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Resident section C M R Daniel Alejandro Benítez Abstract Resumen Advances in technology have made MRI an excellent tool for the diagnosis, prognosis and therapeutic planning for many pathologies affecting the cardiovascular system. We will briefly discuss the technique of Cardiac MRI (or CMR) showing an iconographic presentation of image findings in studies performed in our department. There are two basic sequences, namely: sequence of "dark blood" or spin echo, and sequence of "bright blood" or gradient echo (GE). The first is used to obtain anatomical information and the second is mainly used for a functional cardiac evaluation. The GE sequence used in most resonators is called Steady-State Free Precession (SSFP). The study protocol is not based on the conventional orthogonal views but on views applied to the position of the heart in the thorax. CMR has revolutionized the study of cardiovascular diseases, obtaining high-quality images. El avance de la tecnología ha hecho que la Resonancia Magnética (RM) brinde una excelente herramienta para el diagnóstico, pronóstico y planeamiento terapéutico de muchas de las patologías que afectan al sistema cardiovascular. Expondremos resumidamente la técnica de la Resonancia Magnética Cardíaca (RMC), realizando una presentación iconográfica de los hallazgos imagenológicos en los estudios realizados en nuestro servicio. Existen dos secuencias básicas: la secuencia de “sangre negra” o spin echo, y la secuencia de “sangre blanca” o gradiente de echo (GE). La primera es utilizada para obtener información anatómica y la segunda principalmente para la valoración funcional cardíaca. La secuencia GE utilizada en la mayoría de los resonadores es la llamada SteadyState Free Precession (SSFP) o Secuencia de Estado Estacionario de Precesión Libre. La RMC ha revolucionado el estudio de las patologías cardiovasculares, obteniéndose imágenes de alta calidad. Key words: Magnetic resonance, cardiopathy, cardiovascular disease. Palabras clave: Resonancia magnética, patología cardíaca, enfermedad cardiovascular. Introduction Cardiovascular diseases significantly affect the world population and, in Argentina, it constitutes the leading cause of death. Therefore, the study of this system for early diagnosis has great relevance. For a long time, radiology could not provide effective data on alterations affecting the heart and the great vessels. Due to advances in technology, MRI has become an excellent tool for the diagnosis, prognosis and therapeutic planning for many pathologies affecting the cardiovascular system (1). CMR is a non-invasive, reproducible technique that has several clinical applications. It has become the standard reference to evaluate cardiac anatomy and function. However, the study of the cardiovasContact information: Daniel Alejandro Benítez. Diagnostic Imaging Department, Sanatorio Allende - Córdoba Capital. e-mail: [email protected] Vol. / Nº - Mayo cular pathology through MRI requires an ample knowledge about the cardiac anatomy and function, as well as about the technique used to acquire images. The purpose of this paper is to explain, in a simple way, the technique used to conduct CMR and create an iconographic presentation of the pathologies evaluated through this technique. Generalities In every MRI it is important to take into account the contraindications to perform it, such as Stents, pacemakers or defibrillators (2). The best spatial and quality image resolution is currently obtained with 3T equipment; however, Received: April , / Accepted: July , Recibido: de abril de / Aceptado: de julio de Cardiovascular Magnetic Resonance most diagnostic centers in our country are equipped with 1.5T resonators, which are still useful for those purposes (3). There are two basic sequences in MRI applied to the study of the heart, namely: sequence of "dark blood" or spin echo (SE), and sequence of "bright blood" or gradient echo (GE). Variations are performed on these sequences that allow us to obtain different information of the cardiovascular system. Other sequences are: myocardial tagging, phase-encoding for fluid flow quantification, myocardial delayed enhancement, Inversion-Recovery (IR) and myocardial perfusion. To obtain clean images of the heart through MRI, it is necessary to have systems that minimize the physiological movements of the heart and of the process of breathing. An electrocardiogram (ECG) record of the patient is obtained so that the software can synchronize the acquisition of images with heartbeats. The better the acquisition of the ECG record, the better the synchronization will be. Breathing movement decreases performing the study in sustained expiration or breathing synchronization (4-6). Basic Sequences SE or “dark blood” sequence As the name implies it, this sequence shows the blood in vessels and heart chambers as hypo-intense. Repetition Time (TR) in this sequence has to be the same as the R-R interval of the patient's ECG. Since weighting images depends on TR and TE (Echo Time), when TR is the same as the R-R interval and short TE, T1 images are obtained. Whereas when TR is equal to 2 or more R-R intervals, the TE has to be long in order to obtain T2 images (Fig. 13). They can also be weighted with proton density (3-6). Double inversion recovery radio-frequency