tailieunhanh - Ebook Cardiovascular Imaging: Part 2

(BQ) Part 2 book "Cardiovascular Imaging" presents the following contents: Cardiovascular magnetic resonance (clinical applications, emerging applications of cardiovascular MRI), future prospects of cardiovascular (molecular imaging, specific cardiovascular applications of molecular imaging, multidisciplinary cardiovascular imaging programs). | 120 5. Cardiovascular Magnetic Resonance Imaging André Schmidt Joao AC Lima INTRODUCTION Cardiac magnetic resonance imaging CMRI Lund 2001 is a promising imaging modality with substantial clinical applications thanks to its unique diagnostic versatility. CMRI provides detailed anatomical information about the heart and also allows for the assessments of global and regional cardiac function volumes and mass and the assessments of myocardial perfusion valvular function and tissue characterization. In this chapter various established and emerging clinical applications of CMRI will be discussed. MRI principles Paramagnetic substances with an odd number of protons and or neutrons such as 1H 14N 31P 13C and 23Na have the property of spinning precession around their axes and can be used for imaging by MRI. When exposed to a magnetic field these atoms will align with the magnetic field and continue to precess. Hydrogen is the atom most widely used in MRI because of its abundant presence in the human body and optimal signal strength. Therefore unless stated otherwise the MRI described in this chapter is referred to 1H MRI. From the basic physics it is known that a moving charged particle generates a magnetic field. When exposed to an intense magnetic field such as that generated by MRI equipment all individual magnetic fields are aligned and a resultant vector is obtained. Another important concept of MRI is the Larmor equation f yM where f is frequency in revolutions per second of the precessing substance y is the gyromagnetic ratio of the substance . hydrogen which is a constant and M is the strength of the magnetic field expressed in Tesla T . According to this equation the frequency of precession is directly proportional to the strength of the magnetic field and since the gyromagnetic ratio is a constant being specific for each substance the frequency of precession is unique. The strength of the magnetic field in a specific location can be manipulated to obtain .