Biomedical subjects

M L Chuang

Publications and source records attributed to M L Chuang.

25 records · Page 2Linked to original sources

PubMed1997

Prospective adaptive navigator correction for breath-hold MR coronary angiography.

Current MR coronary angiography (MRCA) methods use breath-holding to minimize respiratory motion. A major limitation to this technique is misregistration between imaging slices due to breath-hold variability. Prospective adaptive correction of image location using real-time navigator measurement of diaphragm position is a potential method for improving slice registration in breath-hold MRCA. Ten subjects underwent MRCA using an ECG-gated, fat-suppressed, segmented k-space, gradient-echo sequence. Transverse and coronal images were acquired using standard breath-holding with and without prospective navigator correction. Breath-hold MRCA with prospective navigator correction resulted in a 47% reduction in craniocaudal slice registration error compared to standard breath-holding (0.9 +/- 0.2 mm versus 1.7 +/- 0.4 mm, P = 0.04). Prospective adaptive navigator correction of image location significantly improves slice registration for breath-hold MRCA and is a promising motion correction technique for cardiac MR.

Adult↗

PubMed1997

Prospective navigator correction of image position for coronary MR angiography.

PURPOSE: To determine the potential benefit of prospective navigator correction of image position for coronary magnetic resonance (MR) angiography. MATERIALS AND METHODS: Two-dimensional MR angiograms were obtained with free breathing in 12 adult subjects. Navigator gating was used with and without prospective correction and with gating windows set at 3, 5, and 7 mm. MR angiograms were compared with those obtained with conventional, end-expiratory breath holding. RESULTS: Navigator gating with correction resulted in image quality equivalent to that obtained with breath holding, even with the 7-mm gating window. In contrast, navigator gating without correction allowed only maintenance of image quality similar to that obtained with breath holding for the 3- and 5-mm windows and resulted in decreased image quality with the 7-mm window (P < .05). Use of navigator gating with correction and the 7-mm window resulted in a 28% decrease in imaging time compared with breath holding and a 33% decrease compared with the 3-mm gating window (P < .05 for both comparisons). CONCLUSION: Prospective, adaptive navigator correction of image position for free-breathing coronary MR angiography is a promising, novel approach to compensate for respiratory motion.

Adult↗

PubMed1997

Bilateral diaphragmatic paralysis--a rare cause of acute respiratory failure managed with nasal mask bilevel positive airway pressure (BiPAP) ventilation.

A 68 yr old woman presented with acute respiratory failure. She was suspected of having a phrenic-diaphragmatic impairment, without evidence of an intrinsic lung disease or generalized neuromuscular disorder, after 3 weeks of prolonged mechanical ventilation. A series of studies, including fluoroscopy, phrenic nerve stimulation test and diaphragmatic electromyography, was performed before the diagnosis of bilateral diaphragmatic paralysis (BDP) was confirmed. The patient was successfully weaned from the conventional mechanical ventilator, and was placed on nasal mask bi-level positive airway pressure (BiPAP) ventilation. A high degree of clinical suspicion of bilateral diaphragmatic paralysis should always be raised in patients suffering respiratory failure without definite predisposing factors. Weaning with noninvasive nasal mask ventilation should be tried first instead of direct tracheostomy.

Acute Disease↗

PubMed1997

Comparison of respiratory suppression methods and navigator locations for MR coronary angiography.

OBJECTIVE: Currently, breath-holding during MR coronary angiography is used to minimize respiratory motion. This technique requires patient cooperation and is associated with slice registration errors. The goal of this study was to evaluate alternative non-breath-hold techniques for MR coronary angiography during free breathing. SUBJECTS AND METHODS: Subjects underwent MR coronary angiography using an ECG-gated, fat-suppressed, segmented K-space, gradient-echo sequence. Images were obtained during free breathing using both real-time navigator gating and respiratory bellows gating. These were compared with images obtained during conventional breath-holding. The optimal navigator location (diaphragmatic or cardiac) was also studied. Image quality, registration error, and scan time were measured for all scans. RESULTS: Navigator gating for MR coronary angiography during free breathing resulted in image quality equivalent to that obtained during breath-holding and was superior to that obtained with respiratory bellows gating (p < .04). Also, navigator gating reduced registration errors by 75% compared with breath-holding (p < .01) and did not increase scan time. No significant differences in the parameters measured were observed among the different navigator locations. CONCLUSION: Real-time navigator gating for MR coronary angiography during free breathing achieved image quality and scan time equivalent to breath-holding. Navigator gating also significantly reduced registration error. Compared with breath-holding and respiratory bellows gating, navigator gating during free breathing is a more optimal approach for suppression of respiratory motion during MR coronary angiography.

Adult↗

PubMed1995

Magnetic resonance mapping demonstrates benefits of VEGF-induced myocardial angiogenesis.

Coronary occlusive disease is the leading cause of death in industrial nations and affects one in four adults. Although heart attacks are caused by occlusion of a coronary artery, some patients have occlusions without infarction because they have sufficient collateral vessels providing an alternate pathway for blood supply. Vascular endothelial growth factor (VEGF) is an angiogenic peptide that can stimulate collateral vessel development in the ischaemic myocardium. We used magnetic resonance imaging (MRI) and image processing to identify and quantify non-invasively the benefits related to VEGF infusion on collateral development in the heart. This was accomplished as a placebo-controlled study in the porcine model of chronic ischaemia that most closely mimics the human pathophysiology of progressive coronary occlusion. Image series converted to a space-time map demonstrated that with treatment the ischaemic zone was smaller and the contrast arrival delay was less, which resulted in better ejection fraction and regional wall thickening. These findings demonstrate in a manner applicable to humans, that VEGF improves collateral blood supply, resulting in improved cardiac global and regional function after and in spite of coronary artery occlusion.

Angiogenesis Inducing Agents↗

PubMed1993

Early chylopneumothorax in a patient with pulmonary lymphangioleiomyomatosis.

A 50-year-old woman was admitted with the complaint of cough and dyspnea on exertion for the previous two months. A radiograph of the chest showed a right-sided hydropneumothorax, which was proven to be a chylous effusion by lipoprotein electrophoresis and was very refractory to tetracycline-pleurodesis. The chylopneumothorax was cured by ligation of the thoracic duct and surgical pleurodesis. After an open lung biopsy, lymphangioleiomyomatosis (LAM) was diagnosed histopathologically with smooth muscle nodules scattered throughout the lungs, obstructing the small airways, venules and lymphatics. An immunohistochemistry study using the avidin biotin complex method with monoclonal antibodies for actin and desmin showed the small nodules to be of muscle origin. During the past two years, the patient has remained stable both in respiratory status and roentgenographically without hormonal manipulation or oophorectomy. We present this case to illustrate the heterogeneous nature of this condition. While our patient's initial presentation was acute and associated with chylothorax, her postoperative course has shown no progression despite withholding of hormonal therapy.

Biopsy↗

PubMedDate not supplied

Adaptive correction of imaging plane position in segmented k-space cine cardiac MRI.

Variability among breath-holds frequently produces registration errors, a situation that may contribute to reproducibility error in anatomic indices. A navigator-echo-based method for real-time prospective correction of imaging slice level was applied to breath-hold cine cardiac imaging of 13 subjects. Repeat acquisitions with correction in the cardiac short-axis orientation showed significantly improved reproducibility in fractional area change and endocardial centroid location as compared with conventional noncorrected methods.

Adult↗