MR evaluation of cardiac/juxtacardiac masses.

With its superb contrast resolution, multiplanar imaging capability, and large field of view, magnetic resonance imaging is the gold standard in the imaging evaluation of cardiac and juxtacardiac masses. Spin echo images graphically display the pathoanatomy of intracavitary, valvular, myocardial, pericardial, and juxtacardial masses. Dynamic imaging techniques are used to identify their pathophysiologic consequences on myocardial contraction dynamics, valvular function, or blood flow mechanics. Echocardiography is a good modality to evaluate the heart and in most institutions, remains the initial test in the workup of cardiac masses. However, equivocal echocardiographic studies are common and, in fact, are the leading indication for the use of MR in the workup of cardiac/juxtacardiac masses.

Magnetic resonance imaging of the thoracic aorta.

Magnetic resonance imaging (MRI) is steadily becoming recognized as a premier imaging modality for evaluating the thoracic aorta. Its noninvasive, nonimaging approach and refined resolution capabilities effectively combine the advantages of echocardiography, angiography, and computed tomography (CT) under the auspices of a single imaging device. On static spin-echo MRI, blood flow appears dark, allowing superb depiction of both intra- and extra vascular anatomy. With dynamic MR studies, gradient echo (cine) and phase velocity mapping techniques have proven effective in assessing the physiological consequences of anatomic vascular abnormalities in a qualitative and quantitative manner, respectively. Magnetic resonance angiography (MRA) is fast becoming a prominent vascular imaging method. Although still evolving, MRA bolsters the vascular imaging capabilities of MRI by enhancing the imaging resolution of the major branch vessels and collateral vessels. With continued advances in this area, MRI may adopt the role as the primary imaging method for assessing the thoracic aorta.

Magnetic resonance imaging of the mediastinum.

Magnetic resonance (MR) imaging is becoming a primary modality for evaluating the mediastinum. MR affords multiplanar imaging capabilities without exposing patients to ionizing radiation. The inherent contrast effect of different mediastinal tissues sharply delineates anatomic structures on MR images without contrast enhancement. Gradient-echo and phase-mapping techniques permit noninvasive qualitative and quantitative assessment of mediastinal blood flow. High soft tissue contrast and flow analysis capabilities make MR imaging a valuable modality for evaluating mediastinal vascular disorders. Various mediastinal tumors and their extent are best identified by the use of T1-weighted, T2-weighted, and gadolinium-enhanced images. Both primary and secondary chest wall lesions may be assessed with standard spin-echo MR images. Complex pleuroparenchymal lesions may be evaluated by means of a multiplanar approach and modified pulse sequences. This article addresses the technical parameters governing MR imaging of the mediastinum and describes MR characteristics of various pathologic conditions.

Cardiopulmonary vascular imaging.

Magnetic resonance angiography (MRA) effectively maximizes the flow sensitivity of MR imaging (MRI) to display the body's vasculature. Although MRA has proven quite effective in imaging the intracranial and extracranial vessels, cardiopulmonary MRA faces several additional inherent challenges. Cardiorespiratory motion, vessel pulsatility, and irregular flow patterns all degrade image quality and necessitate appropriate compensation schemes. Although preliminary cardiopulmonary MRA methods appear promising, near instantaneous scan times may be necessary to fully maximize the potential of this technique. Multislice spin-echo and gradient-echo techniques have also proven effective. These methods may compensate for cardiac motion through either ECG-gating or referencing, and may maximize the signal characteristics from the intrinsic slow blood flow of the pulmonary vasculature. Phase velocity mapping techniques, which have proven capable of quantifying blood flow in the body, appear equally promising in preliminary studies in evaluating the cardiopulmonary vascular system. Because of the nature of blood flow dynamics in the cardiopulmonary vascular system, spin-echo (SE), gradient refocussed echo (GRE), and possibly phase mapping technique appear well suited for evaluating these regions.

The role of MR imaging in the evaluation of acquired diseases of the thoracic aorta.

Because MR imaging combines the major attributes of angiography, echocardiography, and CT, its role in the evaluation of the thoracic aorta is steadily increasing. When standard spin-echo techniques are used, flowing blood produces a signal void that allows excellent depiction of the anatomy and simultaneous evaluation of the lumen, vessel wall, and periaortic structures. On dynamic or cine MR, flowing blood generates a signal that allows visualization of the blood as it pulsates through the aorta. Turbulent blood generates a signal void, thereby allowing the detection and qualitative assessment of the pathophysiologic consequences of anatomic abnormalities. With phase-mapping techniques, blood velocity can be measured and used to calculate pressure gradients. Recent advances in the field of MR angiography will greatly enhance the overall role of MR in the evaluation of the thoracic vasculature by allowing detection and assessment of the branch vessels. Although the technique is still evolving, it has shown extraordinary potential as a tool for studying the thoracic aorta. The exact role of MR in patient care will depend on advances in transesophageal echocardiography. However, it is not unreasonable to think that someday MR imaging will be the primary technique for evaluation of the thoracic aorta.

Magnetic resonance imaging in the evaluation of congenital heart disease.

Magnetic resonance imaging is a powerful tool for studying patients with congenital heart disease. Its phenomenal contrast resolution, improved spatial resolution, and large field-of-view allow for graphic depiction of a wide array of congenital defects. Although this method was originally handicapped by the time it took to perform an exam and by poor image quality, advances in hardware and software coupled with attention to technique have led to a reliable diagnostic imaging modality. Although the technology is still evolving, it is not unreasonable to hope that the noninvasive imaging modalities of magnetic resonance and echocardiography will ultimately replace angiography in the evaluation of congenital heart disease.