Small Focal Spot Size Research Articles

Large focal length planar focusing of Dyakonov polaritons in hyperbolic metamaterial

Achieving subwavelength optical focusing is of great importance in nanophotonics. However, achieving focusing with both a small focal spot size and a large focal length remains elusive so far. Here, a large focal length planar focusing device is presented, utilizing highly oriented Dyakonov polaritons in hyperbolic metamaterial with periodic silver rings as the excitation source. Experimental results show that by controlling the size of the excitation sources, the focal length can reach 6λ0 (where λ0 is the illumination wavelength), and the focal spot size can be reduced to λ0/10. This method provides new prospects for planar polariton optical applications.

Effect of beam and gate offset size on x-ray focal spot resolution of a cold cathode electron beam

In x-ray imaging, high resolution is essential, particularly in sectors such as medical and industries where the need for nondestructive defect detection is required. Previous research has shown that altering beam design and the number of gates offset holes has an impact on focal spot size (FSS). However, the specific effects of beam size and offset size were not thoroughly assessed. In the present study, the influence of beam size and gate offset size was evaluated by utilizing a cold cathode electron beam. Various beam sizes were employed to achieve a small FSS, and subsequently, the smallest beam was utilized to examine the impact of gate offset size. In doing so, the smallest FSS of 0.25 mm vertical and 0.33 mm horizontal was attained without the utilization of any additional focusing lens. This illustrates that by adjusting the beam size and gate offset size, it is possible to attain a small FSS, facilitating the development of an economically viable x-ray imaging beam.

Geant4 Simulation of Scatter Radiation Removal: Comparison and Validation of Anti-scatter Grid and Air Gap for X-ray Mammography

Abstract: X-ray mammography modality provides excellent low-contrast resolution images with low scatter radiation, making it the gold standard in diagnosing breast cancer. Anti-scatter grid and air gap techniques are typically used to further minimize the scatter radiation and improve image quality. Thus, Geant4 simulation was used to investigate the effectiveness of these techniques in removing scatter radiation in X-ray mammography. The effectiveness of an anti-scatter grid was evaluated using the Bucky factor, where it linearly increased with increasing the anti-scatter grid ratio. It was found that increasing the grid frequency affects the Bucky factor depending on the design of the grid ratio. This research proved that designing an anti-scatter grid with high grid frequency (80 lp/mm), low grid ratio (2:1), and proper orientation minimized common anti-scatter grid artifacts. The effectiveness of the air gap technique was also evaluated using the air gap dose factor. It increased non-linearly with increasing magnification. This research validated that using smaller pixel sizes and small focal spot sizes improved spatial resolution with magnification. Our simulation validated that the anti-scatter grid and air gap were effective techniques in removing scatter radiation. By comparing these techniques, the anti-scatter grid was more effective in removing scatter radiation at the expense of increasing the radiation absorbed dose with the exception of 2.0 magnification. It’s recommended to be extremely cautious when using 2.0 magnification or a grid ratio higher or equal to 8:1. These parameters may cause the radiation absorbed dose to be increased by several folds. Keywords: Geant4, Gate, X-ray mammography, Scatter removal, Anti-scatter grid, Air gap.

Proof-of-concept for a thin conical X-ray target optimized for intensity and directionality for use in a carbon nanotube-based compact X-ray tube.

Carbon nanotube-based cold cathode technology has revolutionized the miniaturization of X-ray tubes. However, current applications of these devices required optimization for large, uniform fields with low intensity. This work investigated the feasibility and radiological characteristics of a novel conical X-ray target optimized for high intensity and high directionality to be used in a compact X-ray tube. The proposed device uses an ultrathin, conical tungsten-diamond target that exhibits significant heat loading while maintaining a small focal spot size and promoting forward-directedness of the X-ray field through preferential attenuation of oblique-angled photons. The electrostatic and thermal properties of the theoretical tube were calculated and analyzed using COMSOL Multiphysics software. The production, transport, and calculation of radiological properties associated with the resultant X-ray field were performed using the Geant4 toolkit via its wrapper, TOPAS. Heat transfer analysis of this X-ray tube demonstrated the feasibility of a 200-kV electron beam bombarding the proposed target at a maximum current of 100mA using a 1-ms symmetric duty cycle. The cathode of the X-ray tube was designed to be segmented into nine switchable electrical segments for modulation of the focal spot size from 0.4- to 10.8-mm. After importing the COMSOL-derived electron beam into TOPAS for X-ray production simulations, radiological analysis of the resultant field demonstrated high levels of intrinsic beam collimation while maintaining high intensity. A maximum dose rate of 17,887 cGy/min was calculated for 1-mm depth in water at 7-cm distance. The proposed X-ray tube design can create highly directional X-ray fields with superior fluence compared to that of current commercial X-ray tubes of comparable size.

