Distinguishing hemangiomas from metastases on liver MRI performed with gadoxetate disodium: Value of the extended washout sign.

OBJECTIVE: To describe the enhancement pattern of hemangiomas with gadoxetate disodium and propose a new sign - the "extended washout sign" - to diagnose hemangiomas on hepatobiliary MR imaging. MATERIALS AND METHODS: In this retrospective IRB approved study, quantitative and qualitative image analysis of 45 hemangiomas and 37 metastases in 77 patients was performed. Gadoxetate disodium-enhanced MR imaging was obtained during arterial and portal venous phases as well as with delays of 3, 8, and 20min. Lesion signal intensity was measured at each phase. Quantitatively, extended washout was defined as a 10% or greater decrease in signal intensity from 8 to 20min on 3D gradient echo images. Statistical analysis was performed using unpaired Student's t-test. Qualitative analysis was also performed to assess observer confidence based on T2-weighted images, dynamic images, and combined early (8min) and late (20min) hepatobiliary phases. Extended washout was defined as a perceptible change in signal from 8 to 20min. RESULTS: On quantitative analysis, 84% of hemangiomas demonstrated a positive extended washout sign while only 18% of metastases did. Qualitatively, 78% of hemangiomas demonstrated a perceptible change in signal from 8 to 20min, while only 5.4% of metastases did. When extended washout was used in combination with T2 hyperintensity, specificity increased to 100%, with a sensitivity of 87% and area under the curve of 0.99. CONCLUSIONS: When combined with T2 signal intensity, the extended washout sign can be used to increase accuracy of differentiating hemangiomas from metastases on gadoxetate disodium-enhanced MRI.

Stratification of patients with liver fibrosis using dual-energy CT.

Assessing the severity of liver fibrosis has direct clinical implications for patient diagnosis and treatment. Liver biopsy, typically considered the gold standard, has limited clinical utility due to its invasiveness. Therefore, several imaging-based techniques for staging liver fibrosis have emerged, such as magnetic resonance elastography (MRE) and ultrasound elastography (USE), but they face challenges that include limited availability, high cost, poor patient compliance, low repeatability, and inaccuracy. Computed tomography (CT) can address many of these limitations, but is still hampered by inaccuracy in the presence of confounding factors, such as liver fat. Dual-energy CT (DECT), with its ability to discriminate between different tissue types, may offer a viable alternative to these methods. By combining the "multi-material decomposition" (MMD) algorithm with a biologically driven hypothesis we developed a method for assessing liver fibrosis from DECT images. On a twelve-patient cohort the method produced quantitative maps showing the spatial distribution of liver fibrosis, as well as a fibrosis score for each patient with statistically significant correlation with the severity of fibrosis across a wide range of disease severities. A preliminary comparison of the proposed algorithm against MRE showed good agreement between the two methods. Finally, the application of the algorithm to longitudinal DECT scans of the cohort produced highly repeatable results. We conclude that our algorithm can successfully stratify patients with liver fibrosis and can serve to supplement and augment current clinical practice and the role of DECT imaging in staging liver fibrosis.

New and evolving concepts in CT for abdominal vascular imaging.

Computed tomographic (CT) angiography has become the standard of care, supplanting invasive angiography for comprehensive initial evaluation of acute and chronic conditions affecting the vascular system in the abdomen and elsewhere. Over the past decade, the capabilities of CT have improved substantially; simultaneously, the expectations of the referring physician and vascular surgeons have also evolved. Increasingly, CT angiography is used as an imaging biomarker for treatment selection and assessment of effectiveness. However, the growing use of CT angiography has also introduced some challenges, as potential radiation-associated and contrast media-induced risks need to be addressed. These concerns can be partly confronted by modifying scanning parameters (applying a low tube voltage) with or without using software-based solutions. Most recently, multienergy technology has endowed CT with new capabilities offering improved CT angiographic image quality and novel plaque characterization while decreasing radiation and iodine dose. In this article, we discuss current and new approaches using both conventional and multienergy CT for studying vascular disease in the abdomen. We propose various approaches to overcoming commonly encountered image quality challenges in CT angiography. In addition, we describe supplemental strategies for improving patient safety that leverage the available technology.

Inflammatory hepatocellular adenomas can mimic focal nodular hyperplasia on gadoxetic acid-enhanced MRI.

OBJECTIVE: Inflammatory hepatocellular adenoma (HCA) is a recently categorized entity of hepatocellular neoplasms. We investigated whether gadoxetic acid-enhanced MRI can distinguish inflammatory HCA from focal nodular hyperplasia (FNH). MATERIALS AND METHODS: From January 1, 2009, through January 1, 2013, gadoxetic acid-enhanced MRI examinations from two institutions were reviewed for HCA, with specific histologic features of inflammatory HCA. Biopsy and resection slides were reviewed, and immunohistochemistry for glutamine synthetase was performed in a subset to confirm the initial diagnosis. RESULTS: A total of 10 possible cases of inflammatory HCA were identified in the pathology database. On the basis of glutamine synthetase staining performed for this study, three cases were rediagnosed as FNH and thus were excluded from the study. Therefore, a total of seven patients with inflammatory HCA were identified. On gadoxetic acid-enhanced MRI, four of these patients had classic features of FNH (group A, FNH mimics), and three had imaging features suggestive of HCA (group B, typical inflammatory HCA). Imaging features that were considered diagnostic of FNH included isointense or minimal T2 hyperintensity, arterial enhancement, and diffuse hyperintensity on hepatobiliary phase. Three of the four patients with FNH mimics had slides available for pathologic rereview, and the diagnosis of inflammatory HCA was supported by glutamine synthetase immunohistochemistry findings. The pathology reports of the remaining four cases were rereviewed and were also found to have features consistent with inflammatory HCA. CONCLUSION: Inflammatory HCA can mimic FNH on MRI, including hepatobiliary phase hyperintensity. Moreover, conventional pathology using histopathology alone may lead to misclassification of inflammatory HCA.

