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Biomedical subjects

G M Preminger

Publications and source records attributed to G M Preminger.

At least 37 records · Page 2Linked to original sources
PubMed2000

Renal surgery in the new millennium.

In the not too distant future, the minimally invasive renal surgeon will be able to practice an operation on a difficult case on a three-dimensional virtual reality simulator, providing all attributes of the real procedure. The patient's imaging studies will be imported into the simulator to better mimic particular anatomy. When confident enough of his or her skills, the surgeon will start operating on the patient using the same virtual reality simulator/telepresence surgery console system, which will permit the live surgery to be conducted by robots hundreds of miles away. The robots will manipulate miniature endoscopes or control minimally or noninvasive ablative technologies. Endoscopic/laparoscopic footage of the surgical procedure will be stored digitally in optical disks to be used later in telementoring of a surgery resident. All this and more will be possible in the not so distant third millennium.

Cryotherapy↗
PubMed2000

Management of residual stones.

Stone-free status is highly dependent on selection of the appropriate surgical technique, which should be tailored according to the individual stone and patient parameters. Although a stone-free state is the desired outcome of surgical intervention of urolithiasis, the authors believe that the presence of noninfection, nonobstructive, asymptomatic postprocedural residual fragments can be managed metabolically in order to prevent stone growth adequately. Further surgical intervention in the case of residual fragments is warranted if the clinical indications that prompted the original surgery persist.

Humans↗
PubMed2000

Combined antegrade and retrograde endoscopic approach for the management of urinary diversion-associated pathology.

BACKGROUND: Endourologic management of stones and strictures in patients with a urinary diversion is often cumbersome because of the absence of standard anatomic landmarks. We report on our technique of minimally invasive management of urinary diversion-associated pathology by means of a combined antegrade and retrograde approach. PATIENTS AND METHODS: Five patients with urinary diversion-associated pathology were treated at our institution between May 1997 and October 1998. Their problems were: an obstructing ureteral stone in a man with ureterosigmoidostomy performed for bladder extrophy; two men with a valve stricture in their hemiKock urinary diversions; an anastomotic stricture in a man with an ileal loop diversion; and a long left ureteroenteric stricture in a man with a right colon pouch diversion. After percutaneous placement of an guidewire across the area of interest, the targeted pathology was accessed via a retrograde approach using standard semirigid or flexible fiberoptic endoscopes. Postoperative follow-up with intravenous urography, differential renal scan, or both was performed at 3 to 24 months (mean 12 months). RESULTS: The combined antegrade and retrograde approach allowed successful access to pathologic areas in all patients. Holmium laser/Acucise incision of stenotic segments or ballistic fragmentation of stones was achieved in all cases without perioperative complications. None of the strictures with an initially successful outcome has recurred; however, in one patient, the procedure failed as soon as the internal stent was removed. The patient with the ureteral calculus remains stone free, and his ureterosigmoidostomy is patent without evidence of obstruction on his last imaging study, 24 months postoperatively. CONCLUSIONS: Combined antegrade and retrograde endoscopic access to the area of interest is our preferred method of approaching pathologic problems in patients with a urinary diversion. An antegrade nephrostogram provides better delineation of anatomy, while through-and-through access enables rapid and easier identification of stenotic segments that may be hidden by mucosal folds. Furthermore, this approach allows the use of larger semirigid or flexible endoscopes in conjunction with more efficient fragmentation devices, resulting in enhanced vision from better irrigation. Finally, an initial endoscopic approach may be preferred because its failure does not compromise the success of future open surgery.

Aged↗
PubMed2000

Ureteroscopic management of recurrent renal cystine calculi.

BACKGROUND AND PURPOSE: Patients with recurrent cystine nephrolithiasis oftentimes require multiple procedures for stone removal. As the majority of cystine stones are resistant to the effects of shockwave lithotripsy, repeat percutaneous surgery is often required and may cause renal damage. Moreover, repeat percutaneous access may become more difficult as perinephric fibrosis develops. Small-caliber ureteroscopes along with the holmium laser now enable routine intrarenal ureteroscopic access to symptomatic renal stones. Herein, we present our experience in managing recurrent renal cystine calculi using flexible ureterorenoscopy and assess whether such an approach may be used as an alternative to percutaneous surgery in selected patients. PATIENTS AND METHODS: Three patients with large-volume (mean diameter 22 mm) renal cystine stones were managed with a 7.5F flexible ureterorenoscope combined with holmium laser lithotripsy to fragment the stones completely. RESULTS: The mean treatment time was 97 minutes, with successful fragmentation in all cases. Two of the three patients were completely stone free on follow-up intravenous urography, with the third patient having only small-volume residual fragments in a lower pole calix. All patients are currently asymptomatic and are being maintained on high oral fluid intake, urinary alkalization with potassium citrate, and alpha-mercaptopropionylglycine to reduce urinary cystine excretion. CONCLUSION: Flexible ureterorenoscopy with holmium laser lithotripsy provides a reasonable alternative for the management for recurrent cystine calculi in patients who are not candidates for repeat percutaneous procedures. Although it is time consuming, complete stone fragmentation, along with clearance of fragments, can be achieved in the majority of patients.

