Biomedical subjects
Publications and source records attributed to C S Poon.
A method employing solvent-activated tape electrode was adapted for locating electropermeable points, minimizing possible errors due to human and external factors. Measurements along two meridians on the forearm showed that these points were somewhat scattered about the conventional acupuncture loci and their observable occurrence was probably the result of localized thermal damage of the epidermis.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Fast spin-echo (FSE) sequences are becoming popular for T2-weighted clinical imaging because they result in a severalfold reduction in imaging time and because they provide conventional spin-echo contrast for most tissues. Fat, however, has been observed to have anomalously high signal intensity on FSE images. The present study shows that the brighter fat results from the multiple 180 degrees refocusing pulses, which eliminate diffusion-mediated susceptibility dephasing and suppress J-coupling modulation of the echo train.
Many studies have investigated the use of magnetic resonance relaxation times for tissue characterization. A number have been performed in vivo with clinical whole-body imagers. Unfortunately, the results have yet to establish the role of quantitative tissue relaxation time measurements in clinical diagnosis. One of the major problems is that the techniques used in many of these studies are error prone, making the results inconclusive. In the present study, the problems associated with clinical T2 measurements were systematically evaluated in an attempt to obtain reliable in vivo quantitation. The authors demonstrate that spoiler gradients are the most effective technique for artifact suppression but that they render ineffective radio-frequency phase schemes such as the Meiboom-Gill modification to the Carr-Purcell sequence to compensate experimental imperfections. The present study results in a more reliable multi-echo sequence for T2 measurement. Preliminary clinical results in brain and cervix demonstrate the performance of the new technique.
Specimens from modified radical hysterectomies performed for invasive carcinoma of the cervix were analyzed with quantitative T2 magnetic resonance (MR) imaging and histologic study to determine to what degree there was a correlation between the findings of the two modalities. The mean T2 of cervical stroma was 48 msec, while the outer zone of the cervix had a mean T2 of 62 msec and the central canal region typically had T2 values of 115 msec +/- 20 (standard deviation). A total of nine cervical cancers were analyzed, and their mean T2 value was 79 msec. Separation between cervical stroma and tumor was good, with stromal T2 values ranging from 30 to 66 msec, while tumor T2s ranged from 60 to 97 msec. Statistical analysis indicated that these data were associated with a sensitivity of 89% and a specificity of 95%, with 95% confidence intervals of [50%, 99.4%] and [74%, 99.7%], respectively, for separating tumor from stroma on the basis of T2 value. Quantitative T2 imaging was found to provide an effective, nonsubjective means of classifying cervical anatomy and neoplastic disease.
An adaptive neural network model that exhibits the optimality and homeostasis characteristics of the respiratory control system is described. Based upon the Hopfield network structure and a postulated Hebb-like respiratory synapse with correlational short-term potentiation, the model is capable of mimicking the normal ventilatory responses to exercise and CO2 inputs without the need for an explicit exercise stimulus. Results suggest the possibility of an adaptive neuronal mechanism that effects optimal homeostatic regulation of respiration in mammals.
The use of chemical shift imaging for fat and water quantitation and differential measurement of relaxation times for the fat and water component is demonstrated using a hybrid technique. The efficacy of the imaging technique for fat and water quantitation has been tested by comparing the results of imaging to the results of volumetric measurements in phantoms with oil and water homogeneously mixed, fat extraction in ground meat of different grades, and biopsy in preliminary clinical studies. Good correlation is found between the fat and water content measured by imaging and that measured by other means except for the inability to differentiate unsaturated fat protons from water protons. Longitudinal (T1) and transverse (T2) relaxation times for water and fat are also shown to be measurable independently when fat and water signal are suppressed accordingly. The independently measured relaxation times correspond closely to those of the pure samples except that unsaturated protons give decreased water relaxation estimates.
An uncommon occurrence of actin inclusions in the stromal cells of a benign fibroepithelial tumor of breast is reported. Histologically, many of the stromal cells contained round and eosinophilic intracytoplasmic inclusions identical to those seen in inclusion body fibromatosis. Ultrastructurally, these inclusions represented dense spherical clumps of microfilaments derived from rough endoplasmic reticulum. The literature was reviewed and follow-up data showed that the clinical course of these morphologically distinctive benign fibroepithelial tumors was relatively indolent if completely excised, in contrast to inclusion body fibromatosis, which commonly recurs. The pathogenesis may be related to abnormal production of truncated actin filaments or alteration in microenvironment.
T2-weighted images (spin echo 2,000/60) show a high signal intensity rim around the prostate. Our investigations show that this rim is not part of the pelvic fat; it has T1 and T2 relaxation times similar to heparinized blood; it demonstrates little inflow effect; and after an intravenous injection of Gd-diethylenetriamine pentaacetic acid, its signal intensity increases. We conclude that this rim is the periprostatic venous plexus.
OBJECTIVE: To describe the fine needle aspiration cytology findings of invasive micropapillary carcinoma and correlate them with the histologic appearance. STUDY DESIGN: We reviewed the cytologic features of three cases of pure invasive micropapillary carcinoma in the files of Pamela Youde Nethersole Eastern Hospital from 1998 through 2000. Immunohistochemical study for epithelial membrane antigen was performed retrospectively on the cell block sections. Ultrastructural examination was also carried out on one of the cases. RESULTS: Two of the tumors were at pathologic stage II, and the remaining case was at stage III. Ipsilateral axillary lymph node metastases with similar morphology were seen in two of them. Cytologically, the smears were of moderate cellularity and composed of three-dimensional tumor cell balls, abortive and sometimes branching papillae, angulated tumor cell clusters, morules and occasional acini. Some of the tumor cell balls possessed scalloped borders. Focally, the tumor morules clustered together and were separated from each other by small, slitlike spaces. A small number of isolated malignant cells was also present in the background. The cell block sections showed mainly dispersed acini of tumor cells. The "reverse polarity" highlighted in histologic sections by immunohistochemical study for epithelial membrane antigen was not consistently demonstrated in the cell block material. Ultrastructural examination confirmed the focal presence of surface microvilli on the periphery of the tumor cell morules. CONCLUSION: Invasive micropapillary carcinoma of the breast possesses some subtle but distinctive cytologic features. With the help of cell block morphology and ancillary techniques, the preoperative suspicion of this rare subtype of ductal carcinoma, which carries a high propensity for lymphatic permeation, is possible.