Modulation Transfer Function Analysis Research Articles

Multiplane differential phase contrast imaging using asymmetric illumination in volume holographic microscopy.

.Significance: Differential phase contrast (DPC) is a well-known imaging technique for phase imaging. However, simultaneously acquiring multidepth DPC images is a non-trivial task. We propose simultaneous multiplane DPC imaging using volume holographic microscopy (VHM).Aim: To design and implement a new configuration of DPC-VHM for multiplane imaging.Approach: The angularly multiplexed volume holographic gratings (AMVHGs) and the wavelength-coded volume holographic gratings (WC-VHGs) are used for this purpose. To obtain asymmetric illumination for DPC images, a dynamic illumination system is designed by modifying the regular Köhler illumination using a thin film transistor panel (TFT-panel).Results: Multidepth DPC images of standard resolution chart and biosamples were used to compare imaging performance with the corresponding bright-field images. An average contrast enhancement of around three times is observed for target resolution chart by DPC-VHM. Imaging performance of our system is studied by modulation transfer function analysis, which suggests that DPC-VHM not only suppresses the DC component but also enhances high-frequency information.Conclusions: Proposed DPC-VHM can acquire multidepth-resolved DPC images without axial scanning. The illumination part of the system is adjustable so that the system can be adapted to bright-field mode, phase contrast mode, and DPC mode by controlling the pattern on the TFT-panel.

Noise reduction in CT image using prior knowledge aware iterative denoising

The clinical demand for low image noise often limits the slice thickness used in many CT applications. However, a thick-slice image is more susceptible to longitudinal partial volume effects, which can blur key anatomic structures and pathologies of interest. In this work, we develop a prior knowledge aware iterative denoising (PKAID) framework that utilizes spatial data redundancy in the slice increment direction to generate low-noise, thin-slice images, and demonstrate its application in non-contrast head CT exams. The proposed technique takes advantage of the low noise of thicker images and exploits the structural similarity between the thick- and thin-slice images to reduce noise in the thin-slice image. Phantom data and patient cases (n = 3) of head CT were used to assess performance of this method. Images were reconstructed at clinically utilized slice thickness (5 mm) and thinner slice thickness (2 mm). PKAID was used to reduce image noise in 2 mm images using the 5 mm images as low-noise prior. Noise amplitude, noise power spectra (NPS), modulation transfer function (MTF), and slice sensitivity profiles (SSPs) of images before/after denoising were analyzed. The NPS and MTF analysis showed that PKAID preserved noise texture and resolution of the original thin-slice image, while reducing noise to the level of thick-slice image. The SSP analysis showed that the slice thickness of the original thin-slice image was retained. Patient examples demonstrated that PKAID-processed, thin-slice images better delineated brain structures and key pathologies such as subdural hematoma compared to the clinical 5 mm images, while additionally reducing image noise. To test an alternative PKAID utilization for dose reduction, a head exam with 40% dose reduction was simulated using projection-domain noise insertion. The image of 5 mm slice thickness was then denoised using PKAID. The results showed that the PKAID-processed reduced-dose images maintained similar noise and image quality compared to the full-dose images.

Multizonal Design Multifocal Intraocular Lens-Induced Astigmatism According to Orientation.

To evaluate the differences in intraocular lens (IOL)-induced astigmatism according to differences in orientation of a multizonal multifocal IOL, the Precizon Presbyopic NVA IOL (Ophtec BV). The clinical study reviewed 80 eyes from 40 patients with cataracts who underwent Precizon Presbyopic IOL implantation. Residual astigmatism, as measured by autorefraction and manifest refraction, was investigated using vector analysis of eyes implanted with vertical (90 ± 30 degrees) and horizontal (180 ± 30 degrees) orientations of the first near segment of the IOL. In the ray-tracing simulation study, pseudophakic eyes with the Precizon Presbyopic IOL were modeled. The modulation transfer function (MTF) of each case was compared with respect to the amount of corneal astigmatism of the model eyes and the orientation of the first near segment. The mean IOL-induced astigmatism measured by autorefraction was 0.68 ± 0.58 diopters (D) at 1 degree in the vertical orientation of the first near segment (n = 52) and 1.05 ± 0.81 D at 96 degrees in the horizontal orientation (n = 28). However, the mean IOL-induced astigmatism measured by manifest refraction was 0.14 ± 0.44 D at 171 degrees and 0.46 ± 0.40 D at 95 degrees. The MTF analysis showed that the highest MTF values were measured in eyes without corneal astigmatism in both the vertically and horizontally implanted IOLs. Autorefraction measurement indicates induction of with-the-rule astigmatism by the Precizon Presbyopic IOL when implanted vertically with respect to the first near segment, and against-the-rule astigmatism when implanted horizontally. However, this astigmatism is clinically insignificant according to manifest refraction and ray-tracing simulation. [J Refract Surg. 2020;36(11):740-748.].

