Agnes J Wang

Duke University, Durham, North Carolina, United States

Are you Agnes J Wang?

Claim your profile

Publications (28)110.52 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose Different factors can determine the outcomes of percutaneous nephrolithotomy (PNL). We analyzed the effect of tract length (TL) on outcomes after PNL. Methods We performed a retrospective review of patients undergoing PNL between 2006 and 2011. Patients with preoperative computed tomography (CT), one percutaneous access tract and follow-up imaging within 3 months were included. TL was defined as distance between the skin to the calyx of puncture as measured on preoperative CT. Measurements were independently performed by two urologists and the average was used for analysis. Stone-free rate (SFR) was defined as zero fragments on follow-up imaging. Factors independently associated with the likelihood of being stone-free after PNL were determined using multivariable analysis adjusted for TL, location of access, the presence of incomplete or complete staghorn calculi and type of follow-up imaging. Complications (Clavien score) were independently assessed. Results A total of 222 patients were included. Median stone burden and body mass index (BMI) was 239.4 mm2 and 30.5 [interquartile range (IQR): 25.7–36.2]. The median TL was 85.0 mm (IQR: 70.3–100.0) and highly correlated with BMI (ρ = 0.66, p
    International Urology and Nephrology 08/2014; 46(12). DOI:10.1007/s11255-014-0812-0 · 1.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Objective: To compare the risks of fever from different lithotrites after percutaneous nephrolithotomy (PNL). Materials and methods: The Clinical Research Office of the Endourological Society (CROES) PNL database is a prospective, multi-institutional, international PNL registry. Of 5,803 total patients, 4,968 received preoperative antibiotics, were supplied with complete information and included in this analysis. The lithotrites assessed included no fragmentation, ultrasonic, laser, pneumatic and combination ultrasonic/pneumatic. Risk of fever was estimated using multivariate logistic regression with adjustment for diabetes, steroid use, a history of positive urine culture, the presence of staghorn calculi or preoperative nephrostomy, stone burden and lithotrite. Results: The overall fever rate was 10%. Pneumatic lithotrites were used in 43% of the cohort, followed by ultrasonic (24%), combination ultrasonic/pneumatic (17.3%), no fragmentation (8.4%) and laser (7.3%). Fever rates were no different between patients who underwent no or any fragmentation (p = 0.117), nor among patients when stratified by lithotrite (p = 0.429). On multivariate analysis, fragmentation was not significantly associated with fever [Odds Ratio (OR) 1.17, p = 0.413], while diabetes (OR 1.32, p = 0.048), positive urine culture (OR 2.08, p < 0.001), staghorn calculi (OR 1.80, p < 0.001) and nephrostomy (OR 1.65, p < 0.001) increased fever risk. Fever risk among lithotrites did not differ (p ≥ 0.128). Conclusions: Risk of post-PNL fever was not significantly different among the various lithotrites used in the CROES PNL study.
    Urologia Internationalis 08/2013; 91(3). DOI:10.1159/000351752 · 1.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose: Computerized tomography use increased exponentially in the last 3 decades, and it is commonly used to evaluate many urological conditions. Ionizing radiation exposure from medical imaging is linked to the risk of malignancy. We measured the organ and calculated effective doses of different studies to determine whether the dose-length product method is an accurate estimation of radiation exposure. Materials and methods: An anthropomorphic male phantom validated for human organ dosimetry measurements was used to determine radiation doses. High sensitivity metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ locations to measure specific organ doses. For each study the phantom was scanned 3 times using our institutional protocols. Organ doses were measured and effective doses were calculated on dosimetry. Effective doses measured by a metal oxide semiconductor field effect transistor dosimeter were compared to calculated effective doses derived from the dose-length product. Results: The mean±SD effective dose on dosimetry for stone protocol, chest and abdominopelvic computerized tomography, computerized tomography urogram and renal cell carcinoma protocol computerized tomography was 3.04±0.34, 4.34±0.27, 5.19±0.64, 9.73±0.71 and 11.42±0.24 mSv, respectively. The calculated effective dose for these studies Was 3.33, 2.92, 5.84, 9.64 and 10.06 mSv, respectively (p=0.8478). Conclusions: The effective dose varies considerable for different urological computerized tomography studies. Renal stone protocol computerized tomography shows the lowest dose, and computerized tomography urogram and the renal cell carcinoma protocol accumulate the highest effective doses. The calculated effective dose derived from the dose-length product is a reasonable estimate of patient radiation exposure.
    The Journal of urology 06/2013; 190(6). DOI:10.1016/j.juro.2013.06.013 · 4.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Objective: To compare the effective doses (EDs) associated with imaging modalities for follow-up of patients with urolithiasis, including stone protocol non-contrast computed tomography (NCCT), kidney, ureter, and bladder radiograph (KUB), intravenous urogram (IVU), and digital tomosynthesis (DT). Methods: A validated Monte-Carlo simulation-based software PCXMC 2.0 (STUK) designed for estimation of patient dose from medical X-ray exposures was used to determine the ED for KUB, IVU (KUB scout plus three tomographic images), and DT (two scouts and one tomographic sweep). Simulations were performed using a two-dimensional stationary field onto the corresponding body area of the built-in digital phantom, with actual kVp, mAs, and geometrical parameters of the protocols. The ED for NCCT was determined using an anthropomorphic male phantom that was placed prone on a 64-slice GE Healthcare volume computed tomography (VCT) scanner. High-sensitivity metal oxide semiconductor field effect transistors dosimeters were placed at 20 organ locations and used to measure organ radiation doses. Results: The ED for a stone protocol NCCT was 3.04±0.34 mSv. The ED for a KUB was 0.63 and 1.1 mSv for the additional tomographic film. The total ED for IVU was 3.93 mSv. The ED for DT performed with two scouts and one sweep (14.2°) was 0.83 mSv. Conclusions: Among the different imaging modalities for follow-up of patients with urolithiasis, DT was associated with the least radiation exposure (0.83 mSv). This ED corresponds to a fifth of NCCT or IVU studies. Further studies are needed to demonstrate the sensitivity and specificity of DT for the follow-up of nephrolithiasis patients.
    Journal of endourology / Endourological Society 06/2013; 27(10). DOI:10.1089/end.2013.0255 · 1.71 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Journal of endourology / Endourological Society 04/2013; 27(3-3):288-93. DOI:10.1089/end.2012.0211 · 1.71 Impact Factor

