Magnetic Resonance Angiography

Background

Magnetic resonance angiography is a form of magnetic resonance imaging (MRI). MRI is a non-invasive method of taking images of the body. Electromagnetic radio waves create 2-dimensional or 3-dimensional images. The effects of magnetic resonance imaging, unlike computer tomography (CT scan) and X-rays, offer no risk to the humanbody. The principle of the MRI is not commonly known. It is in fact quite simple and unique.

The Process Explained

The coils of the MRI machine create powerful electromagnetic fields. These electromagnetic fields cause hydrogen atoms inside the body to align themselves like the way the magnetic needle of a compass behaves when it is brought near to a magnetic field. The radio waves from the MRI machine impinge on these aligned hydrogen atoms causing them to bounce back. The computer records this movement in the form of a signal. The computer then interprets the signal and gives us information about the condition of that area of the body which is being scanned.

Magnetic Resonance Angiography

This is a special kind of magnetic resonance imaging where images of the vascular system (blood vessels, such as veins and arteries) are taken. This kind of test detects anomalies such as atherosclerosis, clots, and aneurisms and so on. The flow of blood can also be evaluated in this way.

The Purpose of the Test

The vascular system of the human body is a life-supporting network. If there are any aberrations in this, the body is adversely impacted. It can lead to illness and in more extreme cases, death. Therefore it is very important that the vascular system is kept healthy. Due to the location of the vascular system in the human body, it is not possible to detect a problem through external means. The only way to diagnose abnormalities in the vascular system is by studying the symptoms or by the use of sophisticated diagnostic equipment. Magnetic resonance angiography allows us to scan the entire vascular system the heart and all the associated blood vessels (veins and arteries).

The following parts of the body come under the purview of magnetic resonance angiography:

  • Head and Neck: This area is scanned to detect blood clots of more than 3mm in size or constrictions in the blood vessels caused by disease or injury known as stenosis. It also helps in detection of causes of stiff neck, headaches and tinnitus.
  • Chest: Magnetic resonance angiography is useful when planning thoracic surgery, and for post-operative monitoring. It can also help to detect pulmonary embolisms (blood clots in the lung).
  • Spine: Magnetic resonance angiography is done on the spine to monitor patients who are already diagnosed with arterio-venous fistulae of the spinal cord or any other such vascular defect in the spinal cord.
  • Abdomen: The abdomen can be scanned by this procedure if there is any problem in renal arteries. This area is also covered under incidences of hypertension under certain circumstances. It is used to examine pelvic arteries and detection of abdominal aortic aneurysms (bulging of the Aorta). Magnetic resonance angiography also helps to detect mesenteric ischemia which is a condition cause by insufficient blood supply to the small intestine.
  • Lower Extremity: Here again, an MRA can be done if any surgery on the blood vessels is planned as in treatment in the case of arterial disease in the lower extremities.  
  • Allergy, etc: Magnetic resonance Angiography can be required if a patient is allergic to iodinated contrast material and also for people with accelerating renal insufficiency or accelerating hypertension.

When to have a Magnetic Resonance Angiography

From what we have seen so far, it is obvious that an MRA is a more specialized form than an MRI. It should be however understood as to when an MRA needs to be done, rather than an MRI.

Differences between MRI and MRA

To highlight the difference between magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA), we can say that an MRI on the brain will show ventricles, tissue, internal auditory canals, ventricles, pituitary gland and sinus cavities. An MRA will show only the blood vessels in the brain. In the case of a neck MRI, the spinal canal will be shown in detail, including soft tissue, intervertebral disc spaces and thyroid gland. An MRA will show the carotid artery and associated blood vessels only.

An MRI creates images based on the difference in concentration of water in human tissues. It is mostly useful for detection of tumors and disorders of the nervous system, basically anomalies in the structure of the tissue. An MRA on the other hand is able to highlight irregularities in the blood vessels of the head and neck and is best for detecting aneurysms and blockages.

Conclusion

Therefore, it is seen that there is actually a very thin line between magnetic resonance angiography and magnetic resonance imaging. The equipment is more or less the same for both processes and the difference more or less the way in which the test is conducted.  It can be then concluded that it is appropriate to conduct an MRA when the imaging needs to highlight the vascular system.