Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a diagnostic procedure that uses a combination of a large magnet, radiofrequencies, and a computer to produce detailed high-resolution cross-sectional images of the inside of the body that help diagnose a variety of problems. MRI is based on the principles of nuclear magnetic resonance imaging. It is based on the nuclear properties of hydrogen atoms in the body. This works like a magnet when the patient is placed in a strong magnetic field. The radiology technique uses a very powerful magnet to align the nuclei of atoms in the body, and a variable magnetic field that resonates atoms, a phenomenon called nuclear magnetic resonance. The nuclei produce their own rotating magnetic fields that a scanner detects and uses to create an image. 

Magnetic resonance imaging (MRI)

 MAGNETIC RESONANCE IMAGING (MRI)

 BLOCK DIAGRAM OF MAGNETIC RESONANCE IMAGING SYSTEM
COMPONENTS AND FUNCTIONS OF THE MAGNETIC RESONANCE IMAGING

THE COMPONENTS OF AN MRI SYSTEM
 1. MAGNET

 MAGNET  
The magnet is the most important and largest part of the MRI device. It is this magnet that allows the MRI machine to produce high quality images. The basic design involves a coil of conducting wire, a cooling system, and a power supply. There is a horizontal tube that passes through the magnet and is called a bore. The magnet is extremely powerful and its strength is measured in ‟teslaˮ. The magnetic field is produced by passing current through multiple coils inside the magnet.

 GRADIENT COIL

RADIO FREQUENCY (RF) COILS
The basic function of the RF coils is to transmit radio frequency waves into the patient’s body. There are different coils located inside the MRI scanner to transmit waves into different body parts. These components are attached to the RF coils, which are made with varying designs. It composes the transmitter and receiver coils of the same type of materials as the gradient coils. They are also constructed much like the main magnet.

  PATIENT TABLE OF MRI 

    THE POWERFUL MRI COMPUTER SYSTEM (MRI SCAN, 2016)
MAGNETIZATION IN A MRI SCANNER (HIGGINS, 2010)
TECHNIQUE

• The relaxation time T1 refers to the restoration of magnetic moments towards their original direction. ( Karnam  et al., 2016)

• The relaxation time T2 refers to the loss of phase in nuclear precession after the electromagnetic field is removed. ( Karnam  et al., 2016)

HOW DOES MRI SCANNER WORK? (LYME DISEASE ORGINE, 2014)
APPLICATIONS OF MAGNETIC RESONANCE IMAGING
1. MAGNETIC RESONANCE IMAGING OF THE HEAD

                                              MAGNETIC RESONANCE IMAGING OF THE HEAD (MEDIM, 2015)
2. MAGNETIC RESONANCE IMAGING (MRI) OF THE ABDOMEN

MRI OF THE ABDOMEN (RESEARCH GATE, 2016)
3. MAGNETIC RESONANCE IMAGING OF THE BREAST

MRI of the breast (MDLinx, 2015)
4. MAGNETIC RESONANCE IMAGING OF THE SPINE

Magnetic Resonance Imaging of The Spine (ALARMY, 2016).
   5.MAGNETIC RESONANCE IMAGING (MRI) OF THE SHOULDER

MRI of shoulder (GE Healthcare,2016)
6. MAGNETIC RESONANCE IMAGING (MRI) OF THE KNEE

MRI of the knee (MRI scan, 2016)
SPECIALIZED TYPES OF MRI
Some specialized MRI techniques are described below.
1  MAGNETIC RESONANCE ANGIOGRAPHY (MRA)
2  Functional MAGNETIC REONANCE IMAGING (fMRI)
3  MAGNETIC RESONANCE SPECTROSCOPY (MRS)
4  CARDIAC MAGNETIC RESONANCE IMAGING
COMMON PROBLEMS AND TROBLESHOOTING OF MRI

No	Fault	Possible Cause	Solution
1	MRI helium level is low	failure in cooling system and helium is burning off	Schedule a fill immediately
2	Power Outages	“glitches”, system shut downs and boot-up issues	Check your breakers
3	Image artifacts	damage to the coils	Ship your MRI coils out for off-site repairs
4	Heat exchanger temperature errors	system is not cool enough and disallow scanning	contact your service provider
5	MRI coil failures	frequent use, failure due to impact, or improper use	MRI coil repair and replacement.

