Large variation in radiation dose for routine abdomen CT: reasons for excess and easy tips for reduction.

OBJECTIVE: To characterize the use and impact of radiation dose reduction techniques in actual practice for routine abdomen CT. METHODS: We retrospectively analyzed consecutive routine abdomen CT scans in adults from a large dose registry, contributed by 95 hospitals and imaging facilities. Grouping exams into deciles by, first, patient size, and second, size-adjusted dose length product (DLP), we summarized dose and technical parameters and estimated which parameters contributed most to between-protocols dose variation. Lastly, we modeled the total population dose if all protocols with mean size-adjusted DLP above 433 or 645 mGy-cm were reduced to these thresholds. RESULTS: A total of 748,846 CTs were performed using 1033 unique protocols. When sorted by patient size, patients with larger abdominal diameters had increased dose and effective mAs (milliampere seconds), even after adjusting for patient size. When sorted by size-adjusted dose, patients in the highest versus the lowest decile in size-adjusted DLP received 6.4 times the average dose (1680 vs 265 mGy-cm) even though diameter was no different (312 vs 309 mm). Effective mAs was 2.1-fold higher, unadjusted CTDIvol 2.9-fold, and phase 2.5-fold for patients in the highest versus lowest size-adjusted DLP decile. There was virtually no change in kV (kilovolt). Automatic exposure control was widely used to modulate mAs, whereas kV modulation was rare. Phase was the strongest driver of between-protocols variation. Broad adoption of optimized protocols could result in total population dose reductions of 18.6-40%. CONCLUSION: There are large variations in radiation doses for routine abdomen CT unrelated to patient size. Modification of kV and single-phase scanning could result in substantial dose reduction. CLINICAL RELEVANCE: Radiation dose-optimization techniques for routine abdomen CT are routinely under-utilized leading to higher doses than needed. Greater modification of technical parameters and number of phases could result in substantial reduction in radiation exposure to patients. KEY POINTS: • Based on an analysis of 748,846 routine abdomen CT scans in adults, radiation doses varied tremendously across patients of the same size and optimization techniques were routinely under-utilized. • The difference in observed dose was due to variation in technical parameters and phase count. Automatic exposure control was commonly used to modify effective mAs, whereas kV was rarely adjusted for patient size. Routine abdomen CT should be performed using a single phase, yet multi-phase was common. • kV modulation by patient size and restriction to a single phase for routine abdomen indications could result in substantial reduction in radiation doses using well-established dose optimization approaches.

Extremity radiographs derived from low-dose ultra-high-resolution CT: a phantom study.

OBJECTIVE: To demonstrate the potential of low-dose ultra-high-resolution CT (UHRCT) images to generate high-quality radiographic images on extremity phantoms and to estimate the radiation dose required for this. MATERIALS AND METHODS: A hand and knee phantom containing real human bones was imaged on an UHRCT scanner at full-dose, half-dose, and quarter-dose levels using a high-resolution extremity protocol. The raw data was reconstructed using both filtered back projection (FBP) and an iterative reconstruction algorithm (AIDR3D). Using custom designed software, each CT volume data set was converted to attenuation coefficients, and then a synthesized radiograph (synDX) was generated by forward projecting the volume data sets from a point source onto a 2D synthetic detector. The signal-to-noise ratio (SNR) was measured in the synDXs across all dose levels and the root-mean-squared error (RMSE) was computed with the FD synDXs as the reference. RESULTS: The proposed workflow generates high-quality synDXs at any arbitrary angle. For FBP, the SNR largely tracked with the radiation dose levels for both the knee and hand phantoms. For the knee phantom, iterative reconstruction provided a 6.1% higher SNR when compared to FBP. The RMSE was overall higher for the lowest dose levels and monotonically decreased with increasing dose. No substantial differences were observed qualitatively in the visualization of skeletal detail of the phantoms. CONCLUSION: The fine detail provided by UHRCT acquisitions of extremities facilitates the ability to generate quality radiographs, potentially eliminating the need for additional scanning on a conventional digital radiography system.

Utility of combined gadoxetic acid and ferumoxytol-enhanced liver MRI for preoperative detection of colorectal cancer liver metastases: a pilot study.

