Rectangular Field Of View Research Articles

Layout Design of Strapdown Array Seeker and Extraction Method of Guidance Information

This paper proposed a multi-view surface array to enlarge the field-of-view (FOV) from 45° × 45° to 72° × 75° and improve the estimation precision of guidance information. First, based on circular and rectangular FOV sensors, the superposition characteristics of FOV in the +-shaped layout and the X-shaped layout were explored and analyzed. Secondly, normalization processing was applied to obtain the equivalent measurement value of the central sensor and the corresponding error distribution. Based on such measurement value and error distribution, the filtering model could be constructed, which could effectively solve the problem of observation number variation caused by multiple sensors. Thirdly, a multivariate iterated extended Kalman filter (MIEKF) was proposed to make full use of multiple measurements. By iterating multiple unequal observations and making full use of the known error distribution information, the noise of filtered data was found to be effectively reduced and the estimation precision of guidance information was improved. Finally, based on a 6-DOF trajectory simulation, the correctness and effectiveness of the proposed method were verified. Simulation results show that MIEKF can improve the estimation accuracy of the line-of-sight (LOS) angle by at least 30% and the estimation accuracy of the LOS angle rate by nearly 80% compared with EKF.

Comments on the 2013 ICNIRP Laser Guidelines.

Comments on the 2013 ICNIRP Laser Guidelines.

Fast Phase-Contrast Cine MRI for Assessing Intracranial Hemodynamics and Cerebrospinal Fluid Dynamics.

We propose fast phase-contrast cine magnetic resonance imaging (PC-cine MRI) to allow breath-hold acquisition, and we compared intracranial hemo- and hydrodynamic parameters obtained during breath holding between full inspiration and end expiration. On a 3.0 T MRI, using electrocardiogram (ECG)-synchronized fast PC-cine MRI with parallel imaging, rectangular field of view, and segmented k-space, we obtained velocity-mapped phase images at the mid-C2 level with different velocity encoding for transcranial blood flow and cerebrospinal-fluid (CSF) flow. Next, we calculated the peak-to-peak amplitudes of cerebral blood flow (ΔCBF), cerebral venous outflow, intracranial volume change, CSF pressure gradient (ΔPG), and intracranial compliance index. These parameters were compared between the proposed and conventional methods. Moreover, we compared these parameters between different utilized breath-hold maneuvers (inspiration, expiration, and free breathing). All parameters derived from the fast PC method agreed with those from the conventional method. The ΔPG was significantly higher during full inspiration breath holding than at the end of expiration and during free breathing. The proposed fast PC-cine MRI reduced scan time (within 30 s) with good agreement with conventional methods. The use of this method also makes it possible to assess the effects of respiration on intracranial hemo- and hydrodynamics.

Optical design of the freeform reflective imaging system with wide rectangular FOV and low F-number

In recent years, freeform optical surfaces have been used increasingly in a variety of off-axis reflective imaging systems with high performance levels. However, it is a difficult and challenging task to design an off-axis reflective imaging system that has a low F-number and a wide rectangular field-of-view (FOV) simultaneously. In this paper, the field extension construction (FEC) design method is proposed to design a freeform imaging system with both a low F-number and a wide rectangular FOV. When using an existing normal system with a small rectangular FOV as the input, an initial configuration that simultaneously has both a low F-number and a wide rectangular FOV can be obtained after several system construction attempts. A freeform reflective infrared camera is then successfully designed after optimization and has a focal length of 9.3 mm, an F-number of 1.39, and a wide rectangular FOV of 40° × 30°. The image quality is close to the diffraction-limited level in the far-infrared band and the maximum relative distortion is 5.5%. In addition, the system prototype is presented after fabrication and its good practical imaging performance is demonstrated.

Analytic Determination of Rectangular-Pinhole Sensitivity With Penetration.

