Magnetic resonance imaging or MRI is a “high-tech” imaging system using high strength magnetic fields, radio waves, and computers to derive series of two dimensional “slice” images of items placed inside the machine. It is particularly used for diagnostic imaging of the human body for medical purposes. MRI scans are particularly good at viewing soft tissues of the body, but can be used to take clear pictures of all kinds of bodily tissues and structures without the use of radiation.
Our new MRI scanner has a 1.5T scanner, which allows for shorter acquisitions times and greater clarity to the images. This, combined, with our specialized techniques will greatly reduce any feelings of claustrophobia.
I. How an MRI Works
Much of the human body is comprised of water and hydro-carbons. Hydrocarbons are series of molecules comprised a lot of hydrogen and carbon atoms. Both water and hydrocarbons have a lot of hydrogen in them.
The hydrogen atom itself is the simplest atom, comprised of one electron and one proton. Electrons are considered to have a negative charge, protons a positive charge. Such charges can both cause and be affected by magnetic fields. The hydrogen atom is easily polarized (or oriented north-south) in a magnetic field without breaking any chemical bonds.
In an MRI machine, hydrogen atoms in the body are first oriented by a strong uniform magnetic field, and then another magnetic field at an angle to it is pulsed at a specific rate and strength so as to give the protons a certain temporary rate of spin. Electric current pulsing through coiled wires at a specific rate and strength cause magnetic fields in the test area to rise and fall.
When the magnetic pulse is relaxed, the protons of the hydrogen atoms (in particular) returns to normal position–but in doing so, emits a radio frequency “signature” or response which MRI sensors and the computer read and use to generate spatial images of human tissues.
II. Contrast Agents
Sometimes medical professionals desire to enhance the contrast of the mri imaging. For this purpose typically a chelated Gadolinium based substance is injected intravenously to track blood flow. Or a similar contrasting agent may be taken orally to view the digestive tract in more crisp image relief and diagnostic precision where needed. The contrasting agent provides more protons in a desired area of the body that retreat back into normal position, revealing position and shape more clearly for the MRI sensors and computer.
Normal human kidneys will filter the contrasting agent out of the blood stream, so patients with kidney problems are generally advised not to use contrasting agents when they have MRI scans. Otherwise contrasting agents have proven to be quite safe, with a very low incidence of negative reaction.
Our high strength 1.5 Tesla MRI magnet gives optimally clear images in most cases without need for a contrasting agent.
III. An MRI Is Avoided When …
If a patient, for example, has a pacemaker or cochlear implant containing any ferrous (iron) content, an MRI scan may damage the device or cause heating and burning of the flesh around the device during the test. Obviously such cases must be avoided. Indeed though not all metals react strongly to magnetic fields (Titanium metal tends not to), generally metal should be carefully removed (for example, from clothing) before testing or the MRI avoided altogether. Talk to your doctor or technician and see “Preparing for an MRI Scan: FAQ” for more details.
If you are or may be pregnant, special care should be taken, especially within the first trimester. Talk to your doctor before the test.
Some persons are unable to remain still for the duration of the test (for example some young children or elderly persons with advanced Parkinson’s Disease). Unless drugs can be used to maintain stillness, movement during the test will blur the images.
And sometimes large persons may not be able to fit a part of the body scheduled for scanning into the machine. Others may feel claustrophobic in such machines, though our large MRI machine easily accommodates most persons with no claustrophobic feelings.
IV. Being Still for the Duration of the Scanning Procedure
To obtain images of a particular region of the body, say head (a “brain scan”) or chest area, many “slices” or two-dimensional cross-sections must be read by the machine, with many pulses of magnetic field and many emissions of radio frequency. MRI usage since the early 1980s has shown no significant negative reactions in people within the ranges of magnetic fields and pulsing used by commercially available MRI machines. There is no recovery time required for MRI scans, but time may be required for example before driving if a sedating medication is administered prior to the test.
But for purposes of garnering each of many “slices,” the patient must remain still lest bodily movement cause images to appear blurred. Its a bit like the need to remain still while the shutter on a camera opens and closes to take your portrait, but with many portraits of internal cross sections of you.
Technicians assist patients in getting into a comfortable position on a platform before the platform is inserted into the open MRI machine. An MRI scan procedure can last 30 to 60 minutes, to give patients some idea of what to expect. Ask the technician for expected time duration of your particular procedure(s).
If your doctor prescribes an MRI scan for your condition, see “Preparing for an MRI Scan: FAQ” for details. An MRI scan can be the best and safest way to discover your medical needs.
Disclaimer: This page and website are intended for informational purposes only and should not be taken as medical advice.
–John Loebel, RT(N) and Dr Gregory Goldstein, MD