Macroscopic investigation of the transient hydrodynamic memory behavior of preparative packed chromatography beds

The goal of the present work was to examine the hydrodynamic behavior of preparative scale packed chromatography beds during long-term cyclical operation at high loads using an experimental set-up with a high resolution measuring device of bed height. One agarose-based resin and one methacrylic-based resin were examined in a 140 mm column. Both resins exhibited hysteresis behavior during compression/relaxation cycles. The hystereses were less pronounced with decreasing hydrodynamic stress rate. The occurrence of hystereses was an indication for hydrodynamic memory behavior of the chromatography packing. During long-term cyclical operation at high loads of the column filled with methacrylic resin, oscillations of the steadily with time decreasing flow rate were observed for the first time. These oscillations were attributed to the viscoelasticity of the polymer particles network representing a system with materials with fading memory. Such nonlinear systems with feed-back are known to exhibit inherent self-oscillations. A decoupling of the two processes of bed compression and decrease of bed permeability was observed. The presented results explain why preparative packed-bed chromatography often yields unsatisfactory reproducible data and why unwanted phenomena like medium wall detachment or other symptoms of deteriorated chromatography beds are frequently observed.     

Visual estimation of the extent of myocardial hyperenhancement on late gadolinium-enhanced CMR in patients with hypertrophic cardiomyopathy

Aim

So far different approaches have been used to quantify late gadolinium enhancement (LGE) in patients with hypertrophic cardiomyopathy (HCM), but there is no general consensus on the gold standard, since histological data are scarce. The aim of our study was to investigate whether the determination of LGE in patients with HCM using a semiquantitative score based on the 17-segment model is feasible and has comparable accuracy to manual planimetry.

Methods

Forty-two patients with HCM underwent LGE cardiovascular magnetic resonance imaging. Determination of LGE by planimetry based on visual assessment was used as reference standard. Then the extent of LGE was assessed using a semiquantitative score based on the standard left ventricular 17-segment model. Each segment was scored for the distribution of LGE. The resulting summed score expressed as percentage of the maximum possible score was thereafter compared with the manual planimetric evaluation of LGE, expressed as a percentage of the left ventricular myocardial area.

Results

In 28 patients (66%), LGE was present. There was a good correlation between the semiquantitative score and the planimetric approach (r=0.89; y=0.819x+2.45; standard error of estimation=2.327; P<.0001). Additionally, the Bland–Altmann plot showed a high concordance between the two approaches (mean of the difference +1.7%). The inter- and intraobserver limits of agreement and the coefficients of repeatability based on measurements with the semiquantitative score of the extent of LGE were superior to planimetric measurements. Besides, the time requirement for the LGE determination using the semiquantitative score was found to be significantly reduced compared to manual planimetry (median 2 vs. 10 min).

Conclusions

Thus, a reliable global index of the size of the LGE is feasible and can easily be obtained from visual assessment with a semiquantitative score of the extent of the hyperenhancement.     

Highly undersampled supraaortic MRA at 3.0 T: initial results with parallel imaging in two directions using a 16-channel neurovascular coil and parallel imaging factors up to 16

PurposeTo present the feasibility of highly undersampled contrast-enhanced MRA (CE-MRA) of the supraaortic arteries with a 16-channel neurovascular coil at 3.0 T using parallel imaging in two directions with parallel imaging factors (PIF) up to 16.Materials and MethodsInstitutional review board approval and informed consent were obtained. In a prospective study, MRA protocols including PIF of 1, 2, 4, 9 and 16 yielding a spatial resolution from 0.81×0.81×1.0 mm³ to 0.46×.46×0.98 mm³ were acquired. In 32 examinations, image quality and vascular segments were rated independently by two radiologists. SNR estimations were performed for all MRA protocols.ResultsThe use of high PIF allowed to shorten acquisition time from 2:09 min down to 1:13 min and to increase the anatomic coverage while maintaining or even increasing spatial resolution down to 0.46×0.46×0.98 mm³. The larger anatomic coverage that was achieved with the use of high PIF allowed for visualization of vascular structures that were not covered by the standard protocols. Despite the resulting lower SNR using high PIF, image quality was constantly rated to be adequate for diagnosis or better in all cases.ConclusionThe use of high PIF yielded diagnostic image quality and allowed to increase the anatomic coverage while maintaining or even improving spatial resolution and shortening the acquisition time.