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Biomedical subjects

O Nalcioglu

Publications and source records attributed to O Nalcioglu.

At least 55 records · Page 3Linked to original sources
PubMed1985

Determination of the optimal timing for performing digital ventriculography during atrial pacing stress tests in coronary heart disease.

To determine the optimal time for recording left ventricular angiograms during atrial pacing stress tests, digital subtraction left ventriculograms were obtained using 12 ml of contrast material in 40 patients at rest and at peak pacing. Nineteen of the 40 patients had a third digital left ventriculogram performed between 5 and 10 seconds and 21 patients had a third digital left ventriculogram performed 30 seconds after pacing was stopped. Coronary angiography showed significant coronary artery disease (CAD) in 29 patients and no evidence of significant CAD in 11 patients. Ejection fraction (EF) increased or did not change at peak pacing in 10 of 11 patients without CAD. In the 29 patients with CAD, mean EF decreased an average of 10 percentage points (p less than 0.001) and fell 2 or more percentage points in 25 patients (86%) at peak pacing. These changes in EF were accompanied by the development of wall motion abnormalities, which occurred in segments of myocardium that were supplied by coronary arteries with angiographic CAD (more than 50% diameter narrowing). In contrast, the mean EF during the postpacing studies decreased only 2.2 percentage points (difference not significant) over rest values. Moreover, 15 of 29 patients (52%) with CAD had a decrease in EF of 2 or more percentage points. Therefore, the sensitivity of the atrial pacing stress test was diminished when the analysis was performed at 10 or 30 seconds after pacing. It is concluded that EF changes and wall motion abnormalities induced by atrial pacing are of short duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Digital coronary roadmapping as an aid for performing coronary angioplasty.

In an attempt to improve visualization of the position of the guidewire and dilatation balloon during coronary angioplasty, a method was developed called digital coronary roadmapping. With this method a digitally acquired coronary angiogram is interlaced with the live fluoroscopic image of the guidewire and balloon catheter. The digital coronary angiogram is superimposed at the same magnification and radiologic projection as the live fluoroscopic image onto the video monitor above the catheterization table. The digital roadmap image thus provides immediate feedback to the angiographer to assist in directing the guidewire into the appropriate coronary artery branch and to help in placement of the balloon so that it straddles the site of stenosis.

Adult↗
PubMed1985

Chemical-shift artifact correction scheme using echo-time encoding technique.

An investigation has been undertaken to study the effects of chemical shift on NMR image obtained by the projection reconstruction technique. Mathematical simulation studies indicate that chemical shift causes blurring in NMR images regardless of the image reconstruction technique. A systematic study of such artifacts is presented and possible correction schemes are proposed. Exemplary results with and without correction of the chemical-shift artifact and pulse schemes employed for projection reconstruction are presented. The present chemical-shift correction scheme is basically the same as a spectroscopic imaging technique such as the existing 4-D NMR imaging method except that the encoding steps required can be reduced substantially in the case of modest spectroscopic resolution.

Magnetic Resonance Spectroscopy↗
PubMed1984

Detection and quantitation of coronary artery stenoses from digital subtraction angiograms compared with 35-millimeter film cineangiograms.

To assess the ability to detect coronary artery narrowings from computer-acquired angiograms, a panel of 4 observers independently identified and measured focal coronary narrowings from digital subtraction angiograms and compared the results to those obtained from standard 35-mm cine film angiograms. Both cine and digital angiograms were obtained sequentially using selective intracoronary artery injection of standard amounts of iodinated contrast media. Digital images were obtained at 8 frames/s with a 512 X 512 X 8-bit pixel matrix. Modifications in the imaging chain for computer acquisition included a slower pulsed radiographic mode, a progressive scan camera, and initial storage of the images on an 80-megabyte digital hard disk. Postprocessing computer algorithms were used to enhance the unsubtracted digital images; these included single-frame, mask-mode subtraction, vessel boundary edge enhancement, and 4-fold pixel magnification. In 19 patient studies, 32 arteries were reduced more than 25% in diameter according to at least 1 of 4 observers on either the digital or cine film angiograms. There was no significant difference in the mean percent diameter narrowing for all the narrowings between the digital angiograms (53 +/- 31%) and the cineangiograms (52 +/- 31%). In addition, a 2-way analysis of variance yielded no significant difference between the amount of variability in the measurements between the cine film and the digital technique. This similar variability persisted when subsets of patients based on the degrees of stenosis were considered (e.g., only narrowings from 50 to 90% diameter reduction).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

