Magnetic resonance angiography (MRA) is a method of examination that utilizes electromagnetic waves to produce two-dimensional or three-dimensional images of the body. It is sometimes referred to as “nuclear magnetic resonance imaging.” The advantage that MRA has over CT and conventional radiology is that it does not need contrast agent; rather, the flow of fluid is the inherent physiological contrast agent of the MRI. The performance of fluid on MRI images depends on its organizational characteristics, flow velocity, flow direction, flow pattern, and sequence parameters used.
Common MRA methods have time to overfly (TOF) and phase contrast (PC) methods. The main advantages of three-dimensional TOF method are less signal loss, high spatial resolution, and short time of collection. The two-dimensional TOF method can be used in large volume screening imaging to examine the non-complex slow bleeding tube. The three-dimensional PC method can be used to analyze the details of suspicious lesions and check the flow and direction. The two-dimensional PC method can be used to display lesions requiring very short time imaging, such as the observation of cardiac cycle from a single perspective.
In recent years, a new MRA method, called contrast enhancement MRA, has been developed, which is widely applicable and highly practical. The method is the gd-dtpa contrast agent with 2-3 times the conventional dose in intravenous mass injection. The ultra-short TR and TE rapid gradient echo technique is adopted for three-dimensional collection.
The current clinical indications of MRA are expanding day by day. In recent years, it has been used for the examination of cranial and cervical artery and vertebral artery diseases (obstruction and stenosis, etc…), intracranial vascular malformation, vascular occlusion, aneurysm, arterial vein, etc… It is also used to assess the hepatic vascular system, renal artery stenosis, and peripheral vascular disease before liver transplantation. In terms of the application of cardiac large vessels, MRA in addition to the observation of morphology and energy cardiac large vessels, has been basically successful in the display of coronary arteries. It has great application value in the diagnosis of major branches of coronary artery stenosis, the monitoring of postoperative patency, and the diagnosis of pulmonary embolism.
From the overall perspective, however, the practical value of MRA still needs to be further improved, mainly showing that the observation of dynamics and hemodynamics, spatial resolution ability and diagnostic reliability are not as good as those of conventional X-ray angiography. At present, MRA is mostly used as a preliminary screening method in most clinical cases, and is still not completely replaced by conventional X-ray angiography.
