Biomedical subjects

L P Panych

Publications and source records attributed to L P Panych.

8 recordsLinked to original sources

PubMed1994

Dynamically adaptive MRI with encoding by singular value decomposition.

A new MRI spatial encoding method based upon the singular value decomposition (SVD) and using spatially selective RF excitation is described. This encoding technique is particularly applicable to dynamic adaptive MRI, because it provides a near minimal set of spatial encoding profiles computed using an image estimate that is determined from a previously obtained image. Experimental results are presented for two cases, which exemplify its potential use in different dynamic imaging tasks. SVD-encoded MRI has demonstrated to be a highly efficient encoding scheme.

Brain↗

PubMed1994

A dynamically adaptive imaging algorithm for wavelet-encoded MRI.

A new adaptive algorithm based on wavelet-encoded MRI is presented for application in dynamic imaging. This algorithm is adaptive because the strategy for updating image data in the dynamic series of images is determined by the processing of the most recently acquired data. The spatially selective multi-resolution properties of the wavelet transform are exploited to selectively update only those regions of the field of view where change is actually occurring. A theoretical imaging model is presented to motivate use of the adaptive algorithm, and simulation results using both artificial and experimental wavelet-encoded data are presented.

Algorithms↗

PubMed1989

Practical digital filters for reducing EMG artefact in EEG seizure recordings.

In long-term scalp EEG monitoring of epileptic patients it is virtually impossible, in the present state of the technology, to avoid movement-related artefacts. These often obscure EEG information about the location of the seizure focus. One important example of such artefact is EMG activity. Its removal or suppression is sometimes enough to make otherwise useless EEG traces readable. Different methods of filtering have been applied towards that end. We routinely use a 15 Hz setting on our polygraph in obtaining EEG seizure printouts. We have recently examined digital filters which attenuate EMG beyond what is possible with the 15 Hz filter. A concern has been that the filters are practical in that they run in real time on a simple microprocessor and cause a minimum of confusion between smoothed artefact and actual brain activity.

Electroencephalography↗

PubMed1985

Automation of the seizure investigation unit at the University of British Columbia Health Sciences Centre Hospital.

At the University of British Columbia Health Sciences Centre Hospital we have constructed an automated Seizure Investigation Unit for long term monitoring of epileptic patients. A central component of this system is a new device, developed at the University of British Columbia, which prevents video and EEG records of seizures recorded on video tape from being over-recorded. Computer technology is relied upon to a considerable degree in our unit. Computers are seen, in this phase of development of the SIU, as a means of making patient monitoring less dependent on supervision. They can help to redirect human energy towards complex analysis rather than time consuming and simple monitoring tasks.

Automation↗

PubMedDate not supplied

Comparing the FAISE method with conventional dual-echo sequences.

The FAISE (fast-acquisition interleaved spin-echo) technique consists of a hybrid rapid-acquisition relaxation-enhanced (RARE) sequence combined with a specific phase-encode reordering method. Implemented on a 1.5-T unit, this multisection, high-resolution technique permits convenient contrast manipulation similar to that of spin-echo imaging, with selection of a pseudo-echo-time parameter and a TR interval. With a TR of 2 seconds, eight 256 x 256 images are obtained in 34 seconds with either T2 or proton-density weighting. A direct comparison between FAISE and spin echo for obtaining T2-weighted head images in healthy subjects indicates that FAISE and spin-echo images are qualitatively and quantitatively similar. Image artifacts are more pronounced on "proton-density" FAISE images than on the T2-weighted FAISE images. T1 contrast can be obtained with inversion recovery and short TR FAISE images. Preliminary temperature measurements in saline phantoms do not indicate excessive temperature increases with extended FAISE acquisitions. However, extensive studies of radio-frequency power deposition effects should be performed if the FAISE technique is to be fully exploited.

Artifacts↗

PubMedDate not supplied

Effects related to temperature changes during MR imaging.

Magnetic resonance (MR) imaging has been proposed as a method of monitoring the interstitial laser heating of tissue for the clinical treatment of tumors (laser hyperthermia). The treatment causes considerable temperature changes over the time that image data are acquired, and therefore an analysis of the time-dependent effects of heating is required. The problem is expressed mathematically, and computer-simulated images are compared with those obtained from experimental heating and imaging of gel phantoms. Results show that at the rates of heating typical for laser hyperthermia and even with the relatively slow standard imaging techniques used, generation of artifact is not a major concern. It is also shown that a spatial spin signal magnitude distribution, evolving in time, is effectively sampled at the time to when the low-numbered phase-encoding steps are collected at to. It is noted, however, that substantial temperature changes during image data acquisition make accurate temperature determination difficult and place limits on MR imaging for quantitative spatial temperature mapping.

Gels↗

PubMedDate not supplied

Implementation of wavelet-encoded MR imaging.

Reconstructions of images from wavelet-encoded data are shown. The method of MR wavelet encoding in one dimension was proposed previously by Weaver and Healy. The technique relies on selective excitation with wavelet-shaped profiles generated by special radio-frequency waveforms. The result of the imaging sequence is a set of inner products of the image with orthogonal functions of the wavelet basis. Inversion of the wavelet data is accomplished with an efficient algorithm with processing times comparable with those of a fast Fourier transform. The experiments show that wavelet encoding by selective excitation of wavelet-shaped profiles is feasible. Wavelet-encoded images are compared with phase-encoded images that have a similar signal-to-noise ratio, and there is no discernible degradation in image quality due to the wavelet encoding. Potential benefits of wavelet encoding are briefly discussed.

Artifacts↗

PubMedDate not supplied

A simple noninvasive stereotactic device for routine MR head examinations.

A simple device to define reproducible reference points in MR examinations was designed. The device can be worn like a pair of eyeglasses and has reference structure visible in MR images. Combined with a specially designed algorithm, the imaging plane can be aligned to a predefined coordinate system in one step, using a single slice through the device. The device can be produced at low cost and is suitable for routine examinations as well as surgical planning.

Head↗