Compact Scanning Research Articles

PO-1417: A GPU Monte Carlo to support clinical routine in a compact spot scanning proton therapy system

PO-1417: A GPU Monte Carlo to support clinical routine in a compact spot scanning proton therapy system

Beam Characteristics of the First Clinical 360°-rotational Compact Scanning Pencil Beam Proton Treatment System and Comparisons against a Multi-Room System

This paper is to present the dosimetric characteristics of the first clinical CBCT guided 360˚-rotational compact/single-room scanning pencil beam proton treatment system (SRPT) and comparisons against a recent beam data from a multi-room proton therapy system (MRPT) by the same vendor. The proton beam commissioning was conducted on the first clinical, newly-designed compact ProBeam 360˚ for its scanning pencil beams for protons ranging from 70MeV to 220MeV. The integrated depth dose curves (IDDs) were acquired in water with AP monogenic proton beams using a PTW Bragg peak chamber. The dose output factors, measured by a Marcus chamber at 15 mm transmission beam portion using single layer 10x10 cm2 proton plans, were then incorporated to the iDD's along with a factor of 1.1 for RBE offset. The beam spot sigma sizes were then derived from single Gaussian fitting for the in-air measured spot profiles. After beam modeling and validation for a treatment planning system, the proton dosimetric characteristics were compared against the recent data of MRPT. In contract to MRPT data, the Bragg peaks of SRPT have shown moderately extended proton beam range straggling in the peak region accompanied by a marginally elevated proximal transmission beam portion. This phenomenon displayed more noticeably in the mid-ranged or even high energies. Consequently, IDDs of SRPT showed about 0.41 to 0.94 mm broader Bragg peak widths (Rb80 - Ra80) in energies of 140 MeV or greater, peaked at 180 MeV. About 0.65-0.79 mm slightly extended distal falloffs (Rb20-80) were noticeable for energies between 140 MeV and 170 MeV, consistent with the findings of minimally raised energy sigma in AcurosPT Monte Carlo model. An independent check for the dose and energy accuracy of a spread-out Bragg peak plan on a simple phantom by the IROC showed 1.00 accuracy with 1.00 ±5% allowance. Additional comprehensive end-to-end independent check using a more realistic prostate phantom offered by IROC was reported a 96% accuracy and the passing score at a set passing criterion of 85%. The result over 108 patient specific individual field QAs with Octavius 1500 2D ionization chamber array showed 100% passing rate using a Gamma index of 3%/3mm or tighter from fields with or without range shifters. The high QA passing rates suggest a high confidence on the accuracy and quality of the commissioning for the newly designed SRPT. The commissioning results of the new-designed SRPT showed slightly widened proton Bragg peaks, elevated beam transition region and extended peak distal falloffs, particularly in mid-high energies, suggest minimally broader spectra for selected proton energies in comparing against MRPT data. This did not show a meaningful impact on the quality and accuracy of proton therapy program, indicated by high scores from independent dosimetry end-to-end checks and over 108 patient’s specific beam QA’s.

Combined atomic force microscope and scanning tunneling microscope with high optical access achieving atomic resolution in ambient conditions.

Performing atomic force microscopy (AFM) and scanning tunneling microscopy (STM) with atomic resolution under ambient conditions is challenging due to enhanced noise and thermal drift. We show the design of a compact combined atomic force and scanning tunneling microscope that uses qPlus sensors and discuss the stability and thermal drift. By using a material with a low thermal expansion coefficient, we can perform constant height measurements and achieve atomic resolution in both AFM and STM on various samples. Moreover, the design allows a wide angle optical access to the sensor and the sample that is of interest for combining with optical microscopes or focusing optics with a high numerical aperture.

Reducing PNS with minimal performance penalties via simple pulse sequence modifications on a high-performance compact 3T scanner