BACKGROUND: Colorectal cancer (CRC) is the second-leading cause of cancer-related death worldwide and resection of CRC metastases confined to the liver is the treatment of choice when feasible. Ferumoxytol is an off-label contrast agent that opacifies vasculature and may be helpful in distinguishing metastases from small hemangiomas and blood vessels on gadoxetic acid-enhanced magnetic resonance imaging (MRI). PURPOSE: To compare the diagnostic accuracy of MRI using a standard gadoxetic acid protocol and a combined gadoxetic acid/ferumoxytol protocol in patients with suspected colorectal hepatic metastases. MATERIAL AND METHODS: In this institutional review board-approved, single-institution, retrospective study, eight patients underwent gadoxetic acid-enhanced liver MRI, supplemented with additional T1-weighted ferumoxytol enhanced sequences. Two radiologists in consensus identified all metastases using all available sequences, which served as the reference standard. Two different radiologists reviewed each exam twice, once using the standard protocol and once with additional ferumoxytol sequences. The detection rate was estimated as the predicted probability of a metastasis along with the 95% confidence interval (CI) using hierarchical logistic regression models. RESULTS: A total of 49 metastases were identified. The mean diameter was 10 mm, measured in greatest axial dimension (median=7 mm; range=2-70 mm). Readers 1 and 2 had detection rates of 69.6% (95% CI = 48.2-85.0) and 53.1% (95% CI = 35.2-70.3) for gadoxetic acid alone and 98.0% (95% CI = 86.3-99.7) and 83.5% (95% CI = 59.3-94.7) for combined protocol. CONCLUSION: In this preliminary investigation, adding ferumoxytol-enhanced sequences to gadoxetic acid liver MRI protocol increased the detection rate of CRC hepatic metastases and may aid in preoperative decision making.

Sonographically Diagnosed Urothelial Thickening in Kidney Allografts: A Noninvasive and Clinically Highly Relevant Marker for the Detection of Acute Rejection.

OBJECTIVE. The objective of our study was to investigate the significance of sonographic features in assessing for acute kidney allograft rejection in the modern era. MATERIALS AND METHODS. In this retrospective study, 107 adult patients with a kidney allograft biopsy performed between 2015 and 2018 and diagnostic ultrasound performed within 2 weeks of the biopsy were included. Acute rejection was diagnosed on the basis of biopsy tissue sample results using the Banff criteria. The following ultrasound features were assessed: perfusion, cortical echogenicity, corticomedullary differentiation, urothelial thickening, change in renal length, renal artery velocity, and intraparenchymal arterial resistive index. Subjective measures of perfusion, echogenicity, corticomedullary differentiation, and urothelial thickening were assessed independently and in consensus by three abdominal radiologists; multirater kappa values were calculated for interobserver variability. The Wilcoxon rank sum test and chi-square test were used to evaluate the differences between two groups (rejection vs no rejection) and the sonographic features. Sensitivity, specificity, positive predictive value, and negative predictive value (NPV) were calculated for sonographic features that are associated with acute rejection. RESULTS. Of the sonographic features, only the presence of urothelial thickening was significantly associated with acute rejection (p < 0.001) and had substantial agreement (κ = 0.61) among readers. Urothelial thickening was highly sensitive (96%; 95% CI, 79-100%) with a high NPV (98%; 95% CI, 86-100%). CONCLUSION. Urothelial thickening on ultrasound is a highly sensitive finding for acute kidney rejection with a high NPV and thus may play a role in sonographic prebiopsy screening. Other historically associated sonographic features seem to play little, if any, role in the screening and assessment for kidney allograft rejection in the modern era.

Reorganizing Cross-Sectional Interventional Procedures Practice During the Coronavirus Disease (COVID-19) Pandemic.

OBJECTIVE. The purpose of this article is to present strategies and guidelines that can be implemented in the performance of cross-sectional interventional procedures during the coronavirus disease (COVID-19) pandemic. CONCLUSION. Radiologists who perform cross-sectional interventional procedures can take several steps to minimize the risks to patients and radiology personnel, including screening referred patients to decide which procedures can be postponed, using appropriate personal protective equipment (PPE), minimizing the number of people involved in procedures, preserving PPE when possible, and applying proper room and equipment cleaning measures.

Radiation Dose Reduction of Unenhanced CT Limited to the Kidneys for Follow-Up of Patients With Known Nephrolithiasis Without Symptoms.

