Image Distortion Correction Research Articles

An inverse problem approach to the correction of distortion in EPI images.

Magnetic resonance imaging using the echo planar imaging (EPI) technique is particularly sensitive to main (B0) field inhomogeneities. The primary effect is geometrical distortion in the phase encoding direction. In this paper, we present a method based on the conjugate gradient algorithm to correct for this geometrical distortion, by solving the EPI imaging equation. Two versions are presented: one that attempts to solve the full four-dimensional (4-D) imaging equation, and one that independently solves for each profile along the blip encoding direction. Results are presented for both phantom and in vivo brain EPI images and compared with other proposed correction methods.

An efficient geometric image distortion correction method for a biplanar planar gradient coil

An efficient geometric image distortion correction method for a biplanar planar gradient coil

An efficient geometric image distortion correction method for a biplanar planar gradient coil.

Since the spatial field non-linearity of gradient coils translates into image geometric distortion in MRI, in many applications, such as cardiac function analysis and interventional MR-based device tracking/guidance, where the precise geometric information is needed, the presence of geometric image distortion can not be simply ignored. To address the concern for geometric image distortion, we have developed and validated a general and efficient numerical technique for parameterizing the global image distortion for a bi-planar gradient coil as well as accomplishing image restoration as a post-imaging processing. This image correction methodology is based on a global distortion coordinate mapping function which can be systematically defined directly from the gradient field non-linearity in 3-dimension (3D) of a given gradient coil. The image correction was carried out in two steps: (1) map each pixel of the corrected image representation onto its distorted image according to the distortion mapping; (2) interpolate the pixel intensity in the distorted image using its neighboring points via a bi-linear interpolation procedure. The results showed clearly that the distortion correction method was robust in term of the capability of reducing image geometric distortion dramatically. Also it is shown that the magnetic field non-linearity or the image distortion of a typical bi-planar gradient coil can be adequately parameterized using a finite Taylor series expansion based on its design parameters. Furthermore, this image distortion correction method is very efficient in practice for performing 3D correction for any image orientation since a compact parameterized field expression contains non-zero terms.

回帰モデルによる標高歪み補正とその標高計測への応用

The authors evaluated the actual performance of some kinds of regression models for correcting image distortion due to surface topography in various kinds of satellite images including SAR data. For optical sensor images like SPOT/HRV, it was verified that a simple regression model in which only one height term is added to affine or pseudo-affine transformation can be applied with the error of about one pixel. On the other hand SAR data by RADARSAT resulted in the error twice of that for optical data, which was considered due to a difficulty in tie point selection between SAR and optical sensor images. Next, this technique was extended to height measurement. A case study with a SPOT panchromatic stereo pair verified that the similar regression model as that for height correction is possible to be applied for height measurement and the partial revision of a conventional DEM was attempted by using this regressive method.

The Development of Camera Calibration Methods and Models

Correction for image distortion in cameras has been an important topic for as long as users have wanted to faithfully reproduce or use observed information. Initially the main application was mapping. While this task continues today, other applications also require precise calibration of cameras, such as close range three dimensional measurement and many two dimensional measurement tasks. In the past, the cameras used were few in number and highly expensive whereas today a typical large industrial company will have many inexpensive cameras being used for highly important measurement tasks. Cameras are used more today than they ever were but the golden age of camera calibration for aerial mapping is now well in the past. This paper considers some of the key developments and attempts to put them into perspective. In particular the driving forces behind each improvement have been highlighted.

Combined analysis of digital terrain models and remotely sensed data in landscape investigations

This article presents a review of the combined analysis of digital terrain models (DTMs) and remotely sensed data in landscape investigations. The utilization of remotely sensed data with DTMs has become an important trend in geomatics in the past two decades. Models of more than ten quantitative topographic variables are employed as ancillary data in the treatment of images. The article reviews the methods for DTM derivation and the basic problems of DTM operation that are important for handling DTMs with imagery, namely: 1) the choice of a DTM network type; 2) DTM resolution; 3) DTM accuracy; and 4) the precise superimposition of DTMs and images. The processing of remotely sensed data and DTMs in combination is used in the following procedures: 1) the image correction of the topographic effect; 2) the correction of geometric image distortion; 3) image classification; 4) statistical and comparative analyses of landscape data; and 5) three-dimensional landscape modelling. These procedures are applied to solve a wide range of problems in geobotany, geochemistry, soil science, geology, glaciology and other sciences. The joint use of imagery and DTMs can increase the total amount of information extracted from both types of data. The trend has been towards the incorporation of the combined analysis of remotely sensed data and DTMs into mixed environmental models. The following potential applications of the treatment of imagery in association with DTMs are identified: 1) the prediction of the migration and accumulation zones of water, mineral and organic substances moved by gravity along the land surface and in the soil; 2) the investigation of the relationships between topographically expressed geological structures and landscape properties; 3) the improvement of geological engineering in industrial planning (e.g., the construction of nuclear power stations, oil and gas pipelines and canals); and 4) the monitoring of existing industries. Digital models of plan, profile, mean and total accumulation curvatures, and nonlocal and combined topographic attributes should be included in data processing both to solve the problems indicated and to improve the outcome of some regular tasks (for example, the prediction of soil moisture distribution and fault recognition).

