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Y L Chan

Publications and source records attributed to Y L Chan.

At least 73 records · Page 4Linked to original sources
PubMed1999

MRI evaluation of multifidus muscles in adolescent idiopathic scoliosis.

BACKGROUND: The role of the multifidus muscles in the initiation and progression of curve in adolescent idiopathic scoliosis is not fully understood and controversy exists as to the side of the abnormality. OBJECTIVE: To evaluate on MRI the multifidus muscles at the apex of the major curve in adolescent idiopathic scoliosis to ascertain if the multifidus muscles on the convex or concave side are abnormal and the relationship to curve severity. MATERIALS AND METHODS: Forty-six patients with adolescent idiopathic scoliosis, separated into two groups, were studied using a 1.5-T MR scanner with the synergy spine coil, employing a modified STIR (short tau inversion recovery) axial sequence obtained at the apex of the major scoliotic curve. RESULTS: No hyperintense signal change was demonstrated in the convex side multifidus muscles in any patient. In group I, 16 of 18 patients with severe or rapidly progressive curve showed increase in signal intensity in the multifidus muscle on the concave side of the apex of the curve. In group II, of the 15 patients with mild curve (Cobb angle 10-30 degrees), 4 had increased signal intensity in the multifidus muscle on the concave side; of the 13 with more severe curve (Cobb angle greater than 30 degrees), 10 had increase in multifidus signal intensity on the concave side. CONCLUSIONS: The concave-side multifidus muscle at the apex of a scoliotic curve was morphologically abnormal. A significant association between abnormal signal change and curve severity was also established.

Adolescent↗
PubMed1999

Potential utility of MRI in the evaluation of children at risk of renal scarring.

BACKGROUND: Gadolinium-enhanced MRI has recently been employed in the diagnosis of acute pyelonephritis. Its potential utility in the diagnosis of renal scars in children is unknown. Objective. To evaluate the potential utility of MRI using fat-saturated T1-weighted (T1-W) and post-gadolinium, short-tau inversion-recovery (STIR) sequences in detecting renal scarring by comparison with technetium dimercaptosuccinic acid ((99 m)Tc-DMSA) renal scintigraphy in children at risk of renal scarring. MATERIALS AND METHODS: A group of 24 children with spina bifida and neurogenic bladder or anorectal anomaly was studied. No patient had a history of acute pyelonephritis. Documented urinary tract infection (UTI) was present in 10 children (42 %). The remaining 14 (58 %) children had a history of asymptomatic bacteriuria. None had clinical signs or symptoms of acute UTI at the time of the study. (99 m)Tc-DMSA and MRI were performed to detect renal scarring. (99 m)Tc-DMSA scans were supplemented with pinhole imaging. MRI of the kidneys employed a fat-saturated T1-W sequence and a post-gadolinium STIR sequence employing a short echo time. RESULTS: Of the kidneys studied, 33 % (n = 16) had evidence of a renal parenchymal defect suggestive of scarring on (99 m)Tc-DMSA. The concordance in the detection of a scarred kidney by post-gadolinium STIR sequence and (99 m)Tc-DMSA is 94 %; that by fat-saturated T1-W sequence and (99 m)Tc-DMSA is 82 %; that by both sequences (positive result on either sequence) and (99 m)Tc-DMSA is 100 %. Using (99 m)Tc-DMSA as the gold standard, MRI had a sensitivity of 100 % and a specificity of 78 % in the diagnosis of a scarred kidney. The concordance in the detection of a scarred zone by post-gadolinium STIR sequence and (99 m)Tc-DMSA is 68 %; that by fat-saturated T1-W sequence and DMSA is 44 %; that by both sequences (positive result on either sequence) and (99 m)Tc-DMSA is 84 %. MRI had a sensitivity of 84 % and a specificity of 86 % in the diagnosis of a scarred zone, using (99 m)Tc-DMSA as the gold standard. CONCLUSION: The detection rate for renal scarring on MRI using the fat-saturated T1-W and post-gadolinium STIR sequences is comparable to planar (99 m)Tc-DMSA. MRI is of potential utility in the evaluation of children at risk of renal scarring.

