Search PubMed⌕ Search

Biomedical subjects

S Chopra

Publications and source records attributed to S Chopra.

At least 55 records · Page 3Linked to original sources
PubMed2001

Tumor recurrence after radiofrequency thermal ablation of hepatic tumors: spectrum of findings on dual-phase contrast-enhanced CT.

OBJECTIVE: We conducted this study to determine the spectrum of CT findings of tumor recurrence after radiofrequency ablation of primary and secondary malignant hepatic tumors. MATERIALS AND METHODS: Twenty-five patients, 10 with hepatocellular carcinoma (HCC) and 15 patients with metastases who developed tumor recurrence after radiofrequency ablation of hepatic neoplasms, formed the study population. Three observers reviewed the CT scans of these patients and evaluated the location (local intrahepatic, remote intrahepatic, or extrahepatic) of all recurrent lesions and the morphology and enhancement characteristics of local intrahepatic recurrences. RESULTS: Local intrahepatic recurrences were seen in nine patients (90%) and 11 patients (73%); remote intrahepatic recurrences, in five patients (50%) and seven patients (45%); and extrahepatic recurrences, in zero and six patients (40%) with recurrent HCC and recurrent metastases, respectively. Of the 12 nodules of local intrahepatic recurrences in HCC and the 24 in metastases, the patterns of local intrahepatic recurrences were of nodular, halo, and gross enlargement types in eight (67%) and nine (38%), four (33%) and six (38%), and zero and nine (37%) nodules in HCC and hepatic metastases, respectively. The number of local intrahepatic recurrent lesions enhancing in the arterial phase was significantly greater in HCC. CONCLUSION: Tumor recurrences occurred at intra- and extrahepatic sites after radiofrequency ablation of hepatic neoplasms. The local intrahepatic recurrences appeared in three patterns: nodular, halo, or gross enlargement. The sites of recurrence and the morphologic patterns of local intrahepatic tumor recurrence differed between primary and secondary hepatic neoplasms.

Carcinoma, Hepatocellular↗
PubMed2001

Radiofrequency thermal ablation: computer analysis of the size of the thermal injury created by overlapping ablations.

OBJECTIVE: The purpose of this study was to perform a computer analysis of the size of the thermal injury created by overlapping multiple thermal ablation spheres. MATERIALS AND METHODS: A computer-assisted design system was used to create three-dimensional models of a spherical tumor, a spherical tissue volume consisting of the tumor plus a 1-cm tumor-free margin, and individual spherical ablations. These volumes were superimposed in real-time three-dimensional space in different geometric relationships. The effect of the size and geometric configuration of the ablation spheres was analyzed with regard to the ability to ablate the required volume of tissue (tumor plus margin) without leaving untreated areas or interstices. RESULTS: The single-ablation model showed that if a 360-degree 1-cm tumor-free margin is included around the tumor targeted for ablation, radiofrequency ablation devices producing 3-, 4-, and 5-cm ablation spheres can be used to treat 1-, 2-, and 3-cm tumors, respectively. The six-sphere model, in which six ablation spheres are placed in orthogonal planes around the tumor, showed that the largest tumor that may be treated with a 3-cm ablation device is 1.75 cm, whereas 4- and 5-cm ablation spheres can be used to treat tumors measuring 3 and 4.25 cm, respectively. The 14- sphere model showed that addition of eight more spheres to the six-sphere model increased the treatable tumor size to 3, 4.6, or 6.3 cm, depending on the diameter of the ablation sphere used. For treating larger tumors, we found a cylindrical model to be less efficient but easier to control. CONCLUSION: Our computer analysis showed that the size of the composite thermal injury created by overlapping multiple thermal ablation spheres is surprisingly small relative to the number of ablations performed. These results emphasize the need for a methodic tumor ablation strategy.

Computer Simulation↗
PubMed2000

Measurement of the W-->taunu production cross section in pp collisions at square root s=1.8 TeV.

We report on a measurement of sigma(pp-->W+X)B(W-->taunu) in pp collisions at sqrt[s]=1.8 TeV at the Fermilab Tevatron. The measurement is based on an integrated luminosity (lum) of 18 pb-1 of data collected with the D0 detector during 1994-1995. We find that sigma(pp-->W+X)B(W-->taunu)=2.22+/-0.09 (stat)+/-0. 10 (syst)+/-0.10 (lum) nb. Lepton universality predicts that the ratio of the tau and electron electroweak charged current couplings to the W boson, gWtau/gWe, be unity. We find gWtau/gWe=0.980+/-0.031, in agreement with lepton universality.