New approaches for precise response evaluation in hepatocellular carcinoma.

With the increasing clinical use of cytostatic and novel biologic targeted agents, conventional morphologic tumor burden assessments, including World Health Organization criteria and Response Evaluation Criteria in Solid Tumors, are confronting limitations because of their difficulties in distinguishing viable tumor from necrotic or fibrotic tissue. Therefore, the investigation for reliable quantitative biomarkers of therapeutic response such as metabolic imaging or functional imaging has been desired. In this review, we will discuss the conventional and new approaches to assess tumor burden. Since targeted therapy or locoregional therapies can induce biological changes much earlier than morphological changes, these functional tumor burden analyses are very promising. However, some of them have not gone thorough all steps for standardization and validation. Nevertheless, these new techniques and criteria will play an important role in the cancer management, and provide each patient more tailored therapy.

Performance of iterative reconstruction and automated tube voltage selection on the image quality and radiation dose in abdominal CT scans.

OBJECTIVE: To study the impact of sinogram-affirmed iterative reconstruction (SAFIRE) and concurrent application of automated tube voltage selection (ATVS) on image quality (IQ) and radiation dose. METHODS: A phantom was scanned using various computed tomography (CT) parameters (kV, 80-120; mAs, 50-200). Abdomen contrast-enhanced CT (CECTs) in 170 adults were performed using dose-modified protocols: in 145 patients (group I), ATVS was applied (mAs, 111-649); in 25 (group II), the kV was fixed at 120 (reference mAs, 150). In 95 patients, standard-dose (SD) scan was available. Two readers evaluated the IQ of filtered back projection (FBP) and SAFIRE (levels 1, 3, and 5) images. RESULTS: In phantom, nonlinear drop in noise with increasing strengths of IR (levels S1-S5) was noted. The dose-modified IR scan was rated diagnostic in all 170 patients, with IQ score comparable to that of SD-FBP (P = 0.3). Lower kV (100/80) was prescribed by ATVS in 70% examinations in group I. In comparison with SD-FBP, the mean dose in CT dose index in group I (IR, 3.2 mGy; SD-FBP, 13.02 mGy; P < 0.0001) and in group II (IR, 4.8 mGy; SD-FBP, 11.8 mGy; P < 0.001) was 75.4% and 59.3% lower. CONCLUSIONS: Use of SAFIRE and ATVS provides diagnostic quality images at 59.3% to 75.4% reduced dose compared with SD-FBP scan.

Dose-modified 256-MDCT of the abdomen using low tube current and hybrid iterative reconstruction.

RATIONALE AND OBJECTIVES: To evaluate the performance of hybrid iterative reconstruction technique (h-IRT) on image quality (IQ) in abdominal dose-modified (DM) scans in phantom and in patients in comparison to filtered back projection (FBP). MATERIALS AND METHODS: An anthropomorphic phantom was scanned using various kVp (80-140) and mAs (25-100) settings. Images were reconstructed with FBP and h-IRT levels (1-6). In 69 adults (59.6 ± 13.54 years; 20 male, 49 female), DM computed tomography (CT) scans were performed using 120 kVp and 100-120 mAs. In 25/69, 5-mm FBP and h-IRT (levels 1-4 and 5) images were analyzed to validate IQ. The subsequent 44/69 had FBP and h-IRT (level 4) images reconstructed. Two readers evaluated 188 image series for IQ, noise, and artifacts. Objective and subjective data were analyzed using t-test and Wilcoxon signed-rank test, respectively. In 46/69 patients, prior dose CT was available for dose comparison. RESULTS: In the phantom, noise reduction ranged from 12% (h-IRT level 1) to 50% (level 6). In patients, h-IRT level 4 images were rated diagnostic in 69/69 exams but DM-FBP images were found nondiagnostic in 20/69 patients. The size-specific dose estimate (SSDE) was reduced by 55% in the dose-modified CT group, (SSDE:4.55 ± 1.15 mGy) over the prior dose protocol (SSDE:10.21 ± 3.5 mGy, P < .0001). CONCLUSION: h-IRT improved IQ in abdominal DM-CT scans in phantom and in patients. Dose improvements were greater in smaller patients than larger ones.

Low-dose CT in clinical diagnostics.

INTRODUCTION: Computed tomography (CT) has become key for patient management due to its outstanding capabilities for detecting disease processes and assessing treatment response, which has led to expansion in CT imaging for diagnostic and image-guided therapeutic interventions. Despite these benefits, the growing use of CT has raised concerns as radiation risks associated with radiation exposure. AREAS COVERED: The purpose of this article is to familiarize the reader with fundamental concepts of dose metrics for assessing radiation exposure and weighting radiation-associated risks. The article also discusses general approaches for reducing radiation dose while preserving diagnostic quality. The authors provide additional insight for undertaking protocol optimization, customizing scanning techniques based on the patients' clinical scenario and demographics. Supplemental strategies are postulated using more advanced post-processing techniques for achieving further dose improvements. EXPERT OPINION: The technologic offerings of CT are integral to modern medicine and its role will continue to evolve. Although, the estimated risks from low levels of radiation of a single CT exam are uncertain, it is prudent to minimize the dose from CT by applying common sense solutions and using other simple strategies as well as exploiting technologic innovations. These efforts will enable us to take advantage of all the clinical benefits of CT while minimizing the likelihood of harm to patients.