Biomedical subjects

D K Yeung

Publications and source records attributed to D K Yeung.

8 recordsLinked to original sources

PubMed2005

Human cervical lymphadenopathy: evaluation with in vivo 1H-MRS at 1.5 T.

AIM: To evaluate the feasibility of performing in vivo proton magnetic resonance spectroscopy ((1)H-MRS) of cervical lymph nodes, and the clinical usefulness of the technique in the characterization of cervical lymphadenopathy. MATERIALS AND METHODS: Cervical lymphadenopathy was examined in 20 individuals with malignant disease, i.e. 10 with squamous cell carcinoma (SCC), 6 with undifferentiated carcinoma (UDC) and 4 with non-Hodgkin's lymphoma (NHL). Cervical lymphadenopathy was also examined in 4 individuals with benign disease, i.e. 3 with tuberculosis (TB) and 1 with Castleman's disease. A point-resolved spectroscopic sequence with echo times (TE) of 136 and 272 ms and a time-domain spectral fitting procedure were used to estimate peak amplitude of choline (Cho), creatine (Cr) and unsuppressed water. Cho/Cr and Cho/water ratios were measured for each lesion. The mean ratio for each lesion group was obtained and results were compared statistically. RESULTS: At TE of 136 ms, spectra were interpretable in all 24 cases and a Cr peak was identified with post-processing in 15 cases. The Cho/Cr and Cho/water ratios for NHL were 9.1 +/- 5.2 and 1.7 +/- 0.2 x 10(-3), for UDC were 4.4 +/- 0.9 and 1.2 +/- 0.4 x 10(-3), and for SCC were 2.1 +/- 0.6 and 0.5 +/- 0.3 x 10(-3), respectively. Both Cho/Cr and Cho/water ratios for UDC were significantly higher than SCC (p = 0.002 and 0.026, respectively). At TE of 272 ms, spectra were interpretable in 22 of 24 cases and a Cr peak was identified with post-processing in 11 cases. Cho/Cr and Cho/water ratios for NHL were 5.4 and 4.6 +/- 1.4 x 10(-3), for UDC were 4.2 +/- 1.5 and 2.6 +/- 1.0 x 10(-3) and for SCC were 2.5 +/- 1.1 and 1.3 +/- 0.6 x 10(-3), respectively. The Cho/water ratio for UDC was significantly higher than for SCC (p = 0.04). The Cho/Cr ratio for UDC was also higher than for SCC, but this difference was not statistically significant (p = 0.07). Neither Cho nor Cr was detected in the 3 cases of TB. CONCLUSION: In vivo (1)H-MRS is a feasible technique for the evaluation of cervical lymph nodes and it offers potential as a clinical tool in the investigation of cervical lymphadenopathy. However, further studies with larger patient cohorts are needed to validate the findings of this initial report.

Adult↗

PubMed2001

Detection of an intense resonance at 2.4 ppm in 1H MR spectra of patients with severe late-delayed, radiation-induced brain injuries.

Proton MRS and MRI were used to monitor the progression of severe cerebral radiation injuries in 10 patients over a period of 18 months. An unknown resonance (Px) in the 2.37-2.40 ppm region was consistently detected in the affected temporal lobes of four patients. The detection of Px was only confined to spectra with lactate (Lac) and in patients with the highest severity grading of radiation injury. The incidence of Px in Lac-positive spectra was 42.8% (15/35) and in lesions with highest injury grading was 46.8% (15/32). Lesions with Px had significantly higher Lac/creatine (Cr) ratios and more extensive mass effect changes when compared to lesions without Px. The probable identity of Px was examined in the context of anaerobic glycolysis producing pyruvate (2.37 ppm) and the model of metabolic changes in brain abscess formation implicating succinate (2.40 ppm).

Adult↗

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

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

Human liver regeneration: hepatic energy economy is less efficient when the organ is diseased.

