Stable Image Quality Research Articles

Compressive Sensing Techniques for mm-Wave Nondestructive Testing of Composite Panels

This paper presents imaging results from measurements of an industrially manufactured composite test panel, utilizing two introduced algorithms for data postprocessing. The system employs a planar near-field scanning setup for characterizing defects in composite panels in the 50–67-GHz band, and can be considered as a complementary diagnostic tool for nondestructive testing purposes. The introduced algorithms are based on the reconstruction of the illuminating source at the transmitter, enabling a separation of the sampled signal with respect to the location of its potential sources, the scatterers within the device under test or the transmitter. For the second algorithm, an $L_{1}$ -minimization problem formulation is introduced that enables compressive sensing techniques to be adapted for image retrieval. The algorithms are benchmarked against a more conventional imaging technique, based on the Fourier transform, and it is seen that the complete imaging system provides increased dynamic range, improved resolution, and reduced measurement time by removal of a reference measurement. Moreover, the system provides stable image quality over a range of frequencies.

Simultaneous Multislice Diffusion-Weighted Imaging of the Kidney: A Systematic Analysis of Image Quality.

The aims of this study were to implement a protocol for simultaneous multislice (SMS) accelerated diffusion-weighted imaging (DWI) of the kidneys and to perform a systematic analysis of image quality of the data sets. Ten healthy subjects and 5 patients with renal masses underwent DWI of the kidney in this prospective institutional review board-approved study on a 3 T magnetic resonance scanner. Simultaneous multislice DWI echo-planar sequences (acceleration factors [AFs] 2 and 3) were compared with conventional echo-planar DWI as reference standard for each acquisition scheme. The following 3 acquisition schemes were applied: comparison A, with increased number of acquisitions at constant scan time; comparison B, with reduction of acquisition time; and comparison C, with increased slice resolution (constant acquisition time, increasing number of slices). Interreader reliability was analyzed by calculating the intraclass correlation coefficient (ICC). Qualitative image quality features were evaluated by 2 independent radiologists on a 5-point Likert scale. Quantification accuracy of the apparent diffusion coefficients (ADCs) and signal-to-noise ratios (SNRs) were assessed by region of interest analysis. Furthermore, lesion conspicuity in the 5 patients was assessed using a 5-point Likert scale by 2 independent radiologists. Interreader agreement was substantial with an ICC of 0.68 for the overall image quality and an ICC of 0.73 for the analysis of artifacts. In comparison A, AF2 resulted in increased SNR (P < 0.05) by 21% at stable image quality scores (image quality: P = 0.76, artifacts: P = 0.21). In comparison B, applying AF2, the scan time could be reduced by 46% without significant reduction in qualitative image quality scores (P = 0.059) or SNR (P = 0.126). In comparison C, slice resolution could be improved by 28% using AF2 with stable image quality scores and SNR. In general, AF3 resulted in reduced image quality and SNR. Significantly reduced ADC values were observed for AF3 in comparison C (cortex: P = 0.003; medulla: P = 0.001) compared with the standard echo-planar imaging sequence. The conventional DWI and the SMS DWI with AF2 showed stable lesion conspicuity ([AF1/AF2]: reader 1 [1.8/1.4] and reader 2 [1.8/1.4]). The lesion conspicuity was lower using AF3 (reader 1: 2.2 and reader 2: 1.8). In conclusion, SMS DWI of the kidney is a potential tool to substantially reduce scan time without negative effects on SNR, ADC quantification accuracy, and image quality if an AF2 is used. Although AF3 results in even higher scan time reduction, a negative impact on image quality, SNR, ADC quantification accuracy, and lesion conspicuity must be considered.

Sharp-Tip Silver Nanowires Mounted on Cantilevers for High-Aspect-Ratio High-Resolution Imaging.

