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J W Chai

Publications and source records attributed to J W Chai.

13 recordsLinked to original sources
PubMed2005

Myocardial border detection by branch-and-bound dynamic programming in magnetic resonance images.

Dynamic programming (DP) is a mathematical technique for making optimal decisions on the sequencing of interrelated problems. It has been used widely to detect borders in magnetic resonance images (MRI). MRI is noninvasive and generates clear images; however, it is impractical for manual measurement of the huge number of images generated by dynamic organs such as those of the cardiovascular system. A fast and effective algorithm is essential for on-line implementation of MRI-based computer aided measurement and diagnosis. In this paper, a branch-and-bound dynamic programming technique is applied to detect the endocardial borders of the left ventricular. The proposed branch-and-bound method drastically reduces the computational time required in conventional exhaustive search methods. Statistical tests are conducted to verify the CPU time performance of the branch-and-bound technique in comparison to the conventional exhaustive search method.

Computers↗
PubMed2002

De-noising of left ventricular myocardial borders in magnetic resonance images.

In short axis left ventricular MR images, endocardial borders are the major parameters in evaluation of cardiovascular functions such as end diastolic volume, end systolic volume, and ejection fraction. Functional analysis captures the dynamic behavior of the cardiovascular system as revealed by the movement of the endocardial borders over time. Because of the huge number of MR images, an effective computerized tool is required for real time applications. One of the widely used automatic border detection algorithm-dynamic programming-generates zigzag borderlines, which lead to measurement errors. This paper surveys the performance of the wavelet adaptive filter, the snake, and the medial filter in smoothing over the zigzag borders generated by dynamic programming. Statistical analysis of two hundred and sixty four images from sixteen subjects show that all three algorithms can reduce the border line errors in terms of Hausdorff distance and border area error; however, only the wavelet adaptive filter is effective in providing the physiological measurements such as ejection fraction, end systolic volume and end diastolic volume.

Algorithms↗
PubMed2001

In vivo magnetic resonance (MR) study of fatty liver: importance of intracellular ultrastructural alteration for MR tissue parameters change.

Fatty liver is thought to have a shorter T1 relaxation time than normal liver tissue, due to the accumulation of triglyceride. Previous studies regarding T1 and T2 relaxation times, however, show widely different results. In order to elucidate the mechanism responsible for the changes and diversity of relaxation times in fatty liver, we created two animal models in 14 rabbits, one acute form (N = 6) and the other chronic form (N = 8). Four rabbits were taken as a control group. Tissue relaxation times and the magnetization transfer (MT) effect of the liver tissue in these two models were measured. The results were correlated with biochemical analysis of water and fat content and histological examination, including findings in light microscopy and electron microscopy. Although the fatty ratio in both forms of fatty liver was similar, their tissue relaxation rate and MT effect were significantly different. The acute form showed prolongation of both T1 and T2 relaxation times (512 +/- 51 msec vs. 710 +/- 95 msec and 39 +/- 1.8 msec vs. 48 +/- 3.7 msec, respectively) and a decrease of the MT effect (50 +/- 5.1% vs. 38 +/- 6.3%), compared to those of the control group and preinduction liver. The chronic form showed shorter T1 and T2 values (526 +/- 36 msec vs. 406 +/- 56 msec and 36 +/- 1.6 msec vs. 33 +/- 2.3 msec, respectively) and a stronger MT effect (21 +/- 0.9% vs. 26 +/- 2.3%). In acute form fatty liver, electron microscopic examination revealed dramatic subcellular changes, such as vesicular transformation, a markedly increased amount of smooth endoplasmic reticulum (SER), and disruption of the crista. These changes were not found in the chronic form fatty liver. From this study, we concluded that the ultrastructural alteration in the subcellular organelles of hepatocyte might play a crucial role for the chameleonic presentation of MR tissue parameters in fatty liver.

Animals↗
PubMed2000

Wavelet-based enhancement for detection of left ventricular myocardial boundaries in magnetic resonance images.

MRI is noninvasive and generates clear images, giving it great potential as a diagnostic instrument. However, current methods of image analysis are too time-consuming for dynamic systems such as the cardiovascular system. Since dynamic imagery generate a huge number of images, a computer aided machine vision diagnostic tool is essential for implementing MRI-based measurement. In this paper, a wavelet-based image technique is applied to enhance left ventricular endocardial and epicardial profiles as the preprocessor for a dynamic programming-based automatic border detection algorithm. Statistical tests are conducted to verify the performance of the enhancement technique by comparing borders manually drawn with 1. borders generated from the enhanced images, and 2. borders generated for the original images.

