Continuous single pass diafiltration with alternating permeate flow direction for high efficiency buffer exchange

Looking at current trends within downstream processing (DSP) of high value bioproducts, it shows that there are ongoing efforts in replacing batch processes by continuous variants. However, a unit procedure which still lacks a simple and compact continuous variant is diafiltration. Here, we present such a single piece of diafiltration equipment achieving continuous buffer exchange of up to 99.90%. The device is composed of a 3D-printed single pass diafiltration (SPDF) module containing two commercial ultrafiltration membranes. While the retentate is flowing through a narrow channel between the two membranes, the channels above and below can supply diafiltration buffer or remove permeate solution. The obtained results illustrate systematically the vulnerability of the device to the effect of concentration polarization at the membrane surface, and that this problem can be strongly reduced using an alternating direction of diafiltration buffer perfusion through the membranes as process inherent backflush. By this, a quasi-stationary operation could be obtained during continuous diafiltration, making the device an interesting option for in-process buffer exchange

Acoustic cardiac triggering: a practical solution for synchronization and gating of cardiovascular magnetic resonance at 7 Tesla

<p>Abstract</p> <p>Background</p> <p>To demonstrate the applicability of acoustic cardiac triggering (ACT) for imaging of the heart at ultrahigh magnetic fields (7.0 T) by comparing phonocardiogram, conventional vector electrocardiogram (ECG) and traditional pulse oximetry (POX) triggered 2D CINE acquisitions together with (i) a qualitative image quality analysis, (ii) an assessment of the left ventricular function parameter and (iii) an examination of trigger reliability and trigger detection variance derived from the signal waveforms.</p> <p>Results</p> <p>ECG was susceptible to severe distortions at 7.0 T. POX and ACT provided waveforms free of interferences from electromagnetic fields or from magneto-hydrodynamic effects. Frequent R-wave mis-registration occurred in ECG-triggered acquisitions with a failure rate of up to 30% resulting in cardiac motion induced artifacts. ACT and POX triggering produced images free of cardiac motion artefacts. ECG showed a severe jitter in the R-wave detection. POX also showed a trigger jitter of approximately Δt = 72 ms which is equivalent to two cardiac phases. ACT showed a jitter of approximately Δt = 5 ms only. ECG waveforms revealed a standard deviation for the cardiac trigger offset larger than that observed for ACT or POX waveforms.</p> <p>Image quality assessment showed that ACT substantially improved image quality as compared to ECG (image quality score at end-diastole: ECG = 1.7 ± 0.5, ACT = 2.4 ± 0.5, p = 0.04) while the comparison between ECG vs. POX gated acquisitions showed no significant differences in image quality (image quality score: ECG = 1.7 ± 0.5, POX = 2.0 ± 0.5, p = 0.34).</p> <p>Conclusions</p> <p>The applicability of acoustic triggering for cardiac CINE imaging at 7.0 T was demonstrated. ACT's trigger reliability and fidelity are superior to that of ECG and POX. ACT promises to be beneficial for cardiovascular magnetic resonance at ultra-high field strengths including 7.0 T.</p

