Kuniyuki Hidaka

Elasticity and viscoelasticity of embolization microspheres.

The present study investigates the mechanical properties of three embolization microspheres (E-ms): tris-acryl gelatin microspheres (TG-ms), acrylamido polyvinyl alcohol microspheres (APVA-ms), and polyphosphazene-coated polymethylmethacrylate microspheres (PP-PMMA-ms). Compression and relaxation tests were performed on monolayers of particles and their Youngs moduli and relaxation half times (RHTs) were determined. The elasticity of E-ms was evaluated by applying Hertz theory with the assumptions of incompressibility and a Poissons ratio of 0.5. The Youngs moduli of TG-ms, APVA-ms, and PP-PMMA-ms were 39.6±5.05 kPa, 18.8±4.00 kPa, and 13.6±1.98 kPa, respectively. The RHTs of TG-ms, APVA-ms, and PP-PMMA-ms were 52.3±5.56 s, 59.1±8.16 s, and 31.0±7.01 s, respectively. TG-ms have a high rigidity and deform slightly under a sustained compression since they have a high elasticity. PP-PMMA-ms are soft and deform a lot under sustained compression. They are more viscous than the other two microspheres. APVA-ms have intermediate material properties, having the same low rigidity as PP-PMMA-ms and being more elastic than TG-ms.

Elastic characteristics of microspherical embolic agents used for vascular interventional radiology

Embolic agents are used in vascular interventional radiology to occlude arteries under pathological conditions. The present study was performed to investigate the material properties of two microspherical embolic agents (MSEAs), tris-acryl gelatin microspheres (TGMS) and superabsorbent polymer microsphere (SAP-MS), using a loading-unloading compression test. The results demonstrated that for both TGMS and SAP-MS, the stress-strain relationship appeared to be linear up to 25% deformation. Therefore, one can reasonably treat TGMS and SAP-MS as linearly elastic materials for this range of deformation and apply the Hertz contact theory for analysis of the Youngs modulus. The Youngs moduli of TGMS and the SAP-MS obtained by applying Hertz theory under the assumption of a Poissons ratio of 0.5 were 19.33 +/- 4.97 kPa and 9.64 +/- 2.46 kPa, respectively (mean +/- SD, P<0.001, Mann-Whitney U-test), indicating that TGMS showed higher stiffness than SAP-MS. The effects of a difference in these mechanical characteristics of embolic agents on the performance of interventional radiology were discussed from a viewpoint of their flowing behavior and clinical aspects.

Evaluation of the Effect of Varying MPEG-2 Compression Ratios on Digital Coronary Angiographic Assessment of Stenosis Severity

The purpose of this study is to evaluate the influence of MPEG-2 compression scheme on coronary angiography and to search the highest compression ratio at which no significant effect to accuracy of assessment of stenosis severity occurs. Forty-Four digital cine angiographies were used. Three cardiologists participated in a subjective study in which they read both uncompressed images and compressed images. Furthermore, an objective study was carried out to measure vessel stenosis ratio by using software. The influence of compression was evaluated by kappa statistics in case of subjective study and by both systematic error and random error in case of objective study. Kappa statistics between uncompressed image and compressed image at a ratio of 80:1 was significantly lower than that of other compression ratios such as 40:1. Similar results were obtained in objective evaluation. In this report, the authors provide the baseline for further studies on observer performance for motion images.