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Magnetic field imaging | |
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![]() Patient during an MFI acquisition | |
Purpose | non-invasive cardiac diagnostic method |
Magnetic Field Imaging (MFI) is a non-invasive and side-effect-free cardiac diagnostic method. In more recent technology, magnetocardiography (MCG) has become the clinically predominant application for recording the heart's magnetic signals. that detects and records the electromagnetic signals that are associated with the heartbeat using a multi-channel magnetic sensor array. The electric signals are known from the ECG. In the 1990s and beyond, more recent technology has supplanted the MFI, particularly MCG (xref. Cardiomag Imaging, Inc.). Through clinical research in Europe, Asia, and the U.S. (see publications in footnotes), MCG has been proven to have practical application for diagnosis of cardiac disease, and has become the clinically predominant application for recording the heart's magnetic signals. In comparison to MCG, MFI, among others, records the whole relevant area above the chest of the person.
The general principal of MFI is based on two facts:
The difference between the electric and the magnetic signals:
In comparison to the electric signals, which are influenced by the differently conductive tissue of the body and varying resistance of the skin before they can be recorded, the magnetic signals travel through the body almost without disturbance. The differences in the electric potentials, that are recorded by the ECG, are directly depending on the inhomogeneity and geometry of the thorax, the magnetic signals outside of the thorax depend primarily on the intracellular currents of the cardiac tissue and only secondarily on the secondary currents generating the electric signal. Furthermore, the magnetic signals of so-called vortex currents, which occur regularly in every heartbeat and include important information for an advanced and more accurate cardiac diagnosis (first theoretically described by John Wikswo), [1] [2] can be acquired with an MFI system, but cannot be recorded electrically on the body surface (First experimental hint by Brockmeier et al. 1994 [3] and comprehensive demonstration Brockmeier et al. 1997). [4]
Recording technology
The magnetic field changes detected by the MFI are about one million times weaker than the magnetic field of the earth. High end acquisition electronics and noise reduction concepts are necessary. As sensors the most sensitive magnetic sensors presently available, SQUIDs (superconducting quantum interference devices), which are cooled down to 4 K (-269 °C) with liquid helium, are used to acquire the signals.
The main fields of use are the risk stratification of ventricular tachycardia (VT) and the detection of stress induced ischemia. The MFI system can detect the onset of arrhythmic and ischemic diseases in a very early stage with high accuracy for both acute and asymptomatic patients.
As MFI is absolutely risk free and harmless for the patient, the procedure can be repeated without any negative effects for the patient, which gives the cardiologist the opportunity to observe a patient's progressive changes. The non-invasiveness of MFI makes it an ideal tool for the diagnosis of pregnant women as well as it can in addition detect the cardiac signal of a fetus starting from the 4th month of pregnancy.
In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the fore head(superficial temporal artery),neck ,elbow(brachial artery),wrist, at the groin, behind the knee, near the ankle joint, and on foot. Pulse is equivalent to measuring the heart rate. The heart rate can also be measured by listening to the heart beat by auscultation, traditionally using a stethoscope and counting it for a minute. The radial pulse is commonly measured using three fingers. This has a reason: the finger closest to the heart is used to occlude the pulse pressure, the middle finger is used get a crude estimate of the blood pressure, and the finger most distal to the heart is used to nullify the effect of the ulnar pulse as the two arteries are connected via the palmar arches. The study of the pulse is known as sphygmology.
Electrocardiography is the process of producing an electrocardiogram, a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin. These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle (heartbeat). Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances, inadequate coronary artery blood flow, and electrolyte disturbances.
Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart.
In medicine, a Holter monitor is a type of ambulatory electrocardiography device, a portable device for cardiac monitoring for at least 24 hours.
A cardiac stress test is a cardiological test that measures the heart's ability to respond to external stress in a controlled clinical environment. The stress response is induced by exercise or by intravenous pharmacological stimulation.
Acute coronary syndrome (ACS) is a syndrome due to decreased blood flow in the coronary arteries such that part of the heart muscle is unable to function properly or dies. The most common symptom is centrally located chest pain, often radiating to the left shoulder or angle of the jaw, crushing, central and associated with nausea and sweating. Many people with acute coronary syndromes present with symptoms other than chest pain, particularly women, older people, and people with diabetes mellitus.
Atrioventricular block is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatrial node produces an electrical signal to control the heart rate. The signal travels from the SA node to the ventricles through the atrioventricular node. In an AV block, this electrical signal is either delayed or completely blocked. When the signal is completely blocked, the ventricles produce their own electrical signal to control the heart rate. The heart rate produced by the ventricles is much slower than that produced by the SA node.
Impedance cardiography (ICG) is a non-invasive technology measuring total electrical conductivity of the thorax and its changes in time to process continuously a number of cardiodynamic parameters, such as stroke volume (SV), heart rate (HR), cardiac output (CO), ventricular ejection time (VET), pre-ejection period and used to detect the impedance changes caused by a high-frequency, low magnitude current flowing through the thorax between additional two pairs of electrodes located outside of the measured segment. The sensing electrodes also detect the ECG signal, which is used as a timing clock of the system.
