W. Neal Simmons

Renal Stone Assessment with Dual-Energy Multidetector CT and Advanced Postprocessing Techniques: Improved Characterization of Renal Stone Composition—Pilot Study

PURPOSE To prospectively evaluate the capability of noninvasive, simultaneous dual-energy (DE) multidetector computed tomography (CT) to improve characterization of human renal calculi in an anthropomorphic DE renal phantom by introducing advanced postprocessing techniques, with ex vivo renal stone spectroscopy as the reference standard. MATERIALS AND METHODS Fifty renal calculi were assessed: Thirty stones were of pure crystalline composition (uric acid, cystine, struvite, calcium oxalate, calcium phosphate, brushite), and 20 were of polycrystalline composition. DE CT was performed with a 64-detector CT unit. A postprocessing algorithm (DECT(Slope)) was proposed as a pixel-by-pixel approach to generate Digital Imaging and Communications in Medicine dataset gray-scale-encoding ratios of relative differences in attenuation values of low- and high-energy DE CT. Graphic analysis, in which clusters of equal composition were identified, was performed by sorting attenuation values of color composition-encoded calculi in an ascending sequence. Multivariate general linear model analysis was used to determine level of significance to differentiate composition on native and postprocessed DE CT images. RESULTS Graphic analysis of native DE CT images was used to identify clusters for uric acid (453-629 HU for low-energy CT, 443-615 HU for high-energy CT), cystine (725-832 HU for low-energy CT, 513-747 HU for high-energy CT), and struvite (1337-1530 HU for low-energy CT, 1007-1100 HU for high-energy CT) stones; high-energy clusters showed attenuation value overlap. Polycrystalline calcium oxalate and calcium phosphate calculi were found throughout the entire spectrum, and dense brushite had attenuation values of more than 1500 HU for low-energy CT and more than 1100 HU for high-energy CT. The DE CT algorithm was used to generate specific identifiers for uric acid (77-80 U(Slope), one outlier), cystine (70-71 U(Slope)), struvite (56-60 U(Slope)), calcium oxalate and calcium phosphate (17-59 U(Slope)), and brushite (4-15 U(Slope)) stones. Statistical analysis showed that all compositions were identified unambiguously with the DECT(Slope) algorithm. CONCLUSION DE multidetector CT with advanced postprocessing techniques improves characterization of renal stone composition beyond that achieved with single-energy multidetector CT acquisitions with basic attenuation assessment.

High Definition Laparoscopy: Objective Assessment of Performance Characteristics and Comparison with Standard Laparoscopy

INTRODUCTION High definition (HD) digital imaging represents a major advance in endoscope technology. The development of the charge-coupled device chip and its location at the distal end of the endoscope allows for image capture and digitization, as well as specific light filtration and processing. We assessed the capability of HD technology combined with digital imaging to provide improved image quality and enhanced spatial three-dimensional positioning. METHODS A HD digital laparoscope and a standard definition (SD) laparoscope were evaluated in the laboratory setting to assess and compare image resolution, brightness, contrast, and color reproducibility, using standard industry testing protocols. RESULTS Compared with the SD laparoscope, the HD laparoscope had superior resolution at 50 mm distance (2.4 line pairs/mm v 2.0 line pairs/mm), increased image brightness (129 lumens v 112 lumens), increased depth of field, and decreased distortion. Color and grayscale reproduction were found to be similar for the two laparoscopes. CONCLUSION HD laparoscopy has superior objective performance characteristics compared with standard laparoscopes. Further investigation is required to determine whether these objective findings translate into subjective improvements, and which characteristics can be adjusted to obtain the best possible results. These improved optics may lead to easier identification of anatomic structures, finer dissection, and enhanced three-dimensional spatial positioning during HD laparoscopic procedures.

Organ-specific radiation dose rates and effective dose rates during percutaneous nephrolithotomy.

