Search PubMed⌕ Search

Biomedical subjects

Y L Chan

Publications and source records attributed to Y L Chan.

At least 37 records · Page 2Linked to original sources
PubMed2003

Relative anterior spinal overgrowth in adolescent idiopathic scoliosis. Results of disproportionate endochondral-membranous bone growth.

We undertook a comparative study of magnetic resonance imaging (MRI) vertebral morphometry of thoracic vertebrae of girls with adolescent idiopathic thoracic scoliosis (AIS) and age and gender-matched normal subjects, in order to investigate abnormal differential growth of the anterior and posterior elements of the thoracic vertebrae in patients with scoliosis. Previous studies have suggested that disproportionate growth of the anterior and posterior columns may contribute to the development of AIS. Whole spine MRI was undertaken on 83 girls with AIS between the age of 12 and 14 years, and Cobb's angles of between 20 degrees and 90 degrees, and 22 age-matched controls. Multiple measurements of each thoracic vertebra were obtained from the best sagittal and axial MRI cuts. Compared with the controls, the scoliotic spines had longer vertebral bodies between T1 and T12 in the anterior column and shorter pedicles with a larger interpedicular distance in the posterior column. The differential growth between the anterior and the posterior elements of each thoracic vertebra in the patients with AIS was significantly different from that in the controls (p < 0.01). There was also a significant positive correlation between the scoliosis severity score and the ratio of differential growth between the anterior and posterior columns for each thoracic vertebra (p < 0.01). Compared with age-matched controls, the longitudinal growth of the vertebral bodies in patients with AIS is disproportionate and faster and mainly occurs by endochondral ossification. In contrast, the circumferential growth by membranous ossification is slower in both the vertebral bodies and pedicles.

Adolescent↗
PubMed2003

Role of magnetic resonance imaging for preoperative evaluation of patients with refractory epilepsy.

OBJECTIVE: To investigate the magnetic resonance imaging characteristics of patients with refractory epilepsy and the relationship to progression to surgery. DESIGN: Prospective observational study. SETTING: University teaching hospital, Hong Kong. PATIENTS: Patients undergoing preoperative evaluation for epilepsy surgery. MAIN OUTCOME MEASURE: Cranial magnetic resonance imaging findings, correlation with electroencephalographic results, and percentage of patients who were considered suitable candidates for surgery. RESULTS: Structural abnormalities associated with refractory epilepsy in 100 consecutive patients were mesial temporal sclerosis (30%), neocortical sclerosis (23%), vascular malformation (7%), neuronal migration disorders (7%), and tumours (5%). Normal brain scans were found for 28% of patients. Fourteen of 30 (46%) patients with medial temporal lobe lesions at magnetic resonance imaging were suitable candidates for surgery compared with 8/42 (19%) patients with extrahippocampal lesions (odds ratio=3.7; 95% confidence interval, 1.3-10.6; P<0.012). CONCLUSION: Mesial temporal sclerosis was the most common pathology in patients with refractory epilepsy. At the Prince of Wales Hospital, for patients who have undergone a basic magnetic resonance imaging protocol and surface electroencephalography, the result of cranial magnetic resonance imaging is an important determinant for whether patients will undergo surgery.

Adolescent↗
PubMed2002

Determination and pharmacokinetic study of meropenem in rat bile using on-line microdialysis and liquid chromatography.

Meropenem is a carbapenem antibiotic with a wide spectrum of activity against both Gram-positive and Gram-negative bacteria. Because of its clinical efficacy, meropenem is an excellent choice for the treatment of serious infections in both adults and children. The knowledge of tissue concentrations of antibiotic in an infection site is valuable for the prediction of treatment outcome. To investigate the biliary disposition of meropenem, we utilized a minimally invasive sampling technique with a shunt linear microdialysis probe for continuous sampling in the biliary excretion studies. Analysis of meropenem in the dialysates was achieved using a LiChrosorb RP-18 column (Merck, 250 x 4.6 mm I.D.; particle size 5 microm) maintained at ambient temperature. The mobile phase was 50 mM monosodium phosphoric acid-methanol (80:20, v/v, pH 3.0). The UV detector wavelength was set at 298 nm. The area under the concentration-time curve and elimination half-lives of meropenem were about 6144 +/- 1494 min microg/ml and 61 +/- 17 min, respectively. This study represents a successful application of the microdialysis technique, which is an effective method for pharmacokinetic and biliary drug excretion studies.

