A new open-source software project is presented, JEMRIS, the Jü lich Extensible MRI Simulator, which provides an MRI sequence development and simulation environment for the MRI community. The development was driven by the desire to achieve generality of simulated three-dimensional MRI experiments reflecting modern MRI systems hardware. The accompanying computational burden is overcome by means of parallel computing. Many aspects are covered that have not hitherto been simultaneously investigated in general MRI simulations such as parallel transmit and receive, important offresonance effects, nonlinear gradients, and arbitrary spatiotemporal parameter variations at different levels. The latter can be used to simulate various types of motion, for instance. The JEMRIS user interface is very simple to use, but nevertheless it presents few limitations. MRI sequences with arbitrary waveforms and complex interdependent modules are modeled in a graphical user interface-based environment requiring no further programming. This manuscript describes the concepts, methods, and performance of the software. Numerical simulation of MRI experiments, based on the Bloch equation, is an essential tool for a variety of different research directions. In the field of pulse sequence optimization, e.g., for artifact detection and elimination, simulations allow one to differentiate between effects arising principally from MRI physics and those due to hardware imperfections. Another prominent application is the design of specialized radiofrequency (RF) pulses. In general, the interpretation and validation of experimental results benefits from comparisons to simulated data. Many more applications possibly add to this list, not to forget that controlled numerical MRI experiments are also valuable for educational purposes.In its most general form, numerical simulation of an MRI experiment is a demanding task. This is due to the fact that a huge spin ensemble has to be simulated in order to obtain realistic results. To overcome this, several published approaches reduce the problem size in different ways. The most prominent method is to consider analytical solutions of the problem (1-3). In cases of simultaneous RF excitation and time-varying gradient fields, no general analytical solution exists and, thus, the important field of selective excitation cannot be studied with analytical approaches. In the past, numerical solutions have also been considered (4,5) but hardware and software architectures pertaining at that time limited simulations to small spin systems with reduced flexibility in setup and extensibility of the numerical experiments. Apart from the computational demand, the complexity of the MRI imaging sequence is also an obstacle. A multipurpose MRI simulation environment should provide functionality for rapid-sequence prototyping; otherwise, it will be of limited interest only. However, providing an easy-to-use framework should by no means increase the internal complexity thereof. This would reduce the possibility of extending and...
The zonal rate model (ZRM) has previously been applied for analyzing the performance of axial flow membrane chromatography capsules by independently determining the impacts of flow and binding related non-idealities on measured breakthrough curves. In the present study, the ZRM is extended to radial flow configurations, which are commonly used at larger scales. The axial flow XT5 capsule and the radial flow XT140 capsule from Pall are rigorously analyzed under binding and non-binding conditions with bovine serum albumin (BSA) as test molecule. The binding data of this molecule is much better reproduced by the spreading model, which hypothesizes different binding orientations, than by the well-known Langmuir model. Moreover, a revised cleaning protocol with NaCl instead of NaOH and minimizing the storage time has been identified as most critical for quantitatively reproducing the measured breakthrough curves. The internal geometry of both capsules is visualized by magnetic resonance imaging (MRI). The flow in the external hold-up volumes of the XT140 capsule was found to be more homogeneous as in the previously studied XT5 capsule. An attempt for model-based scale-up was apparently impeded by irregular pleat structures in the used XT140 capsule, which might lead to local variations in the linear velocity through the membrane stack. However, the presented approach is universal and can be applied to different capsules. The ZRM is shown to potentially help save valuable material and time, as the experiments required for model calibration are much cheaper than the predicted large-scale experiment at binding conditions. Biotechnol. Bioeng. 2013; 110: 1129–1141. © 2012 Wiley Periodicals, Inc.
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