pulses are applied to suppress the blood signal. When a R wave (trigger) is detected in the ECG, a nonselective inversion radio-frequency (RF) pulse is applied, immediately followed by a selective reversion RF pulse. In this way, it is possible for a potential source of artifact, such as the slow flow of the blood that can appear bright and can be mixed with anatomical structures, not to emit signal with Benítez D. successive RF pulses applied in the acquisition of images. The acquisition of an image in a cardiac cycle is used in many protocols as a previous anatomical reference. Nowadays, high definition images of the heart are not acquired in real-time. They are divided in lines or groups of lines and each of them is acquired at the same time as the cardiac cycle of different heartbeats. That is why the movement of the heart is synchronized with the QRS complex of the ECG. Fast Spin Echo (FSE) or Turbo Spin Echo (TSE) sequences acquire several images with each heartbeat, reducing the duration of the study, unlike conventional SE which acquires one image per heartbeat. All of the "dark blood" sequences are used to obtain anatomical information (3-6). GE or “bright blood” sequence In this sequence, the blood emits a signal making it hyper-intense. It becomes more hyper-intense when the direction of the flow is perpendicular to the view of the image. They present a high temporal resolution making it possible to analyze them in Cine-MR. They are used for functional cardiac studies (Fig. 4-6) (3-6). There are two types of fast GE sequences. With the earliest one, the residual transverse magnetization (TM) is discarded (Spoiled GE) and it is not used for the creation of signal. Examples of this sequence are FLASH, SPGR, T1-FFE, depending on the brand name. They are produced through the emission of an excitation radio-frequency pulse, generally smaller than 90°, followed by a reversion gradient in, at least, two directions, creating a detectable echo signal (3-6). Steady-State (SS) sequences constitute the second type of GE sequences. The TM is not discarded but reoriented to contribute to the formation of a steady state. They provide a better space-time resolution and a better contrast between circulating blood and the myocardium. When there is a balance between the TM and the longitudinal magnetization (LM) two types of signals appear. The first type is a postexcitation signal (S+), created by the most recent RF pulse. The second signal (S-) constitutes the recreation of the echo, prior to the next RF pulse. There are three types of SS sequences depending on the signal sampling that is used to create the image. The S- sampling, that is, the pre-excitation Revista Argentina de Diagnóstico por Imágenes Cardiovascular Magnetic Resonance Benítez D. signal, is the one of interest for CMR, also called Steady-State Free Precession (SSFP). Their names depend on the resonator brand: FIESTA (Fast Imaging Employing Steady-State Acquisition) or FISP (Fast Imaging with Steady-State Precession) (7-9). They are very useful in Cine-MR sequences. Fig. : a b c d CMR Bright blood and dark blood sequence. Ventricular fibroma (*) located in the anteroposterior sector of the left ventricle (A and C) showing in T (B) an irregular peripheral hypersignal with intramural septa. The SPAIR sequence (D) shows a homogeneous hyper-signal. Fig. : CMR: Cine sequences in four-chama b c d Vol. / Nº - Mayo ber (A) and short axis (B) views showing a rounded formation (arrow) with a thin wall, hypo-intense in T (C) and hyper-intense in T (D), of cystic nature, in the lateral wall of the left ventricle, close to the apex. Cardiovascular Magnetic Resonance Benítez D. Fig. : a b c d CMR: Cine sequences in four-chamber (A and C) showing an important dilation of the right atrium (*) with an endocavity image, compatible with a thrombus adhered to the wall (arrow). Right ventricle with a dysmorphic aspect and decreased size, with parietal thickening (curved arrow). IR sequence after gadolinium (B) showing an endocardial enhancement of the apex (arrowhead). "Dark blood" T weighted sequence (D) showing areas of laminar hyper-signal, probably in relation to a replacement of the fibroadipose tissue of the apex. Findings compatible with endocardial fibroelastosis. Fig. : Outflow Tract of the Pulmonary Artery. a-b Postsurgical control of pulmonary atresia showing a narrowing (arrowhead) of the pulmonary valve (arrow) with irregularities, related to calcifications. The narrowing conditions a turbulent flow post-valvular (curved arrow) in systole (S). Fig. : Cine Sequence in Four-chamber View. MRI of two patients showing two inter-articular communications. One is of ostium secundum type (arrow) and the other is of sinus venosus type (arrowhead), showing an enlargement of the right atrium. a-b Revista Argentina de Diagnóstico por Imágenes Cardiovascular Magnetic Resonance Benítez D. Fig. : Cine Sequence in Four-chamber View. Slight inter-ventricular and sub-valvular communication with a diameter of mm (arrowhead). Study Protocol The reconstruction views applied to the thorax (coronal, sagittal and axial) cannot be applied to the study of the heart since it is located 45° measuring from the vertebral column, by its long axis. This is why specific views are used. First, multiplanar localizing images are obtained in the strict orthogonal