Recovery of liver cell mass following hepatectomy requires a metabolic compromise between differentiated function and organ regrowth. Clinical experience has shown that hepatic failure after resection is more common when the organ is diseased. We have evaluated intracellular hepatic biochemistry in patients with normal and cirrhotic livers undergoing partial hepatectomy, using 31-phosphorus magnetic resonance spectroscopy ((31)P MRS). Eighteen patients were studied, half with normal liver architecture (normal group, n = 9) and half with cirrhotic parenchyma (cirrhosis group, n = 9). Magnetic resonance examinations were performed preoperatively and on postoperative days 2, 4, 6, 14, and 28. Hepatic volume (estimated by magnetic resonance imaging [MRI]) and blood chemistries were measured at the same intervals. Following a comparable reduction in parenchymal volume, the cirrhotic group demonstrated a more sustained fall in adenosine triphosphate (ATP) energy state. Disturbance of membrane phospholipid metabolism and duration of acute-phase reaction were more marked when the liver was diseased. The pattern of derangement of hepatic function, however, was similar in the two groups. Overall, the recovery process was less efficient in the cirrhotic organ, and culminated in a diminished rate and extent of the regenerative response. These outcomes indicate that liver regeneration after partial hepatectomy involves modulation of hepatic energy economy in response to changing work demands. The efficiency of this process is influenced by the histopathologic state of the organ, and in turn governs the physiologic reserve. These findings may explain the mechanism of posthepatectomy liver failure, and offer a rational basis for the assessment of novel hepatic support strategies.

Adenosine Triphosphate↗

PubMed2001

Human breast lesions: characterization with contrast-enhanced in vivo proton MR spectroscopy--initial results.

PURPOSE: To assess the clinical usefulness of localized proton (hydrogen 1) magnetic resonance (MR) spectroscopy in the characterization of contrast material-enhanced breast lesions on the basis of choline detection. MATERIALS AND METHODS: Examinations were performed at 1.5 T with use of a standard breast coil. Contrast-enhanced MR imaging was performed in 30 consecutive patients (mean age, 50 years; age range, 20--80 years) who had nonspecific lesions (>1.5 cm in diameter) on sonograms or mammograms. Single-voxel (1)H MR spectroscopy was performed in the enhancing lesions by using a point-resolved spectroscopic sequence with echo times of 38, 135, and 270 msec. MR spectroscopic and histopathologic findings were determined in blinded fashion and compared. RESULTS: Twenty-four patients had carcinoma of the breast (tumor size, 2.0--11.2 cm; mean, 4.7 cm), and six had benign lesions (lesion size, 1.8--3.8 cm; mean, 2.7 cm). Choline was detected in 22 patients with carcinoma. Choline was not detected in five patients with benign lesions and in two patients with carcinoma. The preliminary results indicate that this technique had a sensitivity of 92%, specificity of 83%, and accuracy of 90%. CONCLUSION: Choline can be reliably detected in less than 45 minutes in large contrast-enhanced breast lesions by using a multiecho point-resolved spectroscopic protocol. The presence of water-soluble choline metabolites obtainable with (1)H MR spectroscopy could complement MR imaging findings to improve specificity and to reduce the number of unnecessary biopsies.

Adult↗

PubMed1999

Proton magnetic resonance spectroscopy of late delayed radiation-induced injury of the brain.

We prospectively evaluated metabolite changes in late delayed radiation-induced injury to the temporal lobes on proton ((1)H) magnetic resonance spectroscopy (MRS) in 34 patients. Morphologically more severe injury on imaging tended to have lower N-acetyl aspartate (NAA)/creatine (Cr) and NAA/choline (Cho) ratios. A significantly higher Cho/Cr ratio was found in the most severe grade of cerebral necrosis, in which lactate might be present. The progressive decrease in NAA with increasing severity reflected neuronal loss at different stages of late delayed radiation-induced brain injury. The absence of Cho elevation in mild and moderate lesions did not suggest demyelination or glial hyperplasia as an etiologic mechanism of late delayed radiation-induced brain injury. The association of severe morphologic lesions with elevated lactate suggests ischemia as the underlying mechanism for severe lesions. (1)H MRS may provide metabolite information conducive to the understanding of the pathophysiology of late radiation-induced brain injury. J. Magn. Reson. Imaging 1999;10:130-137.

Adult↗

PubMed1996

Dosimetric considerations for a multileaf collimator system.

A commercial linear accelerator with a factory-fitted multileaf collimator (MLC) was commissioned for clinical use. Measurements made of dosimetric parameters included central axis depth-dose, field-size factors, wedge factors, penumbra, and leaf leakage for the 6-MV and 15-MV photon beams available on this accelerator. The depth-dose characteristics, output factors, and transmission factors were similar to those reported in the literature for a machine by the same manufacturer with a standard treatment head. Because of scalloping, the effective penumbra for the MLC was 3 to 4 mm wider than that for the conventional collimator jaws. The output for the fields shaped by the MLC was generally lower than that for similar fields shaped with Lipowitz's metal (Cerrobend). The magnitude of the difference was field-size dependent and ranged from 0.5% to 4.5% for open shaped fields, increasing to 1% to 5% in the presence of wedges. Further analysis of this observation has shown it to be primarily due to differences in the scattered radiation from the collimator head.

Biophysical Phenomena↗