Journal Article↗
PubMed2000

Probing Balitsky-Fadin-Kuraev-Lipatov dynamics in the dijet cross section at large rapidity intervals in pp collisions at sqrt[s]=1800 and 630 GeV.

Inclusive dijet production at large pseudorapidity intervals (Deltaeta) between the two jets has been suggested as a regime for observing Balitsky-Fadin-Kuraev-Lipatov (BFKL) dynamics. We have measured the dijet cross section for large Deltaeta in pp collisions at sqrt[s]=1800 and 630 GeV using the D0 detector. The partonic cross section increases strongly with the size of Deltaeta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of alphaBFKL(20 GeV)=1.65+/-0.07.

Journal Article↗
PubMed2000

Operative management of diverticular emergencies: strategies and outcomes.

HYPOTHESIS: A selective surgical approach using either a 1- or a 2-stage resection is relatively safe and effective in the management of acute complicated colonic diverticulosis. DESIGN: A consecutive cohort study. SETTING: A university hospital. PATIENTS: Eighty-nine consecutive patients who underwent emergency operations for diverticular disease between July 1, 1984, and June 30, 1999. There were 53 male and 36 female patients (mean age, 47 years). The ethnic background was predominantly Mexican American (58 patients [65.2%]). INTERVENTIONS: Resections of the affected colon (n = 83) plus construction of a Hartmann pouch or mucous fistula (n = 72) or primary anastomosis (n = 11). MAIN OUTCOME MEASURES: Morbidity, mortality, and length of hospital stay. RESULTS: Sixty-eight operations were performed for perforation at an annual rate that has increased greater than 75% in the past 15 years. Another 14 patients underwent operations for obstruction, and 7 underwent operations to control unremitting hemorrhage. Surgical therapy included resection of the affected segment of the bowel in 83 (93%) of the 89 patients, and a Hartmann pouch or mucous fistula was added in 72 (81%). A primary anastomosis was performed in 4 (80%) of 5 right-sided lesions but in only 7 (8%) of 84 left-sided lesions. Morbidity occurred in 38 (43%) of the 89 patients, and the mortality was 4%, with 4 deaths occurring secondary to sepsis in high-risk patients with perforations (n = 3) or obstructions (n = 1). The average length of hospital stay was 19.7 days (range, 5-80 days). CONCLUSIONS: Emergency operations for diverticular disease are uncommon but may be associated with substantial morbidity and occasional mortality. Complicated diverticulosis may present at a relatively young age, and perforated forms appear to be increasing rapidly in prevalence. Most diverticular lesions can be satisfactorily managed using a selective approach based on resection with either a primary anastomosis or a temporary colostomy.

Adult↗
PubMed2000

Hepatitis C.

In the latter half of the 20th century, HCV emerged as the most common cause of chronic liver disease, and will likely remain so. Since its initial discovery in 1989, rapid progress has been made in our understanding of the virology, epidemiology, natural history, diagnosis, and treatment of HCV. Over the next few decades, as further advancements are made, superior treatment options will become available.

Antiviral Agents↗
PubMed2000

Complex structure of a maize Myb gene promoter: functional analysis in transgenic plants.

The maize P gene encodes a Myb-like transcription factor that regulates synthesis of red flavonoid pigments in floral organs. To study the transcriptional regulation of the P gene, candidate regulatory sequences of the P1-rr gene promoter were identified by Ac insertional mutagenesis and subjected to functional testing in transgenic maize plants. The results indicate that a 561 bp fragment (Pb) encompassing the transcription start site (-235 to +326) supports weak expression of a GUS reporter gene in floral organs, including husk, silk, kernel pericarp, cob and male inflorescence. Two other fragments, located approximately 1 and 5 kb 5' of the transcription start site, increased the levels of GUS activity in floral tissues and thus appear to contain enhancer elements. All of the tested constructs gave similar patterns of GUS expression, suggesting that the 561 bp Pb fragment that is common among the transgene constructs contains regulatory elements that promote activation in floral organs. The basal promoter and proximal enhancer fragments contain putative binding sites for bZip regulatory factors, and a complex arrangement of palindromes including a large inverted repeat of two tRNA-like genes. Possibly, interconversions between linear and cruciform conformations of the palindromes may affect protein/DNA interactions and thereby modulate P1-rr expression.

Base Sequence↗
PubMed2000

Iron reduction as an adjuvant to interferon therapy in patients with chronic hepatitis C who have previously not responded to interferon: a multicenter, prospective, randomized, controlled trial.

