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Biomedical subjects

Y M Ro

Publications and source records attributed to Y M Ro.

16 recordsLinked to original sources
PubMed1998

Microvascular integrity as a predictor of left ventricular remodeling after acute anterior wall myocardial infarction.

The purpose of this study was to investigate the relation of microvascular integrity and ventricular remodeling after acute myocardial infarction. Twenty-six patients with first acute anterior myocardial infarction were studied before discharge with myocardial contrast echocardiography (MCE). Opacification index (OI) and wall motion index were calculated in the left anterior descending artery territory and left ventricular diastolic volume was measured at baseline and during a 9-month follow-up. In total 26 patients, the regional wall motion improved but the left ventricular volume and global function was not changed significantly at follow-up. When the patients were divided into 3 groups according to opacification index (> or = 0.75, 0.5 approximately 0.75, < or = 0.5) at baseline, functional recovery was not observed and significant left ventricular dilatation was developed in patients with < or = 0.5 OI. Among the baseline echo-parameters such as ejection fraction, wall motion score, left ventricular volume and opacification index, the best predictor for long term left ventricular dilatation was the opacification index by multivariate analysis. In patients with acute anterior wall infarction the assessment of microvascular integrity by MCE at acute stage provides useful information regarding recovery of dysfunctional regional wall motion and ventricular remodeling.

Coronary Vessels↗
PubMed1996

NMR functional imaging using a tailored RF gradient echo sequence: a true susceptibility measurement technique.

The tailored radio frequency gradient echo (TRFGE) technique that has been used in venography (Cho et al., Magn. Reson. Med. 28, 25-38, 1992; Ro, Cho, Magn. Reson. Med. 28, 237, 1992) is applied to functional imaging. The TRFGE technique has the advantage that it is sensitive to the field gradient created by the susceptibility effect, thereby enhancing only the signals from the regions with local field gradient. In addition, the method is insensitive to the in-flow effect, especially from the arterial blood. The latter further simplifies the functional MRI data analysis. The TRFGE sequence is, therefore, suitable for functional MR imaging for which true susceptibility effect measurements are of prime importance. To examine the TRFGE functional imaging systematically, experiments with various imaging parameters such as flip angle alpha, repetition time, and echo time were performed and the results were compared with the data obtained from the conventional gradient echo functional MR imaging. The experimental results shown were all obtained from human volunteers with a 2.0T whole body MRI system.

Arousal↗
PubMed1996

Some new observations on pulse sequence dependent diffusion related edge enhancement in MR microscopy.

Self-diffusion of nuclear spins has been suggested to cause edge enhancement in images especially on a microscopic scale. According to previously published work, theory suggests that edge enhancement is caused by motional narrowing due to the boundaries and spin self-diffusion during the data acquisition period. More careful examination reveals that edge enhancement due to motional narrowing develops only under a few specific conditions. This lack of generality of motional narrowing theory, as well as experimental observations, indicate that edge enhancement due to effects other than motional narrowing alone can exist. It is found that edge enhancement depends greatly on the data acquisition mode; therefore, the images obtained are different depending on the pulse sequence employed. For example, excessive attenuation of DC components due to diffusion can result in edge enhancement in the spin echo signal. However, in the case of FID-like signals, DC components are preserved while positive high frequency parts are attenuated, thereby degrading resolution. The new phenomenon observed has been termed selective spectral suppression since the observed edge enhancement results from the selective attenuation of certain frequency components in the nuclear signals due to diffusion-dependent signal attenuation for a given pulse sequence.

Diffusion↗
PubMed1995

Susceptibility magnetic resonance imaging using spectral decomposition.

Susceptibility differences of materials in magnetic resonance imaging (MRI) usually lead to the intravoxel spin phase variations. Subsequently, the phase variation in the voxel results in a reduction of the signal intensity. This signal intensity reduction is known as the susceptibility effect in MRI and has been studied extensively. In this paper, a new spectral decomposition technique is proposed with which the signal change due to the susceptibility effect can be analyzed. Further, an NMR pulse sequence for the spectral decomposition of the susceptibility was developed and applied to susceptibility imaging of venous blood possessing paramagnetic properties. The computer simulations of the spectral decomposition method and their corresponding experimental results obtained using both a phantom and human volunteers are reported.

