China
Africa
Explore chapters and articles related to this topic
Other MRI Approaches to Perfusion Imaging (ASL, DSC, DCE)
Published in Denis Le Bihan, Mami Iima, Christian Federau, Eric E. Sigmund, Intravoxel Incoherent Motion (IVIM) MRI, 2018
Emmanuel L. Barbier, Sylvie Grand, Alexandre Krainik, Jan M. Warnking
Signal readouts sensitive to a specific MR contrast may add information about the environment of the labeled spins in ASL. For example, the difference in T2 between blood and tissue spins enables observation of the extravasation of labeled spins by combining T2 relaxometry with a multi-PLD ASL sequence, either globally [128] or spatially resolved [129]. Inversely, ASL combined with a short PLD may be used as a magnetization preparation to specifically target vascular spins. Since blood oxygenation has an impact on T2, ASL targeted to the venous blood, followed by T2 relaxometry, has been proposed to measure venous blood oxygenation, since ASL is insensitive to the T2 of tissue and since label and tissue signals subtract out during ASL processing [130, 131].
Gel Dosimetry
Published in Gad Shani, Radiation Dosimetry, 2017
Nuclear magnetic resonance (NMR) methods have been very useful in the study of the structure, composition, and molecular dynamics of various materials. Of particular interest are NMR relaxation or relaxometry studies of radiation chemical dosimeters such as the ferrous sulfate-doped or Fricke gels and polymer gels. The radiation-induced changes in the solutes of these aqueous dosimeters affect the relaxation properties of the water protons (hydrogen nuclei) constituting most of the magnetization signal studied using proton NMR or magnetic resonance imaging (MRI) methods. Models show that the NMR dose response of the gel dosimeters is governed by two mechanisms: the chemical response of the gel to radiation and the response of NMR parameters to radiation products. NMR dose response models allow for the absorbed radiation dose to be determined from fundamental physical variables rather than a calibration of the dosimeter’s response. [4]
Magnetic resonance imaging
Published in C M Langton, C F Njeh, The Physical Measurement of Bone, 2016
Laurent Pothuaud, Sharmila Majumdar
The three-dimensional non-invasive imaging capabilities of MRI have been widely used clinically to assess and diagnose osteoporotic and vertebral fractures. Figure 13.1 shows an example of such clinical images, depicting the morphology and signal differences that are seen in MR images of vertebral fractures. In recent years, MRI has also been developed to assess the characteristics of trabecular bone. It permits not only the depiction but also the quantification of TBS, and hence reveals its biomechanical properties. MR can be used to assess the properties of trabecular bone in two fundamental ways. The first is an indirect measure, often termed relaxometry or quantitative magnetic resonance (QMR). This method takes advantage of the fact that trabecular bone alters the adjoining marrow relaxation properties in proportion to its density and structure, and thereby provides information regarding trabecular bone network. The second is the direct visualization of the dark, trabecular bone which, because of its low water content and short MR relaxation times, appears in stark contrast to the bright marrow fat and water, in high resolution MR images.
Correlated analytical and functional evaluation of higher order structure perturbations from oxidation of NISTmAb
Published in mAbs, 2023
Tsega L. Solomon, Frank Delaglio, John P. Giddens, John P. Marino, Yihua Bruce Yu, Marc B. Taraban, Robert G. Brinson
Another emerging analytical technology that to date has only been sparingly applied in a pharmaceutical context is water proton NMR (wNMR) relaxometry implemented using time-domain, low-field benchtop instruments. While this is a low-resolution technique, recent work has demonstrated its general utility for use in pharmaceutical CQA assessment such as measurement of aggregation of biological therapeutics including mAbs.29,30 The wNMR method involves measuring the effect of HOS change of a solute on the proton transverse relaxation rate of water used as the solvent (R2(1H2O)). This rapid R2(1H2O) measurement involves no sample handling or consumption, and data can be collected noninvasively while the sample is within pharmaceutical vials.31 Compared to other current analytical methods such as size-exclusion chromatography (SEC), microflow imaging, and dynamic light scattering, wNMR afforded greater sensitivity to distinguish different levels of aggregation in mAb products, demonstrating the potential advantages of this simple, rapid measurement technique for monitoring additional mAb modifications that affect HOS-relevant CQAs.30,32
Quantitative evaluation of liver function with gadoxetic acid enhanced MRI: Comparison among signal intensity-, T1-relaxometry-, and dynamic-hepatocyte-specific-contrast-enhanced MRI- derived parameters
Published in Scandinavian Journal of Gastroenterology, 2022
Qiang Wang, Savas Kesen, Maria Liljeroth, Henrik Nilsson, Ying Zhao, Ernesto Sparrelid, Torkel B. Brismar
To overcome the above-mentioned limitations, T1-relaxometry measurements, which better reflect the real uptake rate of the contrast agent, have been proposed. The common method to calculate the T1-relaxometry parameters is through T1 mapping obtained by an additional scanning sequence (such as Look-Locker Sequence or Modified Look-Locker Imaging Sequence, MOLLI), in which T1 relaxation time can be manually determined by placement of ROIs on T1 maps or automatically by a dedicated software [13]. When analyzing contrast enhancement from images obtained in clinical practice another method of T1 relaxation time calculation has been developed [16]. It is based on an ideal model where T1 relaxation time is obtained by calculating the increase of the relaxation rate (ΔR1) after contrast agent administration. A linear relationship between the contrast agent concentration and ΔR1 is then assumed. Thereby Khep can be estimated according to an assumption of a two-compartment model taking the pharmacokinetics of the contrast agent into account.
Clinical neuroimaging in intracerebral haemorrhage related to cerebral small vessel disease: contemporary practice and emerging concepts
Published in Expert Review of Neurotherapeutics, 2022
Martina Goeldlin, Catriona Stewart, Piotr Radojewski, Roland Wiest, David Seiffge, David J Werring
To overcome limitations of conventional, qualitative MRI analysis, quantitative MRI provides measures of biophysical parameters including free water, water bound to micro- and macromolecules and the amount of paramagnetic substances (i.e. iron) which has a high sensitivity and specificity to focal and diffuse pathology that are not available through conventional MRI [118]. Quantitative T1 and T2-relaxometry mapping has been used in other chronic diseases of the central nervous system like multiple sclerosis to derive personalized pathology maps [131]. A new approach to quantitative magnetic resonance imaging that allows simultaneous measurement of multiple tissue properties in a single, time-efficient acquisition is Magnetic Resonance Fingerprinting (MRF) [132].