Overview of MR Angiogram
Magnetic resonance angiography, or MRA for short, is a type of medical imaging that uses magnetic resonance imaging (MRI) technology to take pictures of your arteries and veins. The great thing about an MRA is that unlike traditional methods of looking at your blood vessels, it doesn’t involve any invasive procedures, there’s no exposure to potentially harmful radiation, and there’s the possibility of doing the examination without any contrast (a type of dye used to make blood vessels more visible on the images).
In addition to these benefits, the contrast material used in an MRA, called gadolinium, is less likely to cause an allergic reaction compared to the iodine-based contrasts used for CT scans, another type of medical imaging. This document takes a look at the variety of ways MRAs can be performed and when they might be used to help diagnose different medical conditions.
Why do People Need MR Angiogram
Magnetic Resonance Angiography (MRA) is a type of imaging test that doctors use to examine blood vessels in key areas of the body. This helps them diagnose and monitor certain health conditions.
These are some of the conditions that MRA can help with:
* Arterial aneurysm: This is a bulge or swelling in an artery, which can be life-threatening if it bursts.
* Arteriovenous malformations: These are defects in the blood vessels that occur before birth.
* Aortic coarctation: This is a narrowing of the large blood vessel that carries blood from your heart to your body (the aorta).
* Aortic dissection: This is a serious condition where the inner layer of the aorta tears.
* Cerebral stroke: This usually happens when blood supply to part of the brain is cut off or reduced, causing brain cells to die.
* Carotid artery disease: This occurs when fatty deposits in the arteries that supply your brain and head block the blood flow.
* Peripheral atherosclerosis: This happens when the arteries that supply blood to your limbs, usually legs, get blocked.
* Congenital heart disease: This is a group of heart defects that people are born with.
* Coronary artery disease and graft patency: Coronary artery disease happens when the heart’s blood vessels are narrowed or blocked. Graft patency refers to how well a graft (a surgically placed vessel) is working.
* Mesenteric artery ischemia: This is a condition where the blood flow in the arteries that supply the intestines is disrupted.
* Renal artery stenosis: This is a narrowing of the arteries that supply blood to the kidneys.
* Pulmonary embolism: This is a blockage in one of the arteries in your lungs.
* Trigeminal neuralgia: This is a chronic pain condition that affects the trigeminal nerve, which carries sensation from your face to your brain.
* Moyamoya disease: This is a rare condition where certain arteries at the base of the brain are blocked.
MRA is also used to screen for certain diseases and to monitor how well current treatments are working. In general, MRA helps physicians to get a closer look at how well blood is flowing through your body and identify any blockages or abnormalities.
When a Person Should Avoid MR Angiogram
Magnetic Resonance Angiography (MRA) uses the same safety guidelines as a regular MRI scan without any contrast dye. MRA is a type of scan that does not use harmful radiation. There has also been no reported side effects from the magnetic fields and radio waves it uses for
imaging. However, the gadolinium-based contrast agents used in some MRAs can cross the placenta. This means it shouldn’t be given to pregnant women, especially in the first trimester. While there are studies showing gadolinium can get deposited in the brain, particularly in areas known as the dentate nuclei and globus pallidus, no clear negative effects on brain function have been observed.
A scan without using a contrast dye has strict safety guidelines. Particularly, you shouldn’t have this scan if you have a heart electronic device, mechanical metallic heart valves, metal objects in your body, a neurostimulation implant, ear cochlear implant, non-removable drug pumps, metallic catheters, brain artery clips that aren’t MRI-safe, expandable tissue with magnetic ports.
There are also some conditions where you may have the scan, but caution is required. These include having coronary and peripheral artery stents, adjustable shunts, airway stents, intrauterine devices (birth control implants), eye prosthetics, ear bone implants, surgical clips, or wire stitches, penile implants, recent joint replacements, inferior vena cava filter (a device to prevent blood clots from reaching the heart), physical limitations, and non-removable piercings.
