic imaging system realized with lensless, 1D measurements of microwave fields generated by dynamic metasurface apertures.

Optimization of spatial resolution and scattering effects for biomedical fluorescence imaging by using sub-regions of the shortwave infrared spectrum.

We evaluated the impact of light-scattering effects on spatial resolution in different shortwave infrared (SWIR) sub-regions by analyzing two SWIR emissive phantoms made of polydimethylsiloxane (PDMS)-gold nanoclusters (Au NCs) composite covered with mice skin, or capillary tubes filled with Au NCs or IRDye 800CW at different depth in intralipids and finally, after administration of the Au NCs intravenously in mice. Our findings highlighted the benefit of working at the highest tested spectral range of the SWIR region with a 50% enhancement of spatial resolution measured in artificial model when moving from NIR-II (1000-1300 nm) to NIR-IIa (1300-1450 nm) region, and a 25% reduction of the scattering from the skin determined by point spread function analysis from the NIR-II to NIR-IIb region (1500-1700 nm). We also confirmed that a series of Monte Carlo restoration of images significantly improved the spatial resolution in vivo in mice in deep tissues both in the NIR-II and NIR-IIa spectral windows.

Three-dimensional Yarnball k-space acquisition for accelerated MRI.

To introduce an efficient sampling technique named Yarnball, which may serve as a direct alternative to 3D Cones. Yarnball evolves through 3D k-space with increasing loop size, and the differential equations defining this flexible trajectory are presented in detail. The sampling efficiencies of Yarnball and 3D Cones were compared through point spread function analysis and simulated imaging (which highlights undersampling in the absence of other scanning effects). The feasibility of Yarnball implementation was demonstrated for fully sampled T1 -weighted images of the human head at 3 T. The mostly large 3D loops of the Yarnball trajectory facilitate rapid sampling under peripheral nerve stimulation constraint, an advantage that increases with readout duration (TRO ). Point spread function analysis yielded 89% (TRO = 2 ms) and 77% (TRO = 10 ms) of Yarnball voxels with magnitude less than 0.01% of the point spread function peak. For 3D Cones, these values were only 52% and 29%. The 3D-Cones technique required 1.4 times (TRO = 2 ms) and 1.8 times (TRO = 10 ms) more trajectories than Yarnball to produce simulated images of a sphere free from undersampling artifact. For a prolate spheroidal (head-like) object, 1.75 times and 2.6 times more trajectories were required for 3D Cones. Yarnball produced 0.72 mm (1/2kmax ) isotropic T1 -weighted human brain images free from undersampling artifact in only 98 seconds at 3 T. Yarnball demonstrated greater k-space sampling efficiency than directly comparable 3D Cones, and may have value wherever 3D Cones has been considered. Yarnball may also have value in the context of rapid T1 -weighted brain imaging.

Comparative Evaluation of Visual Outcomes After Bilateral Implantation of a Diffractive Trifocal Intraocular Lens and an Extended Depth of Focus Intraocular Lens.

To compare visual outcomes and clinical performance of diffractive trifocal and extended depth of focus (EDOF) intraocular lenses (IOLs). This prospective, consecutive, nonrandomized, comparative study of 6-month duration included assessment of 160 eyes of 80 patients (40 patients in each group). The patients had bilateral cataract surgery with implantation of a trifocal (FineVision Micro F; PhysIOL SA, Liège, Belgium) or EDOF IOL (TECNIS Symfony; Abbott Medical Optics, Inc., Abbott Park, IL) in both eyes. Ophthalmological evaluation included measurement of monocular uncorrected distance visual acuity (UDVA) and corrected distance VA (CDVA), uncorrected intermediate VA (UIVA) and distance-corrected intermediate VA (DCIVA), uncorrected near VA (UNVA) and distance-corrected near VA (DCNVA). Analysis of point-spread function and modulation transfer function was also performed postoperatively, and quality of vision and spectacle-dependence questionnaires were assessed. There was no statistically significant difference between groups in monocular UDVA (P=0.65), CDVA (P=0.82), and binocular UDVA (P=0.81). The monocular UIVA, monocular DCIVA, and binocular UIVA were also comparable among the two groups (P=0.70, 0.74, and 0.81, respectively). Monocular UNVA, DCNVA, and binocular UNVA were statistically and significantly better for the trifocal group than for the EDOF (P=0.01, P=0.009, and P=0.001, respectively). There were no differences in visual symptoms and quality among groups. Trifocal IOL had a clear advantage over EDOF IOLs in near VA, while both IOLs showed excellent performance in distance and intermediate VA. Both IOLs provided high percentage of spectacle independence and patient satisfaction with minimal level of disturbing photic phenomena.

