Biomedical subjects

O Nalcioglu

Publications and source records attributed to O Nalcioglu.

At least 37 records · Page 2Linked to original sources

PubMed1994

Magnetic resonance imaging analysis of age-related changes in the brains of individuals with Down's syndrome.

Neuroanatomic characteristics of the brains of individuals with Down's syndrome (DS) are typically characterized at autopsy. Apparent anatomic differences in brain between DS and normal individuals are observable upon gross inspection of MRIs. Area measurements from coronal MRIs are used in this study to determine quantitative structural differences that may occur in DS and during aging. In DS individuals, a significantly larger parahippocampal gyrus, and smaller hippocampus and neocortex, are reported relative to age-matched controls. We also examine two DS individuals with a clinical diagnosis of dementia who exhibit atrophy similar to that typically observed in Alzheimer's disease. MRI appears to be a useful tool for quantitative anatomic analysis and may be beneficial for determining baseline anatomic measures that can be useful in the diagnosis of changes associated with dementia.

Adult↗

PubMed1994

Monitoring of pO2 by spin-spin relaxation rate 1/T2 of 19F in a rabbit abscess model.

The purpose of this study was to confirm the relationship of T1 and T2 relaxation rate vs. pO2 in vivo of 19F MR signal measured from intracellular perflubron. Our work to date has demonstrated that 1/T2 is more sensitive to pO2 than 1/T1 in the in vitro environment. The advantage of 1/T2 vs. 1/T1 is the speed of measurement and sensitivity. Seven alternating T1 and T2 measurements were obtained during a continuous acquisition using the TTISS pulse sequence. An abscess model was used for the in vivo experiments where rabbits were infused with 5ml/kg Oxygent HT 10 days prior to scanning. The abscess model was used because it has been shown that perflubron accumulates in macrophages located in the abscess wall. This technique thus provided signal from the intracellular milieu. The results of this study proved that pO2 monitoring by measuring T2 of 19F is feasible and can be used in-lieu of the T1 measurement. Given that the T2 measurement is much more rapid than the T1 measurement and that T2 changes are more sensitive than T1 changes with alterations in pO2, T2 should prove to be practical and useful for monitoring transient rapid changes in pO2.

Abscess↗

PubMed1993

Flow field mapping by multi-zone adiabatic passage excitation.

This paper describes a robust method for flow field mapping by multi-zone adiabatic fast passage (AFP). It provides a quick and simple way to simultaneously acquire flow profiles at several locations and arbitrary orientations inside the field-of-view. The flow profile is the time-averaged evolution of the labeled flowing material. Results obtained using a carotid bifurcation and jet phantoms are similar to the previous experimental studies employing Laser Doppler Anemometry (LDA), and other flow visualization techniques. In addition, the preliminary results obtained with a human volunteer support the feasibility of the technique for in vivo flow quantification.

Blood Flow Velocity↗

PubMed1992

Correction of chemical-shift artifacts in 19F imaging of PFOB: a robust signed magnitude method.

This paper describes a method for correcting the chemical-shift artifacts in 19F NMR imaging of perfluoroctylbromide emulsion (PFOB) by utilizing the two spectral peaks of PFOB which have a long T2 value in conjunction with the Dixon method. Corrected images are obtained from the magnitude of the measured images using the sign determined from the phase images. The method was tested in the presence of several phase deformation factors, such as static magnetic field inhomogeneity and inaccurate time shift of the pi refocusing pulse, which affect the phase errors of each pixel in the reconstructed image. The advantage of the signed magnitude method is demonstrated experimentally by comparing it with the currently used complex and magnitude summation/subtraction methods.

Artifacts↗

PubMed1992

Correction of chemical-shift artifacts in multislice F-19 imaging with perfluorooctyl bromide.

