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Biomedical subjects

Thomas Kahn

Publications and source records attributed to Thomas Kahn.

At least 19 recordsLinked to original sources
PubMed2005

Intraoperative MRI to guide the resection of primary supratentorial glioblastoma multiforme--a quantitative radiological analysis.

Patients with supratentorial high-grade glioma underwent surgery within a vertically open 0.5-T magnetic resonance (MR) system to evaluate the efficacy of intraoperative MR guidance in achieving gross-total resection. For 31 patients, preoperative clinical data and MR findings were consistent with the putative diagnosis of a high-grade glioma, in 23 cases in eloquent regions. Tumor resections were carried out within a 0.5-T MR SIGNA SP/i (GE Medical Systems, USA). The resection of the lesion was carried out using fully MR compatible neurosurgical equipment and was stopped at the point when the operation was considered complete by the surgeon viewing the operation field with the microscope. We repeated imaging to determine the residual tumor volume only visible with MRI. Areas of tissue that were abnormal on these images were localized in the bed of resection by using interactive MR guidance. The procedure of resection, imaging control and interactive image guidance was repeated where necessary. Almost all tissue with abnormal characteristics was resected, with the exception of tissue localized in eloquent brain areas. The diagnosis of glioblastoma was confirmed in all 31 cases. When comparing the tumor volume before resection and at the point where the neurosurgeon would otherwise have terminated surgery ("first control"), residual tumor tissue was detectable in 29/31 patients; the mean residual tumor volume was 30.7 +/- 24%. After repeated resections under interactive image guidance the mean residual tumor volume was 15.1%. At this step we found tumor remnants only in 20/31 patients. The perioperative morbidity (12.9%) was low. Twenty-seven patients underwent sufficient postoperative radiotherapy. We found a significant difference (log(rank)p = 0.0037) in the mean survival times of the two groups with complete resection (n = 10, median survival time 537 days) and incomplete resection (n = 17, median survival time 237 days). The resection of primary glioblastoma multiforme under intraoperative MR guidance as demonstrated is a possibility to achieve a more complete removal of the tumor than with conventional techniques. In our small but homogeneous patient group we found an increase in the median survival time in patients with MRI for complete tumor resection, and the overall surgical morbidity was low.

Adult↗
PubMed2005

MR Imaging-guided percutaneous procedures in children.

Magnetic resonance imaging (MRI)-guided therapeutic interventions in children are very rare. In comparison to other imaging techniques, it is very unusual for MRI to be used for diagnostic percutaneous interventions despite its imaging benefits. We provide a brief description of available MRI systems and instruments and use clinical examples to present and discuss typical indications for percutaneous procedures while showing possibilities for percutaneous therapeutic interventions.

Biopsy↗
PubMed2005

Quantitative analysis of human papillomavirus type 16 in cervical neoplasm: a study in Chinese population.

BACKGROUND: Human papillomavirus (HPV) infection was recognized as a major causal factor for the development and progression of squamous intraepithelial lesions (SIL). It is possible to use HPV test for the detection of cervical lesions as an adjunct to cervical cytology. OBJECTIVES: To evaluate the relation between HPV 16 viral load and the severity of cervical lesions in a Chinese population. METHODS: Study population was recruited from the colposcopy and general outpatient clinic. The presence of HPV 16 E6 and E7 in cytological specimens was detected using HPV 16 specific polymerase chain reaction (PCR). The viral load in the specimens that were positive for HPV 16 specific PCR, was quantified by using real-time PCR assay. RESULTS: The study recruited 394 women, in which 148 were high-grade SIL (HG-L), 121 were low-grade SIL (LG-L) and 125 were Normal. Sufficient DNA integrity was proven in 347 samples. Among 121 positive cases for HPV 16, 70 were HG-L, 34 were LG-L and 17 were Normal. Using quantitative real-time PCR, the percentages of samples with greater DNA copies were found to increase with the severity of diseases. There was also a significant difference in DNA copies among the three groups (HG-L versus Normal, p<0.001; HG-L versus LG-L, p<0.001). Area under receiver operating characteristic (ROC) curve of the HG-L versus LG-L and Normal was 0.836 indicating that quantitative PCR had a good diagnostic value in differentiating HG-L from the LG-L and Normal groups. CONCLUSIONS: Our data suggested HPV 16 viral load was significantly related to the severity of cervical lesions. Evaluation of viral burden could be a potential clinical tool in management of cervical lesions.