Brain↗
PubMed1994

Multipoint K-space point mapping (KPM) technique for NMR microscopy.

An extended version of point mapping in k-space for microscopic imaging applications is analyzed and described. Because the method can offer a number of advantages over the other conventional techniques due to the short echo time (TE), the technique is ideally suited for microscopic imaging where field inhomogeneity dependent signal degradation is one of the main causes of image resolution degradation (1-3). Another application area is the case of imaging in a highly inhomogeneous situation such as the fringe field imaging (Z.H. Cho, E. Wong, U.S. Patent #5023554 (1990). The first original point mapping technique described by Nauert et al. (1) and Emid and Creyghton (2) is analyzed as a k-space point mapping technique, and the original technique is extended to a multipoint k-space point mapping (MKPM) technique. With the extended MKPM technique, much faster microscopic imaging that is free of susceptibility and diffusion effects can be performed (4-6). To examine this idea, computer simulations are performed and their results are given.

Magnetic Resonance Spectroscopy↗
PubMed1993

A novel flow-suppression technique using tailored RF pulses.

The pulsatile nature of blood flow makes zipper-like artifacts along the coding direction in the two-dimensional Fourier transform NMR image. So far, spatial presaturation, one of the correction methods, is known to be effective in eliminating flow artifacts when the Fourier spin echo acquisition is employed. However, this method requires an additional RF pulse and a spoiling gradient for presaturation. Described in this paper is a new flow suppression technique, based on spin dephasing, using a set of tailored RF pulses. The proposed method does not require additional saturation RF pulses or spoiling gradient pulses, making it advantageous over other methods. In addition, the method is relatively robust to flow velocity. The proposed technique is equivalent to the existing flow saturation technique except that the elimination of the flow component is achieved by a pair of tailored 90-180 degrees RF pulses in the spin echo sequence. The principle of the proposed method is the creation of a linear phase gradient within the slice along the slice selection direction for the moving material by use of two opposing quadratic phase RF pulses, i.e., 90 degrees and 180 degrees RF pulses with opposing quadratic phase distributions. That is to say, all the spins of the moving materials along the slice selection direction become dephased. Therefore, no observable signal is generated. Computer simulations and experimental results obtained using a 2.0-T whole-body imaging system on both a phantom and a human volunteer are also presented.

Arteries↗
PubMed1992

Reduction of susceptibility artifact in gradient-echo imaging.

A new technique with which susceptibility artifact in gradient-echo imaging can be reduced substantially by use of a tailored RF pulse is described. The proposed technique can ideally be applied to the case where high local magnetic field inhomogeneity is dominated by the susceptibility. The signal loss and void phenomena due to susceptibility in a voxel are studied and a correction method is also proposed. The description of the tailored RF pulse and its proposed application are given and experimental results obtained using a human volunteer with a 2.0-T KAIS NMR system are presented.

Artifacts↗
PubMed1992

NMR venography using the susceptibility effect produced by deoxyhemoglobin.

A new angiography technique using the susceptibility effect is proposed. Blood containing deoxyhemoglobin is more paramagnetic than surrounding tissue and thereby produces a susceptibility effect at blood-tissue interfaces. By use of a specially tailored RF pulse, signals from normal tissues are suppressed while the signals from blood interfaces, where strong susceptibility-induced fields are created, are enhanced. The design and characteristic behavior of the tailored RF pulse are discussed and experimental results obtained using both a phantom and a human volunteer with a 2.0-T whole-body NMR system are also presented.

Blood Vessels↗
PubMed1992

A new frontier of blood imaging using susceptibility effect and tailored RF pulses.