OBJECTIVE. The purpose of this study is to identify the landmarks and associated radiation dose reduction for limited CT of the kidneys of patients requiring follow-up for known nephrolithiasis. MATERIALS AND METHODS. This retrospective study included all adult patients who underwent CT examination type "CT abdomen + pelvis renal stone" at our institution during 2017. Several exclusion criteria were identified, including scoliosis and congenital renal abnormalities. A total of 299 patients met the inclusion and exclusion criteria. The radiation dose and z-axis length associated with the original CT scan were recorded. The upper and lower limits of both kidneys in relation to the vertebral body endplates were recorded, to determine the z-axis length for a CT scan limited to the kidneys. A commercially available radiation dose analytics software package was used to provide estimates of whole-body-and individual organ-equivalent doses for the original CT scan and the limited range CT scan. RESULTS. The superior endplate of T11 and the inferior endplate of L5 are landmarks that will include both kidneys on almost all scans. A limited z-axis range leads to a mean scan length reduction of 50%. The whole-body mean effective dose is reduced by 41.5%, and the doses to the breast and the gonadal and bladder organs are reduced by 71.7%, 73.8%, and 81.8%, respectively. CONCLUSION. For patients without symptoms who are undergoing CT surveillance to evaluate renal calculi growth, new stone formation, or both, a limited-range scan extending from the superior endplate of T11 to the inferior endplate of L5 results in a significant reduction in radiation dose.

Prevalence of Solid Tumors in Incidentally Detected Homogeneous Renal Masses Measuring > 20 HU on Portal Venous Phase CT.

OBJECTIVE: The purpose of this study was to determine the prevalence of solid tumors in incidental homogeneous renal masses with attenuation greater than 20 HU on portal venous phase CT images. MATERIALS AND METHODS: In this retrospective study, the records of patients with incidental indeterminate (> 20 HU) homogeneous renal masses on portal venous phase CT scans from September 11, 2007, through March 18, 2017, were identified. Adult patients were included if they had undergone follow-up ultrasound, contrast-enhanced MRI, multiphase contrast-enhanced CT, or pathologic analysis alone to confirm the solid or cystic nature of the lesion. A single ROI was placed in the center of the mass, and lesions were characterized as ≥ 50% exophytic, < 50% exophytic, or entirely surrounded by renal parenchyma. RESULTS: There were 322 masses in 267 patients. The mean lesion size was 16.6 (SD, 9.8) mm (range, 9-45 mm). Lesions were ≥ 50% exophytic in 92 cases, < 50% exophytic in 111 cases, and completely surrounded by renal parenchyma in 119 cases. All nonsolid lesions were characterized as benign cysts. The numbers of solid lesions per total number of lesions in each attenuation group were: 20-30 HU (0/140), 30-40 HU (0/67), 40-50 HU (1/38), 50-60 HU (3/24), 60-70 HU (5/17), 70-80 HU (5/17), and > 80 HU (8/19). All 207 lesions in the 20- to 40-HU range were benign cysts with no solid lesions (0%; 95% CI, 0.0-1.4%). CONCLUSION: Small homogeneous renal masses measuring 20-40 HU on portal venous phase CT images are highly likely to be benign cysts.

Incidentally Detected Bilateral Adrenal Nodules in Patients Without Cancer: Is Further Workup Necessary?

OBJECTIVE: The purpose of this study was to determine the rate of malignancy in incidentally detected bilateral adrenal masses in patients with no known history of cancer. MATERIALS AND METHODS: A retrospective search of CT reports of patients with incidentally detected bilateral adrenal nodules was performed from January 1, 2002, to January 1, 2014. Patients were excluded if they had a known cancer or suspected functioning adrenal tumor; 161 patients were included. Nodules were characterized as benign or malignant on the basis of imaging features at the index CT examination, imaging features at subsequent adrenal protocol CT or MRI, imaging stability for a minimum of 1 year, or clinical follow-up of a minimum of 2 years. RESULTS: Mean nodule size was 1.8 cm (range, 0.7-4.9 cm). There were no cases of primary or secondary adrenal malignancy (95% CI, 0.00-0.023). The nodules diagnosed on index CT scans were 73 adrenal adenomas and two myelolipomas. Seventy-four nodules were subsequently characterized as adrenal adenomas on the basis of imaging findings. Of the 113 indeterminate nodules that had imaging follow-up, 111 were stable at the latest follow-up examination. One nodule grew 26% over 8.1 years, and the other grew 59% over 12.4 years. Clinical follow-up of patients with 60 indeterminate nodules revealed no evidence of adrenal malignancy. CONCLUSION: No case of malignancy was found in 322 incidentally detected bilateral adrenal nodules at CT of patients without known cancer. Imaging follow-up of such lesions may be unnecessary.

