Medical Imaging News

Magnetic Resonance Angiography (MRA)

By Dr Ali Zaman MBBS FRCR EBIR

What is MR, Angiography?

MR Angiography is a technique to study blood vessels. To accurately diagnose and effectively treat blood vessel-related infections, doctors use Angiography.

How does the process work?

Angiography examinations produce images of blood vessels throughout the body.  In certain instances, the contrast material is used. To test blood vessels and help detect anomalies, MR angiography (MRA) uses a strong magnetic field and radio waves.

Contrast Material:

The test that is conducted does not use chemical radiation rather, it uses an injection of contrast-based material Gadolinium.

Gadolinium is much less likely to trigger an allergic response than the iodinated contrast material used during CT. By placing a small intravenous (IV) catheter in a vein in the arm, the physician typically administers the contrast material.

How is Angiography performed?

Angiography is performed by physicians using:

  • Fluoroscopy (x-rays) to help place catheters in and inject contrast into blood vessels to visualize them.
  • Computerized tomography • (CT)
  • Imaging with magnetic resonance (MRI)

What are some common uses of the procedure?

Doctors use MRA to examine blood vessels in key areas, including the:

  • brain
  • neck
  • heart
  • chest
  • abdomen (such as the kidneys and liver)
  • pelvis
  • legs and feet
  • arms and hands

Doctors use MRA to:

  • identify abnormalities, such as aneurysms, in the aorta, both in the chest and abdomen, or in other arteries.
  • detect atherosclerotic (plaque) disease in the carotid artery of the neck, which may limit blood flow to the brain and cause a stroke.
  • identify a small aneurysm or arteriovenous malformation (AVM)—an abnormal connection between blood vessels—inside the brain or elsewhere.
  • detect plaque disease that has narrowed the arteries to the legs and help prepare for endovascular intervention or surgery.
  • detect disease in the arteries to the kidneys or visualize blood flow to help prepare for a kidney transplant or stent placement.
  • guide interventional radiologists and surgeons making repairs to diseased blood vessels, such as implanting stents or evaluating a stent after implantation.
  • detect injury to one or more arteries in the neck, chest, abdomen, pelvis or limbs after trauma.
  • evaluate arteries feeding a tumor prior to surgery or other procedures such as chemoembolization or selective internal radiation therapy.
  • identify dissection or splitting in the aorta in the chest or abdomen or its major branches.
  • show the extent and severity of coronary artery disease and its effects and plan for an intervention, such as a coronary bypass and stenting.
  • examine pulmonary arteries in the lungs to detect pulmonary embolism (blood clots, such as those traveling from leg veins) or pulmonary AVMs.
  • look at congenital abnormalities in blood vessels, especially arteries in children (e.g., malformations in the heart or other blood vessels due to congenital heart disease).
  • evaluate stenosis and obstructions of vessels.
  • screen individuals for arterial disease, especially patients with a family history of it.

MRA is also used as a substitute for CT angiography when iodinated contrast material cannot be used.

How should I prepare?

Inform your doctor:

  • Before going for an MR Angiography test, it is important to inform your doctor about your medical history. Inform your doctor if you recently had any surgery. The magnetic field is not dangerous, but it may cause the failure of certain medical devices
  • The majority of orthopedic implants pose no danger, so if you have any tool or metal in your body, you can always inform the doctor. Your doctor would often send you a card with your implant details.

Take your doctor’s recommendations before the test:

  • Take your usual medicines as normal until your doctor tells you otherwise. End up leaving jewelry at home and wear clothes that are also loose. You might be required to wear a gown.

Report if you are pregnant or breastfeed: 

  • The women need to report to her doctor if she is pregnant. Since the 1980s, MRI has been used with no records of any adverse effects on expectant mothers or their infants.
  • The kid will be in a powerful magnetic field, however. Consequently, in the first trimester, pregnant women do not get an MRI until the test result outweighs any possible dangers. Unless required, pregnant women do not obtain contrast gadolinium. For more pregnancy and MRI, details visit MRI Safety During Pregnancy
  • If, at the time of the test, you are breastfeeding, consult the doctor. It will help to collect breast milk in advance for future use. However, the most recent Contrast Media Manual from the American College of Radiology (ACR) states that findings indicate that the amount of contrast ingested by the baby during breastfeeding is exceedingly limited. Please refer to the ACR Manual on Contras for more details.

Report if you are claustrophobic:

  • If you have anxiety or fear of closed spaces, ask your doctor to administer a mild sedative before the test.
  •  Sedation or anaesthesia is also required for infants to pass an MRI examination. This depends on the age of the infant, intellectual maturity, and the form of testing at certain hospitals that can include sedation.
  • A paediatric sedation or anaesthesia specialist should be available for your child’s wellbeing during the test. You’ll be told how to get your child ready.