Chemical-shift artifact correction methods for multislice F-19 imaging with perfluorooctyl bromide are described and results obtained with physical phantoms presented. Utilization of the two long-T2 spectral peaks of PFOB in multislice imaging enhances the imaging efficiency considerably. Simultaneous imaging of the adjacent slices is achieved by appropriately adjusting the slice selection gradient amplitude, the bandwidth, and the slice position offset frequency of the selective RF pulses in relation to the frequency separation between the two peaks.

Algorithms↗

PubMed1991

A modified pulse sequence for in vivo diffusion imaging with reduced motion artifacts.

A modified spin-echo diffusion imaging pulse sequence incorporating bipolar gradients that is less sensitive to macroscopic motion-induced artifacts is presented. Expressions for apparent diffusion coefficient in the presence of microcirculation and macroscopic motions and contrast-to-noise ratio in the diffusion map are derived. Diffusion coefficients of liquid phantoms have been measured using a 1.5-T GE Signa system. Experiments performed to demonstrate the immunity to motion-induced errors are reported. Brain images from human volunteer have also been included to show the potential clinical application of the proposed pulse sequence.

Brain↗

PubMed1991

Correction for chemical-shift artifacts in 19F imaging of PFOB: simultaneous multislice imaging.

One of the difficulties encountered in 19F NMR imaging of fluorinated blood substitutes is that these compounds often exhibit complex multipeak spectra. These peaks result in chemical-shift artifacts along the readout direction and blurred images. In addition, each peak excites a different slice (mis-selection) when a slice selection gradient is applied during the selective rf pulse. A simultaneous multislice imaging method has been developed to solve the inherent problem of mis-selection. The essence of this method is to use the two strongest peaks of the spectrum to excite controlled different multiple slices simultaneously, with or without a slice gap. The images corresponding to the two spectral lines are then separated from in- and out-of-phase images (Dixon method). This method corrects the problem of mis-selection and either improves the SNR or increases the number of slices over spectrally selective methods which image only one peak.

Artifacts↗

PubMed1991

NMR angiography with enhanced quasi-half-echo scanning.

Flow dephasing effects in NMR images can be significantly reduced by the use of gradient quasi-half-echo signals. They can also be reduced by moment-nulling techniques. In this paper, an efficient imaging pulse sequence, the flow-insensitive enhanced quasi-half-echo method is developed in which these two techniques are combined. This pulse sequence is used to reduce dephasing effects in images acquired to enhance blood vessels in gradient echo subtraction angiography. Both phase corrected and uncorrected quasi-half-echo reconstruction techniques are used to determine the effect on image resolution and vessel enhancement.

Blood Vessels↗

PubMed1991

Spatially resolved flow velocity measurements and projection angiography by adiabatic passage.

This paper describes the basic principles of gradient modulated adiabatic passage using a CW radiofrequency excitation. The possible applications of this technique include a direct assessment of in-plane and oblique directional flow velocities, and visualization of flow velocity profiles. Flow angiography based on the time-of-flight technique is also discussed with experimental results.

Angiography↗

PubMed1991

Absolute cross-sectional area measurements in quantitative coronary arteriography by dual-energy DSA.

Recent studies have emphasized the limitations of conventional coronary angiography. These limitations include the lack of correlation between the severity of coronary stenosis as estimated from coronary angiograms and the actual severity of stenotic lesions measured in postmortem hearts. As a result, attempts have been made to quantitate luminal dimension more precisely. The application of quantitative digital subtraction angiography (DSA) in the assessment of coronary artery lesion dimension has been limited by cardiac and respiratory motion artifacts. We have reported previously on a motion-immune dual-energy (DE) cardiac mode in which kVp and filtration are switched at 30 Hz. To assess the potential advantages of a videodensitometric technique for quantification of absolute vessel cross-sectional area (CSA), three different quantitative coronary arteriography (QCA) algorithms were compared. The three algorithms under comparison were a videodensitometric (V) algorithm, which does not require any geometric assumption for absolute vessel CSA measurement, and videodensitometric (VC) and edge detection (ED) algorithms, which do require the assumption of circular cross-section for CSA measurements. A cylindrical vessel phantom (0.5-4.75 mm in diameter) and a crescentic vessel phantom, producing 25% to 90% area stenosis, were imaged over the chest of a humanoid phantom. The low- and high-energy images were corrected for scatter and veiling glare before energy subtraction. For CSA measurements in crescentic vessel phantoms, the V algorithm produced significantly improved results (slope = 0.87, intercept = 0.51 mm2, r = .95) when compared to the VC (slope = 1.05, intercept = 4.19 mm2, r = .75) and the ED (slope = 1.57, intercept = 5.21 mm2, r = .60) algorithms.