High Resolution Imaging with Focused kV X-Rays for Small Animal Radio-Neuromodulation

High precision radiotherapy for small animal radio-neuromodulation requires conformal treatment to very small targets down to 2.5 mm. A focused kV technique based on novel usage of polycapillary x-ray lenses can focus x-ray beams to <0.2 mm in diameter, which is ideal for such uses. Such application also requires high resolution CT images for treatment planning and setup, which was hard to achieve using conventional x-ray tube. In this work, we demonstrate the feasibility of using a virtual focal spot generated with an x-ray lens to perform high-resolution CBCT acquisition. The experiment with x-ray lens was set up on an x-ray tabletop system to generate a virtual focal spot. A pinhole image was acquired for the virtual focal spot and compared with the one acquired with the conventional focal spot without the lens. The planar imaging resolution with and without the lens were evaluated using a line pair resolution phantom. The spatial resolution of the two settings were estimated by reconstructing a 0.15-mm wire phantom and comparing its full width half maximum (FWHM). A CBCT scan of a rodent head was also acquired to further demonstrate the improved resolution using the x-ray lens. Compared to conventional imaging acquisition with a measured x-ray focal spot of 0.395 mm FWHM, the virtual focal spot size was measured at 0.175 mm. The reduction in focal spot size with lens leads to an almost doubled planar imaging resolution and a 26% enhancement in 3D spatial resolution. A realistic CBCT acquisition of a rodent head mimicked the imaging acquisition step for radio-neuromodulation and further showed the improved visualization for fine structures. This work demonstrated that the focused kV x-ray technique was capable of generating small focal spot size of <0.2 mm. The proposed method provides an adaptive imaging platform to acquire x-ray and CBCT images for treatment planning and setup with improved spatial resolution compared to conventional CBCT image acquisition.

High resolution imaging with focused kV x-rays for small animal radio-neuromodulation.

High precision radiotherapy with small irradiator size has potential in many treatment applications involving small shallow targets, with small animal radio-neuromodulation as an intriguing example. A focused kV technique based on novel usage of polycapillary x-ray lenses can focus x-ray beams to <0.2mm in diameter, which is ideal for such uses. Such an application also requires high resolution CT images for treatment planning and setup. In this work, we demonstrate the feasibility of using a virtual focal spot generated with an x-ray lens to perform high-resolution CBCT acquisition. The experiment with x-ray lens was set up on an x-ray tabletop system to generate a virtual focal spot. The flood field images with and without the x-ray lens were first compared. A pinhole image was acquired for the virtual focal spot and compared with the one acquired with the conventional focal spot without the lens. The planar imaging resolution with and without the lens were evaluated using a line pair resolution phantom. The spatial resolution of the two settings were estimated by reconstructing a 0.15-mm wire phantom and comparing its full width half maximum (FWHM). A CBCT scan of a rodent head was also acquired to further demonstrate the improved resolution using the x-ray lens. The proposed imaging setup with x-ray lens had a limited exposure area of 5cm by 5cm on the detector, which was suitable for guiding radio-neuromodulation to a small target in rodent brain. Compared to conventional imaging acquisition with a measured x-ray focal spot of 0.395mm FWHM, the virtual focal spot size was measured at 0.175mm. The reduction in focal spot size with lens leads to an almost doubled planar imaging resolution and a 26% enhancement in 3D spatial resolution. A realistic CBCT acquisition of a rodent head mimicked the imaging acquisition step for radio-neuromodulation and further showed the improved visualization for fine structures. This work demonstrated that the focused kV x-ray technique was capable of generating small focal spot size of <0.2mm, which substantially improved x-ray imaging resolution for small animal imaging.

