Introduction to focus issue: dynamics in systems biology

The methods of nonlinear systems form an extensive toolbox for the study of biology, and systems biology provides a rich source of motivation for the development of new mathematical techniques and the furthering of understanding of dynamical systems. This Focus Issue collects together a large variety of work which highlights the complementary nature of these two fields, showing what each has to offer the other. While a wide range of subjects is covered, the papers often have common themes such as "rhythms and oscillations," "networks and graph theory," and "switches and decision making." There is a particular emphasis on the links between experimental data and modeling and mathematical analysis.     

The use of T2*-weighted multi-echo GRE imaging as a novel method to diagnose hepatocellular carcinoma compared with gadolinium-enhanced MRI: a feasibility study

Background

The goal of the study was to assess a T2*-weighted MRI sequence for the ability to identify hepatocellular carcinoma (HCC).

Methods

Hepatic iron deposition, which is common in chronic liver disease (CLD), may increase the conspicuity of HCC on GRE imaging due to increased T2* signal decay in liver parenchyma. In this study, a breath-hold T2*-weighted MRI sequence was evaluated by a blinded observer for HCC and the results compared to a reference standard of gadolinium-enhanced MRI in these same patients. Forty-one patients (mean age 56.2 years; 17 females) were included in this approved, retrospective study.

Results

By the reference standard, 14 of 41 patients had a total of 25 HCCs. The sensitivity of the T2*-weighted MR sequence for identifying HCC, per lesion, was 60%, while the specificity was 100%. There was a significantly lower T2* value of liver parenchyma in patients with HCC identified by the T2*-weighted sequence than in those with HCCs which were not identified by the T2*-weighted sequence (27.8±2.2 vs. 21.9±2.1 ms; P=.02).

Conclusions

A T2*-weighted MRI sequence can identify HCC in patients with CLD. This technique may be beneficial for imaging of patients contraindicated for gadolinium.     

Neutron enhancement from laser interaction with a critical fluid

We discuss experimentally and theoretically neutron production from the laser driven explosion of gas clusters prepared near the liquid-gas critical point. We let deuterated methane that was prepared very close to its critical temperature and pressure expand through a conical nozzle to create clusters, and then irradiated those clusters with a high intensity pulse from the Texas Petawatt Laser. After ionization, the clusters explode producing energetic ions, some of which fuse with resultant neutron emission. We show that the critical fluctuations present in the nozzle before the expansion influence the dynamics of neutron production. Neutron production near the critical point follows a power law, which is a signature of a second order phase transition and it is consistent with the Fisher model. This result might be relevant for energy production from fusion reactions.