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Re: Radiation Dose Reduction at Multidetector CT with Adaptive Statistical Iterative Reconstruction for Evaluation of Urolithiasis: How Low Can We Go?
1360
IMAGING
Re: Abnormalities of 24-Hour Urine Composition in First-Time and Recurrent Stone-Formers B. H. Eisner, S. Sheth, S. P. Dretler, B. Herrick and V. M. Pais, Jr. Department of Urology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts Urology 2012; 80: 776 –779.
Objective: To examine differences in 24-hour urine composition between recurrent and first-time stone-formers. Methods: A retrospective review of patients evaluated in 2 metabolic stone clinics was performed. Recurrent stone formation was defined as patients with a history of more than 1 stone episode and first-time stone-formers were those with a history of a single-stone episode. Frequencies of urine metabolic abnormalities were noted. Multivariate linear regression was performed to evaluate the likelihood of abnormalities of 24-hour urine composition. Results: Three-hundred eleven patients met inclusion criteria: 71 (22.8%) were first-time stone-formers and 240 (77.1%) were recurrent stone-formers. On univariate analysis, the likelihood of having a single abnormality of 24-hour urine composition (ie, hypercalciuria, hyperoxaluria, hyperuricosuria, or hypocitraturia) was similar between the 2 groups (83.1% for first-time vs 88.8% for recurrent, P ⫽ NS). In addition, there were similar rates of hypercalciuria (39.4% vs 43.3%, P ⫽ NS), hyperoxaluria (32.4% vs 33.3%, P ⫽ NS), hyperuricosuria (29.6% vs 23.3%, P ⫽ NS), and hypocitraturia (45.0% vs 45.0%, P ⫽ NS). On multivariate logistic regression, there was no difference in detection of any urine abnormality (ie, hypercalciuria or hyperoxaluria or hypocitraturia or hyperuricosuria) between first-time (referent) or recurrent stone-formers (OR 1.68, 95% CI .8 –3.5, P ⫽ .2). Conclusion: In this study, detection of urine abnormalities was similar in first-time and recurrent stone-formers. Given the strong patient preference for stone prevention and the high success of directed therapy in the literature, we believe it is not unreasonable to offer comprehensive metabolic evaluation to first-time stone-formers who express a desire to undergo evaluation. Editorial Comment: The 24-hour urine test is a mechanism for assessing phenotypic risk profile. The results are influenced by genetic and environmental factors such as diet. There is no question that such testing is warranted in certain first time stone formers such as children, patients with a solitary kidney or chronic kidney disease, individuals with bowel or bone disease, commercial airline pilots and patients with multiple remaining stones. If such testing is ordered in other first timers, a discussion with these patients about their willingness to proceed to medical therapy should be conducted. Dean Assimos, M.D.
Suggested Reading Pak CY: Should patients with single renal stone occurrence undergo diagnostic evaluation? J Urol 1982; 127: 855.
Imaging Re: Radiation Dose Reduction at Multidetector CT with Adaptive Statistical Iterative Reconstruction for Evaluation of Urolithiasis: How Low Can We Go? N. M. Kulkarni, R. N. Uppot, B. H. Eisner and D. V. Sahani Departments of Abdominal Imaging and Intervention, Urology, Massachusetts General Hospital, Boston, Massachusetts Radiology, 2012 265: 158 –166.
Purpose: To evaluate the performance of computed tomographic (CT) examinations at 80 and 100 kV with tube current-time products of 75–150 mA and the effect of adaptive statistical iterative recon-
IMAGING
1361
struction (ASIR) on CT image quality in patients with urinary stone disease. Materials and Methods: In this HIPAA-compliant institutional review board-approved study, verbal consent for prospective low-dose CT and waivers of consent for retrospective review of CT scans were obtained. Between November 2010 and April 2011, 25 patients (15 men, 10 women; mean age, 35 years) with urolithiasis underwent 64-section multidetector CT with 75–150 mA and noise index of 30. Modified protocol was based on body weight (⬍200 lb [90 kg], 80 kV; ⬎200 lb [90 kg], 100 kV). Images of 5-mm section thickness were reconstructed with filtered back projection (FBP) and 60% and 80% ASIR techniques, with 3-mm coronal and sagittal reformations. Two readers independently reviewed FBP and ASIR data sets for image quality (scale, 1–5), noise (scale, 1–3), and calculi (number, size, location). Confidence levels for urolithiasis and alternate diagnoses were rated (scale, 1–3). In 13 patients, FBP CT images acquired with the reference standard departmental protocol were available for comparison. Radiation dose was compared between imaging series. Statistical analysis was performed with Wilcoxon signed rank and paired t tests. Results: Modified-protocol FBP images showed low image quality (score, 2.5), with improvement on modified-protocol ASIR images (score, 3.4) (P⫽.03). All 33 stones (mean diameter, 6.1 mm; range, 2–28 mm) at modified-protocol CT were diagnosed by both readers. In 20 of 25 patients (80%), ASIR images were rated adequate for rendering other diagnoses in the abdomen (score, 2.0), as opposed to FBP images (score, 1.3). Mean radiation dose for