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Biomedical subjects

R Ravichandran

Publications and source records attributed to R Ravichandran.

At least 19 recordsLinked to original sources
PubMed2003

Prevalence of renovascular abnormality in patients undergoing cardiac catheterization.

OBJECTIVE: To determine the prevalence of renal artery disease and to correlate the underlying risk factors like age, sex, diabetes, hypertension, urea and creatinine in patients who have undergone angiogram for cardiovascular diseases. METHODS: Retrospective analysis of the reports of angiogram of patients who have undergone cardiac catheterization in Vijaya Heart Foundation for cardiovascular diseases. RESULTS: The prevalence of renovascular stenosis is 12.4%. Prevalence of hypertension and diabetes in the group of patients with renovascular stenosis compared with group having coronary artery disease is not statistically significant (p > 0.8). Univariate and multivariate logistic identified age, diabetes, hypertension and urea as independent predicators of renal artery stenosis; while variables like sex and serum creatinine were not associated. CONCLUSION: High prevalence of unsuspected renovascular abnormalities is found in patients who undergo angiography for cardiovascular disease. Factors like age, diabetes, hypertension and urea could be clinical predicators of renal artery stenosis. Hence renal arteries should be visualized routinely in patients undergoing coronary angiogram for cardiovascular disease.

Adolescent↗
PubMed2002

Spontaneous bilateral perirenal hematoma in a patient with tetrology of Fallot.

We report a patient with tetralogy of Fallot who developed spontaneous bilateral perirenal hematoma at the age of 35. Polycythemia was seen from the age of 3 in this patient. Prolonged clotting time and partial thromboplastin time were observed on various occasions before he developed perirenal hematoma. Blood letting was done periodically according to the value of hemoglobin level and packed cell volume. Resolution of hematoma was seen sonographically.

Adult↗
PubMed2001

Forward scatter dose effect at metallic interfaces irradiated by X and gamma ray therapy beams.

AIM: In this study forward scattering effects near different metallic interfaces are measured for Co-60 gamma and 6 and 18 MV photon beams. The studied effects are the transport of secondary electrons across the metallic interface and the scattering of photons by the metallic inhomogeneity. MATERIALS AND METHODS: All measurements were carried out with a PTW thin-window, parallel plate ionisation chamber (B 23344-036) and an RDM-1F electrometer with digital readout. Thin sheets of aluminium, mild steel, copper, cadmium and lead were used as inhomogeneities. The inhomogeneities were placed between the polystyrene phantom and the front window of the chamber which was maintained at 100 cm SSD. RESULTS: It was noticed that for a high energy photon beam (18 MV) the forward scatter dose factor (FSDF) increases rapidly as the thickness of the metallic inhomogeneity increases. For low energy photons, there is a sharp initial decrease of the FSDF until a minimum value is reached followed by a slow increase with increasing thickness of the inhomogeneity. It was also noted that the FSDF variation at off-axis distances has slightly more slope compared with the ionization ratio (IR) curves for both 6 MV and 18 MV photons. However, the variation in slope is prominent for 18 MV compared with 6 MV photon beam. CONCLUSION: The sharp dose decrease observed downstream of a metallic inhomogeneity at relatively low photon energies (Co-60, 6 MV) is attributed to the internal scattering of secondary electrons within the metal. The dose enhancement observed for high energy photon beams is attributed to the domination of the pair production process, increasing with atomic number. Since FSDF is dependent on the photon beam spectra, it can be used as a measure of beam quality across the beam.

Gamma Rays↗
PubMed2001

Measurement of backscattered radiation from secondary collimator jaws into the beam monitor chamber from a dual energy linear accelerator.