Modern small-animal SPECT systems use multiple pinhole collimators per detector to increase sensitivity while still maintaining high resolution. This resolution is a combination of aperture resolution combined with detector resolution, which is mitigated by magnification. Higher magnification results in better resolution, but fewer apertures per detector. When multiple pinhole collimators project onto the same detector, those with a rectangular field of view (FOV) can be packed more tightly than those with a circular FOV. In addition, a rectangular aperture can be used to obtain different resolution-sensitivity tradeoffs in the two orthogonal directions. Thus, these rectangular-pinhole collimators can have independent FOVs and independent resolution values in the two directions of the rectangular aperture. Previous work has determined the amount of penetration for circular pinholes (i.e., circular apertures with circular FOVs), where the pinhole walls were modeled as cones. In this work, a formula for the penetrative sensitivity for rectangular apertures with a rectangular FOV is determined. The formula was validated using numerical calculations for various combinations of acceptance angles, aperture sizes, linear attenuation coefficients, and incidence angles.

The Novel Evaluation Method of Geometric Distortion for 3D-MRI

Recently, many imaging methods are developed in magnetic resonance imaging and in particular, the release of the 3D acquisition method is remarkable. The image distortion often becomes the problem by the gradient echo method and the echo planar imaging (EPI) -based method, but the image distortion of the 3D acquisition is not established. A purpose of this study is to examine the utility of the novel evaluation method of the image distortion for the 3D acquisition image. The spin echo image was used as a criteria image, and EPI was used as a target image for 3D acquisition imaging. Image J was used for the image processing. The value that divided the volume of the different shape of criteria image and the target image by the volume of the criteria image was defined as a distortion rate. Hence, we refer this method to the volume method. It is reported that the distortion rate of the EPI is proportional to a rectangle rate of rectangular field of view (RFOV). The distortion rate of the volume method for 50-100% of rectangle ratio was compared with the theoretical value. In addition, the dependence by the threshold of the binarization was considered. Furthermore, the comparison with the NEMA (National Electrical Manufacturers Association) method was carried out. As a result, the distortion rate decreased according to a rectangular rate of RFOV by the volume method, and the numerical value was equal with a theoretical value. In addition, the distortion rate did not have the effect by the thresholding of binarizing. The volume method had less error of measurement than the NEMA method.

SU‐E‐I‐50: Ultrahigh Resolution Reduced Field‐Of‐View Diffusion Tensor Imaging in the Spinal Cord

Purpose:Diffusion Tensor Imaging (DTI) is a well‐established MRI imaging modality for applications in the brain. The typically attainable imaging resolution for clinical DTI sequences is insufficient to image small lesions and assess injury with microstructural changes in the spinal cord (SC). Attempts to reduce the field‐of‐view (FOV) for increasing the imaging resolution have been made using rectangular FOV geometries that work well to efficiently image the sagittal plane. The highest structural details in the SC are however in the axial plane, most efficiently covered by a circular FOV. The aim of this study was to increase the axial DTI resolution in the SC to distinguish the dorsal spinal white‐matter bundles within clinically acceptable acquisition times.Methods:A multishot reduced FOV DTI technique named eZOOM that utilizes spatially selective radio‐frequency (RF) pulses and spiral readout has recently been developed by the author (Gaggl, MRM 2014) for application in the brain. In this study the method was adapted to the unique geometry of multichannel spinal RF coil arrays, with improved correction of blurring and misregistration and including peripheral gating to minimize cerebrospinal fluid flow‐artifacts. Several diffusion metrics including the novel normalized axial diffusivity DAn=λ1/∑λ (Gaggl, ASFNR 2013) were calculated and compared to current methods.Results:Sub‐millimeter square‐voxel imaging resolutions with image voxel volumes of approximately 1mm3 for a circular axial 8‐cm FOV and 15 diffusion weighting gradient directions were achieved in human for multislice image stacks in the SC with total imaging times of less than 30 minutes at 3T, enabling the separation of important spinal fiber tracts.Conclusion:The presented technique improves imaging resolution for DTI in the spinal cord compared to current clinical sequences while allowing to prescribe imaging geometries that excite only a small axial circular FOV in and around the spinal cord and reducing blurring and artifacts.

