Ramit Lamba

Contrast-Induced Nephropathy after Intravenous Administration: Fact or Fiction?

Recent prospective clinical investigations in high-risk patients receiving intravenous contrast media for computed tomography (CT) suggest that the incidence and serious negative clinical outcomes are much less common than previously believed. Additional perspectives comparing random variations in serum creatinine in subjects not receiving contrast media show similar fluctuations that would equate to contrast-induced nephrotoxicity (CIN). Putative mechanisms for how CIN could cause death or other serious adverse clinical consequences have not been elucidated.

Radiation doses in consecutive ct examinations from five university of California medical centers 1

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.

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.

Multidetector CT of Vascular Compression Syndromes in the Abdomen and Pelvis

Certain abdominopelvic vascular structures may be compressed by adjacent anatomic structures or may cause compression of adjacent hollow viscera. Such compressions may be asymptomatic; when symptomatic, however, they can lead to a variety of uncommon syndromes in the abdomen and pelvis, including median arcuate ligament syndrome, May-Thurner syndrome, nutcracker syndrome, superior mesenteric artery syndrome, ureteropelvic junction obstruction, ovarian vein syndrome, and other forms of ureteral compression. These syndromes, the pathogenesis of some of which remains controversial, can result in nonspecific symptoms of epigastric or flank pain, weight loss, nausea and vomiting, hematuria, or urinary tract infection. Direct venography or duplex ultrasonography can provide hemodynamic information in cases of vascular compression. However, multidetector computed tomography is particularly useful in that it allows a comprehensive single-study evaluation of the anatomy and resultant morphologic changes. Anatomic findings that can predispose to these syndromes may be encountered in patients who are undergoing imaging for unrelated reasons. However, the diagnosis of these syndromes should not be made on the basis of imaging findings alone. Severely symptomatic patients require treatment, which is generally surgical, although endovascular techniques are increasingly being used to treat venous compressions.

Is Segmental Enhancement Inversion on Enhanced Biphasic MDCT a Reliable Sign for the Noninvasive Diagnosis of Renal Oncocytomas

OBJECTIVE The objective of our study was to retrospectively determine whether segmental enhancement inversion or other CT patterns seen at enhanced biphasic MDCT are predictive for the diagnosis of renal oncocytoma. MATERIALS AND METHODS Twenty-nine patients with 32 oncocytomas diagnosed by either biopsy or resection who had undergone enhanced biphasic CT between January 2004 and March 2010 were included in this study. Biphasic CT scans were analyzed for the presence of segmental enhancement inversion. Segmental enhancement inversion was defined as a renal mass with two distinctive segments in which the attenuation of the segments changed between the two phases of CT. The masses were further characterized on imaging to determine if any imaging feature is predictive of renal oncocytoma. RESULTS Of the 32 renal oncocytomas, 16 oncocytomas were eliminated from analysis. These masses were eliminated because they were larger than 4 cm (n = 4), the CT examinations were inadequate (n = 10), or the pathology results were questionable (n = 2). The remaining 16 tumors (mean size, 2.6 cm; range, 1.8-3.9 cm) were included in our study. Only two tumors showed distinct segments of variable degrees of enhancement, with one of those tumors having segmental enhancement inversion. Three masses had a central region of low density. The most common feature, identified in eight of the 16 oncocytomas, was a slightly heterogeneous mass that became homogeneous on the later phase of CT. Three oncocytomas had a homogeneous appearance on both phases. CONCLUSION Contrary to a prior report, we did not find segmental enhancement inversion to be a characteristic enhancement pattern of small renal oncocytomas on biphasic MDCT. We found no specific features on biphasic CT that could be considered reliable and could strongly suggest the diagnosis of renal oncocytoma.

Orthotopic liver transplantation: reversible Doppler US findings in the immediate postoperative period.

Orthotopic liver transplantation (OLT) is the only definitive treatment for irreversible acute liver failure and chronic liver disease. In the immediate postoperative period after OLT, patients are closely monitored with Doppler ultrasonography (US) to detect treatable vascular complications and ensure graft survival. The first postoperative Doppler US examination is performed fairly early on the first postoperative day, before surgical wound closure has been performed. The immediate postoperative images, obtained when the effects of surgery are very recent, often reveal an array of findings that may appear alarming but that tend to normalize within a few days and are compatible with changes related to the surgery itself. These findings include a starry-sky appearance of reperfusion hepatic edema, transient foci of increased echogenicity, pneumobilia, small fluid collections, perihepatic hematomas, pleural effusion, temporary elevation of hepatic arterial velocity, transient elevation of resistive index (RI), decreased RI with tardus parvus waveform, increased portal venous flow and mono- or biphasic waveforms of the hepatic veins. Most of these changes revert to normal in the first postoperative week; deterioration atypical of transient changes requires further evaluation.

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.

Ovarian Fibromas and Fibrothecomas Sonographic Correlation With Computed Tomography and Magnetic Resonance Imaging: A 5-Year Single-Institution Experience

To evaluate imaging characteristics of ovarian fibromas and fibrothe‐comas and to identify select clinical markers and imaging features to help in their diagnosis.

Methods for CT Automatic Exposure Control Protocol Translation between Scanner Platforms

PURPOSE An imaging facility with a diverse fleet of CT scanners faces considerable challenges when propagating CT protocols with consistent image quality and patient dose across scanner makes and models. Although some protocol parameters can comfortably remain constant among scanners (eg, tube voltage, gantry rotation time), the automatic exposure control (AEC) parameter, which selects the overall mA level during tube current modulation, is difficult to match among scanners, especially from different CT manufacturers. METHODS Objective methods for converting tube current modulation protocols among CT scanners were developed. Three CT scanners were investigated, a GE LightSpeed 16 scanner, a GE VCT scanner, and a Siemens Definition AS+ scanner. Translation of the AEC parameters such as noise index and quality reference mAs across CT scanners was specifically investigated. A variable-diameter poly(methyl methacrylate) phantom was imaged on the 3 scanners using a range of AEC parameters for each scanner. The phantom consisted of 5 cylindrical sections with diameters of 13, 16, 20, 25, and 32 cm. The protocol translation scheme was based on matching either the volumetric CT dose index or image noise (in Hounsfield units) between two different CT scanners. A series of analytic fit functions, corresponding to different patient sizes (phantom diameters), were developed from the measured CT data. These functions relate the AEC metric of the reference scanner, the GE LightSpeed 16 in this case, to the AEC metric of a secondary scanner. RESULTS When translating protocols between different models of CT scanners (from the GE LightSpeed 16 reference scanner to the GE VCT system), the translation functions were linear. However, a power-law function was necessary to convert the AEC functions of the GE LightSpeed 16 reference scanner to the Siemens Definition AS+ secondary scanner, because of differences in the AEC functionality designed by these two companies. CONCLUSIONS Protocol translation on the basis of quantitative metrics (volumetric CT dose index or measured image noise) is feasible. Protocol translation has a dependency on patient size, especially between the GE and Siemens systems. Translation schemes that preserve dose levels may not produce identical image quality.

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

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.