BACKGROUND AND PURPOSE Radiation exposure during medical procedures continues to be an increasing concern for physicians and patients. We determined organ-specific dose rates and calculated effective dose rates during right and left percutaneous nephrolithotomy (PCNL) using a validated phantom model. MATERIALS AND METHODS A validated anthropomorphic adult male phantom was placed prone on an operating room table. Metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ locations in the model and were used to measure the organ dosages. A portable C-arm was used to provide continuous fluoroscopy for three 10 minute runs each to simulate a left and right PCNL. Organ dose rate (mGy/s) was determined by dividing organ dose by fluoroscopy time. The organ dose rates were multiplied by their tissue weighting factor and summed to determine effective dose rate (EDR) (mSv/s). Two-dimensional radiation distribution in the abdomen during a left-sided PCNL was visually determined using radiochromic film. RESULTS The EDR for a left PCNL was 0.021 mSv/s ± 0.0008. The EDR for a right PCNL was 0.014 mSv/s ± 0.0004. The skin entrance was exposed to the greatest amount of radiation during left and right PCNL, 0.24 mGy/s and 0.26 mGy/s, respectively. Radiochromic film demonstrates visually the nonuniform dose distribution as the x-ray beam enters through the skin from the radiation source. CONCLUSIONS The effective dose rate is higher for a left-sided PCNL compared with a right-sided PCNL. The distribution of radiation exposure during PCNL is not uniform. Further studies are needed to determine the long-term implications of these radiation doses during percutaneous stone removal.

Effect of lithotripter focal width on stone comminution in shock wave lithotripsy

Using a reflector insert, the original HM-3 lithotripter field at 20 kV was altered significantly with the peak positive pressure (p(+)) in the focal plane increased from 49 to 87 MPa while the -6 dB focal width decreased concomitantly from 11 to 4 mm. Using the original reflector, p(+) of 33 MPa with a -6 dB focal width of 18 mm were measured in a pre-focal plane 15-mm proximal to the lithotripter focus. However, the acoustic pulse energy delivered to a 28-mm diameter area around the lithotripter axis was comparable ( approximately 120 mJ). For all three exposure conditions, similar stone comminution ( approximately 70%) was produced in a mesh holder of 15 mm after 250 shocks. In contrast, stone comminution produced by the modified reflector either in a 15-mm finger cot (45%) or in a 30-mm membrane holder (14%) was significantly reduced from the corresponding values (56% and 26%) produced by the original reflector (no statistically significant differences were observed between the focal and pre-focal planes). These observations suggest that a low-pressure/broad focal width lithotripter field will produce better stone comminution than its counterpart with high-pressure/narrow focal width under clinically relevant in vitro comminution conditions.

Assessment of a Modified Acoustic Lens for Electromagnetic Shock Wave Lithotripters in a Swine Model

PURPOSE The acoustic lens of the Modularis electromagnetic shock wave lithotripter (Siemens, Malvern, Pennsylvania) was modified to produce a pressure waveform and focal zone more closely resembling that of the original HM3 device (Dornier Medtech, Wessling, Germany). We assessed the newly designed acoustic lens in vivo in an animal model. MATERIALS AND METHODS Stone fragmentation and tissue injury produced by the original and modified lenses of the Modularis lithotripter were evaluated in a swine model under equivalent acoustic pulse energy (about 45 mJ) at 1 Hz pulse repetition frequency. Stone fragmentation was determined by the weight percent of stone fragments less than 2 mm. To assess tissue injury, shock wave treated kidneys were perfused, dehydrated, cast in paraffin wax and sectioned. Digital images were captured every 120 μm and processed to determine functional renal volume damage. RESULTS After 500 shocks, the mean ± SD stone fragmentation efficiency produced by the original and modified lenses was 48% ± 12% and 52% ± 17%, respectively (p = 0.60). However, after 2,000 shocks, the modified lens showed significantly improved stone fragmentation compared to the original lens (mean 86% ± 10% vs 72% ± 12%, p = 0.02). Tissue injury caused by the original and modified lenses was minimal at a mean of 0.57% ± 0.44% and 0.25% ± 0.25%, respectively (p = 0.27). CONCLUSIONS With lens modification the Modularis lithotripter demonstrates significantly improved stone fragmentation with minimal tissue injury at a clinically relevant acoustic pulse energy. This new lens design could potentially be retrofitted to existing lithotripters, improving the effectiveness of electromagnetic lithotripters.

