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Biomedical subjects

L Kwock

Publications and source records attributed to L Kwock.

At least 19 recordsLinked to original sources
PubMed2000

Proton MR spectroscopy in children with bipolar affective disorder: preliminary observations.

BACKGROUND AND PURPOSE: Bipolar affective disorder (BPAD) can have its onset during childhood, but the diagnosis may be difficult to establish on the basis of clinical findings alone. Our purpose was to determine whether proton MR spectroscopy can be used to identify abnormalities in the brain of children with BPAD. METHODS: Ten children, ages 6 to 12 years, underwent clinical testing to establish the diagnosis of BPAD. After a drug washout period, all patients underwent MR spectroscopy in which a TE of 135 was used along with a single-voxel placement in both frontal and temporal lobes during a single session. Peaks from N-acetylaspartate (NAA), choline (Cho), glutamate/ glutamine (Glu/Gln), and lipids were normalized with respect to the creatine (Cr) peak to obtain ratios of values of peak areas. These data were compared with those obtained in 10 non-age-matched control subjects. To corroborate our data, five children with BPAD also underwent 2D MR spectroscopic studies of the frontal lobes with parameters similar to those used in the single-volume studies. RESULTS: All children with BPAD had elevated levels of Glu/Gln in both frontal lobes and basal ganglia relative to the control group. Children with BPAD had elevated lipid levels in the frontal lobes but not in the temporal lobes. Levels of NAA and Cho were similar for all locations in both groups. Two-dimensional MR spectroscopic studies in five children with BPAD confirmed the presence of elevated lipids in the frontal lobes. CONCLUSION: Our preliminary observations suggest that MR spectroscopy may show abnormalities in children with BPAD not found in unaffected control subjects. It remains to be established whether these abnormalities are a signature of the disease and can be used as a screening test.

Aspartic Acid↗
PubMed1999

Sydenham's chorea: MRI and proton spectroscopy.

We present the MRI and proton spectroscopy findings in a child with clinical diagnosis of Sydenham's chorea. MRI showed high signal in the caudate nuclei and putamina on T2-weighted images. We believe that the spectra showed an abnormality in the number and/or function of neurons, lipids from cellular breakdown (cytolytic effect of antibodies), aminoacids (related to the presence of antibodies in the neostriatum), and sugars (also related to the presence of antibodies). The spectroscopy features correlate well with the histopathology and biochemistry of this rare disorder.

Basal Ganglia↗
PubMed1998

Usefulness of proton MR spectroscopy in the evaluation of temporal lobe epilepsy.

OBJECTIVE: The purpose of our study was to compare the ability of MR spectroscopy with that of standard presurgical methods to accurately lateralize the abnormal hippocampus in a group of patients with complex partial seizures. SUBJECTS AND METHODS: Ten healthy volunteers (five male, five female) without a history of seizures, significant head trauma, or other neurologic abnormalities were chosen to participate in the study. Twelve consecutive patients (three male, nine female) having intractable temporal lobe epilepsy and undergoing presurgical evaluation for temporal lobectomy were chosen to participate in the study. The condition of all patients was refractory to medications. All patients underwent presurgical examination with interictal and video ictal electroencephalography, ictal single-photon emission computed tomography, interictal positron emission tomography, MR imaging, and neuropsychologic testing. When noninvasive data were inconclusive, depth or grid recordings were performed. The results of MR spectroscopy were also compared with postsurgical seizure control as defined by the Engel classification. RESULTS: Nine (90%) of 10 control subjects showed no significant difference in N-acetyl aspartate. One control subject showed 16% asymmetry in N-acetyl aspartate between sides. The control group showed no statistically significant differences in ratios of N-acetyl aspartate:creatine, N-acetyl aspartate:choline, or creatine:choline when comparing sides (p < .05). All 12 patients showed clearly lateralizing values identified by the index of asymmetry in N-acetyl aspartate (range, 24-93%), with a mean difference of 51% (SD, 22) (p = .01). Additionally, as a group, statistically significant indexes of asymmetry (p = .01) were seen in ratios of N-acetyl aspartate:choline (mean, 42; SD, 22%), N-acetyl aspartate:creatine (mean, 41; SD, 27), and N-acetyl aspartate:creatine + choline (mean, 42; SD, 22). Using an N-acetyl aspartate index of asymmetry of greater than 15%, which represents the mean index of asymmetry of the control subjects +/- two SDs, as our cutoff level for lateralization, the correct side was identified in all patients. When comparing both hippocampi using an asymmetry index of 15% for N-acetyl aspartate:choline + creatine, 11 (92%) of 12 were correctly lateralized. When comparing the unaffected temporal lobes between patients and control subjects, no statistically significant differences were detected in any metabolites or ratios. CONCLUSION: Our study agrees with others in showing decreased N-acetyl aspartate in the hippocampus of seizure patients when compared with control subjects. Using N-acetyl aspartate, N-acetyl aspartate:creatine, N-acetyl aspartate:choline, and N-acetyl aspartate:creatine + choline as our parameters, patients with mesial temporal lobe epilepsy were correctly lateralized with MR spectroscopy when compared with clinical consensus criteria. We consider MR spectroscopy to be complementary to MR imaging. Both studies can be performed as a single integrated examination.

