Basics of non-invasive angiography contrast-enhanced magnetic resonance angiography

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Contrast-enhanced magnetic resonance angiography is a non-invasive imaging modality without catheterization or nephrotoxicity. This is accomplished by using paramagnetic contrast agents in combination with very rapid acquisition sequences. Paramagnetic contrast agent is injected intravenously and image data are collected during the first-pass of contrast agent through the vascular territory of interest. Due to the strong enhancement effect of paramagnetic contrast agents, a small dose injected as an intravenous bolus is sufficient to briefly enhance the entire arterial vascular tree. This allows imaging with a large field-of view that encompasses an extensive region of vascular anatomy. By using a dedicated 3D imaging sequence on scanners with high-performance gradient systems, high-resolution 3D volumes of image data can be acquired in a single breath-hold. This has vastly improved image quality of 3D contrast-enhanced MRA (CE-MRA) exams, particularly in the chest and abdomen. Subsequent postprocessing allows an angiographic display of image data in any desired obliquity. The following part gives an overview and the basic principles of the methods used for CE-MRA.

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... In addition, gadolinium-based contrast agents give a precise spatial localization and resolution because the MR sequences are less sensitive to susceptibility effects, as demonstrated in common MR angiography. 23 Consequently, gadolinium appears as a good candidate to visualize precisely a cell population in vivo. 24 Using the properties of phagocytosis, microglia could become visible vectors in vivo. ...
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Microglia are phagocytic cells that are chemoattracted by brain tumors and can represent up to 70% of the tumor cell population. To get insight into gene therapy against glioma, we decided to take advantage of those microglia properties and to use those cells as vehicles to transport simultaneously a suicide gene (under the control of a heat-sensitive promoter) and contrast agents to localize them by magnetic resonance imaging before applying any therapeutic treatment. Thymidine kinase (TK) expression and its functionality after gancyclovir administration were investigated. After the heat shock (44 degrees C and 20 min), TK was expressed in 50% of the cells. However, after gancyclovir treatment, 90% of the cells died by apoptosis, showing an important bystander effect. Then, the cells were incubated with new lanthanide contrast agents to check both their potential toxicity and their MR properties. Results indicate that the nanoparticles did not induce any cell toxicity and yield a hypersignal on MR images at 4.7 T. These in vitro experiments indicate that microglia are good candidates as vectors in gene therapy against brain tumors. Finally, microglia containing gadolinium-grafted nanoparticles were injected in the close vicinity of C6 tumor, in a mouse. The hyperintensive signal obtained on in vivo images as well as its retention time show the potential of the novel contrast agents for cellular imaging.
The detection of the association between nephrogenic systemic fibrosis (NSF), a rare but potentially life-threatening disease only encountered in patients with severely impaired renal function, and the previous administration of some Gd-chelates has cast a shadow on the administration of Gd-chelates in patients with chronic renal failure. So far, contrast-enhanced MR-angiography (MRA) was considered the best diagnostic modality in patients with suspected renal disease. This review explores the most appropriate use of renal MRA with a focus on newly developed nonenhanced MRA techniques. Nonenhanced MRA techniques mainly based on SSFP with ECG-gating allow for acceptable spatial resolution to visualize at least the proximal parts of the renal arteries. In addition functional renal imaging techniques and their current clinical role are critically appreciated. J. Magn. Reson. Imaging 2009;30:1323-1334. (c) 2009 Wiley-Liss, Inc.
So far, magnetic resonance angiography (MRA) of rodents has only been performed by using time-of-flight (TOF) MRI techniques. This is because applications of first-passage contrast agents as in humans are hampered by pronounced physiologic differences (blood volume and heart beat rate). Here we describe the use of low-dose Gd-DOTA to enhance the performance of TOF MRA in rat brain. While no improvement in contrast was achieved, the measuring time could be reduced by almost a factor of three. This decrease in total acquisition time has been used to study the impact of a model of ligatured common carotid on the upper part of the blood system of the rat.
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