On the relationship of image intensifier contrast ratios measured by two techniques.

In recent years the contrast ratio (CR) has played an important role in the quantitation of imaging performance of X-ray image intensifiers. In practice, one uses either a lead disc or strip for measurement of contrast ratios. A theoretical relationship relating contrast ratios measured by both disc and strip techniques is discussed and experimental results are presented. The theoretical analysis uses the point spread function model to describe veiling glare for an image intensifier. It has been shown that one can predict strip contrast ratios after a determination of the veiling glare point spread function from a measurement of disc contrast ratios.

Methods↗
PubMed1984

Limits to signal-to-noise improvement by FID averaging in NMR imaging.

We studied the improvement of signal-to-noise ratio (SNR) in NMR images by free induction decay (FID) averaging. We found that as the number of FIDS averaged increases, a region is reached where the image SNR levels off asymptotically. A theoretical explanation for this behaviour is offered. Agreement between experimental results and theoretical prediction is excellent. It is also pointed out that the exact location of the point at which further averaging does not pay-off is dependent on the individual NMR imaging system used.

Information Theory↗
PubMed1983

Measurement of left ventricular ejection fraction by videodensitometric analysis of digital subtraction angiograms.

Left ventricular ejection fraction (LVEF) was calculated from 25 first-pass digital subtraction angiograms using a densitometric analysis. Digital subtraction angiograms are obtained in a computerized format; therefore, they can be readily analyzed with computer software to measure the density of the iodine signal within the image. The video signals from the image intensifier were logarithmically amplified so that there was a linear correlation between the video signal intensity and the depth of the iodine contrast material represented by that video signal. LVEF was also calculated by the area-length method from the same digital subtraction angiograms. There was close correlation between these two techniques (r = 0.94, standard error of the estimate = 5.04%). The videodensitometric EF technique is simple to perform, it correlates well with the standard area-length method, and is not dependent on geometric assumptions of LV geometry.

Absorptiometry, Photon↗
PubMed1983

Digital angiography in assessment of ventricular function and wall motion during pacing in patients with coronary artery disease.

Using digital subtraction angiography, left ventriculograms were obtained with 10 ml of iodinated contrast material in 21 patients both at rest and during atrial pacing. In 15 patients with significant coronary artery lesions (CAD) (greater than 50% diameter narrowing in at least 1 major artery), ejection fraction decreased during atrial pacing from a mean of 62 +/- 14% to 51 +/- 15% (p less than 0.001). In 14 (93%) of 15 patients, ejection fraction decreased or was unchanged during pacing. In 6 patients with chest pain but normal coronary arteries, ejection fraction increased from a mean of 66 +/- 9% at rest to 72 +/- 6% during atrial pacing (p less than 0.01). Ejection fraction increased by greater than or equal to 5% during pacing in 5 of 6 patients with normal coronary arteries. Patients with CAD also had an abnormal response in end-systolic volume during atrial pacing (50 +/- 31 ml at rest versus 47 +/- 24 ml during pacing) compared with patients with normal coronary arteries (46 +/- 16 ml at rest versus 26 +/- 9 ml during pacing; p less than 0.01). The digital ventriculograms demonstrated new or increased wall motion abnormalities during atrial pacing in 4 of 5 patients with CAD who had wall motion abnormalities at rest and in 8 of 10 patients with CAD who had normal wall motion at rest. Moreover, these wall motion abnormalities occurred in myocardial wall segments that were supplied by coronary arteries with significant lesions. Thus, because digital subtraction angiography allows multiple left ventriculograms to be obtained during routine cardiac catheterization, intervention studies such as atrial pacing can be used to obtain a functional assessment of the severity of coronary arterial lesions.