Cystine↗
PubMed2000

Successful management of lower-pole moiety ureteropelvic junction obstruction in a partially duplicated collecting system using minimally invasive retrograde endoscopic techniques.

Although the true incidence of ureteropelvic junction (UPJ) obstruction in the lower-pole moiety of an incompletely duplicated renal collecting system remains elusive, the description of this entity in the published literature is exceedingly rare. To our knowledge, we report the first case of this entity managed successfully by ureteroscopic holmium laser incision of the stenotic UPJ segment. This case underscores the utility of minimally invasive techniques in the management of selected cases of UPJ obstruction associated with a partially duplicated collecting system.

Humans↗
PubMed2000

Endoscopic management of urologic disease with the holmium laser.

The efficiency and safety profile of the holmium laser have made this tool a versatile multipurpose instrument for use in the endoscopic treatment of a wide variety of urologic disorders. Herein are reviewed holmium laser physics and current endourologic applications, as well as the performance of new low-power holmium lasers.

Endoscopy↗
PubMed2000

Clinical efficacy of combined lithoclast and lithovac stone removal during ureteroscopy.

PURPOSE: Pneumatic lithotripsy has proved to be an extremely safe, efficient and low cost intracorporeal fragmentation modality. Unfortunately proximal migration of fragments into inaccessible areas in the intrarenal collecting system is a potential limitation during ureteroscopic procedures. Moreover, the lack of an efficient mechanism of stone retrieval further limits the widespread application of this technique. The newly developed Lithovacdagger suction device was designed to be combined with pneumatic lithotripsy during ureteroscopic stone removal. We evaluated the effectiveness of this combination for overcoming these limitations. MATERIALS AND METHODS: Between February and December 1998, 21 patients underwent pneumatic lithotripsy of ureteral calculi combined with use of the Lithovac suction probe. Stone area was 20 to 320 mm.2 (mean 84). Of the stones 71% and 29% were in the distal, and proximal and/or mid ureter, respectively. We used a 0.8 mm. pneumatic lithotripsy probe placed through a 4.8Fr Lithovac probe at a pulse frequency of 12 Hz. and pressure of 2 atmospheres. RESULTS: Mean operative time was 42 minutes and the stone fragmentation rate was 100%. There were no complications in our series and no proximal migration of fragments. The overall stone-free rate was 95% at 3-month followup. CONCLUSIONS: Using the Lithovac suction device greatly facilitates pneumatic lithotripsy during ureteroscopic stone removal. This combination not only prevents fragment migration, but also aids in maintaining a clear endoscopic field of view, allowing efficient, safe and effective stone fragmentation.

Adolescent↗
PubMed2000

Acoustic and mechanical properties of artificial stones in comparison to natural kidney stones.

PURPOSE: Standardized and reproducible artificial kidney stone models are important for performing comparative studies of different lithotripsy modalities. The acoustic and mechanical properties of renal calculi dictate the manner by which stones interact with the mechanical stresses produced by shock wave lithotripsy (SWL) or intracorporeal lithotripsy modalities. We have developed a novel artificial kidney stone model that is made of natural substances found in real kidney stones. These stone models appear to be much closer in physical properties to natural kidney stones than previously used stone models. MATERIALS AND METHODS: The acoustic and mechanical properties of six groups of artificial stone models were compared to corresponding natural stones of similar compositions. Moreover, three groups of artificial stone models made of plaster-of-Paris were compared to their natural counterparts. In terms of acoustic properties, stone density was measured using a pycnometer based on Archimedes' principle, whereas longitudinal and transverse (or shear) wave propagation speeds were measured using an ultrasound pulse transmission technique. These values were used to calculate wave impedance and dynamic mechanical properties (bulk modulus, Young's modulus, and shear modulus) of the stones. The microhardness of the stones was measured and the effect of composition on stone fragility was evaluated. RESULTS: Artificial stones, when compared to natural stones of similar composition, showed similar trends in longitudinal and transverse wave speeds, wave impedance, and dynamic elastic moduli. However, values for the artificial stones were uniformly low compared to those of natural stones, suggesting that these artificial stones may be more amenable to shock wave fragmentation. The results of SWL on stone fragmentation of artificial and natural stones also revealed similar trends with the exception of artificial cystine stones which were found to be the most resistant to shock wave fragmentation. CONCLUSIONS: The results indicate that the physical properties of artificial stones made of natural stone materials are comparable to renal calculi of the same chemical composition. The data suggests that these stone phantoms are suitable for performing standardized and reproducible in vitro investigations, especially with regards to fragility of kidney stones of different chemical compositions during SWL.