Pathologic evaluation of hemostatic agents in percutaneous nephrolithotomy tracts in a porcine model.

BACKGROUND AND PURPOSE Hemostatic agents have been suggested as an adjunct for tubeless percutaneous nephrolithotomy (PCNL). We pathologically evaluated the percutaneous tracts injected with the fibrin sealant (FS) Evicel and hemostatic gelatin matrix (HGM) Surgiflo at various time intervals to determine their absorption and tract closure rates. We also evaluated whether these agents reduced urine leak rates in a porcine model. MATERIALS AND METHODS Percutaneous access was obtained in 19 kidneys in 10 domestic swine. The tracts were dilated to 30F using a balloon dilating catheter. Ten kidneys served as controls. Surgiflo was injected into the tract of four kidneys, and Evicel was injected into the tract of five kidneys. Intravenous urography (IVU) was performed on postoperative days (POD) 1 and 10 to 14. IVU was performed on two pigs at POD 30. The pigs were sacrificed and kidneys were harvested for pathologic evaluation. RESULTS Two (20%) control kidneys had a urine leak on IVU on POD 1. None of the kidneys treated with HGM or FS had a urine leak on POD 1. None of the kidneys had a leak on POD 10 to 14 or POD 30. On pathologic inspection, the tracts of all the control kidneys and HGM kidneys had closed completely at POD 14. Two kidneys treated with FS had fistula at POD 6 and POD 14. At POD 30, the tracts in the control kidneys and kidney treated with HGM had completely healed. Fibrin sealant remained in the tract at POD 30. CONCLUSION Fibrin sealant should be used with caution because it can persist in the tract for up to 30 days and may inhibit wound healing. Hemostatic gelatin matrix is the preferable agent because the tract closed by POD 10 to 14, similar to the findings in the control animals. The use of hemostatic agents in a nephroscopy tract may reduce the risk of early urine leak after tubeless PCNL.

Optimization of Treatment Strategy Used During Shockwave Lithotripsy to Maximize Stone Fragmentation Efficiency

BACKGROUND AND PURPOSE Previous studies have demonstrated that treatment strategy plays a critical role in ensuring maximum stone fragmentation during shockwave lithotripsy (SWL). We aimed to develop an optimal treatment strategy in SWL to produce maximum stone fragmentation. MATERIALS AND METHODS Four treatment strategies were evaluated using an in-vitro experimental setup that mimics stone fragmentation in the renal pelvis. Spherical stone phantoms were exposed to 2100 shocks using the Siemens Modularis (electromagnetic) lithotripter. The treatment strategies included increasing output voltage with 100 shocks at 12.3 kV, 400 shocks at 14.8 kV, and 1600 shocks at 15.8 kV, and decreasing output voltage with 1600 shocks at 15.8 kV, 400 shocks at 14.8 kV, and 100 shocks at 12.3 kV. Both increasing and decreasing voltages models were run at a pulse repetition frequency (PRF) of 1 and 2 Hz. Fragmentation efficiency was determined using a sequential sieving method to isolate fragments less than 2 mm. A fiberoptic probe hydrophone was used to characterize the pressure waveforms at different output voltage and frequency settings. In addition, a high-speed camera was used to assess cavitation activity in the lithotripter field that was produced by different treatment strategies. RESULTS The increasing output voltage strategy at 1 Hz PRF produced the best stone fragmentation efficiency. This result was significantly better than the decreasing voltage strategy at 1 Hz PFR (85.8% vs 80.8%, P=0.017) and over the same strategy at 2 Hz PRF (85.8% vs 79.59%, P=0.0078). CONCLUSIONS A pretreatment dose of 100 low-voltage output shockwaves (SWs) at 60 SWs/min before increasing to a higher voltage output produces the best overall stone fragmentation in vitro. These findings could lead to increased fragmentation efficiency in vivo and higher success rates clinically.

Optical performance comparison of deflectable laparoscopes for laparoendoscopic single-site surgery.