Reconstruction algorithm for improved ultrasound image quality

A new algorithm is proposed for reconstructing raw RF data into ultrasound images. Previous delay-and-sum beamforming reconstruction algorithms are essentially one-dimensional, because a sum is performed across all receiving elements. In contrast, the present approach is two-dimensional, potentially allowing any time point from any receiving element to contribute to any pixel location. Computer-intensive matrix inversions are performed once, in advance, to create a reconstruction matrix that can be reused indefinitely for a given probe and imaging geometry. Individual images are generated through a single matrix multiplication with the raw RF data, without any need for separate envelope detection or gridding steps. Raw RF data sets were acquired using a commercially available digital ultrasound engine for three imaging geometries: a 64-element array with a rectangular field-of- view (FOV), the same probe with a sector-shaped FOV, and a 128-element array with rectangular FOV. The acquired data were reconstructed using our proposed method and a delay- and-sum beamforming algorithm for comparison purposes. Point spread function (PSF) measurements from metal wires in a water bath showed that the proposed method was able to reduce the size of the PSF and its spatial integral by about 20 to 38%. Images from a commercially available quality-assurance phantom had greater spatial resolution and contrast when reconstructed with the proposed approach.

047 Time-Resolved Imaging with Interleaved Stochastic Trajectories (Twist) Improves Magnetic Resonance Angiography in Pediatric Patients

BACKGROUND: High spatial resolution contrast-enhanced magnetic resonance angiography (CEMRA) is routinely used to assess vascular morphology. In children, however, faster heart rates and variable arterial-to-venous transit times may produce venous contrast contamination and make CEMRA of the pulmonary artery (PA) and aorta (Ao) difficult using a single dose of gadolinium contrast. A newer technique, known as time-resolved imaging with interleaved stochastic trajectories (TWIST), allows rapid dynamic vascular imaging and may be used to determine optimal contrast arrival time in the great arteries for conventional CEMRA. The aim of this study is to assess TWIST bolus timing for optimizing CEMRA of the great arteries using a single dose of contrast in pediatric patients with congenital heart disease (CHD). METHODS/RESULTS: Patients underwent clinically indicated angiographyonaSiemensAvanto1.5Tsystem.TWISTwasperformed using a 4 mL (2 mmol) test bolus of gadopentetate. TWIST parameterswere:TR,2.3ms;TE,0.8ms;flipangle, 20°; rectangularfieldof view (rFOV), 300 320 mm; matrix, 120 128; 36 partitions; voxel size 2.5 2.5 3.5 mm^3; acceleration factor, 6; measurements, 24; temporal resolution per measurement, 1 second. Test bolus duration, acquisition time, and time to peak signal intensity in the PA and Ao were derived from TWIST datasets and used to perform twosequential conventionalCEMRAacquisitions in thegreatarteries following a single 0.1 mmol/kg contrast bolus. CEMRA parameters were: TR, 3.03 ms; TE, 1.11 ms; flip angle, 25°; rFOV, 332 380 mm;matrix,236 512;120partitions; voxel size0.99 0.99 1.0 mm^3; acceleration factor, 3. TWIST and CEMRA were evaluated for image quality and degree of separation of arterial and venous phases using a 4 point scale. To date, 3 patients (13 1 years; 53 11 kg, heart rate 69 20 / min) have been studied. TWIST yielded separate venous and arterial phases but with a greater degree of vessel-margin blurring. Two sequential CEMRA acquisitions based on TWIST bolus timing resulted in visualization of the great arteries with a distinct PA and Ao phase and without contrast contamination (Figure 1). CONCLUSION: TWIST bolus timing may be used to determine optimal contrast arrival time. This dynamic information allows sequential acquisition of conventional high spatial resolution CEMRA images of the PA and Ao using a single contrast bolus. This technique is valuable in performing angiography in pediatric patients with CHD. 048 THE IMPACT OF FETAL DIAGNOSIS ON DUCT-DEPENDENT CONGENITAL HEART LESIONS