Animals↗
PubMed2002

Hepatic malignant tumour versus cavernous haemangioma: differentiation on multiple breath-hold turbo spin-echo MRI sequences with different T2-weighting and T2-relaxation time measurements on a single slice multi-echo sequence.

AIM: We evaluated the signal intensity change on breath-hold turbo spin-echo (TSE) T2-weighted sequences using different echo times (TE) and T2-relaxation time measurements on a single slice eight-echo sequence in the differentiation of hepatic malignancy from cavernous haemangioma. MATERIALS AND METHODS: Breath-hold TSE T2-weighted axial images of the liver were performed at TEs of 80, 120 and 160 ms in 34 patients with focal liver lesions (13 with cavernous haemangiomas, 14 with hepatocellular carcinomas and seven with metastases). The lesion percentage signal intensity change on the lower TE image to the higher TE image was calculated. T2-relaxation time was measured on a single slice eight-echo sequence. RESULTS: The TE pair 80/160 ms on breath-hold TSE T2-weighted sequences gave a performance (100% sensitivity, 92% specificity, 95% positive predictive value and 100% negative predictive value) better than other TE pairs in differentiating haemangioma from malignancy. Addition of fat-suppression compromised the diagnostic performance for all TE-pairs. The use of T2 relaxation time threshold of < 112 ms as indicative of malignant lesion achieved a 100% sensitivity, 77% specificity, 88% positive predictive value and 100% negative predictive value. CONCLUSION: Percentage signal intensity change on breath-hold TSE T2-weighted sequences at TE 80/160 ms appears to be a quick and potentially useful means of differentiating hepatic malignancy from haemangioma.

Adult↗
PubMed2002

Back pain in pregnancy--magnetic resonance imaging correlation.

AIM: To study the relationship of disk abnormality and signal changes of the uterine cervix on magnetic resonance imaging (MRI) with back pain in pregnancy at 36-39 weeks of gestation. MATERIAL AND METHODS: One hundred and five pregnant Chinese women with previous Caesarean section at 36-39 weeks gestation undergoing magnetic resonance pelvimetry performed for a study for trial of vaginal delivery were questionnaired for back pain. Sagittal T2-weighted images were analysed for intervertebral disk abnormality, and signal intensity of the uterine cervix on the same sagittal images. The findings on MRI were correlated with back pain. RESULTS: Seventy-three (70%) of the pregnant women had back pain. Disk bulge or prolapse were infrequent but correlated significantly with the presence of back pain (P=0.02). Women with back pain in the current pregnancy tended to have a higher signal intensity of the uterine cervix compared with those without (P=0.006). Women with a history of back pain also had higher cervical signal intensity compared with those without (P=0.02). CONCLUSION: Disk bulge or prolapse was associated with back pain in pregnancy but were relatively infrequent. The significant correlation of high signal intensity in the uterine cervix and back pain suggested that soft tissue laxity may be a more important cause of back pain in pregnancy than disk bulge or prolapse.

Adult↗
PubMed2002

Respiratory function in patients with thalassaemia major: relation with iron overload.

