Depth Scanning Research Articles

Quantitative subsurface analysis using frequency modulated thermal wave imaging

Quantitative depth analysis of the anomaly with an enhanced depth resolution is a challenging task towards the estimation of depth of the subsurface anomaly using thermography. Frequency modulated thermal wave imaging introduced earlier provides a complete depth scanning of the object by stimulating it with a suitable band of frequencies and further analyzing the subsequent thermal response using a suitable post processing approach to resolve subsurface details. But conventional Fourier transform based methods used for post processing unscramble the frequencies with a limited frequency resolution and contribute for a finite depth resolution. Spectral zooming provided by chirp z transform facilitates enhanced frequency resolution which can further improves the depth resolution to axially explore finest subsurface features. Quantitative depth analysis with this augmented depth resolution is proposed to provide a closest estimate to the actual depth of subsurface anomaly. This manuscript experimentally validates this enhanced depth resolution using non stationary thermal wave imaging and offers an ever first and unique solution for quantitative depth estimation in frequency modulated thermal wave imaging.

Risk Factors for Opaque Bubble Layer in Small Incision Lenticule Extraction (SMILE).

To assess the independent effect of myopia and astigmatism on the risk of the occurrence of opaque bubble layer (OBL) in small incision lenticule extraction (SMILE) and further investigate the relationship between scanning depth and OBL. Twenty-two cases and 317 controls were included in a case-control study from the database of Tianjin Eye Hospital from April 2015 to July 2016. Baseline characteristics were recorded and all of the eyes were manually reviewed by two different observers masked to preoperative refractive status. Multiple regression analysis was used to assess the independent relationship between the attempted correction in diopters and the risk of OBL and to further analyze the association between scanning depth and the risk. The risk of OBL significantly decreased with increasing myopia (diopters) (odds ratio [OR] = 0.44; 95% confidence interval [CI]: 0.30 to 0.64; P < .0001). The risk of OBL also significantly decreased with increasing astigmatism (diopters) (OR = 0.10; 95% CI: 0.02 to 0.42; P = .0017). Lenticular thickness changed by 14.86 μm per diopter for myopia (β =14.86; 95% CI = 14.56 to 15.15; P < .0001) and 15.10 μm per diopter for astigmatism (β = 15.10; 95% CI = 13.96 to 16.24; P < .0001), respectively. A low correction was a significant independent risk factor for OBL during SMILE and the effect of astigmatism on OBL was greater than that of myopia. Deepening the photodisruption plane appropriately may reduce the risk of OBL. [J Refract Surg. 2017;33(11):759-764.].

Multifocus optical-resolution photoacoustic microscope using ultrafast axial scanning of single laser pulse

A tunable acoustic gradient (TAG) lens has been introduced in the fast axial scanning in optical imaging. However, it still needs additional imaging time for depth scanning. In this study, we split a single laser pulse into three sub-pulses and introduce them into three fibers with different lengths. The sub-pulses out of the fibers were combined thereafter. We then obtained a pulse train with a time interval of 120 ns. By controlling the fire time of the pulse train and the driving signal of the TAG lens, we can receive three focal spots in one A line data acquisition using a single input laser pulse. The depth of focus (DoF) of the system was measured to be 360 μm, which is three times of that of previous systems without the sacrifice of time resolution. A mouse ear and mouse cerebral vasculature were imaged in-vivo to demonstrate the feasibility of the extended DoF of our system.

Underwater 3D Reconstruction Based on Geometric Transformation of Sonar and Depth Information

3D reconstruction is of vital importance to detect and monitor the underwater environment. A method based on geometric transformation of mechanical scanning sonar and depth information is proposed, in which the point cloud data from sonar and depth gauge are acquired to reconstruct the underwater 3D environment. However, noise and interference can affect the measurement of sonar, and movement of sonar during measurement can lead to distortion of the received data. Meanwhile, translation and rotation movement of sonar head may happen when ROV dives which can lead to different body reference coordinates of different scanning. To solve this, pre-processing and motion compensation are implemented at first, and underwater matching correction algorithm is used to calculate the translation and rotation of the sonar head. Then the inverse operation is implemented to convert the scan data of every depth into the same coordinate reference system. Finally, surface reconstruction of point clouds from sonar the depth information are used to reconstruct underwater environment based on MLS (Moving Least Square Method) using PCL (Point Cloud Library). Water tank experiments verify the effectiveness of the proposed method.