Algorithms↗

PubMed1991

Quantification of magnetic resonance scans for hippocampal and parahippocampal atrophy in Alzheimer's disease.

The brains of patients with Alzheimer's disease (AD) invariably exhibit neuropathology in the hippocampus and entorhinal cortex when examined postmortem. Magnetic resonance imaging (MRI) offers a noninvasive, high-resolution method for quantifying volumetric changes in the AD brain antemortem. Eight patients diagnosed with probable AD and 7 age-matched controls had MRI scans and were tested on a battery of cognitive and olfactory tests. The hippocampus and entorhinal cortex (parahippocampal gyrus) showed significant atrophy, with over 40% reduction in size. Areas of the brain that are not highly involved in the degenerative state of AD, such as the striatum, did not show significant volumetric changes. Hippocampal and parahippocampal gyrus volumes had the highest correlation with scores on the Mini-Mental State Examination (r = 0.89), with lower correlations for a smell identification test (r = 0.65), odor match-to-sample test (r = 0.72), and a visual match-to-sample test (r = 0.26).

Aged↗

PubMed1991

Measurement of three-dimensional radiation dose distributions using MRI.

Recent investigations have shown that nuclear magnetic resonance (NMR) can be used in conjunction with a suitable chemical dosimeter to estimate the dose from ionizing radiation (Gore et al., Phys Med. Biol. 29, 1189-1197, 1984). Based on this fact it was proposed that spatial dose distributions can be measured in gels infused with the chemical dosimeter using NMR imaging. There have been few such attempts and they provided only qualitative results. In this paper, we report results demonstrating the feasibility of obtaining quantitative dose distribution measurements by this technique. It is shown that quantitative dose distribution measurements necessitate the calculation of relaxation rate maps. We have determined that the spin-spin relaxation rate is a more sensitive parameter than the spin-lattice relaxation rate. It is also demonstrated that the addition of chemical sensitizers could improve the dose sensitivity of the measured NMR parameters. The two features characterizing a photon beam, depth-dose relationship, and beam profile as measured by this technique are in good agreement with the measurements using conventional methods, ionization chambers, and film dosimetry.

Ferrous Compounds↗

PubMed1990

Projection images of the position-velocity joint spin density distribution.

A new concept of phase encoding called position-velocity combined oblique Fourier phase encoding is introduced. It encodes both spatial and velocity information in a single oblique direction in the position-velocity space. Using this method, two-dimensional projection images of the three-dimensional position-velocity joint spin density distribution along different directions can be obtained. These projection images can provide detailed information on the flow system under study. The imaging of the two-dimensional projection is less time consuming compared to three-dimensional Fourier flow imaging and can be easily implemented on a conventional magnetic resonance imaging scanner.

Fourier Analysis↗

PubMed1990

Investigation of blood flow dynamics by NMR angiography.

Gradient-echo sequences with different amount of flow velocity compensation have been studied using cardiac gating in cine mode MR angiography. The initial results on the leg of a healthy volunteer indicate that the circulatory dynamics may be studied qualitatively by means of these flow-sensitive angiograms.

Blood Flow Velocity↗

PubMed1989

Differential flow imaging by NMR.