Despite many efforts to fabricate high-aspect-ratio atomic force microscopy (HAR-AFM) probes for high-fidelity, high-resolution topographical imaging of three-dimensional (3D) nanostructured surfaces, current HAR probes still suffer from unsatisfactory performance, low wear-resistivity, and extravagant prices. The primary objective of this work is to demonstrate a novel design of a high-resolution (HR) HAR AFM probe, which is fabricated through a reliable, cost-efficient benchtop process to precisely implant a single ultrasharp metallic nanowire on a standard AFM cantilever probe. The force-displacement curve indicated that the HAR-HR probe is robust against buckling and bending up to 150 nN. The probes were tested on polymer trenches, showing a much better image fidelity when compared with standard silicon tips. The lateral resolution, when scanning a rough metal thin film and single-walled carbon nanotubes (SW-CNTs), was found to be better than 8 nm. Finally, stable imaging quality in tapping mode was demonstrated for at least 15 continuous scans indicating high resistance to wear. These results demonstrate a reliable benchtop fabrication technique toward metallic HAR-HR AFM probes with performance parallel or exceeding that of commercial HAR probes, yet at a fraction of their cost.

Registration and Summation of Respiratory-Gated or Breath-Hold PET Images Based on Deformation Estimation of Lung from CT Image

Lung motion due to respiration causes image degradation in medical imaging, especially in nuclear medicine which requires long acquisition times. We have developed a method for image correction between the respiratory-gated (RG) PET images in different respiration phases or breath-hold (BH) PET images in an inconsistent respiration phase. In the method, the RG or BH-PET images in different respiration phases are deformed under two criteria: similarity of the image intensity distribution and smoothness of the estimated motion vector field (MVF). However, only these criteria may cause unnatural motion estimation of lung. In this paper, assuming the use of a PET-CT scanner, we add another criterion that is the similarity for the motion direction estimated from inhalation and exhalation CT images. The proposed method was first applied to a numerical phantom XCAT with tumors and then applied to BH-PET image data for seven patients. The resultant tumor contrasts and the estimated motion vector fields were compared with those obtained by our previous method. Through those experiments we confirmed that the proposed method can provide an improved and more stable image quality for both RG and BH-PET images.

Simultaneous exoplanet detection and instrument aberration retrieval in multispectral coronagraphic imaging

High-contrast imaging for the detection and characterization of exoplanets relies on the instrument's capability to block out the light of the host star. Some current post-processing methods for calibrating out the residual speckles use information redundancy offered by multispectral imaging but do not use any prior information on the origin of these speckles. We investigate whether additional information on the system and image formation process can be used to more finely exploit the multispectral information. We developed an inversion method in a Bayesian framework that is based on an analytical imaging model to estimate both the speckles and the object map. The model links the instrumental aberrations to the speckle pattern in the image focal plane, distinguishing between aberrations upstream and downstream of the coronagraph. We propose and validate several numerical techniques to handle the difficult minimization problems of phase retrieval and achieve a contrast of 10^6 at 0.2 arcsec from simulated images, in the presence of photon noise. This opens up the the possibility of tests on real data where the ultimate performance may override the current techniques if the instrument has good and stable coronagraphic imaging quality. This paves the way for new astrophysical exploitations or even new designs for future instruments.

Design of Visual Light and Middle Infrared Zoom Optical System

In order to achieve wide range for target search and monitor in all-weather, a zoom optical system with long focus length is designed which is used for visual light and middle infrared observation in this paper. In this system, the visible and infrared optical paths share a fixed R-C mirror in the foreside, on whose image surface the parallel plates is used to separate the light beam. Then the dual wavelength band zoom is achieved by two optical transmitted systems whose aperture is 100mm, Zoom range is 300mm~900mm for visual light and 250mm~750mm for middle infrared.This system has stable image and good imaging quality, satisfies the requirements of the application.

