Establishing the Calibration Curve of a Compressive Ophthalmodynamometry Device.

The relationship between externally applied force and intraocular pressure was determined using an ex-vivo porcine eye model (N=9). Eyes were indented through the sclera with a convex ophthalmodynamometry head (ODM). Intraocular pressure and ophthalmodynamometric force were simultaneously recorded to establish a calibration curve of this indenter head. A calibration coefficient of 0.140 ± 0.009 mmHg/mN was established and was shown to be highly linear (r = 0.998 ± 0.002). Repeat application of ODM resulted in a 0.010 ± 0.002 mmHg/mN increase to the calibration coefficient.Clinical Relevance- ODM has been highlighted as a potential method of non-invasively estimating intracranial pressure. This study provides relevant data for the practical performance of ODM with similar compressive devices.

Magnetic Resonance Elastography Reconstruction for Anisotropic Tissues.

Elastography has become widely used clinically for characterising changes in soft tissue mechanics that are associated with altered tissue structure and composition. However, some soft tissues, such as muscle, are not isotropic as is assumed in clinical elastography implementations. This limits the ability of these methods to capture changes in anisotropic tissues associated with disease. The objective of this study was to develop and validate a novel elastography reconstruction technique suitable for estimating the linear viscoelastic mechanical properties of transversely isotropic soft tissues. We derived a divergence-free formulation of the governing equations for acoustic wave propagation through a linearly transversely isotropic viscoelastic material, and transformed this into a weak form. This was then implemented into a finite element framework, enabling the analysis of wave input data and tissue structural fibre orientations, in this case based on diffusion tensor imaging. To validate the material constants obtained with this method, numerous in silico phantom experiments were run which encompassed a range of variations in wave input directions, material properties, fibre structure and noise. The method was also tested on ex vivo muscle and in vivo human volunteer calf muscles, and compared with a previous curl-based inversion method. The new method robustly extracted the transversely isotropic shear moduli (G⊥', G∥', G″) from the in silico phantom tests with minimal bias, including in the presence of experimentally realistic levels of noise in either fibre orientation or wave data. This new method performed better than the previous method in the presence of noise. Anisotropy estimates from the ex vivo muscle phantom agreed well with rheological tests. In vivo experiments on human calf muscles were able to detect increases in muscle shear moduli with passive muscle stretch. This new reconstruction method can be applied to quantify tissue mechanical properties of anisotropic soft tissues, such as muscle, in health and disease.

Comparison of outcomes and costs between laparoscopic distal pancreatectomy and open resection at a single center.

BACKGROUND: The cost implications of laparoscopic distal pancreatectomy (LDP) and a detailed breakdown of hospital expenditures has not been presented in the literature to date. This study aimed to compare hospital costs and short-term clinical outcomes between LDP and open distal pancreatectomy (ODP). METHODS: The authors evaluated all the distal pancreatic resections performed at their center between January 2004 and March 2010. Parametric and nonparametric statistical analysis was used to compare hospital departmental and total hospital costs as well as oncologic and surgical outcomes. RESULTS: A total of 118 cases (42 laparoscopic resections, including 5 conversions, and 76 open resections) were analyzed. The demographic characteristics were similar between the groups except for a predominance of females in the laparoscopic group (P = 0.036). The indications for surgery differed by a paucity of malignant tumors being approached laparoscopically (P < 0.001). Intraoperatively, there were no differences in estimated blood loss, operating room time, or transfusion requirement. The pathologic outcomes did not differ significantly. The median hospital length of stay (LOS) was 5 days (range 3-31 days) for the LDP cohort and 7 days (range 4-19 days) for the ODP cohort (P < 0.001). Postoperative pancreatic fistula occurred for 22 patients, with a higher proportion observed in the LDP group (28.57%; n = 12) than in the open group (13.16%; n = 10; P = 0.05). However, the rates for grade B and higher grade fistula were higher in the ODP group (0 LDP and 4 ODP). The median preadmission and operative costs did not differ significantly. The ODP cohort had significantly higher costs in all other hospital departments, including the total cost. CONCLUSION: LDP is both a cost-effective and safe approach for distal pancreatic lesions. This series showed a shorter LOS and lower total hospital costs for LDP than for ODP, accompanied by equivalent postoperative outcomes.