AIMS: (1) To determine the pattern of respiratory impairment in children with thalassaemia major (TM); (2) to assess the relation between the degree of respiratory impairment and total body iron content. METHODS: Twenty nine TM patients were recruited. All underwent physical examination, standardised pulmonary function tests (spirometry, lung volume, and single breath diffusion capacity for carbon monoxide), and magnetic resonance imaging measurements of the liver. Serum ferritin was measured. The signal intensity ratio of liver to that of paraspinal muscle (T1 weighted sequence) and serum ferritin were used as surrogate index of body iron content. RESULTS: Sixteen boys and 13 girls (median age 14.2 years) were studied. None had clinical evidence of congestive heart failure. Sixteen had normal lung function. Impairment of diffusion capacity (median DL(co) 83.5% predicted) was the most common abnormality, being observed in 34% of patients. Pure restrictive and obstructive ventilatory impairment was found in one and two patients respectively. Five patients had a combination of ventilation and diffusion defects. There was no correlation between the degree of impairment of each respiratory abnormality and body iron content. CONCLUSION: Diffusion impairment was the commonest abnormality found in our cohort of paediatric TM patients. Our data did not support the notion that respiratory function impairment was correlated with body iron content.

Adolescent↗
PubMed2002

(31)phosphorous and single voxel proton MR spectroscopy and diffusion-weighted imaging in a case of star fruit poisoning.

We herein describe the case of a patient with chronic renal failure complicated by star fruit poisoning. T2-weighted and diffusion-weighted MR imaging showed hyperintense lesions at the thalami and right temporo-occipital cortex. Single voxel proton MR spectroscopy revealed elevation of lactate and (31)phosphorous MR spectroscopy revealed elevation of inorganic phosphate and decrease of phosphocreatine and nucleoside triphosphates. The imaging and metabolic changes indicated energy deprivation, with subsequent cortical necrosis proved at autopsy.

Aspartic Acid↗
PubMed2002

Pseudoaneurysm complicating osteochondromas: symptom relief with embolization.

Pseudoaneurysm is a recognized vascular complication of osteochondromas. The diagnosis is confirmed by various imaging techniques including ultrasound, magnetic resonance imaging, and conventional angiography. Surgical repair and excision of the adjacent osteochondroma is considered the treatment of choice. The authors report a case of successful transarterial embolization using helical microcoils in the treatment of osteochondroma-related pseudoaneurysm of the superficial femoral artery. It resulted in complete obliteration of blood flow to the pseudoaneurysm and good symptomatic relief before subsequent semielective surgery. No complication was encountered during the procedure. Transarterial embolization is a safe mode of treatment in experienced hands. In patients with contraindications to surgery, embolization may be considered a definitive treatment.

Adolescent↗
PubMed2001

Long-term cerebral metabolite changes on proton magnetic resonance spectroscopy in patients cured of acute lymphoblastic leukemia with previous intrathecal methotrexate and cranial irradiation prophylaxis.

PURPOSE: To evaluate the long-term brain metabolite changes on (1)H-MRS in acute lymphoblastic leukemia (ALL) patients who had intrathecal methotrexate (ITMTX) and cranial irradiation (CRT) for central nervous system (CNS) prophylaxis against CNS relapse. METHODS AND MATERIALS: Thirty-seven ALL patients (12 females, 25 males) with history of ITMTX and CRT for CNS prophylaxis were studied. Age ranges at the time of diagnosis and at magnetic resonance examination were 0.8-13 years and 12-27 years, respectively. The interval since diagnosis was 5.6-19 years. T2-weighted and gradient-recalled echo (GRE) magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy ((1)H-MRS) were performed to assess brain injury. RESULTS: On MRI, 3 leukoencephalopathy (LEP) and 1 infarct were detected. Twenty-two patients had evidence of hemosiderin. On (1)H-MRS no statistically significant difference in choline (Cho)/creatine (Cr) and N-acetylaspartate (NAA)/Cr was associated with LEP. A lower Cho/Cr (p = 0.006) and NAA/Cr (p = 0.078) was observed in brains with hemosiderin. Linear-regression analysis showed no statistically significant relationship between NAA/Cr or Cho/Cr with age at diagnosis, but there was a statistically significant decreasing trend of NAA/Cr and Cho/Cr with the interval since diagnosis. CONCLUSION: Long-term brain injury in ALL survivors after CNS prophylaxis with ITMTX and CRT was reflected by decreasing NAA/Cr and Cho/Cr with the interval since diagnosis. The lower Cho/Cr associated with hemosiderin but not LEP suggested a different pathophysiology for these brain lesions.

