Full Full Field Of View Research Articles

Photon counting-energy integrating hybrid flat panel detector systems for image-guided interventions: an experimental proof-of-concept

Objective. Current C-arm x-ray systems equipped with scintillator-based flat panel detectors (FPDs) lack sufficient low-contrast detectability and spectral, high-resolution capabilities much desired for certain interventional procedures. Semiconductor-based direct-conversion photon counting detectors (PCDs) offer these imaging capabilities, although the cost of full field-of-view (FOV) PCD is still too high at the moment. The purpose of this work was to present a hybrid photon counting-energy integrating FPD design as a cost-effective solution to high-quality interventional imaging. Approach. In the proposed hybrid detector design, the central scintillator and thin-film transistor elements in the FPD are replaced with a semiconductor PCD module to upgrade the imaging capabilities of the C-arm system while preserving the full FOV coverage. The central PCD module can be used for high-quality 2D and 3D region-of-interest imaging with improved spatial- and temporal-resolution as well as spectral resolving capability. An experimental proof-of-concept was conducted using a 30 × 2.5 cm2 CdTe PCD and a 40 × 30 cm2 CsI(Tl)-aSi(H) FPD. Main results. Phantom and in vivo animal studies show (1) improved visualization of small stent wires in both 2D and 3D images due to the better spatial resolution of the PCD; (2) dual-energy angiography imaging capability by using the spectral PCD; (3) better conspicuity of small peripheral iodinated vessels (contrast-to-noise ratio improvement range: (29%, 151%)); (4) the central PCD outputs can be fused seamlessly with the surrounding scintillator detector outputs to provide full field imaging: A post-processing chain was developed by leveraging the PCD’s spectral information to match the image contrast of the PCD images to the surrounding scintillator detector, followed by spatial filtering of the PCD image to match noise texture and spatial resolution. Significance. The hybrid FPD design provides a cost-effective option to upgrade C-arm systems with spectral and ultra-high resolution capabilities without interfering with the clinical need for full FOV imaging.

Aliasing-free reduced field-of-view parallel imaging.

To reconstruct aliasing-free full field-of-view (FOV) images for reduced FOV (rFOV) parallel imaging (PI) with Cartesian and Wave sampling, which suffers from aliasing artifacts using existing PI methods. The sensitivity encoding method (SENSE) was extended to the Soft-SENSE models supporting multiple-set coil sensitivity maps (CSM) and point spread functions (PSF) for Cartesian and Wave sampled rFOV PI, respectively. The multiple-set CSM and PSF were created from full FOV CSM and PSF according to the image folding process induced by rFOV sampling. The Soft-SENSE reconstructions could be solved by the same algorithms for the conventional full FOV SENSE reconstruction. Soft-SENSE using multiple-set full FOV CSM and PSF successfully reconstruct aliasing-free full FOV image from rFOV PI data with Cartesian and Wave sampling. The proposed rFOV PI enables flexible control of the aliasing and achieves comparable geometry factors as the standard full FOV PI with the same net acceleration factor. Reduced FOV PI improves the computational efficiency of iterative compressed sensing (CS) and PI reconstruction, especially for high-resolution volumetric imaging, thanks to the reduced fast Fourier transform (FFT) size. Moreover, rFOV PI reconstruction provides a potential alternative to the phase oversampling for the FOV aliasing problem. The proposed Soft-SENSE using full FOV CSM and PSF could reconstruct aliasing-free full FOV image for rFOV PI, and make it a viable solution enabling more flexible PI acceleration and effectively improving the computational efficiency of iterative CSPI reconstruction.

Pixels of Interest (POI) empowered higher speed CAOS camera imaging and spectrometry for multi-target applications

Designed and demonstrated for the first time is Pixels of Interest (POI) centric camera design empowered higher speed, better computational efficiency, Coded Access Optical Sensor (CAOS) time–frequency Code Division Multiple Access (CDMA)-mode imaging versus the classic Hadamard (H) spatial transform-based imaging. The showcased CAOS camera is highly suited for faster tracking of multiple distributed targets within a large pixel count full Field of View (FOV) over a full multi-band optical spectrum. A demonstration white light experiment with 3 different shaped targets distributed in a 16384 pixels full FOV shows an 6.12 times faster CAOS imaging operation versus Hadamard Transform (HT)-imaging with a CAOS POI frame update time of 143.4 ms. An additional experiment using 3 similar shaped white light targets with different brightness values also demonstrates the CAOS CDMA-mode speed advantage. Potential areas of use are multi-target tracking in manufacturing, microscopy, security such as Unmanned Aerial Vehicles based surveillance, air traffic monitoring, and astronomy. Apart from imaging applications, the CAOS CDMA-mode is also suited for higher speed spectrometry across a broad optical spectrum with distributed discrete targeted spectral lines.

