![]() ![]() Furthermore, with its dynamic sequences, MRI permits assessment of functional information and improved visualization of the entire bowel. Superior tissue contrast and lack of ionizing radiation are its major advantages over computed tomography (CT) and contrast-enhanced fluoroscopy. MRI provides a number of advantages over more conventional techniques for imaging the small bowel. in pediatric patients and in those with a history of iodinated contrast media adverse reactions.With recent advances in magnetic resonance imaging (MRI) software and hardware, and increasing expertise among technologists and radiologists, MR techniques have come to the forefront of imaging patients with known or suspected bowel pathology in both emergent and outpatient settings. Furthermore, the lack of ionizing radiation and need for iodinated contrast media are important factors to consider e.g. However, the accompanying standard sequences are more sensitive to cerebral morphological changes, such as edema, and focal lesions than CT 1. MRV takes generally longer to obtain than a CTV, and accessibility is generally also more limited. However, it necessitates the use of gadolinium-based contrast media, and enhancing clots can be challenging to detect with this technique. Contrast-enhanced dynamic MRV is more sensitive and specific in the diagnosis of intracranial venous sinus thrombosis than non-contrast techniques such as time of flight 2,3. Time-resolved (4D) techniques allow a dynamic evaulation of both flow and vessel patency. The main benefits are relatively short acquisition time and absent artifacts caused by e.g in-plane flow or background signal. After 15 days the thrombus can become iso to hyperintense on T2 and isointense on T1-weighted sequences. On gradient-recalled echo (GRE) and susceptibility weighted (SW) sequences the thrombus causes signal loss, which can accentuate clots not well depicted by other sequences. In the first 5 days after clotting the thrombus is typically isointense on T1 and hypointense on T2-weighted images due to its high deoxyhemoglobin content. These methods depict the thrombus due to the presence of paramagnetic blood products: deoxyhemoglobin, methemoglobin, or hemosiderin. It is also significantly longer to acquire than e.g. However it is vulnerable to motion-derived artifacts and turbulent flow within vessels. The technique offers excellent contrast compared to background signal, and can determine the direction of flow. in-plane flow mimicking thrombus, while tissues with short T1 relaxation can obscure smaller thrombi. However it is prone to artifacts due to e.g. The main advantages are sensitivity to slow flow, and no need for contrast media, as well as relatively rapid acquisition time. ![]() Non-contrast-enhanced flow related MRI Time-of-flight (TOF) MRV Multiple MRI techniques can be used to visualize the cerebral veins 1. The purpose of this exam is to visualize the cerebral veins and venous sinuses allowing their anatomy and patency to be assessed either using non-contrast or contrast-enhanced depiction of venous blood flow. CT venography is a reliable and very rapid alternative exam, however it utilizes ionizing radiation and iodinated contrast media. retrosigmoid craniotomies) may also warrant an MRV. Preoperative assessment of anatomy, particularly for posterior fossa surgery where the sigmoid sinuses may be compressed (e.g. Suspected cerebral venous thrombosis is the primary indication.
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