Anal Canal↗
PubMed1999

A new management algorithm for impalpable undescended testis with gadolinium enhanced magnetic resonance angiography.

PURPOSE: We evaluated the diagnostic accuracy of preoperative localization of impalpable undescended testis using ultrasound and gadolinium (Gd) enhanced magnetic resonance angiography (MRA). MATERIALS AND METHODS: Ultrasound and Gd-MRA were performed prospectively in 21 boys (23 impalpable testes) with cryptorchidism before laparoscopy and surgical exploration. Gd-MRA was done using a 1.5 Tesla magnetic resonance scanner with a turbo field echo technique after bolus intravenous injection of 0.4 mmol./kg. body weight of Gd diethylenetriaminepentaacetic acid. A total of 10 dynamic scans were acquired during 15 minutes after Gd injection to cover the early arterial and delayed venous phases. All patients subsequently underwent diagnostic laparoscopy and definitive surgery. RESULTS: Ultrasound correctly localized 9 of 10 intracanalicular testes but failed to reveal any intra-abdominal or vanishing testes. In contrast, Gd-MRA correctly localized 4 intra-abdominal, all 10 intracanalicular and 8 canalicular vanishing testes. In 1 patient with an intra-abdominal vanishing testis ultrasound and Gd-MRA failed to make the diagnosis. When correlated with the findings of subsequent laparoscopy and surgical exploration, Gd-MRA had a diagnostic sensitivity of 96% and a specificity of 100% for localizing impalpable undescended testes. Based on Gd-MRA and ultrasound findings laparoscopy could have been avoided in 18 of 23 cases (78%). No adverse effect was associated with Gd use in this study. CONCLUSIONS: Gd-MRA accurately diagnoses vanishing testes and reliably differentiates intraabdominal from intracanalicular impalpable testes, allowing definite preoperative planning of the surgical approach and avoiding unnecessary laparoscopy. A new management algorithm for impalpable testis in patients with cryptorchidism is proposed based on ultrasound and Gd-MRA findings.

Algorithms↗
PubMed1999

MR imaging in amyopathic dermatomyositis.

PURPOSE: Amyopathic dermatomyositis is a distinct clinical entity with cutaneous involvement but no myopathy. We conducted a prospective study to investigate the role of MR imaging in these patients. MATERIAL AND METHODS: Out of 40 Chinese patients presenting with dermatomyositis, based on clinical assessment and normal serum muscle enzymes 10 were diagnosed as having amyopathic dermatomyositis. These 10 patients underwent MR imaging for evaluation of any subclinical muscle involvement. RESULTS: Three patients demonstrated abnormal signal intensity in muscles on both T2- and fat suppression sequences. Thus, one-third of patients with dermatomyositis and clinically normal muscles may have detectable muscle inflammation on MR images, indicating that MR has a potential role for locating the relevant biopsy site and for longitudinal follow up. Six of the 10 patients had malignant disease diagnosed before or after diagnosis of the cutaneous manifestation. Nasopharyngeal carcinoma was the most common malignant disease in this group of patients. CONCLUSION: MR imaging is recommended for demonstrating subclinical muscle involvement in patients with the clinical diagnosis of amyopathic dermatomyositis. We also recommend screening for malignancy, particularly nasopharyngeal carcinoma, in Southern Chinese patients with dermatomyositis.

Adult↗
PubMed1999

Late radiation injury to the temporal lobes: morphologic evaluation at MR imaging.