method development and application

Die Gewebedifferenzierung des Myokards mittels suszeptibilitäts- (T2*) gewichteter Kartierungstechniken findet in der (prä)-klinischen kardiovaskulären Magnetresonanzbildgebung steigenden Einsatz. Der Anstieg der Suszeptibilitätsempfindlichkeit bei steigenden Magnetfeldstärken macht die myokardiale T2* Kartierung bei hohen Magnetfeldstärken konzeptionell besonders attraktiv. Die Anwendungsmöglichkeiten der T2* gewichteten Herz MRT sind unter anderem die Erkennung myokardialer Ischämien, die Charakterisierung der Sauerstoffversorgung und die Darstellung der Mikrostruktur des Herzmuskels. In dieser Arbeit werden geeignete Methoden entwickelt um die myokardialen T2* gewichtete Bildgebung bei hohen (3 T) und ultrahohen (7 T) Magnetfeldstärken durchzuführen. Zu diesem Zweck werden T2* gewichtete Pulssequenzen an die Anforderungen der Hochfeld MRT angepasst und Hochfrequenzspulen mit 4, 8, 16 und 32 Sende- und Empfangskanälen für die Herzbildgebung bei 7 T entwickelt und evaluiert. In Phantomexperimenten werden diese Pulssequenzen, welche eine dynamische, zeitlich aufgelöste (CINE) Kartierung erlauben mit etablierten Techniken validiert. In einer Studie mit gesunden Probanden werden zudem B0 Shimming Techniken angewendet um makroskopische Feldinhomogenitäten zu reduzieren und dadurch die Suszeptibiltätsempfindlichkeit gegenüber mikroskopischen Effekten zu verstärken. Diese Arbeit liefert erste in-vivo Normwerte für T2* Zeiten im gesunden humanen Herzmuskel bei 7 T und vergleicht diese Ergebnisse mit Daten welche bei 1.5 T und 3 T erhoben wurden. Die maximale B0 Differenz konnte durch einen volumenselektiven Shim von etwa 400 Hz auf etwa 80 Hz für den Vierkammerblick und auf etwa 65 Hz für einen mitventrikulären Kurzachsenblick des Herzens reduziert werden. Die längsten T2* -Werte wurden für anteriore (T2* = 14,0 ms), anteroseptale (T2* = 17,2 ms) und inferoseptale (T2* = 16,5 ms) Myokardsegmenten gefunden. Die kürzesten T2* -Werte hingegen wurden für beobachtet inferiore (T2* = 10,6 ms) und inferolaterale (T2* = 11,4 ms) Segmente. Zwischen der end-diastolischen und end-systolischen Herzphase wurden signifikante Unterschiede (p = 0,002) in den T2*-Werten beobachtet mit Änderungen von T2* -Werten von bis zu ca. 27% über den Herzzyklus, welche besonders in der Herzscheidewand ausgeprägt waren. Die T2* gewichtete Bildgebung bei 7 T bietet die Möglichkeit Änderungen der Sauerstoffsättigung im Herzmuskel zu visualisieren und zu quantifizieren. Bestehende Limitationen bezüglich räumlicher und zeitlicher Auflösung der konventionell eingesetzten Perfusions-Bolusmessungen mit Kontrastmittel könnten dadurch umgangen werden. Der endogene Kontrast des BOLD Effekts ermöglicht es, Änderungen im Gleichgewicht zwischen Sauerstoffversorgung und Sauerstoffnachfrage früh zu erkennen und zu visualisieren. Zusammenfassend unterstreichen diese Ergebnisse die Herausforderungen des myokardialen T2* Kartierung bei 7 T, zeigen jedoch, dass diese Probleme durch maßgeschneiderte B0-Shimming Techniken und angepasste Akquisitionstechniken kompensiert werden können.Myocardial tissue characterization using T2* relaxation mapping techniques is an emerging application of (pre)clinical cardiovascular magnetic resonance imaging. The increase in microscopic susceptibility at higher magnetic field strengths renders myocardial T2* mapping at ultrahigh magnetic fields conceptually appealing. Applications of T2* weighted cardiac MR include the detection of myocardial ischemia, the characterization of oxygen supply and the microstructure of the cardiac muscle. This work develops methods for myocardial T2* mapping at high (3 T) and ultrahigh (7 T) magnetic field strengths. For this reason T2* weighted pulse sequences are adapted to the requirements of highfield MRI and dedicated RF coils with 4, 8, 16 and 32 transmit and receive channels are developed for cardiac imaging at ultrahigh field strengths. In phantom experiments the pulse sequences, which provide dynamic, time resolved maps are benchmarked against conventional techniques. In a volunteer study B0 shimming techniques are applied to reduce macroscopic field inhomogeneities and therefore increase the susceptibility sensitivity for microscopic effects. This work presents the first in-vivo norm values T2* values in the healthy human cardiac muscle at 7 T and compares it to results which were collected at 1.5 T and 3 T. for . The peak-to-peak B0 difference following volume selective shimming was reduced from approximately 400 Hz to approximately 80 Hz for the four chamber view and mid-ventricular short axis view of the heart and to 65 Hz for the left ventricle. The longest T2* values were found for anterior (T2* = 14.0 ms), anteroseptal (T2* = 17.2 ms) and inferoseptal (T2* = 16.5 ms) myocardial segments. Shorter T2* values were observed for inferior (T2* = 10.6 ms) and inferolateral (T2* = 11.4 ms) segments. A significant difference (p = 0.002) in T2* values was observed between end-diastole and end-systole with T2* changes of up to approximately 27% over the cardiac cycle which were pronounced in the septum. T2* weighted imaging at 7 T offers the potential to visualize and quantify changes in oxygen supply in the cardiac muscle. Existing limitations regarding spatial and temporal resolution of conventional first-pass perfusion imaging with contrast agents can avoided. The endogenous contrast provided by the BOLD effect allows the early detection of imbalances in oxygen supply and demand. To conclude, these results underscore the challenges of myocardial T2* mapping at 7.0 T but demonstrate that these issues can be offset by using tailored shimming techniques and dedicated acquisition schemes

Quantification of myocardial effective transverse relaxation time with magnetic resonance at 7.0 tesla for a better understanding of myocardial (patho)physiology

Cardiovascular magnetic resonance imaging (CMR) has become an indispensable tool in the assessment of cardiac structure, morphology, and function. CMR also affords myocardial tissue characterization and probing of cardiac physiology, both being in the focus of ongoing research. These developments are fueled by the move to ultrahigh magnetic field strengths, which permits enhanced sensitivity and spatial resolution that help to overcome limitations of current clinical MR systems. This chapter reviews the potential of using CMR as a means to assess physiology in the heart muscle by exploiting quantification of myocardial effective transverse relaxation times (T2 * ) for the better understanding of myocardial (patho)physiology. For this purpose the basic principles of T2 * mapping, the biophysical mechanisms governing T2 * , and Otherwise this implies that all preclinical applications of myocardial T2 * mapping ever done are being presented which is not the case. Technological challenges and solutions for T2 * -sensitized CMR at ultrahigh magnetic field strengths are discussed followed by a survey of acquisition techniques and post processing approaches. Preliminary results derived from myocardial T2 * mapping of healthy subjects and in patients at 7.0 T are presented. A concluding section provides an outlook including future developments and potential applications

B₀ distribution for global and volume selective shimming of a mid-ventricular short axis view of the heart.

<p><b>A</b>) Mid-ventricular short axis view of the heart illustrating the positioning of the volume (marked in red) used for volume selective shimming. <b>B</b>) B₀ field maps. <b>C</b>) B₀ profile along the direction of the strongest B₀ gradient which is highlighted by the dashed black line in <b>B</b>). To guide the eye the epicardial borders are marked in <b>B</b>) and <b>C</b>) by two triangles. <b>D</b>) Frequency histogram across the left ventricle. After volume selective shimming a strong susceptibility gradient at the inferior region of the heart could be reduced. The full width at half maximum is approximately 300 Hz for the globally shimmed field map and was reduced to about 80 Hz after volume selective shimming.</p