الفهرس 
CARDIAC ANATOMYOnly 14 pages are availabe for public view
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Abstract
MRI offers diagnostic information on characteristics of tissue and pathological changes such as fibrosis or fatty infiltration and gives images with a high spatial resolution allowing for a wealth of histopathological information that would otherwise be obtained only in an invasive manner.
Echocardiography is the most commonly employed technique for the study of heart morphology. This technique satisfies most clinical necessities but may present some problems with the acoustic window and produce poor quality images. In such cases, aid may be provided by an additional Magnetic Resonance Imaging (MRI) study. Indeed, MRI has no window limitations, has a large Field of View (FOV), allows to obtain images on any spatial plane and to acquire both static and dynamic images, and provides three-dimensional (3D) images. Furthermore, this technique allows accurate non-invasive assessment of the Right Ventricular (RV) mass; its evaluation is limited when using two-dimensional echocardiography or radionuclide ventriculography because of the required geometric assumptions regarding RV anatomy or overlapping of other cardiac chambers.
One of the fundamental targets of cardiac imaging is to evaluate cardiac function in an accurate and reproducible manner, in order to provide the proper tools for the diagnostic-prognostic management of different cardiomyopathies. Echocardiography fulfills the clinician’s expectations in the vast majority of cases. Availability, exam cost and the image quality of modern echocardiographic equipments is such that this technique remains the key examination in assessing cardiac function. However, MRI is nowadays an alternative when Echocardiography, which is still largely dependent on the operator and on the patient’s acoustic window, gives suboptimal results. The quantification of cardiac function by MRI is not limited by geometrical assumptions.
All the issues concerned to a functional quantification of the ventricles in echocardiography are stigmatized by the fact that in clinical practice the qualitative evaluation of cardiac function performed by expert operators, the quality still dominates over any effort of quantification.
The advantages of evaluation by MRI, compared to other techniques, are represented by its non-invasiveness, the use of non-ionizing radiation, the independence from anatomical windows, and the non-administration of contrast mediums and even if you inject C.M. it has a low possibility of allergy and side effect. In addition, MRI acquisition techniques can produce 3D reconstructions of the heart with, oriented on any plane of space, and with high contrast between muscular structures and blood, hence providing accurate and reproducible quantitative evaluations. MRI represents the complementary survey to echocardiography, especially when one wants to pass from a qualitative to a quantitative evaluation.
CE in contrast-enhanced cardiac MRI is not specific for ischemic infarction. CE in ischemic infarction always involves the subendocardial layer, whereas it does not necessarily do so in other myocardial diseases. Therefore, if CE omits the subendocardial layer, different nonischemic myocardial diseases have to be considered. The pattern of CE might be helpful for the differential diagnosis of myocardial disease and in distinguishing it from ischemic disease.
CMR is capable of identifying regions of LV hypertrophy not readily recognized by echocardiography and was solely responsible for diagnosis of the HCM phenotype in an important minority of patients. CMR enhances the assessment of LV hypertrophy, particularly in the anterolateral LV free wall, and represents a powerful supplemental imaging test with distinct diagnostic advantages for selected HCM patients.
Modern MRI systems and the new scanning techniques, high temporal and spatial resolution can be achieved in cine MRI sequences. For cine MRI, sequences have been adapted allowing for imaging in real time. Since the acquisition duration is short, breath-holding is optional, so it can be used even in critically ill patients. A further advantage is that these images can be accepted by post processing software as triggered cardiac studies and can be quantitatively analyzed. Cine images (SPGR, SSFP, etc.), allow to give a precise measure of wall thickening, end-diastolic and end-systolic volumes of the left ventricle and thus of the ejection fraction and allows to verify if there is an obstructive pattern in correspondence to the outflow tract of the left ventricle. Cine-MRI also gives the possibility of measuring the thickness of the free wall of the right ventricle which is taken at its different segments, because this wall is very thin.
Breath-held CMR is a fast comprehensive technique for the assessment of cardiac volumes, function, and mass in cardiomyopathies because of its accuracy and high reproducibility. This allows to reduce considerably the number of patients required to prove the hypothesis in research studies, which suggests a potential for important research cost savings.