Biomedical Imaging Magnetic Resonance Imaging
Lawrence S. Chan, William C. Tang in Engineering-Medicine, 2019
Perfusion is a process that brings nutritive blood supply to the tissue through the arterial system and drains the metabolic byproducts into the veins. Perfusion measurement using MRI can be divided into two categories, those employing exogenous agents as a tracer, and those using water protons in the arterial blood as an endogenous label. Among exogenous agents for perfusion MRI, gadolinium chelates are most frequently used. To perform perfusion measurements, a bolus of gadolinium contrast agent is intravenously administered, followed by the rapid acquisition of a series of snap-shot images with either -weighting or T1-weighting. The former is known as dynamic susceptibility contrast (DSC) imaging, while the latter dynamic contrast-enhanced (DCE) imaging. In DSC, the time-series images are processed to extract perfusion-related parameters, such as cerebral blood volume, mean transient time, and time to peak. In DCE, the images are analyzed with a pharmacokinetic model to yield a number of parameters relating to permeability, surface area, transfer constants, etc. (Jahng et al. 2014).
Development and Optimization of Preservation Solutions
John J. Lemasters, Constance Oliver in Cell Biology of Trauma, 2020
For clinical organ preservation there are two methods. Simple cold storage, the most popular, involves flushing the blood out of the organ and infusing it with the cold (about 4°C) preservation solution. The second method, machine perfusion, involves continuous perfusion of the organ with a perfusate at 4 to 8°C. Perfusion is done at a low pressure (about 40 to 55 mmHg systolic) and usually with a pulsatile flow at a rate of about 0.6 to 1.0 ml/min/g of tissue. Perfusion is used clinically only for the kidney. An advantage of perfusion is that end products of metabolism can be removed and that oxygen and other substrates can be delivered to the organ. Thus, energy-requiring reactions that continue even at hypothermia can be supplied with a constant source of ATP derived from mitochondrial oxidative phosphorylation. Perfusion, therefore, provides longer preservation of organs than cold storage, and in general it preserves the quality of organs better for short periods of time. However, the ease of cold storage and the fact that only about 24 h of preservation is required to meet most needs has made it the method of choice.
Functional MR Imaging
Phillip M. Boiselle, Charles S. White in New Techniques in Cardiothoracic Imaging, 2007
While a variety of pathologies can lead to pulmonary arterial hypertension, one of three histological patterns is typically identified: plexogenic arteriopathy, thrombotic arteriopathy, or veno-occlusive disease. The distinction between these causes is important, as different therapies and outcomes are expected for each pattern of disease. It is difficult to distinguish among these causes clinically. However, different patterns of pulmonary perfusion may be identified with each of these causes. Patients with thrombotic hypertension frequently have a patchy distribution of blood flow, while patients with plexogenic angiopathy may have a more uniform distribution of flow (34,35). MR evaluation of pulmonary blood flow may be able to distinguish between these two etiologies. An ASL image from a patient with chronic thromboembolic pulmonary hypertension is shown in Figure 9. A nonuniform decrease in pulmonary perfusion is present with multiple regions of markedly decreased signal intensity. While MR perfusion techniques are able to document changes in blood flow with pulmonary hypertension, the importance of these techniques in the diagnosis and management of these diseases is not known.
Thermophysical and mechanical properties of biological tissues as a function of temperature: a systematic literature review
Published in International Journal of Hyperthermia, 2022
Leonardo Bianchi, Fabiana Cavarzan, Lucia Ciampitti, Matteo Cremonesi, Francesca Grilli, Paola Saccomandi
Another fundamental factor affecting the thermal outcome during hyperthermia treatments concerns the blood flow in perfused tissues. Blood perfusion refers to the passage of a certain blood volume through vessels embedded in biological tissues, in order to provide oxygen and deliver important nutrients to tissues, as well as remove waste substances [178]. The blood flow can be expressed as the volume of blood, which is forced to flow within a tissue, per tissue mass per unit of time [179], i.e., mL/100 g/min. Moreover, knowing the tissue density, the blood perfusion rate (i.e., the volumetric rate per unit tissue volume, often expressed in 1/s [180]) can be attained as the product of blood flow and the tissue density [181]. The blood flow has been investigated at both normothermic conditions and at temperatures that do not lie in the physiological range, by imposing a temperature variation to biological media through different methods. Likewise, the temperature sensitivity of the blood perfusion has been assessed in different tissues; preclinical studies on healthy tissues and on tumor models have been set, as well as evaluations on blood flow upon temperature changes during clinical trials.
Bioengineering lungs — current status and future prospects
Published in Expert Opinion on Biological Therapy, 2021
Vishal Swaminathan, Barry R. Bryant, Vakhtang Tchantchaleishvili, Taufiek Konrad Rajab
In order to create an effective environment for cell growth, the bioreactor must be sterile. Moreover, the bioreactor provides access to the vascular and respiratory compartments for perfusion through vasculature and ventilation of the respiratory tree with physiologic parameters [35]. Perfusion of the pulmonary vasculature depends on pressures created by the right ventricle. The repetitive force of the heart pumping blood through the circulatory system, in particular through the lung vasculature, can directly affect the stretch and size of vessel walls [36]. The stress from the stroke volume influences cell alignment and homeostasis [41]. Moreover, perfusion promotes nutrient delivery and waste removal, which is necessary for cell functioning. Perfusion of the cellularized scaffold can be implemented in a constant flow and pressure or a cyclic one. Perfusate composition is another challenge that has yet to be completely addressed. Currently, cell culture media is often used, although considering the many types of cells populating a singular scaffold, choosing a media can be challenging. As bioreactors improve, so will the perfusate.
Development of a high yielding expression platform for the introduction of non-natural amino acids in protein sequences
Published in mAbs, 2020
Gargi Roy, Jason Reier, Andrew Garcia, Tom Martin, Megan Rice, Jihong Wang, Meagan Prophet, Ronald Christie, William Dall’Acqua, Sanjeev Ahuja, Michael A Bowen, Marcello Marelli
The use of orthogonal aaRS/tRNA for the incorporation of nnAAs has proven to be a very precise method for delivering a nnAA at preselected sites. However, the major limitation of nnAA technologies has been the low productivity in cell-based systems. Previous reports demonstrating >1g/L yields show that the limitations of this system can be overcome in stable cells and with careful cell line selection.15,18 To further improve the robustness of this system, and further increase the expected overall titers, we developed a process for the expression of nnAA-containing proteins using perfusion bioreactors. Perfusion systems allow for the addition of fresh media and nutrients and the simultaneous removal of cell waste to maintain optimal growth and expression conditions. Thus, stable cells expressing an antibody directed against human epidermal growth factor receptor 2 (HER2)/neu, containing an amber codon encoded in the antibody constant heavy domain 2 (CH2), were generated in host 43 and Y306A36 hosts and IgG-expressing stable primary isolates were subjected to perfusion fermentations. The site of incorporation can affect expression levels of the system; in this assessment, we selected a CH2 domain site that represents a challenging position for incorporation efficiency and is functionally significant for ADC assembly. The expression line derived from host 43 was exposed to AzK (S/AzK), and the expression cell line derived from Y306A36 was exposed to either AzK (V/AzK), CpHK (V/CpHK) or SCpHK (V/SCpHK) starting on day 5 of the fermentation.