Ultrawidefield OCT

SummaryRetinal wide‐field imaging plays an increasingly important role for the diagnosis of various types or pathologies, some of which start or prevalently appear in the periphery. Despite the great value of wide field fundus cameras and scanning laser ophthalmoscopes for diagnosis and documentation, these devices only acquire 2‐dimensional data in form of en face projections. However, cross‐sectional imaging with optical coherence tomography (OCT) can provide a wealth of additional information. To cover a wide area of the retina of 100° or more of viewing angle, 5 – 10 million OCT scans are required. Current commercially available OCT technology is not able to capture such large data sets and the acquisition time would be prohibitively long.We recently developed retinal Megahertz OCT (MHz‐OCT), an OCT system that can acquire more than 1 million depth scans per second. It can achieve the high speed by using a new type of swept laser source: the Fourier Domain Mode Locked (FDML) laser. This high speed enables us to acquire a densely sampled 3‐dimensional OCT data set in the non‐mydriatic eye, covering an area of up to 100° angle on the human retina. Technology development and diagnostic potential of such devices will be discussed.

Synchronization-free light sheet microscopy based on a 2D phase mask

High-speed 3D microscopic imaging methods have led to numerous biological discoveries. In this Letter, we present a sync-free light sheet microscope (LSM) based on a static phase mask that eliminates the need for coupling the detection plane, thereby enabling high-speed volumetric imaging that is only limited by the speed of cameras, e.g., ∼1000 cross sections/s. In the sync-free design, the emission signals are first guided to the back of a galvanometric mirror, which laterally scans the emissions across a 2D phase mask, converting it to axial scanning that automatically compensates the focal shifts in the detection optics. Parametric models are developed to guide the phase mask design as well as to relate the axial scanning depth and magnification to design parameters. To quickly evaluate the different mask designs, a liquid-crystal-based spatial light modulator (LC-SLM) is used in the system. In the experiments, we scanned pollen and tissue samples via both the 2D phase mask and a piezoelectric objective scanner. The results show that the new method can generate clear images with comparable quality throughout the scanning range. The overall efficiency of the LSM is ∼10%. It is worthwhile to note that the efficiency will be significantly improved by replacing the LC-SLM with a custom-made lens. The new method realizes a compact LSM for high-speed 3D imaging that may find important applications in in vivo biological imaging.

Compact flexible multi-pass rotary delay line using spinning micro-machined mirrors

We propose a new method to extend the path length tunability of rotary delay-lines. This method was shown to achieve a duty cycle of >80% and repetition rates of over 40 kHz. The new method relies on a new multi-segmented micro-machined mirror and serial injection of a single reflection onto separate segments of this mirror. The tunability is provided by the relative positioning of each reflective point on the mirror segments. There are two distinct modes of operation: synchronous and asynchronous. By simply manipulating the spatial position of the returning paths over the respective mirror segments, we can switch between increasing the repetition rate (asynchronous mode) or the total delay path (synchronous mode). We experimentally demonstrated up to 8 m/s scans with repetition rates of up to 42.7 kHz. Furthermore, we present numerical simulations of 18 reflection points to illustrate possibility of achieving a scan speed of up to 80 m/s. Through intermediate combinations of synchronous and asynchronous operation modes with 4 or more passes, we also show that the system can simultaneously increase both repetition rate and scan depth.

Reliability of Entire Corneal Thickness Mapping in Normal Post-Laser in situ Keratomileusis and Keratoconus Eyes Using Long Scan Depth Spectral Domain Optical Coherence Tomography

