Terri J. Vrtiska

Dual-Energy CT Iodine-Subtraction Virtual Unenhanced Technique to Detect Urinary Stones in an Iodine-Filled Collecting System: A Phantom Study

OBJECTIVE The objective of our study was to evaluate the feasibility of virtual unenhanced images reconstructed from a dual-energy CT scan to depict urinary stones in an iodine solution in a phantom study. MATERIALS AND METHODS Twenty urinary stones of different sizes (1.4-4.2 mm in short-axis diameter) were placed in plastic containers. The containers were consecutively filled with different concentrations of iodine solution (21, 43, 64, 85, and 107 mg/dL; CT attenuation value range, 510-2,310 H at 120 kVp). Dual-energy CT was repeated with 80-140 and 100-140 kVp pairs, two collimation-slice thickness combinations, and the presence or absence of a 4-cm-thick oil gel around the phantom. The iodine-subtraction virtual unenhanced images were reconstructed using commercial software. The images were evaluated by three radiologists in consensus for the visibility of the stones and the presence of residual nonsubtracted iodine. Stone visibility rates were compared between the 80-140 and 100-140 kVp pairs and the five different iodine concentrations. RESULTS Stone visibility rates with the 80-140 kVp pair were 99%, 93%, 96%, 94%, and 3% and those with the 100-140 kVp pair were 98%, 95%, 99%, 94%, and 99% for an iodine concentration of 21, 43, 64, 85, and 107 mg/dL, respectively. The poor visibility rate with 80-140 kVp and 107 mg/dL iodine concentration was due to the failure of iodine subtraction. CONCLUSION Dual-energy CT iodine-subtraction virtual unenhanced technique is capable of depicting urinary stones in iodine solutions of a diverse range of concentrations in a phantom study.

Fat malabsorption and increased intestinal oxalate absorption are common after Roux-en-Y gastric bypass surgery.

BACKGROUND Hyperoxaluria and increased calcium oxalate stone formation occur after Roux-en-Y gastric bypass (RYGB) surgery for morbid obesity. The etiology of this hyperoxaluria is unknown. We hypothesized that after bariatric surgery, intestinal hyperabsorption of oxalate contributes to increases in plasma oxalate and urinary calcium oxalate supersaturation. METHODS We prospectively examined oxalate metabolism in 11 morbidly obese subjects before and 6 and 12 months after RYGB (n = 9) and biliopancreatic diversion-duodenal switch (BPD-DS) (n = 2). We measured 24-hour urinary supersaturations for calcium oxalate, apatite, brushite, uric acid, and sodium urate; fasting plasma oxalate; 72-hour fecal fat; and increases in urine oxalate following an oral oxalate load. RESULTS Six and 12 months after RYGB, plasma oxalate and urine calcium oxalate supersaturation increased significantly compared with similar measurements obtained before surgery (all P ≤ .02). Fecal fat excretion at 6 and 12 months was increased (P = .026 and .055, 0 vs 6 and 12 months). An increase in urine oxalate excretion after an oral dose of oxalate was observed at 6 and 12 months (all P ≤ .02). Therefore, after bariatric surgery, increases in fecal fat excretion, urinary oxalate excretion after an oral oxalate load, plasma oxalate, and urinary calcium oxalate supersaturation values were observed. CONCLUSION Enteric hyperoxaluria is often present in patients after the operations of RYGB and BPD-DS that utilize an element of intestinal malabsorption as a mechanism for weight loss.

