Adaptive iterative dose reduction algorithm in CT: effect on image quality compared with filtered back projection in body phantoms of different sizes

Objective

To evaluate the impact of the adaptive iterative dose reduction (AIDR) three-dimensional (3D) algorithm in CT on noise reduction and the image quality compared to the filtered back projection (FBP) algorithm and to compare the effectiveness of AIDR 3D on noise reduction according to the body habitus using phantoms with different sizes.

Materials and Methods

Three different-sized phantoms with diameters of 24 cm, 30 cm, and 40 cm were built up using the American College of Radiology CT accreditation phantom and layers of pork belly fat. Each phantom was scanned eight times using different mAs. Images were reconstructed using the FBP and three different strengths of the AIDR 3D. The image noise, the contrast-to-noise ratio (CNR) and the signal-to-noise ratio (SNR) of the phantom were assessed. Two radiologists assessed the image quality of the 4 image sets in consensus. The effectiveness of AIDR 3D on noise reduction compared with FBP were also compared according to the phantom sizes.

Results

Adaptive iterative dose reduction 3D significantly reduced the image noise compared with FBP and enhanced the SNR and CNR (p < 0.05) with improved image quality (p < 0.05). When a stronger reconstruction algorithm was used, greater increase of SNR and CNR as well as noise reduction was achieved (p < 0.05). The noise reduction effect of AIDR 3D was significantly greater in the 40-cm phantom than in the 24-cm or 30-cm phantoms (p < 0.05).

Conclusion

The AIDR 3D algorithm is effective to reduce the image noise as well as to improve the image-quality parameters compared by FBP algorithm, and its effectiveness may increase as the phantom size increases.

Monopolar radiofrequency ablation using a dual-switching system and a separable clustered electrode: evaluation of the in vivo efficiency

OBJECTIVE

To determine the in vivo efficiency of monopolar radiofrequency ablation (RFA) using a dual-switching (DS) system and a separable clustered (SC) electrode to create coagulation in swine liver.

MATERIALS AND METHODS

Thirty-three ablation zones were created in nine pigs using a DS system and an SC electrode in the switching monopolar mode. The pigs were divided into two groups for two experiments: 1) preliminary experiments (n = 3) to identify the optimal inter-electrode distances (IEDs) for dual-switching monopolar (DSM)-RFA, and 2) main experiments (n = 6) to compare the in vivo efficiency of DSM-RFA with that of a single-switching monopolar (SSM)-RFA. RF energy was alternatively applied to one of the three electrodes (SSM-RFA) or concurrently applied to a pair of electrodes (DSM-RFA) for 12 minutes in in vivo porcine livers. The delivered RFA energy and the shapes and dimensions of the coagulation areas were compared between the two groups.

RESULTS

No pig died during RFA. The ideal IEDs for creating round or oval coagulation area using the DSM-RFA were 2.0 and 2.5 cm. DSM-RFA allowed more efficient RF energy delivery than SSM-RFA at the given time (23.0 ± 4.0 kcal vs. 16.92 ± 2.0 kcal, respectively; p = 0.0005). DSM-RFA created a significantly larger coagulation volume than SSM-RFA (40.4 ± 16.4 cm(3) vs. 20.8 ± 10.7 cm(3); p < 0.001). Both groups showed similar circularity of the ablation zones (p = 0.29).

CONCLUSION

Dual-switching monopolar-radiofrequency ablation using an SC electrode is feasible and can create larger ablation zones than SSM-RFA as it allows more RF energy delivery at a given time.

Shear wave elastography for liver stiffness measurement in clinical sonographic examinations: evaluation of intraobserver reproducibility, technical failure, and unreliable stiffness measurements

OBJECTIVES

The purpose of this study was to determine the optimal minimum number of liver stiffness measurements on shear wave elastography (SWE) and to evaluate the frequency of technical failures and unreliable stiffness measurements and the intraobserver reproducibility of SWE.

METHODS

This retrospective study was approved by our Institutional Review Board, and informed consent was waived. From August 2011 to January 2013, 540 patients underwent abdominal sonography, including SWE. In 86 patients (group 1), the minimum number of examinations was determined by comparing the intraclass correlation coefficient (ICC) of subsets of the first 2 to 14 measurements with that from 15 measurements. In 454 patients (group 2), 2 SWE sessions were performed in the right lobe within 1 day. Technical failure was defined as when no or little signal was obtained in the elastogram during the first 5 acquisitions; unreliable SWE results were defined as when the interquartile range/median liver stiffness value exceeded 30%. Intraobserver reproducibility was assessed using ICCs and Bland-Altman plots.

RESULTS

In group 1, the ICCs did not significantly increase after the first 6 measurements. In group 2, there were technical failures and unreliable results in 47 patients (10.35%) and 74 patients (16.29%), respectively. In 407 patients, after excluding technical failures, there was no significant difference in the median liver stiffness values between the 2 sessions (6.95 versus 6.86 kPa; P > .05). The overall intraobserver reproducibility was excellent (ICC, 0.95).