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.

Increasing iterative reconstruction strength at low tube voltage in coronary CT angiography protocols using 3D-printed and Catphan® 500 phantoms.

PurposeThe purpose of this study was to investigate the effect of increasing iterative reconstruction (IR) algorithm strength at different tube voltages in coronary computed tomography angiography (CCTA) protocols using a three‐dimensional (3D)‐printed and Catphan® 500 phantoms.MethodsA 3D‐printed cardiac insert and Catphan 500 phantoms were scanned using CCTA protocols at 120 and 100 kVp tube voltages. All CT acquisitions were reconstructed using filtered back projection (FBP) and Adaptive Statistical Iterative Reconstruction (ASIR) algorithm at 40% and 60% strengths. Image quality characteristics such as image noise, signal–noise ratio (SNR), contrast–noise ratio (CNR), high spatial resolution, and low contrast resolution were analyzed.ResultsThere was no significant difference (P > 0.05) between 120 and 100 kVp measures for image noise for FBP vs ASIR 60% (16.6 ± 3.8 vs 16.7 ± 4.8), SNR of ASIR 40% vs ASIR 60% (27.3 ± 5.4 vs 26.4 ± 4.8), and CNR of FBP vs ASIR 40% (31.3 ± 3.9 vs 30.1 ± 4.3), respectively. Based on the Modulation Transfer Function (MTF) analysis, there was a minimal change of image quality for each tube voltage but increases when higher strengths of ASIR were used. The best measure of low contrast detectability was observed at ASIR 60% at 120 kVp.ConclusionsChanging the IR strength has yielded different image quality noise characteristics. In this study, the use of 100 kVp and ASIR 60% yielded comparable image quality noise characteristics to the standard CCTA protocols using 120 kVp of ASIR 40%. A combination of 3D‐printed and Catphan® 500 phantoms could be used to perform CT dose optimization protocols.

Visual outcomes after refractive laser corneal surgery and phakic IOL in amblyopic eyes.

To evaluate the outcomes of laser corneal surgery and phakic IOL surgery in adult amblyopic eyes. Retrospective assessment was done in 688 amblyopic eyes 640 patients who underwent LASIK or phakic IOLs. Ophthalmological evaluation included measurement of uncorrected (UDVA) and corrected (CDVA) distance visual acuities. Analysis of modulation transfer function (MTF) was also done post-operatively as a measure of contrast sensitivity. Patients completed follow-up examinations at 1day, 3day, 3months and 12months after surgery. The mean patient age was 24.30 ± 3.04years with 59% females. The CDVA of amblyopic eyes improved significantly from the mean preoperative level of 0.48 ± 0.18 to 0.59 ± 0.18 at 12months. There was improvement in the contrast sensitivity at all spatial frequencies. Refractive errors were corrected in both LASIK and phakic IOL group, but there was no clinically significant difference in visual outcomes between each group. Laser vision correction and phakic IOL surgery for amblyopic eyes are promising alternative methods for improving visual outcomes in adult refractive amblyopia patients who have failed with conventional approaches.

Dependence of the Modulation Transfer Function on the Material and Design Parameters of HgCdTe IR FPAs

The calculation methods of the modulation transfer function (MTF) infrared (IR) focal plane arrays (FPAs) on the base of photodiodes are presented. The obtained results are based on the preliminary calculations of the areal distribution of quantum efficiency by modeling the 3-D diffusion process of photogenerated charge carriers in the photosensitive layer of IR FPA by the Monte Carlo method. The analysis of MTF is carried out for 1-D test patterns and 2-D “chess-type” test patterns, taking into account the basic photoelectric and design parameters of photosensitive elements.