Adult↗
PubMed1998

Proton MR spectroscopy in neoplastic and non-neoplastic brain disorders.

The basic principles of proton MR spectroscopy as well as newer and more advanced related techniques are reviewed. Spectroscopy is capable of differentiating normal from pathologic brain and provides tissue specificity greater than that of imaging in many instances. Spectroscopic mapping allows for the visualization of the concentration of different metabolites and their distribution within a lesion. This article emphasizes the utility of proton MR spectroscopy in the diagnosis of brain tumors, postradiation therapy changes, infections, degenerative brain disorders, hepatic encephalopathy, ischemia, and demyelination.

Brain↗
PubMed1998

MR spectroscopy in the evaluation of epilepsy.

MR spectroscopy may be a helpful, reliable, noninvasive test with which to lateralize the seizure focus in patients with partial complex seizures. MR spectroscopy is complementary to other studies, especially MR imaging, and both may be performed in a single integrated examination and result in improved surgical management and outcome.

Brain↗
PubMed1998

Localized MR spectroscopy: basic principles.

Radiologic techniques such as positron-emission tomography and single-photon emission tomography have been used for many years to determine metabolic changes in disease processes. Because of increased radiation exposure, these techniques are normally not used to perform extended serial studies to monitor disease processes. This article discusses the basics of MR spectroscopy, various techniques, and terminology used in clinical MR spectroscopy.

Humans↗
PubMed1998

Proton MR spectroscopy of common brain tumors.

Proton MR spectroscopy allows differentiation of normal tissues from pathologic ones. There is now evidence that this technique may be able to distinguish different histological grades of tumors. The proton MR spectroscopic changes due to treatment of brain tumors is discussed in this article.

Brain Neoplasms↗
PubMed1998

Proton MR spectroscopy in psychiatric and neurodevelopmental childhood disorders: early experience.

Variations in brain morphology are increasingly being found in patients with psychiatric disorders. There is early evidence that some metabolic abnormalities may also be present in these patients. In many patients with psychiatric disorders, the diagnosis is not straight forward and may be confounded by co-morbid processes. Establishing the correct diagnosis is important as it leads to institution of appropriate therapies. Descriptions of the authors early experience using proton MR spectroscopy in the evaluation of children with bipolar affective disorder, attention deficit hyperactivity disorder, neurodevelopmental abnormalities in patients with neurofibromatosis type 1, and the effects of certain types of treatment used for these disorders are discussed.

Attention Deficit Disorder with Hyperactivity↗
PubMed1997

Postmortem MR imaging of the brains of patients with AIDS.

Forty-two postmortem formalin-fixed brains of known patients with AIDS were examined with T2-weighted MR imaging before brain cutting. The gross and microscopic brain findings were correlated with the T2 signal changes in the postmortem MR imaging. The brains included examples of progressive multifocal leukoencephalopathy with involvement of the central brain and cerebellum. The authors also encountered the coexistence of progressive multifocal leukoencephalopathy and HIV encephalitis, and the T2 signal changes for each were compared. The T2 signal changes of leptomeningeal and perivascular space cryptococcal infection and CMV ependymitis are documented. Several expressions of primary cerebral lymphoma, including large nodules, choroid plexus infiltration, and diffuse microscopic sites of tumor also are assessed.