A ROBOTIC SYSTEM FOR PERCUTANEOUS RENAL ACCESS

Percutaneous renal access can be challenging, particularly when the collecting system is not distended. Precise entry into a selected calyx facilitates subsequent percutaneous manipulations, but this skill requires extensive experience. In an attempt to improve accuracy while decreasing technical challenges, we developed a robotic system that automates the task of fluoroscopic image-guided percutaneous needle placement. The prototype system consisted of a three degree-of-freedom robot with a needle injector end-effector. Imaging was provided by a biplanar fluoroscope. After correction of image distortion and fluoroscope calibration, robot to image-space registration was completed. To validate the system's ability to insert a needle into a calyx, ex vivo porcine kidneys suspended in agarose gel and distended with iodinated contrast solution were used as a model. In situ renal access tests with three 20 kg. pigs were performed. Access was confirmed by passing a flexible wire or aspirating iodinated contrast from the collecting system. The diameter of target calyces ranged from 3 to 7 mm. The in vitro accuracy of final needle tip positioning was 0.43 mm. In the ex vivo model, successful "one stick" access occurred on 10 of 12 attempts (83%). In situ access on the first attempt was successful for 6 of 12 target calyces (50%). Needle or tissue deflection accounted for each failure. The feasibility of a robotic system to assist in the percutaneous access of small and delicate renal calyces has been demonstrated. Additional work in reducing procedural steps and correcting for tissue deflection during needle passage is necessary to improve accuracy and to allow for clinical application.

New method to estimate step heights in scanning-probe microscope images

A new algorithm, the polynomial step-function fit (PSFF), is presented. The PSFF algorithm extracts step heights from noisy and distorted scanning-probe microscope (SPM) images. A one-dimensional, line-by-line implementation as well as a two-dimensional, full-image version are presented. The PSFF algorithm allows the correction of image distortions due to nonlinearities in the piezoelectric scanner and Abbé offset errors, but piezoelectric creep and hysteresis must be corrected separately, and may set the ultimate physical limitations on the accuracy of the PSFF algorithm. The PSFF algorithm is demonstrated with a real sample.

Effect of geometrical distortion correction in MR on image registration accuracy.

In this article we investigate the effect of geometrical distortion correction in MR images on the accuracy of the registration of X-ray CT and MR head images for both a fiducial marker (extrinsic point) method and a surface-matching technique. We use CT and T2-weighted MR image volumes acquired from seven patients who underwent craniotomies in a stereotactic neurosurgical clinical trial. Each patient had four external markers attached to transcutaneous posts screwed into the outer table of the skull. The MR images are corrected for static field inhomogeneity by using an image rectification technique and corrected for scale distortion (gradient magnitude uncertainty) by using an attached stereotactic frame as an object of known shape and size. We define target registration error (TRE) as the distance between corresponding marker positions after registration and transformation. The accuracy of the fiducial marker method is determined by using each combination of three markers to estimate the transformation and the remaining marker to calculate registration error. Surface-based registration is accomplished by fitting MR contours corresponding to the CSF-dura interface to CT contours derived from the inner surface of the skull. The mean point-based TRE using three noncollinear fiducials improved 34%-from 1.15 to 0.76 mm-after correcting for both static field inhomogeneity and scale distortion. The mean surface-based TRE improved 46%-from 2.20 to 1.19 mm. Correction of geometrical distortion in MR images can significantly improve the accuracy of point-based and surface-based registration of CT and MR head images. Distortion correction can be important in clinical situations such as stereotactic and functional neurosurgery where 1 to 2 mm accuracy is required.

5498963 Correction of geometric distortion in MRI phase and phase difference images

Lipid-shelled microbubbles have received extensive interest to enhance ultrasound-responsive drug delivery outcomes due to their high biocompatibility. While therapeutic effectiveness of microbubbles is well established, there remain limitations in sample homogeneity, stability profile and drug loading properties which restrict these formulations from seeing widespread use in the clinical setting. In this review, we evaluate and discuss the most encouraging leads in lipid microbubble design and optimisation. We examine current applications in drug delivery for the systems and subsequently detail shell compositions and preparation strategies that improve monodispersity while retaining ultrasound responsiveness. We review how excipients and storage techniques help maximise stability and introduce different characterisation and drug loading techniques and evaluate their impact on formulation performance. The review concludes with current quality control measures in place to ensure lipid microbubbles can be reproducibly used in drug delivery.

