Biomedical subjects

Yongmin Chang

Publications and source records attributed to Yongmin Chang.

9 recordsLinked to original sources

PubMed2005

Magnetic resonance voiding cystography in the diagnosis of vesicoureteral reflux: comparative study with voiding cystourethrography.

PURPOSE: To evaluate the feasibility of magnetic resonance voiding cystography (MRVC) compared with voiding cystourethrography (VCUG) for detecting and grading vesicoureteral reflux (VUR). MATERIALS AND METHODS: MRVC was performed upon 20 children referred for investigation of reflux. Either coronal T1-weighted spin-echo (SE) or gradient-echo (GE) (fast multiplanar spoiled gradient-echo (FMPSPGR) or turbo fast low-angle-shot (FLASH)) images were obtained before and after transurethral administration of gadolinium solution, and immediately after voiding. The findings of MRVC were compared with those of VCUG and technetium-99m ((99m)Tc) dimercaptosuccinic acid (DMSA) single-photon emission computed tomography (SPECT) performed within 6 months of MRVC. RESULTS: VUR was detected in 23 ureterorenal units (16 VURs by both methods, 5 VURs by VCUG, and 2 VURs by MRVC). With VCUG as the standard of reference, the sensitivity of MRVC was 76.2%; the specificity, 90.0%; the positive predictive value, 88.9%; and the negative predictive value, 78.3%. There was concordance between two methods regarding the grade of reflux in all 16 ureterorenal units with VUR detected by both methods. Of 40 kidneys, MRVC detected findings of renal damage or reflux nephropathy in 13 kidneys, and (99m)Tc DMSA renal SPECT detected findings of reflux nephropathy in 17 kidneys. CONCLUSION: Although MRVC is shown to have less sensitivity for VUR than VCUG, MRVC may represent a method of choice offering a safer nonradiation test that can additionally evaluate the kidneys for changes related to reflux nephropathy.

Adolescent↗

PubMed2004

Auditory neural pathway evaluation on sensorineural hearing loss using diffusion tensor imaging.

Diffusion tensor imaging is a new in vivo tool not only for the assessment of white matter structural integrity but also for diagnosis and assessment of disease conditions which disturb tissue structural coherence. In this study, we investigated the integrity of auditory pathway in patients of sensorineural hearing loss by means of fractional anisotropy of water diffusion to see any subtle changes of auditory pathways resulting from sensorineural hearing loss. In addition, this study suggests that the diffusion anisotropy measured by diffusion tensor imaging is highly sensitive to otherwise subtle disease processes not normally seen with conventional magnetic resonance imaging or computed tomography contrast.

Adolescent↗

PubMed2004

The predictive value of cortical activation by passive movement for motor recovery in stroke patients.

PURPOSE: Contralateral primary sensori-motor cortex (SM1) activation by passive movement was investigated by functional MRI (fMRI) at the early stage of stroke, to determine whether SM1 activation can be used to predict the degree of motor recovery of the hemiplegic hand. METHODS: We studied 17 stroke patients who showed complete paralysis of a hemiplegic hand at onset. The motor function of the hemiplegic hand was assessed on 4 separate occasions (at onset, at fMRI evaluation (performed < 4 weeks after onset), and 3 and 6 months after onset). Significant motor recovery was defined as recovery of the affected hand to the extent of it being able to prehend an object against gravity at least at 6 months after onset. RESULTS: The patients having an activated contralateral SM1 showed better motor recovery than those who did not. Only a fourth of the patients with an activated contralateral SM1 experienced a significant motor recovery, whereas none of the patients with an inactivated SM1 showed an improvement 6 months after onset, however, the incidence of significant motor recovery was not significantly difference between the two groups. CONCLUSION: It appears that contralateral SM1 activation by passive movement in the early stage of stroke has a low predictive value for the motor recovery of the hemiplegic hand, because the activation of the contralateral SM1 by passive movement appears to be mediated by somatosensory input to the cortex from the thalamus rather than from the motor pathway.

Adult↗

PubMed2003

Cortical reorganization associated with motor recovery in hemiparetic stroke patients.

We investigated the cortical activation changes associated with motor recovery in eight hemiparetic patients with cerebral infarct by using functional MRI (fMRI), which was performed at 1.5 T in parallel with finger flexion-extension movements at a fixed rate. The first fMRI was performed when the patient was able to flex and extend fingers of the affected hand against gravity, and the second fMRI was done when the motor function of the affected hand showed definite improvement. The main cortical activation changes that occurred with motor recovery were an increment in the affected and a decrement in the unaffected primary sensori-motor cortex (SMC) activities. In conclusion, it seems that cortical reorganization occurred in parallel with motor recovery in hemiparetic patients with cerebral infarct.

Adult↗

PubMed2003

Bilateral primary sensori-motor cortex activation of post-stroke mirror movements: an fMRI study.

This fMRI study was undertaken to test whether the pathophysiological mechanism of mirror movements in hemiparetic stroke patients involves activation of the unaffected motor cortex. We studied 16 control subjects and 51 stroke patients. fMRI was performed at 1.5 T using a finger flexion-extension movement paradigm. The incidence of bilateral primary sensorimotor cortex activation was significantly increased during movements of the affected hand of stroke patients who showed mirror movements. Moreover, the incidence of bilateral primary sensorimotor cortex activation increased with the severity of mirror movements and primary sensorimotor cortex was activated bilaterally in all patients who showed sustained mirror movements. We conclude that the motor cortex activation on the non-stroke side is associated with mirror movements and is correlated with the severity of mirror movements. It seems that the pathophysiological mechanism of sustained mirror movements in stroke patients involves the unaffected motor cortex.

