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Biomedical subjects

George Mathew

Publications and source records attributed to George Mathew.

11 recordsLinked to original sources
PubMed2006

Nonlinear equalization for holographic data storage systems.

Despite the fact that the channel in a holographic data-storage system is nonlinear, most of the existing approaches use linear equalization for data recovery. We present a novel and simple to implement nonlinear equalization approach based on a minimum mean-square-error criterion. We use a quadratic equalizer whose complexity is comparable to that of a linear equalizer. We also explore the effectiveness of a nonlinear equalization target as compared with the conventional linear target. Bit-error-rate (BER) performance is studied for channels having electronics noise, optical noise, and a different span of intersymbol interference. With a linear target, whereas the linear equalizer exhibits an error floor in the BER performance, the quadratic equalizer significantly improves the performance with no sign of error floor even up to 10(-7). With a nonlinear target, whereas the quadratic equalizer provides an additional performance gain of 1-2 dB, the error-floor problem of the linear equalizer has been considerably alleviated, thereby significantly improving the latter's performance. A theoretical performance analysis of the nonlinear receiver with non-Gaussian noise is also presented. A simplified approach is developed to compute the underlying probability density functions, optimum detector threshold, and BER using the theoretical analysis. Numerical results show that the theoretical predictions agree well with simulations.

Journal Article↗
PubMed2006

Acquired Fanconi's syndrome associated with tenofovir therapy.

Tenofovir (Viread) is a nucleotide reverse transcriptase inhibitor introduced into the United States in 2001. It is frequently prescribed not only for its efficacy but also for its decreased side effect profile compared with other nucleoside analogs. It is now increasingly recognized as a cause of acquired Fanconi's syndrome (FS) in human immunodeficient individuals. We describe a case of a patient with AIDS, who, after starting tenofovir therapy, developed myalgias, renal failure, and profound electrolyte abnormalities compatible with the classic features of FS. On discontinuation of tenofovir and replacement of electrolytes, the individual improved clinically with normalization of his renal failure and electrolyte abnormalities. With the success of tenofovir in the anti-HIV drug market, practitioners should remain alert to the possibility of the development of FS. Frequent urine, renal, and electrolyte parameters should be measured at regular intervals following initiation of tenofovir therapy.

Adenine↗
PubMed2005

Effect of genotyping error in model-free linkage analysis using microsatellite or single-nucleotide polymorphism marker maps.

Errors while genotyping are inevitable and can reduce the power to detect linkage. However, does genotyping error have the same impact on linkage results for single-nucleotide polymorphism (SNP) and microsatellite (MS) marker maps? To evaluate this question we detected genotyping errors that are consistent with Mendelian inheritance using large changes in multipoint identity-by-descent sharing in neighboring markers. Only a small fraction of Mendelian consistent errors were detectable (e.g., 18% of MS and 2.4% of SNP genotyping errors). More SNP genotyping errors are Mendelian consistent compared to MS genotyping errors, so genotyping error may have a greater impact on linkage results using SNP marker maps. We also evaluated the effect of genotyping error on the power and type I error rate using simulated nuclear families with missing parents under 0, 0.14, and 2.8% genotyping error rates. In the presence of genotyping error, we found that the power to detect a true linkage signal was greater for SNP (75%) than MS (67%) marker maps, although there were also slightly more false-positive signals using SNP marker maps (5 compared with 3 for MS). Finally, we evaluated the usefulness of accounting for genotyping error in the SNP data using a likelihood-based approach, which restores some of the power that is lost when genotyping error is introduced.

Chromosome Mapping↗
PubMed2005

Local false discovery rate and minimum total error rate approaches to identifying interesting chromosomal regions.

The simultaneous testing of a large number of hypotheses in a genome scan, using individual thresholds for significance, inherently leads to inflated genome-wide false positive rates. There exist various approaches to approximating the correct genomewide p-values under various assumptions, either by way of asymptotics or simulations. We explore a philosophically different criterion, recently proposed in the literature, which controls the false discovery rate. The test statistics are assumed to arise from a mixture of distributions under the null and non-null hypotheses. We fit the mixture distribution using both a nonparametric approach and commingling analysis, and then apply the local false discovery rate to select cut-off points for regions to be declared interesting. Another criterion, the minimum total error, is also explored. Both criteria seem to be sensible alternatives to controlling the classical type I and type II error rates.

Chromosomes, Human↗
PubMed2005

Jejunogastric intussusception: an unusual cause of hematemesis.