Effect of Ultra High-Resolution Computed Tomography and Model-Based Iterative Reconstruction on Detectability of Simulated Submillimeter Artery

To evaluate the effect of ultra high-resolution computed tomography (UHRCT) and model-based iterative reconstruction (MBIR) on the detectability of simulated submillimeter artery. A small vessel phantom ranging from 0.4 to 2.0 mm in diameter and edge phantoms of low to high attenuation values were scanned by UHRCT (super-high-resolution mode and normal-resolution-mode) and conventional CT, and data were reconstructed by MBIR and filtered back projection (FBP). Vessel detectability was assessed subjectively and the effective size at which 50% of response was achieved (ES50 [mm]) was calculated. Modulation transfer function (MTF) was calculated by an edge spread function method. ES50 of super high-resolution mode (0.36 mm for MBIR and 0.50 mm for FBP) was significantly smaller than those of normal-resolution mode (P < 0.01). In the MTF analysis, the MTF of MBIR improved as the edge phantom attenuation increased, whereas that of FBP was stable. Both UHRCT and MBIR are effective for the detectability of simulated submillimeter artery.

Analysis of Dynamic Modulation Transfer Function for Complex Image Motion

In remote-sensing imaging, the modulation transfer function (MTF) for image motion relevant to the mixing of multiple forms of motions is hard to calculate because of the complicated image motion expression. In this paper, a new method for calculating the MTF for complex image motion is proposed. The presented method makes it possible to obtain an analytical MTF expression derived from the mixing of linear motion and sinusoidal motion at an arbitrary frequency. On this basis, we used the summation of infinitely many terms involving the Bessel function to simplify the MTF expression. The truncation error obtained by the use of finite order sum approximations instead of infinite sums is investigated in detail. In order to verify the MTF calculation method, we proposed a simulation method to calculate the variation of MTF in an actual optical system caused by image motion. The mean value of the relative error between the calculation method and the simulation method is less than 5%. The experimental results are consistent with the MTF curve calculated by our method.

Optimization of back projection with different geometry configurations of X-ray sources in digital breast tomosynthesis: A Monte Carlo simulation study

Breast cancer is the second leading cause of cancer-related mortality among women all over the world. The earlier the breast cancer is detected, the higher the possibility of cure. Digital breast tomosynthesis (DBT) is an effective technique for early breast cancer diagnosis. The DBT system obtains several projection images at a limited range of view angle and thus reduces the radiation dose delivered to patient effectively. Back projection (BP) is a classic algorithm for image reconstruction. In this work, 25 projection images were acquired by simulating seven different geometry configurations of X-ray sources on GATE (Geant4 Application for Tomographic Emission) platform. BP algorithm and its two variants (i.e., α-trimmed BP and PCA-based BP) were used for image reconstruction. Our experimental results demonstrated that among the seven geometry configurations of X-ray sources, the rectangular non-uniform configuration performed the best; it showed a better capability in eliminating out-of-plane artifacts and resolving spatial details than others. In addition, the α-trimmed BP had a better image quality among all of the three algorithms in the modulation transfer function analysis.

A phantom study comparing technical image quality of five breast tomosynthesis systems