Dual-energy dual-source CT with additional spectral filtration can improve the differentiation of non-uric acid renal stones: An ex vivo phantom study

OBJECTIVE The purpose of this study was to determine the ex vivo ability of dual-energy dual-source CT (DSCT) with additional tin filtration to differentiate among five groups of human renal stone types. MATERIALS AND METHODS Forty-three renal stones of 10 types were categorized into five primary groups on the basis of effective atomic numbers, which were calculated as the weighted average of the atomic numbers of constituent atoms. Stones were embedded in porcine kidneys and placed in a 35-cm water phantom. Dual-energy DSCT scans were performed at 80 and 140 kV with and without tin filtration of the 140-kV beam. The CT number ratio, defined as the ratio of the CT number of a given material in the low-energy image to the CT number of the same material in the high-energy image, was calculated on a volumetric voxel-by-voxel basis for each stone. Statistical analysis was performed, and receiver operating characteristic (ROC) curves were plotted to compare the difference in CT number ratio with and without tin filtration, and to measure the discrimination among stone groups. RESULTS The CT number ratio of non-uric acid stones increased on average by 0.17 (range, 0.03-0.36) with tin filtration. The CT number ratios for non-uric acid stone groups were not significantly different (p > 0.05) between any of the two adjacent groups without tin filtration. Use of the additional tin filtration on the high-energy x-ray tube significantly improved the separation of non-uric acid stone types by CT number ratio (p < 0.05). The area under the ROC curve increased from 0.78 to 0.84 without fin filtration and to 0.89-0.95 with tin filtration. CONCLUSION Our results showed better separation among different stone types when additional tin filtration was used on dual-energy DSCT. The increased spectral separation allowed a five-group stone classification scheme. Some overlapping between particular stone types still exists, including brushite and calcium oxalate.

Left renal vein transposition for nutcracker syndrome.

OBJECTIVE Nutcracker syndrome, caused by compression of the left renal vein (LRV) between the superior mesenteric artery and the aorta, results in left renal and gonadal venous hypertension. Several treatment options have been described to relieve associated symptoms. The purpose of this study was to evaluate late results of LRV transposition and identify risk factors affecting outcomes. METHODS Clinical data from 23 consecutive patients diagnosed with nutcracker syndrome from January 1996 to October 2007 were retrospectively reviewed. RESULTS There were 10 males and 13 females (median age 22 years; range, 14-67) with radiologic evidence of LRV compression. On ultrasound evaluation (15/23 patients), the mean ratio of LRV peak systolic velocity measured at the site of compression and the renal hilum was 7.3 (range, 2.5-12). On venography (14/23 patients), the mean renocaval pressure gradient was 4 mm Hg (range, 2-6 mm Hg). Twelve patients with atypical abdominal pain (n = 4), hematuria (n = 5), and varicocele (n = 6) were managed expectantly. Eleven patients underwent LRV transposition through a transperitoneal exposure. Symptoms in these patients included left flank pain (n = 10), hematuria (n = 7), and varicocele (n = 3). In 2/11 patients, the LRV was found to be occluded at operation. There were no early postoperative complications. Most conservatively managed patients remained stable or improved over a mean follow-up period of 26 months (range, 0.2-59 months). Two patients were lost to follow-up at our institution and ultimately underwent intervention with LRV stenting and autotransplantation elsewhere. One patient was diagnosed with thin basement membrane disease on renal biopsy. Five patients with varicocele remained asymptomatic; 1 underwent local repair. Over a mean follow-up of 39 months (range, 0.13-144 months) in surgically managed patients, symptoms of flank pain and hematuria resolved or improved in 8/10 and 7/7, respectively. Varicoceles recurred in 2/3 patients in spite of resolution of flank pain. Both preoperatively occluded LRVs rethrombosed; one underwent thrombolysis with stenting, the other reimplantation of the left gonadal vein into the IVC. CONCLUSION Evaluation of the clinical significance of radiologic LRV compression remains challenging, as does selection of patients for intervention. LRV transposition is a safe, effective procedure in selected patients with persistent, severe symptoms. Patients with progression to occlusion of the LRV should be considered for alternative therapeutic procedures. Varicoceles, in the setting of nutcracker syndrome, may need independent repair.