Predictors of CT Radiation Dose and Their Effect on Patient Care: A Comprehensive Analysis Using Automated Data.

Purpose To determine patient, vendor, and institutional factors that influence computed tomography (CT) radiation dose. Materials and Methods The relevant institutional review boards approved this HIPAA-compliant study, with waiver of informed consent. Volume CT dose index (CTDIvol) and effective dose in 274 124 head, chest, and abdominal CT examinations performed in adult patients at 12 facilities in 2013 were collected prospectively. Patient, vendor, and institutional characteristics that could be used to predict (a) median dose by using linear regression after log transformation of doses and (b) high-dose examinations (top 25% of dose within anatomic strata) by using modified Poisson regression were assessed. Results There was wide variation in dose within and across medical centers. For chest CTDIvol, overall median dose across all institutions was 11 mGy, and institutional median dose was 7-16 mGy. Models including patient, vendor, and institutional factors were good for prediction of median doses (R2 = 0.31-0.61). The specific institution where the examination was performed (reflecting the specific protocols used) accounted for a moderate to large proportion of dose variation. For chest CTDIvol, unadjusted median CTDIvol was 16.5 mGy at one institution and 6.7 mGy at another (adjusted relative median dose, 2.6 mGy [95% confidence interval: 2.5, 2.7]). Several variables were important predictors that a patient would undergo high-dose CT. These included patient size, the specific institution where CT was performed, and the use of multiphase scanning. For example, while 49% of patients (21 411 of 43 696) who underwent multiphase abdominal CT had a high-dose examination, 8% of patients (4977 of 62 212) who underwent single-phase CT had a high-dose examination (adjusted relative risk, 6.20 [95% CI: 6.17, 6.23]). If all patients had been examined with single-phase CT, 69% (18 208 of 26 388) of high-dose examinations would have been eliminated. Patient size, institutional-specific protocols, and multiphase scanning were the most important predictors of dose (change in R2 = 8%-32%), followed by manufacturer and iterative reconstruction (change in R2, 0.2%-15.0%). Conclusion CT doses vary considerably within and across facilities. The primary factors that influenced dose variation were multiphase scanning and institutional protocol choices. It is unknown if the variation in these factors influenced diagnostic accuracy. © RSNA, 2016.

Comparison of ferumoxytol-enhanced MRA with conventional angiography for assessment of severity of transplant renal artery stenosis.

PURPOSE: To determine the accuracy of ferumoxytol-enhanced magnetic resonance angiography (MRA) in assessing the severity of transplant renal artery stenosis (TRAS), using digital subtraction angiography (DSA) as the reference standard. MATERIALS AND METHODS: Our Institutional Review Board approved this retrospective, Health Insurance Portability and Accountability Act-compliant study. Thirty-three patients with documented clinical suspicion for TRAS (elevated serum creatinine, refractory hypertension, edema, and/or audible bruit) and/or concerning sonographic findings (elevated renal artery velocity and/or intraparenchymal parvus tardus waveforms) underwent a 1.5T MRA with ferumoxytol prior to DSA. All DSAs were independently reviewed by an interventional radiologist and served as the reference standard. The MRAs were reviewed by three readers who were blinded to the ultrasound and DSA findings for the presence and severity of TRAS. Sensitivity, specificity, and accuracy for identifying substantial stenoses (>50%) were determined. Intraclass correlation coefficients (ICCs) were calculated among readers. Mean differences between the percent stenosis from each MRA reader and DSA were calculated. RESULTS: On DSA, a total of 42 stenoses were identified in the 33 patients. The sensitivity, specificity, and accuracy of MRA in detecting substantial stenoses were 100%, 75-87.5%, and 95.2-97.6%, respectively, among the readers. There was excellent agreement among readers as to the percent stenosis (ICC = 0.82). MRA overestimated the degree of stenosis by 3.9-9.6% compared to DSA. CONCLUSION: Ferumoxytol-enhanced MRA provides high sensitivity, specificity, and accuracy for determining the severity of TRAS. Our results suggest that it can potentially be used as a noninvasive examination following ultrasound to reduce the number of unnecessary conventional angiograms. LEVEL OF EVIDENCE: 3 J. Magn. Reson. Imaging 2017;45:779-785.

Accuracy and Radiation Dose Reduction of Limited-Range CT in the Evaluation of Acute Appendicitis in Pediatric Patients.