Acoustics↗
PubMed2000

Quantification of the tip movement of lithotripsy flexible pneumatic probes.

PURPOSE: We developed an optical system to quantify in vitro tip movement of the Lithoclastdouble dagger flexible probe, and correlated various physical parameters of the vibrating probe tip with resultant stone fragmentation. MATERIALS AND METHODS: A noncontact optical measurement system was developed to quantify in vitro tip movement of the Lithoclast flexible probe. This system and an in vitro fragmentation model were used to determine the tip displacement, velocity, impact momentum, impact energy and stone fragmentation of the flexible probe at 5 deflection angles between 0 and 48 degrees, and the 2 pneumatic pressure levels of 2.0 and 2.5 bar. RESULTS: An increase in maximum probe tip displacement, velocity, impact momentum and energy, and stone fragmentation was seen as the pneumatic pressure was increased from 2.0 to 2.5 bar. A progressive decrease in these parameters was demonstrated as the probe tip was deflected, especially at deflection angles greater than 24 degrees. Impact momentum appears to be the physical parameter most closely correlated with stone fragmentation efficiency. CONCLUSIONS: The optical measurement system and in vitro fragmentation model developed allow one to quickly and reliably assess the performance of flexible pneumatic probes in vitro. This system can be used for general bench testing and basic research that can provide critical information for the design of more effective and efficient flexible pneumatic lithotripsy probes.

Calibration↗
PubMed1999

How to improve lithotripsy and chemolitholysis of brushite-stones: an in vitro study.

Because of their resistance to fragmentation, treatment of brushite stones is a big problem. This study was performed to look for an improvement in therapeutic strategies by using artificial stones made of brushite (Bon(n)-stones), which are comparable to their natural counterparts. Using an ultrasound transmission technique, longitudinal wave propagation speeds were measured at different time intervals during treatment with hemiacidrin. From these and density measurements, transverse wave speed, wave impedance and dynamic mechanical properties of the artificial stones were calculated. Moreover, the microhardness of artificial stones was measured and investigations on shock wave lithotripsy (SWL) combined with initial chemolytic treatment of the stones were performed. The suggestion was confirmed that stone fragility and thus SWL can be improved by varying the physical properties of brushite stones through treatment with hemiacidrin. Additionally, we demonstrated the efficacy of Suby G in dissolving artificial brushite stones using an experimental arrangement simulating the physiological conditions in the upper urinary tract. Moreover, the efficacy of four different intracorporeal lithotripsy devices (electrohydraulic, pneumatic, laser and ultrasound) was tested and it was shown that electrohydraulic lithotripsy seems to be the best system for comminution of brushite stones.

Calcium Phosphates↗
PubMed1999

The incidence of nephrolithiasis in patients with spinal neural tube defects.

PURPOSE: Bladder stones are common in patients with spinal neural tube defects but there are little data on the incidence of renal calculi in this population. We examined the incidence, nature and risk factors of nephrolithiasis in our clinic population of patients with neural tube defects. MATERIALS AND METHODS: We retrospectively reviewed the charts and radiological studies of 327 patients followed at our neural tube defects clinic with routine radiological imaging of the urinary tract. Additional confirmatory studies were performed when stones were noted. RESULTS: Renal calculi were identified in 20 patients with neural tube defects (6.1%). The incidence of nephrolithiasis increased with age. Renal stones were noted in 19 patients (10.7%) 12 years old or older. Management of the stones in these patients resulted in overall 53% stone-free and 87% recurrence rates after intervention. Major risk factors for new and/or recurrent renal stone formation were bacteriuria in 95% of the cases, lower urinary tract reconstruction in 80%, pelvicalicectasis in 70%, vesicoureteral reflux in 65%, a thoracic level spinal defect in 60% and renal scarring in 55%. CONCLUSIONS: These data suggest that there is a higher incidence of nephrolithiasis in patients with neural tube defects than in the general population and the risk of stone recurrence is also elevated. Most patients with stones had undergone lower urinary tract reconstruction. Other risk factors were bacteriuria, pelvicalicectasis, vesicoureteral reflux and a thoracic level neural tube defect.