AIM: The photons and electrons backscattered from the upper and lower secondary collimator jaws give rise to a significant increase in the ion charge measured by the monitor chamber, and this increase varies between different accelerators. We have studied the effect of backscatter into the monitor chamber at 6 MV and 18 MV photon energies for the linear accelerator Clinac-1800. MATERIALS AND METHODS: The variation of the output factor was first studied for variable asymmetric fields of fixed field size defined by variable right upper collimator jaw together with a variable Cerrobend block low melting point alloy, with constant lower jaw position. Output measurements were carried out at Dmax in a polystyrene phantom at the geometric center of the asymmetric field. The backscatter radiation effect was also analyzed applying a pair of 20 x 20 x 7.5 cm Cerrobend alloy blocks with 6.0 mm diameter pin-holes in the center aligned telescopically with the field defining light beam. The ion chamber with build-up cap was placed at 25 cm behind the second pin-hole. The in air measurements were made varying upper and lower collimators individually and together. For comparison, a similar study was conducted in a Theratron-780C cobalt-60 beam. RESULTS: In the asymmetric field experiment it was noticed that till the collimator jaw crosses the midline, the output factor is almost constant for 6 and 18 MV photon beams. For extreme field asymmetry, the decreases in output factor were 3.2% and 4.3% for 6 and 18 MV, respectively. The telescopic experiment demonstrated 4.0% and 3.9% reduction in output factor for 6 and 18 MV beams when only the upper jaws were varied. Field definition by the lower jaws only reduced the output factor by 3.3% and 3% for 6 and 18 MV photon beams. For square fields achieved by both the jaws, the output factor variation was similar to that achieved with the upper collimator for both energies. Cobalt-60 measurements with the telescopic arrangement did not show significant dependency of output with field variation, provided that the field-dependent scatter from source capsule and collimator jaws is excluded. CONCLUSION: From this study a maximum reduction of 4% and 4.3% in dose delivery was observed for 6 MV and 18 MV photon beams due to backscattered radiation originating mainly from upper collimator reaching the beam monitor chamber. For asymmetric fields it is felt that direct output measurement is more reliable in order to avoid errors in output factor due to radiation backscattered from the collimator jaws into beam monitor chamber.

Humans↗
PubMed2000

Dose measurements in the build-up region for the photon beams from Clinac-1800 dual energy medical linear accelerator.

AIM: Since the skin dose becomes the limiting factor while deciding the tumorcidal dose, the detailed analysis of dose distribution in the build-up region is necessary for high-energy photon beams. In this study the beam characteristics affecting the build-up and skin dose for 6- and 18-MV photons are analyzed. MATERIALS AND METHODS: Measurements were made with 6- and 18-MV photons using a PTW parallel-plate ionization chamber (B 23344-036) and a RDM-1F electrometer. Build-up ionization measurements were made with the chamber fitted into a 25 x 25 x 25 cm polystyrene phantom with a fixed SSD of 100 cm. The entrance and build-up dose measurements were made with a polycarbonate and a mesh type metallic shielding tray and a 45 degrees wedge. Exit dose measurements were carried out for the graphite patient supporting assembly table top, 1.0 cm thick piece of wood and the 1.0 cm thick patient supporting perspex base frame for head and neck treatments. RESULTS: It was observed that the dmax decreased slightly with field size as with other accelerators. For both photon energies the surface dose was observed to increase with increase in field size. It was also noticed that the dose in the build-up region increases slightly when the polycarbonate secondary blocking tray is introduced with the increase in surface dose. The data show that the tray perturbation factor (TPF) at surface decreases steadily with tray-surface distance for both photon beams for all field sizes. It was noted that the TPF was more when the polycarbonate tray was introduced at shorter tray-surface distances for both energies. At tray-surface distances above 60 cm the TPF almost remained close to unity for 6-MV photons for all field sizes, whereas the continuous decrease in TPF could be noted for 18-MV photon beams even after the TPF reached unity. CONCLUSION: The increase in surface dose with field size for both photon energies is due to the electron scattering from the intervening materials. The use of wedge filters absorbs low-energy scattered electrons significantly and hence, the relative surface dose (RSD) is always less than unity. The increase in dose enhancement percentage with graphite compared to perspex supporting assembly indicates that the electron backscatter is proportional to the atomic number of the medium.

Electrons↗
PubMed1999

Effect of granulocyte macrophage colony stimulating factor on hepatitis-B vaccination in haemodialysis patients.