BackgroundDigital breast tomosynthesis (DBT) is a three-dimensional breast imaging method. DBT vendors employ various approaches in both image acquisition and data processing, which may affect image quality and radiation exposure to patients. ObjectiveThis study aimed to evaluate the performance of five DBT systems: Fujifilm Amulet Innovality (using both a standard mode and high-resolution mode), GE Senographe Essential, Hologic Selenia Dimensions, Planmed Clarity 3D, and Siemens Mammomat Inspiration. Materials and methodsThe performance of each device and imaging technique was evaluated and compared by phantom measurements performed with four quality assurance phantoms. Technical image quality assessments consisted of measuring artefact extent, in-plane resolution, relative noise power spectrum, and geometric accuracy. ResultsArtefact spreading varied remarkably between the devices, and the full width at half maximum values of artefact spread functions varied from 3.5 mm to 10.7 mm. Noticeable in-plane resolution anisotropy, determined using modulation transfer function (MTF) analysis, was typically observed between tube travel direction and chest wall-nipple direction. The MTF50 varied from 1.1 mm−1 to 1.6 mm−1 and from 1.5 mm−1 to 4.1 mm−1 in the tube travel and chest wall-nipple directions, respectively. Moreover, distinctly different noise power spectra were observed between the systems. The geometric accuracy in every system was within 0.5%. ConclusionTechnical image quality assessments with image quality phantoms revealed remarkable differences in artefact spread, in-plane resolution, and noise properties between the DBT systems and imaging methods.

Measurement and analysis of modulation transfer function of digital image sensors

With the ceaseless development of technology, optical imaging systems have been extensively used in numerous different fields. As a result, verifying the performance of such systems has taken on significant importance. To test these systems, a commonly used metric is the modulation transfer function (MTF) because it reflects the spatial-frequency response of optical systems. To determine how best to measure the MTF of an image sensor, we use the slanted-knife-edge method to measure optical patterns and a black-and-white face sensor to receive patterns, following which we numerically calculate the MTF. We use the MTF of the Nyquist frequency (50 lp/mm) of an image sensor as the measured value, and the slanting angle for the slanted-knife-edge method ranges from 2° to 10°, which is known to provide accurate results. We then compare and analyze the experimental data and explore how inaccurate slanting angles affect the measured MTF. Finally, we propose a “program correction method” in which we input a corrected slanting angle into the region-of-interest program to correct for errors in the measurement of the MTF. The corrected parameters provide a more accurate measurement of the MTF of the given pattern.

Influence of ambient temperature on the modulation transfer function of an infrared membrane diffraction optical system.

In this paper, we present a model that analyzes the influence of the temperature on the modulation transfer function (MTF) of an infrared membrane diffraction optical system. Based on the physical imaging mechanism of diffractive optical systems, the imaging characteristics of the diffraction optical system are characterized by using diffraction efficiency. Then we establish the corresponding calculation model and MTF analysis model based on scalar diffraction theory. In particular, considering the material properties of flexible membrane optical elements and thermal environment effect, the Zernike polynomials are used to establish the thickness distribution model of the membrane diffractive optical components combined with the finite element analysis. After that, we modify the MTF calculation model of diffraction optical system and accordingly propose the model of the infrared membrane diffraction optical system. Finally, we present some experimental results for a 2-m infrared membrane diffraction optical system. The results show that when the temperature is -40°C and wavelength band is 80nm at the center field of view, the diffraction efficiency is reduced to 81%, and MTF at 75 lp/mm is reduced to 0.12. And when the temperature is -40°C at edge field of view, the efficiency at center wavelength is reduced to 71%, and MTF at 75 lp/mm is reduced to 0.02. The established model and method can be used to estimate the imaging performance of a space infrared membrane diffractive telescope and provide theoretical guidance for the processing algorithm and imaging system design.

Dynamic modulation transfer function analysis and short exposure technique for planar flow cytometric microimaging system

A planar flow cytometric microimaging system is introduced for cell recognition and classification in urinary sediment analysis. In order to make clear imaging of the motor cells, the dynamic modulation transfer function(DMTF) is analyzed. At the Nyquist frequency, the DMTF of the imaging system must be more than 0.9 to achieve the imaging quality of static system. Based on this, the exposure time requirement of the system is derived. The system adopts LED optical pulse acceleration circuit and rising edge exposure. In this way, 1μs exposure time can be reached. The dynamic transmission is also up to 0.93, and the image clarity is improved significantly.

