Feature Article

What is cardiac magnetic resonance?

Cardiology is the branch of medicine that addresses the heart and blood vessels, also known as the cardiovascular system. Cardiologists deal with a wide variety of diseases, which isn't surprising when considering that 610,000 people die of heart disease every year.1 It is often best that heart disease be diagnosed and monitored as soon as possible. One of the best methods for both diagnosing and monitoring heart disease may be magnetic resonance imaging (MRI).

How can MRI help?

An MRI scanner creates and manipulates a strong magnet field that produces signals from a patient's body which are then transmitted to the computer. The computer's data is then converted into images through the use of computer software and radiologists' knowledge. These images may show the physician the anatomy and function of the heart.2,3 This may include the heart chambers, valves, vessels, and the surrounding structures, as well as the blood flow within. MR technology, with the help of motion correction technology, generally produces  more complete, detailed and precise imaging than other imaging tests.4 It does not expose patients to ionizing radiation like CT scans do and has the potential to form similar functions to an echocardiogram.

One of the main obstacles to accurate and clear magnetic resonance images is the natural motion that occurs within the body. This is mainly respiratory and cardiac motion. Respiratory motion occurs when a patient breathes, causing the air to go in and out of their lungs and move the organs and structures in the abdomen. This motion used to be reduced by breath holds during their scan but has recently begun to be replaced by motion correction techniques and software. Cardiac motion occurs every time the heart beats, because it must pump blood out, which results in a squeezing motion and results in less motion artifacts than respiratory motion. Cardiac motion is useful for physicians to see. One method that can be useful for cardiac MR which allows physicians to observe cardiac motion is cine MRI.5 Cine MRI must be collected over multiple cardiac cycles to produce images that are as accurate as possible.6 These frames show the motion of the heart throughout a part of the cardiac cycle.

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When and why is cardiac MR used?

Cardiac MR (also called cardiovascular MR) can be used to monitor a number of different heart-related conditions and changes. It can be used to plan treatment for heart conditions, monitoring treatment progression and evaluating the effects of surgical changes.2,3 It may be especially useful for evaluating the effects of coronary artery disease and congenital heart defect, among many others.

Coronary artery disease (CAD) occurs when the blood vessels become damaged and diseased. It is usually caused by a build-up of plaque in the arteries and causes a reduced supply of blood, nutrients oxygen to the heart. Some of the symptoms of coronary artery disease are chest pain, shortness of breath and heart attack. CAD may be imaged using multi-detector row computed tomography, X-ray angiography or MRI.2,3,7 All of these techniques allow radiologists and doctors to visualize the structures of the coronary arteries non-invasively. MRI enables the visualization of not only the coronary arteries but also the surrounding structures.7

Congenital heart defects are present at birth and symptoms may occur in infancy and return during adulthood.8,9 They are abnormalities in the heart's structures, and one patient may have a single defect or multiple. These defects can include holes in the heart and do not have any set cause, though genetics, medications and infections during pregnancy are suspected. The most common may alter blood flow, though there are a variety of different defects that affect other aspects of the cardiovascular system. Imaging of congenital heart defects using MR could include black blood imaging, gradient echo cine imaging and contrast enhanced MR angiogram.10 Each provides images for the analysis of the anatomical and functional data.

Cardiac MR provides images of the heart and surrounding structures for radiologists to observe. These images can tell physicians about the structures and function of the heart and allow them to prepare treatment plans and monitor disease progression, especially in the cases of coronary artery disease and congenital heart disease. The heart is one of the most important organs in the body, causing imaging to be nearly a necessity. Cardiac MR helps to provide a solution for patients and doctors with cardiovascular concerns.

References

1. "Heart Disease: Heart Disease Facts." CDC.gov. 28 November 2018. Web. 30 January 2019. <https://www.cdc.gov/heartdisease/facts.htmf >.

2. Brian Krans. "Heart MRI." healthline.com. 24 January 2018. Web. 30 January 2019. <https://www.healthline.com/health/heart-mri>.

3. "Magnetic Resonance Imaging - Cardiac (Heart)." RadiologyInfo.org. 16 July 2018. Web. 30 January 2019. <https://www.radiologyinfo.org/en/info.cfm?pg=cardiacmr>.

4. Richard N. Fogoros. "Cardiac MRI: Uses and Limitations." verywellhealth.com. 20 September 2018. Web. 30 January 2019. <https://www.verywellhealth.com/cardiac-mri-definition-1745353>.

5. Andrew C. Larson, et al. "Self-Gated Cardiac Cine MRI." Magn Reson Med. January 2004; 51(1): 93-102. Web. 30 January 2019. doi: 10.1002/mrm.10664.

6. "Cine-cardiac motion studies." MRIQuestions.com. Web. 30 January 2019. <http://mriquestions.com/beating-heart-movies.html>.

7. SC Gerretsen. "Magnetic resonance imaging of the coronary arteries." Cardiovasc J Afr. July-August 2007; 18(4): 248-259. Web. 30 January 2019. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4170228/>.

8. Mayo Clinic Staff. "Congenital heart disease in adults." MayoClinic.org. Web. 30 January 2019. <https://www.mayoclinic.org/diseases-conditions/adult-congenital-heart-disease/symptoms-causes/syc-20355456>.

9. Suzanne R. Steinbaum. "Congenital Heart Disease Explained." WebMD.com. 24 August 2017. Web. 30 January 2019. <https://www.webmd.com/heart-disease/guide/congenital-heart-disease#2>.

10. Aparna Deshpande. "MRI in the assessment of congenital heart disease." Applied Radiology. Web. 30 January 2019. <https://appliedradiology.com/articles/mri-in-the-assessment-of-congenital-heart-disease>.