In MRI, image contrast can be controlled by use of the susceptibility effect if an object contains paramagnetic substances. The localized linear gradient dephases spins in the voxel, leading to phase cancellation and thus reduced signal. This signal void phenomenon, can be exploited if the intrinsic linear gradient is either enhanced or compensated by externally applied RF generated phase distributions. In this paper, a new concept which utilizes the susceptibility effect through the use of tailored RF pulses is proposed. As potential applications of the method, two different types of tailored RF pulses are introduced: one for the enhancement of the susceptibility effect and the other for the correction of the susceptibility artifact, respectively. The former, for example, can be applied to angiography utilizing the paramagnetic property of deoxygenated blood, suggesting a new avenue for the angiography which, for the first time, is not based on flow, although the method is currently limited to imaging of venous blood or venography. Both a theoretical study of the method and experimental results are reported.

Blood↗
PubMed1991

Coronary vasoconstriction induced by vasopressin. Production of myocardial ischemia in dogs by constriction of nondiseased small vessels.

BACKGROUND: We studied the effect of intracoronary administration of arginine-8-vasopressin on blood flow in nondiseased coronary arteries and determined whether this vasoconstriction was severe enough to produce ischemia in 30 dogs. METHODS AND RESULTS: In group 1 (n = 6), after vasopressin administration coronary blood flow was decreased by 41% (p less than 0.002) without changes in heart rate or aortic pressure, and left ventricular ejection fraction measured by radionuclide angiocardiography was decreased by 18% (p less than 0.0005). In group 2 (n = 6), ischemia was confirmed by measurement of transmural pH changes. Administration of vasopressin decreased subendocardial pH of the infused zone from 7.40 +/- 0.03 to 7.31 +/- 0.07 (p less than 0.01). The subendocardial pH of the zone not infused with vasopressin did not change. To overcome the intrinsic regulation of blood flow, operating primarily in small coronary arteries, we hypothesized that vasopressin must increase resistance primarily in large rather than small coronary arteries. After intracoronary infusion in group 3 (n = 6), however, most (94%) of the increase in resistance during vasopressin administration was explained by an increase of resistance in small coronary arteries. In group 4 (n = 9), vasopressin decreased coronary blood flow by 50% and decreased local shortening by 90% at a time when systemic hemodynamics were unchanged. Coronary constriction induced by vasopressin, or the recovery from it, also was not altered by cyclooxygenase blockade. CONCLUSIONS: Thus, vasopressin produces myocardial ischemia by constricting small, nondiseased coronary arteries severely enough to overcome the competition from normal coronary regulation, and this ischemic event is not mediated by prostaglandin products.

Animals↗
PubMed1990

MR Fourier transform arteriography using spectral decomposition.

Reliable separation of arteries from other stationary tissues is accomplished through spectral decomposition by exploiting the pulsatile nature of the blood flow in the arteries. Fourier transformation of a series of projection images in the temporal direction along the cardiac cycle results in spectral images where the arteries are a part of the harmonic component images while stationary tissues and veins are represented as a de component image. From the magnitude of the spectral images an arteriogram can be obtained by summation of the harmonic component images excluding the de component image. This principle is applied to Fourier imaging in a cine mode data acquisition as well as line scan imaging. Since there is no need for the encoding of the flow-sensitive gradient, this technique is free from eddy current artifacts which have been one of the major obstacles to projection angiography using the flow-encoding gradient.

Arteries↗
PubMed1989

Contrasting effects of verapamil and nifedipine on pH of ischemic myocardium in the dog.