OBJECTIVE: The purpose of this article is to determine the accuracy and radiation dose reduction of limited-range CT prescribed from the top of L2 to the top of the pubic symphysis in children with suspected acute appendicitis. MATERIALS AND METHODS: We performed a retrospective study of 210 consecutive pediatric patients from December 11, 2012, through December 11, 2014, who underwent abdominopelvic CT for suspected acute appendicitis. Two radiologists independently reviewed the theoretic limited scans from the superior L2 vertebral body to the top of the pubic symphysis, to assess for visualization of the appendix, acute appendicitis, alternative diagnoses, and incidental findings. Separately, the same parameters were assessed on the full scan by the same two reviewers. Whole-body effective doses were determined for the full- and limited-range scans and were compared using the paired t test. RESULTS: The appendix or entire cecum was visualized on the limited scan in all cases, and no cases of acute appendicitis were missed on the simulated limited scan compared with the full scan. Two alternative diagnoses were missed with the limited scan: one case of hydronephrosis and one of acute acalculous cholecystitis. The mean effective dose for the original scan was 5.6 mSv and that for the simulated limited scan was 3.0 mSv, resulting in a dose reduction of 46.4% (p < 0.001). CONCLUSION: A limited-range CT examination performed from the top of L2 to the top of the pubic symphysis is as accurate as a full-range abdominopelvic CT in evaluating pediatric patients with suspected appendicitis and reduces the dose by approximately 46%.

Detection of Renal Stones on Portal Venous Phase CT: Comparison of Thin Axial and Coronal Maximum-Intensity-Projection Images.

OBJECTIVE: The objective of our study was to determine the sensitivity of thin axial and coronal maximum-intensity-projection (MIP) images for the detection of renal stones on contrast-enhanced CT performed in the portal venous phase. MATERIALS AND METHODS: This retrospective study included 72 patients, 59 of whom had at least one renal stone, who underwent unenhanced CT immediately followed by contrast-enhanced CT in the portal venous phase. Two abdominal imaging fellowship-trained radiologists independently recorded the number of stones on both thin (1-1.50 mm) axial and 5-mm coronal MIP images in the portal venous phase. The reference standard was determined by consensus review of the thin axial unenhanced images. Reviewer sensitivity was calculated and categorized by stone diameter. RESULTS: One hundred forty-eight stones were present; the mean number of stones per patient was 2.5 (SD, 2.7). The mean stone size was 2.5 mm (SD, 2.7). The sensitivity of thin axial images was 89.9%, 99.0%, and 100.0% for reviewer 1 and 83.1%, 98.0%, and 100.0% for reviewer 2 for all stones, stones ≥ 2 mm, and stones ≥ 3 mm, respectively. The sensitivity of coronal MIP images was 86.5%, 96.2%, and 100.0% for reviewer 1 and 79.0%, 91.4%, and 96.6% for reviewer 2 for all stones, stones ≥ 2 mm, and stones ≥ 3 mm, respectively. CONCLUSION: Thin axial images are highly sensitive for the detection of renal stones ≥ 2 mm on portal venous phase CT. Coronal MIP images do not improve renal stone detection over thin axial images.

JOURNAL CLUB: Quantification of Fetal Dose Reduction if Abdominal CT Is Limited to the Top of the Iliac Crests in Pregnant Patients With Trauma.

OBJECTIVE: The purposes of this study were to correlate fetal z-axis location within the maternal abdomen on CT with gestational age and estimate fetal dose reduction of a study limited to the abdomen only, with its lower aspect at the top of the iliac crests, compared with full abdominopelvic CT in pregnant trauma patients. MATERIALS AND METHODS: We performed a study of pregnant patients who underwent CT of the abdomen and pelvis for trauma at a single institution over a 10-year period. The inferior aspect of maternal liver, spleen, gallbladder, pancreas, adrenals, and kidneys was recorded as above or below the iliac crests. The distance from the iliac crest to the top of the fetus or gestational sac was determined. The CT images of the limited and full scanning studies were independently reviewed by two blinded radiologists to identify traumatic injuries. Fetal dose profiles, including both scatter and primary radiation, were computed analytically along the central axis of the patient to estimate fetal dose reduction. Linear regression analysis was performed between gestational age and distance of the fetus to the iliac crests. RESULTS: Thirty-five patients were included (mean age, 26.2 years). Gestational age ranged from 5 to 38 weeks, with 5, 19, and 11 gestations in the first, second, and third trimesters, respectively. All solid organs were above the iliac crests in all patients. In three of six patients, traumatic findings in the pelvis would have been missed with the limited study. There was high correlation between gestational age and distance of the fetus to the iliac crests (R(2) = 0.84). The mean gestational age at which the top of the fetus was at the iliac crest was 17.3 weeks. Using the limited scanning study, fetuses at 5, 20, and 40 weeks of gestation would receive an estimated 4.3%, 26.2%, and 59.9% of the dose, respectively, compared with the dose for the full scanning study. CONCLUSION: In pregnant patients in our series with a history of trauma, CT of the abdomen only was an effective technique to reduce fetal radiation exposure compared with full abdomen and pelvis CT.