Coronary Artery Tortuosity in Spontaneous Coronary Artery Dissection Angiographic Characteristics and Clinical Implications

Background—Spontaneous coronary artery dissection (SCAD) is an increasingly recognized nonatherosclerotic cause of acute coronary syndrome. The angiographic characteristics of SCAD are largely undetermined. The goal of this study was to determine the prevalence of coronary tortuosity in SCAD and whether it may be implicated in the disease. Methods and Results—Patients with confirmed SCAD (n=246; 45.3±8.9 years; 96% women) and 313 control patients without SCAD or coronary artery disease who underwent coronary angiography were included in this case–control study. Angiograms were reviewed for coronary tortuosity and assigned a tortuosity score. Tortuosity was common in patients presenting with their first SCAD event (78% versus 17% in controls; P<0.0001; tortuosity score, 4.41±1.73 versus 2.33±1.49 in controls; P<0.0001) despite a low prevalence of hypertension (34%). Recurrent SCAD (n=40) occurred within segments of tortuosity in 80% of cases. Severe tortuosity (≥2 consecutive curvatures ≥180°) was associated with a higher risk of recurrent SCAD (hazard ratio, 3.29; 95% confidence interval, 0.99–8.29; P=0.05). Tortuosity score >5 was associated with a trend toward higher risk of recurrent SCAD (P=0.16). Prespecified angiographic markers of tortuosity including corkscrew appearance and multivessel symmetrical tortuosity were associated with extracoronary vasculopathy including fibromuscular dysplasia (P<0.05 for both). Conclusions—Coronary artery tortuosity is highly prevalent in the SCAD population and is associated with recurrent SCAD. Recurrent SCAD most often occurs within segments of tortuosity. Angiographic features of SCAD are associated with extracoronary vasculopathy, including fibromuscular dysplasia. These findings suggest that coronary tortuosity may serve as a marker or potential mechanism for SCAD.

Detectability of urinary stones on virtual nonenhanced images generated at pyelographic-phase dual-energy CT.

PURPOSE To evaluate the detectability of urinary stones on virtual nonenhanced images generated at pyelographic-phase dual-energy computed tomography (CT). MATERIALS AND METHODS This retrospective HIPAA-compliant study was institutional review board approved. All included patients had previously consented to the use of their medical records for research. Sixty-two patients (38 men, 24 women; age range, 35-91 years) had undergone CT urography, which consisted of nonenhanced and pyelographic-phase dual-energy CT performed by using a dual-source scanner. Commercial software was used to create virtual nonenhanced images by suppressing the iodine signal from the pyelographic-phase dual-energy CT scans. Two radiologists, in consensus, evaluated the virtual nonenhanced images for the presence of stones. Sensitivity for detecting stones was calculated on a per-stone basis. Sensitivity, specificity, and accuracy were also calculated on a per-renal unit (defined as the intrarenal collecting system and ureter of one kidney) basis. The true nonenhanced scan was considered the reference standard. A jackknife method was used because any patient may have multiple stones. RESULTS Of 62 patients with 122 renal units, 21 patients with 25 renal units had a total of 43 stones (maximal transverse diameter range, 1-24 mm; median, 3 mm). The overall sensitivity for detecting stones was 63% (27 of 43 stones) per stone. Sensitivities were 29% (four of 14 stones) for 1-2-mm stones, 64% (nine of 14 stones) for 3-4-mm stones, 83% (five of six stones) for 5-6-mm stones, and 100% (nine of nine stones) for 7-mm or larger (7, 7, 7, 8, 8, 9, 11, 15, and 24 mm) stones. All three ureteral stones (3, 4, and 8 mm) were correctly identified. The sensitivity, specificity, and accuracy for detecting stones on a per-renal unit basis were 65% (17 of 26 renal units), 92% (88 of 96 renal units), and 86% (105 of 122 renal units), respectively. CONCLUSION Virtual nonenhanced images generated at pyelographic-phase dual-energy CT enabled the detection of urinary stones with moderate accuracy. The detection of small (1-2-mm) stones was limited.

