Biomedical subjects

M Düren

Publications and source records attributed to M Düren.

16 recordsLinked to original sources

PubMed2006

Double-hadron leptoproduction in the nuclear medium.

The first measurements of double-hadron production in deep-inelastic scattering within the nuclear medium were made with the HERMES spectrometer at DESY HERA using a 27.6 GeV positron beam. By comparing data for deuterium, nitrogen, krypton, and xenon nuclei, the influence of the nuclear medium on the ratio of double-hadron to single-hadron yields was investigated. Nuclear effects on the additional hadron are clearly observed, but with little or no difference among nitrogen, krypton, or xenon, and with smaller magnitude than effects seen on previously measured single-hadron multiplicities. The data are compared with models based on partonic energy loss or prehadronic scattering and with a model based on a purely absorptive treatment of the final-state interactions. Thus, the double-hadron ratio provides an additional tool for studying modifications of hadronization in nuclear matter.

Journal Article↗

PubMed2005

Measurement of the tensor structure function b1 of the deuteron.

The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a negligible residual vector polarization enabled the first measurement of the tensor asymmetry A(d)zz and the tensor structure function b(d)1 for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV2 < <5 GeV2. The quantities A(d)zz and b(d)1 are found to be nonzero. The rise of b(d)1 for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.

Journal Article↗

PubMed2005

Single-spin asymmetries in semi-inclusive deep-inelastic scattering on a transversely polarized hydrogen target.

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.

Journal Article↗

PubMed2004

Flavor decomposition of the sea-quark helicity distributions in the nucleon from semiinclusive deep inelastic scattering.

Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.

Journal Article↗

PubMed2003

Evidence for quark-hadron duality in the proton spin asymmetry A1.

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A1. Longitudinally polarized positrons were scattered off a longitudinally polarized hydrogen target for values of Q2 between 1.2 and 12 GeV2 and values of W2 between 1 and 4 GeV2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable x. This finding implies that the description of A1 in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q2 above 1.6 GeV2.

Journal Article↗

PubMed2003

Q2 dependence of nuclear transparency for exclusive rho0 production.

Exclusive coherent and incoherent electroproduction of the rho(0) meson from 1H and 14N targets has been studied at the HERMES experiment as a function of coherence length (l(c)), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon (-Q2). The ratio of 14N to 1H cross sections per nucleon, called nuclear transparency, was found to increase (decrease) with increasing l(c) for coherent (incoherent) rho(0) electroproduction. For fixed l(c), a rise of nuclear transparency with Q2 is observed for both coherent and incoherent rho(0) production, which is in agreement with theoretical calculations of color transparency.

Journal Article↗

PubMed2001

Minimally invasive video-assisted parathyroidectomy: multiinstitutional study.

Unilateral and minimally invasive parathyroidectomies with endoscopic and video-assisted technique have been introduced. Most of these procedures utilize preoperative localization and intraoperative monitoring of parathyroid hormone. There are only a few reports on these procedures. The objective of this study was to evaluate video-assisted parathyroidectomy (MIVAP) for surgery in patients with primary hyperparathyroidism (pHPT). From February 1997 to June 1999 a series of 123 consecutive patients with pHPT at four surgical centers were evaluated. The patients' ages ranged from 18 to 77 years (median 50 years). Preoperatively, sestamibi scintigraphy and ultrasonography for localization were performed for all patients. Selection criteria for a MIVAP procedure excluded patients with negative localization, suspicion of multiglandular disease (MGD) or thyroid malignancy, a large thyroid mass, and prior surgery or irradiation to the neck. MIVAP was performed with a 1.5 cm suprasternal incision; the operation was then done through this incision with a 30 degree 5 mm endoscope and microsurgical instruments with brief CO2 insufflation for adenoma identification. We then proceeded with an open technique through the small incision under video-assistance. Intraoperative monitoring of intact parathyroid hormone (iPTH) assays was used in all patients. Among the 123 patients in whom MIVAP was attempted, the procedure was accomplished in 109 (89%). Conversion to conventional cervicotomy was required in 14 (11%) patients because of failed localization, failure of the iPTH level to fall appropriately, or technical problems. There was no persistent or recurrent HPT during the 3 to 12-month follow-up. Oral calcium replacement for symptomatic hypocalcemia postoperatively was given in 7 (6%) cases. A unilateral transient laryngeal nerve palsy, resolving within 6 months postoperatively, occurred in two (2%) patients. The median hospital stay was 1.5 days (range 0.5-5.0 days). This study showed the feasibility of MIVAP as an alternative surgical treatment for pHPT in a selected group of patients. Further studies are necessary to evaluate the efficacy and rationale of MIVAP compared to other techniques for parathyroidectomy in pHPT patients.