Differences in Liver Imaging and Reporting Data System Categorization Between MRI and CT.

OBJECTIVE: The purpose of this study is to determine whether focal liver observations are categorized differently by CT and MRI using the Liver Imaging and Reporting Data System (LI-RADS). MATERIALS AND METHODS: We performed a retrospective review of 58 patients at risk for hepatocellular carcinoma who underwent liver protocol CT and MRI within 1 month of each other. Two readers assigned a LI-RADS category for all focal liver observations in consensus. A significant category upgrade was defined as a change from LI-RADS categories 1 and 2 or nonvisualization to LI-RADS categories 3-5, from LI-RADS category 3 to category 4 or 5, from LI-RADS category 4 to category 5, or from any category to LI-RADS category 5V. A significant downgrade was defined as a change from LI-RADS category 5 to categories 1-4, from LI-RADS category 4 to categories 1-3, or from LI-RADS category 3 to categories 1 or 2. RESULTS: The LI-RADS category was different between CT and MRI for 77.2% (176/228) of observations. A significant upgrade occurred on MRI for 42.5% (97/228) of observations because of nonvisualization by CT (n = 78), capsule (n = 8), arterial hyperenhancement (n = 4), intratumoral fat (n = 2), larger size (n = 2), tumor in portal vein (n = 2), and wash-out (n = 1). Of these 97 upgraded observations, two were upgraded to LI-RADS category 5V, 15 were upgraded to category 5, and 13 were upgraded to category 4. A significant downgrade occurred on MRI for 8.8% (20/228) of observations because of marked T2 hyperintensity (n = 14), smaller size (n = 2), wedge shape (n = 2), and marked T2 hypointensity (n = 2). CONCLUSION: LI-RADS categorization of focal liver observations is dependent on imaging modality. MRI results in both upgraded and downgraded categorization compared with CT in an important proportion of observations.

Incidence of Contrast-Induced Nephropathy After Renal Graft Catheter Arteriography Using Iodine-Based Contrast Medium.

OBJECTIVE: The objective of our study was to assess the incidence of contrast-induced nephropathy (CIN), dialysis, and graft loss after direct intraarterial infusion of iodine-based contrast medium (CM) in renal allograft recipients. MATERIALS AND METHODS: One hundred patients underwent renal graft catheter arteriography between 2006 and 2014. CIN was defined as an increase in serum creatinine value of 0.5 mg/dL or more above the creatinine value before arteriography. CIN could be assessed in 37 patients with creatinine levels obtained before arteriography and 24-72 hours after arteriography. Dialysis requirement and renal allograft loss at 30 days after the procedure were recorded in all 100 patients. RESULTS: In the 37 patients who could be assessed for CIN, three patients (8%) met the criteria for CIN. In a subgroup analysis, there was an increased incidence of CIN in patients undergoing angiography alone (25%) compared with those in the angioplasty and stenting group (0%) (p = 0.028). At 30 days after the procedure, none (0/100) of the patients required dialysis or had graft failure. CONCLUSION: In a cohort of patients with a single renal allograft undergoing renal graft catheter arteriography using iodine-based CM, the overall incidence of CIN was low and no major adverse outcomes were noted at 30 days after the procedure. However, in a subgroup analysis, the patients who underwent arteriography alone-that is, without angioplasty or stenting-had a statistically significant higher rate of CIN.

Radiation Doses in Consecutive CT Examinations from Five University of California Medical Centers.