OBJECTIVES: Haemodialysis patients often fail to respond to hepatitis B vaccination. There are various agents that can be used as vaccine adjuvant in chronic renal failure patients on haemodialysis. In this study, the adjuvant effect of granulocyte macrophage colony stimulating factor (GMCSF) is compared with that of control subjects. METHODS: In this study, eight patients were started on 150 mcg of GMCSF subcutaneously 24 hours prior to intramuscular hepatitis B vaccination (20 mcg of genetically engineered vaccine at the same site). The antibody response to surface antigen (anti HBsAg) in these patients were compared with those of eight control subjects who received standard three doses of monthly 40 mcg of same hepatitis B vaccine. RESULTS: In the control study, only two patients developed significant antibody response to surface antigen whereas seven of eight patients in GMCSF group developed significant antibody titres (> 10 IU/L). The sero-protection rate was 87.5% in GMCSF group and 25% in control group. CONCLUSION: This study shows that GMCSF offers significantly better seroprotection against hepatitis B compared to standard dose of vaccination in patients with chronic renal failure on haemodialysis.

Adjuvants, Immunologic↗
PubMed1998

Role of electron beam treatment in postoperative management of carcinoma of the breast.

The aim of post operative radiotherapy to chest wall and drainage areas in advanced breast cancer is to sterilize the possible microscopic disease. Fifty cases of post surgical breast cancers were evaluated in a prospective study of chest wall radiation therapy by electrons. Fifty women of histologically proved post operative invasive breast cancers underwent simple mastectomy with axillary dissection followed by post-operative radiotherapy (Electron) to chest wall +/- drainage area. The chest wall and IMC was treated by a direct electron beam (9/12 MeV and 12 MeV) at fixed angle. 6 MV X-ray beam was used to treat axillary apex and supraclavicular area. In some cases, supplement RT was given by 6 MV X-rays through small posterior axillary portal. The energy of electron beam was 9 MeV or 12 MeV depending on the thickness of treated area. The supraclavicular and axillary lymphatic regions were treated, by direct custom shaped anterior portal. The dose delivered was 50 Gy over 5 weeks at 2 Gy per fraction. Adjuvant chemotherapy was given to patients who were pre-menopausal with histologically proved axillary node involvement as Cyclophosphamide, Methotrexate and 5-Fluorouracil (CMF) after radiotherapy. Post menopausal patients received adjuvant tamoxifen 10 mg.bid. The overall time varied from 26 to 87 days with a median of 41.5 days (SD 11.7). The followup period varied from 4-32 months with a mean of 22 months (SD 6.4). All the fifty patients developed dense pigmentation towards the end of radiation therapy, along with patchy dry desquamation. Moist desquamation occurred in 6 patients. The median OTT in the patients who developed moist desquamation was 34.5 days. The moist reaction healed over 10-15 days after completion of radiotherapy. Lung Fibrosis (Apical lobe) occurred in four patients. The fibrosis was evident at a median of 12 months of follow up. Lymphoedema of the ipsilateral arm occurred in six patients. None of 50 patients developed late sequalae like Cardiac effects, Rib fracture, Brachial Plexopathy, Shoulder joint impairement and Soft tissue effects. Local control in this study was 96% (48 patients). The two year actuarial overall survival was 80%. In early stages survival was significantly better compared to late stages. The actuarial two year DFS was 72%. In early stages DFS was significantly better compared to late stages.

Adult↗
PubMed1996

Improving cancer radiotherapy with 2-deoxy-D-glucose: phase I/II clinical trials on human cerebral gliomas.

PURPOSE: Evaluation of tolerance, toxicity, and feasibility of combining large fraction (5 Gy) radiotherapy with 2-deoxy-D-glucose (2DG), an inhibitor of glucose transport and glycolysis, which has been shown to differentially inhibit repair of radiation damage in cancer cells. METHODS AND MATERIALS: Twenty patients with supratentorial glioma (Grade 3/4), following surgery were treated with four weekly fractions of oral 2DG (200 mg/kg body weight) followed by whole brain irradiation (5 Gy). Two weeks later, supplement focal radiation to the tumor (14 Gy/7 fractions) was given. Routine clinical evaluation, x-ray computerized tomography (CT), and magnetic resonance (MR) imaging were carried out to study the acute and late radiation effects. RESULTS: All the 20 patients completed the treatment without any interruption. The vital parameters were within normal limits during the treatment. None reported headache during the treatment. Mild to moderate nausea and vomiting were observed during the days of combined therapy (2DG + RT) in 10 patients. No significant deterioration of the neurological status was observed during the treatment period. Seven patients were alive at 63, 43, 36, 28, 27, 19, and 18 months of follow-up. In these patients, the clinical and MR imaging studies did not reveal any late radiation effects. CONCLUSIONS: Feasibility of administering the treatment (2DG + 5 Gy) is demonstrated by the excellent tolerance observed in all 20 patients. Further, the clinical and MR studies also show the absence of any brain parenchymal damage.

