How Does A Head Mri Work
An MRI uses powerful magnets, radio waves and a computer to take images of your brain. MRI images are;clearer and more precise;than other forms of diagnostic imaging. Unlike CT scans and x-rays, an MRI does not use radiation.
When your body is placed in an MRI scanner, it enters a strong magnetic field which causes your;hydrogen protons to realign. This;does not cause chemical changes;to your bodys tissues. As the protons move back to their original alignment, they emit energy. The MRI machine captures this energy to create pictures. Radio waves transmit a signal to a computer which then processes MRI images.
Because an MRI provides clear pictures of soft tissues, its a reliable tool for diagnosing brain conditions. Soft tissues;refer to muscles, fat, blood vessels, nerves and other tissues in the body. The human brain is;almost 60 percent fat;and around 75 percent water. Brain tissue is also made up of;about 100 billion nerve cells. An MRI is the;most sensitive imaging test for brain scans;today.
What Are The Risks Of Having An Mri
- If dye is used during the MRI, it may damage your kidneys. This risk is higher if you have diabetes or kidney disease. If you have metal in or on your body during the MRI, the metal may heat to a dangerous level and cause a burn. If you had surgery to have a coil, stent, or filter placed in your body recently, it may move out of place during the MRI. An MRI can make medical devices work wrong or stop working. You may have short-term hearing loss after an MRI.
- If you do not have an MRI, a medical problem may not be found. If a medical problem is not found and treated, it may get worse. Without an MRI, your caregiver may not find a disease in the early stages when it may be treated more easily. If you have symptoms, such as headaches or dizziness, they may get worse. If you have a lump, it may grow bigger. Having an MRI before or during surgery helps caregivers plan for and complete the surgery. If you are being treated for a disease and do not have an MRI, caregivers may not know if the treatment is working. Your condition may get worse, and you may die. Talk to your caregiver if you are worried or have questions about having an MRI of the head and neck.
Preparing For Your Mra
Before your test, the doctor will most likely give you instructions, such as not eating or drinking for four to six hours. You might not be able to have an MRA done if you have a metallic device, such as an artificial heart valve or pacemaker, are pregnant or weigh more than 300 pounds.
Once its time for your test, youll change into medical scrubs or a hospital gown and remove all jewelry or metal objects that could interfere with the magnetic field. Let your doctor know if youre claustrophobic or nervous as they might give you a sedative to help you relax.
Let your doctor about any health issues, allergies and recent surgeries or if its possible youre pregnant. Also let your doctor know if youre wearing an orthopedic implant of some kind. Most pose no risk, but you should inform the technologist, or your doctor may give you a card to present to the technologist that has information about your implant.
Take all medications as you normally would, unless the doctor instructs you not to.
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How Is The Procedure Performed
MRI exams may be done on an outpatient basis.
You will be positioned on the moveable exam table. Straps and bolsters may be used to help you stay still and maintain your position.
Devices that contain coils capable of sending and receiving radio waves may be placed around or next to the area of the body being scanned.
MRI exams generally include multiple runs , some of which may last several minutes.
For an MRI of the head, a device is positioned around the head.
You will be placed into the magnet of the MRI unit. The technologist will perform the exam while working at a computer outside of the room.
When the exam is complete, you may be asked to wait while the radiologist checks the images in case more are needed.
Your IV line will be removed after the exam is over.
The entire examination is usually completed within 45 minutes.
MR spectroscopy, which provides additional information on the chemicals present in the body’s cells, may also be performed during the MRI exam. This may add about 15 minutes to the total exam time.
Magnetic Resonance Imaging In Neurologic Disorders
, MD, College of Medicine, University of Saskatchewan
provides better resolution of neural structures than CT. This difference is most significant clinically for visualizing the following:
Abnormalities of the posterior fossa
CT images of these regions are often marred by bony streak artifacts. MRI is especially valuable for identifying spinal abnormalities compressing the spinal cord and requiring emergency intervention. Also, MRI is better for detecting demyelinating plaques, early infarction, subclinical brain edema, cerebral contusions, incipient transtentorial herniation, abnormalities of the craniocervical junction, and syringomyelia.
MRI is contraindicated if patients
Have had a pacemaker or cardiac or carotid stents for < 6 weeks
Have ferromagnetic aneurysm clips or other metallic objects that may overheat or be displaced within the body by the intense magnetic field
Visualization of inflammatory, demyelinated, and neoplastic lesions may require enhancement with IV paramagnetic contrast agents . Although gadolinium is thought to be much safer than contrast agents used with CT, nephrogenic systemic fibrosis has been reported in patients with impaired renal function and acidosis. Before using gadolinium in patients with renal disease, clinicians should consult with a radiologist and a nephrologist.
