Magnetic resonance imaging (MRI) is a safe, non-invasive test that creates detailed pictures of your organs and tissues. "Non-invasive" means that no surgery is done and no instruments are inserted into your body.
Cardiac MRI creates both still and moving pictures of your heart and major blood vessels.
Doctors use cardiac MRI to get pictures of the beating heart and to look at its structure and function. These pictures can help them decide the best way to treat people who have heart problems.
CMR uses the same basic principles as other MRI techniques with the addition of ECG gating. Most CMR uses only H-nuclei MR, which are abundant in human tissue. By using magnetic fields and radiofrequency (RF) pulses, the patient's own H-nuclei absorb and then emit energy, which can be measured and translated into images, without using ionising radiation. Therefore, because an MRI uses radio waves, magnets, and a computer to create pictures of your organs and tissues. Unlike other imaging tests, MRI doesn't use ionizing radiation or carry any risk of causing cancer.
Cardiac MRI is a commonly used to diagnose and assess many diseases and conditions, including:
- Coronary heart disease
- Damage caused by a heart attack
- Heart failure
- Heart valve problems
- Congenital heart defects
- Pericarditis (a condition in which the membrane, or sac, around your heart is inflamed)
- Cardiac tumours
- Cardiac MRI can help explain results from other tests, such as x rays and computed tomography scans (also called CT scans).
Doctors sometimes use cardiac MRI instead of invasive procedures or tests that involve radiation (such as x rays) or dyes containing iodine (these dyes may be harmful to people who have kidney problems). A contrast agent, such as gadolinium, might be injected into a vein during cardiac MRI. The substance travels to the heart and highlights the heart and blood vessels on the MRI pictures. This contrast agent often is used for people who are allergic to the dyes used in CT scanning.
People who have severe kidney or liver problems may not be able to have the contrast agent. As a result, they may have a non-contrast MRI (an MRI that does not involve contrast agent).
Some recent CMR research innovations
Research to improve Cardiac magnetic resonance (CMR) imaging accuracy by removing the patients need to breathe has been presented at Euro CMR 2016 by Professor Juerg Schwitter, director of the Cardiac MR Centre at the University Hospital Lausanne, Switzerland.
"In many imaging techniques, but particularly in CMR, you need a relatively long acquisition time and must correct for respiratory motion," said Professor Schwitter. "For decades we have had to correct for respiration when estimating the position and motion of the heart by CMR, and this is not always accurate." The lack of motion allows acquisition of higher quality images in less time.
He continued: "In Lausanne, radio-oncologists are exploring a technique called high frequency percussive ventilation. Patients do not need to breathe naturally and no correction for respiratory motion is required. This enables the physicians to more accurately plan the field of radiation to apply in each patient."
For the technique, patients put a mask over their mouth which is connected to a ventilator that delivers small volumes of air, called "percussions". Instead of the 10 to 15 large breaths patients would take naturally per minute, air is provided in 300 to 500 small ventilations per minute. Air volumes are small so the chest does not move. The procedure is non-invasive, patients are conscious, not sedated, and do not need to breathe.
For the current study, the ventilator was adapted for use in the CMR environment. CMR uses a magnet which means that metal parts had to be swapped for MR-compatible ones. Tubes were used to connect equipment inside and outside the scanning room.
Professor Schwitter said: "Patients lie face up in the CMR machine and do not need to breathe. They say their chest feels a bit inflated during the ventilation but otherwise it feels okay."
The study was designed to test the feasibility and tolerability of high frequency percussive ventilation during CMR. It included one healthy volunteer aged 38 years and one patient aged 55 years with a thymic lesion. The procedure was well tolerated in both cases. The average time without breathing was ten minutes in the volunteer and six minutes in the patient.
The investigators could clearly see the coronary arteries. Lung volumes were "frozen" in full inspiration and the pulmonary vessels were also seen clearly. There was no need to correct for respiratory motion.
Professor Schwitter said: "We found that this type of ventilation was feasible and there was no problem with tolerating it. Of course, we are in a very early stage of development and we now need to test it in more patients. Some patients may find it difficult because the CMR machine is small and on top of that they will be ventilated by a machine."
Dr John Sandham CEng FIHEEM MIET