SYSTEMATIC MOTION OF FINE-SCALE JETS AND SUCCESSIVE RECONNECTION IN SOLAR CHROMOSPHERIC ANEMONE JET OBSERVED WITH THE SOLAR OPTICAL TELESCOPE/HINODE

The Solar Optical Telescope (SOT) on board Hinode allows observations with high spatiotemporal resolution and stable image quality. A {lambda}-shaped chromospheric anemone jet was observed in high resolution with SOT/Hinode. We found that several fine-scale jets were launched from one end of the footpoint to the other. These fine-scale jets ({approx}1.5-2.5 Mm) gradually move from one end of the footpoint to the other and finally merge into a single jet. This process occurs recurrently, and as time progresses the jet activity becomes more and more violent. The time evolution of the region below the jet in Ca II H filtergram images taken with SOT shows that various parts (or knots) appear at different positions. These bright knots gradually merge into each other during the maximum phase. The systematic motion of the fine-scale jets is observed when different knots merge into each other. Such morphology would arise due to the emergence of a three-dimensional twisted flux rope in which the axial component (or the guide field) appears in the later stages of the flux rope emergence. The partial appearance of the knots could be due to the azimuthal magnetic field that appears during the early stage of the flux rope emergence.more » If the guide field is strong and reconnection occurs between the emerging flux rope and an ambient magnetic field, this could explain the typical feature of systematic motion in chromospheric anemone jets.« less

Organ-Based Computed Tomographic (CT) Radiation Dose Reduction to the Lenses

Recently, a new specific organ dose adaption and reduction protocol, or SODAR tool (X-CARE, Siemens Healthcare), which reduces dose to the anterior aspect of the body of patients, was installed on our computed tomographic scanner. The purpose of this pilot project was to evaluate image quality and dose distribution in the acquired data with the new protocol. Sixteen consecutive patients were scanned with the new SODAR head protocol. The findings were compared with 16 matched patients who were imaged with the standard computed tomographic head trauma protocol. Image quality was assessed qualitatively using a scale of 1 to 4 (1, excellent; 2, good; 3, fair; 4, nondiagnostic). Additionally, 1-cm regions of interest were placed in the white matter of the cerebral hemispheres, the cerebellar hemispheres, and the brain stem at the level of the pons for a quantitative analysis. The standard deviation of each measurement was recorded as an indicator for image noise. Dose measurement trials were performed using optically stimulated luminescence dosimeters on head phantoms and then on patients. Subjective image quality ranged between 1 and 3; no scan areas were considered nondiagnostic. Overall image quality of the posterior fossa averaged at 1.656 was slightly reduced compared to the cerebral hemispheres (mean, 1.141). The mean standard protocol brain stem image quality was 1.604, with only minimal deterioration to 1.708 in the SODAR group.No significant difference in image noise could be found between the SODAR group with a mean noise of 4.515 and standard images with a mean of 4.721 (P > 0.05).The dose to the anterior aspect of the patient was lowered to 3.2 mGy compared to 4.5 mGy on the lateral aspect of the scan (P > 0.05). To compensate for the photon loss in the posterior aspect, the dose has to be slightly increased to a mean of 6 mGy, but overall, a significant dose reduction with stable image quality could be achieved by reducing the dose length product from 1489 to 1347 mGy·cm using SODAR (P < 0.0001). Using the SODAR protocol resulted not only in an impressive 46% to 59% frontal dose reduction but also in the overall dose reduction. This dose reduction was obtained without sacrificing image quality, providing diagnostic images of the brain while protecting radiosensitive structures like the eye lenses in trauma brain imaging. Future applications will be reducing dose to other radiosensitive structures such as the thyroid gland and breast tissue from potentially harmful low-energy radiation without compromising image quality.

三次元PET収集における被写体断面積と画質の関係

The image quality in (18)FDG PET/CT often degrades as the body size increases. The purpose of this study was to evaluate the relationship between image quality and the body size using original phantoms of variable cross-sectional areas in PET/CT. We produced five water phantoms with different cross-sectional areas. The long axis of phantom was 925 mm, and the cross-sectional area was from 324 to 1189 cm(2). These phantoms with the sphere (diameter 10 mm) were filled with (18)F-FDG solution. The radioactivity concentration of background in the phantom was 1.37, 2.73, 4.09 and 5.46 kBq/mL. The scanning duration was 30 min in list mode acquisition for each measurement. Background variability (N(10 mm)), noise equivalent count rates (NECR(phantom)), hot sphere contrast (Q(H,10 mm)) as physical evaluation and visual score of sphere detection were measured, respectively. The relationship between image quality and the various cross-sectional areas was also analyzed under the above-mentioned conditions. As cross-sectional area increased, NECR(phantom) progressively decreased. Furthermore, as cross-sectional area increased, N(10 mm) increased and Q(H,10 mm) decreased. Image quality became degraded as body weight increased because noise and contrast contributed to image quality. The visual score of sphere detection deteriorated in high background radioactivity concentration because a false positive detection in cross-sectional area of the phantom increased. However, additional increases in scanning periods could improve the visual score. We assessed tendencies in the relationship between image quality and body size in PET/CT. Our results showed that time adjustment was more effective than dose adjustment for stable image quality of heavier patients in terms of the large cross-sectional area.