Leave your belongings at home:

  • Before the MRI scan, leave all jewellery and other items at home.
  • Metal and electronic objects can conflict with the MRI unit’s magnetic field and are not permitted during the test
  •  Inside the MRI scanner space, things like body piercing, eyeglasses, credit cards, metallic items, pocket knives, mobile phones, and tracking devices can cause burns.

Tell your doctor if you have any metal implant:

  • In almost 80% of the cases, an MRI exam is safe for patients with metal implants.
  • If you have medical or electrical equipment in your body, notify the technician. These devices can intervene or pose a danger to the exam.
  • Several embedded instruments have a booklet describing the MRI dangers. Bring it to the notice of the scheduler before the test if you have the booklet.
  • Without clarification and evidence of the implant type and MRI compatibility, the MRI cannot be done.

But people with the following implants can not be screened without first being assessed by their doctor. These patients include:

  • Certain implants of cochlear (ear)
  • Some sorts of clips used for aneurysms of the brain
  • Any kinds of metal coils that are positioned in blood vessels
  • Certain older heart defibrillators and pacemakers

Tell your doctor if you have any tattoo:

  • .Dyes used in tattoos may contain iron and could heat up during an MRI scan. This is rare.
  •  Tooth fillings, braces, eyeshadows, and other cosmetics usually are not affected by the magnetic field. However, they may distort images of the facial area or brain. Tell the radiologist about them.

What does the equipment look like?

A standard MRI is surrounded by a circular magnet and is cylindrical. You will lie on a table that slides into the center of the magnet.

Short-bore systems:

Many MRI units are built so that the magnet does not cover you, called short-bore systems. Many modern MRI devices have a wider bore diameter that can be more suitable for claustrophobic patients. Those MRI that are open on the side are known as “Open MRI”They are extremely useful for testing bigger or claustrophobic patients. For certain kinds of studies, open MRI units may provide high-quality images. Using an open MRI, certain scans can not be conducted. Consult the radiologist for more detail.

How does the procedure work?

Realignment of radio waves:

MRI does not use radiation, unlike x-ray and computed tomography (CT) examinations. Instead, hydrogen atoms that naturally exist within the body are re-aligned by radio waves. In the tissues, this does not cause any chemical changes. As the hydrogen atoms return to their usual alignment, depending on the type of body tissue they are in, they emit different amounts of energy. Using this information, the scanner captures this energy and creates a picture.

Production of a magnetic field:

The magnetic field is generated in most MRI units by passing an electric current via wire coils. In the unit, other coils are located and in some situations, are positioned around the portion of the body being imaged. Radio waves are sent and received by such coils, producing signals that the machine detects. There is no contact between the electric current and the patient.

Processing of signals:

The signals are interpreted by a computer and a series of photographs are produced, each of which displays a thin slice of the body. The radiologist will study certain images from various angles.MRI can tell the difference better than x-ray, CT, and ultrasound between diseased tissue and normal tissue.During the operation, when a contrast substance is applied to the bloodstream, it specifically distinguishes the studied blood vessels by making them look bright white.

How is it performed?

This examination is usually done on an outpatient basis.

Positioning:

You will be placed on the removable exam table. To help you keep very still hold straps and bolsters can be used.Tools that contain coils can transmit and receive radio waves that be mounted in or around the region of the body being scanned.

IV line:

The MRI exams normally require several runs (sequences), each of which can last several minutes. When a contrast drug is used, the doctor, nurse, or technician will implant an intravenous catheter (IV line) into a vein in the hand or arm that will be used to administer the contrast material.

Test:

You’re going to be put in the magnet of the MRI machine. The technician will administer the test while working on a computer outside the room. If a contrast substance is used during the examination, it will be inserted into the intravenous line (IV) following an initial sequence of scans. More pictures can be taken before or after the injection.

Review:

If the test is complete, you will be asked to wait while the radiologist reviews the photos if anything is needed. Your IV line will be deleted after the end of the test. The entire analysis is normally performed about 60 minutes after the start of the imagery.

What will I experience during and after the procedure?

No pain:

Most MRI exams are painless. However, some patients find it uncomfortable to remain still. Others may feel closed-in (claustrophobic) while in the MRI scanner. The scanner can be noisy. Sedation may be arranged for anxious patients, but fewer than one in 20 require it.

Temperature:

It is normal for the area of your body being imaged to feel slightly warm. If it bothers you, tell the radiologist or technologist. It is important that you remain perfectly still while the images are being taken. This is typically only a few seconds to a few minutes at a time.

Loud tapping sounds:

You will know when images are being recorded because you will hear and feel loud tapping or thumping sounds. These are made when the coils that generate the radio waves are activated. You will be provided with earplugs or headphones to reduce the sounds made by the scanner. You may be able to relax between imaging sequences. However, you will be asked to keep the same position without moving as much as possible.

Two way interaction:

You will usually be alone in the exam room. However, the technologist will be able to see, hear and speak with you at all times using a two-way intercom. Many facilities allow a friend or parent to stay in the room if they have also been screened for safety.

