Ravi K. Kaza

Comparison of Acute Transient Dyspnea after Intravenous Administration of Gadoxetate Disodium and Gadobenate Dimeglumine: Effect on Arterial Phase Image Quality

PURPOSE To determine whether acute transient dyspnea and/or arterial phase image degradation occurs more or less often after intravenous administration of gadoxetate disodium than with intravenous administration of gadobenate dimeglumine. MATERIALS AND METHODS Institutional review board approval and patient consent were obtained for this prospective observational study. One hundred ninety-eight gadolinium-based contrast media administrations (99 with gadoxetate disodium [10 mL, n = 97; 8 mL, n = 1; 16 mL, n = 1] and 99 with gadobenate dimeglumine [0.1 mmol per kilogram of body weight, maximum dose, 20 mL]) for hepatobiliary indications were assessed in 192 patients. Subjective patient complaints were assessed. Objective respiratory motion degradation on T1-weighted precontrast and dynamic postcontrast (arterial, venous, or late dynamic or extracellular) magnetic resonance (MR) imaging datasets were independently assessed in a randomized, blinded fashion by five readers using a five-point scale, with mean scores of 4 or greater indicating severe motion. Comparisons between agents were made by using χ(2) or Fisher exact test, where appropriate. RESULTS Significantly more patient complaints of acute transient dyspnea occurred after gadoxetate disodium administration than gadobenate dimeglumine (14% [14 of 99] vs 5% [five of 99], P = .05). There were significantly more severely degraded arterial phase data sets for gadoxetate disodium than for gadobenate dimeglumine for both the general population (17% [17 of 99] vs 2% [two of 99], P = .0007) and the subpopulation with cirrhosis (19% [14 of 72] vs 3% [one of 37], P = .02). This effect did not extend to venous (1% [one of 99] vs 2% [two of 99], P > .99 [overall population]) or late dynamic or extracellular (2% [two of 99] vs 0% [zero of 99], P = .5 [overall population]) phases. No patient required treatment for self-limited dyspnea. CONCLUSION Intravenous gadoxetate disodium can result in acute self-limiting dyspnea that can have a deleterious effect on arterial phase MR image quality and occurs significantly more often than with intravenous gadobenate dimeglumine.

Dual-Energy CT with Single- and Dual-Source Scanners: Current Applications in Evaluating the Genitourinary Tract

Several promising clinical applications for dual-energy computed tomography (CT) in genitourinary imaging have been reported. Dual-energy CT not only provides excellent morphologic detail but also can supply material-specific and quantitative information that may be particularly useful in genitourinary imaging. Dual-energy CT has unique capabilities for characterizing renal lesions by quantifying iodine content and helping identify the mineral contents of renal stones, information that is important for patient care. Virtual unenhanced images reconstructed from dual-energy CT datasets can be useful for detecting calculi within the iodine-filled urinary collecting system, potentially reducing the need for an unenhanced scanning phase at CT urography. Although the underlying principles of dual-energy CT are the same regardless of scanner type, single-source dual-energy scanners with fast kilovoltage switching differ from dual-source dual-energy scanners both in image data acquisition and in processing methods; an understanding of these differences may help optimize dual-energy CT genitourinary protocols. Dual-energy CT performed with a dual-source scanner or with a single-source scanner with fast kilovoltage switching also has some important limitations. Further advances in scanning protocols and refinement of processing techniques to reduce image noise may lead to more widespread use of dual-energy CT.

Distinguishing enhancing from nonenhancing renal lesions with fast kilovoltage-switching dual-energy CT