Adolescent↗
PubMed1999

Incorporation of patient preferences in the treatment of upper urinary tract calculi: a decision analytical view.

PURPOSE: Patient preferences, or utilities, may be crucial to select an appropriate treatment plan for stone disease. We used decision modeling to understand better patient choices and decision making in the overall management of recurrent nephrolithiasis. MATERIALS AND METHODS: We interviewed 180 consecutive patients with active stone disease. Demographic data and historical experiences with calculi were recorded. Patients were presented with 6 hypothetical clinical scenarios and various treatment options. The standard gamble method was used to obtain utility values for each option. RESULTS: Nephrectomy had the lowest mean utility value of 0.883. Percutaneous nephrolithotomy for severe, moderate and mild pain had utilities of 0.924, 0.932 and 0.947, respectively. Shock wave lithotripsy for the management of mild pain was the most attractive option (mean utility 0.968). The utility for long-term medical therapy was 0.949, which was between that of percutaneous nephrolithotomy and shock wave lithotripsy for mild pain. Patients with a surgical history of stone removal assigned lower utilities to invasive procedures (nephrectomy, percutaneous nephrolithotomy, p <0.05). As the incidence of spontaneous stone passage increased, a higher utility was given to long-term medical therapy (p <0.05). Patients on medical therapy less than 1 year did not appreciate a significant benefit of medical prophylaxis. However, longer compliance with medical management led patients to perceive increasing benefits of continuing such medical treatment (p <0.05). Patients who had undergone stone removal via endoscopic or open surgery also had a higher preference for medical therapy (p <0.05). CONCLUSIONS: Patients who had undergone stone removal wanted to avoid future invasive procedures. They ranked long-term medical therapy below shock wave lithotripsy but above invasive procedures, such as percutaneous nephrolithotomy. Most importantly, patients appreciated the benefits of medical therapy the longer that they complied with specific recommendations. These results support the concept that patients perceive long-term medical therapy to prevent recurrent nephrolithiasis as a desirable treatment option.

Adolescent↗
PubMed1999

Use of a digital camera in the urologic setting.

Urologists are faced with increasing demands for clear documentation of their work. We report the use of a digital camera in our practice to capture images throughout the urologic setting. The digital camera was a quick and convenient means of obtaining good quality reproductions of radiographic and pathologic findings. Use of the camera greatly enhanced the efficiency of our practice by allowing incorporation of images into patient records and an image library.

Humans↗
PubMed1999

Secure transmission of urologic images and records over the Internet.

PURPOSE: Telemedicine has become a common method for the transmission of images and patient data across long distances. Our goal was to assess the efficiency and accuracy of Photomailer MD software, a store-and-forward telemedicine system, in the urologic setting. METHODS: Photomailer MD software was loaded on two computers in the host institution, one with a T1 connection to the Internet and the other with a dial-up modem connection (24,000 bits/second), and computers at three remote sites. A total of 14 clinical cases, comprised of digitized histories and radiographic images, were sent to the remote institutions four separate times using the four transmission modes available: nonencrypted, 56-bit encryption, 128-bit encryption, and 128-bit encryption with password. The following data points were recorded: file size before and after encryption, file transmission times, and diagnostic accuracy of the remote urologists. One-way ANOVA was used to compare mean values statistically, while the z-test was used to compare diagnostic accuracies. RESULTS: Encryption increased the file size by a mean of 37.8%, with the three encryption modes increasing file sizes by the same number of kilobytes. When a dial-up modem was used, encrypted files required a significantly longer transmission time (P < 0.05) than the unencrypted files. The same trend was seen with the T1 connection, although the differences often were not significant. When T1 transmission times were compared with modem times with other variables held constant, modem times were significantly longer (P < 0.05). Diagnostic accuracies for each of the three remote centers ranged from 85.7% to 100%. Differences in accuracy rates between attending physicians and residents were not significant. CONCLUSIONS: Photomailer MD provides a secure, convenient, and affordable method of transmitting patient images and records via the Internet. Transmission speed was significantly greater when using a T1 line and also tended to be faster when files were not encrypted. There was no significant difference in transmission time among the three encryption modes; therefore, 128-bit encryption with a password should be used to maximize security. Diagnostic accuracies were comparable to those in the literature. In general, 640 x 480-pixel resolution was adequate for urologic diagnoses, although higher-resolution images may improve accuracy.