New Technologies for Printed Material's Advanced Value in the Production Printing Market

RICOH Pro C901 was launched in the late last year. It was successor of Pro C900 which was launched in the late 2008 and has gotten favorable reviews.Pro C901 has newly chosen RICOH original chemical toners called &#x201C;PxP (polyester x polymerization)&#x201D; and achieved near&#x2013;offset, high image quality. Pro C901 is also focused on being used in production printing market. And we have given priority to making printed materials valuable.In this report as the technologies for enhancing the printed materials, we will introduce the designing for stable image quality and the designing for UV varnish coating.

デジタルファントムと臨床画像を用いた肝臓領域における低コントラスト分解能の評価

The high performance of multi detector-row computed tomography (MDCT), enables a flow dynamic study of the liver that can be carried out within 10 seconds per one phase. In addition, it has been possible to obtain a stable image quality by utilizing the auto exposure control system. However, no clear standard of minimal CT value differences and minimal tumor sizes for detecting liver tumors has ever been shown. In order to help in their standardization, we developed novel software to make an arbitrary digital phantom. The limit of space occupied lesion (SOL) detection in each image quality could be determined by a detection study using digital phantoms superimposed on liver CT images. As a result, the detection rate of simulated tumors was significantly different, in comparisons of different image qualities for the late arterial phase and in comparison between the late arterial and equilibrium phases for the same image quality. Our method could help standardize the scan conditions for performing a liver CT.

Prospectively gated axial CT coronary angiography: comparison of image quality and effective radiation dose between 64- and 256-slice CT

To compare image quality and effective radiation dose for prospectively gated axial CT coronary angiography on 64- and 256-slice CT. The patient cohort consisted of 80 consecutive patients undergoing imaging with 256-slice CT and 80 patients with 64-slice CT. The two patient groups were demographically matched according to age, gender, body mass index and heart rate. For both groups, two observers independently assessed image quality for all coronary segments on a five-point ordinal scale. The two groups were compared with regard to image quality and effective radiation dose. Image quality scores less than 3 were considered non-diagnostic. Mean effective radiation dose did not significantly differ between the two groups (3.4 +/- 0.8 mSv in both groups; p > 0.1). Vessel-based image quality was significantly better in patients undergoing 256-slice CT compared with those undergoing 64-slice CT (p < 0.001). The proportion of assessable coronary segments significantly increased from 95.6% in the 64-slice group to 98.9% in the 256-slice group (p < 0.05). Prospectively gated axial CT coronary angiography performed on 256-slice CT provides significantly improved and more stable image quality at an equivalent effective radiation dose compared with 64-slice CT.

Prospectively ECG-triggered high-pitch spiral acquisition for coronary CT angiography using dual source CT: technique and initial experience

We evaluated radiation exposure and image quality of a new coronary CT angiography protocol, high-pitch spiral acquisition, using dual source CT (DSCT). Coronary CTAwas performed in 25 consecutive patients with a stable heart rate of 60 bpm or less after premedication, using 2 x 128 0.6-mm sections, 38.4-mm collimation width and 0.28-s rotation time. Tube settings were 100 kV/320 mAs and 120 kV/400 mAs for patients below and above 100-kg weight, respectively. Data acquisition was prospectively ECG-triggered at 60% of the R-R interval using a pitch of 3.2 (3.4 for the last 10 patients). Images were reconstructed with 75-ms temporal resolution, 0.6-mm slice thickness and 0.3-mm increment. Image quality was evaluated using a four-point scale (1 = excellent, 4 = unevaluable). Mean range of data acquisition was 113 +/- 22 mm, mean duration was 268 +/- 23 ms. Of 363 coronary artery segments, 327 had an image quality score of 1, and only 2 segments were rated as "unevaluable". Mean dose-length product (DLP) was 71 +/- 23 mGy cm, mean effective dose was 1.0 +/- 0.3 mSv (range 0.78-2.1 mSv). For 21 patients with a body weight below 100 kg, mean DLP was 63 +/- 5 mGy cm (0.88 +/- 0.07 mSv; range 0.78-0.97 mSv). Prospectively ECGtriggered high-pitch spiral CT acquisition provides high and stable image quality at very low radiation dose.