Hepatic iron concentration has consistently been observed as being directly correlated with the response to interferon therapy in chronic hepatitis C virus (HCV). We therefore conducted a randomized, controlled trial comparing iron reduction by phlebotomy with iron reduction followed by retreatment with interferon in 96 patients with chronic hepatitis C who had previously not responded to a course of interferon. During the initial phase when all patients were undergoing phlebotomy, we found that serum alanine transaminase (ALT) activities decreased but by less than 50% from baseline in 67 patients (89%), decreased by more than 50% in 12 patients (13%) and became normal in 9 patients (9%) with no overall change in HCV-RNA levels. Subsequently no patient in either treatment group achieved a sustained virologic response. Improvements in necroinflammatory changes were noted in liver biopsy specimens in those patients receiving phlebotomy plus interferon (mean index 8.59 vs. 7.37, P <. 05). A slight but not statistically significant decrease in histologic activity index was noted in those subjects treated by phlebotomy alone (mean index 8.4 vs. 7.75, P not significant). We conclude that, although prior phlebotomy therapy does not improve the rate of sustained response to interferon retreatment, it does result in less liver injury manifested by a decrease in serum transaminase activity and a slight improvement in liver histopathology.

Adult↗
PubMed2000

Hierarchical patterns of transgene expression indicate involvement of developmental mechanisms in the regulation of the maize P1-rr promoter.

The maize P1-rr gene encodes a Myb-homologous transcription factor that regulates the synthesis of red flavonoid pigments. Maize plants transformed with segments of the P1-rr promoter driving a GUS reporter gene exhibit significant variation in transgene expression, both between independent transformation events and among sibling plants derived from a single event. Interestingly, variability in spatial expression is not random; rather, transgene activity occurs predominantly in five patterns that fit a hierarchy: expression is most common in kernel pericarp, with sequential addition of expression in cob glumes, husk, silk, and tassel. The hierarchical expression pattern of P-rr::GUS transgenes suggests a possible model for developmental regulation of the P1-rr gene. Our results demonstrate that variability in transgene expression, a common occurrence in transgenic plant studies, can be informative if adequately analyzed to uncover underlying patterns of gene expression.

Enhancer Elements, Genetic↗
PubMed2000

A segmental gene duplication generated differentially expressed myb-homologous genes in maize.

The myb-homologous p1 gene regulates the synthesis of flavonoid pigments in maize kernel pericarp and cob; these floral organs are greatly modified in size and shape compared with their counterparts in teosinte, the progenitor of maize. To elucidate the molecular evolution of the p1 gene in relation to its expression and possible functions in maize and teosinte, we have isolated a second maize gene (p2) that is highly homologous with the p1 gene, and a related gene (p2-t) from Zea mays subsp parviglumis. We present evidence that the maize p1 and p2 genes were generated by duplication of an ancestral p gene (p(pre)) and its downstream sequences; the duplicated 3' flanking sequences were inserted upstream of the p(pre) gene, thereby changing its transcription pattern. This model accounts for the structural organization and the observed differential expression of the p1 and p2 genes: p1 transcripts accumulate in kernel pericarp, cob, tassel glumes, and silk, whereas p2 transcripts are found in developing anther and silk. The duplication is estimated to have occurred 2.75 million years ago; subsequently, multiple retroelements have been inserted between the p1 and p2 genes. Our results demonstrate the evolution of a single gene into a compound locus containing two component genes with different tissue specificities. Expression of the p1 gene in the kernel pericarp may have provided a selective advantage during the evolution of maize kernel morphology.

Amino Acid Sequence↗
PubMed2000

Primary gallbladder cancer: recognition of risk factors and the role of prophylactic cholecystectomy.

The objective of this article is to review the available literature on the epidemiology, predisposing factors, and conditions associated with primary gallbladder cancer, and to discuss the role of prophylactic cholecystectomy in high-risk patient populations. Gallbladder cancer is a highly malignant tumor with a poor 5-yr-survival rate. It is a tumor of the elderly and has striking genetic, racial, and geographic characteristics, with an extremely high prevalence in Native Americans and Chileans. Cholelithiasis is a well-established risk factor for gallbladder cancer and the risk seems to correlate with stone size. Polyps that are >1 cm, single, sessile, and echopenic are associated with a higher risk of malignancy. Anomalous junction of pancreaticobiliary ducts (AJPBD), especially without choledochal cyst, and porcelain gallbladder are additional factors that predispose to gallbladder cancer. Lesser associations include chronic bacterial infections of the gallbladder, typhoid carrier state, certain occupational and environmental carcinogens, hormonal changes in women, and certain social, dietary, and familial factors. It is important to identify high-risk groups for gallbladder cancer because of the dismal nature of this tumor. In patients with porcelain gallbladder and anomalous junction of the pancreatic and biliary ducts, cholecystectomy is recommended provided that the patient is a good operative candidate. Patients with large solitary polyps or gallstones require close ultrasonic follow-up. With the advent of endoscopic ultrasound it is expected that early changes of malignancy in polyps will be reliably detected, and more patients will potentially be cured with a simple cholecystectomy. Through a MEDLINE/PAPERCHASE search we identified and reviewed articles regarding gallbladder cancer published in English-language journals between 1966 and 1999, using the key words biliary tract and gallbladder diseases, cancer, neoplasms, surgery, cholelithiasis, gallstones, cholecystitis, gallbladder polyps, risk factors, chemical industry, occupational diseases, typhoid, porcelain gallbladder, bacteremia, and precancerous conditions. We also used the bibliography of relevant articles to increase our search. A total of 122 publications were selected using the mentioned data source.