There are also strict safety guidelines for the use of contrast dye. Patients who have previously had allergic or severe allergic reactions to gadolinium, or patients with a kidney function below 30 mL/min/1.73 m^2 should not have these types of scans. Caution should also be used with patients who have a history of kidney disease, are on dialysis, or are pregnant. Patients with impaired kidney function may be at risk of a skin and organ condition called nephrogenic systemic fibrosis (NSF), previously known as nephrogenic fibrosing dermopathy.
How is MR Angiogram performed
Magnetic Resonance Angiography (MRA) is a group of various imaging techniques we use to look at different areas of your body. These techniques fall into two main categories: “non-contrast” and “contrast-enhanced.”
Non-contrast MRA
In a non-contrast MRA, we use techniques which basically make the blood vessels appear darker or brighter compared to surrounding body tissues.
“Black-blood” sequences make the blood appear darker than surrounding tissues. These aren’t typically used for examining peripheral blood vessels (those in the arms and legs), but they’re very useful for specific cases like inflammation of blood vessels (vasculitis), heart imaging, and susceptibility venography (a visual examination of the veins).
Methods we use in black-blood sequences include adjusting the length of time between radio pulses (known as repetition time), setting time for inversion recovery (a process to enhance image contrast), and applying techniques to alter the signal of the blood coming from outside the area being examined.
“Bright-blood” sequences, on the other hand, make the blood vessels appear brighter than surrounding tissues. These sequences are great for examining the interior of blood vessels, but they may not be as accurate for examining the vessel walls.
Two key techniques used in non-contrast MRA are the Time of Flight (TOF) Technique and the Phase-Contrast (PC) Technique.
The TOF technique uses the natural flow of blood to create an image of the blood vessels. This technique is particular useful for studying areas where the blood flows rapidly, like arteries, and is the first choice for studying cerebral blood vessels (in the brain) and the second choice for vessels near the aorta (major artery in the chest) when contrast medium (a special dye to make blood vessels visible) can’t be used.
The PC technique uses a range of gradients (changing magnetic fields) and pressure parameters to get selective imaging of arterial and venous blood vessels.
Newer non-contrast techniques include the Hybrid of Opposite-contrast (HOP-MRA), Quiescent Interval Single-shot (QISS) and Electrocardiographically gated 3D Partial-Fourier Fast Spin-echo FSE. They’re used for visualizing fine cerebral vessels, doing run-off studies in peripheral arteries and aorta, pulmonary, and peripheral imaging respectively.
Possible Complications of MR Angiogram
Magnetic Resonance Angiography (MRA), which is a type of MRI exam, can sometimes have complications. A review of nearly 717,000 of these scans from 9 various studies showed that allergic-like reactions happened at a rate of about 9.2 in every 10,000 scans. Serious allergic-like reactions were very rare, at about 0.52 in every 10,000 scans.
In another study that looked at reports of negative side effects related to MRI exams sent to the Food and Drug Administration over a 10-year period, about 1,548 adverse events were noted. These events were sorted into eight different categories:
- Thermal: Skin getting red, blisters forming, or sensations of warmth or heat.
- Acoustic: Loss of hearing and/or ringing in ears.
- Image Quality: Problems with the quality of the scan, like missing exams, low-quality pictures, or images being attributed to the wrong patient.
- Projectile: Items getting drawn towards or into the primary stationary magnetic field of the machine.
- Mechanical: Accidents like falls, crush injuries, bone breaks, cuts or injuries to the muscles or skeleton.
- Peripheral Nerve Stimulation: Sensations of the nerves or muscles including tingling, twitching, or involuntary movements.
- Miscellaneous: Any negative side effect that couldn’t be classified in the other categories.
- Unclear: Instances where there wasn’t enough information available to make a clear connection to the MRI exam.
What Else Should I Know About MR Angiogram?
Magnetic Resonance Angiography (MRA) is a type of scan that uses magnetic fields and radio waves to create detailed pictures of our blood vessels. It is a good alternative to a more traditional and invasive technique called angiography, especially for patients who might be dealing with diseases affecting their blood vessels. Thanks to its non-invasive nature and effectiveness, the use of MRA has become quite common in routine clinical practices.