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Biomedical subjects

K K Yu

Publications and source records attributed to K K Yu.

At least 37 records · Page 2Linked to original sources
PubMed1994

Inversion recovery EPI of bolus transit in rat myocardium using intravascular and extravascular gadolinium-based MR contrast media: dose effects on peak signal enhancement.

Inversion recovery gradient recalled echo planar imaging (TI/TR/TE = 700/2000/10 ms) was used to dynamically monitor the first pass of an intravascular (GdDOTA-polylysine) and an extravascular (GdDTPA-BMA) contrast agent through normal rat myocardium. It was found that myocardial enhancement increased with dose of the intravascular agent to a limiting value of approximately 50% of fully relaxed intensity, consistent with enhancement of 40% of myocardial water content during the first pass. Larger doses produced no further increase in peak response. On the other hand, the extravascular agent caused incrementally increased enhancement throughout the dose range examined to a final value of 68 +/- 2% of fully relaxed intensity. The profile of dose dependence for both agents was inconsistent with monoexponential T1 relaxation. It was concluded that: (a) compartmentalization of myocardial water combined with restricted myocardial water diffusion limits the peak response during bolus transit; (b) extraction of the extravascular agent during transit elevates the peak response over that obtained from agent confined to the vascular volume; and (c) models that assume simple monoexponential T1 relaxation to derive time-density curves do not adequately describe the relationship between changes in signal intensity, R1 and contrast concentration.

Albumins↗
PubMed1994

The use of contrast-enhanced magnetic resonance imaging to define ischemic injury after reperfusion. Comparison in normal and hypertrophied hearts.

RATIONALE AND OBJECTIVES: Magnetic resonance imaging (MRI) was used to demonstrate the infarction size in reperfused ischemic myocardium of normal and hypertrophied hearts, and to test the hypothesis that hypertrophied hearts manifest greater susceptibility to ischemia. METHODS: Normal rats (n = 11) and rats subjected to left ventricular hypertrophy (LVH) by aortic banding (n = 13) were studied. After 7 weeks, the left coronary artery was occluded for 25 minutes and reperfused for 1 hour before MRI. Electrocardiogram-gated spin-echo images were acquired before and after administration of 0.3 mmol/kg gadoteridol. To quantify the hyperintense area demarcated by gadoteridol, 3 transaxial images were acquired at different levels. Jeopardy and infarcted areas were measured in the same three slices postmortem using blue dye and triphenyltetrazolium chloride (TTC) stain, respectively. RESULTS: Before administration, there was no significant difference in signal intensity between nonischemic (0.42 +/- 0.03 arbitrary units) and ischemic (0.41 +/- 0.03) myocardium in either group. After gadoteridol injection, signal intensity of the reperfused injured region was higher than that of nonischemic myocardium (1.48 +/- 0.16 vs. 0.72 +/- 0.06, P < .05). Magnetic resonance delineation of the hyperintense area persisted for at least 30 minutes. The size of the hyperintense area was larger in LVH than in control hearts (25 +/- 5% vs. 7 +/- 3% of LV surface area, P < .05) and did relate closely to the area of myocardial infarction (r = .97), but not with the jeopardy area (r = .42). On TTC staining, the infarction size also was significantly greater in LVH than in normal group (18 +/- 5% vs. 5 +/- 2% of LV surface area, P < .05). The jeopardy areas of normal and LVH hearts showed no significant difference (46 +/- 2% vs. 47 +/- 3%). CONCLUSION: Magnetic resonance imaging confirms the concept that reperfused myocardial injury is larger in LVH than normal hearts after brief coronary occlusion. Contrast-enhanced MRI can define the size of reperfused myocardial injury. Thus, MRI is a suitable technique to assess conditions accentuating ischemic injury.

Animals↗
PubMed1994

Identification of myocardial reperfusion with echo planar magnetic resonance imaging. Discrimination between occlusive and reperfused infarctions.

