Purpose To assess the determinants of technical failure of magnetic resonance (MR) elastography of the liver in a large single-center study. Materials and Methods This retrospective study was approved by the institutional review board. Seven hundred eighty-one MR elastography examinations performed in 691 consecutive patients (mean age, 58 years; male patients, 434 [62.8%]) in a single center between June 2013 and August 2014 were retrospectively evaluated. MR elastography was performed at 3.0 T (n = 443) or 1.5 T (n = 338) by using a gradient-recalled-echo pulse sequence. MR elastography and anatomic image analysis were performed by two observers. Additional observers measured liver T2* and fat fraction. Technical failure was defined as no pixel value with a confidence index higher than 95% and/or no apparent shear waves imaged. Logistic regression analysis was performed to assess potential predictive factors of technical failure of MR elastography. Results The technical failure rate of MR elastography at 1.5 T was 3.5% (12 of 338), while it was higher, 15.3% (68 of 443), at 3.0 T. On the basis of univariate analysis, body mass index, liver iron deposition, massive ascites, use of 3.0 T, presence of cirrhosis, and alcoholic liver disease were all significantly associated with failure of MR elastography (P < .004); but on the basis of multivariable analysis, only body mass index, liver iron deposition, massive ascites, and use of 3.0 T were significantly associated with failure of MR elastography (P < .004). Conclusion The technical failure rate of MR elastography with a gradient-recalled-echo pulse sequence was low at 1.5 T but substantially higher at 3.0 T. Massive ascites, iron deposition, and high body mass index were additional independent factors associated with failure of MR elastography of the liver with a two-dimensional gradient-recalled-echo pulse sequence. RSNA, 2017.

Epoxy-imide resins were obtained by curing the epoxy resin Araldite GY 250 (DGEBA; difunctional) and Araldite EPN 1138 (Novolac epoxy; polyfunctional) with the diimide-diacid, 2,2-bis[4-(4-trimellitimidophenoxy)phenyl]propane. The adhesive lap shear strength of epoxy-imide resins at room temperature and at 100 and 150°C was determined on a stainless-steel substrate. The effect of solvent on the adhesive strength of epoxy-imide resins was studied, and tetrahydrofuran was found to give the best results for improving the wetting behavior of epoxy resins. It is observed that with the increase in imide content the adhesive strength at room temperature as well as at elevated temperature increases when tetrahydrofuran is used as a solvent in the adhesive formulation. The room temperature adhesive strength for GY 250-based systems is in the range of 20.8 -23.5 MPa and 45-58% of this strength is retained at 150°C. For EPN 1138-based systems, the room temperature adhesive strength is in the range of 14.3-20.3 MPa, and in fact, an increase in adhesive strength by 1-26% is observed at 150°C. All these systems are stable up to 370°C, and char residues of GY 250-and EPN 1138-based systems at 800°C are in the range of 27-31 and 33-41%, respectively, in nitrogen atmosphere. The overall thermal stability and retention of room temperature adhesive strength at elevated temperature are higher for EPN 1138-based systems when compared to those of GY 250-based systems, and this observation has been attributed to the higher crosslinking possible for EPN-based systems when compared to GY 250-based systems.

Epoxy-imide resins obtained through the reaction of epoxy resins such as Araldite 1 GY 250=Araldite 1 EPN 1138 with N-(4-and 3-carboxyphenyl)trimellitimides (IDA-I and IDA-II, respectively) have been modified with 10 wt% of epoxidized hydroxyl-terminated polybutadiene (EHTPB), 10 phr of carboxyl-terminated butadiene-acrylonitrile liquid copolymer (CTBN-L), and 10 phr of carboxyl-terminated butadiene-acrylonitrile solid copolymer (CTBN-S) without sacrificing much of their performance at elevated temperatures. Adhesive lap shear strength on stainless steel substrate at room temperature and at 100, 125, and 150 C has been evaluated for the modified and unmodified systems. CTBN-S offers a remarkable increase of 13 MPa and 8 MPa in the room temperature adhesive strength of GY 250-based system and EPN 1138-based system, respectively. EHTPB gives only a marginal improvement and CTBN-L offers an improvement by 4 MPa for GY 250-based system whereas CTBN-L reduces the adhesive strength of EPN 1138-based system. SEM studies suggest that in general, the modification with EHTPB and CTBN-L results only in improving the ductility of epoxy-imide systems, whereas the modification with CTBN-S results in phase separation of rubber particles in the epoxy-imide matrix.

Epoxy–imide resins were obtained by curing Araldite GY 250 (diglycidyl ether of bisphenol‐A and epichlorohydrin; difunctional) and Araldite EPN 1138 (Novolac–epoxy resin; polyfunctional) with N‐(4‐ and 3‐carboxyphenyl)trimellitimides derived from 4‐ and 3‐aminobenzoic acids and trimellitic anhydride. The adhesive lap shear strength of epoxy–imide systems at room temperature and at 100, 125, and 150°C was determined on stainless‐steel substrates. Araldite GY 250‐based systems give a room‐temperature adhesive lap shear strength of about 23 MPa and 49–56% of the room‐temperature adhesive strength is retained at 150°C. Araldite EPN 1138‐based systems give a room‐temperature adhesive lap shear strength of 16–19 MPa and 100% retention of room‐temperature adhesive strength is observed at 150°C. Glass transition temperatures of the Araldite GY 250‐based systems are in the range of 132–139°C and those of the Araldite EPN 1138‐based systems are in the range of 158–170°C. All these systems are thermally stable up to 360°C. The char residues of Araldite GY 250‐ and Araldite EPN 1138‐based systems are in the range of 22–26% and 41–42% at 900°C, respectively. Araldite EPN 1138‐based systems show a higher retention of adhesive strength at 150°C and have higher thermal stability and Tg when compared to Araldite GY 250‐based systems. This has been attributed to the high crosslinking possible with Araldite EPN 1138‐based systems arising due to the polyfunctional nature of Araldite EPN 1138. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1729–1736, 2000