CONCLUSIONS

In this study, the optimal minimum number of SWE measurements was 6, and SWE using 6 measurements showed excellent intraobserver reproducibility.

Prospective comparison of 3T MRI with diffusion-weighted imaging and MDCT for the preoperative TNM staging of gastric cancer

PURPOSE

To compare the diagnostic performance of 3T magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) and multidetector-row computed tomography (MDCT) for the preoperative TNM staging of gastric cancer.

MATERIALS AND METHODS

This prospective study was approved by our Institutional Review Board. Forty-nine consecutive patients with histologically confirmed gastric cancers underwent MDCT and 3T MRI followed by surgery. MRI without DWI, MRI with DWI, and MDCT were reviewed to determine preoperative TNM staging. Using the pathologic stages as the reference standard, the diagnostic performance of each imaging modality was compared.

RESULTS

Diagnostic accuracies of MRI with DWI, MRI without DWI, and MDCT did not show a significant difference (≤T2 vs. ≥T3: 85.1%, 78.7%, and 80.9%; ≤T3 vs. T4: 76.6%, 74.5%, and 72.3%; N-negative vs. N-positive: 76.6%, 66.0%, and 63.8%; M0 vs. M1: all 95.9%, respectively) (P > 0.05). For N staging, MRI with DWI demonstrated higher sensitivity but lower specificity (86.7% and 58.8%, respectively) than MRI without DWI (50.0% and 94.1%) or MDCT (43.3% and 100%) (P < 0.05).

CONCLUSION

The diagnostic accuracy of 3T MRI is comparable to that of MDCT for the preoperative TNM staging of gastric cancer, and for assessing LN metastasis, the addition of DWI to conventional MRI may increase the sensitivity.

Hepatic steatosis in living liver donor candidates: preoperative assessment by using breath-hold triple-echo MR imaging and 1H MR spectroscopy

PURPOSE

To evaluate the diagnostic performance of both breath-hold T2*-corrected triple-echo spoiled gradient-echo water-fat separation magnetic resonance (MR) imaging (triple-echo imaging) and high-speed T2-corrected multiecho hydrogen 1 ((1)H) MR spectroscopy in the assessment of macrovesicular hepatic steatosis in living liver donor candidates by using histologic assessment as a reference standard.

MATERIALS AND METHODS

The institutional review board approved this retrospective study with waiver of the need to obtain informed consent. One hundred eighty-two liver donor candidates who had undergone preoperative triple-echo imaging and single-voxel (3 × 3 × 3 cm) MR spectroscopy performed with a 3.0-T imaging unit and who had also undergone histologic evaluation of macrovesicular steatosis were included in this study. In part 1 of the study (n = 84), the Pearson correlation coefficient was calculated. Receiver operating characteristic (ROC) curve analysis was performed to detect substantial (≥10%) macrovesicular steatosis. In part 2 of the study, with a different patient group (n = 98), diagnostic performance was evaluated by using the diagnostic cutoff values determined in part 1 of the study.

RESULTS

The correlation coefficients of triple-echo MR imaging and MR spectroscopy with macrovesicular steatosis were 0.886 and 0.887, respectively. The areas under the ROC curve for detection of substantial macrovesicular steatosis were 0.959 and 0.988, with cutoff values of 4.93% and 5.79%, respectively, and without a significant difference (P = .328). In the part 2 study group, sensitivity and specificity were 90.9% (10 of 11) and 86.2% (75 of 87) for triple-echo MR imaging and 90.9% (10 of 11) and 86.2% (75 of 87) for MR spectroscopy, respectively.

CONCLUSION

Either breath-hold triple-echo MR imaging or MR spectroscopy can be used to detect substantial macrovesicular steatosis in living liver donor candidates. In the future, this may allow selective biopsy in candidates who are expected to have substantial macrovesicular steatosis on the basis of MR-based hepatic fat fraction.

Intravoxel incoherent motion diffusion-weighted MR imaging for characterization of focal pancreatic lesions

PURPOSE

To evaluate the diagnostic potential of apparent diffusion coefficient (ADC) and intravoxel incoherent motion (IVIM)-derived parameters for differentiation of common pancreatic tumors, chronic pancreatitis, and normal pancreas and for characterization of the malignancy potential of intraductal papillary mucinous neoplasms (IPMNs).

MATERIALS AND METHODS

The institutional review board approved this retrospective study, and informed consent was waived. Ninety-three consecutive patients with surgically resected and pathologically confirmed pancreatic tumors (39 pancreatic adenocarcinomas [PACs], 17 neuroendocrine tumors [NETs], and 37 IPMNs), seven patients with chronic pancreatitis, and 26 patients with a normal pancreas were included in this study. All patients underwent pancreatic 3.0-T magnetic resonance imaging, including IVIM diffusion-weighted imaging with 10 b values used (from 0 to 1000 sec/mm(2)). The ADC, slow component of diffusion (D(slow)), incoherent microcirculation (D(fast)), and perfusion fraction (f) were calculated. Steel-Dwass and Mann-Whitney U tests were used for comparison. The diagnostic performance of the parameters was evaluated by using receiver operating characteristic (ROC) analysis with Bonferroni correction.

