Imaging Field Of View Research Articles

WE-D-224C-08: Peripheral Dose to the Patient Due to Kilovoltage Cone Beam Computed Tomography

Purpose: To quantify the peripheral dose outside the imaging field of view (FOV) received by patients undergoing kV CBCT procedures. Methods and Material: A 0.6 cc Farmer‐type chamber and specially designed cylindrical water phantom were utilized to make the dose measurements. The main section of the phantom, constructed of Plexiglas©, is 30 cm in diameter and 50 cm in length, simulating an average patient body. The phantom is placed on the treatment couch with its axis coinciding with the axis of rotation of the gantry. An ion chamber holder rests in a slot on the top of the phantom, and allows the ion chamber to be placed at any depth, and at any point along the length of the phantom. A solid water cylindrical phantom 20 cm in diameter and 16 cm long was placed at the superior end of the water phantom to simulate a patient's head. Measurements were made on an Elekta Synergy treatment unit for various kVp, FOV, depths and distances from the central axis. A limited set of measurements were also made with a RANDO phantom to simulate the effects of typical in homogeneities. For comparison, dose measurements were made in similar geometry using 6MV and 18MV beams at doses equivalent to a typical treatment fraction. Results: For an acquisition technique of 120 kV, 80 mA, 1.6 mAs/frame and 620 projections, using the M10 collimator, the dose 20 cm from the CAX was measured to be 0.15 cGy at depth 15 cm depth and 0.11 cGy at depth 2 cm. The dose outside the FOV was typically a factor of 6 smaller than the MV dose. Conclusions: Although small when compared to the dose from the MV beam, the peripheral dose due to kV imaging may be significant if the CBCT procedure is applied daily.

Extended volume ultrasound data acquisition

Three or four-dimensional ultrasound data acquisition for extended field of view imaging is provided. Multiple volumes are registered with respect to each other and spliced together to form an extended volume. The extended volume is a contiguous volume larger than a volumetric region that a multi-dimensional or wobbler transducer array is capable of imaging without movement. Information representing different volumes is registered with respect to each other by sensing the transducer position associated with each of the different volumes. The position is sensed using a position sensing mechanism, such as magnetic optical or gyroscope measurements. Acoustic data may be used to determine decorrelation of speckle or correlation of features to sense position. After the volumes are registered, any overlapping regions are compounded. The resulting extended field of view volume is displayed and manipulated for viewing by the user. A large volume or extended volume of the patient is used for assessing an organ, such as an entire fetus in OB applications.

A real-time 3D large field-of-view MRI system with interactive table motion

Data acquisition using a continuously moving table (CMT) is a new method that is capable of generating three-dimensional (3D) large field-of-view (FOV) MR images. To obtain artifact-free large FOV images or arterial-phase contrast-enhanced large FOV angiograms, a major challenge in CMT is to acquire all of the necessary MR data while matching the table motion to the time-varying images and the physiological dynamics of interest. Rather than restrict CMT techniques to a constant table translation rate and offline reconstruction, here we discuss and implement a more general real-time approach in which the table motion is decoupled from the MR data acquisition. In our implementation, the table moves interactively in response to real-time preview images to ensure optimal imaging conditions. We accomplished this objective by designing and integrating a high-resolution, MR-compatible table position-encoding system to a novel, general-purpose, real-time MR imaging system on a clinical MR scanner. Various technical issues and their practical solutions related to implementation are presented. Experimental results obtained from a lower extremity vascular phantom and five healthy volunteers demonstrate that our proposed approach is robust and able to rapidly and optimally acquire large continuous 3D images by interactively moving the table in response to real-time data reconstruction. We anticipate that the implemented system and its components will be useful for a variety of MR applications, including whole-body screening, angiographic runoff studies, and real-time imaging. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 29B: 28–41, 2006