A new method for spatially resolved NMR flow measurements, named differential flow imaging (DFI), is introduced and experimentally verified. The DFI technique is based on the fact that flow velocity in any direction may cause a pixel position shift in the phase-encoding direction of a 2DFT NMR image. In this method two flow-influenced magnitude images are obtained by properly encoding and/or compensating the flow velocity. A spatial map of the desired component of the flow velocity can consequently be calculated from these two images. Since the DFI technique uses only the magnitude information of the complex images, it is not sensitive to systematic phase errors in contrast to other methods which are based on the phase measurements. On the other hand, the DFI technique can be combined with the phase measurement methods to perform multidimensional flow measurements in a shorter data acquisition time when the phase errors are small or corrected.

Magnetic Resonance Imaging↗

PubMed1988

Correlation of minimum coronary lumen diameter with left ventricular functional impairment induced by atrial pacing.

To understand whether quantitative measurement of minimal coronary luminal diameter is a better method than percent diameter narrowing for assessing the functional impairment of myocardial contractility produced by coronary artery stenoses, measurements were made from 37 stenotic segments in 27 patients with coronary artery disease and from corresponding segments in 10 subjects without coronary artery narrowing. An assessment of the reliability of the 2 types of measurements was made by correlating them with the physiologic parameters of both segmental wall motion and global ejection fraction response induced by atrial pacing. Digitally acquired coronary angiograms were used to facilitate quantitative analysis. Measurements by edge detection and videodensitometry correlated closely (r = 0.94). Percent diameter narrowing correlated moderately with the change in ejection fraction (r = -0.41) or with the change in segmental wall motion (r = -0.44). The measurement of minimal lumen diameter correlated with the change in global ejection fraction (r = 0.61) and did so even better with the change in segmental wall motion (r = 0.78, p less than 0.05). A minimal lumen diameter of less than or equal to 1.5 mm identified patients likely to have a functional impairment during atrial pacing as assessed by either global ejection fraction or segmental wall motion defects. We conclude that minimal coronary luminal diameter provides a better method than percent diameter narrowing calculations to measure the anatomic severity of coronary artery narrowing.

Angiography↗

PubMed1987

Videodensitometric determination of minimum coronary artery luminal diameter before and after angioplasty.

Quantitative measurements of coronary stenoses were made from digital coronary angiograms in 19 patients before and after percutaneous transluminal coronary angioplasty (PTCA). Two methods of measurement were compared. Mean stenosis before PTCA was 67 +/- 10% by the edge detection method and 67 +/- 12% by videodensitometry (difference not significant). After PTCA, the mean stenosis was 32 +/- 14% by edge detection and 30 +/- 13% by videodensitometry (difference not significant). In addition, a new method was developed to rapidly calculate the absolute minimum luminal area and diameter by videodensitometry. The minimum luminal diameter before PTCA was 1.0 +/- 0.5 mm and after PTCA increased to 2.4 +/- 0.5 mm (p less than 0.001). The validity of the videodensitometric method was analyzed in a series of Lucite phantom studies, which suggested that when there is an irregular angiographic appearance, the densitometric method may be more accurate than standard edge detection methods. Digital acquisition of coronary angiograms provides a means for rapid application of quantitative analysis during coronary interventional procedures.

Angioplasty, Balloon↗

PubMed1987

Methods and algorithms for Fourier-transform nuclear magnetic resonance tomography.

In nuclear magnetic resonance (NMR) imaging there are two main image formation approaches, the direct Fourier imaging method proposed by Kumar et al. [J. Mag. Res. 88, 69 (1975)] and the projection reconstruction technique commonly used in conventional computed tomography. In this paper these two approaches are reviewed with particular reference to Fourier-transform NMR imaging or tomography. Although Fourier imaging is the most conventional imaging method, useful applications for projection reconstruction techniques have often been found in NMR imaging. Therefore, in this paper, the emphasis is placed more on the projection reconstruction techniques that may not be readily available in NMR imaging.

Algorithms↗