RESULTS

Among ADC- and IVIM-derived parameters, D(fast) and f values of PACs were significantly lower than those of normal pancreas, chronic pancreatitis, and NETs (all P < .05 in post hoc analyses). For differentiation of PACs from NETs, f and D(fast) showed a significant difference (P < .0001 for both) and were more useful parameters than ADC and D(slow) in ROC analysis (all P < .05). Malignant IPMNs had significantly lower ADC and D(slow) values and higher D(fast) and f values when compared with benign IPMNs (all P < .05). In ROC analysis, f showed the highest area under the ROC curve value for distinguishing malignant from benign IPMNs.

CONCLUSION

IVIM-derived perfusion-related parameters could be helpful for the differentiation of common malignant tumors in the pancreas and for distinguishing malignant from benign IPMNs. D(fast) and f were more valuable parameters in the differentiation of PACs from NETs than were ADC and D(slow).

Preoperative staging of gallbladder carcinoma using biliary MR imaging

PURPOSE

To evaluate the performance of biliary MRI, including unenhanced imaging, gadolinium-enhanced (Gd-E) dynamic imaging, and MR cholangiography, for the preoperative staging of gallbladder cancer (GBC).

MATERIALS AND METHODS

Our institutional review board approved this retrospective study. Eighty-six, consecutive patients with surgically resected and pathologically confirmed GBCs and who underwent preoperative MRI, including unenhanced T1- and T2-weighted images, MR cholangiography, and dynamic imaging, were enrolled in this study. Two observers independently evaluated the biliary MR images regarding the T- and N-staging of GBCs and graded their diagnostic confidence for the staging using a 5-point scale. Receiver operating curve analysis was performed to evaluate the diagnostic performance of MR in the staging of GBC. Interobserver agreement was evaluated using kappa statistics.

RESULTS

The overall accuracy of T- and N-staging using biliary MRI was 84.9% and 77.9% for observer 1 and 69.8% and 74.4% for observer 2. There was good interobserver agreement regarding the T stage (k = 0.828). The Az (AUC: area under the curve) values of the diagnostic ability of MRI to differentiate ≥ T1b from ≤ T1a lesions, were 0.979 and 0.955 for both observers (P < 0.0001).

CONCLUSION

Biliary MRI with MR cholangiography allows moderately accurate preoperative T staging and N staging of GBCs. It also shows an excellent diagnostic ability for differentiating ≥ T1b lesions from ≤ T1a lesions, which can be helpful for preoperative planning.

Early quantification of the therapeutic efficacy of the vascular disrupting agent, CKD-516, using dynamic contrast-enhanced ultrasonography in rabbit VX2 liver tumors

Purpose:

To evaluate the usefulness of dynamic contrast-enhanced ultrasonography (DCE-US) in the early quantification of hemodynamic change following administration of the vascular disrupting agent (VDA) CKD-516 using a rabbit VX2 liver tumor model.

Methods:

This study was approved by our institutional animal care and use committee. Eight VX2 liver-tumor-bearing rabbits were treated with intravenous CKD-516, and all underwent DCE-US using SonoVue before and again 2, 4, 6, and 24 hours following their treatment. The tumor perfusion parameters were obtained from the time-intensity curve of the DCE-US data. Repeated measures analysis of variance was performed to assess any significant change in tumor perfusion over time. Relative changes in the DCE-US parameters between the baseline and follow-up assessments were correlated with the relative changes in tumor size over the course of seven days using Pearson correlation.

Results:

CKD-516 treatment resulted in significant changes in the DCE-US parameters, including the peak intensity, total area under the time-intensity curve (AUC_total), and AUC during wash-out (AUC_out) over time (P<0.05). Pairwise comparison tests revealed that the AUC_total and AUC during wash-in (AUC_in) seen on the two-hour follow-up were significantly lower than the baseline values (P<0.05). However, none of early changes in the DCE-US parameters until 24-hour follow-up showed a significant correlation with the relative changes in tumor size during seven days after CKD-516 treatment.

Conclusion:

Our results suggest that a novel VDA (CKD-516) can cause disruption of tumor perfusion as early as two hours after treatment and that the therapeutic effect of CKD-516 treatment can be effectively quantified using DCE-US.

Differentiation of large (≥ 5 cm) gastrointestinal stromal tumors from benign subepithelial tumors in the stomach: radiologists' performance using CT

PURPOSE

To identify significant CT findings for the differentiation of large (≥ 5 cm) gastric gastrointestinal stromal tumors (GIST) from benign subepithelial tumors and to assess whether radiologists' performance in differentiation is improved with knowledge of significant CT criteria.