Adult↗
PubMed1996

Congenital adrenal hyperplasia presenting as massive adrenal incidentalomas in the sixth decade of life: report of two patients with 21-hydroxylase deficiency.

Divergent recommendations exist regarding the evaluation of adrenal incidentalomas. Recent data have indicated a prevalence of adrenal tumors of 71% in nonclassical congenital adrenal hyperplasia (CAH) and unmasked heterozygotes. These data expand the differential diagnosis of such incidental tumors and substantially modify the approach to their evaluation. We present two patients, female pseudohermaphrodites with the simple virilizing form of CAH and 21-hydroxylase deficiency, who functioned successfully as married phenotypic males. Both came to medical attention in the sixth decade by virtue of massive adrenal incidentalomas encountered in the evaluation of recurrent urinary tract infections. Each had a 46, XX karyotype, no palpable testes, and markedly elevated baseline levels of 17-hydroxyprogesterone (17-OH Prog) of 6086 ng/dL and 6750 ng/dL. Both responded appropriately to dexamethasone suppression with reduction of 17-OH Prog, androgens and, in the second patient, ACTH to normal or near normal levels. Histologic and autopsy examination of the first patient's tumor and computed tomographic characteristics of the second revealed a benign adenoma and myelolipoma respectively. We extend and confirm previous recommendations that CAH be included in the differential diagnosis of adrenal incidentaloma and that baseline 17-OH Prog. levels be obtained, with ACTH stimulation if necessary, to diagnose the presence of nonclassical CAH.

Adenoma↗
PubMed1991

Effects of radiation therapy on the human normal brain (white matter) visualized by MR imaging.

Sequential MR imaging could provide information related to the pathological changes due to the application of external cytotoxic agents such as radiotherapy on the central nervous system. This paper describes the results of our attempt to demonstrate short-term changes associated with normal brain during and immediately following radiotherapy when the whole brain is irradiated for malignant conditions. No observable changes were found in the normal brain parenchyma in any of the patients (n = 8) in T1-, T2-, and proton-density-weighted images in the sequential scans in the first and second weeks and immediately following radiotherapy. Also, no changes were observed in the normal brain appearance at 2 mo (n = 6), up to 6 mo (n = 1), and up to 15 mo (n = 1) after completion of radiotherapy.

Brain↗
PubMed1986

Potential antiradiation drugs containing no nitrogen, and related compounds.

Capabilities are reported of di- and higher sulfides (RSnR') terminated by sulfinate functions [-S(O)O-] for protecting mice against otherwise lethal effects of ionizing radiation. With the use of congeners, structure-activity correlations are developed for the effects of esterification of the sulfinate function, of changing the length of the chain of sulfur atoms, of reduction to a mercapto sulfinate, and of changing the substituents R and R' to chiral and other types of groups. Neither a trisulfide nor a sulfinate by itself was significantly radioprotective. The key requirement for radio-protection in the series appears to be the presence of a sulfur function (-Sn-) from which a thiol can be engendered by a neighboring-group effect of an electron-donating group; sulfoxide functions may afford alternatives to sulfinate functions as such neighboring groups. The relevance of structure-activity relations to the chemical and biological mechanisms involved in the radioprotective activities is discussed.

Animals↗
PubMed1984

Influence of penicillamine and various analogs on matrix-induced bone formation in rats.

D-penicillamine and a variety of analogs have been tested for their ability to interfere with the various stages of bone development using a model for endochondral bone formation. At the highest dose tested (40 mg/rat/day), D-penicillamine inhibited mineralization, D-2-Amino-3-methyl-3-[(2-acetamidoethyl)dithio]butanoic acid (II), at a relatively low dose (10 mg/day), decreased the amount of insoluble collagen in skin, mesenchymal cell proliferation on Day 3, and inhibited bone formation on Day 14. Several other compounds tested, sodium 4-[(D-1, 1-dimethyl-2-amino-2-carboxyethyl)-dithio]butanesulfinate (IV), 2-acetamidoethyl-2-acetamidoethanethiolsulfonate (V), and sodium 4-mercaptobutanesulfinate trihydrate (VI), also inhibited osteogenesis on Day 14.

Animals↗