quarta-feira, 25 de julho de 2012

Non-contrast enhanced MR angiography: Physical principles

A utilizacão do meio de contraste em ressonância magnética é importante em muitos casos e a técnica angiografica é um deles, mas devido alguns pontos negativos como pacientes com alergia ao contraste e pacientes com insuficiência renal, cada vez mais o desenvolvimento de métodos em MR caminha para técnicas de angiografia sem contraste. O artigo abaixo apresenta uma introducão muito boa sobre algumas técnicas novas como "spin labeling" e "flow-dependency on cardiac phase".

Non-contrast enhanced MR angiography: Physical principles:

Abstract

Noncontrast-enhanced magnetic resonance angiography (NCE-MRA) methods have been demonstrated in anatomies throughout the body. Previously established NCE-MRA techniques suffered from long scan times or low sensitivity. Advances in hardware and software have made NCE-MRA scan times clinically feasible. Recent concerns over the safety of gadolinium-based contrast material combined with the expense of the material and its administration have generated a demand for NCE-MRA. In response, several new NCE-MRA methods have been developed. The physical mechanisms underlying five general classes of NCE-MRA methods (inflow effect, flow-dependency on cardiac phase, flow-encoding, spin labeling, and relaxation) are explained. The original techniques of time-of-flight (TOF) and phase contrast MRA (PC-MRA) are briefly introduced. New developments in NCE-MRA, including hybrid of opposite-contrast (HOP-MRA), four dimensional PC-MRA (4D Flow), cardiac-gated 3D fast-spin-echo, flow-sensitive dephasing (FSD), arterial spin labeling (ASL), and balanced steady-state free-precession (bSSFP) are highlighted. The primary applications, advantages, and limitations of established and emerging NCE-MRA techniques are discussed. J. Magn. Reson. Imaging 2012;36:286–304. © 2012 Wiley Periodicals, Inc.

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