AIDS-Related Opportunistic Infections↗
PubMed1997

Proton MR spectroscopy in Coats disease.

We describe a case of acute left-sided visual loss in a 4-year-old boy. CT showed hyperdense retinal detachment with a tiny calcification, and MR imaging showed subretinal hyperintensity on both T1- and T2-weighted images. Proton MR spectroscopy showed a large peak between 1 and 1.6 ppm that we believe corresponds mainly to lipids, which are characteristic of the exudate present in Coats disease.

Blood-Retinal Barrier↗
PubMed1997

Extraneous lipid contamination in single-volume proton MR spectroscopy: phantom and human studies.

PURPOSE: To determine the degree of extraneous lipid contamination in defined volumes of interest studied with single-volume proton MR spectroscopy. METHODS: Single-volume proton MR spectroscopy was performed on a fat/water phantom and in three volunteers using the stimulated-echo acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) localization methods. Three different volumes of interest (8, 27, and 64 cm3) were examined at echo times of 20, 135, and 270 for the STEAM sequences and 135 and 270 for the PRESS acquisitions in both the phantom and the volunteers (volumes of interest were placed adjacent to but not encompassing fat-containing structures, such as the scalp and retroorbital fat). The degree of lipid contamination was then correlated with measurements of the section profiles. RESULTS: The PRESS method resulted in less extraneous lipid contamination in both phantom and volunteer studies. The STEAM method had the highest level of lipid contamination signal in phantom and human studies. In the volunteers, volumes of interest abutting fat-containing structures obtained with PRESS or STEAM sequences showed no lipid contamination. However, the STEAM sequences showed lipid signal in the volume of interest adjacent to orbital fat whereas the PRESS sequences did not. These observations are supported by the section profile studies, which showed that the actual volume excited by the STEAM sequence was 7% to 32% larger than that originally selected, while with PRESS the actual excited volume was 12% to 16% smaller than that originally selected. CONCLUSION: In our MR unit, short-echo-time STEAM sequences (< or = 135 milliseconds) resulted in extraneous lipid contamination in phantom and human studies adjacent to the orbits. PRESS sequences showed no lipid contamination in volumes abutting fat structures in phantoms or humans. These results correlated closely with the configuration of the section profiles. Although these findings might be dependent on the MR unit used, our study could help determine extraneous lipid contamination for other MR units.

Adipose Tissue↗
PubMed1996

Tumor retention of 5-fluorouracil following irradiation observed using 19F nuclear magnetic resonance spectroscopy.

PURPOSE: The combination of 5-fluorouracil (5FU) and radiation results in improved tumor control in a variety of gastrointestinal cancers. We propose the enhancement is related to radiation potentiating the antitumor effects of 5FU. To better understand the mechanism of the 5FU-radiation interaction, 19F nuclear magnetic resonance (NMR) spectroscopy experiments were performed to observed the tumor clearance and metabolism of 5FU. METHODS AND MATERIALS: Experiments were performed on 10 3-6-week-old female (Nu/Nu) athymic nude mice. Flank tumors measuring approximately 1.0 cm in diameter 3 weeks following a subcutaneous injection of 1 x 10(6) human colon adenocarcinoma (HT-29) cells were studied. In our first group, all animals received an intravenous bolus injection of 5FU (100 mg/kg) immediately before spectroscopic analysis. Animals in the second group were first treated with a single tumor radiation dose of 10 Gy just before the 5FU injection and subsequent spectroscopy. Spectroscopic analysis was performed with a 2.0-T NMR spectroscopy system. RESULTS: The tumor retention of 5FU was prolonged in animals receiving radiation before the drug infusion. The tumor clearance rate of the 5FU for nonirradiated animals was 0.0178 +/- 0.0082/min vs. 0.0055 +/- 0.0027/min for irradiated animals, reflecting a threefold reduction in drug clearance in the irradiated tumors. The difference was significant at p < 0.005. CONCLUSION: Our preliminary experiments suggest the enhanced cytotoxicity seen with concurrent 5FU and radiation is related to prolonged tumor retention of 5FU induced by radiation. This is consistent with the hypothesis that radiation is potentiating the cytotoxic effects of 5FU.