Analysis of Variance↗
PubMed1999

Advances in digital imaging during endoscopic surgery.

BACKGROUND AND OBJECTIVE: Digital imaging capabilities have recently been incorporated into a number of video systems. Contrast enhancement when using a rigid or semirigid endoscope improves image definition by seeking out existing transitions in detail. Only the areas of transition are accentuated, whereas areas without detail are unaffected. During flexible endoscopy, fiberoptic bundles create a classic honeycomb appearance. The use of "fiberscope" filters minimizes this appearance by expanding the image of each fiberoptic fiber. We therefore assessed whether new developments in digital video image processing have improved image quality for endoscopic surgery. MATERIALS AND METHODS: Fifty urologists reviewed a video playback of various endourologic procedures. The type of endoscope was identified, but the urologic surgeon was blinded to the level of enhancement (high or low) or fiberscope filter (A or B) used. Each video clip was scored from 1 to 5 for the following image variables: identification of structure, detail of image, and background noise or interference. All results were averaged and compared using Student's paired t-test. RESULTS: During rigid endoscopy, the high and low digital enhancement settings were both superior to no enhancement (P < 0.001), and high enhancement was better than low (P < 0.001). With semirigid endoscopic procedures, high and low digital enhancement were comparable but were superior to no enhancement (P < 0.001). Filters A and B were no better than no enhancement. There was a significant improvement noted with the use of filter A or B during flexible ureteroscopy over no enhancement (P < 0.001). In addition, filter A was better than filter B (P < 0.001). CONCLUSIONS: Digital enhancement settings during video endoscopy significantly improve images from rigid and semirigid endoscopes. The digital fiberscope filter significantly improves images obtained during flexible ureteroscopy. Digital image enhancement capabilities should be strongly considered when upgrading video systems. Digital technology must be further studied to improve clinical video imaging during endoscopic surgery.

Endoscopy↗
PubMed1999

A new generation of semirigid fiberoptic ureteroscopes.

BACKGROUND: Further advances in endoscope technology have allowed the development of a new generation of tightly packed fiberoptics encased within a rigid ureteroscope. The tips of these semirigid ureteroscopes measure between 5.0F and 11.9F, and their working channels measure between 1.8F and 5.5F, which allows passage of routine endoscopc instruments. Additionally, several manufacturers have recently produced straight-channel fiberoptic semirigid endoscopes with an offset lens which allow usage of rigid lithotripsy devices. New fiber-packing techniques provide numerous pixels within the image bundle. These ureteroscopes have varied distal lens systems, but all have excellent vision in the field of view. METHODS: Over the past 28 months, we have performed transurethral ureteroscopy in 187 patients, having utilized semirigid ureteroscopes in 158 patients for diagnostic procedures (8.7 %), stone manipulation (78.7 %), removal of migrated stents (4.4%), and surgery of stricture, tumor, or foreign bodies (8.2%). In more than 50% of our cases, ureteral dilation was not necessary, and the semirigid ureteroscope was passed to the area of interest without difficulty. RESULTS: We accessed the site of pathology in 96.2% of patients. Overall, complications occurred in 6.9% of patients. However, of these problems, 93.6% were small ureteral perforations (only three of which were caused by the semirigid ureteroscope itself), and all cases but one were managed successfully by a ureteral stent. No postoperative strictures were noted. CONCLUSION: This new generation of semirigid fiberoptic ureteroscopes represents another significant advance in the endourologic management of ureteral disease.

Fiber Optic Technology↗
PubMed1999

Digital still image recording during video endoscopy.

With the advances in telemedicine and virtual consultation services comes the need for state-of-the-art endoscopic imaging techniques and equipment. Concomitant with current day concerns of cost containment, the ability to utilize the aforementioned tools in a cost-effective fashion that lowers operating expenses, accurately depicts procedures, and expedites chart documentation is paramount. We report on a fast and efficient way to obtain and store images during endoscopic procedures, which can be stored on standard 3.5-inch floppy disks using an innovative digital image recorder. These images are stored as high-resolution (640x480x24) JPEG files, which can be placed in electronic medical records, imported into Internet Web pages, incorporated into slide presentations, and, most importantly, stored in easily accessed archives.

Computer Communication Networks↗