Purpose: To investigate the repeatability and reproducibility of mapping the entire corneal thickness using spectral domain optical coherence tomography (SD-OCT). Methods: Thirty normal eyes, 30 post-laser in situ keratomileusis (LASIK) surgery eyes, and 30 keratoconus eyes were analyzed. A custom-built long scan depth SD-OCT device was used to obtain entire corneal images. Ten-millimeter-diameter corneal thickness maps were generated by an automated segmentation algorithm. Intraclass correlation coefficients of repeatability (ICC₁) and reproducibility (ICC₂), and coefficients of repeatability (CoR₁) and reproducibility (CoR₂), were calculated to quantify the precision and accuracy of corneal pachymetry measurements using the Bland-Altman method. Results: For SD-OCT measurements in healthy subjects, CoR₁ and CoR₂ were less than 5.00 and 5.53 μm. ICC₁ and ICC₂ were more than 0.997 and 0.996. For SD-OCT measurements in LASIK patients, CoR₁ and CoR₂ were less than 5.09 and 5.34 μm. ICC₁ and ICC₂ were more than 0.997 and 0.996. For SD-OCT measurements in keratoconus patients, CoR₁ and CoR₂ were less than 11.57 and 10.92 μm. ICC₁ and ICC₂ were more than 0.995 and 0.996. Conclusions: The measurements of corneal pachymetric mapping by long scan depth SD-OCT can be assessed over the entire corneal area with good repeatability and reproducibility.

Templateless Non-Rigid Reconstruction and Motion Tracking With a Single RGB-D Camera.

We present a novel templateless approach for nonrigid reconstruction and motion tracking using a single RGB-D camera. Without any template prior, our system achieves accurate reconstruction and tracking for considerably deformable objects. To robustly register the input sequence of partial depth scans with dynamic motion, we propose an efficient local-to-global hierarchical optimization framework inspired by the idea of traditional structure-from-motion. Our proposed framework mainly consists of two stages, local nonrigid bundle adjustment and global optimization. To eliminate error accumulation during the nonrigid registration of loop motion sequences, we split the full sequence into several segments and apply local nonrigid bundle adjustment to align each segment locally. Global optimization is then adopted to combine all segments and handle the drift problem through loop-closure constraint. By fitting to the input partial data, a deforming 3D model sequence of dynamic objects is finally generated. Experiments on both synthetic and real test data sets and comparisons with state of the art demonstrate that our approach can handle considerable motions robustly and efficiently, and reconstruct high-quality 3D model sequences without drift.

Laser induced strong-field ionization gas jet tomography

We introduce a novel in-situ strong field ionization tomography approach for characterizing the spatial density distribution of gas jets. We show that for typical intensities in high harmonic generation experiments, the strong field ionization mechanism used in our approach provides an improvement in the resolution close to factor of 2 (resolving about 8 times smaller voxel volume), when compared to linear/single-photon imaging modalities. We find, that while the depth of scan in linear tomography is limited by resolution loss due to the divergence of the driving laser beam, in the proposed approach the depth of focus is localized due to the inherent physical nature of strong-field interaction and discuss implications of these findings. We explore key aspects of the proposed method and compare it with commonly used single- and multi-photon imaging mechanisms. The proposed method will be particularly useful for strong field and attosecond science experiments.

Efficient Top-k Dominating Computation on Massive Data

In many applications, top-k dominating query is an important operation to return k tuples with the highest domination scores in a potentially huge data space. It is analyzed that the existing algorithms have their performance problems when performed on massive data. This paper proposes a novel table-scan-based TDTS algorithm to efficiently compute top-k dominating results. TDTS first presorts the table for early termination. The early termination checking is proposed in this paper, along with the theoretical analysis of scan depth. The pruning operation for tuples is devised in this paper. The theoretical pruning effect shows that the number of tuples maintained in TDTS can be reduced substantially. The extensive experimental results, conducted on synthetic and real-life data sets, show that TDTS outperforms the existing algorithms significantly.

En-face time-domain optical coherence tomography with dynamic focus for high-resolution imaging.

Optical coherence tomography (OCT) is capable of imaging microstructures within translucid samples. A time-domain version of the OCT technology is employed here due to its compatibility with the dynamic focus (DF) procedure. DF means moving the confocal gate in synchronism with the depth scanning via the coherence gate. A DF-OCT setup was implemented for imaging samples at 1300 nm. Its confocal gate of 180 ?? ? m allows the achievement of good and similar transversal resolution along its much larger axial range. Images of a phantom, human skin, teeth, and larynx with and without DF are demonstrated.