 ARTICLE PREPARED BY: 
LOCIKA KARUNARAJAH

 It is used to find the body for a variety of conditions, tumors, diseases of the liver, inflammation and vascular abnormalities and bowel. It is also used to diagnose a variety of disorders, such as strokes, tumors, aneurysms, spinal cord injuries, multiple sclerosis and eye or inner ear problems. It can monitor an unborn child in the womb. MRI is noninvasive and does not use ionizing radiation. 

BLOCK DIAGRAM OF MAGNETIC RESONANCE IMAGING

 An MRI system is typically manufactured separately and then assembled into a large unit. The scanner is composed of a 24-inch-wide tube, within which the examination takes place. It contains a magnet, a radiofrequency coil, gradient coils (3), patient table, and a computer system.

2. GRADIENT COILS

There are three different types of gradient coils that are inside the MRI machine and are located inside the main magnet. Each one of coils produces three different magnetic fields which are each less strong than the main field. A variable field (x, y, z) is created by gradient coils that can be increased or decreased to allow specific and different parts of the body to be scanned by altering and adjusting the main magnetic field.

3. RADIO FREQUENCY (RF) COILS

4. PATIENT TABLE

The position in which the patient lies on the table is determined by the part of the body that is being scanned. Once the examined body part is in the exact center of the magnetic field, which is known as the isocenter, the scanning process begins. 

 5.   ANTENNA/COMPUTER SYSTEM

The antenna is a very sensitive device that easily detects the RF signals emitted by the body of the patient while it undergoes an examination and feeds this information to the computer system. The computer system is major function is to receive, record, and analyze the images of the patient’s body that have been scanned. It interprets the data sent by the antenna and then helps to produce an understandable image of the body part being examined (Rashid and Kibria, 2016).

 BASIC PRINCIPLES OF MAGNETIC RESONANCE IMAGING

Magnetic resonance imaging (MRI) is based on the magnetic characteristics of the imaging tissue. It includes creation magnetization of tissues and detection magnetization of tissues revealed by signal intensity (Ajtai et al, 2015). MRI uses the magnetic characteristics inherent to the protons of hydrogen nuclei in the tissue. The protons spin about their own axes, creating a magnetic dipole moment for each proton (Ajtai et al, 2015). In the absence of an external magnetic field, the axes of these dipoles are arranged randomly.

When the patient is placed in the strong magnetic field of the MRI scanner, the magnetic field is generated by an electric current that circulates in wire coils that surround the open bore of the scanner (Ajtai et al, 2015). The magnetic dipoles in the tissues are aligned in relation to the external magnetic field. Protons absorb the energy of the magnetic field and can be rotated using radio waves. When the field is shut down, the protons gradually return to their normal rotation, a process called precession that describes a proton that revolves around its own axis and its simultaneous movement around the axis of the external field (Ajtai et al, 2015).

A pulse of radiofrequency is applied to the part of the body that is forming an image. Resonance process, protons receive the energy of a radio frequency pulse applied. As a result, the inversion of the protons and the net magnetization vector of the tissue temporarily cease to align with that of the external field, but move to another plane, so transverse magnetization occurs (Bradley, 2005). The rotating transverse magnetization in the fabric induces electric currents in the receiving coils, thus achieving the detection of signals (Ajtai et al, 2015). Several cycles of excitation pulses are repeated by the scanner with detection of the resulting electromagnetic signal of the subject with image per image stretch. This occurs as two additional magnetic field gradients are varied along the x and y axes for each cycle (Lasanti, 2016).

During realignment of the protons, the energy is released and sampled at different time intervals. The relaxation times T1 and T2 are important parameters that determine the image contrast and lesion with reference to the normal hepatic parenchyma(Karnam  et al., 2016)

    HOW DOES MRI SCANNER WORK?

An MRI is a cylindrical tube surrounded by a giant cylindrical magnet (James, 2017), consists two powerful magnets (Lam, 2017), used to get images of the human body. The patient is placed on a narrow table that is inserted into the magnet that creates a strong magnetic field (James, 2017).The human body is made of water molecules, which contains hydrogen and oxygen atoms. The hydrogen atoms have single proton. Every proton is a tiny magnet spinning randomly about its axis (Lam, 2017). When this proton is subjected to a strong magnetic field from an MRI magnet, the proton's magnetic field aligns with the MRI magnet (James, 2017).the first magnet causes the body's water molecules to align in one direction, either north or south. The second magnetic field is then turned on and off in a series of quick pulses, causing each hydrogen atom to alter its alignment and then quickly switch back to its original relaxed state when switched off (Lam, 2017).