China↗
PubMed2005

Caroli's disease: liver resection and liver transplantation. Experience in 33 patients.

BACKGROUND: The aim of this study was to review and discuss our observations on 33 patients who underwent surgical treatment for Caroli's disease (CD), focusing on diagnosis, current surgical management, and long-term outcome. METHODS: Between May 1993 and June 2004, 642 liver resections and 286 liver transplantations in 252 patients were performed in our department of surgery. Thirty-three patients were referred to our center for diagnostic and therapeutic management of CD. Prior surgical interventions for hepatobiliary disorders, current diagnostic and surgical procedures, procedure-specific complications, duration of hospital stay, duration of follow-up, outpatient information, and long-term outcome were reviewed. RESULTS: Fifteen male and 18 female patients were treated in this study. Initial symptoms and signs of the disease noted in our patients included right upper quadrant pain, fever, and jaundice. In 2 of the 33 patients, we noted clinical evidence of cirrhosis followed by histologic confirmation. One patient suffered from variceal bleeding. In 26 patients, diagnoses were established by a combined endoscopic retrograde cholangiopancreatography, ultrasonography, and computed tomographic studies. The disease was localized in 25 and diffuse in 8 patients. Liver resection was carried out in 29 patients. Partial hepatectomies were performed in 27 of these 29 at our institution. Two female patients with the diffuse disease underwent orthotopic liver transplantation. Thirteen of the 31 patients who underwent surgery at our institution had an uneventful postoperative course. Fourteen patients had minor postoperative complications and responded well to medical management. Four patients had major complications that required further surgical treatment. Two patients died of complications related to postoperative hemorrhage and sepsis. Two patients with intrahepatic cholangiocarcinoma died because of primary tumor progress. One patient with cholangiocarcinoma died 1 year after a successful left hepatectomy because of metastatic disease recurrence. The long-term results of the 26 surviving patients were assessed during a mean follow-up of 3.7 years (range, 1-11 years). All 26 patients remained free of biliary symptoms or complications. In 25 patients, surgery including liver transplantation was curative. CONCLUSIONS: Partial hepatectomy for localized CD is potentially curative. In patients with diffuse CD, liver transplantation provides gratifying long-term results.

Adult↗
PubMed2004

Interventional and intraoperative MR: review and update of techniques and clinical experience.

The concept of interventional magnetic resonance imaging (MRI) is based on the integration of diagnostic and therapeutic procedures, favored by the combination of the excellent morphological and functional imaging characteristics of MRI. The spectrum of MRI-assisted interventions ranges from biopsies and intraoperative guidance to thermal ablation modalities and vascular interventions. The most relevant recently published experimental and clinical results are discussed. In the future, interventional MRI is expected to play an important role in interventional radiology, minimal invasive therapy and guidance of surgical procedures. However, the associated high costs require a careful evaluation of its potentials in order to ensure cost-effective medical care.

Biopsy, Needle↗
PubMed2004

Surgical impact of computerized 3D CT-based visualizations in living donor liver transplantation.

For living donor liver transplantation (LDLT), accurate diagnostic evaluation is essential. Problems arise in assessment of the vascular, bile duct anatomy, liver graft volume, and vascular territories involved. Requirements for the realization of decision-support and enhanced precision in the planning of surgery in LDLT engineering fields are a three-dimensional (3D) visualization system that improves anatomic assessment, allows for interactive surgery planning, and acts as an intraoperative guide. Thirteen LDLT candidates and three LDLT recipients were assessed by "multislice" computer-tomographic examinations. Image processing for 3D visualization included segmentation and calculation of centre lines. A hierarchical mathematical model representing the vascular and biliary tree was created, which allowed calculation of individual vascular territories. Precision of 3D computed tomography (CT)-based visualizations was superior to diagnostic modalities used currently. In addition to detection of decisive anatomic variants, computerized interactive insertion of splitting lines allowed for better planning of the surgical approach and image-guided surgery. 3D CT-based visualization in LDLT facilitates diagnostic evaluation with high accuracy. Multiple examinations, especially with regard to invasive diagnostics, may be avoided. Surgical strategy was directly influenced by the detection of vascular and biliary variants.