One of the major concerns associated with high-performance gradients is peripheral nerve stimulation (PNS) of the subject during MRI exams. Since the installation, more than 680 volunteer subjects (patients and controls) have been scanned on a compact 3 T MRI system with high-performance gradients, capable of 80 mT m−1 gradient amplitude and 700 T m−1 s−1 slew rate simultaneously. Despite PNS concerns associated with the high-performance gradients, due to the smaller physical dimensions of the gradient coils, minimal or no PNS sensation was reported with most pulse sequences. The exception was PNS reported by only five of 252 subjects (about 2%) scanned with a specific 3D fast spin echo pulse sequence (3DFLAIR). Rather than derating the entire system performance across all pulse sequences and all gradient lobes, we addressed reported PNS effect with a simple and specific modification to the targeted lobes of the problematic pulse sequence. in addition, the PNS convolutional model was adapted to predict sequence-specific PNS threshold level and its reduction after derating. The effectiveness of the targeted pulse sequence modification was demonstrated by successfully re-scanning four of the subjects who previously reported PNS sensations without further reported PNS. The pulse sequence modification did not result in noticeable degradation of image quality or substantial increase in scan time. The results demonstrated that PNS was rarely reported on the compact 3 T, and when it was, utilizing a specific modification of the gradient waveform causing PNS was an effective strategy, rather than derating the performance of the entire gradient system.

Versatile Single-Element Ultrasound Imaging Platform using a Water-Proofed MEMS Scanner for Animals and Humans

Single-element transducer based ultrasound (US) imaging offers a compact and affordable solution for high-frequency preclinical and clinical imaging because of its low cost, low complexity, and high spatial resolution compared to array-based US imaging. To achieve B-mode imaging, conventional approaches adapt mechanical linear or sector scanning methods. However, due to its low scanning speed, mechanical linear scanning cannot achieve acceptable temporal resolution for real-time imaging, and the sector scanning method requires specialized low-load transducers that are small and lightweight. Here, we present a novel single-element US imaging system based on an acoustic mirror scanning method. Instead of physically moving the US transducer, the acoustic path is quickly steered by a water-proofed microelectromechanical (MEMS) scanner, achieving real-time imaging. Taking advantage of the low-cost and compact MEMS scanner, we implemented both a tabletop system for in vivo small animal imaging and a handheld system for in vivo human imaging. Notably, in combination with mechanical raster scanning, we could acquire the volumetric US images in live animals. This versatile US imaging system can be potentially used for various preclinical and clinical applications, including echocardiography, ophthalmic imaging, and ultrasound-guided catheterization.

Ultrasonic fingerprint sensor in underglass prototype using impedance mismatching

Fingerprint imaging is a powerful tool in biometric identification systems. There are several methods for measuring fingerprints, such as optics, capacitive, and ultrasonic methods. The previous ultrasonic imaging techniques have been available in immersion systems which require the hands to be put into water. Also, pulse-echo system in dry condition has coupling layer which is similar acoustic impedance to human tissue or high impedance materials based on waveguide. For fingerprint imaging in the dry state, we propose an ultrasonic imaging technique in underglass by using the impedance mismatch between the fingertip and the solid plate. We present the image results according to the plate material such as acrylic, glass and PDMS. In addition, simulation results based on small 2-D array transducers in a near field suggest the feasibility of compact and fast fingerprint scanning system. Therefore, this work presents feasibility of ultrasonic pulse-echo fingerprint sensing method for dry hand.

Broadband Frequency Scanning Spoof Surface Plasmon Polariton Design with Highly Confined Endfire Radiations

This paper proposes a compact broadband frequency scanning spoof surface plasmon polariton (SSPP) based design for efficient endfire radiations with high field confinement. Through the dispersion engineering, highly confined field distribution has been obtained in the operating frequency region. The proposed SSPP antenna has achieved a continuous through endfire scanning in the X-band at other operating frequencies which is in general difficult to obtain for SSPP based antennas. In the proposed design methodology, the swore-shaped surface plasmon antenna has both edges corrugated with an array of rectangular grooves which effectively confines the electromagnetic field into a slow travelling wave. The surface impedances along both edges were engineered to be different at operating frequencies as to force the surface current to preferentially flow along either edge of the antenna to a different extent. The design with overall dimensions of (55 × 30) mm2 has achieved a broadband of 4 GHz with high peak measured gain of 9.8 dBi and peak efficiency of about 95 percent in the X-band. The antenna has been further tested experimentally for scanning application of target location also.

Terahertz diffractive structures for compact in-reflection inspection setup.

Two diffractive optical elements are used to create a compact raster THz scanning setup in reflective configuration. The first one focuses the radiation into the small focal spot on the sample, while the second one collects reflected radiation and focuses it on the detector. To assure small size of the setup and large apertures of optical elements, structures work in the off-axis geometry. Thus, the focal spot is formed 100 mm after and 60 mm below the optical axis of the element, which measures 75 mm in diameter. The designed iterative algorithm allows further minimization of these values.