A robust and scalable electron transparent multi-stacked graphene gate for effective electron-beam convergence in field emission digital X-ray sources

Recently, carbon nanotube (CNT)-based field emission digital X-ray sources have received enormous attention in medical and industrial imaging systems. For high-resolution X-ray images, the field-emitted electron-beam (e-beam) must create a small focal spot size onto an anode by properly converging and focusing of e-beam. Here, multi-stacked graphene by using a layer-by-layer (LBL) stacking method was fabricated as an electron transparent graphene gate (ETGG) for effective e-beam convergence. The ETGG that was completely made on molybdenum (Mo) apertures with scalable diameters of 300 µm extracted and then effectively converged e-beams onto the anode in a triode structure. From the current–voltage measurements, the ETGG reduced turn-on voltage of CNT paste emitters by approximately 24%, as compared with an aperture-gate. The e-beam area originating from the CNT paste emitters with the ETGG was largely converged (almost 77%) compared to the aperture-gate, and scattering of the primary e-beams was eliminated with an optimized collimation module. Long-term durability of the ETGG was confirmed, as the graphene on the apertures robustly remained without any deterioration even upon the 140,000 shots of several-keV-electron bombardment in pulse operation mode. These results demonstrate the potential and suitability of the ETGG for application in field emission digital X-ray sources.

High-Performance Cold Cathode X-ray Tubes Using a Carbon Nanotube Field Electron Emitter.

A cold cathode X-ray tube was fabricated using a carbon nanotube (CNT) field electron emitter made by a free-standing CNT film which is composed of a highly packed CNT network. A lot of CNT bundles with a sharp tip are vertically aligned at the edge of the thin CNT film with a length of 10 mm and a thickness of 7 μm. The cold cathode X-ray tube using the CNT field emitter presents an extremely high tube current density of 152 A/cm2 (corresponding to tube current of 106.4 mA), the electron beam transmittance of 95.2% and a small focal spot size (FSS) of 0.5 mm. In addition, the cold cathode X-ray tube also shows stable lifetime during 100 000 shots. High emission current density of the cold cathode X-ray tube is mainly attributed to a lot of electron emission sites at an edge of the CNT film. The small FSS is caused by an ensemble of the CNT field electron emitter made by a free-standing thin CNT film and the optimized curve-shape elliptical focusing lens. Based on obtained results, the cold cathode X-ray tube can be widely used for various X-ray applications such as medical diagnosis systems and security check systems in the future.

Finite-difference propagation for the simulation of x-ray multilayer optics

Recent progress in nanofabrication, namely of multilayer optics, and the construction of coherent hard x-ray sources has enabled high resolution x-ray microscopy with large numerical aperture optics for small focal spot sizes. Sub-10 nm and even sub-5 nm focal spot sizes have already been achieved using multilayer optics such as multilayer Laue lenses and multilayer zone plates. However these optics can not be described by the kinematic theory given their extreme aspect-ratio between the depth (thickness) and the layer width. Moreover, the numerical simulation of these optics is challenging, and the absence of an accessible numerical framework inhibits further progress in their design and utilization. Here, we simulate the propagation of x-ray wavefields within and behind optical multilayer elements using a finite-difference propagation method. We show that the method offers high accuracy at reasonable computational cost. We investigate how small focal spot sizes and highest diffraction efficiency of multilayer optics can be achieved, considering volume diffraction effects such as waveguiding and Pendellösung. Finally, we show the simulation of a novel imaging scheme, allowing for a detailed study of image formation and the development of customized phase retrieval schemes.

Generation of an optical needle beam with a laser inscribed Pancharatnam-Berry phase element under imperfect conditions.

Beams exhibiting long focal lines and small focal spot sizes are desired in a variety of applications and are called optical needles, with Bessel beams being a common example. Conical prisms are regularly used to generate Bessel beams, however, this method is usually plagued by an appearance of on-axis oscillations. In this work, we consider an optical element based on the space-domain Pancharatnam-Berry phase (PBP) to generate a high-power optical needle with a smooth and constant on-axis intensity profile. The phase in PBP elements is not introduced through optical path differences but results from the geometric phase that accompanies space-variant polarization manipulation. Our implementation is based on a type 2 modification of bulk transparent glass material, resulting in the formation of nanogratings with slow axes aligned perpendicular to the grating corrugation. We investigate both numerically and experimentally the stability of an optical needle generation under imperfect conditions. Influences of misalignments in the optical schema are investigated numerically and experimentally.