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How To Prepare For A Head Mri
You should;not have to do too much;to prepare for a head MRI. You may be able to eat, drink and take your medications as usual. However, if your doctor ordered a scan for other parts of your body, such as your abdominal region, they may instruct you not to drink or eat;four to six hours before the test.
Because an MRI machine is essentially a magnet, it can interact with metals, thus creating a blurry image. Thats why it helps to leave metal items at home before your appointment, or remove them before you enter the scanning room. You can prepare for your scan ahead of time by removing the following items from your body and pockets:
- Body piercings
- Zippers or any metal clothing fasteners
- Removable dental work
Its also best to avoid wearing makeup, nail polish, hair products, sunscreen and antiperspirants, as these items could contain metal particles. If you wear glasses, you will need to remove them when its time for the scan.
Before you schedule your appointment for a brain MRI, make sure to inform the medical staff if you have any of the following conditions.
Some items can pose a risk during an MRI. Make sure your doctor and medical staff know about any of the following items before you get your MRI:
- Brain aneurysm clips, metal plates or any metal implants
- Artificial heart valve
- Metal fragments in the body
- Any type of implantable pump
- Bullet wound
How Should I Prepare
You may need to wear a hospital gown. Or, you may be allowed to wear your own clothing if it is loose-fitting and has no metal fasteners.
Guidelines about eating and drinking before an MRI vary between specific exams and facilities. Unless you are told otherwise, take food and medications as usual.
Some MRI exams use an injection of contrast material. You may be asked if you have asthma or allergies to iodine contrast material, drugs, food, or the environment. MRI exams commonly use a contrast material called gadolinium. Gadolinium can be used in patients with iodine contrast allergy. A patient is much less likely to be allergic to gadolinium contrast than to iodine contrast. However, even if the patient has a known allergy to gadolinium, it may be possible to use it after appropriate pre-medication. For more information on allergic reactions to gadolinium contrast, please consult the ACR Manual on Contrast Media.
Tell the technologist or radiologist if you have any serious health problems or recently had surgery. Some conditions, such as severe kidney disease, may require the use of specific types of gadolinium contrast that are considered safe for patients with kidney disease. You may need a blood test to determine whether your kidneys are functioning normally.
If you have claustrophobia; or anxiety, you may want to ask your doctor to prescribe a mild sedative prior to your exam.
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Schedule An Appointment At Health Images
When in need of an MRI or MRA, schedule an appointment at Health Images. As a premier medical imaging destination, we offer same day appointments, board-certified radiologists and a professional, compassionate and skilled staff. We have;multiple locations;for your convenience, including in the Boulder, Castle Rock, Denver and surrounding areas, so;contact us today;to book your MRI or MRA.
What Does An Mri Show
Nearly every part of the body may be studied with MRI. MRI gives very detailed pictures of soft tissues like the brain. Air and hard bone do not give an MRI signal so these areas appear black. Bone marrow, spinal fluid, blood and soft tissues vary in intensity from black to white, depending on the amount of fat and water present in each tissue and the machine settings used for the scan. The radiologist compares the size and distributions of these bright and dark areas to determine whether a tissue is healthy.
- Head and neck . MRI can be used to detect brain tumors, traumatic brain injury, developmental anomalies, multiple sclerosis, stroke, dementia, infection, and the causes of headache. Figure 1. MRI of the brain.
- Arteries and veins . MRA can detect aneurysms, blockages of the blood vessels, carotid artery disease, and arteriovenous malformations.
Figure 2. MRA of the brain arteries.
- Spine . MRI is sensitive to changes in cartilage and bone structure resulting from injury, disease, or aging. It can detect herniated discs, pinched nerves, spinal tumors, spinal cord compression, and fractures. Figure 3. MRI of the lumbar spine.
Types of MRI scanners
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Mri Brain With And Without Contrast
Magnetic resonance imaging; is a non-invasive imaging technique used in hospitals and clinics to produce detailed soft tissue anatomical images through emission and absorption of energy of the radiofrequency range of the electromagnetic field by employing powerful magnets that produce a strong magnetic field around the area to be imaged without exposing the body to ionized radiation.;
MRI is the most sensitive imaging test of the head, particularly of the brain. It is performed for either long-standing or abrupt onset symptoms, helping diagnose conditions such as brain infections, stroke, brain tumors, causes of seizures, developmental abnormalities, haemorrhage in trauma patients, multiple sclerosis, disorders of the pituitary gland and vascular problems such as aneurysms, arterial occlusions and venous thrombosis.;;
Whether or not to use a contrast-agent depends on the nature of the disease/condition for which the scan is ordered. Most acute events do not require a contrast MRI. Some other conditions, including brain tumors, infections, seizures and multiple sclerosis do require the use of a contrast agent to differentiate diseased tissue from normal tissue.;
Who Needs An Mri With Contrast
An MRI scan with contrast only occurs when your doctor orders and approves it. During the procedure, theyll inject the gadolinium-based dye into your arm intravenously. The contrast medium enhances the image quality and allows the radiologist more accuracy and confidence in their diagnosis.