MATERIALS AND METHODS

One-hundred twenty patients with pathologically proven large (≥ 5 cm) GISTs (n=99), schwannomas (n=16), and leiomyomas (n=5) who underwent CT were enrolled. Two radiologists (A and B) retrospectively reviewed their CT images in consensus for the location, size, degree and pattern of enhancement, contour, growth pattern and the presence of calcification, necrosis, surface ulceration, or enlarged lymph nodes. CT findings considered significant for differentiation were determined using uni- and multivariate statistical analyses. Thereafter, two successive review sessions for the differentiation of GIST from non-GIST were independently performed by two other reviewers (C and D) with different expertise of 2 and 9 years using a 5-point confidence scale. At the first session, reviewers interpreted CT images without knowledge of significant CT findings. At the second session, the results of statistical analyses were provided to the reviewers. To assess improvement in radiologists' performance, a pairwise comparison of receiver operating curves (ROC) was performed.

RESULTS

Heterogeneous enhancement, presence of necrosis, absence of lymph nodes, and mean size of ≥ 6 cm were found to be significant for differentiating GIST from schwannoma (P<0.05). Non-cardial location, heterogeneous enhancement, and presence of necrosis were differential CT features of GIST from leiomyoma (P<0.05). Multivariate analyses indicated that absence of enlarged LNs was the only statistically significant variable for GIST differentiating from schwannoma. The area under the curve of both reviewers obtained using ROC significantly increased from 0.682 and 0.613 to 0.903 and 0.904, respectively, with information of the significant CT findings differentiating GISTs from non-GISTs (P<0.001).

CONCLUSION

Non-cardial location, heterogeneous enhancement, presence of necrosis, larger lesion size, and absence of lymphadenopathy are highly suggestive CT findings for large GISTs in differentiation from schwannomas or leiomyomas. Regardless of radiologists' expertise, diagnostic performance in differentiation can be significantly improved with knowledge of these CT findings.

MR imaging in patients with suspected liver metastases: value of liver-specific contrast agent gadoxetic acid

Objective

To compare the diagnostic performance of gadoxetic acid-enhanced magnetic resonance (MR) imaging with that of triple-phase multidetector-row computed tomography (MDCT) in the detection of liver metastasis.

Materials and Methods

Our institutional review board approved this retrospective study and waived informed consent. The study population consisted of 51 patients with hepatic metastases and 62 patients with benign hepatic lesions, who underwent triple-phase MDCT and gadoxetic acid-enhanced MRI within one month. Two radiologists independently and randomly reviewed MDCT and MRI images regarding the presence and probability of liver metastasis. In order to determine additional value of hepatobiliary-phase (HBP), the dynamic-MRI set alone and combined dynamic-and-HBP set were evaluated, respectively. The standard of reference was a combination of pathology diagnosis and follow-up imaging. For each reader, diagnostic accuracy was compared using the jackknife alternative free-response receiver-operating-characteristic (JAFROC).

Results

For both readers, average JAFROC figure-of-merit (FOM) was significantly higher on the MR image sets than on the MDCT images: average FOM was 0.582 on the MDCT, 0.788 on the dynamic-MRI set and 0.847 on the combined HBP set, respectively (p < 0.0001). The differences were more prominent for small (≤ 1 cm) lesions: average FOM values were 0.433 on MDCT, 0.711 on the dynamic-MRI set and 0.828 on the combined HBP set, respectively (p < 0.0001). Sensitivity increased significantly with the addition of HBP in gadoxetic acid-enhanced MR imaging (p < 0.0001).

Conclusion

Gadoxetic acid-enhanced MRI shows a better performance than triple-phase MDCT for the detection of hepatic metastasis, especially for small (≤ 1 cm) lesions.

Dynamic contrast-enhanced MRI to evaluate the therapeutic response to neoadjuvant chemoradiation therapy in locally advanced rectal cancer

PURPOSE

To evaluate the usefulness of perfusion parameters derived from dynamic contrast-enhanced MR imaging (DCE-MRI) for assessing the therapeutic response to neoadjuvant chemoradiation therapy (CRT) for locally advanced rectal cancer (LARC).

MATERIALS AND METHODS

Fifty patients with LARC (≥T3 or lymph-node metastasis) who underwent CRT and subsequent surgery, were included in this study. All patients underwent pre- and post-CRT DCE-MRI on a 1.5 Tesla unit. By using a postprocessing software, the following perfusion parameters (K(trans) , kep , ve ) were measured for tumor. Those perfusion parameters were compared not only between the T-downstaged group and the nondownstaged group, but also before and after CRT in each group.

RESULTS

After CRT, the mean K(trans) (min(-1) ) significantly decreased from 1.24 ± 0.53 to 0.76 ± 0.45 in the T-downstaged group (n = 24) (P = 0.0007), whereas it did not significantly decrease in the nondownstaged group (n = 26) (from 1.02 ± 0.53 to 0.87 ± 0.48, P = 0.24). The percentage difference between pre- and post-CRT K(trans) in the T-downstaged group was significantly higher than that in the nondownstaged group (43%, 16%, respectively, P = 0.0092). However, none of the other parameters showed significant differences.