Full field-of-view digital lens-free holography for weak-scattering objects based on grating modulation.

Grating-based single-shot digital lens-free holography with spatial spectral multiplexing is proposed to realize full field-of-view (FOV) imaging for weak-scattering objects. Multiple object waves are generated by a one-dimensional grating that is placed in near contact with the object to avoid the cross talk among different diffraction orders during reconstruction. A multiplexed off-axis hologram is created by interference between the object waves and reference wave and captured by an image sensor in one shot. Multiple imaging areas corresponding to the captured object waves can be simultaneously retrieved during reconstruction. A formula which guarantees full FOV imaging without cross talk or information loss is presented. The imaging experiments of a USAF resolution target are presented to demonstrate the feasibility of this method.

Dynamic electronic collimation method for 3-D catheter tracking on a scanning-beam digital x-ray system.

Scanning-beam digital x-ray (SBDX) is an inverse geometry x-ray fluoroscopy system capable of tomosynthesis-based 3-D catheter tracking. This work proposes a method of dose-reduced 3-D catheter tracking using dynamic electronic collimation (DEC) of the SBDX scanning x-ray tube. This is achieved through the selective deactivation of focal spot positions not needed for the catheter tracking task. The technique was retrospectively evaluated with SBDX detector data recorded during a phantom study. DEC imaging of a catheter tip at isocenter required 340 active focal spots per frame versus 4473 spots in full field-of-view (FOV) mode. The dose-area product (DAP) and peak skin dose (PSD) for DEC versus full FOV scanning were calculated using an SBDX Monte Carlo simulation code. The average DAP was reduced to 7.8% of the full FOV value, consistent with the relative number of active focal spots (7.6%). For image sequences with a moving catheter, PSD was 33.6% to 34.8% of the full FOV value. The root-mean-squared-deviation between DEC-based 3-D tracking coordinates and full FOV 3-D tracking coordinates was less than 0.1mm. The 3-D distance between the tracked tip and the sheath centerline averaged 0.75mm. DEC is a feasible method for dose reduction during SBDX 3-D catheter tracking.

Synchronised multi-scale image analysis of soil deformations

New apparatus and techniques for performing synchronised multi-scale particle image velocimetry or digital image correlation (PIV/DIC) soil deformation measurements have been developed. A central camera records a full field of view (FoV) of the model capturing the ‘macro’ deformation mechanism and the boundaries of the model. Simultaneously, an adjacent slave camera records a subset of the full FoV capturing the ‘micro’ soil response in a region of special interest, such as under the corner of footing. The ‘micro’ FoV images have higher resolution in terms of particle/pixel size ratio (d/p), resulting in the ability to measure localised deformations that are invisible to lower resolution images. Recommendations are made with respect to appropriate subset size and spacing for high-resolution images. A photogrammetric correction process requiring a small number of static control points is proposed and the performance is validated against a conventional photogrammetric calibration utilising a large array of static control points. Lastly, results from a validation experiment are presented comparing the PIV/DIC output from the ‘macro’ and ‘micro’ FoV, illustrating that: (a) the photogrammetric correction method proposed is robust and (b) that there has been an improvement in spatial resolution of the strain measurements that can be obtained through the ‘micro’ FoV camera.