Modelling of the focal spot intensity distribution and the off-focal spot radiation in kilovoltage x-ray tubes for imaging

X-ray tubes for medical applications typically generate x-rays by accelerating electrons, emitted from a cathode, with an interelectrode electric field, towards an anode target. X-rays are not emitted from one point, but from an irregularly shaped area on the anode, the focal spot. Focal spot intensity distributions and off-focal radiation negatively affect the imaging spatial resolution and broadens the beam penumbra. In this study, a Monte Carlo simulation model of an x-ray tube was developed to evaluate the spectral and spatial characteristics of off-focal radiation for multiple photon energies. Slit camera measurements were used to determine the horizontal and vertical intensity profiles of the small and the large focal spot of a diagnostic x-ray tube. First, electron beamlet weighting factors were obtained via an iterative optimization method to represent both focal spot sizes. These weighting factors were then used to extract off-focal spot radiation characteristics for the small and large focal spot sizes at 80, 100, and 120 kV. Finally, 120 kV simulations of a steel sphere (d = 4 mm) were performed to investigate image blurring with a point source, the small focal spot, and the large focal spot. The magnitude of off-focal radiation strongly depends on the anode size and the electric field coverage, and only minimally on the tube potential and the primary focal spot size. In conclusion, an x-ray tube Monte Carlo simulation model was developed to simulate focal spot intensity distributions and to evaluate off-focal radiation characteristics at several energies. This model can be further employed to investigate focal spot correction methods and to improve cone-beam CT image quality.

Fast microfocus x-ray tube based on carbon nanotube array

A full vacuum-sealed macrofocus x-ray tube with a vertically-aligned ring-shaped carbon nanotube (CNT) emitter grown by microwave plasma enhanced chemical vapor deposition is presented in this paper. The external grid allowed the CNT-based x-ray tube to exhibit transient switching on and off. The total emission current was 200 μA, which corresponds to a maximum emission current density of 10.1 A/cm2 from the ring-shaped CNT emitter when the grid voltage was 2.4 kV. The optimized focus electrode controlled the beam convergence on the target to produce a very small x-ray focal spot size less than 5 μm. Consequently, this microfocus x-ray tube could produce x-ray images with very high spatial resolution. X-ray fluoroscopy images of a multilayer printed circuit board (PCB) and field programmable gate array show distinct gold PCB traces with approximately 20 μm width.

Improving resolution of head and neck CTA using the small x-ray tube focal spot.

CT-resolution depends on tube focal spot size. To investigate the effect of reducing focal spot on vessel wall clarity, 22 patients underwent head and neck CTA acquisition with large and small focal spot size. Hounsfield density profile was assessed for each head and neck vessel separately, and significantly sharper density increase at vessel borders was observed using smaller tube focus by an average of 9.9% to 82° angle degrees (p < .05). In conclusion, spatial resolution of CTA of head and neck vessels can be improved by using the small x-ray tube focal spot.

Micro-mirror-array based off-axis flat lens for near-eye displays.

We developed an off-axis diffractive lens using a micro-mirror array on a flat substrate. MMA creates an on-axis converging beam from a 45 degrees off-axis diverging illumination beam and functions similar to a large and bulky elliptical mirror. The array consists of individual micro-mirrors with normal directions that vary across the component. The size, normal direction and the center height of each micro-mirror are optimized to achieve a phase matching condition so that the smallest focal spot size is achieved at the design wavelength. Design can also be optimized for full color applications using a synthetic design wavelength. A sample MMA of size 3 mm by 5 mm is fabricated using grayscale lithography. The designed MMA is used to illuminate a computer-generated hologram in a near-eye display system. Experimental results verify the premises of the designed component.