PURPOSE: To summarize data on computed tomographic (CT) radiation doses collected from consecutive CT examinations performed at 12 facilities that can contribute to the creation of reference levels. MATERIALS AND METHODS: The study was approved by the institutional review boards of the collaborating institutions and was compliant with HIPAA. Radiation dose metrics were prospectively and electronically collected from 199 656 consecutive CT examinations in 83 181 adults and 3871 consecutive CT examinations in 2609 children at the five University of California medical centers during 2013. The median volume CT dose index (CTDIvol), dose-length product (DLP), and effective dose, along with the interquartile range (IQR), were calculated separately for adults and children and stratified according to anatomic region. Distributions for DLP and effective dose are reported for single-phase examinations, multiphase examinations, and all examinations. RESULTS: For adults, the median CTDIvol was 50 mGy (IQR, 37-62 mGy) for the head, 12 mGy (IQR, 7-17 mGy) for the chest, and 12 mGy (IQR, 8-17 mGy) for the abdomen. The median DLPs for single-phase, multiphase, and all examinations, respectively, were as follows: head, 880 mGy · cm (IQR, 640-1120 mGy · cm), 1550 mGy · cm (IQR, 1150-2130 mGy · cm), and 960 mGy · cm (IQR, 690-1300 mGy · cm); chest, 420 mGy · cm (IQR, 260-610 mGy · cm), 880 mGy · cm (IQR, 570-1430 mGy · cm), and 550 mGy · cm (IQR 320-830 mGy · cm); and abdomen, 580 mGy · cm (IQR, 360-860 mGy · cm), 1220 mGy · cm (IQR, 850-1790 mGy · cm), and 960 mGy · cm (IQR, 600-1460 mGy · cm). Median effective doses for single-phase, multiphase, and all examinations, respectively, were as follows: head, 2 mSv (IQR, 1-3 mSv), 4 mSv (IQR, 3-8 mSv), and 2 mSv (IQR, 2-3 mSv); chest, 9 mSv (IQR, 5-13 mSv), 18 mSv (IQR, 12-29 mSv), and 11 mSv (IQR, 6-18 mSv); and abdomen, 10 mSv (IQR, 6-16 mSv), 22 mSv (IQR, 15-32 mSv), and 17 mSv (IQR, 11-26 mSv). In general, values for children were approximately 50% those for adults in the head and 25% those for adults in the chest and abdomen. CONCLUSION: These summary dose data provide a starting point for institutional evaluation of CT radiation doses.

Utility of MRI in the Characterization of Indeterminate Small Renal Lesions Previously Seen on Screening CT Scans of Potential Renal Donor Patients.

OBJECTIVE: The purpose of this study was to determine whether MRI could more confidently characterize indeterminate small renal lesions (< 15 mm) previously seen on CT scans of potential renal donor patients and whether such characterization could impact surgical management and donor candidate status. MATERIALS AND METHODS: After dedicated contrast-enhanced renal CT examinations of a population of renal donor patients identified indeterminate small renal lesions (< 15 mm), dedicated renal MRI examinations were performed for 55 of those patients. Two radiologists used consensus reading of established MRI characteristics to characterize indeterminate small lesions as simple cysts, hemorrhagic cysts, angiomyolipomas, or solid renal masses. RESULTS: A total of 94 indeterminate small renal lesions were detected on CT. MRI was able to confidently diagnose 93 of those lesions, including 83 cysts, eight hemorrhagic cysts, and two angiomyolipomas. MRI directly affected the surgical management of four of the patients (7%). CONCLUSION: For potential renal donor patients, MRI can be an effective means of characterizing lesions that are deemed to be too small to characterize by CT. MRI can also potentially alter the surgical management and donor status of this group of patients.

Accuracy and radiation dose reduction of a limited abdominopelvic CT in the diagnosis of acute appendicitis.

PURPOSE: To determine the accuracy and radiation dose reduction of a limited abdominopelvic CT from the bottom of T10 to the top of the pubic symphysis in patients with suspected acute appendicitis. METHODS: We performed a HIPAA compliant and IRB-approved retrospective study of adult patients who underwent CT abdomen/pelvis for suspected appendicitis. The Z-axis length and whole body effective doses of the original full scan and theoretical limited scan from the bottom of T10 to the top of the pubic symphysis were recorded. Images were reviewed to determine if the appendix or entire cecum would be visualized and if any cases of appendicitis or alternative diagnoses would be missed with the limited scan. RESULTS: 235 patients (89 male, mean age 44.6 years) were included. The limited scan resulted in a mean Z-axis length reduction of 5.1 cm superiorly, 6.1 cm inferiorly, and a total reduction of 11.2 cm (24%). The mean whole body effective dose was 11.8 and 9.1 mSv for the original and limited scans, respectively (23% reduction). The entire appendix or cecum was visualized in all cases. Appendicitis was present in 24 cases and an alternative diagnosis was made in 75. No cases of appendicitis or alternative diagnoses were missed using the limited scan. CONCLUSIONS: A limited range CT from the bottom of T10 to the top of the pubic symphysis is as accurate as full abdominopelvic CT in evaluating patients with suspected acute appendicitis and results in approximately 23% dose reduction.