Contrast Media↗
PubMed2003

Simulations of thermal tissue coagulation and their value for the planning and monitoring of laser-induced interstitial thermotherapy (LITT).

MRI information is widely used for the monitoring of thermal therapies, such as laser-induced interstitial thermotherapy (LITT). However, a detailed knowledge about the relationship between time/temperature exposure and resulting tissue thermal damage is needed to estimate the lesion extent. The aims of this work were to model the thermal response of laser-irradiated tissue and to assess the value of Monte Carlo simulation (MCS) for tumor therapy planning and monitoring. MCS yielded true 3D distributions of laser-induced temperature and thermal damage. These results were compared with 2D MR thermometry data from in vitro experiments performed on animal liver tissue over an ordinary range of laser powers (10-25 W) and irradiation times (5-25 min). Clinical reference data were available from MR-guided liver LITT procedures. MCS correctly predicted the shape of temperature and damage distributions. The quantitative agreement between simulated and measured lesion diameters was within 10% and 15% for the in vitro and in vivo cases, respectively. The simulated 53 degrees C isotherm best estimated the boundary of the final thermal damage (6% variance). This study shows that MCS of interstitial laser coagulation provides unique information that can be of use in the empirical correlation of temperature with thermal damage, and can assist greatly in thermal treatment planning and monitoring.

Animals↗
PubMed2003

[Clinical use of interventional MR imaging].

The integration of diagnostic and therapeutic procedures by MRI is based on the combination of excellent morphologic and functional imaging. The spectrum of MR-guided interventions includes biopsies, thermal ablation procedures, vascular applications, and intraoperative MRI. In all these applications, different scientific groups have obtained convincing results in basic developments as well as in clinical use. Interventional MRI (iMRI) is expected to attain an important role in interventional radiology, minimal invasive therapy, and monitoring of surgical procedures.

Biopsy↗
PubMed2003

[Intraoperative use of an open mid-field MR scanner in the surgical treatment of cerebral gliomas].

The aim of the present study was to evaluate the effectiveness of intraoperative MRI guidance in achieving more gross-total resection in case of primary brain tumors. We studied 12 patients with low-grade glioma and 19 patients with high-grade glioma who underwent surgery within a vertically open 0.5 T MR system. After initial imaging, the resection was stopped at the point in which the neurosurgeon considered the resection complete by viewing the operation field. At this time, intraoperative MRI was repeated ("first control") to identify any residual tumor. Areas of tumor-suspected tissue were localized and resected, with the exception of tissue adjacent to eloquent areas. Final imaging was carried out before closing the craniotomy. Comparison of "first control" and final imaging revealed a decrease of residual tumor volume from 32% to 4.3% in low-grade gliomas, and from 29% to 10% in high-grade gliomas. Intraoperative MRI allows a clear optimization of microsurgical resection of both low-grade and high-grade gliomas.

Brain Neoplasms↗
PubMed2003

[MR-guided laser-induced thermo-ablation of liver tumors: clinical experiences and therapy control concepts].

Minimally-invasive, laser-induced interstitial thermotherapy (LITT) of solid tumors represents a valid alternative to surgical procedures such as tumor resections. Within the framework of a palliative study on 16 patients, a total of 25 metastases in the liver were treated in an open MR system (0.5 T). The intraoperative scanner design allows patient-based navigation, decisive for a safe applicator positioning, as well as temperature monitoring and direct inspection of the therapy result, without need for patient transfer or repositioning. Although the MR thermometry applied in the open scanner assisted LITT monitoring, the current accuracy of temperature data was not sufficient to serve automatic irradiation control. Therefore, an experimental monitoring and control system was developed in a closed MR scanner (1.5 T) featuring a calibrated MR thermometry. The system provides also an interface to the laser system, allowing the automatic off/on switching of the laser power according to preoperatively defined control criteria. The basic functionality of the automatic laser control was successfully demonstrated with laser ablation experiments of liver samples using irradiation parameters close to typical clinical values.

