26 February 2018
CARDIAC MAGNETIC RESONANCE
What is it?
Cardiac magnetic resonance imaging, or the cardiac MRI, is a powerful test with an unparalleled quality of images which makes it possible to visualize the heart and to evaluate its function.
It allows seeing the heart and evaluating its performance, its work. It allows to evaluate the composition of the cardiac muscle (also called “tissue characterization”).
This information is important in case of important congenital diseases, infiltrating diseases of the heart muscle or diseases that thicken the pericardium (the envelope of the heart).
Very different from the other standard cardiac imagery methods
It does not use radiations like X-rays, computer-assisted tomography (also called CT scan) or nuclear medicine.
It uses a magnetic field or magnet (1.5 or 3.0 Tesla intensity), radiofrequencies and a computer to generate the images
It is a very safe exam.
Superb alternative to the echocardiogram
It is particularly useful when cardiac echography do not allow to see the heart with enough precision.
You must make an appointment for these exams.
Commonly, the doctor that orders the test makes the appointment for the patient. In this case, the secretary contacts the patient to confirm the date and to give instructions for the exam.
Two types of resonances
There are 2 types of MRI: cardiac MRI at rest and cardiac MRI with stress.
Cardiac MRI at rest
Just as the MRI for the brain, the liver or the backbone, the cardiac MRI at rest begins with the acquisition of static images to evaluate how the heart is made and how the main vessels enter and exit it.
Then, as with the echography, continuous images, like videos of your heart (also called cine), are acquired under a variety of angles in order to get a 3-dimension view of your heart and to allow for an evaluation of its ability to contract effectively.
A substance to improve the quality of the image
Finally, unless otherwise contra-indicated, a Gandolinium-based substance is administered intravenously to improve the quality of the images.
The images taken afterwards allow for a better detail analysis of the composition of the cardiac muscle.
Duraation of the exam
This exam lasts between 30 and 50 minutes.
No need to have an empty stomach
You can eat normally on the day of the exam and you continue taking your medication as usual.
Cardiac MRI during stress
A cardiac MRI during stress is in fact a MRI at rest compared to one recorded during an effort. However, no treadmill test has to be done. The injection of a substance in the vein simulates an exercise for a few minutes.
At the end of the injection of the stimulant, a intravenous Gadolinium-based contrasting substance is administered and we evaluate how this substance distributes itself inside the heart muscle.
Finally, we analyse the composition of the cardiac muscle. This test is particularly useful if the patient suffers from thoracic pain or from angina. It helps to determine if the heart is the cause of these problems.
Duration of the exam
This test lasts approximately 60-65 minutes and is completed in a single appointment.
You may go home following this exam.
Instructions to follow prior to the exam
Precise instructions on the steps to take will be given to you prior to your exam.
Notably, you must refrain from drinking tea or coffee 24 hours before your exam.
The day of the exam
Before the exam, you will have to fill out a questionnaire. We really want to know:
1) If you are claustrophobic, or if you fear or are uncomfortable in small enclosed areas
2) If you have a pacemaker
3) If you have allergies, particularly to Gadolinium
4) If you are pregnant or breast-feeding
5) If your kidneys function normally. We will verify your renal function (or creatinine) with a blood test on the day of your exam if necessary. We check this by looking at the result of previous blood tests in your file or by taking another one the day of the exam, depending on the case.
6) If you have implants or metallic fragments in your brain or eyes
7) For the stress exam: if you have asthma
Upper-body clothing removed
You will be asked to remove all clothing covering your thorax and asked to put on a hospital gown.
One or two catheters installed in your veins
One (MRI at rest) or two (MRI at stress) intravenous lines will be inserted on one or both of your arms by the technologist. The technologist will accompany you to the examination room.
The MRI equipment doesn't like metal
You must make sure to remove all metallic objects (coins, jewellery, etc.). It is a bit like security control at an airport.
Preparation with the technologist
The technologist verifies if you are respecting the security instructions before asking you to enter the examination room.
The room is bright, but it is a little cool. The technologist will help you sit on the side of the examination table.
He or she will install 3 electrodes on your thorax, the small sensors that will record the heartbeats during the exam.
You will be asked to lay on your back.
Earphones are provided. A pillow and blankets are at your disposal to ensure your comfort.
For the remainder of the exam, your head and thorax must enter inside the scanner, which has the shape of a doughnut. You require no effort. The table is mobile and does all the work.
Most of the time, the tube (doughnut or scanner) is large and open at both ends to minimize claustrophobia.
You may speak with the technologist at any moment to mention how you fell.
Once you're properly set up, the technologist will sit in the control room adjacent to the examination room.
A glass window separates the two rooms allowing the technologist to keep an eye on you during the whole exam.
He or she communicates continually with you through the earphones. There are many microphones in the examination room. You can simply answer and he or she will hear you.
It is a noisy exam
The device is loud while it takes pictures. The earphones have two functions: minimize the sounds emitted by the device and to hear the instructions from the control room.
If you wish, between the instructions, you can listen to your music or to the radio through the earphones. You simply have to ask the technologist.
Follow the instructions
During the exam, the technologist will give you instructions to follow regarding your breathing. To improve the quality of the images obtained, it is very important to follow those instructions as much as possible.
The technologist verifies your blood pressure occasionally during the exam if it is a stress MRI.
Halfway through the exam, he or she comes back into the room to administer the Gadolinium-based substance in your vein. He or she returns to the control room to complete the testing.
The technologist removes the IV lines.
You may put your clothes back on and leave.
The results are sent to your doctor.
You may ask for a copy for another doctor
You may ask that a copy of your results be sent to another doctor. Simply give the name and coordinates of this doctor to the technologist.
You can speak to the technologist about this before or after the exam.