Mechanism of compensation of aberrations in the human eye

We studied the mechanism of compensation of aberrations within the young human eye by using experimental data and advanced ray-tracing modeling. Corneal and ocular aberrations along with the alignment properties (angle kappa, lens tilt, and decentration) were measured in eyes with different refractive errors. Predictions from individualized ray-tracing optical models were compared with the actual measurements. Ocular spherical aberration was, in general, smaller than corneal spherical aberration without relation to refractive error. However, horizontal coma compensation was found to be significantly larger for hyperopic eyes where angle kappa tended to also be larger. We propose a simple analytical model of the relationship between the corneal coma compensation effect with the field angle and corneal and crystalline shape factors. The actual shape factors corresponded approximately to the optimum shapes that automatically provide this coma compensation. We showed that the eye behaves as an aplanatic optical system, an optimized design solution rendering stable retinal image quality for different ocular geometries.

Lossy Strict Multilevel Successive Elimination Algorithm for Fast Motion Estimation

This paper presents a simple and effective method to further reduce the search points in multilevel successive elimination algorithm (MSEA). Because the calculated sea values of those best matching search points are much smaller than the current minimum SAD, we can simply increase the calculated sea values to increase the elimination ratio without much affecting the coding quality. Compared with the original MSEA algorithm, the proposed strict MSEA algorithm (SMSEA) can provide average 6.52 times speedup. Compared with other lossy fast ME algorithms such as TSS and DS, the proposed SMSEA can maintain more stable image quality. In practice, the proposed technique can also be used in the fine granularity SEA (FGSEA) algorithm and the calculation process is almost the same.

Simple PSF based method for pupil phase mask’s optimization in wavefront coding system

By applying the wavefront coding technique to an optical system, the depth of focus can be greatly increased. Several complicated methods, such as Fisher Information on based method, have already been taken to optimize for the best pupil phase mask in ideal condition. Here one simple point spread function (PSF) based method with only the standard deviation method used to evaluate the PSF stability over the depth of focus is taken to optimize for the best coefficients of pupil phase mask in practical optical systems. Results of imaging simulations for optical systems with and without pupil phase mask are presented, and the sharpness of image is calculated for comparison. The optimized results showed better and much more stable imaging quality over the original system without changing the position of the image plane.

A quality assurance program for the on‐board

To develop a quality assurance (QA) program for the On‐Board Imager (OBI) system and to summarize the results of these QA tests over extended periods from multiple institutions. Both the radiographic and cone‐beam computed tomography (CBCT) mode of operation have been evaluated. The QA programs from four institutions have been combined to generate a series of tests for evaluating the performance of the On‐Board Imager. The combined QA program consists of three parts: (1) safety and functionality, (2) geometry, and (3) image quality. Safety and functionality tests evaluate the functionality of safety features and the clinical operation of the entire system during the tube warm‐up. Geometry QA verifies the geometric accuracy and stability of the OBI/CBCT hardware/software. Image quality QA monitors spatial resolution and contrast sensitivity of the radiographic images. Image quality QA for CBCT includes tests for Hounsfield Unit (HU) linearity, HU uniformity, spatial linearity, and scan slice geometry, in addition. All safety and functionality tests passed on a daily basis. The average accuracy of the OBI isocenter was better than with a range of variation of less than over 8 months. The average accuracy of arm positions in the mechanical geometry QA was better than , with a range of variation of less than over 8 months. Measurements of other geometry QA tests showed stable results within tolerance throughout the test periods. Radiographic contrast sensitivity ranged between 2.2% and 3.2% and spatial resolution ranged between 1.25 and . Over four months the CBCT images showed stable spatial linearity, scan slice geometry, contrast resolution (1%; disk) and spatial resolution . The HU linearity was within for all measurements. By combining test methods from multiple institutions, we have developed a comprehensive, yet practical, set of QA tests for the OBI system. Use of the tests over extended periods show that the OBI system has reliable mechanical accuracy and stable image quality. Nevertheless, the tests have been useful in detecting performance deficits in the OBI system that needed recalibration. It is important that all tests are performed on a regular basis.