First results from the high-resolution mouseSPECT annular scintillation camera

High-resolution single-photon emission computed tomography (SPECT) imaging in small animals tends to use long imaging times and large injected doses due to the poor sensitivity of single pinhole gamma cameras. To increase sensitivity while maintaining spatial resolution, we designed and constructed a multipinhole collimator array to replace the parallel hole collimators of a Ceraspect human SPECT brain scanner. The Ceraspect scanner is composed of an annular NaI(TI) crystal within which the eight pinhole collimators (1-mm-diameter holes) rotate while projecting nonoverlapping images of the object onto the stationary annular crystal. In this manner, only one-eighth of a collimator rotation is required to acquire a full circle orbit tomographic data set. The imaging field of view (FOV) has a diameter of 25.6 mm in the transverse direction, which is sufficient to encompass a mouse in the transverse direction. The axial FOV is 25.6 mm at the center of the FOV and 13.9 mm at the edge of the transverse FOV. Data are currently acquired in step-and-shoot mode; however, the system is capable of list mode acquisition with the collimator continuously rotating. Images are reconstructed using a cone-beam ordered subsets expectation maximization method. The reconstructed spatial resolution of the system is 1.7 mm and the sensitivity at the center of the FOV is 13.8 cps/microCi. A whole-body bone scan of a mouse injected with [Tc-99 m]MDP clearly revealed skeletal structures such as the ribs and vertebral bodies. These preliminary results suggest that this approach is a good tradeoff between resolution and sensitivity and, with further refinement, may permit dynamic imaging in living animals.

Sci-PM Thurs - 04: A comparative study between multi-station and moving-table methods with steady-state free precession

Large field‐of‐view (FOV) imaging techniques, such as the multi‐station and moving‐table techniques, are necessary to image systemic diseases such as peripheral vascular disease and metastases. In the multi‐station technique, the full k‐space is acquired for each station, i.e., at each local FOV, and the images are combined offline. For the moving‐table method, the scanner bed is continuously moved through the local FOV during a single acquisition, creating a single large FOV image. Steady‐state free precession is a pulse sequence capable of rapid imagedata acquisition. This study compares large FOV images of healthy volunteers using both the moving‐table method and the multi‐station technique using an SSFP pulse sequence. In the multi‐station technique, six 32 s‐acquisition's are required to cover the large FOV. For the moving table method, the hybrid k‐space is collected during a single 150 s‐scan, creating a seamless large FOV image. Although the moving‐table method is more time‐efficient than the multi‐station technique, image quality is sacrificed. This quality reduction is due to non‐steady‐state conditions caused by table motion and because the k‐space data is partially sampled. By optimizing this moving‐table SSFP technique and integrating it with a tissue suppression algorithm, it may be possible to perform non‐contrast enhanced MR angiograms of the entire peripheral vasculature. Thus, the technique could provide a non‐invasive and time‐efficient method for producing seamless large FOV images for diagnosis of systemic diseases.

Real-time interactive 3D manipulation of particles viewed in two orthogonal observation planes

The generalized phase contrast (GPC) method has been applied to transform a single TEM00 beam into a manifold of counterpropagating-beam traps capable of real-time interactive manipulation of multiple microparticles in three dimensions (3D). This paper reports on the use of low numerical aperture (NA), non-immersion, objective lenses in an implementation of the GPC-based 3D trapping system. Contrary to high-NA based optical tweezers, the GPC trapping system demonstrated here operates with long working distance (>10 mm), and offers a wider manipulation region and a larger field of view for imaging through each of the two opposing objective lenses. As a consequence of the large working distance, simultaneous monitoring of the trapped particles in a second orthogonal observation plane is demonstrated.

Evaluation of image quality with different field of view in CT scan of the body in children

目的 探讨扫描野大小与CT图像质量之间关系.方法分别采用25 cm×25 cm、35 cm×35 cm、42 cm×42 cm扫描野对空间分辨率模体和密度分辨率模体进行扫描,测量出各扫描野时空间分辨率和密度分辨率;对20例病人分别采用25 cm×25 cm和35 cm×35 cm扫描野进行扫描,并请有多年临床经验的医师,采用双盲法对图像质量进行比较.结果不同的扫描野其图像空间分辨率和密度分辨率不同,25 cm×25 cm扫描野的图像空间分辨率最高,可以分辨4个直径0.6 mm 小孔,其密度分辨率也最高,可以分辨5个直径2.5mm 小孔;扫描野为25 cm×25 cm时,临床应用CT扫描的图像明显比35 cm×35 cm的图像清晰(P＜0.05).结论 CT常用的扫描野范围内,当扫描野为25 cm×25cm时,其图像的空间分辨率和密度分辨率最佳。

The SENSE ghost: Field‐of‐view restrictions for SENSE imaging

To describe a known (but undocumented) limitation in parallel imaging using simulation and experiment. This limitation consists of an artifact that appears when the imaging field of view (FOV) is less than the object size. This study demonstrates this artifact in the phase- and partition-encoding dimensions. One-dimensional simulations as well as in vivo experiments were performed with FOVs greater and less than the object being imaged. Full-FOV, reduced-FOV, and SENSE reconstructions were visually compared. Image artifacts occurred when the final SENSE FOV was smaller than the object being imaged. This artifact, termed the SENSE ghost, was a residual fold-over/aliasing artifact. Its location was in the central portion of the image rather than at the edges of the image. This image artifact results from an FOV being smaller than the imaged object. The SENSE reconstruction cannot unfold this additional fold-over, and will place it in a predictable image location based on the SENSE reduction factor. Knowledge of this artifact is necessary when prescribing SENSE acquisitions and interpreting the resulting images.