Technical Note: Direct measurement of continuous TMR data with a 1D tank and automated couch movements

Real-time dynamic control of the linear accelerator, couch, and imaging parameters during radiation delivery was investigated as a novel technique for acquiring tissue maximum ratio (TMR) data. TrueBeam Developer Mode (Varian Medical Systems, Palo Alto, CA, USA) was used to control the linear accelerator using the Extensible Markup Language (XML). A single XML file was used to dynamically manipulate the machine, couch, and imaging parameters during radiation delivery. A TG-51 compliant 1D water tank was placed on the treatment couch, and used to position a detector at isocenter at a depth of 24.5 cm. A depth scan was performed towards the water surface. Via XML control, the treatment couch vertical position was simultaneously lowered at the same rate, maintaining the detector position at isocenter, allowing for the collection of TMR data. To ensure the detector remained at isocenter during the delivery, the in-room camera was used to monitor the detector. Continuous kV fluoroscopic images during 10 test runs further confirmed this result. TMR data at multiple Source to Detector Distances (SDD) and scan speeds were acquired to investigate their impact on the TMR data. Percentage depth dose (PDD) scans (for conversion to TMR) along with traditional discrete TMR data were acquired as a standard for comparison. More than 99.8% of the measured points had a gamma value (1%/1 mm) < 1 when compared with discrete or PDD converted TMR data. Fluoroscopic images showed that the concurrent couch and tank movements resulted in SDD errors < 1 mm. TMRs acquired at SDDs of 99, 100, and 101 cm showed differences less than 0.004. TrueBeam Developer Mode was used to collect continuous TMR data with the same accuracy as traditionally collected discrete data, but yielded higher sampled resolution and reduced acquisition time. This novel method does not require the modification of any equipment and does not use a 3D tank or reservoir.

Full resolution Fourier domain optical coherence tomography

The complex conjugate ambiguity in Fourier domain optical coherence tomography (FDOCT) is a major roadblock that prevents full-detector resolution for the depth scan in single shot operation for the individual A-scan. Current techniques to eliminate this problem involve changing the experimental set-up, usually complicating the OCT system. In this work we show that the standard FDOCT spectrum data when resampled appropriately can be cast exactly in terms of type-1 discrete cosine transform (DCT). Additionally, a sparse reconstruction method in the DCT domain enables image recovery with full-detector resolution, thus effectively doubling the depth scan resolution. In a realistic simulation study we demonstrate full-detector resolution for a discrete reflective target by successfully resolving closely spaced reflective peaks that cannot be separated using the standard Fourier transform based reconstruction. Experimental results on reflective glass sheet targets further validate the methodology. The results of the proposed technique suggest that full resolution FDOCT systems may be implemented practically without additional hardware costs and system complexity.

Automatic Fetal Head Circumference Measurement in Ultrasound Using Random Forest and Fast Ellipse Fitting.

Head circumference (HC) is one of the most important biometrics in assessing fetal growth during prenatal ultrasound examinations. However, the manual measurement of this biometric by doctors often requires substantial experience. We developed a learning-based framework that used prior knowledge and employed a fast ellipse fitting method (ElliFit) to measure HC automatically. We first integrated the prior knowledge about the gestational age and ultrasound scanning depth into a random forest classifier to localize the fetal head. We further used phase symmetry to detect the center line of the fetal skull and employed ElliFit to fit the HC ellipse for measurement. The experimental results from 145 HC images showed that our method had an average measurement error of 1.7 mm and outperformed traditional methods. The experimental results demonstrated that our method shows great promise for applications in clinical practice.

Non-invasive diagnostic system and its opto-mechanical probe for combining confocal Raman spectroscopy and optical coherence tomography.

Non-invasive optical diagnostic methods allow important information about studied systems to be obtained in a non-destructive way. Complete diagnosis requires information about the chemical composition as well as the morphological structure of a sample. We report on the development of an opto-mechanical probe that combines Raman spectroscopy (RS) and optical coherence tomography (OCT), two methods that provide all the crucial information needed for a non-invasive diagnosis. The aim of this paper is to introduce the technical design, construction and optimization of a dual opto-mechanical probe combining two in-house developed devices for confocal RS and OCT. The unique benefit of the probe is a gradual acquisition of OCT and RS data, which allows to use the acquired OCT images to pinpoint locations of interest for RS measurements. The parameters and the correct functioning of the probe were verified by RS scanning of various samples (silicon wafer and ex vivo tissue) based on their OCT images - lateral as well as depth scanning was performed. Both the OCT and RS systems were developed, optimized and tested with the ultimate aim of verifying the functionality of the probe. Picture: Schematic illustration and visualization of the developed RS-OCT probe.