A new method for distortion correction of electronic endoscope images

A new method to correct the barrel distortion of an electronic endoscope image is presented. A correction model assuming circularly symmetric distortion is introduced with the following model parameters: the center of distortion and the coefficients of polynomials representing the distortion correction in the radial direction. If the imaging system is distortion-free, straight lines in the object space should be imaged as straight lines. Based on this criterion, a distorted image of a standard pattern consisting of a grid of several straight lines is recorded, and the model parameters are then estimated as a basis for straightening distorted lines. This method has the advantage of not needing a careful placement of the standard pattern for calibration. Correction results are presented for the grid pattern chart to verify a sufficient degree of correction. Examples of distortion correction of real intestinal images and physicians' comments are also presented.

Distortion correction of NOAA image by statistical method

Abstract Remote sensing technique by satellite has been well-developed in recent years. In this paper two kinds of statistical correction methods are proposed to clarify observation data by NOAA with atmospheric scattering. The first method is the deletion of the path radiance effect by the least squares method. The second uses a smoothing filter. These methods are applied to the original remote sensing data collected on 26 July 1987.

Shape reconstruction from a single thermal image

One of the problems associated with nondestructive testing by infrared thermography with heat injection is related to the inspection of nonplanar objects. A method is proposed to determine the shape of an object present in the field of view from the corresponding single, early-recorded thermal image. Such shape reconstruction enables the correction of thermal image distortions due to object shape.

Adaptive optics experiments using sodium laser guide stars

The Multiple Mirror Telescope (MMT) has been used in experiments with sodium laser guide stars to sense and correct atmospheric image distortion. The major goal was to develop and test concepts for a full adaptative optics system, to be used in 2 yr when the present array of six 1.8 m telescopes will be replaced with a single 6.5 m mirror. The guide star, produced by a continuous-wave dye laser beam projected out along the optical axis of the telescope, was as bright in the V band as a natural star of m<SUB>v</SUB> = 10.4. Our tests culminated in the first demonstration of a sodium laser guide star used to improve the image of an astronomical telescope, in this case formed by two of the six 1.8 m apertures. Two adaptive servo loops were closed simultaneously. The laser beacon provided a measure of the differential wave-front tilt between the two apertures, and a natural guide star was used to measure the overall wave-front tilt. A factor of 2 improvement in the K-band Strehl ratio was measured, and the resolution improved from 0.58 arcsec to 0.41 arcsec. The experiment demonstrated all the features needed for correction of the 6.5 m telescope to the diffraction limit using a sodium beacon. The accuracy with which the laser beacon measures the atmospheric aberration of starlight across the full 6.9 m aperture of the MMT was examined. From more extensive measurements of binary star wave fronts, we deduce that focus anisoplanatism for the 6.5 m telescope will correspond to a Strehl ratio of typically 88% at K under normal seeing conditions. In a laser-based adaptive system, a natural guide star is still required to sense overall wave-front slope. Our measurements of binary stars also yielded the image degradation to be expected from differences in the overall slopes between the wave fronts from the object of scientific interest and the natural guide star. A Strehl ratio of 80% at K was deduced for an offset of 40 arcsec, implying that good sky coverage will be possible. In general, our results are consistent with calculations based on measurements of atmospheric turbulence at the best sites. Our direct measurements over such a large aperture show clearly the effects of a finite and variable outer scale of turbulence.

Correction of distortions in a discontinuous image

Large area position-sensitive NaI detectors have been successfully applied to positron emission tomography (PET). Typical PET studies involve detector singles rates in excess of 500 kcps, which can lead to pile-up and image degradation as a function of countrate. Better high countrate performance can be achieved with a local centroid algorithm, in which the position of each event is calculated from a small group of photomultipliers (PMTs) immediately surrounding the PMT with the highest signal (the peak PMT). The local centroid contains most of the light from the scintillation. If a local centroid of only seven PMTs is used, the position resolution becomes quite stable at high countrates, however, discontinuities appear in the detector flood image as events cluster around each PMT. We therefore developed a method for distortion correction of a discontinuous flood image. For each PMT on the detector, a peak PMT domain is defined. The peak PMT domain is the area on the detector where that PMT could have the highest signal. The peak PMT domains overlap slightly, so that all combinations of peak PMT and position are represented. A collimated source is moved through a regular grid of points - a template - over each peak PMT region. A short collection is performed at each point, and the real and measured position data are recorded. For each point in the spatial range of a given PMT, distortion correction offsets are computed by interpolating between the data points which correspond to that PMT. This new method has been implemented and evaluated. System resolution has been measured at low and high countrates. The high countrate resolution is better with the new method, with no degradation in low countrate resolution. The axial sensitivity profile is also more stable at high countrates, compared to the previously developed method. 3-D brain phantom images show a clear improvement in image quality at high countrates.