A biosignal is any signal in living beings that can be continually measured and monitored. The term biosignal is often used to refer to bioelectrical signals, but it may refer to both electrical and non-electrical signals. The usual understanding is to refer only to time-varying signals, although spatial parameter variations are sometimes subsumed as well.
Magnetocardiography (MCG) is a technique to measure the magnetic fields produced by electrical currents in the heart using extremely sensitive devices such as the superconducting quantum interference device (SQUID). If the magnetic field is measured using a multichannel device, a map of the magnetic field is obtained over the chest; from such a map, using mathematical algorithms that take into account the conductivity structure of the torso, it is possible to locate the source of the activity. For example, sources of abnormal rhythms or arrhythmia may be located using MCG.
Cardiac amyloidosis is a subcategory of amyloidosis where there is depositing of the protein amyloid in the cardiac muscle and surrounding tissues. Amyloid, a misfolded and insoluble protein, can become a deposit in the heart's atria, valves, or ventricles. These deposits can cause thickening of different sections of the heart, leading to decreased cardiac function. The overall decrease in cardiac function leads to a plethora of symptoms. This multisystem disease was often misdiagnosed, with diagnosis previously occurring after death during autopsy. However, recent advancements of technologies have increased the diagnosis of the disease. Cardiac amyloidosis has multiple sub-types including light chain, familial, and senile. One of the most studied types is light chain cardiac amyloidosis. Prognosis depends on the extent of the deposits in the body and the type of amyloidosis. New treatment methods are actively being researched in regards to the treatment of heart failure and specific cardiac amyloidosis problems.
Myocardial perfusion imaging or scanning is a nuclear medicine procedure that illustrates the function of the heart muscle (myocardium).
Cardiac magnetic resonance imaging, also known as cardiovascular MRI, is a magnetic resonance imaging (MRI) technology used for non-invasive assessment of the function and structure of the cardiovascular system. Conditions in which it is performed include congenital heart disease, cardiomyopathies and valvular heart disease, diseases of the aorta such as dissection, aneurysm and coarctation, coronary heart disease and it can be used to look at pulmonary veins.
Coronary ischemia, myocardial ischemia, or cardiac ischemia, is a medical term for a reduced blood flow in the coronary circulation through the coronary arteries. Coronary ischemia is linked to heart disease, and heart attacks. Coronary arteries deliver oxygen-rich blood to the heart muscle. Reduced blood flow to the heart associated with coronary ischemia can result in inadequate oxygen supply to the heart muscle. When oxygen supply to the heart is unable to keep up with oxygen demand from the muscle, the result is the characteristic symptoms of coronary ischemia, the most common of which is chest pain. Chest pain due to coronary ischemia commonly radiates to the arm or neck. Certain individuals such as women, diabetics, and the elderly may present with more varied symptoms. If blood flow through the coronary arteries is stopped completely, cardiac muscle cells may die, known as a myocardial infarction, or heart attack.
Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults – is called tachycardia, and a resting heart rate that is too slow – below 60 beats per minute – is called bradycardia. Some types of arrhythmias have no symptoms. Symptoms, when present, may include palpitations or feeling a pause between heartbeats. In more serious cases, there may be lightheadedness, passing out, shortness of breath or chest pain. While most cases of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure. Others may result in sudden death.
A diagnosis of myocardial infarction is created by integrating the history of the presenting illness and physical examination with electrocardiogram findings and cardiac markers. A coronary angiogram allows visualization of narrowings or obstructions on the heart vessels, and therapeutic measures can follow immediately. At autopsy, a pathologist can diagnose a myocardial infarction based on anatomopathological findings.
Magnetomyography (MMG) is a technique for mapping muscle activity by recording magnetic fields produced by electrical currents occurring naturally in the muscles, using arrays of SQUIDs. It has a better capability than electromyography for detecting slow or direct currents. The magnitude of the MMG signal is in the scale of pico (10−12) to femto (10−15) Tesla (T). Miniaturizing MMG offers a prospect to modernize the bulky SQUID to wearable miniaturized magnetic sensors.
Computer-aided auscultation (CAA), or computerized assisted auscultation, is a digital form of auscultation. It includes the recording, visualization, storage, analysis and sharing of digital recordings of heart or lung sounds. The recordings are obtained using an electronic stethoscope or similarly suitable recording device. Computer-aided auscultation is designed to assist health care professionals who perform auscultation as part of their diagnostic process. Commercial CAA products are usually classified as clinical decision support systems that support medical professionals in making a diagnosis. As such they are medical devices and require certification or approval from a competent authority.
In medicine, monitoring is the observation of a disease, condition or one or several medical parameters over time.
Clinical Electrophysiological Testing is based on techniques derived from electrophysiology used for the clinical diagnosis of patients. There are many processes that occur in the body which produce electrical signals that can be detected. Depending on the location and the source of these signals, distinct methods and techniques have been developed to properly target them.