SU‐E‐J‐167: Improvement of Time‐Ordered Four Dimensional Cone‐Beam CT; Image Mosaicing with Real and Virtual Projections

Purpose:In the previous study, we developed time‐ordered fourdimensional (4D) cone‐beam CT (CBCT) technique to visualize nonperiodic organ motion, such as peristaltic motion of gastrointestinal organs and adjacent area, using half‐scan reconstruction method. One important obstacle was that truncation of projection was caused by asymmetric location of flat‐panel detector (FPD) in order to cover whole abdomen or pelvis in one rotation. In this study, we propose image mosaicing to extend projection data to make possible to reconstruct full field‐of‐view (FOV) image using half‐scan reconstruction.Methods:The projections of prostate cancer patients were acquired using the X‐ray Volume Imaging system (XVI, version 4.5) on Synergy linear accelerator system (Elekta, UK). The XVI system has three options of FOV, S, M and L, and M FOV was chosen for pelvic CBCT acquisition, with a FPD panel 11.5 cm offset. The method to produce extended projections consists of three main steps: First, normal three‐dimensional (3D) reconstruction which contains whole pelvis was implemented using real projections. Second, virtual projections were produced by reprojection process of the reconstructed 3D image. Third, real and virtual projections in each angle were combined into one extended mosaic projection. Then, 4D CBCT images were reconstructed using our inhouse reconstruction software based on Feldkamp, Davis and Kress algorithm. The angular range of each reconstruction phase in the 4D reconstruction was 180 degrees, and the range moved as time progressed.Results:Projection data were successfully extended without discontinuous boundary between real and virtual projections. Using mosaic projections, 4D CBCT image sets were reconstructed without artifacts caused by the truncation, and thus, whole pelvis was clearly visible.Conclusion:The present method provides extended projections which contain whole pelvis. The presented reconstruction method also enables time‐ordered 4D CBCT reconstruction of organs with non‐periodic motion with full FOV without projection‐truncation artifacts.This work was partly supported by the JSPS Core‐to‐Core Program(No. 23003). This work was partly supported by JSPS KAKENHI 24234567.

Comb-Push Ultrasound Shear Elastography (CUSE) With Various Ultrasound Push Beams

Comb-push ultrasound shear elastography (CUSE) has recently been shown to be a fast and accurate 2-D elasticity imaging technique that can provide a full field-of-view (FOV) shear wave speed map with only one rapid data acquisition. The initial version of CUSE was termed U-CUSE because unfocused ultrasound push beams were used. In this paper, we present two new versions of CUSE-focused CUSE (F-CUSE) and marching CUSE (M-CUSE), which use focused ultrasound push beams to improve acoustic radiation force penetration and produce stronger shear waves in deep tissues (e.g., kidney and liver). F-CUSE divides transducer elements into several subgroups which transmit multiple focused ultrasound beams simultaneously. M-CUSE uses more elements for each focused push beam and laterally marches the push beams. Both F-CUSE and M-CUSE can generate comb-shaped shear wave fields that have shear wave motion at each imaging pixel location so that a full FOV 2-D shear wave speed map can be reconstructed with only one data acquisition. Homogeneous phantom experiments showed that U-CUSE, F-CUSE, and M-CUSE can all produce smooth shear wave speed maps with accurate shear wave speed estimates. An inclusion phantom experiment showed that all CUSE methods could provide good contrast between the inclusion and background with sharp boundaries while F-CUSE and M-CUSE require shorter push durations to achieve shear wave speed maps with comparable SNR to U-CUSE. A more challenging inclusion phantom experiment with a very stiff and deep inclusion shows that better shear wave penetration could be gained by using F-CUSE and M-CUSE. Finally, a shallow inclusion experiment showed that good preservations of inclusion shapes could be achieved by both U-CUSE and F-CUSE in the near field. Safety measurements showed that all safety parameters are below FDA regulatory limits for all CUSE methods. These promising results suggest that, using various push beams, CUSE is capable of reconstructing a 2-D full FOV shear elasticity map using only one push-detection data acquisition in a wide range of depths for soft tissue elasticity imaging.

POLARIMETRIC CALIBRATION OF MIMIR AND THE GALACTIC PLANE INFRARED POLARIZATION SURVEY (GPIPS)