X-ray kinematography as a tool for investigations of distal limb movements of the cat

X-ray kinematography was used to investigate the kinematics of cat distal forelimb joints during motor behaviour. These joints are not accessible for instrumentation with external markers normally used in conventional motion analysis systems. To trace the movements in space two X-ray systems positioned rectangularly to each other illuminated the forelimb quasi-simultaneously with pulsed X-ray shots (time resolution: 20 ms). A mathematical model was developed for 3-dimensional reconstruction of the object and includes procedures for correction of image distortions, e.g., pincushion distortions and rotation of the image due to interaction of the earth's magnetic field with the electron optics of the image amplifiers. Accuracy of image correction and object reconstruction is ±1 pixel, corresponding to ±0.5 mm in space which is sufficient for investigation of the kinematics of cat distal forelimb joints. The approach described is of general relevance and useful in kinematic investigations where the structures under study are not directly accessible to external instrumentation with markers.

Endoscopic measurement of lesion size: Improved accuracy with image processing

Endoscopic measurement of lesions is of great importance in the design and performance of clinical trials, as, for example, in studies of ulcer disease. Endoscopes are constructed with wide-angle lenses that significantly distort the image by creating a relative compression of points in its periphery. We have recently developed a computer program to correct the distortion of the wide-angle lens. We sought to determine the accuracy of the currently used open-biopsy forceps measurement technique and compare it to that of an image-processing technique designed to correct image distortion. The overall error of the open-biopsy forceps technique using an in vitro ulcer model was under-estimation of lesion size by 41.8%±23.3%. When image processing was used to correct distortion, error was significantly decreased to 1.8%±2.2% p< 0.05). In vivo measurements were made using an inserted object of known size (coated chewing gum). The mean error of the forceps technique in vivo was 26.5%±5.7%(under-estimation of size), which improved significantly to an error of 2.8%±3.2% p< 0.05) with the image-processing technique. We conclude that image processing significantly enhances the accuracy of measurement at endoscopy. (Gastrointest Endosc 1994;40:178-83.)

High-Performance Photorefractive Polymers

Photorefractive materials can form "instant" holograms without time-consuming development steps. Their potential applications include image processing, optical data storage, and correction of image distortion, but the cost of crystal growth and preparation has been a primary impediment to commercial application. Polymers, on the other hand, are low in cost and readily fabricated in a variety of forms. Photorefractive polymers were constructed with performance that matched or exceeded the performance of available photorefractive crystals. The largest observed two-beam energy coupling gain coefficient for the polymers was 56 per centimeter.

Three‐dimensional blood vessel reconstruction using a high‐speed X‐ray rotational projection system

AbstractThe feature X‐ray angiography is that a blood vessel image with a high spatial resolution is obtained. Consequently, it is a decisive diagnostic tool for the pathology of the blood vessel. However, its precision is still sufficient for the diagnosis of blood vessels with delicate aneurysm or stenosis, as well as for planning surgery. Thus, it is desired to develop further an imaging method for the blood vessel configuration with a higher precision.This paper describes a precise observation method for the blood vessel configuration, where a pair of X‐ray source and the image intensifier (II) with a high‐speed rotation is used to scan and derive multidirectional projection images, and the blood vessel configuration is reconstructed in three‐dimensions for high‐precision 3D observation. As a pre‐processing to the reconstruction, the image distortion correction for II as well as the estimation of the camera coordinate are executed.In the 3D reconstruction of the blood vessel, the filtered backprojection method is used with the short‐scan (details are discussed later) cone‐beam projection. The result of 3D reconstruction of the blood vessel can be observed by the 3D display and the 3D model for the blood vessel configuration. The method is applied to the actual projection image of the cerebral blood vessels, and the effectiveness is demonstrated. By this method, a highly precise measurement of the blood vessel shape is realized, which has not been observed by the past technique, and the configuration of the blood vessel can be analyzed in the 3D space. It is expected that the proposed method with those features will be utilized in the quantitative diagnosis of the cerebral blood vessel diseases and treatment planning.

A polynomial method for image distortion correction and 3-D kinematic analysis using video systems

A polynomial method for image distortion correction and 3-D kinematic analysis using video systems