Blood flow: magnetic resonance imaging.

Abstract

The appearance of flowing fluid has been evaluated in several clinical situations using a flow phantom, computer simulation, and clinical magnetic resonance (MR) images. Unsaturated protons just entering the imaging volume can emit a strong signal relative to the partially saturated adjacent tissue ("flow-related enhancement"). Slow laminar flow in veins can be distinguished on the basis of a stronger second echo due to rephasing effects ("even echo rephasing"). Synchronization of the cardiac cycle and the MR pulsing sequence produces increased signal in sections acquired during diastole ("diastolic pseudogating"). Intraluminal signal is shown to decrease as velocity is increased ("high velocity signal loss"). Onset of turbulence causes further loss of signal. Direction of flow oblique to the imaging plane can be predicted on the basis of decreased upstream and increased downstream signal.

Identification of the Inflow Zone of Unruptured Cerebral Aneurysms: Comparison of 4D Flow MRI and 3D TOF MRA Data

“…[41][42][43][44] In this study, the maximum inflow velocity in our group 2 aneurysms was significantly lower than that in group 1 (P ϭ .029). The sensitivity of 3D TOF MRA, on the other hand, is affected by the direction of the blood flow.…”

“…The sensitivity of 3D TOF MRA, on the other hand, is affected by the direction of the blood flow. [41][42][43][44] We measured the angle of the section plane that identified the aneurysm orifice with respect to the imaging section direction on 3D TOF images. This angle was significantly smaller in group 1 than in group 3 aneurysms (P ϭ .045).…”

“…Our findings suggest that if 3D TOF MRA can depict the putative inflow zone in aneurysms whose neck has a section plane angle below 30°with respect to the imaging section direction, the information it yields is very precise. Concentric flow conditions such as slow or turbulent flow may lead to a regional elimination of TOF signal intensities, [41][42][43][44] and this may result in misidentification of the inflow zone on 3D TOF MRA images. However, in this study, no aneurysms were excluded due to signal loss when estimating the inflow zone and measuring morphologic parameters.…”

Hemodynamic scaling of fMRI-BOLD signal: validation of low-frequency spectral amplitude as a scalability factor

“…Further, interactions between capillary bed distributions and their orientation relative to the magnetic field (e.g., whether the capillaries are parallel or perpendicular to the magnetic field), could affect signal detection sensitivity. This is because the volume of protons excited by any given RF pulse will vary depending on the density, distribution, and orientation of the vascular elements including vessel caliber [11].…”

Magnetic Resonance Imaging of the Thoracic Aorta: A Review of Technical and Clinical Aspects, Including Its Use in the Evaluation of Aneurysms and Acute Vascular Conditions

“…They consist of either conventional or echo-train spin-echo techniques, usually with ECGgating, exploiting the contrast between rapidly flowing blood and the aortic wall (Sakamoto, 2010;Czum, 2005;Fattori, 1999;Russo, 2006;Bradley, 1985). Black-blood MRA may be useful for the depiction of intraluminal abnormalities such as dissection flaps and tumor www.intechopen.com In the first case (a) there is moderate high signal intensity in the false lumen, which correlates with high signal intensity on the bSSFP images (b), associated with slow flow.…”