It remains unknown whether the actions of verapamil to depress and nifedipine to enhance contractile function of ischemic myocardium influence the degree of myocardial ischemic injury. Thus, we measured intramyocardial pH using fiberoptic pH probes in 43 anesthetized open-chest dogs pretreated for 30 min with verapamil, or nifedipine in doses that decreased aortic pressure 10 to 15 mm Hg before ligation of the left anterior descending coronary artery for 15 min. Drugs were continued during the 15-min ischemic period until the animals were euthanized without reperfusion: verapamil, 10-20 micrograms/kg/min and nifedipine, 2 to 4 micrograms/kg/min i.v. Verapamil-treated dogs showed higher pH of ischemic subendocardium after 15 min ischemia (6.75 +/- 0.07) than did the nifedipine (6.48 +/- 0.04) or placebo (6.43 +/- 0.05) groups, even if the animals were paced (6.71 +/- 0.11) to prevent the negative chronotropic effect of verapamil (P less than 0.01). Neither verapamil nor nifedipine changed collateral myocardial blood flow from 0.10 +/- 0.02 in the subendocardium and 0.17 +/- 0.03 ml/min/g in the subepicardium. Left ventricular function estimated by left ventricular dp/dt was depressed 15% by verapamil and enhanced 26% by nifedipine. Thus, verapamil, but not nifedipine, relieves acidosis of ischemic myocardium after acute coronary occlusion in doses that sustain a 10 to 15 mm Hg decrease in aortic pressure. Nifedipine, in doses that produced the same 10 to 15 mm Hg decrease in mean aortic pressure, did not increase intramyocardial pH, as it enhanced contractile function, estimated by left ventricular dp/dt.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Measurement of the magnetic susceptibility effect in high-field NMR imaging.

The magnetic susceptibility effect often obtained in clinical NMR imaging is analysed and a measurement method of the magnetic susceptibility effect is proposed. The method of extraction of the susceptibility effect alone in high-field NMR imaging where usually the chemical shift and main magnetic field inhomogeneity effects are intermingled with the susceptibility effect is discussed. The proposed susceptibility measurement uses the susceptibility weighted echo-time encoding technique (SWEET) to modulate the NMR signal as a function of echo time with which the image intensity can be weighted. Both phantom-oriented physical experiments and human volunteer experiments were performed to demonstrate the usefulness of the technique for human imaging.

Humans↗
PubMed1987

The frequency distribution of cardiovascular diseases in 13 hospital admitted patients in Korea. Korean Society of Circulation.

The frequency distribution of cardiovascular disease are changing recently due to the development of living environment. Unfortunately there are few epidemiological studies of cardiovascular diseases in general population, we tried to estimate the recent trend of cardiovascular diseases studying hospitalized patients in nationwide 13 large hospitals during a year of 1985. The hypertensive disease (24.1%) was the most common cardiovascular disease and the next were cerebrovascular disease (15.8%), arrhythmias (12.2%), ischemic heart disease (9.7%), congenital heart disease (9.1%), and rheumatic heart disease (5.4%) in order. This results showed that hypertensive disease and cerebrovascular disease are still the major cardiovascular disease and ischemic heart disease and arrhythmias are increased. But chronic rheumatic heart disease is declined compared with previous studies in hospitalized patients.

Adolescent↗
PubMed1984

Transmural pH gradient in canine myocardial ischemia.

The subendocardium is more susceptible to ischemia than the subepicardium. Studies during critical coronary stenosis have demonstrated subendocardial hypoperfusion relative to the subepicardium and transmural gradients in certain tissue metabolites. Although ischemia causes acidosis, the existence of a transmural pH gradient has never been demonstrated or quantitated. Thus we reduced coronary blood flow to 20 +/- 5% of normal in eight open chest anesthetized (morphine sulfate and pentobarbital) dogs and to 45 +/- 5% in two dogs. We implanted specially designed miniature fiber-optic pH probes in normal and ischemic subendocardium (depth 5.5-8 mm) and subepicardium (depth 3-4 mm). Separate experiments validated use of the fiber-optic pH probe system to measure tissue pH. Although both probes were located in the ischemic zone, there was a large transmural gradient, i.e., from normal pH values (7.36) in the subepicardium to severely acidotic (pH 6.94) 2 mm deeper in the subendocardium. This marked difference in pH between nearby transmural layers may have important implications regarding arrhythmogenesis in the setting of acute myocardial ischemia.

Animals↗