Jejunogastric intussusception is an uncommon but potentially life-threatening complication of a previous gastrojejunal anastomosis. Although jejunogastric intussusception was first described in 1914, fewer than 200 cases have been reported in the English literature thus far. Awareness of this rare complication would help in early diagnosis and appropriate management. Described here is a case report of a patient who presented with hematemesis due to an acute jejunogastric intussusception associated with gangrene of the intussuscepted jejunum.

Abdomen, Acute↗
PubMed2005

Management of acute bleeding upper gastrointestinal ulcers in the era of endoscopic and intravenous proton pump inhibitor therapy.

BACKGROUND: Despite advances in therapy, the morbidity and mortality of gastrointestinal bleeding remains high. A review of current practice patterns was undertaken in St Boniface General Hospital, Winnipeg, Manitoba to assess the standard of care provided. OBJECTIVE: To determine whether upper gastrointestinal bleeding (UGIB) attributable to a single acute ulcer is treated appropriately with respect to local therapy, acid suppression and Helicobacter pylori status. METHODS: A retrospective chart review identified patients with consecutive acute UGIB attributable to a single gastric or duodenal ulcer presenting to a tertiary care centre over a six-month period. The lesions were classified as high- or low-risk based on endoscopic appearance. Local care of the ulcer, acid suppressive therapy and management of H. pylori were determined by reviewing pertinent chart materials. Appropriate care was defined for all three end points a priori using literature-supported standards of care. RESULTS: Fifty-five patients who met study criteria were identified. Twenty-six of 55 (47%) and 29 of 55 (52%) lesions were considered to be low- and high-risk respectively. Of the high-risk lesions, two of 29 received no local therapy, 24 of 29 received adrenaline injection and two had an endoclip placed. Of the 27 patients whose lesions were treated, 16 received thermal coagulation. Twenty-five of 29 (88%) received intravenous proton pump inhibitors. Thirty-three of 55 (55%) patients did not have H. pylori status considered in their management. CONCLUSION: Weaknesses in the management of UGIB were identified, particularly with respect to addressing the role of H. pylori. Fragmentation and compartmentalization of patient care may be important contributing factors.

Acute Disease↗
PubMedDate not supplied

Palliative gastrectomy in advanced gastric cancer: is it worthwhile?

BACKGROUND: Gastric cancer remains one of the leading causes of cancer-related deaths. Many patients present late, and therefore, resections are often palliative in nature. The aim of this study was to assess the feasibility of resectional operation and the survival advantage of surgical resection in advanced gastric cancer. The effectiveness of palliation and the quality of life following operation for gastric cancer were assessed. METHODS: One hundred and fifty-one patients who underwent operation for gastric cancer at a tertiary centre in South India during a 5-year period between 1999 and 2003, were included in this study. Four sites of tumour spread were used as indicators of incurability in these patients. These were unresectable primary tumour or macroscopic residual primary tumour (T+), unresectable lymph nodal metastasis (L+), unresectable liver metastasis (H+) and peritoneal metastasis (P+). The resectability rate and survival were assessed in relation to these four factors. RESULTS: The resectability rate decreased as the number of sites of tumour spread increased. The overall survival was significantly better in the subgroup of patients who had a resectional operation (total gastrectomy or subtotal gastrectomy), as opposed to the subgroup who had non-resectional operation (exploratory laparotomy or laparotomy with gastrojejunostomy) (P = 0.0003). This survival advantage of resectional operation disappeared when more than two sites of tumour spread were present. The quality of life was significantly better when a resection operation was carried out. CONCLUSION: In advanced gastric cancer, palliative resection has a survival advantage if the tumour spread is restricted to two or less sites. Patients who undergo resectional operation have better palliation of symptoms and their postoperative quality of life is significantly better.

Adenocarcinoma↗
PubMedDate not supplied

The abdominal cocoon and an effective technique of surgical management.

The Abdominal Cocoon is a very rare cause of small bowel obstruction. It is caused by encapsulation of the small bowel by a fibrous membrane. This tropical disease, seen in young females, has also been reported in males. This is one of the largest series of the Abdominal Cocoon, with five new patients (3 males and 2 females) being reported. The traditional surgical treatment of choice is by lysis of adhesions. All patients in this case series had small bowel intubation done in addition to adhesiolysis. Although small bowel intubation is an established procedure for various causes of recurrent small bowel obstruction, to our knowledge this is the first report of its use in the management of the Abdominal Cocoon. We report our surgical technique in the management of this rare disease.

Adolescent↗