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Biomedical subjects

Wen-Yih Isaac Tseng

Publications and source records attributed to Wen-Yih Isaac Tseng.

10 recordsLinked to original sources
PubMed2006

Quantification of the pulse wave velocity of the descending aorta using axial velocity profiles from phase-contrast magnetic resonance imaging.

The pulse wave velocity (PWV) of aortic blood flow is considered a surrogate for aortic compliance. A new method using phase-contrast (PC)-MRI is presented whereby the spatial and temporal profiles of axial velocity along the descending aorta can be analyzed. Seventeen young healthy volunteers (the YH group), six older healthy volunteers (the OH group), and six patients with coronary artery disease (the CAD group) were studied. PC-MRI covering the whole descending aorta was acquired, with velocity gradients encoding the in-plane velocity. From the corrected axial flow velocity profiles, PWV was determined from the slope of an intersecting line between the presystolic and early systolic phases. Furthermore, the aortic elastic modulus (Ep) was derived from the ratio of the brachial pulse pressure to the strain of the aortic diameter. The PWV increased from YH to OH to CAD (541 +/- 94, 808 +/- 184, 1121 +/- 218 cm/s, respectively; P = 0.015 between YH and OH; P = 0.023 between OH and CAD). There was a high correlation between PWV and Ep (r = 0.861, P < 0.001). Multivariate analysis showed that age and CAD were independent risk factors for an increase in the PWV. Compared to existing methods, our method requires fewer assumptions and provides a more intuitive and objective way to estimate the PWV.

Adult↗
PubMed2005

Mitral tetrahedron as a geometrical surrogate for chronic ischemic mitral regurgitation.

The present study tests the hypothesis that a mitral tetrahedron (MT) is a useful geometrical surrogate for assessment of chronic ischemic mitral regurgitation (CIMR). Fifty-eight subjects were divided into three groups on the basis of left ventricular ejection fraction (LVEF) and the presence or absence of CIMR: LVEF > or =0.5 and negative CIMR (group 1, n = 28), LVEF <0.5 and negative CIMR (group 2, n = 12), and LVEF <0.5 and positive CIMR (group 3, n = 18). MT was defined by its four vertices at the anterior annulus, posterior annulus, and medial and lateral papillary muscle roots, determined by MRI at peak systole. The results showed no clear cutoff values of MT parameters between groups 2 and 1. In contrast, all MT indexes were significantly different between groups 3 and 2 (P < 0.05), and significant cutoff values differentiated the two groups. A scoring system employing parameters of the whole MT confirmed the absence of CIMR with total edge length index <268 mm/BSA(1/3), total surface area index <2,528 mm(2)/BSA(2/3), and volume index <5,089 mm(3)/BSA (where BSA is body surface area). The sensitivity, specificity, and positive and negative predictive values were 1.00. This preliminary study demonstrates that MT might serve as a good geometrical surrogate for assessing CIMR. The derived geometrical criteria of MT may be useful in surgical correction of CIMR.

Adult↗
PubMed2005

Mapping complex tissue architecture with diffusion spectrum magnetic resonance imaging.

Methods are presented to map complex fiber architectures in tissues by imaging the 3D spectra of tissue water diffusion with MR. First, theoretical considerations show why and under what conditions diffusion contrast is positive. Using this result, spin displacement spectra that are conventionally phase-encoded can be accurately reconstructed by a Fourier transform of the measured signal's modulus. Second, studies of in vitro and in vivo samples demonstrate correspondence between the orientational maxima of the diffusion spectrum and those of the fiber orientation density at each location. In specimens with complex muscular tissue, such as the tongue, diffusion spectrum images show characteristic local heterogeneities of fiber architectures, including angular dispersion and intersection. Cerebral diffusion spectra acquired in normal human subjects resolve known white matter tracts and tract intersections. Finally, the relation between the presented model-free imaging technique and other available diffusion MRI schemes is discussed.

Algorithms↗
PubMed2004

Effect of calcium channel blockers on vertebral bone marrow perfusion of the lumbar spine.

