MR Angiography Principles and Techniques

Magnetic resonance angiography–also called MRA is a type of MRI developed for studying the arterial and venous systems. The benefits of an MRA in comparison to traditional angiography is that it is noninvasive, it lacks ionizing radiation exposure, it has the potential for a non-contrast examination and it has the ability of high-resolution volumetric images.
MRA used to evaluate an aneurysm or weakness in the wall of an artery ,a narrowing of the aorta, or aortic coarctation ,bleeding in and along the wall of the aorta ,or aortic dissection ,to find the cause of a stroke ,signs of heart disease ,narrowing or blockage of the vessels in the arms or legs ,renal artery stenosis, a narrowing of the blood vessels
in the kidneys that can lead to high blood pressure and even renal failure.
MRA is a term that groups various imaging techniques based on different physical principles and is employed for diverse diagnostic purposes .MRA methods can be divided into two broad categories depending on whether they produce dark blood or bright blood. Bright blood techniques are further subdivided according to whether they are performed with or without gadolinium contrast.
Contrast-enhanced MR angiography (MRA) is a technique involving 3D spoiled gradient- echo (GE) sequences, with administration of gadolinium-based contrast agents . It can be used to assess vascular structures of almost
any part of the body. Its key features are: 1.T1 weighted spoiled gradient-echo sequence
2.Central k-space acquisition corresponding to arterial phase of the study maximizes preferential visualization of arteries3.use of gadolinium contrast to shorten T1 interval of the blood which appears bright as a result.
Non Contrast Enhanced MR Angiography is performed in several ways including: 1. time of flight angiography (TOF) 2. phase contrast angiography (PCA) 3.Three-dimensional(3D) electrocardiograph-triggered half-Fourier fast spin echo. Generally, these techniques are time-consuming as compared with contrast enhanced MR angiography.