Biomedical subjects

Eugene G Kholmovski

Publications and source records attributed to Eugene G Kholmovski.

9 recordsLinked to original sources

PubMed2006

k-space inherited parallel acquisition (KIPA): application on dynamic magnetic resonance imaging thermometry.

In this study, a novel method for dynamic parallel image acquisition and reconstruction is presented. In this method, called k-space inherited parallel acquisition (KIPA), localized reconstruction coefficients are used to achieve higher reduction factors, and lower noise and artifact levels compared to that of generalized autocalibrating partially parallel acquisition (GRAPPA) reconstruction. In KIPA, the full k-space for the first frame and the partial k-space for later frames are required to reconstruct a whole series of images. Reconstruction coefficients calculated for different segments of k-space from the first frame data set are used to estimate missing k-space lines in corresponding k-space segments of other frames. The local determination of KIPA reconstruction coefficients is essential to adjusting them according to the local signal-to-noise ratio characteristics of k-space data. The proposed algorithm is applicable to dynamic imaging with arbitrary k-space sampling trajectories. Simulations of magnetic resonance thermometry using the KIPA method with a reduction factor of 6 and using dynamic imaging studies of human subjects with reduction factors of 4 and 6 have been performed to prove the feasibility of our method and to show apparent improvement in image quality in comparison with GRAPPA for dynamic imaging.

Algorithms↗

PubMed2006

High-resolution DTI of a localized volume using 3D single-shot diffusion-weighted STimulated echo-planar imaging (3D ss-DWSTEPI).

Diffusion tensor MRI (DTI) using conventional single-shot (SS) 2D diffusion-weighted (DW)-EPI is subject to severe susceptibility artifacts. Multishot DW imaging (DWI) techniques can reduce these distortions, but they generally suffer from artifacts caused by motion-induced phase errors. Parallel imaging can also reduce the distortions if the sensitivity profiles of the receiver coils allow a sufficiently high reduction factor for the desired field of view (FOV). A novel 3D DTI technique, termed 3D single-shot STimulated EPI (3D ss-STEPI), was developed to acquire high-resolution DW images of a localized region. The new technique completes k-space acquisition of a limited 3D volume after a single diffusion preparation. Because the DW magnetization is stored in the longitudinal direction until readout, it undergoes T(1) rather than T(2) decay. Inner volume imaging (IVI) is used to limit the imaging volume. This reduces the time required for EPI readout of each complete k(x)-k(y) plane, and hence reduces T(2)(*) decay during the readout and T(1) decay between the readout of each k(z). 3D ss-STEPI images appear to be free of severe susceptibility and motion artifacts. 3D ss-STEPI allows high-resolution DTI of limited volumes of interest, such as localized brain regions, cervical spinal cord, optic nerve, and other extracranial organs.

Algorithms↗

PubMed2005

High-resolution DTI with 2D interleaved multislice reduced FOV single-shot diffusion-weighted EPI (2D ss-rFOV-DWEPI).

Diffusion tensor MRI (DTI), using single-shot 2D diffusion weighted-EPI (2D ss-DWEPI), is limited to intracranial (i.c.) applications far from the sinuses and bony structures, due to the severe geometric distortions caused by significant magnetic field inhomogeneities at or near the tissue-air or tissue-bone interfaces. Reducing these distortions in single-shot EPI by shortening the readout period generally requires a reduced field of view (and the potential of wraparound artifact) in the phase-encoding direction and/or reduced spatial resolution. To resolve the problem, a novel 2D reduced FOV single-shot diffusion-weighted EPI (2D ss-rFOV-DWEPI) pulse sequence applicable for high resolution diffusion-weighted MRI of local anatomic regions, such as brainstem, cervical spinal cord, and optic nerve, has been developed. In the proposed technique, time-efficient interleaved acquisition of multiple slices with a limited FOV was achieved by applying an even number of refocusing 180 degrees pulses with the slice-selection gradient applied in the phase-encoding direction. The two refocusing pulses used for each slice acquisition were separated by a short time interval (typically less than 45 ms) required for the 2D EPI echotrain acquisition. The new technique can be useful for high resolution DTI of various anatomies, such as localized brain structures, cervical spinal cord, optic nerve, heart, or other extra-cerebral organ, where conventional 2D ss-DWEPI is limited in usage due to the severity of image distortions.

Algorithms↗

PubMed2005

Application of phase consistency to improve time efficiency and image quality in dual echo black-blood carotid angiography.