PURPOSE: To investigate the effect of calcium channel blockers on blood perfusion of vertebral bone marrow in the lumbar spine. MATERIALS AND METHODS: Sixteen healthy volunteers (eight men and eight women) underwent dynamic contrast material-enhanced magnetic resonance (MR) imaging of the lumbar spine. One hundred twenty minutes after the first MR examination, each subject ingested 10 mg sublingual nifedipine before undergoing a second MR examination 20-25 minutes later. Semiquantitative (peak enhancement ratio and enhancement slope) and quantitative (amplitude and rate constant of the exchange [K(out)]) parameters were analyzed with the time-intensity curve. Data obtained before and after administration of nifedipine were compared. The Wilcoxon signed rank test and Spearman rank correlation test were used. RESULTS: Median peak enhancement ratio of vertebral bodies decreased from 0.60 (mean +/- SD, 0.68 +/- 0.29) to 0.51 (mean, 0.56 +/- 0.24) after administration of nifedipine. Median and mean decreases were 0.11 and 0.12 +/- 0.15, respectively, and the percentage difference was 17% (P =.005). A P value of less than.05 was considered to indicate a statistically significant difference. Median enhancement slope changed from 0.45 (mean, 0.45 +/- 0.13) to 0.41 (mean, 0.40 +/- 0.24). Median and mean changes were 0.05 and 0.04 +/- 0.23, respectively, and the percentage difference was 9% (P =.334). Median amplitude changed from 0.059 (mean, 0.059 +/- 0.028) to 0.045 (mean, 0.048 +/- 0.023). Median and mean changes were 0.008 and 0.011 +/- 0.025, respectively, and the percentage difference was 18% (P =.072). Median K(out) changed from 0.068 (mean, 0.063 +/- 0.018) to 0.067 (mean, 0.066 +/- 0.028). Median and mean changes were 0.011 and 0.004 +/- 0.028, respectively (P =.404). Nifedipine affected peak enhancement ratio significantly but did not affect enhancement slope, amplitude, or K(out). Data before and after administration of nifedipine showed no differences between men and women. Spearman rank correlation coefficients suggest no significance between the differences in heart rate and blood pressure and the differences in peak enhancement ratio, enhancement slope, amplitude, or K(out). CONCLUSION: After sublingual administration of nifedipine, the peak enhancement ratio of vertebral bone marrow decreased.

Adult↗
PubMed2004

Functional mitral regurgitation in chronic ischemic coronary artery disease: analysis of geometric alterations of mitral apparatus with magnetic resonance imaging.

BACKGROUND: Patients with chronic coronary artery disease have double the mortality rate if the condition is combined with functional mitral regurgitation. An understanding based on geometric alterations of the mitral apparatus in functional mitral regurgitation is desirable. METHODS: Twenty-nine subjects were enrolled in the study, including 9 healthy volunteers (control group), 12 patients with chronic coronary artery disease without functional mitral regurgitation (CAD group), and 8 patients with chronic coronary artery disease with functional mitral regurgitation (CAD+FMR group). Cine magnetic resonance imaging was performed to acquire multiple short-axis cine images from base to apex. Left ventricular end-systolic volume, left ventricular ejection fraction, mitral area, and vertices of the mitral tetrahedron, defined by medial and lateral papillary muscle roots and anterior and posterior mitral annulus, were determined from reconstructed images at end-systole. Anterior-posterior annular distance, interpapillary distance, and annular-papillary distance (the distance from the anterior or posterior mitral annulus to the medial or lateral papillary muscle roots) were calculated. RESULTS: Left ventricular end-systolic volume was inversely associated with left ventricular ejection fraction (R(2) = 0.778). Left ventricular end-systolic volume was highly associated with distances related to ventricular geometry (R(2) = 0.742 for interpapillary distance, 0.792 for the distance from the anterior mitral annulus to the medial papillary muscle root, and 0.769 for distance from the anterior mitral annulus to the lateral papillary muscle root) but was moderately associated with distances related to annular geometry (R(2) = 0.458 for anterior-posterior annular distance and 0.594 for mitral area, respectively). Moreover, interpapillary distance of greater than 32 mm and distance from the anterior mitral annulus to the medial papillary muscle root of greater than 64 mm readily distinguished the CAD+FMR group from the other groups. CONCLUSION: In patients with coronary artery disease, an increase in left ventricular end-systolic volume is associated with inadequate approximation of the mitral tetrahedron during systole, which consequently leads to functional mitral regurgitation. Our study suggests that interpapillary distance and distance from the anterior mitral annulus to the medial papillary muscle root are sensitive to the increase in left ventricular end-systolic volume and reliably indicate the presence of functional mitral regurgitation.

Case-Control Studies↗
PubMed2004

Diffusion tensor images in children with early-treated, chronic, malignant phenylketonuric: correlation with intelligence assessment.

BACKGROUND AND PURPOSE: Diffusion tensor (DT) images can provide information about the nature of white matter changes, including axonal loss and demyelination. We applied DT imaging to verify white matter changes in patients with malignant phenylketonuria (PKU) and to correlate the findings with clinical intelligence quotients (IQs). METHODS: We compared DT images with T2-weighted images in 12 patients with early-treated, chronic, stable malignant PKU and 12 age-matched control subjects. DT parameters included first, second, and third eigenvalues (EV1-3), apparent diffusion coefficients (ADCs), and fractional anisotropy (FA). Regions of interest were placed the frontoparietal, parieto-occipital, frontal and central white matter and in the anterior and posterior corpus callosum. Eight patients older than 3 years underwent IQ assessment including verbal, performance, and full-scale IQ tests. RESULTS: In the eight patients older than 3 years, no definite abnormal signal intensity changes were found on T2-weighted images. EV2, EV3, and FA of the parieto-occipital white matter were significantly different in patients and control subjects older than 3 years. EV3 and ADC of the parieto-occipital white matter were significantly and negatively correlated with verbal IQ (r = -0.79, P = .04) and performance IQ (r = -0.93, P = .03). FA of the parieto-occipital central white matter was positively correlated with verbal IQ (r = 0.75, P = .05). CONCLUSION: Though treated early, patients with chronic, stable malignant PKU had abnormal DT findings in the parieto-occipital central white matter. EV2, EV3, and FA maps are potential tools for demonstrating brain changes due to malignant PKU.