BACKGROUND: The current treatment of many cases of acute myocardial infarction involves the use of thrombolytic agents. Evaluation of this therapy requires determination of the success of reperfusion and assessment of the presence and extent of infarction in the reperfused territory. The present study was designed to simulate in rat models several possible outcomes of reperfusion therapy: (1) successful reperfusion and absence of myocardial infarction, (2) successful reperfusion and presence of myocardial infarction, and (3) unsuccessful reperfusion. The usefulness of contrast-enhanced fast magnetic resonance (MR) imaging in defining the success of reperfusion was investigated. The dynamic effects were examined of low and high doses of gadolinium-BOPTA/dimeglumine (Gd-BOPTA/dimeg) on myocardial signal using MR inversion recovery echo planar imaging (IR-EPI) and gradient recalled echo planar imaging (GR-EPI), respectively. METHODS AND RESULTS: Rats were subjected to one of the following regimens: reperfused reversible myocardial injury (n = 9), reperfused irreversible myocardial injury (n = 9), and occlusive infarction (n = 9). MR echo planar images were acquired every 1 or 2 seconds before, during, and after administration of Gd-BOPTA/dimeg. In all groups, normal myocardial signal was sharply increased on IR-EPI and decreased on GR-EPI at the peak of the bolus, followed by a gradual decline to baseline. In animals subjected to reperfused reversible myocardial injury, normal and previously ischemic regions were indistinguishable during and after the passage of Gd-BOPTA/dimeg. On the other hand, enhancement of reperfused irreversibly injured myocardium was delayed but increased steadily to a higher level than normal myocardium on IR-EPI. The reperfused irreversibly injured myocardium was identified on IR-EPI as a zone of high signal (hot spot). On GR-EPI, signal loss in reperfused irreversibly injured myocardium was significantly less compared with normally perfused myocardium. In animals with occlusive infarctions, there was no change in signal intensity over the ischemic region on either IR-EPI or GR-EPI. Occlusive infarction was identified as zones of either low (cold spot) or high (hot spot) signal compared with normal myocardium, depending on MR pulse sequence and dose of the contrast medium. CONCLUSIONS: The transit of Gd-BOPTA/dimeg monitored by fast MR imaging techniques can be used to distinguish between reperfused reversibly and reperfused irreversibly injured myocardium and between occlusive and reperfused infarctions.

Animals↗
PubMed1993

Comparison of T1-enhancing and magnetic susceptibility magnetic resonance contrast agents for demarcation of the jeopardy area in experimental myocardial infarction.

RATIONALE AND OBJECTIVES: This study compared the areas demarcated by a T1-enhancing agent, Gd-DTPA-BMA, and a magnetic susceptibility agent, Dy-DTPA-BMA, with 201thallium autoradiography (indicator of perfusion) and postmortem histochemical staining with triphenyltetrazolium chloride (TTC)(indicator of infarction). METHODS: Thirteen rats were subjected to coronary artery occlusion for 3 to 4 hours before acquisition of four sets of electrocardiogram-gated spin-echo magnetic resonance (MR) images: T1-weighted images before and after 0.2 mmol/kg Gd-DTPA-BMA; and T2-weighted images before and after 0.3 mmol/kg Dy-DTPA-BMA. After MR imaging, intravenous 201thallium delineated the area of decreased myocardial perfusion. At autopsy, TTC staining delineated the area of myocardial infarction. RESULTS: A myocardial region in the distribution of the occluded artery was delinated as a hyperintense area ("hot-spot") by Dy-DTPA-BMA and as a hypointense area ("cold-spot") by Gd-DTPA-BMA. The hyperintense area demarcated by Dy-DTPA-BMA (51 +/- 3% of the area of the midequitorial slice of the left ventricle) showed a closer relationship to the area of decreased myocardial perfusion (jeopardized area) (46 +/- 3%), determined by 201thallium autoradiography, than the area of myocardial infarction (36 +/- 4%), determined by histochemical staining. However, the hypointense area demarcated by Gd-DTPA-BMA (29 +/- 2%) did not relate as closely to the area of decreased myocardial perfusion (slope = 0.54) or the area of myocardial infarction (r = 0.46). CONCLUSIONS: The abnormal myocardial area delineated by the magnetic susceptibility agent showed a closer relationship to the area of deficient myocardial perfusion (jeopardy area) after coronary occlusion than that defined by T1-enhancing contrast media.