planes (axial, sagittal and coronal). These must be acquired in total expiration. It is necessary to plan the specific cardiac locators over the multiplanar reconstructions (9). We emphasize that orthogonal planes help value the thoracic repercussions of the cardiac pathology and other incidental findings not necessarily associated with cardiac problems. The study protocol is based mainly on the following views: "short-axis", "long-axis" or "two-chamber" views which also assess the mitral and tricuspid valves; "four-chamber" views and views going out of the left and right ventricle tracts, which assess the aortic and pulmonary valves. The length of the study will depend on the pathology; it can vary from 20 to 60 minutes. Current Value CMR produces a reproducible and effective evaluation of the ventricular function, the segmental and global myocardial contractility, the ischemic cardiopathy, and the myocardium (Fig. 7 and 8). The myocardial perfusion study through the use of paramagnetic contrast agents, such as gadolinium with DTPA, for the evaluation of chronic myocardial Vol. / Nº - Mayo necrosis (11) provides information about the contractility, thickness and viability of the myocardium. It is useful for the correct assessment of the myocardium and of the complications after an infarction, such as ventricular aneurysm (Fig. 9), intraventricular thrombosis and valvular dysfunction, among others (Fig. 10). Through the pharmacologic stress (dipirydamole, adenosine, dobutamine) CMR shows ischemic areas that are not evident in ECG alterations (12). Infarctions areas are hyperintense due to contrast uptake (Fig. 11), whereas in ischemic areas there is no Gadolinium uptake during the stress test and it is recovered in the resting phase. The assessment of the pericardium has always been an important challenge for imaging techniques. Many times, findings are indirect or inconclusive, or there is a need for a skillful operator to perform the study. CMR is an accurate and non-ionizing technique that provides effective information for an adequate diagnosis (Fig. 12-14). Transthoracic echocardiogram (TTE) is the leading technique for the detection of cardiac tumors. However, it has some weaknesses: it is operator-dependent, there is a restriction in the visual field (especially in large-sized patients) and the information on right cavities is limited. CMR not only helps in the detection of cardiac tumors, but also in its characterization through different sequences (Fig. 15 and 16) and the relation with cardiac and mediastinal structures (13). Cine-MR has helped with the visualization of the cardiac valves with an excellent resolution (Fig. 17 and 18), and also with the correct quantification of Cardiovascular Magnetic Resonance transvalvular velocity and pressure gradients. It provides an excellent visualization of valve vegetation, thrombus, valve insertion site, valvular area and mobility (14). Congenital cardiac pathologies have been studied with CMR in its early stages and after surgery producing satisfactory results in children and adults, since it provides the most accurate ana- Benítez D. tomical and functional information (15) (Fig. 1923). Many systemic pathologies affect the heart and not only arterial hypertension. CMR helps in their correct assessment, as shown in figure 24 (Fig. 24), a patient with an amyloidosis diagnosis. Fig. : a-b Fig. : a b c Cine Sequences in Short Axis (left) and Four-chamber (right) views. Note the increase in size of the trabecular left ventricle, with deep inter-trabecular recesses (arrows), compatible with non-compacted myocardium. IR Sequences after Gadolinium Injection. Showing focal patched areas of enhancement of the mesocardium at the septum and inferior wall level without relation to an arterial course (arrowheads), compatible with myocarditis. Revista Argentina de Diagnóstico por Imágenes Cardiovascular Magnetic Resonance Vol. / Nº - Mayo Benítez D. Fig. : Ventricular Aneurysm. a b c d Cine sequences in four-chamber and short axis (left) views and IR after Gadolinium injection (right). Left ventricle increased in size with aneurysm of the septa and the anterior wall (*), showing a marked parietal and septa narrowing (arrow). There is a transmural enhancement of the inter-ventricular septa, of the anterior wall of the left ventricle and of the apical region (arrowheads) showing non-viable fibrotic areas after infarction. Fig. : Valvular Dysfunction. a-b Cine sequence of the aorta outflow tract. In diastole (D) there is a reflux jet (arrow) in the aortic valve. In systole (S) there is an aortic valve stenosis conditioning the turbulent blood flow of the ascending aorta (arrowhead). Fig. : Myocardium Infarction. a b c d Cine sequence in four-chamber and long axis views showing parietal narrowing and aneurysm dilation of the apex (arrows), with an endocavitary thrombus (*) adhered to the wall. Below, delayed acquisition IR sequences after Gadolinium injection showing transmural infarction (arrowheads) compromising the anteroseptal region and the apex circumference, evident due to a delayed enhancement (hypersignal). Cardiovascular Magnetic Resonance Benítez D. Fig. : a b c Fig. : a b c d Pericardial Effusion. Cine sequence in four-chamber (on the left) and the short axis views during systole (S) and diastole (D) (on the right) showing a