The effect of spiral trajectory correction on pseudo-continuous arterial spin labeling with high-performance gradients on a compact 3T scanner.

To demonstrate the feasibility of pseudo-continuous arterial-spin-labeled (pCASL) imaging with 3D fast-spin-echo stack-of-spirals on a compact 3T scanner (C3T), to perform trajectory correction for eddy-current-induced deviations in the spiral readout of pCASL imaging, and to assess the correction effect on perfusion-related images with high-performance gradients (80 mT/m, 700T/m/s) of the C3T. To track eddy-current-induced artifacts with Archimedean spiral readout, the spiral readout in pCASL imaging was performed with 5 different peak gradient slew rate (Smax ) values ranging from 70 to 500 T/m/s. The trajectory for each Smax was measured using a dynamic field camera and applied in a density-compensated gridding image reconstruction in addition to the nominal trajectory. The effect of the trajectory correction was assessed with perfusion-weighted (ΔM) images and proton-density-weighted images as well as cerebral blood flow (CBF) maps, obtained from 10 healthy volunteers. Blurring artifact on ΔM images was mitigated by the trajectory correction. CBF values on the left and right calcarine cortices showed no significant difference after correction. Also, the signal-to-noise ratio of ΔM images improved, on average, by 7.6% after correction (P < .001). The greatest improvement of 12.1% on ΔM images was achieved with a spiral readout using Smax of 300~400 T/m/s. Eddy currents can cause spiral trajectory deviation, which leads to deformation of the CBF map even in cases of low value Smax . The trajectory correction for spiral-readout-based pCASL produces more reliable results for perfusion imaging. These results suggest that pCASL is feasible on C3T with high-performance gradients.

A Novel QCA based Compact Scan Flip-flop for Digital Design Testing

Quantum-dot Cellular Automata (QCA) is an emerging technology used for computation at nano scale. It is an excellent alternative for the conventional CMOS technology. QCA provides us with low energy, high speed, faster switching speed and compact structures for logical circuits. Testing is the integral part of the design verification, scan flip-flop is used for device testing. It is used in processors for a built-in self-test. The objective of this paper is to design an optimized structure of a scan flip-flop which occupies less area and dissipates minimum energy compared to the previously designed architectures. The efficiency of the proposed structure is analyzed in terms of cell count, energy dissipation, and area occupied by the logical circuit. Proposed scan flip flop has a cell count of 32 and an energy dissipation of 0.0105 eV which is 20 % more efficient in terms of cell count and 29 % more efficient than the previous designs. The CAD tool, QCA Designer is used for design and simulation. Cells have a dimension of 18 nm in height and 18 nm in breadth and there is a distance of 2 nm between these cells. Bi-stable and coherence vector simulation engines are used in the tool for simulation.

A 45° tilted 3D-printed scanner for compact side-view laser scanning endoscopy

Side viewing, miniaturized laser scanning endoscopes are powerful tools in providing sub-cellular level resolution and multi-layered imaging of the walls of body cavities. Yet, the level of miniaturization for such devices is significantly hampered by the necessity for 45° placement of the whole scanner unit with respect to the cavity axis. With its rapid and low-cost production capability, 3D printing can be employed in addressing the challenge of producing a laser scanner, whose scanning head makes 45°, or any desired angle, with the scanner unit. Producing a 10 × 10 mm2 scanner device with tilted scan head (as opposed to the conventional design with identical size) enabled size shrinkage of a near fully 3D-printed laser scanning imager by × 1.5 in diameter (from 17 to 11 mm). We also share the initial results on 5 × 5 mm2 total die size scanners, having literally identical die size with their MEMS counterparts, and discuss the road steps in producing < 8-mm diameter laser scanning devices with these scanners using 3D printing technology. The frame-rate improvement strategies are discussed in detail. Furthermore overall resolution and frame-rate values that can be achieved with the presented 3D printed scanners are tabulated and compared to MEMS counterparts. Overall with their low cost, easy and rapid fabrication, 3D printed actuators are great candidates for opto-medical imaging applications.

A Lightweight Leddar Optical Fusion Scanning System (FSS) for Canopy Foliage Monitoring.