Algorithms↗
PubMed1999

Evaluation of liver diseases via MTC and contrast agent.

Our goal was to characterize pathological tissues of liver by magnetic resonance (MR)-related parameters such as T1 and magnetization transfer (MT) indices and to evaluate the clinical efficacy of MT contrast (C) in diagnosis of liver diseases via binomial pulsed saturation, with and without the administration of the paramagnetic agent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). Fifty-one cases of liver disorders were included in this study. Among the more important findings were the following: a) cirrhotic livers have significantly higher MT indices than normal liver, while hepatoma, metastatic tumor and fatty liver have sub-normal MT indices; b) in general, although with notable exceptions, images with MT give significantly better contrast indices than control images; and c) MT with Gd-DTPA rarely fares any better than the MT technique alone, although again with notable exceptions. MTC is a potentially powerful technique for diagnosing liver diseases, provided it can be optimally exploited for each individual disease type.

Carcinoma, Hepatocellular↗
PubMed1999

Proximal arterioportal shunting associated with hepatocellular carcinoma: features revealed by dynamic helical CT.

OBJECTIVE: This study investigated the findings revealed by dynamic helical CT of proximal arterioportal shunting associated with hepatocellular carcinoma. We also evaluated the diagnostic capability of this imaging technique to reveal the mass in patients with hepatocellular carcinoma. CONCLUSION: On dynamic helical CT, proximal arterioportal shunting altered liver perfusion and tumor enhancement. Heterogeneous enhancement of liver parenchyma and decreased enhancement of hepatomas diminished diagnostic capability on the arterial dominant phase image. However, with the addition of imaging in the arterial portal phase, lesion conspicuity improved.

Carcinoma, Hepatocellular↗
PubMed1997

Convergent flow phenomenon mimics the appearance of venous thrombosis in gradient-echo images with or without the presence of a contrast agent.

We have observed signal voids at the junction of the renal vein and the inferior vena cava in the Spoiled Grass images. They mimicked the magnetic resonance appearance of an intraluminal thrombus with and without the presence of a contrast agent. The patency of the vessels was unveiled by fast Spoiled Grass sequence with reduced echo time as well as by Doppler ultrasound. Phantom studies revealed patterns of counterrotating vortices at the confluence. The cause of this image artifact was subsequently deduced as the intravoxel spin phase dispersion arising from the impinging flows of the renal vein and inferior vena cava. It is concluded that in regions where complex flow patterns reside, fast imaging sequences that reduce spin phase variations should always be conducted in addition to other routine sequences to exclude uncertainties in image interpretation.

Aged↗
PubMed1997

MRI assessment of regional heart wall motion in the longitudinal axis sections of left ventricle by spatial modulation of magnetization.

BACKGROUND: The goal of the study is to evaluate the spatial modulation of magnetization (SPAMM) technique as a means of assessing cardiac wall motion of the left ventricle, which has been shown by clinical trials to be a better tool for depicting regional myocardial motion than the traditional noninvasive and invasive methods. METHODS: Cardiac magnetic resonance (MR) imaging, using SPAMM, was performed for nine normal volunteers. The regional myocardial strains observed in the long axis views of left ventricle (LV) were quantitatively and qualitatively analyzed in two different directions. RESULTS: The results indicate that the myocardial strains observed in the lateral free wall (LW), posteriolateral free wall (PLW) and posterior free wall (PW) are significantly greater than those in the inter-ventricular septum (SP), anterior septum (AS) and anterior free wall (AW), respectively. It was also found that the greatest strains occurred in the apical halves of LW and in the basal halves of PLW and PW in each of the long axis views, respectively. In general, the circumferential strain was found to be greater in the basal halves than in the apical halves of the LV. CONCLUSIONS: The SPAMM cardiac imaging of the long-axis section of LV is a useful tool for assessment of regional ventricular function and is invaluable for probing deeper into the intricacies of the heart wall motion in long-axis views.

Adult↗
PubMed1996

Estimation of in vivo proton intrinsic and cross-relaxation rate in human brain.

By using on-resonance binomial pulse saturation of the immobile component in tissues and by monitoring the time development of the longitudinal decay of the free water magnetization, it has been shown that it is possible to estimate physical model parameters not directly measurable by conventional methods. Since pulsed saturation is easy and safe to implement in a clinical MRI machine, it should be possible to estimate these parameters in vivo by the same means. In this article, we report the results of such estimates of the parameters of the principal components (gray and white matter) in brains of two normal volunteers.