severe pericardial effusion without thickening of the visceral membranes or parietal pericardium. Pericarditis. Cine sequence in short axis view (B) showing pericardial effusion (curved arrow). The IR sequence after gadolinium (C) shows thickening and laminar uptake of the visceral membrane and the parietal membrane of the pericardium in a global way (arrowheads). Fig. : Pericardial Cyst. a-b Right para-atrial cystic image (arrows) showing communication with the pericardium (arrowhead), compatible with pericardial cyst. Revista Argentina de Diagnóstico por Imágenes Cardiovascular Magnetic Resonance Benítez D. Fig. : a b c d Fig. : a-b Vol. / Nº - Mayo Cardiac Tumor. Male patient with antecedents of melanoma with metastasis in lung and liver, showing an endoluminal, irregular, multi-lobed lesion (*), located in the outflow tract of the right ventricle. It infiltrates the anterior face of the ventricle and the valvular plane. In systole, there is a turbulent blood flow in the pulmonary artery (arrow). After Gadolinium injection there is an intense and homogeneous enhancement (arrowhead). Fig. : Atrial Myxoma. a b c d Cine sequence in four-chamber (on the right above) and short axis (on the left below) views, showing a protruding lesion with septal origin in the left atrial cavity (arrowheads). During atrial systole (Sa) there is an oscillating movement that makes contact with the mitral valve (arrow), with a slight prolapse of it. After Gadolinium injection, there is a moderate enhancement (curved arrow). Perivalvular Fluid Axial acquisition with dark blood T weighted image (to the left) and Cine sequence for the outflow tract of the aorta (to the right), showing the presence of a non-homogeneous fluid (arrowheads) surrounding the prosthetic aortic valve (arrow) and extending to the ascending aorta and the aortic arch, surrounding them in a circumference. Cardiovascular Magnetic Resonance Benítez D. Fig. : a b c d Fig. : a-b Fig. : a-b Aortic Valve. Cine sequences showing bicuspid aortic valve (above). Normal aortic valve with its three valves (below). Open bicuspid (arrow). Normal and open (arrowhead). Interventricular Communication. Cine sequence in four chamber view. Closed interventricular communication. There is a patch (arrow) over the right face of the inter-ventricular septum. Systole (S) and diastole (D). Coarctation. MIP reconstruction sequence (arrow) and sagittal acquisition in dark blood T weighted sequence (arrowhead) showing coarctation of the descending aorta. Revista Argentina de Diagnóstico por Imágenes Cardiovascular Magnetic Resonance Benítez D. Fig. : a-b Fig. : a-b Superior Vena Cava Duplication. Axial acquisition (to the left) and coronal Cine (to the right) sequence after Gadolinium injection showing a superior vena cava duplication. The left vena cava flows into the left atrium (arrowhead). Right vena cava (arrow), pulmonary artery (*). Complex Abnormality. Cine sequence in four-chamber and short axis views showing a sole left ventricle in performing function (*). Interatrial communication (arrowhead) with a sole atrial ventricular valve. It shows an aortic arch and a descending aorta on the right (arrow). There is also a slight pericardial effusion (curved arrow). The patient had a transposition of great vessels and gastric tuberosity on the right (not shown here). Fig. : a bc d e Vol. / Nº - Mayo Transposition of Great Vessels. The aorta (Ao) originates in the right ventricle (VD) showing thickened walls (thin arrows); the pulmonary artery (Ap) originates in the left ventricle (VI). There is a pulmonary vein (thick arrow) flowing into the right atrial (*); the inferior vena cava is ascending towards the left atrial (arrowhead). The curved arrow signals the aorta. Cardiovascular Magnetic Resonance Fig. : a b c d Cardiac Amyloidosis. Outflow tract of the left ventricle in ventricular systole (A) and Cine four-chamber view (C) showing a slight thickening of the aortic open valve (arrowheads) and thickening of both atrial ventricular valves (arrows). The same patient with delayed sequences after Gadolinium injection showing mural and papillary muscles enhancement (curved arrow). The patient has a diagnosis of Amyloidosis. Conclusion CMR is a technique that is overturning cardiovascular pathologies diagnosis, since it can make a correct characterization of the morphological and functional alterations observed. To perform and report these studies requires a great knowledge about the cardiac function and pathologies, as well as the physics used in the creation of images. This is due to the fact that a slight change in the acquisition of images may improve the quality of the study in each patient. We should not forget that we are part of a team; therefore, it is necessary to rely on Bioimaging Technicians specially trained for these type of studies. In many cases, the presence of a cardiologist is necessary to control the patient, especially Benítez D. due to the use of medication for the myocardial stress. This method may not be available in most centers due to several factors, such as the necessary training and the cost of the equipment and the study. However, we believe that CMR will gain ground and that we should be prepared to perform the studies in an adequate way so it serves for a correct diagnosis. 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