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Biomedical subjects

P Alken

Publications and source records attributed to P Alken.

At least 73 records · Page 4Linked to original sources
PubMed2002

Influence of the bridging effect by sequential laser application on tissue ablation in an ex vivo model, taking organ perfusion into account.

OBJECTIVE: To improve the efficacy of interstitial laser coagulation of tissue by causing a 'bridging' effect, using a sequential multiple-probe procedure on an ex vivo kidney model, as only a limited area of tissue is destroyed with a single probe and the coagulation takes longer when multiple punctures are used. MATERIALS AND METHODS: A laser beam was generated using a Nd:YAG laser and applied to kidney tissue by a diffuser tip (quartz glass cap 2 x 19 mm). For sequential laser application (SLA), three probes were placed through punctures into kidney tissue, at 5 or 10 mm apart. The laser energy was applied in different time-energy combinations through the three probes. The effect of SLA was compared with that from one probe delivering the optimal PowerMode 180 protocol (Dornier, Germering, Germany), which represents the standard energy protocol for the clinical treatment of parenchymal organs using this laser device. An isolated porcine kidney was chosen for laser coagulation under different conditions of perfusion. The ablative efficacy was defined as the volume of necrosis per minute. RESULTS: Applying various time-energy combinations to isolated unperfused porcine kidney caused extensive tissue ablation (5.6 mL). In trials with saline and blood perfusion for improved cooling, the necrotic volume was 2.5 and 3.9 mL, respectively (with no carbonization, 3.2 mL). Compared with a single-probe procedure, the ablation efficacy was 10 times better with SLA coagulation. This improvement was initiated by the bridging effect: coagulation in neighbouring areas affects perfusion and convection to an extent that induces the formation of bridges of necrosis between the probes. CONCLUSION: Tissue ablation is markedly improved by interstitial laser coagulation using a sequential multiple-probe technique.

Animals↗
PubMed2002

The URO Mentor: development and evaluation of a new computer-based interactive training system for virtual life-like simulation of diagnostic and therapeutic endourological procedures.

OBJECTIVE: To overcome the current disadvantages of traditional training methods for ureterorenoscopy and percutaneous nephrolitholapaxy, using the URO Mentor (Simbionix, Tel Aviv, Israel) computer-assisted simulator. METHODS: The URO Mentor device for training and quality control in ureterorenoscopy was developed using virtual reality, multimedia technology and intelligent tutoring systems. The central software system features a proprietary visualization engine (the SVE) which allows real-time simulation by offering a high-level object-orientated application program interface (written in C++) available for use with either Microsoft, DirectX 7 or OpenGL as platforms. The SVE includes general procedures to allow two- (2D) and three-dimensional (3D) rendering, collision detection, collision correction, 3D morphing, 2D image manipulation, texture mapping, 'bump' mapping, video texture, X-ray rendering, special effects (blood, smoke, stone fragments and more) and reflections. RESULTS: The system allows a complete training session on a wide range of procedures by offering different types of cases and virtual patients, and features a full representation of the endourological procedures under direct vision and by using interactive fluoroscopy with a contrast agent. The supported tools include: baskets, graspers, intracorporal lithotripters, guidewires, catheters, stents, biopsy and dilatation devices. The endourological procedures that can be performed are lithotripsy, tumour resection, treatment of strictures and obstructions, stent placement and biopsies. CONCLUSION: The URO Mentor introduces a new generation of mannequin equipped with a special haptic device, providing trainees with an unparalleled life-like sensation while training for diagnostic and therapeutic endourological procedures. By bringing key advances into urological simulation (e.g. with the real-time X-ray renderer) and by integrating in a single system both high-quality simulation and learning tools, the URO Mentor provides new perspectives for computer-based urological training systems and methods.

Computer Simulation↗
PubMed2002

Technical characterization of an ultrasound source for noninvasive thermoablation by high-intensity focused ultrasound.

