In vivo determination of urinary stone composition using dual energy computerized tomography with advanced post-acquisition processing.

PURPOSE: We assessed whether dual energy computerized tomography with advanced post-image processing can accurately differentiate urinary calculi composition in vivo. MATERIALS AND METHODS: A total of 25 patients scheduled to undergo ureteroscopic/percutaneous nephrolithotomy were prospectively identified. Dual energy computerized tomography was performed using 64-slice multidetector computerized tomography. Novel post-processing (DECTSlope) used pixel by pixel analyses to generate data sets grayscale encoding ratios of relative differences in attenuation of low (DECT80 kVp) and high energy (DECT140 kVp) series. Surgical extraction and Fourier spectroscopy resulted in 82 calculi. Of these stones 51 showed minor admixtures (uric acid, ammonium urate, struvite, calcium oxalate monohydrate and brushite) and 31 were polycrystalline (mixtures of calcium oxalate monohydrate/dihydrate and calcium phosphate). Analyses identified stone clusters of equal composition and distinct attenuation descriptors on DECT140 kVp, DECT80 kVp and DECTSlope. Iterative cross-validation of the 3 dual energy computerized tomography data sets was used to identify characteristic attenuation limits for each stone type. RESULTS: Attenuatio profiles showed substantial overlap among various stones on DECT140 kVp (uric acid 427.3±168.1 HU, ammonium urate 429.9±99.7 HU, struvite 480.2±123.5 HU, calcium oxalate monohydrate 852.4±301.4 HU, brushite 863.7±180.1 HU and polycrystalline 858.1±210.5 HU) and on DECT80 kVp (uric acid 493.6±182.8 HU, ammonium urate 591.5±157.9 HU, struvite 712.4±173.9 HU, calcium oxalate monohydrate 1,240.5±494.7 HU, brushite 1,532.1±273.1 HU and polycrystalline 1,358.7±316.8 HU). Statistically spectral separation was not sufficient to characterize stones unambiguously based on DECT140 kVp/DECT80 kVp attenuation. Analysis of attenuation showed sufficient spectral separation on DECTSlope (uric acid 14.9±10.9 U, ammonium urate 56.1±1.8 U, struvite 42.7±1.4 U, calcium oxalate monohydrate 62.8±1.8 U and brushite 113.2±5.3 U). Polycrystalline stones (51.8±3.7 U) overlapped with struvite and ammonium urate stones. This overlap was resolved as all struvite/ammonium urate stones measured 900 HU or less and all polycrystalline stones measured more than 900 HU on DECT80 kVp. CONCLUSIONS: Dual energy computerized tomography with novel post-processing allows accurate discrimination among main subtypes of urinary calculi in vivo and, thus, may have implications in determining the optimum clinical treatment of urinary calculi from a noninvasive, preoperative radiological assessment.

Tubeless percutaneous nephrolithotomy--the new standard of care?

PURPOSE: Traditionally the placement of a nephrostomy tube at the conclusion of percutaneous nephrolithotomy is considered the standard of care. However, the need for nephrostomy tube placement has been questioned by numerous authors. We evaluated the literature regarding tubeless percutaneous nephrolithotomy, and determined potential candidates for tubeless percutaneous nephrolithotomy and whether this procedure can be considered the new standard of care for complex stone removal. MATERIALS AND METHODS: A MEDLINE search was conducted between May 1997 and January 2010 to detect studies reporting tubeless percutaneous nephrolithotomy. "Nephrolithiasis," "percutaneous nephrolithotomy," "tubeless" and "lithotripsy" were used as medical subject headings (MeSH) key words. Additional citations were identified by reviewing the reference lists of the included articles. All relevant articles were reviewed for indications, outcomes and complications. RESULTS: The data obtained from 50 reports document comparable complication rates between tubeless and standard percutaneous nephrolithotomy. Tubeless percutaneous nephrolithotomy demonstrated advantages such as less pain, less debilitation, less costs and a shorter hospital stay. Mean stone-free rates for tubeless percutaneous nephrolithotomy were as high as 89%. CONCLUSIONS: Tubeless percutaneous nephrolithotomy appears to be safe and efficacious in uneventful procedures, in children, in obese patients, in simultaneous bilateral procedures, in supracostal access and in renal units with coexisting anatomical anomalies. Nephrostomy tube placement should still be considered in certain cases such as those with more than 2 nephrostomy access tracts, those necessitating a second look and those with intraoperative complications such as significant bleeding or collecting system perforation.

Minimizing radiation exposure during percutaneous nephrolithotomy.

Given the recent trends in growing per capita radiation dose from medical sources, there have been increasing concerns over patient radiation exposure. Patients with kidney stones undergoing percutaneous nephrolithotomy (PNL) are at particular risk for high radiation exposure. There exist several risk factors for increased radiation exposure during PNL which include high Body Mass Index, multiple access tracts, and increased stone burden. We herein review recent trends in radiation exposure, radiation exposure during PNL to both patients and urologists, and various approaches to reduce radiation exposure. We discuss incorporating the principles of As Low As reasonably Achievable (ALARA) into clinical practice and review imaging techniques such as ultrasound and air contrast to guide PNL access. Alternative surgical techniques and approaches to reducing radiation exposure, including retrograde intra-renal surgery, retrograde nephrostomy, endoscopic-guided PNL, and minimally invasive PNL, are also highlighted. It is important for urologists to be aware of these concepts and techniques when treating stone patients with PNL. The discussions outlined will assist urologists in providing patient counseling and high quality of care.