Recent progress and future plans of heavy-ion cancer radiotherapy with HIMAC

The HIMAC clinical study has been conducted with a carbon-ion beam since June 1994. Since 2006, as a new treatment research project, NIRS has developed both the accelerator and beam-delivery technologies for the sophisticated heavy-ion radiotherapy, which brings a pencil-beam 3D rescanning technology for both the static and moving-tumor treatments. In this technology, the depth-scanning technique was improved to the full-energy depth scanning by realizing a variable-energy operation of the HIMAC synchrotron itself. At present, a heavy-ion rotating gantry has been developed with the superconducting technology and is in a beam-commissioning stage. As a future plan, we just start a study of a multi-ions irradiation for more sophisticated LET-painting and a design study of a superconducting synchrotron for more compact heavy-ion radiotherapy facility.

Depth profiling of APTES self-assembled monolayers using surface-enhanced confocal Raman microspectroscopy

The internal structure of self-assembled monolayers (SAMs) such as 3-aminopropyltriethoxysilane (APTES) fabricated on a glass substrate is difficult to characterize and analyze at nanometer level. In this study, we employed surface-enhanced Raman spectroscopy (SERS) to study the internal molecular structure of APTES SAMs. The sample APTES SAMs were deposited with Ag nanoparticles to enhance the Raman signal and to obtain subtler structure information, which were supported by density functional theory calculations. In addition, in order to carry out high-resolution analysis, especially for vertical direction, a fine piezo electric positioner was used to control the depth scanning with a step of 0.1nm. We measured and distinguished the vertical Raman intensity variations of specific groups in APTES, such as Ag/NH2, CH2, and SiO, with high resolution. The interfacial bond at the two interfaces of Ag-APTES and APTES-SiO2 was identified. Moreover, APTES molecule orientation was demonstrated to be inhomogeneous from frequency shift.

Focus scanning with feedback-control for fiber-optic nonlinear endomicroscopy.

Fiber-optic endomicroscopes open new avenues for the application of non-linear optics to novel in vivo applications. To achieve focus scanning in vivo, shape memory alloy (SMA) wires have been used to move optical elements in miniature endomicroscopes. However, this method has various limitations, making it difficult to achieve accurate and reliable depth scanning. Here we present a feedback-controlled SMA depth scanner. With a Hall effect sensor, contraction of the SMA wire can be tracked in real time, rendering accurate and robust control of motion. The SMA depth scanner can achieve up to 490 µm travel and with open-loop operation, it can move more than 350 µm within one second. With the feedback loop engaged, submicron positioning accuracy was achieved along with superior positioning stability. The high-precision positioning capability of the SMA depth scanner was verified by depth-resolved nonlinear endomicroscopic imaging of mouse brain samples.

Commissioning of full energy scanning irradiation with carbon-ion beams ranging from 55.6 to 430 MeV/u at the NIRS-HIMAC

Since 2011, a three-dimensional (3D) scanning irradiation system has been utilized for treatments at the National Institute of Radiological Sciences-Heavy Ion Medical Accelerator in Chiba (NIRS-HIMAC). In 2012, a hybrid depth scanning method was introduced for the depth direction, in which 11 discrete beam energies are used in conjunction with the range shifter. To suppress beam spread due to multiple scattering and nuclear reactions, we then developed a full energy scanning method. Accelerator tuning and beam commissioning tests prior to a treatment with this method are time-consuming, however. We therefore devised a new approach to obtain the pencil beam dataset, including consideration of the contribution of large-angle scattered (LAS) particles, which reduces the time spent on beam data preparation. The accuracy of 3D dose delivery using this new approach was verified by measuring the dose distributions for different target volumes. Results confirmed that the measured dose distributions agreed well with calculated doses. Following this evaluation, treatments using the full energy scanning method were commenced in September 2015.