OBJECTIVE: To develop a generator for high-intensity focused ultrasound (HIFU, a method of delivering ultrasonic energy with resultant heat and tissue destruction to a tight focus at a selected depth within the body), designed for extracorporeal coupling to allow various parenchymal organs to be treated. MATERIAL AND METHODS: The ultrasound generated by a cylindrical piezo-ceramic element is focused at a depth of 10 cm using a parabolic reflector with a diameter of 10 cm. A diagnostic B-mode ultrasonographic transducer is integrated into the source to allow the focus to be located in the target area. The field distribution of the sound pressure was measured in degassed water using a needle hydrophone. An ultrasound-force balance was used to determine the acoustic power. These measurements allowed the spatially averaged sound intensity to be calculated. The morphology and extent of tissue necrosis induced by HIFU was examined on an ex-vivo kidney model. RESULTS: The two-dimensional field distribution resulted in an approximately ellipsoidal focus of 32 x 4 mm (- 6 dB). The spatially maximum averaged sound intensity was 8591 W/cm2 at an electrical power of 400 W. The lesion caused to the ex-vivo kidney at this maximum generator power with a pulse duration of 2 s was a clearly delineated ellipsoidal coagulation necrosis up to 8.8 x 2.3 mm (length x width) and with central liquefied necrosis of 7.9 x 1.9 mm. CONCLUSION: This newly developed ultrasound generator with a focal length of 10 cm can induce clear necrosis in parenchymal tissue. Because of its specific configuration and the available power range of the ultrasound generator, there is potential for therapeutic noninvasive ablation of tissue deep within a patient's body.

Animals↗
PubMed2002

[Control parameters for high-intensity focused ultrasound (HIFU) for tissue ablation in the ex-vivo kidney].

PURPOSE: Therapeutic application of contactless thermoablation by high-intensity focused ultrasound (HIFU) demands precise physical definition of focal size and determination of control parameters. Our objective was to define the focal expansion of a new ultrasound generator and to evaluate the extent of tissue ablation under variable generator parameters in an ex vivo model. MATERIALS AND METHODS: Axial and transversal distribution of ultrasound intensity in the area of the focal point was calculated by needle hydrophone. The extent of tissue necrosis after focused ultrasound was assessed in an ex vivo porcine kidney model applying generator power up to 400 Watt and pulse duration up to 8 s. RESULTS: The measurement of field distribution revealed a physical focal size of 32 x 4 mm. Sharp demarcation between coagulation necrosis and intact tissue was observed in our tissue model. Lesion size was kept under control by variation of both generator power and impulse duration. At a constant impulse duration of 2 s, generator power of 100 W remained below the threshold doses for induction of a reproducible lesion. An increase in power up to 200 W and 400 W, respectively, induced lesions with diameters up to 11.2 x 3 mm. Constant total energy (generator power x impulse duration) led to a larger lesion size under higher generator power. CONCLUSION: It is possible to induce sharply demarcated, reproducible thermonecrosis, which can be regulated by generator power and impulse duration, by means of a cylindrical piezo element with a paraboloid reflector at a focal distance of 10 cm. The variation of generator power was an especially suitable control parameter for the inducement of a defined lesion size.

English Abstract↗
PubMed2001

[Adrenalectomy within the scope of tumor nephrectomy?].

In urology, renal cell carcinoma is the third most frequently diagnosed malignancy. Localized, non-metastatic tumors are generally cured by radical tumor nephrectomy. Since the 1960s, this procedure has routinely included removal of the kidney together with the perirenal fat, Gerota's fascia, and ipsilateral adrenal gland. In recent years, improved diagnostic methods have led to the detection of tumors at earlier stages. These methods widen the scope for organ-sparing surgical strategies and have consequently sparked controversy over adrenal gland removal. Despite this, radical tumor nephrectomy that includes adrenal gland removal is still strongly advocated. This is the only suitable surgical approach for the cure of patients with direct tumor infiltration of the adrenal gland. In the case of adrenal involvement, minimal tumor dimension and the predisposing localization of the primary tumor have to relevance. The imaging procedure for diagnosis is also difficult to assess, especially in slim patients with upper role tumors. Finally, to date, no justifiable disadvantages of adrenalectomy have been described.

Adrenal Glands↗
PubMed2001

[Fibromyxoid pseudosarcoma of the urinary bladder. Case report and review of the literature of a rare disease].

Pseudosarcomatous fibromyxoidtumors (PSF) of the bladder are rare, benign tumors consisting of myofibroblastoid bladder wall proliferations of unknown etiology. Misinterpretation as a sarcoma is common and due to infiltrative growth and cellular pleomorphism and may leaed to false radical treatment. We present a 27 year old man with PSF presenting with microhematuria. Results of clinical, radiological and histopathological examinations and therapy are presented. A. review of the literature data of the to our knowledge 73 cases that have been reported in the literature is given.

Adult↗
PubMed2001

Testosterone reaction after testicular biopsies--further investigation in the normogonad and cryptorchid rat model.