  • The Journal of Urology 04/2013; 189(4):e852. DOI:10.1016/j.juro.2013.02.2495 · 4.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose: Patients with recurrent nephrolithiasis are often evaluated and followed with computerized tomography. Obesity is a risk factor for nephrolithiasis. We evaluated the radiation dose of computerized tomography in obese and nonobese adults. Materials and methods: We scanned a validated, anthropomorphic male phantom according to our institutional renal stone evaluation protocol. The obese model consisted of the phantom wrapped in 2 Custom Fat Layers (CIRS, Norfolk, Virginia), which have been verified to have the same radiographic tissue density as fat. High sensitivity metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ locations in the phantoms to measure organ specific radiation doses. The nonobese and obese models have an approximate body mass index of 24 and 30 kg/m(2), respectively. Three runs of renal stone protocol computerized tomography were performed on each phantom under automatic tube current modulation. Organ specific absorbed doses were measured and effective doses were calculated. Results: The bone marrow of each model received the highest dose and the skin received the second highest dose. The mean ± SD effective dose for the nonobese and obese models was 3.04 ± 0.34 and 10.22 ± 0.50 mSv, respectively (p <0.0001). Conclusions: The effective dose of stone protocol computerized tomography in obese patients is more than threefold higher than the dose in nonobese patients using automatic tube current modulation. The implication of this finding extends beyond the urological stone population and adds to our understanding of radiation exposure from medical imaging.
    The Journal of urology 12/2012; 189(6). DOI:10.1016/j.juro.2012.12.029 · 4.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Background and purpose: The EMS Swiss LithoBreaker is a new, portable, electrokinetic lithotripter. We compared its tip velocity and displacement characteristics with a handheld, pneumatic lithotripter LMA StoneBreaker.™ We also evaluated fragmentation efficiency using in vitro models of percutaneous and ureteroscopic stone fragmentation. Materials and methods: Displacement and velocity profiles were measured for 1-mm and 2-mm probes using a laser beam aimed at a photo detector. For the percutaneous model, 2-mm probes fragmented 10-mm spherical BegoStone phantoms until the fragments passed through a 4-mm mesh sieve. The ureteroscopic model used 1-mm probes and compared the pneumatic and electrokinetic devices to a 200-μm holmium laser fiber. Cylindrical (4-mm diameter, 4-mm length) BegoStone phantoms were placed into silicone tubing to simulate the ureter; fragmented stones passed through a narrowing in the tubing. Results: For both 1-mm and 2-mm probes, the electrokinetic device had significantly higher tip displacement and slower tip velocity, P<0.01. In the percutaneous model, the electrokinetic device needed an average of 484 impulses over 430 seconds to fragment one BegoStone, while the pneumatic device needed 29 impulses over 122 seconds to fragment one stone. Both clearance times and number of impulses needed for percutaneous stone clearance were significantly different at P<0.01. Ureteroscopically, the mean clearance time was 97 seconds for the electrokinetic lithotripter, 145 seconds for the pneumatic lithotripter, and 304 seconds for the laser. Comparing the pneumatic device with the electrokinetic device ureteroscopically, there was no significant difference in clearance time, P=0.55. Both the pneumatic and electrokinetic lithotripters, however, demonstrated decreased clearance times compared with the laser, P=0.027. Conclusions: The portable electrokinetic lithotripter may be better suited for ureteroscopy instead of percutaneous nephrolithotomy. It appears to be comparable to the portable pneumatic device in the ureter. Further clinical studies are needed to confirm these findings in vivo.
    Journal of endourology / Endourological Society 08/2012; 26(11). DOI:10.1089/end.2012.0278 · 1.71 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Malignant ureteral obstruction often necessitates chronic urinary diversion and is associated with high rates of failure with traditional ureteral stents. We evaluated the outcomes of a metallic stent placed for malignant ureteral obstruction and determined the impact of risk factors previously associated with increased failure rates of traditional stents. Patients undergoing placement of the metallic Resonance® stent for malignant ureteral obstruction at an academic referral center were identified retrospectively. Stent failure was defined as unplanned stent exchange or nephrostomy tube placement for signs or symptoms of recurrent ureteral obstruction (recurrent hydroureteronephrosis or increasing creatinine). Predictors of time to stent failure were assessed using Cox regression. A total of 37 stents were placed in 25 patients with malignant ureteral obstruction. Of these stents 12 (35%) were identified to fail. Progressive hydroureteronephrosis and increasing creatinine were the most common signs of stent failure. Three failed stents had migrated distally and no stents required removal for recurrent infection. Patients with evidence of prostate cancer invading the bladder at stent placement were found to have a significantly increased risk of failure (HR 6.50, 95% CI 1.45-29.20, p = 0.015). Notably symptomatic subcapsular hematomas were identified in 3 patients after metallic stent placement. Failure rates with a metallic stent are similar to those historically observed with traditional polyurethane based stents in malignant ureteral obstruction. The invasion of prostate cancer in the bladder significantly increases the risk of failure. Patients should be counseled and observed for subcapsular hematoma formation with this device.
    The Journal of urology 07/2012; 188(3):851-5. DOI:10.1016/j.juro.2012.04.113 · 4.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Abstract 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.
    Journal of endourology / Endourological Society 05/2012; 26(10):1340-5. DOI:10.1089/end.2012.0140 · 1.71 Impact Factor