OBJECTIVE The purpose of this article is to evaluate the accuracy of dual-energy CT in distinguishing enhancing from nonenhancing or equivocally enhancing renal lesions. MATERIALS AND METHODS We retrospectively reviewed fast kilovoltage-switching dual-energy renal mass CT performed in 39 patients. On the contrast-enhanced dual-energy CT scans, renal lesions were graded subjectively for enhancement using iodine density images and iodine overlay images. Lesion iodine density was measured to identify an optimal threshold for detection of enhancement. Lesion attenuation measurements on unenhanced and contrast-enhanced scans were performed to identify enhancing (increase of > 20 HU) lesions, which were used as the reference standard. Sensitivity, specificity, and accuracy for detection of enhancement were calculated for the different dual-energy CT techniques. RESULTS Eighty-three renal lesions were evaluated. On the basis of attenuation measurements, there were 20 enhancing and 63 nonenhancing lesions. The sensitivity, specificity, and accuracy for the detection of enhancement according to the lesion appearance were 70%, 98.4%, and 91.6%, respectively, on iodine density images and were 85%, 90.5%, and 89.2%, respectively, on iodine overlay images generated from contrast-enhanced dual-energy CT scans. Of the various thresholds of measured lesion iodine density (1-3 mg/cm(3)), a threshold of 2 mg/cm(3) showed the highest accuracy for the detection of enhancement, with sensitivity, specificity, and accuracy of 90%, 93.7%, and 92.8%, respectively. CONCLUSION Fast kilovoltage-switching dual-energy CT is highly specific in excluding enhancement and moderately to highly sensitive in detecting enhancement of renal lesions. Of the available dual-energy CT techniques, iodine density measurement using a threshold of 2 mg/cm(3) is most accurate in distinguishing enhancing from nonenhancing renal lesions.

Repeatability of Diagnostic Features and Scoring Systems for Hepatocellular Carcinoma by Using MR Imaging

PURPOSE To determine for expert and novice radiologists repeatability of major diagnostic features and scoring systems (ie, Liver Imaging Reporting and Data System [LI-RADS], Organ Procurement and Transplantation Network [OPTN], and American Association for the Study of Liver Diseases [AASLD]) for hepatocellular carcinoma (HCC) by using magnetic resonance (MR) imaging. MATERIALS AND METHODS Institutional review board approval was obtained and patient consent was waived for this HIPAA-compliant, retrospective study. The LI-RADS discussed in this article refers to version 2013.1. Ten blinded readers reviewed 100 liver MR imaging studies that demonstrated observations preliminarily assigned LI-RADS scores of LR1-LR5. Diameter and major HCC features (arterial hyperenhancement, washout appearance, pseudocapsule) were recorded for each observation. LI-RADS, OPTN, and AASLD scores were assigned. Interreader agreement was assessed by using intraclass correlation coefficients and κ statistics. Scoring rates were compared by using McNemar test. RESULTS Overall interreader agreement was substantial for arterial hyperenhancement (0.67 [95% confidence interval {CI}: 0.65, 0.69]), moderate for washout appearance (0.48 [95%CI: 0.46, 0.50]), moderate for pseudocapsule (0.52 [95% CI: 050, 0.54]), fair for LI-RADS (0.35 [95% CI: 0.34, 0.37]), fair for AASLD (0.39 [95% CI: 0.37, 0.42]), and moderate for OPTN (0.53 [95% CI: 0.51, 0.56]). Agreement for measured diameter was almost perfect (range, 0.95-0.97). There was substantial agreement for most scores consistent with HCC. Experts agreed significantly more than did novices and were significantly more likely than were novices to assign a diagnosis of HCC (P < .001). CONCLUSION Two of three major features for HCC (washout appearance and pseudocapsule) have only moderate interreader agreement. Experts and novices who assigned scores consistent with HCC had substantial but not perfect agreement. Expert agreement is substantial for OPTN, but moderate for LI-RADS and AASLD. Novices were less consistent and less likely to diagnose HCC than were experts.

Matched within-Patient Cohort Study of Transient Arterial Phase Respiratory Motion–related Artifact in MR Imaging of the Liver: Gadoxetate Disodium versus Gadobenate Dimeglumine