From the follow-up of patients undergoing extensive testicular sperm extraction, the question of a consecutive decrease in testosterone levels arose. Further investigation was performed in the normogonad and cryptorchid Sprague-Dawley rat model. From groups A (n = 40 normogonad rats) and B (n = 40 cryptorchid rats), eight animals were taken and the following surgical interventions were performed: general anaesthesia (A-0, B-0), scrotal exploration (A-1, B-1), one testicular biopsy with a 2-mm tunica incision (A-2, B-2), two biopsies with a 4-mm incision (A-3, B-3), and four biopsies with a 2-mm incision (A-4, B-4). Standardised testosterone control was performed 1 day before as well as 1, 7 and 14 days after surgery. No specific testosterone reaction was found in A-0, an insignificant decrease in A-1 (3.8 nmol/l), a significant decrease in A-2 (6.27 nmol/l), in A-3 (12.96 nmol/l) and in A-4 (11.88 nmol/l). In the B rats, even in B-3 and B-4 no significant decrease was measured. The testosterone reaction correlated to the amount of tissue that was extracted, but not to the number of biopsies. The cryptorchid rats did not react in a more sensitive manner.

Animals↗
PubMed2001

Clinical evaluation of a newly developed endoscopic resection device (Rotoresect): physical principle and first clinical results.

BACKGROUND: Endoscopic resection techniques on benign prostatic tissue aim at a high ablation rate and a minimal bleeding rate. Although commercial resection electrodes are effective, they either cause high blood loss (loop electrode) or reduce the bleeding rate with a compromised ablation rate (electrovaporization electrode). To resolve these problems, a new electrosurgical resection device, The Rotoresect, has been developed. METHODS: The Rotoresect incorporates a specially designed working element. The resection electrode is driven by a micromotor with a high-frequency current that enables simultaneous coagulation and vaporization during rotoresection. To date, 40 patients with benign prostatic hyperplasia have undergone transurethral rotoresection of the prostate with this new device. RESULTS: The actively rotating resection electrode enables tissue coagulation and vaporization as well as mechanical tissue ablation. Only slight bleeding was observed during the entire resection procedure. Postoperatively, no significant changes in hemoglobin and sodium concentration were detected. The deobstructive effect of the Rotoresect was comparable to that of the standard loop. CONCLUSIONS: The simultaneous tissue vaporization, coagulation, and mechanical removal by the Rotoresect enables a high ablation rate combined with minimal blood loss. Initial clinical results gained in the transurethral resection of benign prostatic tissue are promising.

Aged↗
PubMed2001

Retroperitoneal laparoscopic nephropexy.

Laparoscopic nephropexy is a suitable and clinically established procedure for the treatment of symptomatic nephroptosis. The availability of a minimally invasive therapy can facilitate decisions regarding the indication after careful selection of patients.

Adolescent↗
PubMed2001

Durability of laser probes in interstitial thermotherapy: investigations on an ex vivo model of effect of carbonization.

BACKGROUND AND PURPOSE: Interstitial laser application is successful for clinical tissue ablation in various organs. One great drawback of this method is the high costs caused by the vulnerability of the probes. Our objective was to investigate whether the prevention of carbonization deposits on laser probes averts reduced transmission after the application of high laser energy. MATERIALS AND METHODS: Interstitial laser probes were used to pierce an in vitro kidney model, and 9900 J of energy (Nd:YAG laser) was applied. The transmission of the laser probe was determined and compared with that of a reference probe. RESULTS: The application of laser energy, up to a total of 49,500 J, did not reduce transmission. The deviation of the transmission comparing working probes and the reference probe was between 2% and 7%. The application of high energy (40 W) over a longer period (>20 seconds) led to carbonization and consequent distinct reduction of transmission. CONCLUSIONS: The durability of laser probes can be prolonged by preventing carbonization. The economic effect achieved is the repeated use of the probes at less expense.

Animals↗
PubMed2001

Microscopic and biochemical fertility characteristics of semen after shockwave lithotripsy of distal ureteral calculi.