BACKGROUND AND PURPOSE Flexible working angles and fine optical visualization are major requisite factors in performing laparoendoscopic single-site (LESS) urologic procedures. Multiple mechanical design approaches have been used to develop deflectable laparoscopes for LESS procedures. We compared the optical characteristics of three such devices using a bench top approach to simulate LESS in straight and deflected positions. MATERIALS AND METHODS A 10-mm fixed-rod rotating lens device (Storz EndoCameleon) and two 5-mm articulating devices (Olympus EndoEye and Stryker IdealEye) were compared using standard industry testing protocols for image resolution (United States Air Force-1951 test target), distortion (multifrequency grid distortion target), and color reproducibility (Gretag Macbeth color checker). RESULTS The 10-mm fixed-rod rotating lens system demonstrated the highest image resolution (5.04 line pairs/mm), but also the highest distortion (22.8%). Among the 5-mm flexible articulating laparoscopes, resolution was superior with the Olympus EndoEye (4.00 line pairs/mm) compared with the Stryker IdealEye (3.17 line pairs/mm). Distortion (7.0%) and color reproduction (1.18) were superior with the IdealEye vs the EndoEye (18.8 %, 1.27). Laparoscope deflection resulted in attenuation of resolution by 11% with both articulating models, but not with the fixed rod system. CONCLUSIONS Definition of these optical characteristics may inform further development and selection of laparoscopic systems optimized for LESS surgery. A narrow but flexible camera can be crucial in the limited working space available during these procedures. Further investigation is warranted to determine if these objective findings translate into improved surgeon performance.

A new acoustic lens design for electromagnetic shock wave lithotripters.

The third‐generation electromagnetic (EM) shock wave lithotripters often have narrow focal width and high‐peak pressure compared to the original HM‐3. In addition, the pressure waveform produced by a typical EM lithotripter has a secondary compressive wave that suppresses lithotripter pulse induced cavitation, which is an important mechanism for stone comminution. These features have been contributed to the reduced effectiveness of the modern EM lithotripters. To overcome these drawbacks, we have designed a new acoustic lens for the Siemens Modularis EM lithotripter that produces an idealized pressure waveform similar to the HM‐3 with broad focal width and low‐peak pressure. At acoustic pulse energy of 53 mJ, the new lens design enlarges the −6 dB focal width of the Modularis by 47% while significantly reducing the second compressive wave throughout its focal plane. After 2000 shocks, in vitro comminution produced by the original and new lens designs are 100% and 99% at the lithotripter focus, and (49.7±1...

Increasing dwell time of mitomycin C in the upper tract with a reverse thermosensitive polymer.

UNLABELLED Abstract Background and Purpose: Topical chemotherapy for urothelial cancer is dependent on adequate contact time of the chemotherapeutic agent with the urothelium. To date, there has not been a reliable method of maintaining this contact for renal or ureteral urothelial carcinoma. We evaluated the safety and feasibility of using a reverse thermosensitive polymer to improve dwell times of mitomycin C (MMC) in the upper tract. MATERIALS AND METHODS Using a porcine model, four animals were treated ureteroscopically with both upper urinary tracts receiving MMC mixed with iodinated contrast. One additional animal received MMC percutaneously. The treatment side had ureteral outflow blocked with a reverse thermosensitive polymer plug. MMC dwell time was monitored fluoroscopically and intrarenal pressures measured. Two animals were euthanized immediately, and three animals were euthanized 5 days afterward. RESULTS In control kidneys, drainage occurred at a mean of 5.3±0.58 minutes. Intrarenal pressures stayed fairly stable: 9.7±14.0 cm H20. In treatment kidneys, dwell time was extended to 60 minutes, when the polymer was washed out. Intrarenal pressures in the treatment kidneys peaked at 75.0±14.7 cm H20 and reached steady state at 60 cm H20. Pressures normalized after washout of the polymer with cool saline. Average washout time was 11.8±9.6 minutes. No histopathologic differences were seen between the control and treatment kidneys, or with immediate compared with delayed euthanasia. CONCLUSIONS A reverse thermosensitive polymer can retain MMC in the upper urinary tract and appears to be safe from our examination of intrarenal pressures and histopathology. This technique may improve the efficacy of topical chemotherapy in the management of upper tract urothelial carcinoma.