CONCLUSION

A large decrease in the mean K(trans) after CRT was associated with a good therapeutic response to CRT for LARC.

Pulsed high-intensity focused ultrasound enhances apoptosis of pancreatic cancer xenograft with gemcitabine

We sought to investigate whether concurrent exposure to pulsed high-intensity focused ultrasound (HIFU) and the chemotherapeutic drug gemcitabine would enhance apoptosis in pancreatic cancer. A pancreatic cancer xenograft model was established using BALB/c nude mice and human pancreatic cancer cells (PANC-1). In the first study, mice were randomly allocated into one of four groups: control (n = 4), HIFU alone (n = 4), gemcitabine (GEM) alone (n = 28) and concurrent treatment with HIFU and gemcitabine (HIGEM) (n = 28). The GEM and HIGEM groups were subdivided into four subgroups (16 mice) according to the drug dose injected (50-200 mg/kg) and another four subgroups (16 mice) according to the time interval between drug injection and HIFU treatment (each subgroup, n = 4). Apoptosis rates were evaluated using the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) assay and percentage of necrosis, as evaluated with Harris' hematoxylin solution and eosin Y stain, 3 d after treatment. The second study was performed to evaluate tumor growth rates of the four groups. Each group was treated weekly for 3 wk, and tumor size was periodically measured for up to 4 wk from the beginning of treatment. In the first study, overall rates of apoptosis were significantly higher in the HIGEM group than in the GEM group (p = 0.02). In a subgroup analysis, HIGEM was superior to GEM in enhancing apoptosis at gemcitabine dosages of 150-200 mg/kg gemcitabine and intervals between gemcitabine and HIFU less than 2 h (p = 0.01). In the second study, HIGEM treatment resulted in the slowest tumor growth. However, despite a visible distinction, none of the differences found between the HIGEM and GEM groups were statistically significant (p > 0.05). Treatment with both HIFU and gemcitabine might enhance cell apoptosis and reduce tumor growth in pancreatic carcinoma. For this concurrent treatment, a high dosage of gemcitabine and a short-term delay before HIFU are recommended to maximize the therapeutic effect.

Intravoxel incoherent motion diffusion-weighted MR imaging of hepatocellular carcinoma: correlation with enhancement degree and histologic grade

PURPOSE

To compare the association of intravoxel incoherent motion (IVIM)-derived parameters and apparent diffusion coefficient (ADC) with the histologic grade of hepatocellular carcinoma (HCC) and evaluate the relationship between IVIM-derived parameters and arterial enhancement degree.

MATERIALS AND METHODS

This retrospective study was institutional review board-approved, and informed consent was waived. Forty patients with 42 surgically confirmed HCCs underwent diffusion-weighted magnetic resonance (MR) imaging with eight b values (0-800 sec/mm(2)). ADC, diffusion coefficient (D), pseudodiffusion coefficient, and perfusion fraction (f) were calculated. Two radiologists determined the enhancement degree in consensus, as well as the percentage of arterial enhancement of HCC. The relationship between the parameters and histologic grade, as well as arterial enhancement, was assessed by using the Spearman or Pearson correlation test. Receiver operating characteristic (ROC) analysis of discrimination between low-grade (grades 1 and 2) and high-grade (grades 3 and 4) HCC was performed for D and ADC values.

RESULTS

D and ADC values were both significantly correlated with histologic grade: r = -0.604 (P < .0001) and r = -0.448 (P = .002), respectively. D and ADC values were both significantly lower in high-grade HCC (D = [0.99 ± 0.13] × 10(-3)mm(2)/sec, ADC = [1.13 ± 0.14] × 10(-3)mm(2)/sec) than in low-grade HCC (D = [1.18 ± 0.16] × 10(-3)mm(2)/sec, ADC = [1.25 ± 0.17] × 10-(3)mm(2)/sec) (P < .0001 and P = .029, respectively). However, ROC analysis demonstrated a higher area under the ROC curve value for D than for ADC for differentiating high-grade HCC from low-grade HCC (0.838 vs 0.728; P = .026). The percentage of arterial enhancement was correlated with f (r = 0.621, P < .0001).

CONCLUSION

IVIM-derived D values of HCC showed significantly better diagnostic performance than ADC values in differentiating high-grade HCC from low-grade HCC, and significant correlation was observed between f and the percentage of arterial enhancement.

Radiofrequency ablation of hepatocellular carcinoma as first-line treatment: long-term results and prognostic factors in 162 patients with cirrhosis

PURPOSE

To evaluate the long-term outcomes of radiofrequency ablation (RFA) as a first-line therapy for early-stage hepatocellular carcinoma (HCC) and determine the prognostic factors for survival.