Adolescent↗
PubMed2001

Sellar and suprasellar medulloepithelioma.

Medulloepithelioma is a rare tumour with a very poor prognosis. The most frequent site in the central nervous system is the cerebral hemispheres. Appearances on MRI are very variable, possibly reflecting the divergent forms of differentiation seen at histological examination. We report a rare case of sellar and suprasellar medulloepithelioma in a 2-year-old boy and discuss the imaging, differential diagnosis and pathologic findings.

Brain Neoplasms↗
PubMed2001

Reversible renal failure in paroxysmal nocturnal hemoglobinuria.

A Chinese patient with paroxysmal nocturnal hemoglobinuria (PNH) developed acute nonoliguric renal failure with intercurrent urinary tract infection and hemolysis. There was no evidence of renal vein thrombosis. Renal biopsy showed features of acute tubular necrosis (ATN) and hemosiderosis. Magnetic resonance imaging (MRI) showed characteristic features of renal hemosiderosis. The patient was stabilized with temporary hemodialysis and intravenous fluid. The renal function fully recovered 3 weeks later. We review the literature and summarize the clinical features of this disease entity. To our knowledge, this case is the first to report such disorder with thorough investigation including concomitant diagnostic MRI imaging and renal biopsy.

Acute Kidney Injury↗
PubMed2001

Comparison of non-breath-hold high resolution gadolinium-enhanced MRA with digital subtraction angiography in the evaluation on allograft renal artery stenosis.

AIM: The study objective was to compare the diagnostic accuracy of non-breath-hold high resolution gadolinium-enhanced magnetic resonance angiography (Gd-MRA) with intra-arterial digital subtraction angiography (DSA) in the evaluation of allograft renal artery stenosis (ARAS). MATERIALS AND METHODS: We studied 17 renal transplant recipients (six men, 11 women, age 34-64 years) with a systolic bruit in the transplant region beyond the early post-operative period. Gadolinium-enhanced magnetic resonance angiography was performed by non-breath-hold high resolution 3D acquisition in the oblique coronal plane using a 256 x 512 matrix.Digital subtraction angiography was performed with AP and oblique views and ARAS was graded as < or =50% or >50% diameter stenosis on the view that displayed the maximal narrowing. RESULTS: Digital subtraction angiography showed >50% stenosis in seven patients, all of whom were diagnosed correctly on Gd-MRA. Gadolinium-enhanced magnetic resonance angiography diagnosed two patients with >50% stenosis which were not confirmed on DSA. Eight patients had no or < or =50% stenosis on both Gd-MRA and DSA. The sensitivity and specificity of Gd-MRA in revealing >50% stenosis were 100% and 75%, respectively, using DSA as the gold standard. CONCLUSION: High resolution Gd-MRA employing a non-breath-hold technique is highly sensitive in the diagnosis of ARAS greater than 50%. It is preferred as a non-invasive screening technique to DSA in suspected ARAS.

Adult↗
PubMed2001

MR imaging of children's knees.

The spectrum of paediatric knee disorders ranges from developmental and growth disorders, traumatic derangement, inflammation, infection, and diffuse marrow disorder to neoplasm. We present in this pictorial review the MR imaging findings used to characterize these various diseases affecting the knee region of children and adolescents.

Adolescent↗
PubMed2001

Liver iron estimation in beta-thalassaemia: comparison of MRI biochemical assay and histological grading.

