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Clinical Applications of IVIM MRI to the Nervous System
Published in Denis Le Bihan, Mami Iima, Christian Federau, Eric E. Sigmund, Intravoxel Incoherent Motion (IVIM) MRI, 2018
Intravoxel incoherent motion (IVIM) refers to translational movements within a given voxel, which result in a distribution in position during measurement time [1] and can be measured using appropriate encoding gradients. The main application of this method was found to be the measurement of the restriction of thermal diffusion through the biological environment, using the concept of apparent diffusion coefficient. In particular, the observation that acute brain ischemia lesions [2] show a restriction in diffusion compared to normal parenchyma has been a tremendous breakthrough in the diagnosis and management of this disease.
Pancreatic malignancy
Published in Anju Sahdev, Sarah J. Vinnicombe, Husband & Reznek's Imaging in Oncology, 2020
Giovanni Morana, Alex Faccinetto, Michele Fusaro
A standard protocol should include: Fast T2-weighted (T2W) spin-echo sequences, axial and coronal single-shot, turbo spin-echo sequences with a short TE (40–80 ms), a long TR, and half field of view. This sequence has low sensitivity to movement artefacts and high sensitivity for fluids, ideal to evaluate cystic lesions.T1-weighted (T1W) two-dimensional gradient-echo (GRE) sequence with fat saturation: the best sequence for differentiating the normal and diseased pancreas. A normal pancreas is homogeneously hyperintense because of the presence of large quantities of aqueous protein in the pancreatic acini, abundant endoplasmic reticulum in the acinar cells, and the paramagnetic ion-rich content, notably manganese. Focal or diffuse pancreatic diseases appear as hypointense areas.T1W three-dimensional GRE sequences can be used to combine parenchymal and vascular imaging. After administering a test bolus to identify the correct acquisition timing, the operator consecutively acquires arterial, pancreatic, portal, and delayed sequences as for a CT examination.Diffusion-weighted imaging (DWI). DWI measures changes in the microscopic diffusion of water due to Brownian motion (see Chapter 42). The DWI signal is also influenced by microcirculation, or blood perfusion, at low b values (6) and, therefore, ADC values calculated from DWI including low b values containing perfusion effects may have limited ability to characterise focal lesions (7). Intravoxel incoherent motion (IVIM) is an imaging method which enables separate estimation of tissue diffusivity and microcapillary perfusion, using a larger number of b values below 200 ms (8).
New magnetic resonance imaging sequences for fibrosis assessment in Crohn’s disease: a pilot study
Published in Scandinavian Journal of Gastroenterology, 2022
Bénédicte Caron, Valérie Laurent, Freddy Odille, Silvio Danese, Gabriela Hossu, Laurent Peyrin-Biroulet
Patients with Crohn’s disease (CD) commonly develop strictures, containing various degrees of inflammation and fibrosis [1]. Characterization of intestinal strictures is crucial for the management of CD [1]. Differentiation of inflammation from fibrosis by currently available cross-sectional imaging techniques remains challenging [1]. No consensus on the most reliable method for evaluating intestinal fibrosis in CD exists [2]. Magnetic resonance enterography (MRE) has excellent capability to assess the degree of inflammation, but fibrosis detection is problematic [1,3–7]. Additional sequences might enhance accuracy of fibrosis detection. Intravoxel incoherent motion imaging (IVIM) can provide contrast-free measurers of tissue perfusion which is related to inflammation [8]. T1 mapping is a sequence allowing quantification of the T1 relaxation time, which is significantly longer in patients with liver fibrosis [9]. We evaluated these new magnetic resonance imaging (MRI) sequences (IVIM and T1 mapping) for assessing fibrosis in CD.
Predicting neoadjuvant chemoradiotherapy response with functional imaging and liquid biomarkers in locally advanced rectal cancer
Published in Expert Review of Anticancer Therapy, 2022
Trang Thanh Pham, Stephanie Lim, Michael Lin
Intravoxel incoherent motion (IVIM) modeling of DWI assesses both diffusion and perfusion motion, providing information on microcirculation without the need for exogenous gadolinium-based contrast. Results from IVIM studies are mixed. A prospective study of 42 patients by Lu et al. [60] found that preD* (pseudo-diffusion coefficient), pref (microvascular volume fraction), post D (true diffusion coefficient), and ΔD was higher in patients with pCR following CRT. ΔD was better than ΔADC in identifying pCR from the non-pCR patients. A prospective study of 98 patients by Zhu et al. [52] performed MRI pre, during and after CRT and found that ADC after CRT was able to predict pCR. However, IVIM-derived parameters D, f, and D* were unable to predict CRT response.
A systematic review of diagnostic techniques to determine tissue perfusion in patients with peripheral arterial disease
Published in Expert Review of Medical Devices, 2019
Kirsten F. Ma, Simone F. Kleiss, Richte C.L. Schuurmann, Reinoud P.H. Bokkers, Çagdas Ünlü, Jean-Paul P.M. De Vries
Arterial spin labeling (ASL), blood oxygen level-dependent (BOLD) imaging, and intravoxel incoherent motion (IVIM) are perfusion techniques that do not require administration of an exogenous contrast agent. In ASL, arterial blood is used as an endogenous contrast agent by magnetically labeling the inflowing blood with radiofrequency pulses. Perfusion contrast is given by the difference in magnetization between a labeled and unlabeled control image induced by the exchange of magnetization at tissue level [18]. Because most ASL MRI techniques acquire the perfusion-weighted images at a fixed time after the initial labeling of the arterial blood, it might be that the magnetic label may not reach the imaging plane, leading to an underestimation of peripheral blood flow. BOLD MRI has been based on the paramagnetic properties of deoxyhemoglobin as an intrinsic contrast agent [19]. An increase of tissue perfusion results in a higher oxyhemoglobin and lower deoxyhemoglobin concentration in the small vessels and local microcirculation of PAD patients. IVIM is based on diffusion-weighted imaging (DWI) using different b-values to measure the signal intensity of diffusion. Quantitative parameters, such as the diffusion coefficient, pseudodiffusion coefficient, and the relative perfusion fraction, can be calculated [20].