A growing need for sampling environmental spaces in high detail is driving the rapid development of non-destructive three-dimensional (3D) sensing technologies. LiDAR sensors, capable of precise 3D measurement at various scales from indoor to landscape, still lack affordable and portable products for broad-scale and multi-temporal monitoring. This study aims to configure a compact and low-cost 3D fusion scanning system (FSS) with a multi-segment Leddar (light emitting diode detection and ranging, LeddarTech), a monocular camera, and rotational robotics to recover hemispherical, colored point clouds. This includes an entire framework of calibration and fusion algorithms utilizing Leddar depth measurements and image parallax information. The FSS was applied to scan a cottonwood (Populus spp.) stand repeatedly during autumnal leaf drop. Results show that the calibration error based on bundle adjustment is between 1 and 3 pixels. The FSS scans exhibit a similar canopy volume profile to the benchmarking terrestrial laser scans, with an r2 between 0.5 and 0.7 in varying stages of leaf cover. The 3D point distribution information from FSS also provides a valuable correction factor for the leaf area index (LAI) estimation. The consistency of corrected LAI measurement demonstrates the practical value of deploying FSS for canopy foliage monitoring.

A Magnetic Scanner for High-Energy Beams of Heavy Ions

—Design of a compact magnetic scanner, which is intended for uniform irradiation of stationary targets with dimensions of up to 200 × 200 mm with a beam of heavy charged particles (HCPs) with a charge-to-mass ratio of Z/A = 0.3–0.5, was performed. It can be used to solve a wide range of applied problems. The scanner is optimized for operating with a beam of heavy ions with Z/A = 0.3, an energy of 800 MeV/amu, and an emittance of 40 π mm mrad in both a single-pulse and a multiframe irradiation modes. The developed scanner consists of two compact scanning dipoles (one after the other) and can be placed together with other ion-optical elements within a limited space of the HCP beam transport channel to the target chamber, where a two-dimensional irradiation field is scanned. The main characteristics of the pulsed power supply of the scanner during slow extraction of ion beams are also presented and discussed.

Dual-Modality Confocal Laser Feedback Tomography for Highly Scattering Medium

The combination of optical modalities is a common practice to improve the efficiency of biomedical optics systems. We propose confocal laser feedback tomography for volumetric dual-modality imaging. Two major modalities of laser Doppler flowmetry and reflectance confocal microscopy were integrated, and the signals were concurrently acquired for cross-sectional and volumetric imaging, by means of a compact laser scanning system. The technique was applied to a two-layered skin tissue phantom containing a 200- $\mu \text{m}$ -diameter intralipid flow channel that features functional and morphological changes at the same time. Results show the potential for concurrent 3-D mapping of dynamic and static inhomogeneities in a highly scattering medium which can improve the contrast in non-invasive biological tissue imaging, providing a confocal image in addition to the Doppler flowmetry image.

Adaptive wavefront correction structured illumination holographic tomography

In this study, a novel adaptive wavefront correction (AWC) technique is implemented on a compactly developed structured illumination holographic tomography (SI-HT) system. We propose a mechanical movement-free compact scanning architecture for SI-HT systems with AWC, implemented by designing and displaying a series of computer-generated holograms (CGH) composed of blazed grating with phase Fresnel lens on a phase-only spatial light modulator (SLM). In the proposed SI-HT, the aberrations of the optical system are sensed by digital holography and are used to design the CGH-based AWC to compensate the phase aberrations of the tomographic imaging system. The proposed method was validated using a standard Siemens star target, its potential application was demonstrated using a live candida rugosa sample, and its label-free three-dimensional refractive index profile was generated at its subcellular level. The experimental results obtained reveal the ability of the proposed method to enhance the imaging performance in both lateral and axial directions.

Design, test and control of a compact piezoelectric scanner based on a compound compliant amplification mechanism

This paper presents the mechanical design, testing and control of a novel piezoelectric scanner to achieve high performance motion tracking. Based on both triangle amplification and differential principles, the scanner is designed with a compound compliant amplification mechanism (CCAM) to realize deflection motion. A strain-type piezoelectric actuator is adopted as the actuation and angle-sensing element for the scanner. Analytical calculations in terms of deflection range, sensor deployment and dynamics are derived, and then the finite element analysis and prototype tests are conducted to verify the analytical results. To facilitate precise angular tracking in front of the existing hysteresis effect, a terminal sliding mode control scheme is implemented for the performance improvement. Experimental results reveal that the developed scanner has an angle resolution of 1.5 μrad, a motion range of ±0.16 mrad, and can achieve accurate angle tracking performance.