Adenoma↗

PubMed2000

[Surgical therapy of Echinococcus granulosus (cysticus)].

Hydatid disease, still frequent in endemic areas, is usually localized in the liver. Despite the benign nature of the disease it is one of the problematic fields of surgery due to the high complication rate and long hospital stay. Based on our experience we recommend evacuation of the cyst and omentoplasty as the surgical method of choice, as it is associated with a relatively low incidence of complications and can be performed easily.

Adult↗

PubMed2000

The role of 99Tcm-tetrofosmin in the evaluation of thyroid nodules.

Various radionuclides, including 67Ga, 201Tl and 99Tcm-sestamibi, have been used to differentiate benign from malignant thyroid nodules. 99Tcm-tetrofosmin, a lipophilic cationic radiotracer, and 99Tcm-sestamibi have also been reported to accumulate in thyroid tumours. In this study, we evaluated the role of 99Tcm-tetrofosmin in the differentiation of malignant from benign thyroid nodules. Seventy-nine patients with solitary non-functioning thyroid nodules were included in the study. Fine-needle aspiration biopsy was performed in all patients. Sixty patients were subsequently operated on and 19 patients refused surgery. After the injection of 370 MBq 99Tcm-tetrofosmin, static images at 5, 30, 60, 120 and 180 min were acquired. Both visual and semi-quantitative analysis was performed. On visual interpretation, the nodules with late retention were classified as positive for malignancy and nodules without late retention were classified as negative for malignancy. In the semi-quantitative analysis, regions of interests were drawn over the nodule and contralateral normal thyroid tissue. The average number of counts was recorded and tumour-to-normal thyroid tissue ratios calculated. Post-operative histology revealed 19 malignant and 41 benign nodules. Of the benign nodules, adenomas behaved similarly to the malignant nodules with late retention of tracer, while adenomatous nodules revealed no late retention on delayed images and could be differentiated from malignant tumours. In the semi-quantitative analysis, there was a significant difference in tumour-to-normal tissue ratios for adenomatous nodules and malignant tumours as well as adenomas. We conclude that it is not possible to differentiate between malignant and benign thyroid nodules with 99Tcm-tetrofosmin. However, 99Tcm-tetrofosmin scintigraphy is helpful in selecting nodules that can be cured by surgical intervention.

Adenoma↗

PubMed1996

Reoperation for persistent or recurrent primary hyperparathyroidism.

OBJECTIVE: To analyze the causes and outcomes of reoperation for persistent or recurrent primary hyperparathyroidism. DATA SOURCES: Medical records of 102 patients with persistent or recurrent primary hyperparathyroidism who underwent reoperation by 1 surgeon between 1985 and 1995. STUDY SELECTION: Only patients with persistent or recurrent primary hyperparathyroidism were selected; patients with secondary hyperparathyroidism, parathyroid cancer, familial hyperparathyroidism, and previous thyroid operations were omitted. DATA EXTRACTION: Performed by a single unblinded researcher. DATA SYNTHESIS: Reasons for failed parathyroid operations included tumor in ectopic position (53%), incomplete resection of multiple abnormal glands (37%), adenoma in normal position missed during previous surgery (7%), and regrowth of previously resected tumor (3%). Of the ectopic glands, 28% were paraesophageal, 26% in the mediastinum (nonthymic), 24% intrathymic, 11% intrathyroidal, 9% in the carotid sheath, and 2% in a high cervical position. Eighty-three percent of ectopic glands were accessible via cervical incision. The success rate of reoperations was 95%. One patient (1%) became permanently hypocalcemic after reoperation; 1 patient (1%) suffered permanent unilateral vocal cord paralysis. The sensitivities of preoperative localization studies were as follows: technetium Tc 99m sestamibi scan, 77%; magnetic resonance imaging, 77%; selective venous catheterization for intact parathyroid hormone, 77%; thallium-technetium scan, 68%; ultrasonography, 57%; and computed tomography, 42%. CONCLUSIONS: Repeated parathyroidectomy can be avoided in more than 95% of patients if an experienced surgeon performs bilateral cervical exploration during the initial parathyroid operation. For patients with persistent or recurrent primary hyperparathyroidism, preoperative localization studies and a focused surgical approach can result in a 95% success rate with minimum complications.

Adult↗

PubMed1995

Tuberculosis of the breast.

