Cardio magnetic resonance imaging (synonyms: cardiac magnetic resonance imaging (cMRI), cardiac MRI, cardio-MRI; cardio-MRI; MRI-cardio; MRI-cardio) refers to a radiologic examination procedure that uses a magnetic field to image the heart. Cardio-MRI provides real-time images and allows a three-dimensional reconstruction of the heart and its surroundings. The procedure can be used to visualize the anatomy of the heart, the function of the heart chambers and damage to the heart muscle. The procedure is now considered the gold standard for all cardiac vitality examinations. This special form of magnetic resonance imaging (MRI) precisely detects the extent and location of circulatory disturbances and provides cardiologists with clear indications as to whether and how further treatment should be given. High-dose “dobutamine stress MRI” (DSMR) shows, for example, whether treatment of vascular stenosis by means of cardiac catheterization (in the sense of therapy using stents) is an option or whether drug therapy should be given priority. The positive predictive value of DSMR for the detection of coronary stenosis of more than 50 percent is high. A positive DSMR finding showing a perfusion defect is a powerful predictor of future cardiac events. And a negative DSMR finding can be used to infer a low risk for subsequent cardiac events. Another form of stress MRI or stress perfusion MRI is performed using adenosine or regadenoson. The use of adenosine (adenosine stress MRI) is an off-label use. Cardiac MRI is now routinely used for many problems because it is a highly informative diagnostic procedure.
Indications (areas of application)
- Heart failure – to differentiate heart failure (class 1C recommendation).
- Cardiac vitiations (valvular defects) with assessment of severity.
- Cardiac space occupying lesions
- Cardiomyopathy (heart muscle disease) – including, in particular, hypertrophic cardiomyopathy (HCM), which can be the cause of sudden cardiac death in athletes
- Coronary artery disease (CAD) – at intermediate pretest probability for CAD if any of the following ECG changes are present: Ventricular rhythm due to pacing or left bundle branch block or inconclusive ergometry for early detection of patients at increased risk of infarction.
- MINOCA (“Myocardial Infarction with Non-Obstructive Coronary Arteries“; acute myocardial infarction (heart attack) without evidence of coronary stenosis ≥ 50%) – for final diagnosis (DD cardiomyopathy (heart muscle disease), myocardial infarction (heart attack), myocarditis (heart muscle inflammation), or normal findings).
- Myocardial activity (after myocardial infarction) – activity of the heart muscle; especially after a heart attack.
- Myocarditis (inflammation of the heart muscle) – for diagnosis or assessment of disease activity.
- Pericardial effusion (pericardial effusion)
- Sarcoidosis – for prognostic assessment.
- Stable angina pectoris (“chest tightness”; sudden pain in the heart area with inconstant symptomatology) – belongs to the group of forms of the so-called “coronary heart disease” (CHD); stable angina pectoris is present when there is freedom from symptoms at rest and the symptoms occur stress-induced.
- Unclear pericardial thickening
Contraindications
The usual contraindications apply to cardiac MRI as to any MRI examination:
- Cardiac pacemaker (with exceptions).
- Mechanical artificial heart valves (with exceptions).
- ICD (implanted defibrillator)
- Metallic foreign bodies in dangerous localization (e.g., in close proximity to vessels or eyeball)
- Other implants such as: Cochlear/ocular implant, implanted infusion pumps, vascular clips, Swan-Ganz catheters, epicardial wires, neurostimulators, etc.
Contrast administration should be avoided in cases of severe renal insufficiency (renal impairment) and existing pregnancy.
The procedure
Magnetic resonance imaging is one of the non-invasive imaging procedures, meaning that it does not penetrate the body. By using the magnetic field, protons (primarily hydrogen) are excited in the body to produce nuclear magnetic resonance. This is a change in the orientation of the particles due to the magnetic field.This is picked up as a signal via the coils set up around the body during the examination and sent to the computer, which calculates the exact image of the body region from the many measurements that take place during an examination. In these images, the differences in the shades of gray are thus caused by the distribution of hydrogen particles. In MRI, one can distinguish between different imaging techniques, such as T1-weighted and T2-weighted sequences. MRI provides very good visualization of soft tissue structures. A contrast agent can be administered for even better differentiation of tissue types. Thus, the radiologist can obtain even more detailed information about any disease processes that may be present through this examination. Anatomy of the heart
Cardiac MRI involves imaging the heart and its surroundings. The anatomy of the heart, the function of the heart chambers and any damage to the myocardium (heart muscle) are depicted. Among other things, all volumetry parameters of the left ventricle (LV; left heart chamber) can be obtained from the data sets. Physiological parameters
Physiological parameters such as heart rate at rest and under maximum stress and blood pressure at rest and under maximum stress are measured. Functional parameters
The following are some of the most important functional parameters:
| Function parameters | Abbreviation | Description | Normal values at rest |
| Left ventricular end-diastolic volume | LV EDV | EDV = blood volume present in a ventricle at the end of diastole after maximal filling of a ventricle, i.e., after atrial contraction and closure of the atrioventricular valves | 130-140 ml approx. |
| Right ventricular end-diastolic volume | RV EDV | approx. 150-160 ml | |
| Left ventricular end-systolic volume | LV ESV | ESV = blood volume present in a ventricle at the end of systole after maximal emptying of a ventricle, i.e., after fully ventricular contraction | approx. 50-60 ml |
| Right ventricular end-systolic volume | RV ESV | approx. 60-70 ml | |
| Left ventricular stroke volume (SV). | LV SV | Volume of blood ejected from the left ventricle during one heartbeat | approx. 70-100 ml |
| Left ventricular ejection fraction | LV EF | Percentage of blood volume ejected from the left ventricle during a cardiac action with respect to the total volume of the corresponding ventricle | approx. 60-70 % |
Myocardial texture
Myocardial texture (heart muscle tissue) is examined. Normal findings are: No evidence of infarct scarring/regional fibrosis of the LV myocardium; no evidence of pericardial effusion (pericardial effusion), normal thickness of the pericardium (heart sac). The extent of focal fibrosis may be indicative of the development of dilated cardiomyopathy (DCM). In DCM, there is a disease of the heart muscle (cardiomyopathy) characterized by enlargement of the ventricles (heart chambers, especially the left ventricle) with cardiomegaly (enlargement of the heart) and primary reduction in systolic ejection fraction (ejection fraction). Edema detection (evidence of water retention) in patients with myocarditis (heart muscle inflammation) provides information about disease activity. MR angiography
MR angiography is used to visualize, among other things: Ascending thoracic aorta (aorta), aortic arch, descending thoracic aorta, pumonal artery (PA) (PA skin trunk and PA right and left), and the four pulmonary veins (pulmonary veins). Cardio-MRI is also a valuable addition to the non-invasive diagnosis of cardiac ventricular disease (valvular heart disease). Furthermore, images under stress are also possible in order to better assess performance limitations.