5-Hydroxytryptophan↗
PubMed2003

Validation of diffusion spectrum magnetic resonance imaging with manganese-enhanced rat optic tracts and ex vivo phantoms.

Diffusion spectrum imaging (DSI) has been demonstrated to resolve crossing axonal fibers by mapping the probability density function of water molecules diffusion at each voxel. However, the accuracy of DSI in defining individual fiber orientation and the validity of Fourier relation under finite gradient pulse widths are not assessed yet. We developed an ex vivo and an in vivo model to evaluate the error of DSI with gradient pulse widths being relatively short and long, respectively. The ex vivo model was a phantom comprising sheets of parallel capillaries filled with water. Sheets were stacked on each other with capillaries crossed at 45 degrees or 90 degrees. High-resolution T2-weighted images (T2WI) of the phantom served as a reference for the orientation of intersecting capillaries. In the in vivo model, manganese ions were infused into rats' optic tracts. The optic tracts were enhanced on T1-weighted images (T1WI) and served as a reference for the tract orientation. By comparing DSI with T2WI, the deviation angles between the primary orientation of diffusion spectrum and the 90 degrees and 45 degrees phantoms were 1.19 degrees +/- 4.82 degrees and -0.71 degrees +/- 4.91 degrees, respectively. By comparing DSI with the T1WI of rat optic tracts, the deviation angle between primary orientation of diffusion spectrum and optic tracts was -0.41 degrees +/- 6.18 degrees. In addition, two sequences of DSI using short and long gradient pulses were performed in a rat brain. The bias of the primary orientation between these two sequences was approximately 10 degrees. In conclusion, DSI can resolve crossing fiber orientation accurately. The effect of finite gradient pulse widths on the primary orientation is not critical.

Algorithms↗
PubMed2002

Normal systolic and diastolic functions of the left ventricle and left atrium by cine magnetic resonance imaging.

Volume and phase characteristics of the left ventricle (LV) and left atrium (LA) were assessed in 31 healthy Asian adults (19 males and 12 females) using cine magnetic resonance imaging (MRI) and an automated boundary detection algorithm. Volume indexes of the LV and LA were smaller than published results obtained mostly from Westerners. Other than LV mass index and percent emptying of the LA, there was no gender difference in all LV/LA indexes. In associating LV/LA functions with the body size and heart rate (HR), we found that LV mass and the minimum LA volume correlated strongly with the body surface area, the maximum LA volume and the reservoir volume correlated strongly with the body weight, and the time to LV peak-filling rate (LVPFRt) and the time to LA peak-emptying rate (LAPERt) correlated strongly with the HR. In associating LV with LA functions, we found that LA conduit volume contributed more than 50% of the LV stroke volume, and correlated with both systolic and diastolic functions of the LV. Moreover, LVPFRt and LAPERt were virtually identical, indicating a mechanical coupling between LV and LA during diastole. In conclusion, using time-resolved, three-dimensional volume data obtained from cine MRI, we have established normative values of LV and LA functions and their functional relationships in healthy Asian adults. The imaging acquisition protocol, data analysis algorithms, and the established normative values provide the basis for the study of left heart function in patients.

Adult↗
PubMedDate not supplied

Diffusion-weighted images in children with meningoencephalitis.

PURPOSE: The objective of the study was to evaluate the maps of apparent diffusion coefficients (ADCs) and diffusion-weighted (DW) images in demonstrating meningoencephalitic lesions in children. MATERIALS AND METHODS: Between May 1998 and May 2000, 18 infants and children (4.5-190 months old) suffering from meningoencephalitis were included in the study. The diagnoses were bacterial meningoencephalitis in 8 and aseptic or viral in 10 patients. All 18 patients had brain MRI examinations. In the axial plane, three pulse sequences were performed on all patients: (1) FSE T2W images; (2) fast FLAIR images; (3) single-shot echoplanar DW images were acquired. Another 18 patients from the control group also received DW image examination. ADCs were computed for all regions on each DW image. RESULTS: The absolute values of CNRs of lesions on T2W (7.27+/-5.51), FLAIR (5.56+/-5.03) and DW (13.36+/-16.64) images were significantly greater than those on ADC maps (0.42+/-0.30) in the study group of patients (P<.01). In addition, absolute CNRs on DW images were significantly greater than on T2W and FLAIR images (P<.01). However, lesions on ADC maps in the study group have significantly greater CNRs than in the control group (0.13+/-0.12) (P<.01). CNRs on initial DW images from patients with atrophy or swelling of meningoencephalitic lesions were significantly different from the CNRs of those patients without significant changes in meningoencephalitic lesions (P=.02<.05). CONCLUSION: The DW image is a sensitive tool for detecting meningoencephalitic lesions and is better than FSE T2W and fast FLAIR images in CNRs. Diffusion MR techniques provides new ways to possibly predict the outcome of intracranial infectious diseases in children.

Brain Mapping↗