Animals↗
PubMed1993

Dual mechanisms for change in myocardial signal intensity by means of a single MR contrast medium: dependence on concentration and pulse sequence.

To determine whether gadodiamide injection can provide sufficient enhancement on both T1- and T2-weighted spin-echo magnetic resonance (MR) images of the heart and skeletal muscles, anesthetized rats were divided into five groups. Groups 1-3 received 0.1 (n = 9), 0.3 (n = 8), or 0.5 (n = 8) mmol/kg gadodiamide injection, respectively, and T1-weighted images were obtained. Groups 4 and 5 received 0.3 or 0.5 mmol/kg gadodiamide injection, respectively, and T2-weighted images were obtained. Gadolinium concentration was measured in myocardium by means of inductively coupled plasma-atomic emission spectroscopy. On T1-weighted images, the 0.1 and 0.3 mmol/kg doses produced a dose-dependent increase in myocardial signal intensity proportional to gadolinium concentration. A dose of 0.5 mmol/kg, which correlated with higher gadolinium concentration and did not further increase myocardial signal intensity, prolonged the imaging window. On T2-weighted images, the 0.3 mmol/kg dose caused a transient decrease in myocardial signal intensity; the 0.5 mmol/kg dose produced greater and persistent loss of signal intensity. In conclusion, the changes in signal intensity induced by gadodiamide injection depend on the dose, pulse sequence, and type of tissue.

Animals↗
PubMed1993

Coping strategies of schizophrenic patients and their relationship to outcome.

The experience and perception of effective sources of help of 101 schizophrenic patients were studied. A combination of professional help, social support, and self-coping efforts was listed as helpful. The more experiences patients had with the various sources of help, the better were their outcomes. Premorbid adjustment, exposure to the magnitude and nature of helpful sources, as well as the patients' own ability and motivation to make use of available helpful sources were thought to be important mediating variables for a better outcome. Apart from psychotropic medications, over half of the patients were not using any one of the sources of help mentioned. It remains an important research question whether or not schizophrenic patients may benefit from direct coaching in self-help skills in conjunction with making optimal use of professional and environmental supports.

Adaptation, Psychological↗
PubMed1992

Delineation of acute myocardial infarction with dysprosium DTPA-BMA: influence of dose of magnetic susceptibility contrast medium.