  • The Journal of Urology 04/2012; 187(4):e838. DOI:10.1016/j.juro.2012.02.2246 · 4.47 Impact Factor

  • The Journal of Urology 04/2012; 187(4):e926-e927. DOI:10.1016/j.juro.2012.02.2476 · 4.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We measured organ specific radiation dose rates and determined effective dose rates during simulated ureteroscopy using a validated model. To calculate the effective dose, patients were exposed to ureteroscopic management of stones at our institution. A validated anthropomorphic male phantom was placed on a fluoroscopy table and underwent simulated ureteroscopy. High sensitivity metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ sites in the phantom and used to measure organ specific radiation doses. These dose rates were multiplied by the appropriate tissue weighting factor and summed to calculate effective dose rates. Also, we retrospectively reviewed the charts of patients who underwent ureteroscopy at our institution. A total of 30 nonobese males with data on fluoroscopy time were included in analysis. The median effective dose was determined by multiplying median fluoroscopy time by the effective dose rate. The skin entrance was exposed to the highest absorbed dose rate, followed by the small intestine (mean ± SD 0.3286 ± 0.0054 and 0.1882 ± 0.0194 mGy per second, respectively). The mean effective dose rate was 0.024 ± 0.0019 mSv per second. Median fluoroscopy time was 46.95 seconds (range 12.9 to 298.8). The median effective dose was 1.13 mSv (range 0.31 to 7.17). The fluoroscopy used during ureteroscopy contributes to overall radiation exposure in patients with nephrolithiasis. Nonobese males are exposed to a median of 1.13 mSv during ureteroscopy, similar to that of abdominopelvic x-ray. More data are needed to determine clinical implications but urologists must be aware and decrease patient radiation during ureteroscopy.
    The Journal of urology 03/2012; 187(3):920-4. DOI:10.1016/j.juro.2011.10.159 · 4.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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. 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. 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. 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.
    Journal of endourology / Endourological Society 09/2011; 26(5):439-43. DOI:10.1089/end.2011.0178 · 1.71 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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. 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. 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. 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.
    Journal of endourology / Endourological Society 08/2011; 25(8):1353-7. DOI:10.1089/end.2011.0041 · 1.71 Impact Factor

  • The Journal of Urology 04/2011; 185(4). DOI:10.1016/j.juro.2011.02.1418 · 4.47 Impact Factor

  • The Journal of Urology 04/2011; 185(4). DOI:10.1016/j.juro.2011.02.1560 · 4.47 Impact Factor

  • The Journal of Urology 04/2011; 185(4). DOI:10.1016/j.juro.2011.02.2367 · 4.47 Impact Factor

  • The Journal of Urology 04/2011; 185(4). DOI:10.1016/j.juro.2011.02.2468 · 4.47 Impact Factor
  • Agnes J Wang · Glenn M Preminger ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Ureteroscopy continues to improve as a method for management of intrarenal stone disease. The development of new technologies and enhanced application of existing therapies is expanding the indications of ureteroscopy for the management of renal calculi. Improvements in image quality have been achieved with the adoption of digital ureteroscopes. Modifications of standard ureteroscopic techniques and improvements in surgical skill training are also being made. Ureteroscopy is demonstrated to be well tolerated and efficacious for the management of intrarenal calculi in multiple-patient populations and is also cost-efficient. The indications for ureteroscopic management of renal calculi are expanding, and this technique is quickly being adopted as a routine option for the management of intrarenal stone disease.
    Current opinion in urology 03/2011; 21(2):141-4. DOI:10.1097/MOU.0b013e32834351b9 · 2.33 Impact Factor