modifiedprotocol CT was 1.8 mGy (1.3 mGy for patients ⬍200 lb; 2.3 mGy for patients ⬎200 lb) in comparison with 9.9 mGy for reference-protocol CT (P⫽.001). Conclusion: Image quality improvements with ASIR at reduced radiation dose of 1.8 mGy enabled effective evaluation of urinary calculi without substantially affecting diagnostic confidence. Editorial Comment: Flank pain is a common problem in the emergency room and is often evaluated with noncontrast CT to find stones, obstruction of the collecting system or other causes of pain. The estimated radiation dose from unenhanced abdominal/pelvic CT is approximately 15 mSv. Various studies have investigated techniques to decrease the overall radiation dose. Unfortunately as the dose is lowered, so is the image quality. Standard low dose CT is reconstructed with a conventional filtered back projection technique. With this technique there is excessive noise on the image, making it difficult for the radiologist to confidently interpret the scan. The ASIR technique applied in this study uses statistical variation in the imaged noise to improve the signal-to-noise ratio. The purpose of this study was to use the ASIR technique in patients with urinary stone disease. The study consisted of 25 consecutive patients with known or suspected urolithiasis. In 13 patients prior unenhanced CT was available for comparison. The standard, filtered back projection, low dose CT images were obtained, as well as the adaptive statistical iterative reconstruction ASIR images. The readers evaluated for calculi and subjectively assessed image quality, with a score of 1 indicating poor quality/not diagnostically acceptable, 2 suboptimal image quality, 3 acceptable image quality, 4 good image quality and 5 excellent image quality. Any score of 3 or higher was believed adequate for interpretation. An assessment was made of image noise and artifact, with a score of 1 indicating minimal, 2 acceptable, and 3 excessive noise and artifact/diagnostic interpretation compromised. A total of 33 stones were identified with the modified reduced radiation protocol CT. The ASIR images were rated as adequate (score 2.0 as opposed to filtered back projection, with a score of 1.3). The ASIR images demonstrated an image quality of 3.4, while the filtered back projection had an image quality of 2.5. The modified low dose technique with the iterative reconstruction with decreased radiation is effective for a diagnosis of urinary calculi and is an improvement over the filtered back projection technique in use. Cary Siegel, M.D.
IMAGING
Re: Abnormalities of 24-Hour Urine Composition in First-Time and Recurrent Stone-Formers B. H. Eisner, S. Sheth, S. P. Dretler, B. Herrick and V. M. Pais, Jr. Department of Urology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts Urology 2012; 80: 776 –779.
Objective: To examine differences in 24-hour urine composition between recurrent and first-time stone-formers. Methods: A retrospective review of patients evaluated in 2 metabolic stone clinics was performed. Recurrent stone formation was defined as patients with a history of more than 1 stone episode and first-time stone-formers were those with a history of a single-stone episode. Frequencies of urine metabolic abnormalities were noted. Multivariate linear regression was performed to evaluate the likelihood of abnormalities of 24-hour urine composition. Results: Three-hundred eleven patients met inclusion criteria: 71 (22.8%) were first-time stone-formers and 240 (77.1%) were recurrent stone-formers. On univariate analysis, the likelihood of having a single abnormality of 24-hour urine composition (ie, hypercalciuria, hyperoxaluria, hyperuricosuria, or hypocitraturia) was similar between the 2 groups (83.1% for first-time vs 88.8% for recurrent, P ⫽ NS). In addition, there were similar rates of hypercalciuria (39.4% vs 43.3%, P ⫽ NS), hyperoxaluria (32.4% vs 33.3%, P ⫽ NS), hyperuricosuria (29.6% vs 23.3%, P ⫽ NS), and hypocitraturia (45.0% vs 45.0%, P ⫽ NS). On multivariate logistic regression, there was no difference in detection of any urine abnormality (ie, hypercalciuria or hyperoxaluria or hypocitraturia or hyperuricosuria) between first-time (referent) or recurrent stone-formers (OR 1.68, 95% CI .8 –3.5, P ⫽ .2). Conclusion: In this study, detection of urine abnormalities was similar in first-time and recurrent stone-formers. Given the strong patient preference for stone prevention and the high success of directed therapy in the literature, we believe it is not unreasonable to offer comprehensive metabolic evaluation to first-time stone-formers who express a desire to undergo evaluation. Editorial Comment: The 24-hour urine test is a mechanism for assessing phenotypic risk profile. The results are influenced by genetic and environmental factors such as diet. There is no question that such testing is warranted in certain first time stone formers such as children, patients with a solitary kidney or chronic kidney disease, individuals with bowel or bone disease, commercial airline pilots and patients with multiple remaining stones. If such testing is ordered in other first timers, a discussion with these patients about their willingness to proceed to medical therapy should be conducted. Dean Assimos, M.D.