OBJECTIVES: The contrast enhancement of acutely infarcted myocardium produced by the nonionic magnetic susceptibility-enhancing agent dysprosium diethylenetriamine pentaacetic acid-bis-methylamide (DyDTPA-BMA [S-043 Injection]) was assessed in the current study to establish the lowest dose that would yield optimal contrast between normal and acutely infarcted myocardium. BACKGROUND: Magnetic susceptibility contrast agents enhance differences between normal and ischemic tissue by reducing the signal of the normally perfused tissue to which they distribute. METHODS: Acute myocardial infarctions were produced by ligation of the left coronary artery. At 3 to 4 h after occlusion, a dose of 0.1, 0.3 or 0.5 mmol/kg of DyDTPA-BMA was injected intravenously into eight rats each in group 1, 2 or 3, respectively; a fourth group of seven rats served as a control group. Nuclear magnetic resonance (NMR) transverse relaxation time (T2)-weighted images (electrocardiographically gated to every 5th beat, echo delay time [TE] = 60 ms) were acquired before and for 1 h after administration of contrast agent. RESULTS: Images obtained before the injection of contrast agent showed moderate differences in signal intensity between normal and infarcted myocardium (p < 0.05). The contrast enhancement and the duration of delineation between infarcted and normal myocardium produced by this agent were dose dependent. At doses of 0.1, 0.3 and 0.5 mmol/kg, DyDTPA-BMA produced signal loss in normal myocardium: 63 +/- 5%, 41 +/- 4% and 28 +/- 4% of the baseline values, respectively, without any significant reduction in signal intensity of the infarcted region. The reduction in signal of normal myocardium and delineation of the infarct persisted for 5 min at a dose of 0.1 mmol/kg, for 20 min at a dose of 0.3 mmol/kg and for 40 min at a dose of 0.5 mmol/kg. No change in signal intensity or signal intensity ratio between normal and infarcted myocardium was observed in the control group during the same observation period. CONCLUSIONS: These results suggest that low doses of this agent, comparable to those of longitudinal relaxation time (T1)-enhancing agents, can delineate acutely infarcted myocardium. A dose of 0.3 mmol/kg of DyDTPA-BMA (S-043 Injection) provides reasonably persistent demarcation of acute myocardial infarction. Because this dose dramatically suppresses the NMR signal of normal myocardium, it shows the infarcted region as a region of high intensity (bright spot) on NMR images.

Animals↗
PubMed1992

Real-time dynamics of an extravascular magnetic resonance contrast medium in acutely infarcted myocardium using inversion recovery and gradient-recalled echo-planar imaging.

RATIONALE AND OBJECTIVES: The purposes of this study are to evaluate the first-pass profile of gadolinium-BOPTA/Dimeg (Gd-BOPTA/Dimeg) during its transit through hearts subjected to acute myocardial infarction, and to delineate these infarcted regions by the use of ultrafast magnetic resonance imaging (MRI). METHODS: Regional ischemia was induced in anesthetized rats by occluding the left coronary artery. Imaging parameters for single shot EPI included TE, 10 mseconds; AT, 33 mseconds; and 64 x 64-pixel matrix. Consecutive images were obtained every 1 to 2 seconds over a 30-second period. After approximately two images, Gd-BOPTA/Dimeg was injected intravenously (0.05 and 0.25 mmol/kg). RESULTS: Gd-BOPTA/Dimeg (0.05 mmol/kg), with inversion recovery EPI, produced a substantial increase in signal intensity of right and then left ventricular blood. Normally perfused myocardium also was enhanced, but not the acutely infarcted region. Clear delineation of the infarcted region as negatively enhanced "cold spots" persisted for at least 20 seconds. Gd-BOPTA/Dimeg (0.25 mmol/kg) with standard gradient-recalled EPI produced a different profile of signal intensity changes. Signal intensities of ventricular blood and normal myocardium were greatly reduced, leaving the infarcted zone as a positively enhanced "hot spot." Delineation of the infarcted region persisted for 6 to 8 seconds. The infarcted zone detected with MRI corresponded to that observed at autopsy. CONCLUSIONS: Regions of acute myocardial infarction can be detected as negatively enhanced "cold spots" or positively enhanced "hot spots" by studying the first-pass dynamics of Gd-BOPTA/Dimeg through hearts with regional ischemia by use of single shot EPI.

Animals↗
PubMed1991

Patterns of outcome in schizophrenia in Hong Kong.

A total of 153 schizophrenic subjects were included for outcome assessment in different aspects of their life functions. The same group of subjects was followed-up 1 year later to assess the consistency of their outcome pattern. A factor analysis on the outcome measures was conducted, and 5 independent factors were noted. Outcome on symptomatic control was most favourable but less consistent over time. Psychosocial deficits, on the other hand, were more enduring and noted in a significant proportion of the subjects.

Activities of Daily Living↗
PubMed1989

Diagnostic significance of interslice gap and imaging volume in body MR imaging.