Adult↗
PubMed1983

Correlation of 10-milliliter digital subtraction ventriculograms compared with standard cineangiograms.

Left ventriculograms were obtained with the use of 10 ml of contrast media by passing fluoroscopic video images through a video image processor. The low concentration of dye in the left ventricle was enhanced by the technique of mask mode subtraction, and the images were postprocessed to increase visibility by manipulation of the gray scale and contrast levels. These digital subtraction angiograms were compared to standard cineangiograms by means of 40 ml of contrast media. Of 30 patients studied, six (20%) had runs of ventricular tachycardia during the cineangiogram and had to be excluded. In the remaining 24 patients, there was a good correlation between the two techniques for left ventricular end-diastolic volume (r = 0.77, end-systolic volume (r = 0.95), and ejection fraction (r = 0.97). Spatial resolution in the digital studies was adequate to appreciate wall motion abnormalities that were visualized on the cineangiograms. Left ventricular end-diastolic pressure (LVEDP) did not change after the 10 ml injection, but the mean LVEDP rose 6.0 mm Hg after the 40 ml cineangiograms (p less than 0.01). Digital subtraction angiography can be used to obtain left ventriculograms with one-fourth the amount of contrast media and one-fourth the x-ray exposure compared to standard cineangiograms. This technology will permit multiple left ventriculograms to be obtained which, in turn, will allow intervention studies to be performed in the catheterization laboratory.

Adult↗
PubMed1979

Post-reconstruction method for beam hardening in computerised tomography.

A method for correcting the beam hardening artefacts in computerised tomography is introduced. After an initial reconstruction of the object the uncorrected image is used to estimate the amount of bone and tissue along each ray. The bone and tissue lengths obtained from the initial reconstruction are used to add a correction term to each original projection. A second reconstruction using the corrected projection data yields the final beam hardening corrected image. The results are presented showing the application of this formalism to a mathematical phantom. The instability of the correction method with respect to various possible sources of error is examined.

Tomography, X-Ray Computed↗
PubMedDate not supplied

Reblurred deconvolution method for chemical shift removal in F-19 (PFOB) MR imaging.

Perfluorocarbons such as perfluoroctylbromide (PFOB) can be used as contrast agents in the vascular system for fluorine-19 magnetic resonance imaging or as synthetic oxygen carriers. F-19 imaging has been proposed for studying the vascular system, capillary flow, tissue perfusion, and tumor oxygenation. A major difficulty is that F-19 compounds often have complex multipeak spectra. These peaks result in chemical shift artifacts, lower signal-to-noise ratios, and blurred images. Each peak also excites a different section when a section-select gradient is applied. Direct inverse filtering is the simplest deconvolution method for correcting such artifacts; however, two major difficulties present themselves: functional singularity and noise amplification at high frequencies. The use of a new reblurred deconvolution (RED) method appears to overcome these problems. Although this method is based on iterative deconvolution in the spatial domain, the computational overhead is negligible. Since the point spread function and object data are already available in the time domain as FID data, RED appears to be useful for eliminating chemical shift artifacts and suppressing noise amplification while restoring the original image without loss of resolution.

Contrast Media↗
PubMedDate not supplied

Reduced-bandwidth method for F-19 imaging of perflubron.