The contrast medium is administered via an arm vein. The contrast medium used, gadolinium (e.g. gadoterate megulumin), is much better tolerated than the X-ray contrast medium. Kidney damage is not a contraindication to the administration of gadolinium. Perfusion analysis
After injection of the contrast agent, slowed or absent distribution in the myocardium, which would indicate threatening ischemia, can be detected if necessary.If more than 6% of the heart muscle is not sufficiently perfused (supplied with blood), percutaneous coronary intervention (PCI) should be performed according to the current guidelines.Percutaneous coronary intervention (PCI; synonym: percutaneous transluminal coronary angioplasty, PTCA) is a therapeutic procedure in cardiology (study of the heart). It serves to widen stenosed (narrowed) or completely blocked coronaries (arteries that surround the heart and supply the heart muscle with blood) (= revascularization). Stress MRI of the heart
Dobutamine stress MRI indicates low risk when no dysfunctional segments (wall motion abnormalities) are detectable. Stress perfusion MRI using adenosine (adenosine stress MRI) (max. 6 minutes duration)/Regadesonon indicates low risk if no signs of ischemia (reduced blood flow) are detectable. During the examination, one is in an enclosed room in which there is a strong magnetic field. Because the MRI machine is relatively noisy, headphones are placed on the patient. Claustrophobia (fear of space) can occur due to the coils located around the region being examined. Newer open devices are already available in some hospitals/practices. Duration of examinations:
- Cardio MRI: 30 to 45 minutes.
- Stress perfusion MRI: 20 to 30 minutes
- Dobutamine MRI: 40 to 60 minutes
Cardio MRI represents a very precise diagnostic procedure that can already be used today to detect many diseases. An end to progress in this field is not yet visible.
Potential complications
Ferromagnetic metal bodies (including metallic makeup or tattoos) can lead to local heat generation and possibly cause paresthesia-like sensations (tingling). Allergic reactions (up to life-threatening, but only very rare anaphylactic shock) may occur due to contrast medium administration. Administration of a contrast agent containing gadolinium may also cause nephrogenic systemic fibrosis in rare cases. Further notes
- Based on current data, there are insufficient data to suggest that cardiac magnetic resonance imaging results in an increased rate of DNA double-strand breaks.
- In one study, CT and MRI scans performed as part of interventional cardiology resulted in noncardiac incidentalomas (incidentally found space occupying lesion (tumor) on imaging, without the presence of clinical symptoms; most commonly renal cysts in 16.3%, pulmonary nodules in 13.3%; cancer was newly detected in 1.6%) in 43.1% of cases.
- The MAGnet study of patients with stable angina who were at intermediate to high risk of CHD was randomized to split into two groups: Adenosine stress MRI or coronary angiography (imaging of the coronary arteries (arteries that surround the heart in a wreath shape and supply blood to the heart muscle) using contrast media).It was shown that only 28.1 percent of patients in the adenosine stress MRI group required revascularization. This included immediate coronary angiography if at least 10% of the myocardium (heart muscle) showed evidence of exercise-induced ischemia (reduced blood flow). After 1 year of follow-up, the primary end point, a composite of cardiac death and nonfatal myocardial infarction, was reached in 3, 1% of patients in the coronary angiography group and in 4, 2% of patients in the MRI group. The difference was not significant. Endpoint events in the postobservation period were all nonfatal myocardial infarctions (heart attacks).
- MR-INFORM trial: a multicenter study compared diagnostic coronary angiography with fractional flow reserve determination (FFR group) with perfusion analysis with MRI (MRI group). The primary end point was the occurrence of death, HMyocardial infarction, or target vessel revascularization within 1 year. This occurred in 15 of 421 patients (3.6%) in the MRI group and in 16 of 430 patients (3.7%) in the FFR group and was below the noninferiority margin established before study entry. CONCLUSION: MRI may replace cardiac catheterization in the diagnosis of patients with stable angina.