PURPOSE: To study the morphologic characteristics of late radiation injury to the temporal lobes of the brain on magnetic resonance (MR) images. MATERIALS AND METHODS: This was a prospective study involving 34 patients (age range, 37-72 years) with known radiation injury to the temporal lobes from radiation therapy administered 2-10 years previously for nasopharyngeal carcinoma MR imaging was performed with T2-weighted gradient- and spin-echo, gradient-recalled echo, T1-weighted spin-echo, fluid-attenuated inversion-recovery, and T1-weighted postcontrast spin-echo sequences. RESULTS: Radiation injury was present in 57 of the 68 temporal lobes. The white matter lesions in radiation-induced injury were predominantly hyperintense on T2-weighted images, but in 37 (65%) of the 57 lobes, foci with heterogeneous signal intensity consistent with necrosis were detected. In the 57 involved lobes, gray matter lesions were detected in 50 (88%); blood-brain barrier disruption based on parenchymal contrast enhancement, in 51 (89%); and hemosiderin deposits, in 30 (53%). There was a significant correlation between white matter necrosis, gray matter lesions, and blood-brain barrier disruption, all of which were located mainly in the inferior temporal lobes that received the highest radiation dose. CONCLUSION: The lesion components of radiation-induced injury to the temporal lobes at MR imaging were more varied than have been previously described. In addition to the classic white matter lesions, gray matter lesions, blood-brain barrier disruption, and hemosiderin deposition also were frequently seen.

Adult↗
PubMed1999

MR features of the denervated tongue in radiation induced neuropathy.

The MR features of the denervated tongue have been described following nerve injury from radical neck dissection and tumour invasion. The purpose of the study was to determine whether similar features are present in the tongue following radiation induced neuropathy (RIN). The clinical records and MR images of 12 patients with RIN of the hypoglossal nerve were reviewed retrospectively. T1 weighted SE images were performed in 12, T2 weighted TSE images in 11, fat suppressed images in 10 and contrast enhanced T1 weighted images in nine patients. The denervated tongue revealed "oedemalike" changes in five, fatty infiltration in six, atrophy in 11 and pseudohypertrophy in one patient. Abnormal enhancement was not identified, and in five patients the signal intensity was normal on all sequences. The oedemalike changes, fatty infiltration and normal signal intensity were seen 2-48, 2-48, and 6-63 months, respectively, after the onset of RIN. In conclusion, there was no discernible relationship between the duration of RIN and the MR appearance of the denervated tongue. Oedemalike changes, previously described in the acute/subacute phase of denervation, were also seen in long-standing disease and there was no associated abnormal enhancement in any case. Furthermore, the signal intensity may be normal, the MR diagnosis relying on asymmetry of the size of the tongue. It is postulated that radiation causes incomplete and ongoing damage of the nerve, the course of which is unpredictable.

Adult↗
PubMed1999

MRI of local disease in nasopharyngeal carcinoma: tumour extent vs tumour stage.

The purpose was to use MRI to study in detail local tumour extension in patients presenting with nasopharyngeal carcinoma (NPC) and to compare the extent of local disease with the current T-stage classification. MR images of 150 patients with newly diagnosed nasopharyngeal carcinoma were obtained on a 1.5 T unit. 10 extranasopharyngeal sites were analysed for tumour involvement. The number of concurrently involved sites was determined. The extent of tumour invasion was compared with staging as defined by the fifth edition of the AJCC classification. The T-stage distribution was T1 21%, T2 16%, T3 41% and T4 22%. The frequencies of tumour invasion into an individual site, and the mean number of other concurrently involved sites were as follows: skull base 63%, 3.9 sites; parapharyngeal 56%, 3.9 sites; nasal cavity 53%, 4.0 sites; oropharyngeal 17%, 5.2 sites; sphenoid sinus 27%, 5.6 sites; cranium 21%, 5.7 sites; infratemporal fossa 2%, 6.3 sites; ethmoid sinus 14%, 6.5 sites; orbit 5%, 7.0 sites; maxillary sinus 5%, 7.1 sites; and hypopharynx 0%, 0 sites. Extranasopharyngeal extension commonly occurred superiorly into the skull base rather than inferiorly to the oropharynx (p < 0.0001). Anatomical sites defined within the same T-stage category had different frequencies of involvement and different frequencies of concurrently involved sites. Oropharyngeal involvement (T2 stage) was associated with a number of concurrently involved sites comparable to structures in the T3 category. Maxillary and ethmoid sinus involvement (T3 stage) were associated with a number of involved sites comparable to the T4 stage. Invasion of the maxillary antrum and orbit are markers of the most bulky form of NPC.