Animals↗
PubMed1996

Postmortem MR imaging of lobar cerebral infarction with pathologic and in vivo correlation.

Postmortem magnetic resonance (MR) imaging features of different types of lobar cerebral infarction are correlated with the findings in gross and histologic specimens. The postmortem findings are also correlated with in vivo findings in similar cases selected from teaching files. In acute infarction, white matter vasogenic edema leads to high signal intensity on T2-weighted images and blurring of the gray-white matter junction. Petechial hemorrhage in the cortex results in inhomogeneous signal intensity on T2-weighted images. In laminar necrosis, the hyperintense cortex on T1-weighted images is due not to hemorrhage but possibly to necrosis and the presence of lipid-laden macrophages. In subacute infarction, cortical edema and necrosis may cause the gyral pattern of enhancement. Meningeal inflammation and early fibrosis are probably responsible for meningeal enhancement. In chronic infarction, gliosis and cystic malacia are responsible for the increased signal intensity of white matter on T2-weighted images. Knowledge of the pathologic features of cerebral infarction helps in understanding the MR imaging findings.

Acute Disease↗
PubMed1996

Proton MR spectroscopy of squamous cell carcinoma of the upper aerodigestive tract: in vitro characteristics.

PURPOSE: To determine the ability of in vitro high-field-strength proton MR spectroscopy to differentiate squamous cell carcinoma of the upper aerodigestive tract from uninvolved muscle. METHODS: Surgical specimens of squamous cell carcinoma arising from the upper aerodigestive tract (n = 18) and from muscle (n = 13) were examined in vitro using high-field (11 T) proton MR spectroscopy. The peak heights of choline and creatine were measured for tumor and muscle at echo times of 136 and 272. The choline/creatine (Cho/Cr) ratio was compared between tumor and normal tissue for each echo time. Student's t test was used to determine whether a significant difference existed between proton MR spectroscopic measurements of the Cho/Cr ratio for tumor and muscle. RESULTS: The mean Cho/Cr ratio was consistently higher in tumor than in muscle at all echo times; however, statistically significant differences between tumor and muscle were identified only at longer echo times (136 and 272). CONCLUSION: The Cho/Cr peak height ratio can be used to differentiate tumor from muscle in vitro (at 11 T).

Carcinoma, Squamous Cell↗
PubMed1995

MELAS syndrome: imaging and proton MR spectroscopic findings.

PURPOSE: To evaluate imaging findings in MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, strokes) syndrome for the presence and location of infarctions and the presence of lactate. METHODS: Eight patients were studied with MR (n = 8) and CT (n = 2). One patient underwent single-photon emission CT with technetium 99m hexamethyl-propyleneamine oxime and one patient had conventional catheter angiography. One fixed brain was studied with MR imaging. Five patients underwent single volume proton MR spectroscopy. Imaging studies were evaluated for atrophy, edema, and infarctions. Proton MR spectroscopy was visually analyzed for presence or absence of lactate. RESULTS: One patient showed a cerebral infarction, and later a second distant infarction developed. One patient showed a transient area of cortical edema. Two patients had small nonspecific periventricular white matter abnormalities and one patient had diffuse white matter hyperintensities. Two patients had nonspecific MR abnormalities (probably age-related changes), and two had normal MR findings. None had basal ganglia involvement. Proton MR spectroscopy showed presence of lactate in one case with transient cortical edema; in two cases with nonspecific (probably age-related) brain findings; and in two patients with normal MR findings. CONCLUSIONS: Patients with MELAS have a variety of MR findings. The fact that proton MR spectroscopy showed lactate in all five cases studied, regardless of MR findings, indicates that proton MR spectroscopy may be more sensitive in the detection of MELAS-associated abnormalities than MR imaging.

Adolescent↗