Music:

Children will be given appropriately sized earplugs or headphones during the exam. MRI scanners are air-conditioned and well-lit. Music may be played through the headphones to help pass the time.

Discomfort caused by IV:

In some cases, IV injection of contrast material may be given before the images are obtained. The IV needle may cause you some discomfort, and you may experience some bruising. There is also a very small chance of skin irritation at the site of the IV tube insertion. Some patients may have a temporary metallic taste in their mouth after the contrast injection.

Slight discomfort:

If you do not require sedation, no recovery period is necessary. You may resume your usual activities and normal diet immediately after the exam. On very rare occasions, a few patients experience side effects from the contrast material. These may include nausea, headache and pain at the site of injection. It is very rare that patients experience hives, itchy eyes or other allergic reactions to the contrast material. If you have allergic symptoms, tell the technologist. A radiologist or other doctor will be available for immediate assistance.

Who interprets the results and how do I get them?

A radiologist, a doctor trained to supervise and interpret radiology exams, will analyze the images. The radiologist will send a signed report to your primary care or referring physician, who will share the results with you.

Follow-up exams may be needed. If so, your doctor will explain why. Sometimes a follow-up exam is done because a potential abnormality needs further evaluation with additional views or a special imaging technique. A follow-up exam may also be done to see if there has been any change in an abnormality over time. Follow-up exams are sometimes the best way to see if treatment is working or if an abnormality is stable or has changed.

What are the benefits vs. risks?

Benefits

  • It is Noninvasive:

MRI is a noninvasive imaging technique that does not involve radiation exposure.

  • It providess more Details:
  • Detailed images of many blood vessels and blood flow can be obtained without having to insert an IV catheter into the blood vessels. When needed, a small IV catheter is inserted into a small vein in the arm so that there is no risk of damaging a major blood vessel. Even without using contrast material, MRA can provide useful high-quality images of many blood vessels. This makes it very valuable for patients prone to allergic reactions or with reduced kidney or liver function.
  • Takes less time:

An MRA scan may take less time than traditional catheter angiography and requires no recovery period, unless sedation was provided. If no sedation was used, you may return to your normal daily activities immediately following the MRA exam.

  • Affordable:

MR angiography is less costly than catheter angiography.

  • Less likely to cause allergy:

The MRI gadolinium contrast material is less likely to cause an allergic reaction than the iodine-based contrast materials used for x-rays and CT scanning.

Risks:

The MRI test poses absolutely no risk to the average patient when acceptable safety protocols are followed.

Sedation:

There is a chance of using too many if sedation is used. However, vital signs will be tracked in order to mitigate this ris. The intense magnetic field is not negative. It can, however, cause the embedded medical devices to fail or cause image distortion.

Nephrogenic systemic fibrosis:

Nephrogenic systemic fibrosis is a known but rare complication of gadolinium contrast injection. It typically happens in patients with extreme kidney disease. Before considering a contrast injection, the doctor will thoroughly test your kidney function.

Allergic reactions:

There is a very limited chance of allergic reactions when contrast media is used. Such responses are generally mild and are regulated by medicine. When you have an allergic reaction, the doctor will be available for urgent assistance.

Complications for new mothers:

IV contrast manufacturers indicate mothers should not breastfeed their babies for 24-48 hours after contrast material is given. However, the most recent American College of Radiology (ACR) Manual on Contrast Media reports that studies show the amount of contrast absorbed by the infant during breastfeeding is extremely low.

What are the limitations of MR Angiography?

  • Unlike CT angiography, MRA is not able to see and capture images of calcium deposits within the blood vessels.
  • MRA images of some arteries may not be as clear as catheter angiography images. MRA evaluation of small vessels, in particular, may be difficult. Sometimes it may be difficult to create separate images of arteries and veins with MRA.
  • Patients who cannot lay still or on their backs may have poor quality MRA images. Some tests involve monitoring the heartbeat or require patients to hold their breath for 15 to 25 seconds at a time in order to get high quality pictures. Any type of motion, such as patient movement, breathing motion, cardiac motion, or other involuntary movements can decrease the image quality and potentially limit diagnosis.
  • High-quality images depend on your ability to remain perfectly still and follow breath-holding instructions while the images are being recorded. If you are anxious, confused or in severe pain, you may find it difficult to lie still during imaging.
  • A person who is very large may not fit into certain types of MRI machines. There are weight limits on the scanners.
  • Implants and other metallic objects can make it difficult to obtain clear images. Patient movement can have the same effect.
  • A very irregular heartbeat may affect the quality of images. This is because some techniques time the imaging based on the electrical activity of the heart.
  • Although there is no reason to believe that MRI harms the fetus, pregnant women should not have an MRI exam during their first trimester unless medically necessary.
  • Doctors usually avoid contrast injections during pregnancy unless they are absolutely necessary for medical treatment.

Leave A Reply

Your email address will not be published.

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More