When this magnetized proton is then bombarded by radio waves, it absorbs the energy (James, 2017), and spins the various protons of the body produce signals that are emitted out of the body (Lam, 2017). These signals that are detected by the receiver portion of the MRI scanner, and are then the receiver is processed by computer to produce a detailed images of the patient’s body organs and tissues. (James, 2017).These images are produced by MRI that pictures are very precise and can detect tiny changes of structures within the body (Lam, 2017).

MRI is used to find problems for many applications such as tumors, bleeding, injury, blood vessel diseases, or infection. MRI also may be done to provide more information about a problem seen in another imaging system. An MRI of the head, spinal cord, thorax, blood vessels, abdomen, bones, and joints may be used (William and Blahd, 2016).

MRI is a test that uses a powerful magnetic field and radio waves to take pictures of the head (Romito and Schaff, 2012). The MRI of the head can be used to observe at the brain for tumors, an aneurysm, nerve injury, tissue damage, infection, a tumor, and seizure (Vlahova, 2015). MRI of the head can also be used to identify causes of headaches, to help diagnose a stroke or blood vessel problems in head, to check blood flow or blood clots in brain, to check symptoms or suspected head injury, to check for "water on the brain", to look for tumors, infections, abscesses, or conditions of brain  or brain stem, such as encephalitis  or meningitis. Further, it is used to check eyes, nerves from the eyes to brain, ears, to find problems of the eyes and optic nerves, and ears and  auditory nerves  and nerves from the ears to the brain and to look for problems of the pituitary gland (Romito et al, 2016).

Information from an MRI can be saved and stored on a computer. It makes photographs or films of certain views (Vlahova, 2015). In some cases, a dye contrast material  may be used during the MRI to show pictures of structures more clearly. The dye can help to show blood flow, look for some types of tumors, and show areas of inflammation (Romito et al, 2016).

MRI is a test that uses a magnetic field and radio wave energy to make pictures of organs and structures inside the belly. During the MRI test, the patient is placed inside the magnet so that the patient’s belly is within the strong magnetic field (William, 2016).

MRI can find changes in the structure of organs or tissue. It can also use to find problems or tumors in the abdominal organs  and tissues, to check lower abdominal and pelvic organs for tumors, bleeding, or problems present since birth, to find a blocked tube or stones in the tube that carry bile from the liver to the gallbladder to check organs and blood vessels prior to organ transplantation or surgery (Romito et al, 2016). Pictures are digital images that can be saved and stored on a computer (William, 2016).

An MRI can be done using contrast material to see abnormal tissue more clearly pictures. The contrast material may be used to check blood flow, find some types of tumors, and show areas of inflammation or infection (Romito et al, 2016).

MRI uses a magnetic field and radio waves to make pictures of the brest (Romito et al, 2010). Breast problems can be shown that can’t be seen on a mammogram, ultrasound, or CT scan. MRI is better than mammography or ultrasound to look at some lumps in the breast. An MRI can be done using contrast material to see abnormal tissues more clearly. It is a safe and valuable test for observing at the breast, but it has a high rate of false-positive results(Romito et al, 2010).

The MRI  is used to show normal structure of breast, tissue damage or disease, such as infection, inflammation or a lump. It can be also used to detect breast cancer, to check women at increased risk for breast cancer, to choose the best treatment for breast cancer, to check breasts with nipples changes and to detect women with breast implants (Romito et al, 2010). MRI can be used to look for breast cancer or to check if the implant is leaking (Romito et al, 2010).

An MRI is a test that uses a magnetic field and radio wave energy to make pictures of the spine (William, 2016). An MRI can show problems that cannot be seen with other imaging tests. During the MRI test, the patient body is placed inside a machine that contains a strong magnet. Images from an MRI can be saved and stored on a computer. An MRI can be done using contrast material to see abnormal tissue more clearly. The contrast material may also help tell the difference between old surgical scars and a new disease or injury (William, 2016).