Modulation transfer function analysis of silicon X-ray sensor with trench-structured photodiodes

Modulation transfer function analysis of silicon X-ray sensor with trench-structured photodiodes

Liquid distribution and holdup in the random packed column

In the present work, a third-generation gamma transmission tomography system was used to evaluate the liquid distributions of a Raschig rings random packed column, at two different water flows: 2 and 6l/min. For each water flow, the measurements were carried out at nine column heights. The liquid-gas holdup was determined by the reconstructed images. The distribution of the Raschig rings, as well as the position and the average accumulated amount of the water concentration among the Raschig rings were capable to be determined, even at low temporal resolution of the system of 8.8h. The regions of accumulated water concentration were similar for the water flow velocities at 2 and 6l/min. The average accumulated water concentration for 6l/min was higher compared to 2l/min. The spatial resolution of the tomography system determined by the modulation transfer function (MTF) analysis was of 1.45mm.

Evaluation of software programs, ImageJ and IQworks, for MTF, NPS and DQE analysis

This study compared two QA analysis programs, ImageJ and IQworks, to establish their repeatability and reproducibility in testing the performance indicators, Modulation transfer function (MTF), Noise Power Spectrum (NPS) and Detective Quantum Efficiency (DQE) as recommended by the European (EU) guidelines for Full Field Digital Mammography. Following the EU guidelines1, a Siemens Novation FFDM system with W/Rh Tube/Filter combination was used to acquire the desired MTF and NPS images. A Cu edge plate of 1 mm thickness used1,2, in addition to 2 × 1 mm Al plates (purity > 99%) at the tube head. Each metric was tested for repeatability and reproducibility on the selected software programs, with this data then used to establish correlation and agreement between programs. Both programs show a confidence interval of >3% for MTF and NPS images, respectively. Bland–Altman statistics showed a strong correlation across all metrics, further supported with R-squared values of 0.95, 0.84 and 0.91 for MTF, NPS and DQE, respectively. However, the DQE % difference showed a >10% differences above 3.5 lp/mm between the two programs. Both programs were capable of producing repeatable and reliable results when considering MTF and NPS; however, the DQE showed differing results between the two indicating that they should not be used interchangeably. From a practicality perspective, the ImageJ program was preferable given its user-friendliness and better repeatability. Additional calculations had to be performed with IQworks to establish DQE.

Analysis of MTF in TDI-CCD Subpixel Dynamic Super-Resolution Imaging by Beam Splitter

The subpixel dynamic imaging technique of a beam splitter is one of the most effective super-resolution imaging methods. Aiming to create a linear time delay integration charge coupled device (TDI–CCD) subpixel imaging system based on the optical assembly method, its modulation transfer function (MTF) is analyzed based on the spatial over-sampling theory. Firstly, Fourier transformation of the sampling point is used to describe the frequency domain characteristics of TDI–CCD, which transform a unit cell of the spatial sampling lattice into a bandwidth cell in the spatial–frequency domain. Considering the effects of velocity mismatch and misalignment, the best subpixel staggering position of the linear TDI–CCD pair is given. Moreover, according to the analysis of the MTF of super-resolution reconstruction results from multiple subpixel images with random spatial offsets, the condition of sampling in the limitation of the enhancement of MTF is obtained. The numerical simulation and real experimental analysis reveal results that are consistent with the theoretical model.

Neutron imaging with lithium indium diselenide: Surface properties, spatial resolution, and computed tomography

An array of lithium indium diselenide (LISe) scintillators were investigated for application in neutron imaging. The sensors, varying in thickness and surface roughness, were tested using both reflective and anti-reflective mounting to an aluminum window. The spatial resolution of each LISe scintillator was calculated using the knife-edge test and a modulation transfer function analysis. It was found that the anti-reflective backing case yielded higher spatial resolutions by up to a factor of two over the reflective backing case despite a reduction in measured light yield by an average of 1.97. In most cases, the use of an anti-reflective backing resulted in a higher spatial resolution than the 50μm-thick ZnS(Cu):6LiF comparison scintillation screen. The effect of surface roughness was not directly correlated to measured light yield or observed spatial resolution, but weighting the reflective backing case by the random surface roughness revealed that a linear relationship exists between the fractional change (RB/ARB) of the two. Finally, the LISe scintillator array was used in neutron computed tomography to investigate the features of halyomorpha halys with the reflective and anti-reflective backing.

航空相机像旋动态调制传递函数分析与研究

航空相机像旋动态调制传递函数分析与研究