Thin interslice gaps and large imaging volumes are detrimental to MR signal and contrast, especially when the body coil is used. To show the influence of these two factors on fat and water signal and contrast, we performed a series of in vitro experiments. A cylinder filled with water and another filled with oil were imaged transaxially (TR = 2000 msec; TE = 20 and 70 msec) with different interslice gaps (0-150% slice thickness). A series of images was obtained to cover a 40-cm imaging volume. Increasing interslice gap thickness increased water signal without affecting fat signal, resulting in a decrease in fat/water contrast on TE = 20 msec (less T1-weighting) and increasing contrast on TE = 70 msec (more T2-weighting). Contrast nearly doubled when the interslice gap was increased from 10% to 75%. As slices moved away from the central slice, fat and water signals decreased slowly to 12.5 cm off center. Signal loss was significant with offsets greater than 12.5 cm. These results emphasize that to obtain proper contrast on T2-weighted images, the optimal interslice gap should be used and the region of interest should be near the central slice. Otherwise, images should be interpreted with caution.

Body Water↗
PubMed1981

Tissue and species-specific effects of small molecular weight nuclear RNA's on transcription in isolated mammalian nuclei.

Small molecular weight nuclear RNA's (SnRNA's) purified from the 0.35 M NaCl extract of chromatin from human and monkey tissues have been found to stimulate transcription of chromatin in isolated nuclei in a tissue- and species-specific manner. While SnRNA from normal human cells (WI38 fibroblasts and placenta) stimulates homologous transcription to some extent, it has a greater activity on transcription of heterologous tissue of the same species and no activity on heterologous tissue of a different species (monkey kidney cells). Likewise SnRNA from monkey cells stimulates transcription of homologous chromatin but has no effect on human cells. Fractionation of the RNA's in polyacrylamide gradient slab gels revealed that in all cases the active RNA was 160-175 nucleotides in length. Our results are compatible with the hypothesis that the active RNA's are involved in the determination and maintenance of tissue differentiation by recognizing promoter or regulator sequences in the DNA and act at the level of the nucleosome to induce tissue-specific genes.

Animals↗
PubMed1980

Stimulation of transcription of chromatin by specific small nuclear RNAs.

Small molecular weight nuclear RNAs (SnRNA) purified from the chromatin of SV40-transformed W138 human fibroblasts have been found to stimulate transcription of chromatin in homologous isolated nuclei as well as in nuclei of untransformed human and monkey cells. Stimulation in normal cell nuclei involves an increase in both initiation sites and rate of elongation of RNA chains. Fractionation of the SnRNA in polyacrylamide gradient slab gels revealed that the "active" RNA was 160-175 nucleotides in length.

Cell Line↗
PubMedDate not supplied

Dual effects of gadodiamide injection in depiction of the region of myocardial ischemia.

The high safety index of the nonionic magnetic resonance (MR) contrast agent gadodiamide injection permits a wide dose range without induction of hemodynamic effects. The wide dose range might confer a diagnostic advantage by providing both T1 enhancing and magnetic susceptibility effects for demarcating pathologic regions. The dual utility of this contrast agent for T1 and T2 enhancement in creating differential contrast between normal and acutely ischemic myocardium was explored. MR imaging was initiated 20-40 minutes after occlusion of the left coronary artery in two groups of rats: Group 1 (n = 8) received 0.3 mmol/kg gadodiamide injection before and after acquisition of T1-weighted images; group 2 (n = 10) received 0.5 mmol/kg before and after acquisition of T2-weighted images. Postcontrast T1-weighted images showed clear delineation of the ischemic region as a relatively low-signal-intensity area for 15 minutes. On postcontrast T2-weighted images, the ischemic region appeared as a relatively high-signal-intensity area for 60 minutes. These effects were obtained with doses of gadodiamide injection that have safety indexes greater than those of gadopentetate dimeglumine.

Animals↗