Differentiation of ovarian endometriomas from hemorrhagic cysts at MR imaging: utility of the T2 dark spot sign.

PURPOSE: To determine sensitivity and specificity of the T2 dark spot sign in helping to distinguish endometriomas from other hemorrhagic adnexal lesions. MATERIALS AND METHODS: This HIPAA-compliant, institutional review board-approved retrospective study, with informed consent waived, included 56 women (mean age, 38.8 years; range, 18-66 years). With a radiology database search of pelvic magnetic resonance images from December 16, 2002, to July 24, 2012, 74 cystic hemorrhagic adnexal lesions with hyperintense signal on T1-weighted images were identified. Lesions were excluded if they had solid enhancing components. Final diagnosis was established with pathologic analysis for all endometriomas and neoplasms. Hemorrhagic cysts were diagnosed with pathologic analysis (n = 7), follow-up imaging (n = 13), or prior ultrasonography (n = 5). Two radiologists independently reviewed cases and recorded the presence or absence of T2 shading and T2 dark spots. T2 dark spots were defined as discrete, well-defined markedly hypointense foci within the adnexal lesion on T2-weighted images. Sensitivity, specificity, and positive and negative predictive values of the T2 dark spot sign in distinguishing endometriomas from nonendometrioma hemorrhagic lesions were calculated. RESULTS: Sixteen of 45 endometriomas (36%), zero of 25 hemorrhagic cysts, and two of four neoplasms (50%) (all serous cystadenomas) demonstrated T2 dark spots. Forty-two of 45 endometriomas (93%), 12 of 25 hemorrhagic cysts (48%), and four of four neoplasms (100%) demonstrated T2 shading. Sensitivity, specificity, positive predictive value, and negative predictive value of T2 dark spots for differentiating endometriomas from other hemorrhagic cystic ovarian masses were 36% (95% confidence interval [CI]: 19.8, 51.3), 93% (95% CI: 83.9, 100), 89% (95% CI: 63.9, 98.1), and 48% (95% CI: 34.8, 61.8), respectively, and for T2 shading, they were 93% (95% CI: 84.0, 100), 45% (95% CI: 27.8, 61.9), 72% (95% CI: 58.9, 83.0), and 81% (95% CI: 53.7, 95.0), respectively. CONCLUSION: The T2 dark spot sign has high specificity for chronic hemorrhage and is useful to differentiate endometriomas from hemorrhagic cysts. The T2 shading sign is sensitive but not specific for endometriomas. Online supplemental material is available for this article.

CT Hounsfield numbers of soft tissues on unenhanced abdominal CT scans: variability between two different manufacturers' MDCT scanners.

OBJECTIVE: The purpose of this study is to determine whether Hounsfield numbers of soft tissues on unenhanced abdominal CT of the same patient vary on repeat scans done on two different manufacturers' MDCT scanners. MATERIALS AND METHODS: A database search was performed to identify patients older than 18 years who underwent unenhanced CT of the abdomen and pelvis performed both on a Volume CT (GE Healthcare) and a Definition AS Plus (Siemens Healthcare) 64-MDCT scanner within 12 months of each other. After excluding those patients for whom Hounsfield unit measurements would be affected by mitigating factors, 48 patients (mean age, 58.8 years) were identified. Hounsfield unit measurements were obtained in nine different soft-tissue anatomic locations on each scan, and the location of these sites was kept identical on each scan pair. Data were analyzed to evaluate Hounsfield unit differences between these scanners. RESULTS: In general, there was a low consistency in the Hounsfield unit measurements for each of these sites on scans obtained by the two scanners, with the subcutaneous fat in the left posterolateral flank showing the lowest correlation (intraclass correlation coefficient, 0.198). There were differences in the Hounsfield unit measurements obtained in all anatomic sites on scans obtained by both scanners. Mean Hounsfield unit measurements obtained on the Definition AS Plus scanner were lower than those obtained on the Volume CT scanner, with the intriguing exception of the anterior midline subcutaneous fat Hounsfield unit measurements, which were higher on the Definition AS Plus scanner. All differences were statistically significant (p < 0.05). CONCLUSION: Hounsfield unit measurements for unenhanced abdominal soft tissues of the same patient vary between scanners of two common MDCT manufacturers.