OBJECTIVE: To present our 20 years experience of tuberculosis of the breast. DESIGN: Retrospective study. SETTING: Teaching hospital, Turkey. SUBJECTS: 9 women with tuberculous mastitis. MAIN OUTCOME MEASURE: Cure. RESULTS: All cases underwent frozen section and excision. One required a simple mastectomy because of the extent of destruction; the remainder underwent lumpectomy. All patients were given rifampicin, ethambutol, and isoniazid, and the three who had tuberculosis of other organs were also treated with streptomycin. Mean follow up was 87 months (range 6-178) and two patients were lost to follow up, at three and six years, respectively. Histological examination showed the presence of tubercle and central caseation in 8 cases and granulomatous infiltration in one. CONCLUSION: Tuberculous mastitis is rare, and should be suspected in any woman with persistent breast abscesses and sinuses, particularly if she lives in an area from which tuberculosis has not been eradicated. Conservative surgery and antituberculous drugs are the treatment of choice.

Adult↗

PubMed1994

[Gastrointestinal tuberculosis. 10 years experience in a surgical university clinic].

Between 1982 and 1992 a total of 38 patients were treated for primary peritoneal tuberculosis in the medical faculty Cerrapaşah, University of Istanbul. Ten patients were operated on as emergency cases because of bowel obstruction, the remaining 28 had elective procedures. Seven patients had a diagnosis made laparoscopically, 31 with a laparotomy. In the latter group 13 patients underwent a laparotomy with biopsy without any morbidity or mortality. On the other hand there was no morbidity or mortality after laparoscopic diagnosis and these patients had an average admission time of 3.5 days. The morbidity and mortality rates of the entire laparotomy group were 6.4 and 3.2% respectively. And the average length of admission was 13.6 days. In view of our results we would favour laparoscopy as the best diagnostic method for intraabdominal tuberculosis in patients with unspecific abdominal pain and no endoscopically proven cause.

Adult↗

PubMed1993

Early wound excision and skin grafting restores cellular immunity after severe burn trauma.

Suppression of cellular immunity following thermal injury may contribute to the high incidence of postburn sepsis. Early excision and skin grafting may remove deleterious local wound factors and prevent immunosuppression. The effect on cellular immunity of early burn wound excision and skin grafting was investigated in an animal model using female Wistar rats. The development of immunosuppression shortly after burn injury was shown by popliteal lymph node assay and a 2,4-dinitrofluorobenzene skin reaction test. Excision and skin grafting 2 days after burn trauma restored parameters to normal. Burned tissue suppresses cellular immunity; this effect is preventable by early excision and skin grafting.

Animals↗

PubMed1991

[Ascariasis pancreatitis. Endoscopic diagnosis and therapy].

Ascariasis lumbricoides is a parasitic disease of the human gastrointestinal tract. Migration of the worm through orifices and into ducts leads to such complications as cholangitis and pancreatitis; even bile duct perforation by Ascaris have been reported. Treatment of biliary ascariasis is usually surgical, although endoscopic removal of the worm has been successfully performed. We report on a case in whom an Ascaris worm in the common bile duct led to acute pancreatitis; the worm was successfully removed endoscopically after performing papillotomy.

Ampulla of Vater↗

PubMed1991

Endoscopic sphincterotomy in the management of postoperative complications of hepatic hydatid disease.

The results obtained using endoscopic sphincterotomy (EST) in the management of postoperative biliary complications of hepatic hydatid disease are presented. The outcome was favourable in all eight patients treated with no associated morbidity or mortality. In three patients the clinical manifestations of cholangitis resolved, and in five of six patients the external bile fistula previously present for 26 to 68 days closed within 3 to 15 days. In one patient with a long-standing fistula (5 years) the bile outflow was reduced from 600cc to 50-100cc per day. No complications due to EST were encountered. The results show that EST can be considered the treatment of choice for biliary fistulae following surgery for hepatic hydatid disease and for drainage of bile in patients with cholangitis due to hydatid disease.

Biliary Fistula↗

PubMed1986

[Caroli syndrome].

In 1958 Caroli described the syndrome of congenital, either segmental or involving the entire bile duct system, saccular extensions of the intrahepatic bile ducts. He differentiated between two types of this disease pattern. The first form concerns pure cystic dilatations of the intrahepatic bile ducts, whereas the second one is combined with hepatic fibrosis and portal hypertension. Both types are characterised by cystic dilatations in the kidneys and in the extrahepatic bile ducts, pancreas and spleen.

Adult↗