Adult↗

PubMed2003

Functional magnetic resonance image finding of cortical activation by neuromuscular electrical stimulation on wrist extensor muscles.

OBJECTIVE: To investigate the effects that neuromuscular electrical stimulation on the wrist extensor muscles have on the cerebral cortex. DESIGN: A functional magnetic resonance imaging study was performed on eight normal volunteers. The activation task was the maximum wrist extension by neuromuscular electrical stimulation, applied through a two-channel electrical stimulator. Monophasic square-wave pulses were used. The activation maps were generated by the threshold test maps. The level of primary motor cortex and primary sensory cortex activations was estimated. RESULTS: Among the eight subjects, seven showed significant activation on contralateral primary sensorimotor cortex by neuromuscular electrical stimulation on the wrist extensor muscles. In these seven subjects, additional bilateral or contralateral supplementary motor area activations were also observed. The number of activated pixels on the primary sensory cortex was slightly greater than that on the primary motor cortex. CONCLUSION: Neuromuscular electrical stimulation, when applied to the peripheral muscles, seems to have a direct effect on the cerebral cortex.

Adult↗

PubMed2003

Diffusion tensor magnetic resonance imaging of microstructural abnormalities in children with brain injury.

We present two pediatric cases demonstrating that diffusion tensor imaging is more efficient at revealing microstructural abnormalities of the brain than conventional magnetic resonance imaging because it enables measurements of the directionality and integrity of white matter fiber tracts. One patient suffered from left hemiparesis, and the other had right hemiparesis. However, whereas conventional magnetic resonance imaging showed only the findings of traumatic contusional hemorrhages in the left temporal and parietal lobes of the first patient and focal encephalomalacia in the left anterior thalamus of the second patient, diffusion tensor imaging successfully disclosed microstructural abnormalities in the right cerebral peduncle of the midbrain of the first patient and in the posterior limb of the left internal capsule of the second. Theses two cases demonstrate that diffusion tensor imaging is more capable than magnetic resonance imaging at detecting the microstructural pathologic lesions that are responsible for clinical motor weakness, especially when conventional magnetic resonance imaging has failed to detect subtle structural abnormalities.

Brain↗

PubMed2002

Functional MRI evidence for motor cortex reorganization adjacent to a lesion in a primary motor cortex.

OBJECTIVE: The object of this study was to verify motor cortex reorganization in patients with primary motor cortex injury using functional magnetic resonance imaging. DESIGN: Ten control subjects and two patients with primary motor cortex injury, caused by a traumatic brain injury in patient 1 and meningioma in patient 2, were evaluated. Functional magnetic resonance imaging was performed using the blood oxygenation level-dependent technique at 1.5 T with hand movements. RESULTS: The contralateral primary sensorimotor cortex was activated by unaffected hand movements. However, only the contralateral primary sensory cortex in patient 1 and the premotor area in patient 2 were activated by affected hand movements, which were totally absent in control subjects. CONCLUSION: We believe that the hand motor function of injured primary motor cortex was shifted into the primary sensory cortex in patient 1 and premotor area in patient 2. In conclusion, this finding may reflect a functional reorganization of the motor area in patients with a primary motor cortex injury.

Adult↗

PubMedDate not supplied

Diffusion-weighted MR imaging of metastatic disease of the spine: assessment of response to therapy.

BACKGROUND AND PURPOSE: In cases of metastatic disease of the spine, monitoring the response to medical therapy with plain radiography, bone scanning, and conventional spin-echo sequence MR imaging is unsatisfactory because of the insensitivity or nonspecific findings of these imaging modalities. The purpose of this study was to investigate signal intensity changes of bone marrow after therapy by using diffusion-weighted MR imaging to monitor the response to medical therapy in cases of metastatic disease of the spine. METHODS: Twenty-four patients with metastatic disease of the spine were examined with MR imaging. Diffusion-weighted MR imaging and spin-echo MR imaging were performed in all patients before and after radiation therapy. Follow-up diffusion-weighted MR imaging and spin-echo MR imaging were performed for comparison purposes in nine cases at 1 month, in seven cases at 2 months, in seven cases at 3 months, and in three cases at 6 months after therapy. The diffusion-weighted MR imaging sequences were based on a steady-state free precession with a low b value (165 s/mm(2)) and a single shot stimulated echo-acquisition mode with a high b value (650 s/mm(2)). Apparent diffusion coefficient maps were obtained using two different b values incorporated in a diffusion-weighted single shot stimulated echo-acquisition mode sequence. Apparent diffusion coefficient maps were obtained in three cases. Signal intensity changes of the metastatic disease of the vertebral bone marrow before and after therapy on conventional spin-echo sequence and diffusion-weighted MR images were evaluated. RESULTS: As shown by diffusion-weighted MR imaging, metastatic disease of the vertebral bone marrow included in our study before therapy was hyperintense to normal vertebral bodies. In 23 patients with clinical improvement, metastatic disease of the spine after therapy was hypointense relative to normal vertebral bodies on the follow-up diffusion-weighted MR images. In one patient with hepatocellular carcinoma, the clinical symptoms did not improve and follow-up bone scanning performed 6 months after therapy showed increased uptake. Persistent hyperintense bone marrow after therapy was also noted on diffusion-weighted MR images. Decreased signal intensity of the metastatic disease of the spine on diffusion-weighted MR images was observed >1 month after therapy. CONCLUSION: Diffusion-weighted MR imaging shows that, with successful therapy, there is decreased signal intensity of metastatic disease of the vertebral bone marrow.

Adult↗