In Vivo Comparison of Radiation Exposure in Third-Generation vs Second-Generation Dual-Source Dual-Energy CT for Imaging Urinary Calculi.

Purpose: To investigate the potential for decreasing radiation dose when utilizing a third-generation vs second-generation dual-source dual-energy CT (dsDECT) scanner, while maintaining diagnostic image quality and acceptable image noise. Materials and Methods: Retrospective analysis of patients who underwent dsDECT for clinical suspicion of urolithiasis from October 2, 2017, to September 5, 2018. Patient demographics, body mass index, abdominal diameter, scanning parameters, and CT dose index volume (CTDIvol) were recorded. Image quality was assessed by measuring the attenuation and standard deviation (SD) regions of interest in the aorta and in the bladder. Image noise was determined by averaging the SD at both levels. Patients were excluded if they had not undergone both third- and second-generation dual-energy CT (DECT), time between DECT was more than 2 years, or scan parameters were outside the standard protocol. Results: A total of 117 patients met the inclusion criteria. Examinations performed on a third-generation DECT had an average CTDIvol 12.3 mGy, while examinations performed on a second-generation DECT had an average CTDIvol 13.3 mGy (p < 0.001). Average image noise was significantly lower for the third-generation DECT (SD = 10.3) compared with the second-generation DECT (SD = 13.9) (p < 0.001). Conclusions: The third-generation dsDECT scanners can simultaneously decrease patient radiation dose and decrease image noise compared with second-generation DECT. These reductions in radiation exposure can be particularly important in patients with urinary stone disease who often require repeated imaging to evaluate for stone development and recurrence as well as treatment assessment.

Perinephric myxoid pseudotumor of fat: A very rare entity that can mimic a renal cyst and retroperitoneal liposarcoma on imaging.

We present a case of perinephric myxoid pseudotumor of fat, a rare benign entity that often occurs in patients with non-neoplastic renal disease. In our case, an 80 year old man with end-stage renal disease was imaged over the course of 5 years during evaluation for renal transplantation. Imaging identified a left perinephric mass whose appearance over time and on different imaging modalities variably suggested a simple cyst, cystic neoplasm, and liposarcoma. Contrast enhanced examination was necessary to discern the solid nature of this mass, and ultimately, tissue sampling with histopathologic evaluation and molecular testing were required to make the diagnosis of myxoid pseudotumor of fat and exclude the imaging mimics.

Multimodality Imaging of Abdominopelvic Tumors with Venous Invasion.

A broad range of abdominal and pelvic tumors can manifest with or develop intraluminal venous invasion. Imaging features at cross-sectional modalities and contrast-enhanced US that allow differentiation of tumor extension within veins from bland thrombus include the expansile nature of tumor thrombus and attenuation and enhancement similar to those of the primary tumor. Venous invasion is a distinctive feature of hepatocellular carcinoma and renal cell carcinoma with known prognostic and treatment implications; however, this finding remains an underrecognized characteristic of multiple other malignancies-including cholangiocarcinoma, adrenocortical carcinoma, pancreatic neuroendocrine tumor, and primary venous leiomyosarcoma-and can be a feature of benign tumors such as renal angiomyolipoma and uterine leiomyomatosis. Recognition of tumor venous invasion at imaging has clinical significance and management implications for a range of abdominal and pelvic tumors. For example, portal vein invasion is a strong negative prognostic indicator in patients with hepatocellular carcinoma. In patients with rectal cancer, diagnosis of extramural venous invasion helps predict local and distant recurrence and is associated with worse survival. The authors present venous invasion by vascular distribution and organ of primary tumor origin with review of typical imaging features. Common pitfalls and mimics of neoplastic thrombus, including artifacts and anatomic variants, are described to help differentiate these findings from tumor in vein. By accurately diagnosing tumor venous invasion, especially in tumors where its presence may not be a typical feature, radiologists can help referring clinicians develop the best treatment strategies for their patients. ©RSNA, 2020.

Multidetector CT Findings in the Abdomen and Pelvis after Damage Control Surgery for Acute Traumatic Injuries.