PURPOSE To compare frequency and severity of arterial phase respiratory motion-related artifact following gadoxetate disodium and gadobenate dimeglumine in matched patients administered both contrast media at different times. MATERIALS AND METHODS Institutional review board approval was obtained, with patient consent waived, for this retrospective, HIPAA-compliant study. Ninety patients underwent gadobenate dimeglumine-enhanced abdominal magnetic resonance (MR) followed by gadoxetate disodium-enhanced abdominal MR and were matched to 90 patients who were administered the same contrast media in reverse order (180 patients). Matching was based on length of time between paired examinations. Gadobenate dimeglumine dose was weight based (0.1 mmol per kilogram body weight). Gadoxetate disodium dose was typically fixed (10 or 20 mL [off label]). Three readers blinded to contrast agent assigned a respiratory motion-related artifact score (1 [none] to 5 [nondiagnostic]) for nonenhanced, arterial, venous, and late dynamic phases. Frequency of greater new arterial phase respiratory motion-related artifact in each within-patient pair and aggregate rate of new severe transient arterial phase respiratory motion-related artifact (scores ≤ 2, nonenhanced and venous and/or late dynamic phases; ≥ 4, arterial phase) were compared (McNemar test). RESULTS For groups 1 and 2, respectively, mean dose (gadoxetate disodium, 16.6 mL vs 16.6 mL, P = .99; gadobenate dimeglumine, 18.0 mL vs 17.8 mL, P = .77) and mean time between examinations (191 days vs 191 days, P = .99) were not significantly different between matched populations. Gadoxetate disodium was associated with significantly higher incidence of new arterial phase respiratory motion-related artifact compared with gadobenate dimeglumine (39% vs 10%, P < .0001) and of new severe transient arterial phase respiratory motion-related artifact (18% vs 2%, P < .0001) in patients administered both agents at different times. CONCLUSION Fixed off-label dose (10 or 20 mL) of gadoxetate disodium is associated with arterial phase respiratory motion-related artifact that is sometimes severe and occurs significantly more often than after gadobenate dimeglumine in patients who received both contrast media.

CT Enterography at 80 kVp With Adaptive Statistical Iterative Reconstruction Versus at 120 kVp With Standard Reconstruction: Image Quality, Diagnostic Adequacy, and Dose Reduction

OBJECTIVE The objective of our study was to evaluate the image quality and diagnostic adequacy of the following two CT enterography protocols in patients weighing less than 160 lb (72 kg): 80-kVp imaging with the adaptive statistical iterative reconstruction (ASIR) in comparison with 120-kVp imaging with the filtered back projection reconstruction. MATERIALS AND METHODS We retrospectively reviewed 133 CT enterography examinations of 127 patients weighing less than 160 lb, 64 80-kVp examinations, and 69 120-kVp examinations. Image quality for evaluation of the bowel wall, mesenteric vessels, and hepatic parenchyma and the overall image quality were graded on a scale of 1-5 (1 = poor, 2 = acceptable, 3 = good, 4 = very good, 5 = excellent). Diagnostic accuracy for the detection of inflammatory bowel disease was evaluated. The volume CT dose index (CTDI(vol)) was recorded and effective dose was calculated from scanner-generated dose-length product. RESULTS There was a statistically significant decrease in the mean image quality scores for 80-kVp examinations compared with 120-kVp examinations for evaluation of the bowel wall (3.19 vs 3.70, respectively) and liver (3.12 vs 3.81) and for overall image quality (3.23 vs 3.68), but there was no significant decrease in score for evaluation of the mesenteric vessels (3.63 vs 3.67). None of the 80-kVp examinations was graded as poor, and all were considered to be of acceptable quality. Both techniques had comparable diagnostic accuracy for the detection of inflammatory bowel disease. Interobserver agreement was fair to moderate for qualitative image grading and was substantial for the detection of features of inflammatory bowel disease. The mean CTDI(vol) and effective dose for the 80-kVp examinations were 6.15 mGy and 4.60 mSv, respectively, and for the 120-kVp examinations, 20.79 mGy and 15.81 mSv. CONCLUSION In patients weighing less than 160 lb, CT enterography examinations at 80 kVp with 30% ASIR produce diagnostically acceptable image quality with an average CTDI(vol) of 6.15 mGy and an average effective dose of 4.60 mSv.