A reduced-bandwidth imaging method has been developed to eliminate the chemical shift artifacts in magnetic resonance (MR) imaging of the blood substitute perflubron (PFB) and simultaneously enhance the signal-to-noise ratio (SNR). The two strongest spectral peaks, which have relatively long T2 values (247 and 471 msec), were used. When the receiver bandwidth is reduced substantially by increasing the data acquisition time Ts, the bandwidth across the object becomes less than the chemical shift frequency. The reduced bandwidth eliminates misregistration by displaying the images corresponding to multiple spectral peaks on the same image plane simultaneously. An additional gain due to the reduced bandwidth is the reduced thermal Gaussian noise. Unfortunately, the increased Ts results in an increased TE, which causes the signal to be attenuated by T2 relaxation. The optimum measured Ts (and TE) values for successful image separation and maximum SNR were 120 and 144 msec for the two spectral peaks, respectively. The long TE also suppresses the rest of the downfield spectral peak cluster of PFB. The degree of magnetic field inhomogeneity and tissue susceptibility across the object may cause some limitations in the application of this technique; however, a composite radio-frequency pulse that will allow use of additional spectral lines and/or localized volume imaging techniques may be incorporated to overcome these limitations.

Artifacts↗
PubMedDate not supplied

Susceptibility effects in porous media in the presence of flow.

Magnetic resonance (MR) imaging of microvascular flow is an important topic in biomedicine because it permits access to the functional state of a biologic system. The internal heterogeneous magnetic field due to susceptibility differences within tissues is one of the factors that can affect signal intensity. A glass bead phantom simulating a porous medium was used to experimentally study the effect of the internal magnetic field on MR flow measurements. A physical model was developed to simulate the paths of the moving spins and the local magnetic field distribution in the medium to estimate the signal intensity with spin-phase analysis. The susceptibility variation inside the glass bead phantom was estimated by comparing the simulation results with the experimental data. Experiments were also performed with a tissue-simulating phantom, and the results indicated that the effect of the internal field inhomogeneity on in vivo microvascular flow measurements was negligible.

Computer Simulation↗
PubMedDate not supplied

Statistical description of microcirculatory flow as measured with an MR method.

Quantification of microcirculatory flow is important for the functional assessment of biologic systems. The authors describe a method of analyzing the dependence of the magnetic resonance (MR) signal intensity on microcirculatory flow. A gel bead phantom was used to simulate the randomly oriented flow capillaries, and the MR signal intensity of the phantom was studied at different flow velocities by using velocity-sensitized and -compensated spin-echo pulse sequences. A theoretical model based on the spin-phase phenomenon is proposed to elucidate the effect of flow on signal intensity. The velocity phase of a spin depends on its path and the corresponding velocity-encoding gradients. A Monte Carlo simulation was used to generate the path of a spin on the basis of a statistical model for flow through a random capillary network. From the velocity-phase distribution of a group of spins within a voxel, the signal attenuation due to flow can be calculated. The results of the statistical model and experimental measurements agreed well. Also, T1 and T2 effects in MR flow measurements were investigated. The current study provides a theoretical framework for understanding MR measurements of microcirculatory flow.

Blood Flow Velocity↗
PubMedDate not supplied

Magnetic resonance imaging of anatomic and vascular characteristics in a canine model of human aging.

Dogs exhibit both neuroanatomical and cognitive changes as a function of age that parallel those seen in aging humans. This study describes in vivo changes in neuroanatomical and cerebrovascular characteristics of the canine brain as a function of age in a group of dogs ranging from 4 to 15 years old. Dynamic contrast-enhanced magnetic resonance imaging (MRI) was used to measure the kinetics of contrast agents in the brain. Measures of vascular volume and blood-brain barrier (BBB) permeability were derived from a pharmacokinetic analysis. Cortical atrophy and ventricular enlargement were characteristic features of the aged canine brain. Vascular volume did not vary as a function of age and BBB permeability exhibited a nonsignificant increasing trend with age. However, BBB dysfunction was detected in one middle-aged dog that in addition to having unusually large ventricles, demonstrated an early onset of diffuse senile plaques at postmortem. These findings indicate that BBB dysfunction detected by magnetic resonance imaging may be useful for predicting and potentially diagnosing early pathological conditions.

Aging↗