Imaging riometer observations of drifting absorption patches in the morning sector

Abstract. Observations by a 7x7-beam imaging riometer in Kilpisjärvi, Finland (~66° MLAT) of the drifting cosmic noise absorption (CNA) structures in the morning sector near the zonal drift reversals are presented. The examination of the absorption intensity images revealed several regions with enhanced CNA (absorption patches) slowly drifting through the riometer field of view (FoV). The absorption patches were found to vary in shape, orientation (for elongated arc-like patches), and drift direction. The latter was calculated from the regression lines to positions of the absorption maxima in the FoV images and compared with the direction of electrojet plasma flow from horizontal magnetic perturbations and (for one event) tristatic ion drift velocities in the F-region. A reasonable agreement was found between these directions both in point-by-point comparisons and in terms of direction reversal timings. The absorption patches of lower intensity appear to have smaller drift velocities and to be associated with weaker magnetic perturbations. These results are consistent with the notion that relatively slow motions of the auroral absorption near the zonal drift reversals are associated with the drift of the entire magnetic flux tube as opposed to the gradient-curvature drift of energetic electrons injected into the ionosphere at the substorm onset. The absorption drift velocity magnitude, on the other hand, was found to be substantially lower than that of the plasma flow based on the results of limited comparison with tristatic ion drift measurements. A comparison of the drift directions with those of the patch elongation showed that a considerable number of patches had these directions close to each other. Using this observation, we demonstrate a satisfactory agreement between the patch drift velocities (both in direction and magnitude) as determined from the absorption images and keograms under the assumption that some patches were propagating in a direction that was significantly different from the perpendicularity to elongation.

Signal-to-noise ratio behavior of steady-state free precession.

Steady-state free precession (SSFP) is a rapid gradient-echo imaging technique that has recently gained popularity and is used in a variety of applications, including cardiac and real-time imaging, because of its high signal and favorable contrast between blood and myocardium. The purpose of this work was to examine the signal-to-noise ratio (SNR) behavior of images acquired with SSFP, and the dependence of SNR on imaging parameters such as TR, bandwidth, and image resolution, and the use of multi-echo sequences. In this work it is shown that the SNR of SSFP sequences is dependent only on pulse sequence efficiency, voxel dimensions, and relaxation parameters (T1 and T2). Notably, SNR is insensitive to bandwidth unless increases in bandwidth significantly decrease efficiency. Finally, we examined the relationship between pulse sequence performance (TR and efficiency) and gradient performance (maximum gradient strength and slew rate) for several imaging scenarios, including multi-echo sequences, to determine the optimum matching of maximum gradient strength and slew rate for gradient hardware designs. For standard modern gradient hardware (40 mT/m and 150 mT/m/ms), we found that the maximum gradient strength is more than adequate for the imaging resolution that is commonly encountered with rapid scouting (3 mm x 4 mm x 10 mm voxel). It is well matched for typical CINE and real-time cardiac imaging applications (1.5 mm x 2 mm x 6 mm voxel), and is inadequate for optimal matching with slew rate for high-resolution applications such as musculoskeletal imaging (0.5 x 0.8 x 3 mm voxel). For the lower-resolution methods, efficiency could be improved with higher slew rates; this provokes interest in designing methods for limiting dB/dt peripherally while achieving high switching rates in the imaging field of view. The use of multi-echo SSFP acquisitions leads to substantial improvements in sequence performance (i.e., increased efficiency and shorter TR).

Time‐resolved 3D contrast‐enhanced MRA of an extended FOV using continuous table motion

A method is presented for acquiring 3D time-resolved MR images of an extended (>100 cm) longitudinal field of view (FOV), as used for peripheral MR angiographic runoff studies. Previous techniques for long-FOV peripheral MRA have generally provided a single image (i.e., with no time resolution). The technique presented here generates a time series of 3D images of the FOV that lies within the homogeneous volume of the magnet. This is achieved by differential sampling of 3D k-space during continuous motion of the patient table. Each point in the object is interrogated in five consecutive 3D image sets generated at 2.5-s intervals. The method was tested experimentally in eight human subjects, and the leading edge of the bolus was observed in real time and maintained within the imaging FOV. The data revealed differential bolus velocities along the vasculature of the legs.