Suggested Reading Pak CY: Should patients with single renal stone occurrence undergo diagnostic evaluation? J Urol 1982; 127: 855.
Imaging Re: Radiation Dose Reduction at Multidetector CT with Adaptive Statistical Iterative Reconstruction for Evaluation of Urolithiasis: How Low Can We Go? N. M. Kulkarni, R. N. Uppot, B. H. Eisner and D. V. Sahani Departments of Abdominal Imaging and Intervention, Urology, Massachusetts General Hospital, Boston, Massachusetts Radiology, 2012 265: 158 –166.
Purpose: To evaluate the performance of computed tomographic (CT) examinations at 80 and 100 kV with tube current-time products of 75–150 mA and the effect of adaptive statistical iterative recon-
IMAGING
1361
struction (ASIR) on CT image quality in patients with urinary stone disease. Materials and Methods: In this HIPAA-compliant institutional review board-approved study, verbal consent for prospective low-dose CT and waivers of consent for retrospective review of CT scans were obtained. Between November 2010 and April 2011, 25 patients (15 men, 10 women; mean age, 35 years) with urolithiasis underwent 64-section multidetector CT with 75–150 mA and noise index of 30. Modified protocol was based on body weight (⬍200 lb [90 kg], 80 kV; ⬎200 lb [90 kg], 100 kV). Images of 5-mm section thickness were reconstructed with filtered back projection (FBP) and 60% and 80% ASIR techniques, with 3-mm coronal and sagittal reformations. Two readers independently reviewed FBP and ASIR data sets for image quality (scale, 1–5), noise (scale, 1–3), and calculi (number, size, location). Confidence levels for urolithiasis and alternate diagnoses were rated (scale, 1–3). In 13 patients, FBP CT images acquired with the reference standard departmental protocol were available for comparison. Radiation dose was compared between imaging series. Statistical analysis was performed with Wilcoxon signed rank and paired t tests. Results: Modified-protocol FBP images showed low image quality (score, 2.5), with improvement on modified-protocol ASIR images (score, 3.4) (P⫽.03). All 33 stones (mean diameter, 6.1 mm; range, 2–28 mm) at modified-protocol CT were diagnosed by both readers. In 20 of 25 patients (80%), ASIR images were rated adequate for rendering other diagnoses in the abdomen (score, 2.0), as opposed to FBP images (score, 1.3). Mean radiation dose for modifiedprotocol CT was 1.8 mGy (1.3 mGy for patients ⬍200 lb; 2.3 mGy for patients ⬎200 lb) in comparison with 9.9 mGy for reference-protocol CT (P⫽.001). Conclusion: Image quality improvements with ASIR at reduced radiation dose of 1.8 mGy enabled effective evaluation of urinary calculi without substantially affecting diagnostic confidence. Editorial Comment: Flank pain is a common problem in the emergency room and is often evaluated with noncontrast CT to find stones, obstruction of the collecting system or other causes of pain. The estimated radiation dose from unenhanced abdominal/pelvic CT is approximately 15 mSv. Various studies have investigated techniques to decrease the overall radiation dose. Unfortunately as the dose is lowered, so is the image quality. Standard low dose CT is reconstructed with a conventional filtered back projection technique. With this technique there is excessive noise on the image, making it difficult for the radiologist to confidently interpret the scan. The ASIR technique applied in this study uses statistical variation in the imaged noise to improve the signal-to-noise ratio. The purpose of this study was to use the ASIR technique in patients with urinary stone disease. The study consisted of 25 consecutive patients with known or suspected urolithiasis. In 13 patients prior unenhanced CT was available for comparison. The standard, filtered back projection, low dose CT images were obtained, as well as the adaptive statistical iterative reconstruction ASIR images. The readers evaluated for calculi and subjectively assessed image quality, with a score of 1 indicating poor quality/not diagnostically acceptable, 2 suboptimal image quality, 3 acceptable image quality, 4 good image quality and 5 excellent image quality. Any score of 3 or higher was believed adequate for interpretation. An assessment was made of image noise and artifact, with a score of 1 indicating minimal, 2 acceptable, and 3 excessive noise and artifact/diagnostic interpretation compromised. A total of 33 stones were identified with the modified reduced radiation protocol CT. The ASIR images were rated as adequate (score 2.0 as opposed to filtered back projection, with a score of 1.3). The ASIR images demonstrated an image quality of 3.4, while the filtered back projection had an image quality of 2.5. The modified low dose technique with the iterative reconstruction with decreased radiation is effective for a diagnosis of urinary calculi and is an improvement over the filtered back projection technique in use. Cary Siegel, M.D.