Essay Example on MRI Magnetic Resonance Imaging MRI








MRI Magnetic Resonance Imaging MRI is a highly flexible reproducible and noninvasive imaging modality In contrast to the other medical imaging methods which expose patients to ionizing radiation MRI uses strong non ionizing electromagnetic fields in the radio frequency range offers excellent spatial resolution is not operator dependent and provides 3D data Compared to other imaging techniques i e nuclear medicine techniques it shows low sensitivity and long acquisition time This is a technique allows evaluate the arterial vascular tree coronary arteries the aorta and its major branches carotid arteries and the arteries of the lower limbs Its use in the diagnosis of carotid atherosclerotic process has been validated and allows to obtain detailed information about the structure of the plaque In addition MRI is capable of discriminating between different component of plaque such as lipid core fibrous cap intraplaque haemorrhage and calcification and has the potential to identify vulnerable plaque before an ischemia Generally these elements appear as isointense ie Lipid component on T1 weighted sequences hypointense ie calcium within the plaque on T1 and T2 weighted sequences or hyperintense regions ie the fibrous cap

The carotid arteries are vessels of good caliber that are not subjected to movement Thus they are ideal for noninvasive imaging studies In contrast the motion artifacts the reduced size the position and the tortuosity of the coronary arteries make their visualization technically difficult Evaluation of the arterial wall although of great clinical utility turns out to be technically more difficult Furthermore the thickness of the coronary artery wall correlated with the temporal progression of the medical signals remains to be investigated COMPUTED TOMOGRAPHY CT Computed Tomography CT is a noninvasive imaging modality and is useful for evaluation of the arterial calcification an early indicator of atherosclerosis It provides a high temporal and spatial resolution and allows detailed anatomical visualisation of atherosclerotic coronary disease and other cardiac abnormalities in medium and large sized vessels Currently the technical limits of CT are poor soft tissue contrast and poor identification of subcomponents plaque In addition unlike MRI CT exposes patients to high radiation dose and the iodinated contrast agents CAs Furthermore the intravascular administration of these agents involves allergic or toxic reactions for patients CT scans can be performed with or without administration of contrast agents In the first case the diagnostic technique allows to detect non calcified plaque components while in the second case it allows to detect coronary calcium POSITRON EMISSION TOMOGRAPHY PET 

Unlike CT or MRI which show anatomic detail Positron Emission Tomography PET is a noninvasive nuclear imaging technique and provides quantitative in vivo assessment of physiological and biological phenomena This modality necessitates the injection of a small quantity of radioisotopes used as tracers PET agents provide a better functional assessment of atherosclerotic plaques than tracers used in current nuclear imaging modalities and one of the most used PET agents for understanding the pathological stages of vascular lesion in vivo is 2 deoxy 2 18F fluoro D glucose 18F FDG a synthetic molecule that competes with glucose for uptake into metabolically active cells ie inflammatory cells but is not metabolized The advantage of PET over other imaging modalities such as SPECT Single Photon Emission Computed Tomography is represented by high spatial resolution and contrast resolution and superior sensitivity that allow detection of picomolar tracer concentrations in the arteries Unfortunately limited spatial resolution 2 mm means that images must be coregistered with CT or MRI for precise anatomical localization of 18F FDG uptake Several clinical and preclinical studies of atherosclerosis show that an high macrophage density correlate with enhanced 18F FDG uptake in vessels with plaque Other works instead have demonstrated that the increased uptake of 18F FDG a transient phenomenon in the large arteries of patients correlated with atherogenic risk factors Furthermore this technique is not yet standardized and 18F FDG uptake or changes in 18F FDG uptake correlated to cardiovascular events can generate false positives or negatives NONINVASIVE MRI MOLECULAR IMAGING

Traditionally cardiovascular imaging has focused principally on anatomy allowing often a diagnosis after an acute or fatal event For this reason the use of a single technique is not recommended to precisely identify the progression of the pathological process As described previously MRI represents the unique technique that combines excellent soft tissue discrimination with high spatial resolution without the use of ionizing radiation Nevertheless this imaging modality is limited by its low sensitivity and requires the use of CAs to display the atherosclerotic plaques clearly 

This restriction may be overcome with a noninvasive molecular imaging approach considered an in vivo equivalent to immunohistochemical techniques and based on a signal imaging element encapsulated or conjugated to a carrier that transports a ligand that is then recognized by the target molecule In fact this strategy can facilitate early diagnosis has the potential to image the pathophysiological process of the disease before the onset of symptoms and can be applied to follow the efficacy of therapy In this scenario the advantage of MRI resides in its ability to provide not only anatomical but also functional information quantifying specific biological processes within a single imaging modality A variety of molecular targets have so far been successfully employed in preclinical models of cardiovascular disease to identify typical features associated with plaques that are prone to rupture Examples of biomarkers are shown below cell adhesion molecules VCAM 1 or E selectin extracellular matrix lipoproteins smooth muscle cells macrophages phosphatidylserine and α V β 3 integrin At first the contrast agents CAs were conjugated with monoclonal antibodies or specific peptides but excellent results are then obtained with nanoparticles NPs that combine a high binding affinity for the target zone with the capacity to transport a sufficient amount of a contrast agent The most widely employed NPs are superparamegnetic iron oxide SPIO micelles liposomes dendrimers and polymeric nanoparticles In this section we will focus on recent progress in the use of nanoparticles for molecular MR imaging in atherosclerosis disease

Write and Proofread Your Essay
With Noplag Writing Assistance App

Plagiarism Checker

Spell Checker

Virtual Writing Assistant

Grammar Checker

Citation Assistance

Smart Online Editor

Start Writing Now

Start Writing like a PRO