Rectal Imaging: Part 2, Perianal Fistula Evaluation on Pelvic MRI???What the Radiologist Needs to Know

OBJECTIVE The purpose of this article is to provide an overview of pelvic MRI for the evaluation of perianal fistulas, with a description of the technique, illustration of relevant normal anatomy, and examples of various fistula types. CONCLUSION MRI evaluation of perianal fistulas can be challenging, and knowledge of relevant pelvic anatomy and fistula classification remains crucial in the diagnosis. MRI is highly accurate for fistula depiction and, by providing an accurate assessment of disease status and extension, can help surgical planning to minimize recurrence and detect clinically unapparent disease.

“Sweet spot” for endoleak detection: Optimizing contrast to noise using low keV reconstructions from fast-switch kVp dual energy CT

Objective To assess endoleak detection and conspicuity using low–kiloelectron volt (keV) monochromatic reconstructions of single-source (fast-switch kilovolt [peak]) dual-energy data sets. Methods With approval of the institutional review board, multiphasic dual-energy computed tomographic (CT) scans for aortic endograft surveillance were retrospectively reviewed for 39 patients. Two abdominal radiologists each performed 2 separate reading sessions, at 55-keV and standard 75-keV reconstruction, respectively. The readers tabulated endoleak presence, conspicuity on 1-to-5 scale, and type overall and in arterial and venous phases. Originally, dictated reports in medical records were used as criterion standard. Results Original dictations identified 19 endoleaks (9 abdominal and 10 thoracic), 13 of which were type II. The blinded readers (R1 and R2) exhibited good to very good intraobserver and interobserver agreement. Endoleak detection was higher at 55 keV than at 75 keV (sensitivity, 100% (95% confidence interval [CI], 82.4%–100.0%) and 84.2% (95% CI, 60.4–96.6%) at 55 keV vs 79% (95% CI, 54.4–94.0%) and 68.4% (95% CI, 43.5%–87.4%) at 75 keV in venous phase). Further, endoleak conspicuity ratings (where original dictation showed positive leak) were higher at 55 keV than at 75 keV, which was a significant difference for R2 in the overall ratings (P = 0.03) and for both readers in the venous phase ratings (R1, P = 0.01; R2, P = 0.004). There was no difference in endoleak type characterization between the kiloelectron volt levels. Conclusion Sensitivity for endoleak detection and overall endoleak conspicuity ratings were both higher at 55 keV than 75 keV, favoring the inclusion of a lower-energy monochromatic reconstruction for endoleak surveillance protocols with dual-energy computed tomography.

Emerging Techniques for Dose Optimization in Abdominal CT

Recent advances in computed tomographic (CT) scanning technique such as automated tube current modulation (ATCM), optimized x-ray tube voltage, and better use of iterative image reconstruction have allowed maintenance of good CT image quality with reduced radiation dose. ATCM varies the tube current during scanning to account for differences in patient attenuation, ensuring a more homogeneous image quality, although selection of the appropriate image quality parameter is essential for achieving optimal dose reduction. Reducing the x-ray tube voltage is best suited for evaluating iodinated structures, since the effective energy of the x-ray beam will be closer to the k-edge of iodine, resulting in a higher attenuation for the iodine. The optimal kilovoltage for a CT study should be chosen on the basis of imaging task and patient habitus. The aim of iterative image reconstruction is to identify factors that contribute to noise on CT images with use of statistical models of noise (statistical iterative reconstruction) and selective removal of noise to improve image quality. The degree of noise suppression achieved with statistical iterative reconstruction can be customized to minimize the effect of altered image quality on CT images. Unlike with statistical iterative reconstruction, model-based iterative reconstruction algorithms model both the statistical noise and the physical acquisition process, allowing CT to be performed with further reduction in radiation dose without an increase in image noise or loss of spatial resolution. Understanding these recently developed scanning techniques is essential for optimization of imaging protocols designed to achieve the desired image quality with a reduced dose.

Primary and secondary neoplasms of the spleen

Abstract With the exception of lymphoma involving the spleen, other primary and secondary neoplasms are rare and infrequently encountered. Primary malignant neoplasms involving the spleen are lymphoma and angiosarcoma. Primary benign neoplasms involving the spleen include hemangioma, lymphangioma, littoral cell angioma and splenic cyst and solid lesions such as hamartoma and inflammatory pseudotumor.