Adult↗
PubMed1999

Postoperative myocardial infarction in a patient with perioperative ST-depression--a case report.

Often we ignore electrocardiogram (EKG) evidence of ischemia and no adverse events occur. However, once in a while these ischemic episodes will turn into a full-blown myocardial infarction. Therefore, studying perioperative events which tilt the balance over to postoperative myocardial infarction (PMI) can enlighten our knowledge in postoperative myocardial infarction (MI) prevention. We present a case of ST depression in perioperative EKG evolving into postoperative MI. In this paper we attempt to explore various possibilities which could have altered this patient from her ischemic state into an infracted event.

Aged↗
PubMed1998

Crystal structure of the ribosomal RNA domain essential for binding elongation factors.

The structure of a 29-nucleotide RNA containing the sarcin/ricin loop (SRL) of rat 28 S rRNA has been determined at 2.1 A resolution. Recognition of the SRL by elongation factors and by the ribotoxins, sarcin and ricin, requires a nearly universal dodecamer sequence that folds into a G-bulged cross-strand A stack and a GAGA tetraloop. The juxtaposition of these two motifs forms a distorted hairpin structure that allows direct recognition of bases in both grooves as well as recognition of nonhelical backbone geometry and two 5'-unstacked purines. Comparisons with other RNA crystal structures establish the cross-strand A stack and the GNRA tetraloop as defined and modular RNA structural elements. The conserved region at the top is connected to the base of the domain by a region presumed to be flexible because of the sparsity of stabilizing contacts. Although the conformation of the SRL RNA previously determined by NMR spectroscopy is similar to the structure determined by x-ray crystallography, significant differences are observed in the "flexible" region and to a lesser extent in the G-bulged cross-strand A stack.

Animals↗
PubMed1998

Obstructive sleep apnea syndrome in a family with Crouzon's syndrome.

Craniofacial anomalies are recognized causes of obstructive sleep apnea syndrome (OSAS) in children. Current literature is limited due to rarity of cases. Furthermore, the mechanism of upper airway obstruction is not clearly understood. We would like to report a family (father and 2 sons) who are suffering from Crouzon's syndrome. The two brothers (ages 1 and 3) were found to have significant obstructive sleep apnea syndrome (OSAS) with failure to thrive. Nasal continuous positive airway pressure (CPAP) markedly improved their OSAS and resulted in accelerated weight gain. The nasoendoscopy and magnetic resonance imaging (MRI) scan taken during natural sleep showed that choanal stenosis, maxillary hypoplasia, posteriorly displaced tongue, lengthened soft palate and adenoid tissues were important in the pathogenesis of upper airways obstruction in Crouzon's syndrome. Nasal CPAP improved airway obstruction by opening a narrow slit as demonstrated by MRI. Our results suggest that OSAS occurred in children with Crouzon's syndrome and that nasal CPAP was a useful treatment modality.

Adult↗
PubMed1998

Magnetic resonance cholangiography--feasibility and application in the paediatric population.

OBJECTIVE: To assess the feasibility of magnetic resonance cholangiography (MRC) in paediatrics. MATERIALS AND METHODS: MRC was attempted in 41 children from 1 week to 14-years. There were three groups: (1) children studied with MRI for non-biliary problems as controls; (2) infants with jaundice; and (3) older children suspected of biliary disease. The examination was successfully performed in 35 children, which included 12 children studied for non-biliary problems, 12 infants with jaundice, and 11 older children with suspected biliary disease. RESULTS: In group 1, the entire common duct was visualised in all 12 children. In group 2, successful demonstration of the common duct was achieved in two of the ten infants with subsequent confirmation of normal bile duct patency. In the last group of patients with suspected biliary disease, MRC gave good anatomical display of six choledochal cysts but failed to demonstrate the anomalous choledochopancreatic channel. It helped to confirm the diagnosis of two cases of pancreatic head cysts, and one case of Caroli's disease. CONCLUSION: MRC can be applied to the paediatric population, but its value depends on the type of problem to be evaluated. With current spatial resolution, its value in the diagnosis of biliary atresia is probably limited because it cannot reliably demonstrate the bile ducts in young infants with non-obstructive jaundice. In older children, it could provide a non-invasive anatomical display of the biliary tree and its disease. It has a potential role in addressing problematic cases encountered during ultrasonography.