Adult↗
PubMed1993

[The chemical shift imaging of liver].

Tissue characterization of different pathologies of the liver can be achieved by differences of relaxation time on changing of pulse sequences in magnetic resonance imaging (MRI). The usefulness of MRI for detection of liver disease is limited when the pathological change is subtle. Chemical shift is a fundamental characteristics in nuclear magnetic resonance (NMR). Chemical shift imaging (CSI) in MRI is based on the different Larmor frequency of proton in water and fat; and therefore it was able to enhance the effectiveness of pathology. For this study, Dixon's method was used to detect liver pathologies and compare its detectability with conventional pulse sequences. Forty cases were enrolled for study; they included 5 health volunteers, 15 hepatomas, 1 cholangiocarcinoma, 5 metastatic hepatic tumors and 14 fatty livers. In hepatic tumors, the lesion number, tumor margination and lesion-to-liver contrast in images were read and analyzed. Signal intensities, signal-to-noise ratio and contrast-to-noise ratio were compared, after measurement, from stored data. In fatty livers, the relative change of signal intensities in different areas of the liver in in-phase and out-phase images were compared with the back muscle and spleen to find where the fatty metamorphosis happened. CSI in spin echo or gradient echo pulse sequences was found to be adequate and valuable for detecting fatty liver, when compared with conventional MRI. CSI not only identified the extension of disease itself but also characterized the fatty change in liver parenchyma. Though CSI affords no further advantages than conventional pulse sequences for detection of hepatic tumors, occasionally, when the image quality of the conventional pulse sequences is not satisfactory or equivocal in lesion detection, the use of CSI might be attempted.

Fatty Liver↗
PubMed1990

[Magnetic resonance imaging of ovarian cystic teratoma].

Two patients with ovarian cystic teratoma were imaged using real-time ultrasound and 1.0-T magnetic resonance imaging (MRI) devices. The ultrasound appearance of cystic teratoma varies with the internal contents. If bone or teeth is present, highly echogenic foci with posterior shadow will be identified. The cysts may contain solid areas, septa and fluid-fluid levels. The dermoid cyst filled with fat showing characteristic echogenic appearance might confused with the pelvic fact tissue. MRI is well suited to the evaluation of pelvic disorders. The T1 and T2 relaxation times in different tissues might present with different signal intensities by changing the pulse sequences. Fat, with its relatively short T1 and long T2 times, appears bright on the T1-weighted images (short TE and TR) and T2-weighted images (long TE and TR). However, old hemorrhage has the MRI characteristics of short T1 and long T2 times as fat. The inversion recovery sequence with short inversion time (STIR) will suppress signal from fat tissue and this is of particular value in differentiating dermoid from hemorrhagic cyst. MRI is quite efficient in cases where ultrasound study is equivocal or difficult in the technique.

Adult↗
PubMedDate not supplied

Magnetization transfer contrast imaging of liver cirrhosis.

BACKGROUND/AIMS: To test the feasibility of magnetization transfer contrast (MTC) imaging in the evaluation of liver cirrhosis. METHODOLOGY: Three normal volunteers and 22 cirrhotic liver patients (13 of them harbored hepatoma) were prospectively studied with on-resonance binomial pulsed MTC imaging using a 1.0 Tesla MR scanner. Both MTC and non-MTC images were acquired. The magnetization transfer (MT) effect (defined as: 1-signal intensity of MTC/signal intensity of non-MTC), was used as an indicator and was correlated with different disease status. Lesion-to-liver contrast of non-MTC versus MTC imaging was also compared. RESULTS: Chronic hepatitis and early fibrosis had a MT effect similar to that of the normal group. Frank cirrhosis had the strongest MT effect. Cirrhosis, when infiltrated by diffuse hepatoma, showed a significantly weaker MT effect than that of the normal group (p<0.05), early cirrhosis (P<0.005), and frank cirrhosis (p<0.05). Overall, the MT effects in these 22 patients were widely variable. There was no significant improvement in lesion contrast of MTC imaging when compared to that of non-MTC imaging due to complex signal attenuation behavior of either the background liver tissue or the tumor itself. CONCLUSIONS: The complex pathological change of the cirrhotic liver tissue may account for the wide variation of the MT effect and the compromised lesion contrast in cirrhotic patients. Caution should be taken when cirrhotic tissue has an unusually weak MT effect. Then, the possibility of a mixed disease process such as fatty metamorphosis or diffuse hepatoma should be highly suspected. Our experience shows that MTC imaging plays a potential role in the evaluation of the multi-facets of cirrhotic tissue change.

Adult↗