Genitourinary Applications of Dual-Energy CT

OBJECTIVE Recent advances in CT technology provide improved diagnostic characterization of materials using dual-energy CT methods. Application of these methods improves lesion conspicuity and detection. In addition, improved material characterization and creation of virtual unenhanced techniques potentially result in decreased radiation dose. We will review the role of dual-energy CT as applied to the genitourinary system. CONCLUSION Dual-energy CT is beginning to play an important role in patients with genitourinary diseases by providing unique characterization tools for calculi and masses.

Prevalence of Renal Artery and Kidney Abnormalities by Computed Tomography among Healthy Adults

BACKGROUND AND OBJECTIVES Management of incidental renal artery and kidney abnormalities in patients undergoing computed tomography scans is a clinical challenge because their frequency in healthy subjects has not been precisely estimated. Therefore, the prevalence and management of these abnormalities were determined among a large cohort of potential kidney donors undergoing protocol evaluations. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS All patients at the Mayo Clinic who underwent computed tomographic angiography and urography as part of their kidney donor evaluation between 2000 and 2008 were identified. Radiographic reports were abstracted for abnormalities of the renal arteries and kidneys. The prevalence of radiographic abnormalities was stratified by age and gender, and the effect on approval for kidney donation was determined. RESULTS Among 1957 potential kidney donors, the mean +/- SD age was 43 +/- 12 years, and 58% were women. The most common abnormalities were kidney stones (11%), focal scarring (3.6%), fibromuscular dysplasia (2.8%), and other renal artery narrowing or atherosclerosis (5.3%). Fibromuscular dysplasia, focal scarring, parenchymal atrophy, and upper tract dilation were more common in women. Renal artery narrowing, focal scarring, and indeterminate masses increased with age. Overall, 25% of potential donors had at least one abnormality. However, these incidental radiographic abnormalities contributed to exclusion from donation in only 6.7% of potential donors. CONCLUSIONS Incidental radiographic abnormalities of the renal arteries and kidneys are common. The majority of imaging findings are not perceived to be harmful enough to prevent kidney donation, but future studies are needed to determine their clinical relevance.

Three-dimensional Physical Modeling: Applications and Experience at Mayo Clinic

Radiologists will be at the center of the rapid technologic expansion of three-dimensional (3D) printing of medical models, as accurate models depend on well-planned, high-quality imaging studies. This article outlines the available technology and the processes necessary to create 3D models from the radiologists perspective. We review the published medical literature regarding the use of 3D models in various surgical practices and share our experience in creating a hospital-based three-dimensional printing laboratory to aid in the planning of complex surgeries.

Vascular Ehlers-Danlos syndrome: Imaging findings

OBJECTIVE Vascular Ehlers-Danlos syndrome (EDS), formerly known as EDS type IV, is an autosomal dominant disorder characterized by fragility of medium and large arteries due to type III procollagen deficiency. Our purpose was to review the imaging findings in a cohort of patients with a diagnosis of vascular EDS. MATERIALS AND METHODS The radiologic, surgical, and genetic databases at a single multispecialty medical practice were reviewed for a 35-year period between 1971 and 2006. Thirty-three patients with a clinical diagnosis of vascular EDS were identified. Imaging studies were available for 28 patients, 13 men and 15 women, with a mean age of 39.8 +/- 16 years at the time of diagnosis. A vascular radiologist reviewed a total of 189 imaging examinations: 87 CT, 27 MRI, 59 sonography, and 16 angiography. RESULTS Vascular abnormalities were present in 22 (78%) of 28 patients. Arterial abnormalities included 41 aneurysms, 19 dissections, 12 ectasias, and 10 occlusions. There was one splenic vein aneurysm and one carotid cavernous fistula. Six patients had a total of 10 parenchymal infarcts involving the brain (n = 5), kidney (n = 3), and spleen (n = 2). Nine patients had 10 hemorrhagic events, five related to spontaneous vascular rupture and five associated with interventional or surgical procedures. Six patients had 13 nonvascular findings. CONCLUSION The most common findings were arterial aneurysms and dissections, followed by arterial ectasias and occlusions. Life-threatening complications included hemorrhage and infarcts.