After experiencing blunt or penetrating trauma, patients in unstable condition who are more likely to die of uncorrected shock than of incomplete injury repairs undergo emergency limited exploratory laparotomy, which is also known as damage control surgery (DCS). This surgery is part of a series of resuscitation steps, with the goal of stabilizing the patient's condition, with rapid surgical control of hemorrhage followed by supportive measures in the intensive care unit before definitive repair of injuries. These patients often are imaged with multidetector CT within 24-48 hours of the initial surgery. Knowledge of this treatment plan is critical to CT interpretation, because there are anatomic derangements and foreign bodies that would not be present in patients undergoing surgery for other reasons. Patients may have injuries beyond the surgical field that are only identified at imaging, which can alter the care plan. Abnormalities related to the resuscitation period such as the CT hypoperfusion complex and ongoing hemorrhage can be recognized at CT. Familiarity with these imaging and clinical findings is important, because they can be seen not only in trauma patients after DCS but also in other patients in the critical care setting. The interpretation of imaging studies can be helped by an understanding of the diagnostic challenges of grading organ injuries with surgical materials in place and the awareness of potential artifacts on images in these patients. Online supplemental material is available for this article. ©RSNA, 2019 See discussion on this article by LeBedis .

Bilateral Sustained Nephrograms After Parenteral Administration of Iodinated Contrast Material: A Potential Biomarker for Acute Kidney Injury, Dialysis, and Mortality.

OBJECTIVE: To determine whether persistent bilateral global nephrograms are associated with acute kidney injury (AKI), dialysis, and mortality. PATIENTS AND METHODS: All patients who underwent (1) contrast-enhanced computed tomography (CT) or cardiac catheterization with iohexol between January 1, 2000, and December 31, 2014, and (2) noncontrast abdominal CT in the subsequent 24±6 hours were identified. Patients without preprocedure and postprocedure creatinine measurements or who received additional contrast material were excluded. Nephrograms were identified by radiologist review and CT attenuation measurements. Univariate and multivariate analyses were performed to determine nephrogram risk factors. Acute kidney injury (defined as a creatinine level of ≥0.5 mg/dL or Kidney Disease: Improving Global Outcomes stages 1-3), dialysis, and mortality proportions were compared between patients with and without bilateral global nephrograms using the Fisher's exact test. RESULTS: A total of 123 patients met all inclusion criteria. The proportion of patients with a nephrogram was 37.4% (n=46), with a higher proportion following interventional (67% [18 of 30]) vs diagnostic (27.3% [9 of 33]) catheterization or contrast-enhanced computed tomography (31.7% [19 of 60]). Age (P=.002), chronic kidney disease (P=.05), and acute hypotension or shock (P=.02) were significant risk factors for nephrogram development. Patients with nephrogram had significantly higher rates of AKI (37.0% [17 of 46] vs 5.2% [4 of 77]; odds ratio [OR], 10.7 [95% CI, 3.31-34.5]; P<.001), dialysis (17.4% [8 of 46] vs 1.3% [1 of 77]; OR, 16.0 [95% CI, 1.93-133]; P=.001), and mortality (15.2% [7 of 46] vs 1.3% [1 of 77]; OR, 13.6 [1.62-115]; P=.003) than patients without nephrogram. CONCLUSION: The presence of persistent bilateral global nephrograms suggests an increased risk of AKI, dialysis, and mortality when compared with patients whose kidneys fully eliminated the contrast material.

The Capabilities and Limitations of Clinical Magnetic Resonance Imaging for Detecting Kidney Stones: A Retrospective Study.

The purpose of this work was to investigate the performance of currently available magnetic resonance imaging (MRI) for detecting kidney stones, compared to computed tomography (CT) results, and to determine the characteristics of successfully detected stones. Patients who had undergone both abdominal/pelvic CT and MRI exams within 30 days were studied. The images were reviewed by two expert radiologists blinded to the patients' respective radiological diagnoses. The study consisted of four steps: (1) reviewing the MRI images and determining whether any kidney stone(s) are identified; (2) reviewing the corresponding CT images and confirming whether kidney stones are identified; (3) reviewing the MRI images a second time, armed with the information from the corresponding CT, noting whether any kidney stones are positively identified that were previously missed; (4) for all stones MRI-confirmed on previous steps, the radiologist experts being asked to answer whether in retrospect, with knowledge of size and location on corresponding CT, these stones would be affirmed as confidently identified on MRI or not. In this best-case scenario involving knowledge of stones and their locations on concurrent CT, radiologist experts detected 19% of kidney stones on MRI, with stone size being a major factor for stone identification.

Contrast-induced nephropathy in outpatients with preexisting renal impairment: a comparison between intravenous iohexol and iodixanol.

BACKGROUND: Concern for contrast-induced nephropathy (CIN) may result in administration of more costly agents. We prospectively compared outpatient CIN incidence of iodixanol to iohexol. METHODS: Patients were randomized to receive 100ml of iohexol (n=47) or iodixanol (n=55). We compared patients who developed CIN using the Wilson score interval and also calculated an odds ratio for the development of CIN. RESULTS: CIN rate for iohexol was 2% compared to 9% for iodixanol. Those receiving iodixanol were almost 5 times more likely to experience CIN. CONCLUSION: These results do not suggest a benefit of iodixanol over iohexol in the study population.