Cholecystectomy↗
PubMed2000

Helical CT cholangiography with oral cholecystographic contrast material.

Twenty asymptomatic volunteers underwent helical computed tomographic (CT) cholangiography 10-12 hours after ingesting iopanoic acid. Three observers assessed the images for the extent of bile duct visualization and image quality. The common bile duct and common hepatic duct were adequately visualized in 19 (95%) subjects. Helical CT cholangiography with oral cholecystographic contrast material is feasible and deserves further clinical studies.

Administration, Oral↗
PubMed2000

Gastrointestinal wall thickening in patients with cirrhosis: frequency and patterns at contrast-enhanced CT.

PURPOSE: To determine the frequency and patterns of gastrointestinal wall thickening at contrast material-enhanced computed tomography (CT) in patients with cirrhosis. MATERIALS AND METHODS: Three radiologists retrospectively assessed the contrast-enhanced abdominal CT scans of 77 patients with cirrhosis and 100 patients without cirrhosis for gastrointestinal wall thickening from the stomach through the descending colon. The frequencies of wall thickening were determined in the cirrhosis and in the control groups and were compared by using the Fisher exact test. The segmental distribution, symmetry, and enhancement pattern were evaluated in all patients with cirrhosis and gastrointestinal wall thickening. RESULTS: Gastrointestinal wall thickening was seen in 49 (64%) patients with cirrhosis and in seven (7%) control subjects (P <.005). The jejunum and ascending colon were the most common sites of gastrointestinal wall thickening; each was involved in 32 (42%; 95% CI: 30%, 53%) patients. The scans of 30 (61%; 95% CI: 47%, 75%) patients with gastrointestinal wall thickening showed multisegmental distribution. Gastrointestinal wall thickening was concentric and homogeneous in all patients with cirrhosis. CONCLUSION: Gastrointestinal wall thickening is common on contrast-enhanced abdominal CT scans in patients with cirrhosis. It frequently involves multiple segments. The jejunum and ascending colon are the most common sites of involvement.

Adult↗
PubMed2000

Transjugular intrahepatic portosystemic shunt: accuracy of helical CT angiography in the detection of shunt abnormalities.

PURPOSE: To determine the sensitivity, specificity, and accuracy of helical computed tomographic (CT) angiography in the detection of transjugular intrahepatic portosystemic shunt (TIPS) stenoses or occlusions. MATERIALS AND METHODS: Thirty-seven patients underwent 50 helical CT angiographic examinations and, within 2 weeks of each examination, portography with measurement of the portosystemic pressure gradient. Helical CT angiograms were independently interpreted by three radiologists who were blinded to the results of portography. Results of helical CT angiography and portography were compared. Sensitivity and specificity of helical CT angiography were separately calculated for the demonstration of morphologic abnormalities and the determination of their hemodynamic significance. RESULTS: Of the 50 portograms, 31 (62%) demonstrated morphologic TIPS abnormalities, 24 (77%) with and seven (23%) without elevated portosystemic pressure gradients. Helical CT angiograms correctly demonstrated 30 (97%) of the 31 morphologic abnormalities and allowed correct diagnosis of 22 (92%) of the 24 hemodynamically significant abnormalities. Nineteen (38%) portograms were normal; helical CT angiograms correctly demonstrated the absence of abnormality in 17 (90%) of these cases. Sensitivity and specificity of helical CT angiography for all morphologic abnormalities were 97% and 89%, respectively, and, for hemodynamically significant abnormalities, 92% and 77%. CONCLUSION: Helical CT angiography holds promise as a screening modality for the detection of TIPS stenoses or occlusions.

Adult↗