Focusing of multi-MeV, subnanosecond proton bunches from a laser-driven source

We report on our latest transverse focusing results of subnanosecond proton bunches achieved with a laser-driven multi-MeV ion beamline. In the frame of the LIGHT collaboration, a target normal sheath acceleration (TNSA) source based 6 m long beamline was installed. In the past years, the laser-driven proton beam was transported and shaped by this beamline. The particle beam is collimated with a pulsed high-field solenoid and rotated in longitudinal phase space with a radio-frequency cavity which leads to an energy compression with an energy spread of $(2.7\ifmmode\pm\else\textpm\fi{}1.7)%$ ($\mathrm{\ensuremath{\Delta}}\mathrm{E}/{\mathrm{E}}_{0}$ at FWHM) or a time compression to the subnanosecond regime. Highest peak intensities in the subnanosecond regime open up an interesting field for several applications, e.g., proton imaging, as injectors in conventional accelerators or precise stopping power measurements in a plasma. We report on achieving highest peak intensities using an installed second solenoid as a final focusing system in our beamline to achieve small focal spot sizes. We measured a focal spot size of $1.1\ifmmode\times\else\texttimes\fi{}1.2\text{ }\mathrm{mm}$ leading to $5.8\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\mathrm{protons}\text{ }\mathrm{per}\text{ }\mathrm{s}\text{ }{\mathrm{cm}}^{2}$ at a central energy bin of $(9.55\ifmmode\pm\else\textpm\fi{}0.25)\text{ }\mathrm{MeV}$, which can be combined with a bunch duration below 500 ps at FWHM.

Array-source X-ray velocimetry.

X-ray velocimetry (XV) has shown promise for investigations into various dynamic biological systems, including the motion of lungs and the flow of blood. Prior research in the field of XV has highlighted the need for both high spatial resolution to resolve features for tracking, and temporal resolution for accurate velocity measurement. In X-ray imaging systems, enhancement of spatial and temporal resolution requires a small focal spot size and high power output respectively, increasing anode power density requirements. In this paper, we present a multi-source XV regime whereby simultaneously illuminating a sample with multiple sources of small focal spot size, overall illumination can be increased whilst maintaining minimal source blurring without increasing power density requirements. Through a series of simulations, we demonstrate the capability for multi-source systems under various practical constraints, such as focal spot size and power density, to provide increased accuracy compared to single source systems.

Evaluation of the Quality Control Program for Diagnostic Radiography and Fluoroscopy Devices in Syria during 2005-2013

Introduction: Extensive use of diagnostic radiology is the largest contributor to total population radiation doses. Thus, appropriate equipment and safe practice are necessary for good-quality images with optimal doses. This study aimed to perform quality control (QC) audit for radiography and fluoroscopy devices owned by private sector in Syria (2005-2013) to verify compliance of performance of X-ray machines with the regulatory requirements stipulated by the national regulatory body. Materials and Methods: In this study, QC audit included 487 X-ray diagnostic machines, (363 radiography and 124 fluoroscopy devices), installed in 306 medical diagnostic radiology centers in 14 provinces in Syria. We employed an X-ray beam analyzer device (NERO model 8000, Victoreen, USA), which was tested and calibrated at the National Secondary Standard Dosimetry Laboratory traceable to the IAEA Network of Secondary Standard Dosimetry Laboratories. Standard QC tool kits were used to evaluate tube and generator of the X-ray machines, which constituted potential (kVp), timer accuracy, radiation output consistency, tube filtration, small and large focal spot sizes, X-ray beam collimation and alignment, as well as high- and low-resolution and entrance surface dose in fluoroscopy. Results: According to our results, most of the assessed operating parameters were in compliance with the standards stipulated by the National Regulatory Authority. In cases of noncompliance for the assessed parameters, maximum value (28.77%) pertained to accuracy of kVp calibration for radiography units, while the lowest value (2.42%) belonged to entrance surface dose in fluoroscopy systems. Conclusion: Effective QC program in diagnostic radiology leads to obtaining information regarding quality of radiology devices used for medical diagnosis and minimizing the doses received by patients and medical personnel. The findings of this QC program, as the main part of QA program, illustrated that most of the considered diagnostic X-ray devices had acceptable performance and few of them need to be recalibrated for some parameters.

Focal spot size reduction using asymmetric collimation to enable reduced anode angles with a conventional angiographic x-ray tube for use with high resolution detectors.