SU‐FF‐T‐374: Quality Assurance of the On‐Board Imager and Cone‐Beam Computed Tomography Systems

Purpose: To develop a comprehensive quality assurance (QA) program for the On‐Board Imager (OBI) used for patient positioning verification and to present the results of QA tests over extended periods from multiple institutions. Radiographic and cone‐beam computed tomography (CBCT) mode have been evaluated. Methods and Materials: The QA program consists of three parts; (1) safety and functionality (2) geometry and (3) image quality. Safety checks evaluate the functionality of collision interlocks and audible alarms. Functional QA checks the flow of clinical operation during tube warm‐up. Geometry QA checks geometrical accuracy and variation of the OBI/CBCT and hardware/software. Image quality QA includes measurements to monitor accuracy and stability of the OBI/CBCT imaging system. Results: All test items show stable functionality for safety and functional QA on a daily bases. The precision of arm positioning is very high with variation of 1mm and average accuracy of &lt; 1mm over 8 months. The average accuracy of the isocenter and couch shift is &lt; 1mm with variation of 1mm over 11 months. Arm position was performed when the results were &gt; 2 mm. Results of geometry QA have been stable within tolerances through the test periods. All tests for Image quality tests also show consistent results within tolerances. Conclusion: We have developed a practical yet comprehensive set of QA tests for the OBI system. Data collected for these tests over the extended period show that the OBI system has mechanical reliability and stable image quality. Nevertheless, the tests were useful in detecting performance deficits in the OBI system that needed recalibration. After accumulating enough experience and confidence on stability and accuracy, some institutions have reduced the frequency of QA checks. However, it is important that all tests are performed on a regular basis within a suggested period to establish a guideline.

Basics of cardiac MDCT: techniques and contrast application

The purpose of this article is to review the basic techniques of cardiac MDCT including the most recent 64-slice scanner generation. Besides the technical developments of different MDCT generations within recent years, the basic principles of ECG-related CT algorithms are discussed. Retrospective ECG-gated data acquisitions are considered as a prerequisite for reliable and reproducible calcium scoring as well as for volumetric assessment of the coronary artery tree. While data acquisition itself is rather straightforward, the optimization of image quality, the knowledge of adequate scan protocols and especially knowledge of possibly arising artefacts is mandatory for a stable high image quality. As data acquisition is becoming faster with the most recent advent of 64-slice MDCT, protocols have to be adapted to this new scanner generation. On the other hand, the improvement in spatial as well as in temporal resolution shows impact on the accuracy and stability of coronary CT angiography. However, the use of dose-reducing technical improvements is strongly recommended.

The Charging Characteristics of CCA

In recent years, printing speed and resolution in digital printing have been increasing according to various market requirements. As a result, it is required that the toner behaviors in developing system is controlled more precisely and uniformly. In the electrophotographic system, toner charge is one of the important factors to identify toner behaviors.In general, Charging Control Agent (CCA) is necessary for toner to obtain stable and superior image quality. CCA provides quick charge and suitable triboelectric charging level. Therefore, toner triboelectric charge can be affected by a variety of CCA, CCA content, and so on. In addition, maintenance of a stable and uniform charge requires a balancing of many complex interactions.In this review, the charging characteristics of CCA are discussed and illustrated using actual experimental data in non-magnetic one component developing system. It is found that the performance of toner charge depends on the type and amount of CCA. We have designed optimum condition to obtain the better performance of toner charging.