AIMS: The aims of the study were to compare the efficacy of magnetic resonance imaging (MRI), biochemical assay and histological grading in estimating liver iron content, and to evaluate the value of liver to muscle signal intensity ratio (L/M ratio) on spin-echo T1-weighted images in this role. MATERIALS AND METHODS: Thirty-nine homozygous beta-thalassaemics had their L/M ratio measured on MRI, followed by ultrasound-guided liver biopsies with histological grading of iron storage and biochemical quantification of liver iron concentration (LIC-b) using atomic absorption spectrophotometry. RESULTS: A significant difference in L/M ratios between the four grades of iron storage on histology was observed (P < 0.001). The coefficient of correlation was -0.67 between L/M ratio and LIC-b ranging from 2 to 21.6 mg/g dry weight. Specific values of L/M ratio reliably reflected liver iron content at clinically important levels. A L/M ratio of < 0.6 has 86% sensitivity and 100% specificity in the prediction of grade 3 or 4 iron storage histologically and 81% sensitivity and 81% specificity in predicting LIC-b > 15 mg/g. A L/M ratio of > 0.8 predicts a histological iron storage grading of 0 or 1 with a 100% sensitivity and 74% specificity. CONCLUSION: L/M ratio on MRI is of value as a non-invasive alternative to repeated liver biopsies for estimating liver iron content at clinically important thresholds.

Adolescent↗
PubMed2001

A pilot study of microembolic signals in patients with middle cerebral artery stenosis.

OBJECTIVE: There has been limited data on the frequency of microembolic signals in patients with middle cerebral artery (MCA) stenosis, especially during the acute phase of stroke. Using transcranial Doppler, the authors prospectively monitored the MCA segments distal to stenosis in 4 groups of patients for 30 minutes: (1) symptomatic patients with acute ischemic stroke and MCA stenosis, (2) asymptomatic group patients with asymptomatic MCA stenosis, (3) control patients with acute ischemic stroke of undetermined etiology, and (4) normal people. A total of 60 patients completed the study. There were no microembolic signals in the asymptomatic, control, and normal groups. Among 20 patients in the symptomatic group, microembolic signals were detected in 3 patients (15%). The number of emboli ranged from 1 to 6 per 30 minutes. This is the first report of the presence of microembolic signals in acute stroke patients with MCA stenosis.

Acute Disease↗
PubMed2001

Acute elbow trauma in children: spectrum of injury revealed by MR imaging not apparent on radiographs.

OBJECTIVE: The objective of this study is to evaluate the frequency and significance of unrecognized bone or soft-tissue injury in pediatric patients with elbow trauma assessed with radiographs alone. SUBJECTS AND METHODS: Fifty children (32 boys and 18 girls; mean age, 7.3 years; age range, 2-12 years) with acute elbow trauma were examined with radiography and MR imaging. Radiographs were categorized into those showing normal findings, an effusion, an equivocal fracture, or an unequivocal fracture. MR examinations were assessed for an effusion, fracture, transphyseal fracture extension, physeal injury, bone bruising, and ligament or muscle injury. Average clinical follow-up was 1.6 years (range, 6-28 months) after injury. RESULTS: Radiographs showed normal findings in seven children (14%), an effusion only in 17 children (34%), and an unequivocal or equivocal fracture in 26 children (52%). MR imaging showed an effusion in 48 children (96%); unequivocal fracture in 37 children (74%), including transphyseal fracture in seven children (14%) and other physeal injury in three children (6%); bone bruising in 45 children (90%); ligament injury in six children (14%); and muscle injury in 19 children (38%). A less severe spectrum of injury occurred in children with normal findings on radiographs than in those with an effusion or fracture seen on radiography. Follow-up radiographs did not help in the detection of radiographically occult fractures. MR findings had no appreciable effect on patient treatment and no value in predicting duration of convalescence or clinical outcome at an average of 1.6 years after injury. CONCLUSION: In children with elbow trauma, MR imaging reveals a broad spectrum of bone and soft-tissue injury beyond that recognizable radiographically. However, the additional information afforded by MR imaging has little bearing on treatment or clinical outcome.

Acute Disease↗