Biliary Tract Diseases↗
PubMed1998

Body fat estimation in children by magnetic resonance imaging, bioelectrical impedance, skinfold and body mass index: a pilot study.

OBJECTIVE: The aim of this study was to identify the clinical method to estimate body fat which gave best correlation of total body fat and percentage body fat as measured on MRI. METHODS: Magnetic resonance imaging (MRI) was used to estimate the total body fat volume and percentage body fat and this was compared with assessment by bioelectrical impedance (BEI), skinfold thickness and body mass index (BMI) in 8- to 12-year-old children. RESULTS: Total body fat measured on magnetic resonance imaging (TBF-MRI) significantly correlated with body mass index, triceps and subscapular skinfolds, and percentage body fat estimations by BEI. Multiple regression analysis showed that BMI and BEI together gave the best prediction of total body fat as measured on MRI from the equation: TBF-MRI=-25277.77+1457.61(BMI)+423.95(%fat-BEI), with R2=0.89. Percentage body fat measurement from MRI, BEI and skinfold were not significantly different but their results were not interchangeable. Linear regression of %body fat from MRI on those obtained from BEI and skinfold measurements showed a modest fit with R2=0.6973 and 0.5501, respectively. CONCLUSIONS: In children 8-12 years old, BMI gives a good estimation of the total body fat as measured on MRI. The estimation will be improved when both BEI and BMI are used in the prediction. Bioelectrical impedance has a low correlation with total body fat and its use alone in estimating total body fat is not recommended. Skinfold measurement also gives a reasonably good prediction of total body fat and addition of BMI and BEI does not improve the prediction. Both BEI and skinfold measurements give a modest prediction of %body fat measured by MRI method.

Adipose Tissue↗
PubMed1998

Magnetic resonance imaging evaluation of the pituitary gland and hypothalamus in thalassaemic children with elevated serum ferritin levels.

OBJECTIVE: Despite modern treatment with hypertransfusion and chelation therapy, growth retardation continues to be observed in a significant proportion of thalassaemic children. The underlying reason remains unclear, but hypothalamic-pituitary axis disorder has been implicated. We aimed to assess iron overloading in the hypothalamus and pituitary gland in thalassaemic children with elevated serum ferritin, with and without growth retardation. METHODOLOGY: Twelve thalassaemic children on hypertransfusion and chelation therapy with high serum ferritin were investigated with magnetic resonance imaging (MRI). Five children, all over 10 years of age, had growth retardation. Gradient recalled echo sequence was used to highlight any susceptibility effect that could be due to iron in the hypothalamus or pituitary gland. RESULT: There was no evidence of abnormal hypointense signal in the hypothalamus or pituitary gland in the patients studied, regardless of the presence of growth retardation. CONCLUSION: There was no apparent characteristic MRI appearances of iron deposition in the hypothalamus or pituitary gland in thalassaemic children with high serum ferritin.

Adolescent↗
PubMed1998

Body fatness and serum lipids of 11-year-old Chinese children.