MATERIALS AND METHODS

The institutional review board approved this retrospective study. From January 2006 to December 2007, 162 consecutive patients with cirrhosis (Child-Pugh class A and B, 137 and 25 patients, respectively) who underwent RFA as a first-line treatment for up to three HCCs with a maximum diameter of 5 cm (182 HCCs; mean diameter ± standard deviation, 2.59 cm ± 0.79; 17 multinodular forms) were included. After a mean follow-up of 50.3 months ± 19.9, results were analyzed for tumor recurrence, as well as overall and recurrence-free survival time. The Kaplan-Meier method and Cox proportional hazards regression model were used to evaluate the prognostic factors.

RESULTS

The cumulative incidence of local tumor progression (LTP) was 14.5% at 5 years, with tumor size as the only significant predictive factor (relative risk = 2.13, P = .007). Overall 5-year survival and recurrence-free survival rates were 67.9% and 25.9%, respectively. Significant predictive factors for poor overall survival were Child-Pugh class B (relative risk = 2.43, P = .011), serum α-fetoprotein level (relative risk per 100 units = 1.01; P < .001), and presence of portosystemic collaterals (relative risk = 2.15, P = .025). The development of LTP significantly shortened median recurrence-free survival (28.0 months without LTP vs 12.0 months with LTP) and necessitated a higher number of interventional procedures (2.2 sessions without LTP vs 5.1 sessions with LTP).

CONCLUSION

RFA is a safe and effective first-line treatment for early-stage HCC, with a 5-year survival rate of 67.9%. High serum α-fetoprotein level, advanced Child-Pugh class, and presence of portosystemic collateral vessels had a significant negative effect on overall survival.

Nonalcoholic fatty liver disease: intravoxel incoherent motion diffusion-weighted MR imaging-an experimental study in a rabbit model

PURPOSE

To evaluate the feasibility of using intravoxel incoherent motion (IVIM) diffusion-weighted imaging with multiple b values for the noninvasive diagnosis of nonalcoholic fatty liver disease (NAFLD).

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. Twenty-seven 8-week-old rabbits were fed a variety of diets (from a standard diet to a high-fat, high-cholesterol diet) before IVIM diffusion-weighted imaging was performed with seven b values by using a 3-T magnetic resonance (MR) imaging unit. At histologic analysis of the animals, livers were categorized by NAFLD severity as normal, NAFLD, borderline nonalcoholic steatohepatitis (NASH), or NASH. The apparent diffusion coefficient and IVIM-derived parameters including true diffusion coefficient, pseudodiffusion coefficient, and perfusion fraction of the liver parenchyma were measured. Each parameter was correlated with NAFLD severity, and optimal cutoff values were determined by means of receiver operating characteristics analysis.

RESULTS

Perfusion fraction was significantly lower in rabbits with NAFLD than in those with a normal liver, and it decreased further as severity of NAFLD increased, with medians of 22.2%, 14.8%, 11.3%, and 9.5% in the rabbits in the normal, NAFLD, borderline, and NASH groups, respectively (ρ = -0.83, P < .001). Apparent diffusion coefficient, true diffusion coefficient, and pseudodiffusion coefficient were not significantly different between the NAFLD severity groups. In terms of the diagnostic performance of perfusion fraction, area under the curve values were 0.984 (normal vs NAFLD or more severe disease), 0.959 (NAFLD or less severe vs borderline or more severe disease), and 0.903 (borderline or less severe vs NASH) with optimal cutoff values of 15.2%, 13.2%, and 11.0%, respectively.

CONCLUSION

Perfusion fractions extracted from IVIM diffusion-weighted imaging may help in the differentiation of early stage NASH from simple steatosis.

Nonalcoholic Fatty Liver Disease: Intravoxel Incoherent Motion Diffusion-weighted MR Imaging-An Experimental Study in a Rabbit Model

Purpose To evaluate the feasibility of using intravoxel incoherent motion (IVIM) diffusion-weighted imaging with multiple b values for the noninvasive diagnosis of nonalcoholic fatty liver disease (NAFLD). Materials and Methods This study was approved by the institutional animal care and use committee. Twenty-seven 8-week-old rabbits were fed a variety of diets (from a standard diet to a high-fat, high-cholesterol diet) before IVIM diffusion-weighted imaging was performed with seven b values by using a 3-T magnetic resonance (MR) imaging unit. At histologic analysis of the animals, livers were categorized by NAFLD severity as normal, NAFLD, borderline nonalcoholic steatohepatitis (NASH), or NASH. The apparent diffusion coefficient and IVIM-derived parameters including true diffusion coefficient, pseudodiffusion coefficient, and perfusion fraction of the liver parenchyma were measured. Each parameter was correlated with NAFLD severity, and optimal cutoff values were determined by means of receiver operating characteristics analysis. Results Perfusion fraction was significantly lower in rabbits with NAFLD than in those with a normal liver, and it decreased further as severity of NAFLD increased, with medians of 22.2%, 14.8%, 11.3%, and 9.5% in the rabbits in the normal, NAFLD, borderline, and NASH groups, respectively (ρ = -0.83, P < .001). Apparent diffusion coefficient, true diffusion coefficient, and pseudodiffusion coefficient were not significantly different between the NAFLD severity groups. In terms of the diagnostic performance of perfusion fraction, area under the curve values were 0.984 (normal vs NAFLD or more severe disease), 0.959 (NAFLD or less severe vs borderline or more severe disease), and 0.903 (borderline or less severe vs NASH) with optimal cutoff values of 15.2%, 13.2%, and 11.0%, respectively. Conclusion Perfusion fractions extracted from IVIM diffusion-weighted imaging may help in the differentiation of early stage NASH from simple steatosis. © RSNA, 2013.