K-Space tutorial: an MRI educational tool for a better understanding of k-space

A main difference between Magnetic Resonance (MR) imaging and other medical imaging modalities is the control over the data acquisition and how it can be managed to finally show the adequate reconstructed image. With some basic programming adjustments, the user can modify the spatial resolution, field of view (FOV), image contrast, acquisition velocity, artifacts and so many other parameters that will contribute to form the final image. The main character and agent of all this control is called k-space, which represents the matrix where the MR data will be stored previously to a Fourier transformation to obtain the desired image.This work introduces 'k-Space tutorial', a MATLAB-based educational environment to learn how the image and the k-space are related, and how the image can be affected through k-space modifications. This MR imaging educational environment has learning facilities on the basic acceleration strategies that can be encountered in almost all MR scanners: scan percentage, rectangular FOV and partial Fourier imaging. It also permits one to apply low- and high-pass filtering to the k-space, and to observe how the contrast or the details are selected in the reconstructed image. It also allows one to modify the signal-to-noise ratio of the acquisition and create some artifacts on the image as a simulated movement of the patient – with variable intensity level – and some electromagnetic spikes on k-space occurring during data acquisition.

Indirect magnetic resonance lymphangiography in patients with lymphedema: Preliminary results in humans

Purpose To assess the feasibility of indirect magnetic resonance (MR) lymphangiography with intracutaneous injection of gadodiamide, a commercially available, non-ionic, extracellular paramagnetic contrast agent for the detection of lymphatic vessels in patients with lymphedema. Materials and methods In 2005, three patients with lymphedema of the lower extremities (1 primary, 2 secondary) were referred by the Foeldi Clinic for Lymphology for indirect magnetic resonance lymphangiography. 4.5 mL of gadodiamide and 0.5 mL of mepivacainhydrochloride 1% were injected intracutaneously into the dorsal aspect of each foot. MR imaging was performed with a 1.5-T system equipped with high-performance gradients. For indirect magnetic resonance lymphangiography, a 3D Fast Low Angle Shot (FLASH) sequence (TR/TE: 5.1/1.23; flip angle: 25; matrix: 448 × 448; bandwidth: 330 Hz/pixel; 6/8 rectangular field of view with a maximum dimension of 500 mm; slices: 88; voxel size: 2.0 mm × 1.0 mm × 1.0 mm; acquisition time: 0 min 31 s) was used. Results Indirect magnetic resonance lymphangiography depicted lymphatic vessels of the lower and upper leg, and inguinal lymph nodes in all three patients. After 5 min of contrast material application, concomitant venous enhancement was detected. Collateral vessels with dermal back-flow were seen in two patients. A lymphocele in the inguinal region with the afferent lymphatic vessel was depicted in one patient. Conclusion In the presented small study group, indirect magnetic resonance lymphangiography was technically feasible, and no complications were observed after intracutaneous injection of gadodiamide. Visualizing the lymphatic vessels and accompanying complications non-invasively and without the use of radiation, the presented method has the capability to become a routine diagnostic imaging tool in patients with primary and secondary lymphedema. The method is not able to characterize lymph node morphology, but could provide additional information about the lymphatic vessels when lymph nodes are examined, e.g. with super-paramagnetic iron oxide particles.

Lesion discrimination in optic neuritis using high-resolution fat-suppressed fast spin-echo MRI.