Body Temperature↗
PubMed2003

Reset osmostat and salt and water retention in the course of severe hyponatremia.

To evaluate whether a reset osmostat and salt and water retention may be features of the course of some patients with hyponatremia, we present the long-term course of 6 selected patients. Three patients had spinal cord injury, 3 had marked psychiatric problems, and 3 had alcoholism. Five developed severe hyponatremia superimposed on chronic hyponatremia consequent to a reset osmostat. In 5 patients marked salt and water retention of unclear etiology occurred during therapy on 11 occasions. In 4 of these 11 episodes hypernatremia developed. Knowledge of a patient's past history and the possibility of developing salt and water overload should influence therapy.

Adult↗
PubMed2002

MR-guided percutaneous core biopsy of small breast lesions: first experience with a vertically open 0.5T scanner.

PURPOSE: The growing use of highly sensitive but only moderate specific breast MRI requires the development of both minimal-invasive as well as precise biopsy systems. The aim of the study was to prove the accuracy and feasibility of a biopsy procedure carried out in prone position in a vertically opened MR imager. MATERIALS AND METHODS: The biopsies were carried out in 21 women with lesions visible on MRI alone using an open breast coil with an integrated biopsy device. A 14 G coaxial needle was placed under near real-time MRI-guidance. After the tip of this needle was verified in contact with the lesion, we used a non MR-compatible, but MR-safe biopsy gun with a 16 G canula to take four to eight cores. RESULTS: We found eight malignant and 12 benign lesions. In one patient the procedure was not successful. In case of malignancy, the operation confirmed the diagnosis in all cases. The 12/21 patients with benign lesions have been followed without evidence of lesions growth over eight to 28 months. CONCLUSION: The described procedure allows MRI-guided minimal invasive core biopsy of small breast lesions (five to 17 mm) with a high degree of accuracy.

Adult↗
PubMed2002

Effects of laser-induced thermotherapy (LITT) on proliferation and apoptosis of glioma cells in rat brain transplantation tumors.

BACKGROUND AND OBJECTIVES: Laser-induced thermotherapy (LITT) is an approach to the treatment of brain tumors especially in poorly accessible regions. Its clinical applicability with tumor cell destruction has been shown in several studies. However, no data are known about specific effects on tumors cells due to LITT in the time course of the lesion. STUDY DESIGN/MATERIALS AND METHODS: LITT was performed in adult Lewis rats with implanted glioma cells in the brain using a standard exposure of 3 W for 30 seconds. Before and following LITT, neoplastic lesions were monitored by MRI. Proliferation of implanted cells and gliosis were assessed by several histological techniques and immunohistochemistry. Apoptosis was detected by TUNEL staining. RESULTS: Our experiments show a destruction of neoplastic cells by LITT but surviving tumor cells at the margin of the lesion. Apoptosis was detected following LITT restricted to residual neoplastic cells. Marginal survival of tumor cells lead to a secondary outgrowth into the necrotic lesion adjacent to sprouting capillaries. CONCLUSIONS: LITT is a suitable technique for the treatment of brain neoplasms. However, further investigations are necessary to prevent tumor recurrences after LITT.

Animals↗
PubMedDate not supplied

Impact of the surgeon on the prevalence of arteriovenous fistulas.

Decreased use of native arteriovenous fistulas and an increased reliance on synthetic grafts as permanent dialysis access have accompanied the growth of the dialysis population in the United States, but not at our institution. Possible reasons for this difference were studied in a cross-sectional analysis in August of 2000. There were 51 chronic dialysis patients, all of whom had their access placed by the same surgeon; 75% of them were dialyzed through an arteriovenous fistula, which compares well with the 23% prevalence at the national level. Among our patients, 57% were diabetic, 98% had a history of hypertension, 35% had amputations or arterial bypass surgery, 37% had coronary artery disease, 12% had suffered a stroke, 35% were active smokers, and 22% had a history of intravenous drug use. The high prevalence of arteriovenous fistulas, despite so many comorbid conditions, suggests that the presence of a skilled and experienced surgeon may be more predictive of better dialysis access than other factors.

Aged↗