It has been suggested that distribution of body fat has a stronger bearing on health risk than total body fat. Magnetic resonance imaging (MRI) was used to examine the distribution of fat and correlated with body fat assessed by the usual clinical methods-weight, weight-for-height, body mass index (BMI), triceps and subscapular skinfold thickness in 11-y-old Chinese children. Lipid profiles were used as indicators for coronary risk. Eighty-eight subjects had body fat distribution estimated by MRI, while 49 had serum lipids measured. Anthropometric parameters correlated significantly with total fat at the umbilical level measured by MRI (weight: r = 0.90 in boys, 0.75 in girls; BMI: r = 0.94 in boys, 0.87 in girls; percent median weight-for-height: r = 0.90 in boys, 0.79 in girls, triceps skinfold thickness: r = 0.89 in boys, 0.90 in girls; subscapular skinfold thickness: r = 0.93 in boys, 0.88 in girls). Obese subjects had proportionally less visceral fat than subcutaneous fat at umbilical level. Using stepwise multiple regression, predictive factors for high-density lipoprotein cholesterol were BMI in boys and breast-staging in girls. For triglycerides, it was genital staging in boys and for total cholesterol, it was breast-staging in girls. Visceral fat was not a significant determinant of serum lipids.

Adipose Tissue↗
PubMed1998

Intracranial stenosis in Chinese patients with acute stroke.

We studied 100 consecutive acute stroke patients in a Chinese population with transcranial Doppler and CT. Twenty patients had intracerebral hemorrhage and 14 patients did not have adequate temporal windows for transcranial Doppler examination. Among the remaining 66 patients, 22 patients (33%) had intracranial occlusive diseases and 3 (6%) had extracranial carotid stenosis. Our data showed that intracranial occlusive disease is the most commonly found vascular lesion in our acute stroke patients.

Adult↗
PubMed1998

Cervical assessment by magnetic resonance imaging--its relationship to gestational age and interval to delivery.

The aim of this cross-sectional study was to assess the uterine cervix in late pregnancy, using MRI, and to study its relationship to the gestational age and the time interval to delivery. 91 women with a singleton cephalic presenting fetus had MRI of the pelvis between 35 and 41 weeks. All had had one prior lower segment Caesarean section and no history of prior vaginal delivery. The cervical length, internal and external os diameter, cervical signal intensity and the angulation of the cervix with the cephalocaudal axis were measured on sagittal T2 weighted images and correlated with the gestational age and the interval from the MRI examination to delivery. It was found that the signal intensity of the cervical stroma increased with the gestational age. A higher signal intensity in the cervical stroma was associated with a shorter time interval to delivery. Deliveries after 40 weeks tended to occur more commonly in those with lower signal intensity in the cervical stroma and also in those with a smaller external os diameter. It is concluded that cervical softening as assessed on MRI correlated with gestational age and the time interval to delivery.

Cervix Uteri↗
PubMed1998

Nasopharyngeal carcinoma: dynamic MR imaging with gadolinium.

OBJECTIVE: To evaluate the use of enhanced dynamic MR images in nasopharyngeal carcinoma (NPC). METHODS: Dynamic enhanced turbo spin-echo transverse images were obtained in 35 patients with newly diagnosed NPC. Comparison was made between the pre-contrast image, last enhanced scan and dynamic series in assessment of the extent of primary tumor and lymph node involvement. RESULTS: Enhanced MR images improved delineation of tumor in the following regions, nasopharyngeal wall (6/35), levator palatini (44/70), tensor palatini (12/70), prevertebral muscles (3/70), medial pterygoid muscle (7/70), pharyngobasilar fascia (30/35), parapharyngeal fat space (23/70), nasal cavity (33/70), oropharynx (6/35), sphenoid sinus (6/35), maxillary sinus (6/70), ethmoid air cells (14/35), cavernous sinus (5/35), cranial fossa (4/35), clivus (13/35) and pterygoid genu (2/70). Eight of the 9 normal and 79/82 abnormal nodal groups, on conventional imaging criteria, enhanced with the same pattern and intensity as the primary tumor. The dynamic series did not improve delineation of tumor extent in comparison with that obtained on last enhanced image. CONCLUSION: Enhanced MR images are valuable in evaluating the extent of primary tumor. Dynamic imaging was of no additional benefit in the evaluation tumor extent.

Adult↗