Fast spin-echo (FSE) is a new sequence with acquisition times currently down to one-sixteenth of those obtained with conventional spin-echo sequences, which allows high-resolution (512 x 512 matrix) images to be acquired in an acceptable time. We compared the higher resolution of FSE with the medium resolution of a short inversion-time inversion-recovery (STIR) sequence in depicting the optic nerves of healthy controls and patients with optic neuritis. Optic nerve MRI examinations were performed in 18 patients with optic neuritis and 10 normal controls. Two sequences were obtained coronally: fat-suppressed FSE (FSE TR 3250 ms/TEef 68 ms, echo-train length 16, 4 excitations, 24 cm rectangular field of view, 3 mm interleaved contiguous slices, in-plane resolution 0.5 x 0.5 mm) and STIR (TR 2000 ms/TE 50 ms/TI 175 ms, in-plane resolution 0.8 x 0.8 mm, slice thickness 5 mm). FSE demonstrated much more anatomical detail than STIR, e.g. distinction of optic nerve and sheath. Lesions were seen in 20 of 21 symptomatic nerves using FSE and in 18 of 21 using STIR. Nerve swelling or partial cross-sectional lesions of the optic nerve were each seen only on FSE in 3 cases. Fat-suppressed FSE imaging of the optic nerve improves anatomical definition and increases lesion detection in optic neuritis.

Evaluation of the pulmonary vasculature with three-dimensional magnetic resonance imaging techniques

Cardiac and respiratory motion during the long acquisition times required in 3d magnetic resonance imaging (MRI) can lead to excessive image degradation and consequently poor diagnosis and interpretation in the thoracic region. This paper addresses the issue of obtaining good image quality with 3d gradient echo (GE) imaging in the study of the pulmonary vascular system and its diseases. To study the pulmonary vascular system two approaches have been considered. First, a proton density/inflow weighted scan consisting of a syncopated 3d FLASH acquisition is used to provide a 3d pulmonary angiogram. Secondly, aT 1 weighted scan using 3d IR-FLASH (inversion recovery FLASH) helps in determining the presence of pulmonary emboli. Multiple acquisitions and rectangular field of view are utilized to pseudogate to the respiratory period in order to reduce motion artifacts while keeping reasonable imaging times. Technical aspects on data collection during the approach to equilibrium and acquisition strategies in the presence of thoracic motion and its impact on vessel resolution are addressed. The method has proven successful for imaging volunteers and, more recently, in obtaining useful clinical information.

Subjective brightness of a very-short-persistence television display compared to one with standard persistence.

In a zero-persistence television display, such as one employing a deflected laser beam or injection luminescent diodes, the “on” time per picture element is determined solely by the system’s finite resolution and is about 120 nsec under current standards, as compared to 60-μsec persistence to 10% of initial luminance for a conventional cathode-ray-tube television display. Therefore, at a given luminance level, much higher peak luminances are encountered in the zero-persistence display. An experiment was performed to see if reasonable approximations to these two types of displays had equal averaged photometric luminances when adjusted for equal subjective brightnesses—i.e., does the Bunson–Roscoe luminance–time reciprocity law hold under these conditions?One half of a television picture was displayed on a cathode-ray tube with 120-nsec decay to 37% of initial luminance; the other half was displayed on a television phosphor whose decay under these conditions was 40 times as long, or about 5 μsec. The viewer was asked to match the two halves for brightness and this match was checked with a photometer. The display covered a 12×14 degree rectangular field of view under simulated home-viewing conditions. Tests were run at approximately 110 and 340 candelas per m2 (33 and 100 ft-L) highlight luminances, with both a standard blank television raster and an Indian-head test pattern. No significant departure from reciprocity was noted under these conditions. A 95% confidence interval of 6% on the raster tests and 13% on the Indian-head-pattern tests was attained.

Image converter — A new high-speed photographic device

The photographic device to be described was designed for an application of the image converter tube to provide a narrow rectangular field of view and a succession of exposures of the object at fixed time intervals. Its distinctive properties are: exposure time, 0.4 microseconds; frame rate, 200,000 per second; magnification from photocathode to fluorescent screen, 4 times; light gain of unity and electrical synchronization from an external source of either a single frame or a sequence of nine frames, arranged to fall parallel to each other in a row across the face of the tube. The size of the frames is controlled by the width of an input slit.