The contrast medium dye doesnt permanently discolor your internal organs. Instead, it temporarily changes how imaging modalities view and interact with your body. After the completion of your imaging exam, either your body absorbs the contrast material, or you eliminate it through your urine.
Not every MRI requires using a contrast agent. MRIs with and without contrast are both effective, and your doctor will determine which scan you need based on your present condition and your medical and health history. But, if the doctor requires a highly detailed image to assess a specific problem area within your body, theyll typically order the contrast agent.
When the radiologist adds the contrast to your veins, it enhances their visibility of:
- Certain organs blood supply
- Blood vessels
While a contrast MRI provides the doctor with valuable information, they typically wont order an MRI with contrast unless they think its necessary. For instance, in most cases, work-related injuries, sports injuries and back pain dont usually call for intravenous contrast exams.
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What Happens After An Mri
You should move slowly when getting up from the scanner table to avoidany dizziness or lightheadedness from lying flat for the length of theprocedure.
If any sedatives were taken for the procedure, you may be required torest until the sedatives have worn off. You will also need to avoiddriving.
If contrast dye is used during your procedure, you may be monitored fora period of time for any side effects or reactions to the contrast dye,such as itching, swelling, rash, or difficulty breathing.
If you notice any pain, redness, and/or swelling at the IV site afteryou return home following your procedure, you should notify your doctoras this could indicate an infection or other type of reaction.
Otherwise, there is no special type of care required after a MRI scanof the spine and brain. You may resume your usual diet and activities,unless your doctor advises you differently.
Your doctor may give you additional or alternate instructions after theprocedure, depending on your particular situation.
What Does An Mra Show
The primary difference between the two procedures is an MRA is specifically used for examining blood vessels. Without making any incisions, the doctor can see the many complex and tiny blood pathways through your body.
Its essential for doctors to see your blood vessels as the way your blood flows through your body can tell the doctor the current state of your body:
- Blood is moving too quickly:;You could have high blood pressure that may cause a cardiovascular episode.
- Blood is moving too slowly:;You may have a blockage in your body that could cause a heart attack if left untreated.
The MRA will allow the doctor to examine your bodys blood pathways between your kidneys, brain and legs. They may use the contrast material to highlight your vessels and potential blockages.
The doctor will likely recommend an MRA test if you or a loved one suffers from a stroke, blood clot, heart disease or a similar health condition.
In many situations, the MRA provides the doctor with the information they cant detect in a regular x-ray, ultrasound or CT scan. Its a noninvasive exam, and the doctor can store the images on the computer or print them on film.
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What Are The Risks Of Gadolinium
Research shows that gadolinium can accumulate in the brain, most notably in the dentate nuclei and globus pallidus. As these regions of the brain are involved in motor function, its conceivable that motor function could be affected over time, particularly in patients who undergo numerous MRIs. Some forms of gadolinium may also disrupt the action of thyroid hormone, which is an important concern to keep in mind when administering MRIs to pregnant patients.
One perinatal in vivo study found that:
when gadoterate meglumine or gadodiamide was intravenously injected into dams during perinatal period , which is the critical period for the functional organization of neuronal circuits, both GBCAs disrupted motor coordination and impaired memory function . The magnitude of disruption was higher with gadodiamide.
However, in human patients, these neurological effects havent been established. Theres no evidence to suggest that gadolinium deposition in the brain affects neurological function, and the mere presence of gadolinium deposits shouldnt be perceived as a reason to forego dye-enhanced MRIs, particularly when dyes would provided a diagnostically useful image that wouldnt be attainable otherwise.
In the vast majority of cases, gadolinium contrast agents could allow for faster, more thorough treatment of serious health conditions, and the benefits of contrast dyes will greatly outweigh the potential risks.
What Is An Mri Without Contrast
Magnetic resonance imaging is a medical diagnostic technique that uses strong magnetic fields to obtain an image of the inside of a patients body. An MRI without contrast, which is usually referred to as a standard MRI scan, doesnt require any medication or contrast agent to be injected into the body. Contrast-enhanced MRIs involve an injection of contrast agent to increase image sensitivity. An MRI without contrast is suitable for most conditions as long as extra detail isnt required.
An MRI machine uses the magnetic properties of particles in the body to form an image. MRI scans are among the most detailed forms of diagnostic imaging available to doctors. A benefit of MRI scans is that they dont require the use of ionizing radiation, which could be potentially damaging to the patient, although the machines are expensive to build and maintain.
A standard MRI scan is known as an MRI without contrast. This means the MRI machine takes an image of the required area without the need for a contrast substance to be injected into the body. In most situations, an MRI without contrast is all thats required to see problems within the body, unless the affected area is very small or difficult to see.
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