The high-resolution requirements for neuro-endovascular image-guided interventions (EIGIs) necessitate the use of a small focal-spot size; however, the maximum tube output limits for such small focal-spot sizes may not enable sufficient x-ray fluence after attenuation through the human head to support the desired image quality. This may necessitate the use of a larger focal spot, thus contributing to the overall reduction in resolution. A method for creating a higher-output small effective focal spot based on the line-focus principle has been demonstrated and characterized. By tilting the C-arm gantry, the anode-side of the x-ray field-of-view is accessible using a detector placed off-axis. This tilted central axis diminishes the resultant focal spot size in the anode-cathode direction by the tangent of the effective anode angle, allowing a medium focal spot to be used in place of a small focal spot with minimal losses in resolution but with increased tube output. Images were acquired of two different objects at the central axis, and with the C-arm tilted away from the central axis at 1° increments from 0°-7°. With standard collimation settings, only 6° was accessible, but using asymmetric extended collimation a maximum of 7° was accessed for enhanced comparisons. All objects were positioned perpendicular to the anode-cathode direction and images were compared qualitatively. The increasing advantage of the off-axis focal spots was quantitatively evidenced at each subsequent angle using the Generalized Measured-Relative Object Detectability metric (GM-ROD). This anode-tilt method is a simple and robust way of increasing tube output for a small field-of-view detector without diminishing the overall apparent resolution for neuro-EIGIs.

Multisource inverse-geometry CT. Part II. X-ray source design and prototype.

This paper summarizes the development of a high-power distributed x-ray source, or "multisource," designed for inverse-geometry computed tomography (CT) applications [see B. De Man et al., "Multisource inverse-geometry CT. Part I. System concept and development," Med. Phys. 43, 4607-4616 (2016)]. The paper presents the evolution of the source architecture, component design (anode, emitter, beam optics, control electronics, high voltage insulator), and experimental validation. Dispenser cathode emitters were chosen as electron sources. A modular design was adopted, with eight electron emitters (two rows of four emitters) per module, wherein tungsten targets were brazed onto copper anode blocks-one anode block per module. A specialized ceramic connector provided high voltage standoff capability and cooling oil flow to the anode. A matrix topology and low-noise electronic controls provided switching of the emitters. Four modules (32 x-ray sources in two rows of 16) have been successfully integrated into a single vacuum vessel and operated on an inverse-geometry computed tomography system. Dispenser cathodes provided high beam current (>1000 mA) in pulse mode, and the electrostatic lenses focused the current beam to a small optical focal spot size (0.5 × 1.4 mm). Controlled emitter grid voltage allowed the beam current to be varied for each source, providing the ability to modulate beam current across the fan of the x-ray beam, denoted as a virtual bowtie filter. The custom designed controls achieved x-ray source switching in <1 μs. The cathode-grounded source was operated successfully up to 120 kV. A high-power, distributed x-ray source for inverse-geometry CT applications was successfully designed, fabricated, and operated. Future embodiments may increase the number of spots and utilize fast read out detectors to increase the x-ray flux magnitude further, while still staying within the stationary target inherent thermal limitations.

SU‐C‐209‐01: Validation of the Simulated Detectability Metric (G‐ROD) Using the Experimental Generalized Measured Relative Object Detectability Metric (GM‐ROD)

Purpose:The Generalized Relative Object Detectability (G‐ROD) family of ideal observer metrics are a well‐characterized set of task‐based metrics used for quantitatively comparing imaging systems that include the detector, focal spot geometry and scatter characteristics on the basis of system abilities in imaging a given simulated object. The G‐ROD metric takes the integral over spatial frequencies of the Fourier transform of a simulated object function weighted with the detector generalized DQE (GDQE), divided by the comparable integral for another detector. When a measured image of an actual object is used, the generalized measured‐ROD (GM‐ROD) metric can compare detector systems without explicitly determining detector MTF. In this work, the results of simulated and measured ROD calculations for the same object are compared for the first time.Methods:G‐ROD calculations were performed to compare a high resolution microangiographic fluoroscopic (MAF) detector to a flat panel detector (FPD) using 5mm segments of simulated copper wires of varying diameter (d=0.05–0.6mm) as the object function for three different focal spot sizes at two magnifications. A GM‐ROD experiment with similar parameters was performed to compare the same detector system using three actual 5mm copper wires (d=0.113mm,0.238mm,0.558mm) imaged under identical but simulated conditions used in G‐ROD calculations to determine the agreement between simulated and experimentally obtained results.Results:The G‐ROD and GM‐ROD calculations examined relative detector system imaging performance. The GM‐ROD results for all three different sized wires imaged with low magnification and a small focal spot size were 2.1, 1.38, and 1.1, respectively, and the G‐ROD results for the same calculation was 1.81, 1.3, and 1.07, corresponding to percent deviations of 13%, 5.8%, and 2.7%.Conclusion:These results indicate experimental validation of the simulated metric results.Partial support from NIH grant R01EB002873 and an equipment grant from Toshiba Medical Systems Corp.