Usefulness of MR elastography for predicting esophageal varices in cirrhotic patients

PURPOSE

To evaluate the usefulness of magnetic resonance elastography (MRE) as a noninvasive tool for predicting esophageal varices and identifying high-risk varices.

MATERIALS AND METHODS

In all, 126 patients with liver cirrhosis, and who underwent both MRI including MRE of the liver as well as upper gastrointestinal endoscopy for variceal screening within 1 month before or after the MRI, were included in this study. The relationship between the liver stiffness values measured by MRE and the degree of esophageal varices was assessed using Spearman's correlation analysis. In addition, the diagnostic performance of MRE for predicting the presence of varices or high-risk varices (grade≥II) was evaluated using the receiver-operating characteristics (ROC) curves.

RESULTS

The mean stiffness values of liver parenchyma measured on MRE were well correlated with the grade of esophageal varices (r=0.63). In addition, the MRE-based liver stiffness values were significantly lower in the lower-risk group than in the higher-risk group (P<0.0001). The area under the ROC curve values of MRE for predicting the presence of varices or high-risk varices (grade≥II) were 0.859 and 0.810, respectively. Using a liver stiffness cutoff value of 5.803 kPa, the sensitivity, specificity, positive predictive value, and negative predictive value for predicting high-grade (≥II) esophageal varices were 96%, 60%, 36%, and 98%, respectively.

CONCLUSION

The MRE-based liver stiffness value may be useful for noninvasively predicting esophageal varices and identifying high-risk varices in cirrhotic patients.

Lymphoepithelial cyst of the pancreas: comparison of CT findings with other pancreatic cystic lesions

OBJECTIVE

To describe the CT findings of lymphoepithelial cysts (LECs) of the pancreas and to investigate the differential findings between LECs and other pancreatic cystic lesions.

MATERIALS AND METHODS

Fifty-eight patients with 8 LECs (M:F = 7:1; mean age 55.1 years), 30 serous cystadenomas (SCA) (M:F = 11:19; 52.5 years), 11 mucinous cystadenomas (MCA) (M:F = 0:11; 47.2 years), and 9 pseudocysts (M:F = 6:3; 50.8 years) were included in this study. Two radiologists analyzed all CT images for 3D location, outer shape, appearance, the presence of calcification, enhancing nodule, and pancreatic duct dilatation. Size of lesions and CT number of cystic portion on precontrast CT were measured. For statistical analysis, Mann-Whitney U test and Fisher's exact test were used.

RESULTS

75 % (6/8) of LECs showed an extrapancreatic location than all other cystic diseases in terms of 3D location (p < 0.0001). LECs showed variable outer shape without a significant difference from that of SCAs and pseudocysts (p > 0.05), but LECs showed microlobulated surface more frequently than the MCAs (p < 0.05). LECs showed a variable appearance from unilocular to multi-microcystic. CT attenuation of LECs (21.2 ± 7.1 HU) was higher than that of SCAs and MCAs (p = 0.005). Size of LECs (34.0 ± 10.8 mm) was smaller than that of MCAs (p = 0.040). There was no calcification, pancreatic duct dilatation, or enhancing nodules in LECs.

CONCLUSION

LECs appear as a highly exophytic medium-sized cystic mass with various morphology occurring predominantly in the middle-aged or older male patients.

Acoustic radiation force impulse elastography for focal hepatic tumors: usefulness for differentiating hemangiomas from malignant tumors

Objective

The purpose of this study is to investigate whether acoustic radiation force impulse (ARFI) elastography with ARFI quantification and ARFI 2-dimensional (2D) imaging is useful for differentiating hepatic hemangiomas from malignant hepatic tumors.

Materials and Methods

One-hundred-and-one tumors in 74 patients were included in this study: 28 hemangiomas, 26 hepatocellular carcinomas (HCCs), three cholangiocarcinomas (CCCs), 20 colon cancer metastases and 24 other metastases. B-mode ultrasound, ARFI 2D imaging, and ARFI quantification were performed in all tumors. Shear wave velocities (SWVs) of the tumors and the adjacent liver and their SWV differences were compared among the tumor groups. The ARFI 2D images were compared with B-mode images regarding the stiffness, conspicuity and size of the tumors.

