MO-D-I-609-01: Improved Target Localization in Low Field MR Using Local Weighted Mean(LWM) for Spatial Distortion Correction

A small field, high resolution γ-Camera system dedicated to radiopharmaceutical research and other clinical SPECT (Single Photon Emission Computed Tomography) applications is currently being developed in our group. The system is equipped with the 3” HAMAMATSU R2486 Position Sensitive PhotoMultiplier Tube (PSPMT) with a 16X+16Y-crossed wire anode and various pixelated and ho- mogeneous scintillation crystals. Planar images are created from the recorded charge signals by applying the resistive chain technique. The main part of this work focuses on the development of new correction methods for the improvement of the spatial resolution and the uniformity of the γ-Camera. The spatial distortion correction technique is based on lookup tables with the coordinates of reference points which are selected during the calibration phase of the system for a given set of collimator and scintillation crystal. The applied algorithm incorporates 2D-interpolation tech- niques and has been developed on a full automated graphics environment making use of the HIGZ (High Level Interface to Graphics and ZEBRA) program libraries from CERN. Both correction methods for the spatial distortion and non-uniformity have been applied to phantom images using several combinations of small capillaries filled with water solution of 99mTc. Comparative studies are shown on planar im- ages for different phantom geometries. The method is also extended to tomographic images and the obtained SPECT improvement in resolution is discussed.

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Evaluation of patient‐specific MR distortion correction schemes for improved target localization accuracy in SRS

Medical Physics ◽

10.1002/mp.14615 ◽

2020 ◽

Author(s):

Dimitrios Dellios ◽

Eleftherios P. Pappas ◽

Ioannis Seimenis ◽

Chryssa Paraskevopoulou ◽

Kostas I. Lampropoulos ◽

...

Keyword(s):

Distortion Correction ◽

Target Localization ◽

Patient Specific ◽

Localization Accuracy

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Mr geometric distortion correction for improved frame-based stereotaxic target localization accuracy

Magnetic Resonance in Medicine ◽

10.1002/mrm.1910340116 ◽

1995 ◽

Vol 34 (1) ◽

pp. 106-113 ◽

Cited By ~ 42

Author(s):

Thilaka Sumanaweera ◽

Gary H. Glover ◽

Paul F. Hemler ◽

Petra A. Den Van Elsen ◽

David Martin ◽

...

Keyword(s):

Distortion Correction ◽

Target Localization ◽

Geometric Distortion ◽

Localization Accuracy

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Image distortion correction for MRI in low field permanent magnet systems with strong B0 inhomogeneity and gradient field nonlinearities

Magnetic Resonance Materials in Physics Biology and Medicine ◽

10.1007/s10334-021-00907-2 ◽

2021 ◽

Author(s):

Kirsten Koolstra ◽

Thomas O’Reilly ◽

Peter Börnert ◽

Andrew Webb

Keyword(s):

Image Reconstruction ◽

Permanent Magnet ◽

Image Distortion ◽

Distortion Correction ◽

Gradient Field ◽

Time Shift ◽

Phase Reconstruction ◽

Low Field ◽

Scan Time ◽

Fourier Reconstruction

Abstract Objective To correct for image distortions produced by standard Fourier reconstruction techniques on low field permanent magnet MRI systems with strong $${B}_{0}$$ B 0 inhomogeneity and gradient field nonlinearities. Materials and methods Conventional image distortion correction algorithms require accurate $${\Delta B}_{0}$$ Δ B 0 maps which are not possible to acquire directly when the $${B}_{0}$$ B 0 inhomogeneities also produce significant image distortions. Here we use a readout gradient time-shift in a TSE sequence to encode the $${B}_{0}$$ B 0 field inhomogeneities in the k-space signals. Using a non-shifted and a shifted acquisition as input, $$\Delta {B}_{0}$$ Δ B 0 maps and images were reconstructed in an iterative manner. In each iteration, $$\Delta {B}_{0}$$ Δ B 0 maps were reconstructed from the phase difference using Tikhonov regularization, while images were reconstructed using either conjugate phase reconstruction (CPR) or model-based (MB) image reconstruction, taking the reconstructed field map into account. MB reconstructions were, furthermore, combined with compressed sensing (CS) to show the flexibility of this approach towards undersampling. These methods were compared to the standard fast Fourier transform (FFT) image reconstruction approach in simulations and measurements. Distortions due to gradient nonlinearities were corrected in CPR and MB using simulated gradient maps. Results Simulation results show that for moderate field inhomogeneities and gradient nonlinearities, $$\Delta {B}_{0}$$ Δ B 0 maps and images reconstructed using iterative CPR result in comparable quality to that for iterative MB reconstructions. However, for stronger inhomogeneities, iterative MB reconstruction outperforms iterative CPR in terms of signal intensity correction. Combining MB with CS, similar image and $$\Delta {B}_{0}$$ Δ B 0 map quality can be obtained without a scan time penalty. These findings were confirmed by experimental results. Discussion In case of $${B}_{0}$$ B 0 inhomogeneities in the order of kHz, iterative MB reconstructions can help to improve both image quality and $$\Delta {B}_{0}$$ Δ B 0 map estimation.

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SPECTRA: A program for processing electron images of crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121065 ◽

1992 ◽

Vol 50 (1) ◽

pp. 132-133

Author(s):

M.F. Schmid ◽

R. Dargahi ◽

M. W. Tam

Keyword(s):

Lattice Distortion ◽

Data Transfer ◽

Reciprocal Lattice ◽

Data Entry ◽

Image Data ◽

Distortion Correction ◽

Specimen Preparation ◽

Electron Image ◽

Computer Controlled ◽

Program Modules

Electron crystallography is an emerging field for structure determination as evidenced by a number of membrane proteins that have been solved to near-atomic resolution. Advances in specimen preparation and in data acquisition with a 400kV microscope by computer controlled spot scanning mean that our ability to record electron image data will outstrip our capacity to analyze it. The computed fourier transform of these images must be processed in order to provide a direct measurement of amplitudes and phases needed for 3-D reconstruction.In anticipation of this processing bottleneck, we have written a program that incorporates a menu-and mouse-driven procedure for auto-indexing and refining the reciprocal lattice parameters in the computed transform from an image of a crystal. It is linked to subsequent steps of image processing by a system of data bases and spawned child processes; data transfer between different program modules no longer requires manual data entry. The progress of the reciprocal lattice refinement is monitored visually and quantitatively. If desired, the processing is carried through the lattice distortion correction (unbending) steps automatically.

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