Methods and observations are described for the full field of view (FOV) polarimetric calibration of the Mimir near-infrared imaging polarimeter in support of the Galactic Plane Infrared Polarization Survey and other applications. Polarimetric calibration consisted of three steps: (1) flat fielding using in-dome images obtained with the compound zero-order half-wave-plate (HWP) in the 16 position angles employed in polarimetric observations, (2) mapping and removing the remaining instrumental polarization via observations of globular cluster stars, and (3) using polarization standard stars to convert instrument-based polarization position angles to equatorial and to determine the linear polarimetric efficiency. For Mimir, the polarization flat fielding reduced systematic variations of the polarization efficiency across the FOV by a factor of 20. The 151 observations of eight globular clusters yielded 40,000 stars for measuring the remaining 0.05%-0.45% instrumental polarization to uncertainties of 0.02%-0.04%. After these corrections, the 444 observations of 23 polarized stars enabled equatorial polarization position angles to be determined to typical uncertainties of 0.{sup 0}5, and the on-axis (corrected to full FOV) polarization efficiency of 91.1% {+-} 0.4% to be determined. Fully corrected standard star observations showed excellent agreement with published values of polarization percentage and position angle. Additionally, the observations of four skymore » fields containing Whittet et al. 'primary' polarization standard stars were analyzed to yield 30 new 'secondary' standards. These are fainter than the primaries, allowing use with larger telescope apertures. The secondary standards have polarization position angle uncertainties under 5 Degree-Sign and range in degree of polarization from 0.4% to 8.5%.« less

Extraspinal Findings at Lumbar Spine CT Examinations: Prevalence and Clinical Importance

To prospectively determine the prevalence and clinical importance of extraspinal abnormalities in adult outpatients undergoing computed tomography (CT) of the lumbar spine. Institutional review board approval was obtained for this prospective study. Informed consent was obtained from 400 consecutive adult outpatients (mean age, 49 years; 212 male and 188 female patients) undergoing lumbar spine CT for low back pain and/or radiculopathy. Those with known malignancy were excluded. Dedicated spinal and abdominal full-field-of-view (FOV) images for each patient were reviewed by at least one neuroradiologist and two body radiologists. Extraspinal abnormalities were classified according to the CT Colonography Reporting and Data System (C-RADS). The electronic medical record of the patients with C-RADS E3 and E4 extraspinal findings were reviewed to assess how many of these findings were previously unknown, and the patients were followed up 24-36 months after the initial CT to determine their work-up and outcome. Extraspinal findings were present on images in 162 (40.5%) of 400 lumbar spine CT examinations; 59 (14.8%) patients had indeterminate or clinically important findings requiring clinical correlation or further evaluation. After review of the electronic medical record, the prevalence of clinically important findings was 4.3%, comprising an early-stage renal cell carcinoma and transitional cell carcinoma, chronic lymphocytic leukemia, sarcoidosis, and 13 abdominal aortic aneurysms. Excluding anatomic variants, the full FOV was required to best visualize extraspinal abnormalities in 127 (79.4%) of 160 patients. Reviewing the full-FOV images from lumbar spine CT examinations will result in the detection of a small number of substantial extraspinal pathologic findings in addition to many benign incidental findings.

Targeted single‐shot methods for diffusion‐weighted imaging in the kidneys

To investigate the feasibility of combining the inner-volume-imaging (IVI) technique with single-shot diffusion-weighted (DW) spin-echo echo-planar imaging (SE-EPI) and DW-SPLICE (split acquisition of fast spin-echo) sequences for renal DW imaging. Renal DWI was performed in 10 healthy volunteers using single-shot DW-SE-EPI, DW-SPLICE, targeted-DW-SE-EPI, and targeted-DW-SPLICE. We compared the quantitative diffusion measurement accuracy and image quality of these targeted-DW-SE-EPI and targeted DW-SPLICE methods with conventional full field of view (FOV) DW-SE-EPI and DW-SPLICE measurements in phantoms and normal volunteers. Compared with full FOV DW-SE-EPI and DW-SPLICE methods, targeted-DW-SE-EPI and targeted-DW-SPLICE approaches produced images of superior overall quality with fewer artifacts, less distortion, and reduced spatial blurring in both phantom and volunteer studies. The apparent diffusion coefficient (ADC) values measured with each of the four methods were similar and in agreement with previously published data. There were no statistically significant differences between the ADC values and intravoxel incoherent motion (IVIM) measurements in the kidney cortex and medulla using single-shot DW-SE-EPI, targeted-DW-EPI, and targeted-DW-SPLICE (P > 0.05). Compared with full-FOV DWI methods, targeted-DW-SE-EPI and targeted-DW-SPLICE techniques reduced image distortion and artifacts observed in the single-shot DW-SE-EPI images, reduced blurring in DW-SPLICE images, and produced comparable quantitative DW and IVIM measurements to those produced with conventional full-FOV approaches.