Results

The mean SWV of the hemangiomas was significantly lower than the malignant hepatic tumor groups: hemangiomas, 1.80 ± 0.57 m/sec; HCCs, 2.66 ± 0.94 m/sec; CCCs, 3.27 ± 0.64 m/sec; colon cancer metastases, 3.70 ± 0.61 m/sec; and other metastases, 2.82 ± 0.96 m/sec (p < 0.05). The area under the receiver operating characteristics curve of SWV for differentiating hemangiomas from malignant tumors was 0.86, with a sensitivity of 96.4% and a specificity of 65.8% at a cut-off value of 2.73 m/sec (p < 0.05). In the ARFI 2D images, the malignant tumors except HCCs were stiffer and more conspicuous as compared with the hemangiomas (p < 0.05).

Conclusion

ARFI elastography with ARFI quantification and ARFI 2D imaging may be useful for differentiating hepatic hemangiomas from malignant hepatic tumors.

Dual switching monopolar radiofrequency ablation using a separable clustered electrode: comparison with consecutive and switching monopolar modes in ex vivo bovine livers

Objective

To compare the in-vitro efficiency of dual-switching monopolar (DSM) radiofrequency ablation (RFA) using a separable clustered electrode (Octopus® electrodes) with consecutive monopolar (CM) and switching monopolar (SM) RFA techniques to create an ablative zone in the explanted bovine liver.

Materials and Methods

For DSM-RFA, we used a prototype, three-channel, dual generator RFA Unit and Octopus® electrodes with three, 17 gauge internally cooled electrodes. The RFA Unit allowed simultaneous radiofrequency (RF) energy delivery to two electrodes of the Octopus® electrodes as well as automatic switching among the three electrode pairs according to the impedance changes. RF energy was sequentially applied to one of the three electrodes for 24 minutes (group A; CM mode, n = 10) or alternatively applied for 12 minutes (group B; SM mode, n = 10) or concurrently applied to a pair of electrodes for 12 minutes (group C; DSM mode, n = 10) in explanted bovine livers. Changes in the impedance and current during RFA as well as the dimensions of the thermal ablative zones were compared among the three groups.

Results

The mean, delivered RF energy amounts in groups A, B, and C were 63.15 ± 8.6 kJ, 72.13 ± 5.4 kJ, and 106.08 ± 13.4 kJ, respectively (p < 0.001). The DSM mode created a significantly larger ablation volume than did the other modes, i.e., 68.1 ± 10.2 cm³ (group A), 92.0 ± 19.9 cm³ (group B), and 115.1 ± 14.0 cm³ (group C) (p < 0.001). The circularity in groups A, B, and C were 0.84 ± 0.06, 0.87 ± 0.04 and 0.90 ± 0.03, respectively (p = 0.03).

Conclusion

DSM-RFA using Octopus® electrodes can help create large ablative zones within a relatively short time.

Evaluation of hepatic focal lesions using diffusion-weighted MR imaging: comparison of apparent diffusion coefficient and intravoxel incoherent motion-derived parameters

PURPOSE

To determine whether parameters obtained from intravoxel incoherent motion (IVIM)-diffusion-weighted imaging (DWI) using multiple b-values can improve characterization of common focal liver lesions (FLLs), compared with the apparent diffusion coefficient (ADCtotal ).

MATERIALS AND METHODS

Our Institutional Review Board approved this retrospective study and informed consent was waived. In all, 142 patients with 169 FLLs underwent liver magnetic resonance imaging (MRI) including IVIM-DWI with multiple b factors at 3.0T. ADCtotal and IVIM-DWI-derived parameters including true diffusion (Dt ), pseudodiffusion (Dp ), and perfusion fraction (f) were calculated for each lesion and compared using dedicated software.

RESULTS

Dt and ADCtotal were significantly lower in malignancies (0.95 ± 0.21, 1.14 ± 0.24, (×10(-3) mm(2) /sec)) than in benign FLLs (1.61 ± 0.34, 1.72 ± 0.37, (×10(-3) mm(2) /sec)). In the differential diagnosis of malignancies from benign lesions, Dt (Az value: 0.971) showed better diagnostic performance than ADCtotal (Az: 0.933) (P < 0.0005). Dt (Az: 0.961) also showed better diagnostic performance than ADCtotal (Az: 0.919) in differentiating hypervascular malignancies from benign hypervascular FLLs (P < 0.0005). In addition, Dp and f were significantly higher in hypervascular FLLs (35.74 ± 20.08 (×10(-3) mm(2) /sec), 28.14 ± 11.82 (%)) than hypovascular FLLs (21.87 ± 13.8 (×10(-3) mm(2) /sec), 12.2 ± 5.92 (%)) (P < 0.0001).

CONCLUSION

Dt provided better diagnostic performance than ADCtotal in differentiating benign from malignant lesions. Dp and f were significant parameters for diagnosing hypervascular FLLs.