PURPOSE: To elucidate the frequency and adversity of the effects of shockwave lithotripsy (SWL) on the male reproductive system. We investigated the possible alterations in the quality of semen in patients treated by SWL for pelvic ureteral stones. PATIENTS AND METHODS: The semen of 10 men was examined 1 day before and 5 and 90 days after SWL for distal ureteral stones, in accordance with the World Health Organisation guidelines. The results were compared with those from the semen samples of 10 healthy male volunteers undergoing SWL for calculi of the upper urinary tract. RESULTS: Microscopic analysis of the semen samples revealed a transient decline in sperm density (24.7%), sperm motility (10%), sperm vitality (8%), and seminal fructose (27.5%) after SWL for distal ureteral stones. A distinctly higher number of spermatozoa of pathological origin was detected after SWL in the same group. There was no trace of microscopic hemospermia before shockwave treatment, but it was detected in 90% of the patients with lower ureteral calculi after SWL. Macroscopic hemospermia was detected in two of these nine patients. No deterioration of the semen characteristics and no hemospermia was observed after treatment in the control group with upper urinary stones. CONCLUSIONS: Our investigations confirmed a transient deterioration in semen quality after SWL for distal ureteral calculi, whereas no deterioration was observed after SWL for upper ureteral stones. Impaired sperm quality values returned to normal within 12 weeks after SWL, clearly indicating a damaging effect of SWL on seminal vesicle or ejaculatory duct function. The initial procreative capacity was restored in all patients.

Adult↗
PubMed2001

Color Duplex sonography vs. computed tomography: accuracy in the preoperative evaluation of renal cell carcinoma.

PURPOSE: Accurate imaging is essential for correct operative planning and successful surgical intervention in renal cell carcinoma (RCC). Our objective was the comparison of color duplex sonography with spiral computed tomography (CT) and surgical-pathological findings in the evaluation of renal masses to determine tumor localization, size, tumor thrombus extent and lymph node metastases. METHODS: We evaluated 60 patients with a renal mass in a prospective study. Both color duplex sonography and CT were performed by different investigators without knowledge of the supposed diagnosis. The color Doppler findings were compared to CT and surgical pathological findings. RESULTS: The sensitivity of color duplex sonography in the detection of RCC and lymph node metastases is comparable to that of CT (100%). Color duplex sonography was superior in the detection of renal vein involvement. Color duplex sonography alone allowed correct planning of the surgical procedure without intraoperative changes in all patients. CONCLUSION: Duplex sonography provides exactly the same information as CT. Although duplex sonography is less expensive with lower exposure to radiation, most surgeons will still probably demand CT for diagnosis, especially as this method is unerring and duplex sonography highly depends on the expertise of the person using it.

Aged↗
PubMed2001

Guidelines on urolithiasis.

OBJECTIVES: A project was initiated by the Health Care Office of the European Association of Urology in order to formulate common recommendations and guidelines for the treatment of patients with urolithiasis. The basic task for the working group therefore was to extract and evaluate evidence from the literature in order to reach a consensus on how these patients could best be managed. METHODS: Extensive reviews of the literature together with a thorough and detailed discussion of the various topics, by a working group including of experts from several European countries, provided the basis for a consensus overview of urolithiasis and its management. RESULTS AND CONCLUSIONS: Recommendations are given for the management of patients with acute stone colic and for active removal of stones from the ureter and kidney. Moreover, the principles for risk evaluation of patients with recurrent stone formation and appropriate recurrence preventive treatment are given.

Calcium↗
PubMed2001

Methylene blue as a successful treatment alternative for pharmacologically induced priapism.

OBJECTIVE: Priapism is defined as prolonged and persistent erection of the penis without sexual stimulation. Etiologies of this condition are numerous. Treatment of priapism varies from a conservative medical to a drastic surgical approach. Recent findings indicate methylene blue (MB), a guanylate cyclase inhibitor, to be a potential inhibitor of endothelial-mediated cavernous relaxation. This prompted us to assess the feasibility, use and effectiveness of MB in the treatment of priapism. METHODS: 12 patients were treated for priapism. Etiologies were: 10 drug-mediated (PGE(1) or papaverine/phentolamine mixture) after corpus cavernosum injection therapy (CCIT); 1 leukemia-induced, and 1 idiopathic high-flow priapism. The age range for all patients was 13-67 years, the average duration of priapism was 5.5 h after CCIT. MB was administered after blood aspiration of the corpora cavernosa. 5 ml of MB was injected intracavernously (i.c.) and left for 5 min. MB was then aspirated and the penis compressed for an additional 5 min. RESULTS: All patients with CCIT-induced priapism were cured with MB alone. The 2 patients who did not respond to MB underwent i.c. phenylephrine administration and embolization of the pudendal artery, respectively. The etiology and duration of priapism were the strongest predictors for success with i.c. administered MB. The primary side effects were a transient burning sensation and blue discoloration of the penis on injection of MB. The initial baseline erectile status was restored in all patients cured by MB. CONCLUSION: These results confirm that MB is a safe and highly effective treatment agent for short-term pharmacologically induced priapism. The application of MB shows virtually no significant side effects compared to the systemic and local complications induced by alpha-adrenergic agonists.