Single-Pixel Imaging Using Multimode Fiber and Silicon Photonic Phased Array

Due to the unique nature of offering minimal invasiveness and high spatial resolution simultaneously, multimode fibers (MMFs) are receiving significant attention in bio-imaging applications. While a spatial light modulator is typically used for controlling the wavefront of the light emitted from the MMF, it makes the system slow, bulky, and expensive. To solve this problem, in this work, we demonstrate the use of a chip-scale integrated optical phased array (OPA) for imaging through an MMF. A silicon OPA with 128 independent phase shifters is fabricated and combined with a 3D waveguide interface to generate speckle patterns at the MMF output. Using the generated speckles and the optical power detected by a bucket detector, we experimentally obtain fine 2D images of the target. From the point spread function analysis of the system, the number of resolvable points is derived to be 1007 points, which is much larger than the number of phase shifters.

Определение функции рассеяния точки компьютерно-синтезированной линзы, сформированной фазовым модулятором света

In various areas of photonics, there is a tendency to move from elements of physical optics to elements of flat optics, primarily due to reducing dimensions of instruments and devices. Usually, spatial light modulators are used to quickly output flat phase elements. In this paper, the possibility of replacing the optical system with a computer-generated lens was investigated. The novelty of the work lies in a comparative analysis of point spread functions formed by an optical system and a computer-synthesized lens. Numerous experiments confirm the result.

Model of the light sword intraocular lens: in-vitro comparative studies.

This work presents the first models of light sword intraocular lenses (LS IOLs) with angularly modulated optical power. We performed an experimental, comparative study with multifocal and extended depth of focus intraocular lenses, which are available on the market. The measurements conducted in an original optical bench were utilised for an analysis of point spread functions, elongated foci, modulation transfer functions and the areas defined by them. The LS IOL models perform homogeneous imaging in the whole range of designed defocus. The proposed concept of extended depth of focus seems to be promising for the development of presbyopia-correcting intraocular lenses capable of regaining fully functional vision.

Volume-recorded hologram modeling, point-spread function analysis, and segmented adaptive equalization for holographic data storage

The rapid growth in digital information throughout the world has demanded storage with a high capacity and high transfer rate. Holographic data storage (HDS) is one promising candidate for next-generation data storage because of its high potential in capacity and transfer rate. However, high-volume HDS usually suffers from inter-signal interference (ISI). Here, we first develop volume recording and reproduction models for HDS. We reveal through optical simulations based on the developed models that ISI differs not only between pages but also between areas on the same page. Then, we develop an advanced equalization technique called segmented adaptive equalization (SAE) that takes into account inter-area ISI difference. We can improve signal quality much more than conventional equalization techniques by using SAE. We are confident that SAE can enhance the realization of HDS.

Whole-heart spiral simultaneous multi-slice first-pass myocardial perfusion imaging.