An MRI may find changes in the spine and in other tissues and problems such as infection or a tumor(Romito et al, 2010). MRI can also observe at the spine in the cervical, thoracic, or lumbosacral spine. The entire spine can be seen in one series of pictures to find a tumor, to find problems of the spinal discs such as ruptured disc, to check low back problems, to find tumors affecting the bones or nerves  of the spine, to find compression fractures of the spine, to check areas of joint inflammation  or bone loss found during an X-ray test or a bone scan, to find areas of the spine that do not have good blood supply(Romito et al, 2010).

MRI is a test that uses a magnetic field and radio wave energy to make pictures of the shoulder. An MRI looks at the muscles, ligaments, cartilage, and other joint structures. During an MRI test, the patient is placed inside the magnet so that your shoulder is inside the strong magnetic field. An MRI can be done using contrast material to see abnormal tissue more clearly in the pictures. The contrast material may be used to check blood flow, find some types of tumors, and show areas of inflammation or infection. The contrast material can be put in a vein (IV) in the patient's arm or directly into the patient shoulder joint (Romito et al, 2010).

MRI of the shoulder may find changes in the structure of organs or other tissues, tissue damage or disease, such as infection or a tumor.  MRI can also detect unexplained shoulder pain, to find problems in the shoulder, such as arthritis, bone tumors, torn ligaments, torn tendons, or infection and to find rotator cuff disorders, including tears and impingement. Images from an MRI scan  are digital images that can be saved and stored on a computer. Photographs or films of selected pictures can also be made (Romito et al, 2010).  

An MRI is a test that uses a magnetic field and pulses of radio wave energy to make pictures of the knee .There are two main types of MRI such as the standard MRI machine  and the open MRI machine. Muscles, ligaments, cartilage, and other joint structures are often best seen with an MRI. During an MRI test, the patient is placed inside the magnet so that the patient, knee is inside the strong magnetic field(Romito et al,  2010).

MRI may find changes in the structure of organs or other tissues. It also can find tissue damage or disease, such as infection or a tumor. MRI can also detect the cause of unexplained pain in the knee or the knee that leaves without reason, and to find problems in the knee joint , such as arthritis, bone tumors, or infection, or damaged cartilage, meniscus, ligaments, or tendon(Romito et al, 2010).

A contrast material can be used during the MRI scan to show certain structures more clearly in the images. The contrast material can be used to check blood flow, to find some types of tumors, and to show areas of inflammation or infection. The contrast material may be put in a vein (IV) in your arm or directly in the knee(Romito et al, 2010).

MRA uses a magnetic field and the energy of the radio waves to look at the blood vessels. It is most commonly used to examine the arteries and veins of the head, neck, brain, and heart. A contrast dye is often used to make blood vessels appear more clearly in the image (Singh and Asija, 2015).

fMRI uses MRI technology to measure brain activity by monitoring blood flow in the brain. This gives an insight into the activity of neurons in the brain as blood flow increases in areas where neurons are active (Beissner and Clin, 2015). A functional MRI scan can detect anomalous activity in those tissues and to determine the effects of tumors, stroke, head and brain injury, or neurodegenerative diseases such as Alzheimer's. (Chernoff, 2005). Additional magnetic fields are used to localize body structures in 3D.

MRS is used to measure the levels of dissimilar metabolites in body tissues. The Magnetic Resonance signal yields a spectrum of resonances that corresponds to different molecular preparations of the isotope individual dynamic. This given name is used to study certain metabolic disorders for the most part individuals distressing the brain, and to achieve in order on tumor metabolism. MRS imaging combines as a group spectroscopic and imaging methods to produce spatially localized spectra from within the sample or patient. The spatial resolution is much lower, but the spectra in each voxel contain information about numerous metabolites. Because the available signal is used to encode spatial and spectral feature (Singh et al, 2015).

CMR is a medical imaging technology for the non-invasive assessment of the function and structure of the cardiovascular system. It’s significant from and depend on the alike basic principles as MRI, but with optimization for use in the cardiovascular system. These optimizations are effectively use for ECG gating and rapid imaging techniques or sequences. With combining a numeral of such techniques interested in protocols, valuable and morphological features of the cardiovascular system are skilled to assess. (Fiechter et al, 2013).

 

Table 1: Common problems and troubleshooting of MRI (Batterbee, 2016)