Detection of different kidney stone types: an ex vivo comparison of ultrashort echo time MRI to reference standard CT.

BACKGROUND AND PURPOSE: With the development of ultrashort echo time (UTE) sequences, it may now be possible to detect kidney stones by using magnetic resonance imaging (MRI). In this study, kidney stones of varying composition and sizes were imaged using both UTE MRI as well as the reference standard of computed tomography (CT), with different surrounding materials and scan setups. METHODS: One hundred and fourteen kidney stones were inserted into agarose and urine phantoms and imaged both on a dual-energy CT (DECT) scanner using a standard renal stone imaging protocol and on an MRI scanner using the UTE sequence with both head and body surface coils. A subset of the stones representing all composition types and sizes was then inserted into the collecting system of porcine kidneys and imaged in vitro with both CT and MRI. RESULTS: All of the stones were visible on both CT and MRI imaging. DECT was capable of differentiating between uric acid and nonuric acid stones. In MRI imaging, the choice of coil and large field of view (FOV) did not affect stone detection or image quality. The MRI images showed good visualization of the stones' shapes, and the stones' dimensions measured from MRI were in good agreement with the actual values (R(2)=0.886, 0.895, and 0.81 in the agarose phantom, urine phantom, and pig kidneys, respectively). The measured T2 relaxation times ranged from 4.2 to 7.5ms, but did not show significant differences among different stone composition types. CONCLUSIONS: UTE MRI compared favorably with the reference standard CT for imaging stones of different composition types and sizes using body surface coil and large FOV, which suggests potential usefulness of UTE MRI in imaging kidney stones in vivo.

The Clinical Impact of Accurate Cystine Calculi Characterization Using Dual-Energy Computed Tomography.

Dual-energy computed tomography (DECT) has recently been suggested as the imaging modality of choice for kidney stones due to its ability to provide information on stone composition. Standard postprocessing of the dual-energy images accurately identifies uric acid stones, but not other types. Cystine stones can be identified from DECT images when analyzed with advanced postprocessing. This case report describes clinical implications of accurate diagnosis of cystine stones using DECT.

Motion artifacts in kidney stone imaging using single-source and dual-source dual-energy CT scanners: a phantom study.

PURPOSE: Dual-energy computed tomography (DECT) has shown the capability of differentiating uric acid (UA) from non-UA stones with 90-100% accuracy. With the invention of dual-source (DS) scanners, both low- and high-energy images are acquired simultaneously. However, DECT can also be performed by sequential acquisition of both images on single-source (SS) scanners. The objective of this study is to investigate the effects of motion artifacts on stone classification using both SS-DECT and DS-DECT. METHODS: 114 kidney stones of different types and sizes were imaged on both DS-DECT and SS-DECT scanners with tube voltages of 80 and 140 kVp with and without induced motion. Postprocessing was conducted to create material-specific images from corresponding low- and high-energy images. The dual-energy ratio (DER) and stone material were determined and compared among different scans. RESULTS: For the motionless scans, all stones were correctly classified with SS-DECT, while two cystine stones were misclassified with DS-DECT. When motion was induced, 94% of the stones were misclassified with SS-DECT versus 11% with DS-DECT (P < 0.0001). Stone size was not a factor in stone misclassification under motion. Stone type was not a factor in stone misclassification under motion with SS-DECT, although with DS-DECT, cystine showed higher number of stone misclassification. CONCLUSIONS: Motion artifacts could result in stone misclassification in DECT. This effect is more pronounced in SS-DECT versus DS-DECT, especially if stones of different types lie in close proximity to each other. Further, possible misinterpretation of the number of stones (i.e., missing one, or thinking that there are two) in DS-DECT could be a potentially significant problem.

Forecasting the Effect of the Change in Timing of the ABR Diagnostic Radiology Examinations: Results of the ACR Survey of Practice Leaders.

The results of a survey sent to practice leaders in the ACR Practice of Radiology Environment Database show that the majority of responding groups will continue to hire recently trained residents and fellows even though they have been unable to take the final ABR diagnostic radiology certifying examination. However, a significant minority of private practice groups will not hire these individuals. The majority of private practices expect the timing change for the ABR certifying examinations to affect their groups' function. In contrast, the majority of academic medical school practices expect little or no impact. Residents and fellows should not expect work time off or protected time to study for the certifying examination or for their maintenance of certification examinations in the future.