To develop and evaluate a simultaneous multislice (SMS) spiral perfusion pulse sequence with whole-heart coverage. An orthogonal set of phase cycling angles following a Hadamard pattern was incorporated into a golden-angle (GA) variable density spiral perfusion sequence to perform SMS imaging at different multiband (MB) factors. Images were reconstructed using an SMS extension of L1-SPIRiT that we have termed SMS-L1-SPIRiT. The proposed sequence was evaluated in 40 subjects (10 each for MB factors of 1, 2, 3, and 4). Images were blindly graded by 2 cardiologists on a 5-point scale (5, excellent). To quantitatively evaluate the reconstruction performance against images acquired without SMS, the MB =1 data were used to retrospectively simulate data acquired at MB factors of 2 to 4. Analysis of the SMS point-spread function for the desired slice showed that the proposed sampling strategy significantly canceled the main-lobe energy of the other slices and has low side-lobe energy resulting in an incoherent temporal aliasing pattern when rotated by the GA. Retrospective experiments demonstrated the SMS-L1-SPIRiT method removed aliasing from the interfering slices and showed excellent agreement with the ground-truth MB =1 images. Clinical evaluation demonstrated high-quality perfusion images with average image-quality scores of 4.3±0.5 (MB =2), 4.2±0.5 (MB =3), and 4.4±0.4 (MB =4) with no significant quality difference in image quality between MB factors (P=0.38). SMS spiral perfusion at MB factors 2, 3, and 4 produces high-quality perfusion images with whole-heart coverage in a clinical setting with high sampling efficiency.

Single-shot spiral imaging at 7 T.

The purpose of this work is to explore the feasibility and performance of single-shot spiral MRI at 7 T, using an expanded signal model for reconstruction. Gradient-echo brain imaging is performed on a 7 T system using high-resolution single-shot spiral readouts and half-shot spirals that perform dual-image acquisition after a single excitation. Image reconstruction is based on an expanded signal model including the encoding effects of coil sensitivity, static off-resonance, and magnetic field dynamics. The latter are recorded concurrently with image acquisition, using NMR field probes. The resulting image resolution is assessed by point spread function analysis. Single-shot spiral imaging is achieved at a nominal resolution of 0.8 mm, using spiral-out readouts of 53-ms duration. High depiction fidelity is achieved without conspicuous blurring or distortion. Effective resolutions are assessed as 0.8, 0.94, and 0.98 mm in CSF, gray matter and white matter, respectively. High image quality is also achieved with half-shot acquisition yielding image pairs at 1.5-mm resolution. Use of an expanded signal model enables single-shot spiral imaging at 7 T with unprecedented image quality. Single-shot and half-shot spiral readouts deploy the sensitivity benefit of high field for rapid high-resolution imaging, particularly for functional MRI and arterial spin labeling.

Snapshot-CEST: Optimizing spiral-centric-reordered gradient echo acquisition for fast and robust 3D CEST MRI at 9.4T.

Gradient echo (GRE)-based acquisition provides a robust readout method for chemical exchange saturation transfer (CEST) at ultrahigh field (UHF). To develop a snapshot-CEST approach, the transient GRE signal and point spread function were investigated in detail, leading to optimized measurement parameters and reordering schemes for fast and robust volumetric CEST imaging. Simulation of the transient GRE signal was used to determine the optimal sequence parameters and the maximum feasible number of k-space lines. Point spread function analysis provided an insight into the induced k-space filtering and the performance of different rectangular reordering schemes in terms of blurring, signal-to-noise ratio (SNR) and relaxation dependence. Simulation results were confirmed in magnetic resonance imaging (MRI) measurements of healthy subjects. Minimal repetition time (TR) is beneficial for snapshot-GRE readout. At 9.4T, for TR = 4ms and optimal flip angle close to the Ernst angle, a maximum of 562k-space lines can be acquired after a single presaturation, providing decent SNR with high image quality. For spiral-centric reordered k-space acquisition, the image quality can be further improved using a rectangular spiral reordering scheme adjusted to the field of view. Application of the derived snapshot-CEST sequence for fast imaging acquisition in the human brain at 9.4T shows excellent image quality in amide and nuclear Overhauser enhancement (NOE), and enables guanidyl CEST detection. The proposed snapshot-CEST establishes a fast and robust volumetric CEST approach ready for the imaging of known and novel exchange-weighted contrasts at UHF.