A Study of Intrinsic Crystal-Pixel Light-Output Spread for Discrete Scintigraphic Imagers Modeling

This paper is focused on the discrete scintillation imaging devices, consisting of crystal arrays and metal-channel dynode Hamamatsu 1" and 2" square position sensitive photomultiplier tubes (PSPMTs). These devices are suitable for nuclear medicine based high resolution applications, and, particularly, for single photon emission computed tomography (SPECT). The model of scintillation light distribution (SLD) previously developed was able to distinguish the responses from crystal-pixels with different side, but it was not detailed enough to explain the influence of crystal-thickness. For this reason the experimental data were reviewed to find a new and more adequate analytical model. The improved SLD model explains the influence both of crystal-side and crystal-thickness on the scintillation light-output spread. The SLD expression is quite simple and its spread depends only on one q-parameter. This expression is well adaptable over the range of examined crystal arrays. Furthermore, in the considered experiments, the SLD q-parameter was found linearly dependent on crystal-pixel shape factor S/V(S=blind-surfacearea,V=volume). An overview of discrete scintillation imager simulator (DISIS) computer code is reported. Major outcomes of this work are: 1) the improved expression of SLD, which consolidates the DISIS performances, and 2) a tool for local SLD-spread control in the imager field of view (FOV).

REAL-TIME X-RAY INSPECTION OF WHEAT FOR INFESTATION BY THE GRANARY WEEVIL, SITOPHILUS GRANARIUS (L.)

A high-resolution real-time x-ray imaging system was assembled using a low-energy, high-current x-ray source,a low-energy x-ray image intensifier, and a CCD camera interfaced to a PC. Overall system resolution was measured at 5 linepairs per mm (100 .m), sufficient for identifying infestations of the granary weevil, Sitophilus granarius (L.) in kernels of wheat.The field of view for imaging of the system was 6 cm2, large enough to image approximately 350 kernels of grain in a single frame.The exposure time for a single frame was 149 ms, yielding a maximum potential throughput rate of around 2500 kernels persecond. For this study, 1500 wheat kernels were x-rayed, both on film and with the system described above. Of the imagedkernels, 682 contained infestations ranging in maturity from the egg to the adult life stage of the granary weevil, while 818 wereuninfested. Both film and digital images were presented to human subjects to compare recognition of the infested kernels.Overall recognition results averaged 84.4% for the images from the intensifier system vs. 90.2% for the film observations.However, when considering only infestations more advanced than the 3rd larval instar, errors for both sets of images fell below2% and were not significantly different.

Method and apparatus for rotation registration of extended field of view ultrasound images

1 method is provided for obtaining an extended field of view diagnostic ultrasound image. image frame and a second image frame of an object of interest are acquired. The image are rotated relative to one another. Pixel points, representing spatial points in the object rest, are identified in the first image frame. Pixel points corresponding to the pixel points first image frame are then computed in the second image frame. A rotation angle en the first and the second image frames is calculated based on a least-squares relation en the pixel points. The first and second image frames are combined to form a part of an ded field of view image.

Space–time relationship in continuously moving table method for large FOV peripheral contrast-enhanced magnetic resonance angiography

Data acquisition using a continuously moving table approach is a method capable of generating large field-of-view (FOV) 3D MR angiograms. However, in order to obtain venous contamination-free contrast-enhanced (CE) MR angiograms in the lower limbs, one of the major challenges is to acquire all necessary k-space data during the restricted arterial phase of the contrast agent. Preliminary investigation on the space–time relationship of continuously acquired peripheral angiography is performed in this work. Deterministic and stochastic undersampled hybrid-space (x, ky, kz) acquisitions are simulated for large FOV peripheral runoff studies. Initial results show the possibility of acquiring isotropic large FOV images of the entire peripheral vascular system. An optimal trade-off between the spatial and temporal sampling properties was found that produced a high-spatial resolution peripheral CE-MR angiogram. The deterministic sampling pattern was capable of reconstructing the global structure of the peripheral arterial tree and showed slightly better global quantitative results than stochastic patterns. Optimal stochastic sampling patterns, on the other hand, enhanced small vessels and had more favourable local quantitative results. These simulations demonstrate the complex spatial–temporal relationship when sampling large FOV peripheral runoff studies. They also suggest that more investigation is required to maximize image quality as a function of hybrid-space coverage, acquisition repetition time and sampling pattern parameters.

Multidetector-row CT image quality and radiation dose: imaging the lung.