In vivo comparison of radiation exposure of dual-energy CT versus low-dose CT versus standard CT for imaging urinary calculi.

PURPOSE: Dual-energy computed tomography (DECT) is an emerging imaging modality with the unique capability of determining urinary stone composition. This study compares radiation exposure of DECT, standard single-energy CT (SECT), and low-dose renal stone protocol single-energy CT (LDSECT) for the evaluation of nephrolithiasis in a single in vivo patient cohort. MATERIALS AND METHODS: Following institutional review board (IRB) approval, we retrospectively reviewed 200 consecutive DECT examinations performed on patients with suspected urolithiasis over a 6-month period. Of these, 35 patients had undergone examination with our LDSECT protocol, and 30 patients had undergone examination of the abdomen and pelvis with our SECT imaging protocol within 2 years of the DECT examination. The CT dose index volume (CTDIvol) was used to compare radiation exposure between scans. Image quality was objectively evaluated by comparing image noise. Statistical evaluation was performed using a Student's t-test. RESULTS: DECT performed at 80/140 kVp and 100/140 kVp did not produce a significant difference in radiation exposure compared with LDSECT (p=0.09 and 0.18, respectively). DECT performed at 80/140 kVp and 100/140 kVp produced an average 40% and 31%, respectively, reduction in radiation exposure compared with SECT (p<0.001). For patients imaged with the 100/140 kVp protocol, average values for images noise were higher in the LDSECT images compared with DECT images (p<0.001) and there was no significant difference in image noise between DECT and SECT images in the same patient (p=0.88). Patients imaged with the 80/140 kVp protocol had equivocal image noise compared with LDSECT images (p=0.44), however, DECT images had greater noise compared with SECT images in the same patient (p<0.001). Of the 75 patients included in the study, stone material was available for 16; DECT analysis correctly predicted stone composition in 15/16 patients (93%). CONCLUSION: DECT provides knowledge of stone composition in addition to the anatomic information provided by LDSECT/SECT without increasing patient radiation exposure and with minimal impact on image noise.

Characterization of ureteral stents by dual-energy computed tomography: Clinical implications.

Dual-energy computed-tomography (DECT) has been suggested as the method of choice for imaging urinary calculi due to the modality's high sensitivity for detecting stones and its capability of accurately differentiating between uric-acid (UA) and non-UA (predominantly calcium) stones. The clinical significance of the latter feature relates to the differences in management of UA vs non-UA calculi. Like calculi, ureteral stents are assigned color by the dual-energy post-processing algorithm, which may lead to improved or worsened stone visualization based on the resulting stent/stone contrast. Herein we depict the case of a nephrolithiasis patient with bilateral stents, each with different color, clearly displaying the effect of stent color on stone visualization. Further, three-dimensional reconstruction of the DECT images illustrates advantages of this enhancement compared to conventional two-dimensional computed tomography. The resulting stent/stone contrast produces an unanticipated potential advantage of DECT in patients with urolithiasis and stents and may promote improved management decision-making.

Accuracy and efficiency of determining urinary calculi composition using dual-energy computed tomography compared with Hounsfield unit measurements for practicing physicians.

OBJECTIVE: To compare speed and accuracy for determining urinary calculi composition between dual-energy computed tomography (DECT) and Hounsfield unit (HU) measurements of calculi by a set of reviewers at varying levels of training and practice. MATERIALS AND METHODS: Sixteen patients with known stone composition were randomly selected. Fourteen reviewers of varying levels of practice interpreted DECT and HU images from the selected patients to predict stone composition in 2 sessions (day 1: tutorial or flow sheet available for image interpretation and day 2: tutorial or flow sheet not available). Reviewers recorded HU values, stone color, and predicted stone composition as they were timed. Accuracy of image interpretation, determination of calculi composition, and interpretation time were compared. RESULTS: DECT accuracy: image interpretation 100% (day 1) and 94% (day 2); predicted stone composition: 100% (day 1) and 73% (day 2). Mean interpretation time was the same for both days, 21 seconds per study (range, 11-40 seconds). HU accuracy: image interpretation 97% (day 1) and 91% (day 2); predicted stone composition was 45% accurate on both days. Mean interpretation time was 53 seconds per study (range, 28-79 seconds) and 41 seconds per study (range, 19-71 seconds) on days 1 and 2, respectively. Overall accuracy of determination of stone composition and interpretation time for DECT were essentially double those of the HU images (87% vs 45% and 21 vs 47 seconds, respectively). Reviewer's experience level did not affect accuracy or speed. CONCLUSION: DECT is easier to learn, faster to interpret, and more accurate than HU in determining urinary calculi composition for physicians at various levels of training and practice.