Adolescent↗
PubMed2001

[Ldr brachytherapy, a minimally invasive alternative in the treatment of organ-confined prostate cancer].

LDR Brachytherapy, a Minimally Invasive Alternative in the Treatment of Organ-Confined Prostate Cancer In den letzten Jahren erlebte die Brachytherapie mit permanenten Implantaten beim organbegrenzten Prostatakarzinom besonders in den USA, wo im Jahre 1999 mehr als 40 000 Implantationen durchgeführt wurden, eine Renaissance. Mit einer gewissen Verzögerung nimmt die Popularität dieser Methode auch in Europa immer mehr zu. Dies, obwohl die Brachytherapie keine absolut neue Methode in der Behandlung des Prostatakarzinoms ist, sie hat im Gegenteil eine lange Tradition.

Brachytherapy↗
PubMed2001

Percutaneous nephrostomy versus ureteral stents for diversion of hydronephrosis caused by stones: a prospective, randomized clinical trial.

PURPOSE: Urinary diversion with percutaneous nephrostomy or ureteral stent is indicated by symptoms, such as persistent colic, high temperature and uremia, of hydronephrosis caused by stones. We evaluate which of these 2 methods is superior concerning the course of procedure, relief of accompanying symptoms and quality of life in regard to patient age and sex. MATERIALS AND METHODS: A total of 40 patients with stone induced hydronephrosis were randomized into either percutaneous nephrostomy or stent insertion groups. These patients were then evaluated by procedure (use of analgesics, x-ray exposure, success of insertion), relief of accompanying symptoms (duration of diversion, intravenous administration of antibiotics for high temperature) and quality of life (questionnaire immediately and 2 to 4 weeks postoperatively). RESULTS: Two comparable groups of patients were formed, with an average age of 55 versus 49 years and a male-to-female ratio of 12:8 versus 9:11 for those who underwent percutaneous nephrostomy versus those who received a stent, respectively. Percutaneous nephrostomy was successfully completed in 100% of patients and stents were successful in 80%, with a 20% conversion to percutaneous nephrostomy. The x-ray exposure was shorter in the percutaneous nephrostomy group (p = 0.052). Administration of analgesics was more frequent in the stent group (p = 0.061). Percutaneous nephrostomy indwelling time was shorter (50% less than 2 weeks) than that of stents (25% less than 2 weeks, p = 0.043). Antibiotics were administered for greater than 5 days in 0% of patients who underwent percutaneous nephrostomy versus 64% in those with stents (p = 0.174). Reduction in quality of life was moderate but more pronounced in patients with stents compared to those who underwent percutaneous nephrostomy, and was more distinct in males and younger patients. The quality of life progressively improved in the course of diversion with percutaneous nephrostomy but deteriorated with stents. CONCLUSIONS: Our results demonstrated that percutaneous nephrostomy is superior to ureteral stents for diversion of hydronephrosis caused by stones, especially in patients with a high temperature, as well as in males and juveniles.

Adult↗
PubMed2001

Combined evaluation of detrusor pressure and bladder wall thickness as a parameter for the assessment of detrusor function: an experimental in vivo study.

PURPOSE: We developed a new method for assessing detrusor function, including active detrusor pressure in relation to bladder wall thickness. This parameter should enable the determination of bladder wall tension, defined as detrusor force per cross-sectional area of bladder tissue. MATERIAL AND METHODS: In acute studies in 8 male foxhounds sacral anterior roots S2 to S3 were placed into a modified Brindley electrode. The bladder was stimulated at different intravesical volumes with bladder filling in 50 ml. stages up to 700 ml. and intravesical pressure was measured and registered. The volume of bladder tissue was determined following cystectomy. Bladder tissue volume and bladder wall thickness were correlated with intravesical pressure during stimulation, resulting in the determination of detrusor force per cross-sectional area in N./cm.2 bladder tissue. RESULTS: The curve of the intravesical pressure rise during stimulation between 0 and 700 ml. showed a rapid incline with a maximum mean of 70.8 cm. water at 100 ml., followed by a slow decline. The bladder wall tension curve had an approximately symmetrical course with a slow incline, a maximum mean of 10.15 N./cm.2 at 350 ml. and a subsequent slow decline. CONCLUSIONS: The different curves of intravesical pressure and bladder wall tension show that these parameters are not identical. Combining detrusor pressure with bladder wall thickness enables further information on detrusor function to be obtained. Therefore, the clinical assessment of bladder wall tension may become a promising supplement to standard diagnostic methods with predictive value in patients with disturbed micturition.

Animals↗