An automatic 3D reconstruction system for texture-less objects

Structure from Motion (SfM) is an image based method for 3D reconstruction of objects. This method coupled with Dense Multi-View Stereo (DMVS) can be used to generate an accurate point cloud of texture-full objects. Although this process is fully automatic, capturing images in proper locations is hard especially for texture-less objects which need a pattern projection procedure to have a successful matching step in SfM. This study aims to propose an automatic and portable system which can provide a pattern on objects and capture a set of high quality images in a way that a complete and accurate 3D model can be generated by the captured images using SFM and DMVS method. The system consists of three parts including a glassy turntable with a novel pattern projection system, a digital camera located on a mono-pod mounted on a length adjustable bar attached to the box of turntable and a controller system to control two other parts. Given the speed and step parameters for the system in a smart phone as the controller system, the digital camera automatically captures an image after every rotation step of the table. To evaluate the system, five different objects were tested under four criteria including plane fitting, structural resolution test, scale resolving test and comparing with a reference 3D model obtained with a commercial accurate laser scanner known as GOM ATOS Compact laser scanner. The average standard deviation for all the cited criteria was around 0.2 mm which illustrates the ability of the proposed system to capture high quality images for 3D reconstruction of texture-less objects.

Design and Control of a Magnetic Laser Scanner for Endoscopic Microsurgeries

State-of-the-art surgical laser systems achieve high-quality tissue ablations with minimal thermal damage to the tissue by providing high-speed laser scanning. However, current technology is not applicable to difficult-to-reach anatomical sites for endoscopic surgery. In these cases, flexible laser fibers are used, but the resulting ablation quality is limited. Therefore, there is a need to improve flexible laser surgery systems. This paper proposes a solution to this issue based on a compact laser scanner and a focusing module designed to be placed at the distal end of a flexible endoscopic system. The device uses magnetic actuation to bend a laser fiber; thus, allowing precise 2-D position control and high-speed scanning of a high-power surgical laser. The design, implementation, and control of such a system are described in this paper, with special focus on its dynamic modeling and controller design to provide real-time control and fast automated execution of surgeon-defined trajectories. Validation experiments performed with different trajectories and scanning frequencies attest the performance of the system, which demonstrates trajectory tracing with 90 $\mu$ m (1.4 mrad) accuracy for scanning frequencies up to 15 Hz. This is a significant result that promises to bring the benefits of free-beam laser scanning systems to endoscopic microsurgeries.

Reprogrammable Graphene-based Metasurface Mirror with Adaptive Focal Point for THz Imaging

Recent emergence of metasurfaces has enabled the development of ultra-thin flat optical components through different wavefront shaping techniques at various wavelengths. However, due to the non-adaptive nature of conventional metasurfaces, the focal point of the resulting optics needs to be fixed at the design stage, thus severely limiting its reconfigurability and applicability. In this paper, we aim to overcome such constraint by presenting a flat reflective component that can be reprogrammed to focus terahertz waves at a desired point in the near-field region. To this end, we first propose a graphene-based unit cell with phase reconfigurability, and then employ the coding metasurface approach to draw the phase profile required to set the focus on the target point. Our results show that the proposed component can operate close to the diffraction limit with high focusing range and low focusing error. We also demonstrate that, through appropriate automation, the reprogrammability of the metamirror could be leveraged to develop compact terahertz scanning and imaging systems, as well as novel reconfigurable components for terahertz wireless communications.

Lensless single-pixel imaging by using LCD: application to small-size and multi-functional scanner.

Single-pixel imaging commonly uses a spatial light modulator (SLM) to encode a scene's spatial information into a one-dimensional light signal sequence so that a single-pixel detector can be used to capture a scene. Digital micromirror device, liquid crystal on silicon, or light emitted diode matrix is a common choice of SLM, but it requires a certain lens system in order to project the structured light pattern that is generated by the SLM onto the scene. Using a lens would not only lead to aberration but also result in difficulty for establishing a compact imaging system. Therefore, we propose to use a liquid crystal display (LCD) as an intensity-only SLM to conduct structured illumination. As such, single-pixel imaging can be performed in a lensless way. As an instance of the proposed technique, a small-size and multi-functional scanner is designed and established to prove the lensless single-pixel imaging concept. As experimentally demonstrated, the single-pixel scanner can not only achieve grayscale and true-color scanning as a typical scanner does, but also achieve distinctive functionalities, such as accurate optical character recognition from under-sampled data, on-the-fly encryption, and genuine document identification. This compact scanner is as thin as 2.48 millimeters. The proposed lensless single-pixel imaging technique might find applications in various fields.