There is a considerable similarity between proton density-weighted (PDw) and T2-weighted (T2w) images acquired by dual echo fast spin-echo (FSE) sequences. The similarity manifests itself not only in image space as correspondence between intensities of PDw and T2w images, but also in phase space as consistency between phases of PDw and T2w images. Methods for improving the imaging efficiency and image quality of dual echo FSE sequences based on this feature have been developed. The total scan time of dual echo FSE acquisition may be reduced by as much as 25% by incorporating an estimate of the image phase from a fully sampled PDw image when reconstructing partially sampled T2w images. The quality of T2w images acquired using phased array coils may be significantly improved by using the developed noise reduction reconstruction scheme, which is based on the correspondence between the PDw and T2w image intensities and the consistency between the PDw and T2w image phases. Studies of phantom and human subject MRI data were performed to evaluate the effectiveness of the techniques.

Algorithms↗

PubMed2004

Statistics-based approach for aneurysm volume measurements.

PURPOSE: To evaluate the ability of high-resolution MRA to monitor changes in intracranial aneurysm volume, and devise a highly reliable technique for obtaining these measurements. MATERIALS AND METHODS: To obtain a baseline estimate of the repeatability of MRA scans and validate the statistics-based technique for aneurysm volume measurement, multiple scans were obtained on individual subjects over a period of up to 1 year. These 3D MRA data sets were coregistered and then analyzed using the volumetric analysis of segmented data and the proposed statistical method. RESULTS: It was shown that high-resolution MRA provides highly repeatable data sets. Both methods used for the aneurysm volume measurements showed consistent results. However, the proposed statistical method had lower error and was much less sensitive to the choice of segmentation parameter than the volumetric analysis of segmented data. A change of 1 mm in the average radius of the aneurysm was detectable with the statistics-based technique. CONCLUSIONS: This study demonstrates that the statistical method of aneurysm volume measurement in high-resolution MRA allows reliable and accurate assessments of aneurysm volume changes.

Cerebrovascular Circulation↗

PubMed2004

POCSENSE: POCS-based reconstruction for sensitivity encoded magnetic resonance imaging.

A novel method for iterative reconstruction of images from undersampled MRI data acquired by multiple receiver coil systems is presented. Based on Projection onto Convex Sets (POCS) formalism, the method for SENSitivity Encoded data reconstruction (POCSENSE) can be readily modified to include various linear and nonlinear reconstruction constraints. Such constraints may be beneficial for reconstructing highly and overcritically undersampled data sets to improve image quality. POCSENSE is conceptually simple and numerically efficient and can reconstruct images from data sampled on arbitrary k-space trajectories. The applicability of POCSENSE for image reconstruction with nonlinear constraining was demonstrated using a wide range of simulated and real MRI data.

Brain Mapping↗

PubMed2004

Triple contrast technique for black blood imaging with double inversion preparation.

This work reports on the development of a pulse sequence to simultaneously acquire proton density, T(1), and T(2) weighted images in a single magnetization prepared fast spin echo acquisition. The technique is based upon the application of a magnetization preparation consisting of a global inversion followed by slice-selective 180 degrees and 90 degrees pulses to prepare the signal of specific slices. Slices are acquired in an interleaved manner with time delays appropriate for the desired image contrasts. Data acquisition is repeated for all combinations of slice interleaving covering the region of interest until images from all slice locations have been acquired with all desired image contrasts. The multiple image contrasts obtained with this technique should be useful in applications where discrimination between different types of tissue components is desired, such as in the analysis of plaque in cervical carotid artery disease.

Arteriosclerosis↗

PubMed2002

Correction of slab boundary artifact using histogram matching.

PURPOSE: To improve the imaging efficiency of multi-slab three-dimensional acquisitions by decreasing slab overlap and the number of blanked slices. MATERIALS AND METHODS: Application of the histogram matching technique for correction of the slab boundary artifact (SBA) due to non-ideal radiofrequency pulse profiles has been proposed. The technique was validated by studying its effectiveness in reducing the SBA in phantom images, as well as in proton density- and T2-weighted brain images. RESULTS: The correction algorithm considerably decreases the disruption of image volume continuity due to the SBA, and improves slice-to-slice intensity continuity. CONCLUSION: The proposed technique can greatly reduce the SBA when the SBA can be described as a global intensity variation along the slab. The technique may be used to improve imaging efficiency of the multi-slab three-dimensional fast spin-echo sequences by decreasing the amount of required slab overlap.

Algorithms↗

PubMed2002

Motion artifact reduction technique for dual-contrast FSE imaging.

There is considerable similarity between proton density-weighted (PDw) and T2-weighted (T2w) images acquired by dual-contrast fast spin-echo (FSE) sequences. The similarity manifests itself in image space as consistency between the phases of PDw and T2w images and in k-space as correspondence between PDw and T2w k-space data. A method for motion artifact reduction for dual-contrast FSE imaging has been developed. The method uses projection onto convex sets (POCS) formalism and is based on image space phase consistency and the k-space similarity between PDw and T2w images. When coupled with a modified dual-contrast FSE phase encoding scheme the method can yield considerable artifact reduction, as long as less than half of the acquired data is corrupted by motion. The feasibility and efficiency of the developed method were demonstrated using phantom and human MRI data.

Artifacts↗