M ULTIDETECTOR COMPUTED tomography (CT) technologies have the potential to produce medical images of high quality. A necessary consequence of using this technology to produce high-quality images is that patients will receive higher radiation doses from their CT examinations. Historically, the maximum x-ray tube output limited the radiation dose to patients, that is, the x-ray tube would melt before high radiation exposures of the patient occurred. Multidetector CT has removed this technological limitation because it enables the transmission of the x-rays emitted from the point source of the tube over a larger solid angle. Consequently, multiderector CT has shifted more responsibility to physicians to control the radiation exposure and determine the required image quality. This presentation will discuss the basic limitations of image quality, the factors that control levels of radiation exposure, and the risks associated with the radiation exposures. The reduced section thickness images produced by multidetector CT pose both a challenge and an opportunity. The opportunity, not available before multidetector CT technology, is to obtain the CT sections with isotropic voxels. Previously, the pixel sizes were typically between 1.0 mm and 0.5 mm. The pixel size is determined by the specification of a 512 × 512 image matrix over a 50-cm field of view for body imaging and 25-cm field of view for imaging of the head. Previously, the axial increment was typically 5 mm to 10 mm with comparable section thickness. The axial increment was determined by the requirements for imaging whole regions of interest, such as the chest, in a single breath hold. Using multidetector technologies, regions of interest can be imaged using 1.0-mm section thickness. Thinner-section images

High frame rate extended field of view ultrasound imaging system and method

A 3-D ultrasound imaging system acquires partially complete image volumes interspersed with substantially complete image volumes. The partially complete image volumes contain speckle that is processed by a cross-correlation algorithm to track the movement of an ultrasound scanhead. By tracking the movement of the scanhead, the substantially complete image volumes can be properly registered with each other and combined to create a 3-D extended field of view image. The partially complete image volumes contain significantly less data than the substantially complete image volumes. Therefore, the partially complete image volumes can be acquired more quickly than the substantially complete image volumes to allow the scanhead to be scanned at a relatively fast speed.

System and method for assessing body-tissue properties using a medical ultrasound transducer probe with a body-tissue parameter measurement mechanism

A system and method for diagnostic ultrasound imaging with a probe combining one or more ultrasound imaging transducer elements and a body-tissue parameter measurement mechanism to detect body-tissue properties. At least one ultrasound transducer element provides an ultrasound image field of view of at least a portion of the body-tissue being measured by the parameter measurement mechanism. The parameter measurement mechanism is typically a mechanically or electrically operated mechanism attached to the probe near at least one ultrasound transducer element in order to combine information from the body-tissue parameter measurement mechanism and ultrasound transducer element for easier identification of abnormal body-tissue properties (e.g., tumors, dead, or diseased body-tissue).

Ultrasound of muscle

Ultrasound examination of muscle is ideally performed with high-frequency linear array transducers, although low frequency probes may be required for deep-seated abnormalities in large individuals.Extended field of view imaging is useful to delineate extensive muscle abnormalities and helps provide clear representation of spatial relationships.Ultrasound grading of muscle injury can be performed, and follow-up studies can assess repair of muscle tissue and identify complications of the healing process.Although the appearances of intramuscular masses may be non-specific in many cases, ultrasound may demonstrate characteristics that help refine the differential diagnosis. Some features such as vascularity and intralesional calcification may be more easily appreciated on ultrasound than MRI.

Scalable Extrinsic Calibration of Omni-Directional Image Networks

We describe a linear-time algorithm that recovers absolute camera orientations and positions, along with uncertainty estimates, for networks of terrestrial image nodes spanning hundreds of meters in outdoor urban scenes. The algorithm produces pose estimates globally consistent to roughly 0.1° (2 milliradians) and 5 centimeters on average, or about four pixels of epipolar alignment. We assume that adjacent nodes observe overlapping portions of the scene, and that at least two distinct vanishing points are observed by each node. The algorithm decouples registration into pure rotation and translation stages. The rotation stage aligns nodes to commonly observed scene line directionss the translation stage assigns node positions consistent with locally estimated motion directions, then registers the resulting network to absolute (Earth) coordinates. The paper's principal contributions include: extension of classic registration methods to large scale and dimensional extents a consistent probabilistic framework for modeling projective uncertaintys and a new hybrid of Hough transform and expectation maximization algorithms. We assess the algorithm's performance on synthetic and real data, and draw several conclusions. First, by fusing thousands of observations the algorithm achieves accurate registration even in the face of significant lighting variations, low-level feature noise, and error in initial pose estimates. Second, the algorithm's robustness and accuracy increase with image field of view. Third, the algorithm surmounts the usual tradeoff between speed and accuracys it is both faster and more accurate than manual bundle adjustment.