http://ee.sharif.edu/~miap/Files/A%20Survey%20of%20Medical%20Image%20Registration.pdf

A survey of medical image registration.

Image interpolation techniques often are required in medical imaging for image generation (e.g., discrete back projection for inverse Radon transform) and processing such as compression or resampling. Since the ideal interpolation function spatially is unlimited, several interpolation kernels of finite size have been introduced. This paper compares 1) truncated and windowed sine; 2) nearest neighbor; 3) linear; 4) quadratic; 5) cubic B-spline; 6) cubic; g) Lagrange; and 7) Gaussian interpolation and approximation techniques with kernel sizes from 1/spl times/1 up to 8/spl times/8. The comparison is done by: 1) spatial and Fourier analyses; 2) computational complexity as well as runtime evaluations; and 3) qualitative and quantitative interpolation error determinations for particular interpolation tasks which were taken from common situations in medical image processing. For local and Fourier analyses, a standardized notation is introduced and fundamental properties of interpolators are derived. Successful methods should be direct current (DC)-constant and interpolators rather than DC-inconstant or approximators. Each method's parameters are tuned with respect to those properties. This results in three novel kernels, which are introduced in this paper and proven to be within the best choices for medical image interpolation: the 6/spl times/6 Blackman-Harris windowed sinc interpolator, and the C2-continuous cubic kernels with N=6 and N=8 supporting points. For quantitative error evaluations, a set of 50 direct digital X-rays was used. They have been selected arbitrarily from clinical routine. In general, large kernel sizes were found to be superior to small interpolation masks. Except for truncated sine interpolators, all kernels with N=6 or larger sizes perform significantly better than N=2 or N=3 point methods (p/spl Lt/0.005). However, the differences within the group of large-sized kernels were not significant. Summarizing the results, the cubic 6/spl times/6 interpolator with continuous second derivatives, as defined in (24), can be recommended for most common interpolation tasks. It appears to be the fastest six-point kernel to implement computationally. It provides eminent local and Fourier properties, is easy to implement, and has only small errors. The same characteristics apply to B-spline interpolation, but the 6/spl times/6 cubic avoids the intrinsic border effects produced by the B-spline technique. However, the goal of this study was not to determine an overall best method, but to present a comprehensive catalogue of methods in a uniform terminology, to define general properties and requirements of local techniques, and to enable the reader to select that method which is optimal for his specific application in medical imaging.

/pdf/survey-interpolation-methods-in-medical-image-processing-erlouqboei.pdf

Survey: interpolation methods in medical image processing

Preschool vision screening : Rationale, methodology and outcome

The purpose of this paper is to present an overview of existing medical image registration methods. These methods will be classified according to a model based on nine salient criteria, the main dichotomy of which is extrinsic versus intrinsic methods. The statistics of the classification show definite trends in the evolving registration techniques, which will be discussed. At this moment, the bulk of interesting intrinsic methods is either based on segmented points or surfaces, or on techniques endeavoring to use the full information content of the images involved.

/pdf/an-overview-of-medical-image-registration-methods-i6pdtrn7xy.pdf

An Overview of Medical Image Registration Methods

Clinical visual optics

Objective Measurement of Small Angles of Strabismus in Infants and Children with Photographic Reflection Pattern Evaluation

Purpose To provide reference data for the measurement of ocular alignment and of angles of strabismus with a new stationary photographic apparatus at near and at distance fixation; to verify quantitative relations between the data by comparing experimental data with theoretical predictions. Methods Use of Purkinje I and IV Reflection Pattern Evaluation in conjunction with a new stationary photographic apparatus; application of previously derived equations; simulation of angles of strabismus of 5 degrees and 10 degrees in the primary position. Results Data from 62 subjects with orthotropia show good linearity of measured angles in different directions of gaze; a 95% confidence interval for errors up to 18.6% in the simulated angles of strabismus; no need for individual calibration of the apparatus; no bias due to wearing of spherical corrections, and a detection threshold for microstrabismus of +/- 0.35 degrees. Conclusions Data concerning orthotropic and simulated strabismus prove the accuracy of Reflection Pattern Evaluation to assess ocular alignment, for instance, for the diagnosis of strabismus in primary and secondary positions, at near and distance fixation. The measuring range can easily be extended to larger angles of strabismus.

Measurement of ocular alignment with photographic Purkinje I and IV reflection pattern evaluation.

Spatial registration is a major problem arising whenever several images of similar contents are to be compared. Considering translations only, two-dimensional cepstral techniques have been proven to be exact and robust against noise or intensity variations. Furthermore, the cepstral filtering is numerically more efficient than most common approaches to image registration based on cross-correlation or template matching. In a previous paper, we proposed a two- dimensional cepstrum based matching technique accessing rotations and translations. The logarithmic polar mapping of the power spectra of both images to be registered is used for the decoupling of rotations and translations (similar to the Fourier-Mellin transform). Rotations are detected first matching the mapped spectra by two-dimensional cepstrum analysis. After rotating back one image, the relative shift is determined using the same cepstrum technique. In clinical practice, the rotation detection step was discovered as the weakness of this registration technique. Based on 855 pairs of dental radiographs acquired in known positions, three different approaches of matching the mapped spectra are compared: the cepstrum technique, the cross-correlation, and the entropy of the one-dimensional histogram distribution function of the substraction image of the mapped spectra. The combination of the log-polar mapped power spectra of both x rays with the entropy-measure allows the best detection of rotations. The union with common cepstrum methods correcting translations results in a robust rotation- extended cepstrum technique.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Rotation-extended cepstrum technique optimized by systematic analysis of various sets of x-ray images

• Background: Accurate assessment of the angle of strabismus, e.g. of variable angles of strabismus, is crucial in preoperative patient management and is usually performed in a clinical environment. Objective assessment by patients themselves, under everyday conditions, could contribute to a better preoperative work-up. A new objective evaluation procedure for the measurement of manifest angles of strabismus for near and distance fixation by the patient himself is presented. • Methods: To account for the modified experimental setup used for the self-assessment, an amended computation procedure of Purkinje reflection pattern evaluation was developed. For measurement, patients and controls placed their head on a head/chin rest and fixated at 33 cm or 4 m distance in primary position. A reflex camera and three photo flash units were positioned on a special frame underneath the visual axis and in front of the subject so that both eyes could be photographed simultaneously. The camera's remote shutter control was released together with the photo flash units by the properly fixating subject. The angles of strabismus were obtained from the series of pictures through later evaluation of the Purkinje I and IV reflection patterns recorded in the photographs of the eyes. • Results: Measurements of the ocular alignment in two control groups and in a group of strabismic subjects showed satisfactory accuracy of the “self-assessment” method compared to “standard” Purkinje reflection pattern evaluation and orthoptic measurements of the angle of strabismus. • Conclusion: The modified “self-assessment” method can be used for the objective recording of angles of strabismus as needed in the preoperative work-up of patients with variable angles of strabismus, over prolonged periods of time, and outside a clinical setting.

Ansgar Kaupp

Papers

Objective Measurement of Small Angles of Strabismus in Infants and Children with Photographic Reflection Pattern Evaluation

Measurement of ocular alignment with photographic Purkinje I and IV reflection pattern evaluation.

Rotation-extended cepstrum technique optimized by systematic analysis of various sets of x-ray images

Self-assessment of angles of strabismus with photographic Purkinje I and IV reflection pattern evaluation.

Automatische Schielwinkelmessung durch Hough-Transformation und Kovarianzfilterung