Friday, April 30, 2010

When might MRI be needed

Your physician may request an MRI study for a number or reasons.
MRI is often used to obtain specific diagnostic inforation not already provided by other imaging technologies such as ultrasound, computed tomography, and nuclear medicine.
MRI has commonly been used as an important diagnostic tool in medicine.
MRI can be considered as the best neuroimaging modality. It has also been very useful in imaging of joints, musculoskeletal structures, pelvic and abdominal cavities, mediastinum, heart and breast. Thanks to different developing hardware and software, MRI is able to delineate vascular, biliary and urinary tract system, effectivly and noninvasively.

Risks And Complications

MRI scans are very safe.

Because MRI technology and the dyes used are relatively recent, the very long-term effects are not known. There are no reasons to suspect any harmful effects but again, the long-term effects are NOT known.

Because of the possible long-term effects, pregnant women should avoid MRIs and the dye except when the benefits clearly outweigh the potential risk to the unborn child.

Allergic reactions to the dye used are possible but not at all likely. It is therefore very important to inform your doctor about allergies that you may have.

Because of the large magnet, patient with cardiac pacemakers or artificial cadiac valves are NOT allowed near the machine. Patient with cerebral aneurysm clips should NOT have an MRI unless the patient has proof that the aneurysm clip is compatible with magnets.

Patient with metallic fragments in or near the eyes or blood vessels should NOT have an MRI. if you suspect you may have metallic fragments anywhere in your body, let the technologist know. They can take x-ray of these areas to determine if it is possible to proceed with the MRI.The patient at highest risk for metal fragments are welders and people injured by shrapnel or bullets.

Patients with epidural electrodes should NOT undergo an MRI. Other implanted metallic material, such as a hip replacment or a knee replacment, may not be a problem.

It is your responsibility to tell your doctor, your radiologist, and your technologist about any possible implants or metallic fragments . It is VERY important. This information can help avoid potentially deadly complications.

Can my child have an MRI


Your child can have an MRI. children under 5 years old are generally given a mild sedative during thescan to keep the child from moving. With the open MRI system, a parent may stay in the scan room with the child, and hold their hand during the scan. this is a great way to relieve any apprehension the child or the parent may have about the procedure.

What happens during the scan

The technologist and /or the MRI nurse will help you onto a padded examination table where you will be comfortably situated. If your Physician has ordered medication to help you complete your MRI, then monitors blood pressure cuff, pulse oximeter, etc may be placed on you so that MRI nurse can better manage your care. While the machine is taking pictures, you will hear knoking noises made by the scanner which is normal and is no cause for alarm. We will provide you with earplugs to make you comfortable while the scan is making noise. The most important thing to remember is that you must remain very still during the study as motion causes the image to blur. throughout the test, you will be able to speak to the technologist when the noise stops. Please communicate your needs, should you have any, to the technologist at these times. Most single exams take from 30-45 minutes, however they will spend the time needed to obtain a diagnostic exam while keeping you comfortable.

Preparing for your MRI

No special preparation is needed prior to the exam. At the time of your appointment you will be asked to complete several forms that detail your billing information, medical history, safey screening, privacy notice and medical information release. Your appointment time is scheduled to include time to complete these forms and counsel with the technician.
Please bring any prior MRI, CTscans, and ultrasounds, X-rays or bone scans which may relate to this MRI scan.
If u have an MRI, you must remove any metallic objects off your body including- jewelry, watches, hair accessories, glasses, wallets, cell phones, pagers, hearing aids, removable dental work, and undergarments with metal under wire or boning. you will be allowed to remove these objects and clothing as needed in private changing room in the relaxation suite.

What if I am breast-feeding, or am pregnant

It is our policy that if a patient thinks that she is pregnant, then she must have a negative pregnancy test done or wait until her next menstrual period before being scanned. In some rare instances, it is possible to be scanned in the first trimester if your referring physician and our radiologist both feel that an MRI is the test of choice. Although there are no known side effects of MRI, we do not recommend MRI scanning in the first trimester of pregnancy, as the fetus is growing rapidly during this period. There is less concern during the second and third trimester of pregnancy.

If you are breast-feeding, and you will have a MRI scan without contrast, then you are completely free to have your scan. if you know that you will have a contrast injection as part of the study, then you should prepare to bottle-feed your baby for 48 hours after the test is complete. The contrast agent will pass through your body after 48 hours, and you may then resume breast-feeding.

MRI: Advantages and Disadvantages

Advantages
The main advantages of magnetic resonance imaging scans are that :
  • They do not involve exposure to radiation, so they can be safely used in people who might be particularly vulnerable to the effects of radiation, such as pregnant women and babies.
  • They are particularly useful for showing soft tissue structures, such as ligaments and cartilage, and organs such as the brain , heart, and eyes.
  • They can provide information about how the blood moves through certain organs and blood vesssels, allowing problems with blood circulation, such as blockages, to be identified.
Disadvantages
The main disadvantages of magnetic resonance imaging scans are listed below:
  • MRI scanners are very expensive, a single scanner can cost over a million pounds.
  • The combination of being put in an enclosed space and the loud noises that are made by the magnets can make some people feel claustrophobic while they are having a MRI scan.
  • MRI scanners can be affected by movement, making them unsuitable for investigating problems such as mouth tumours because of coughing, or swallowing, can make the image that are produced less clear.
Lastly, people wth kidney disease or dialysis or people who didnt know they had kidney disease are likely to develop an incurable condition called Nephrogenic Systemic Fibrosis from the MRI dye injection gadolinium. NSF causes a hardening or stiffening of the skin and joints.

Thursday, April 29, 2010

Contraindications for MRI

All persons coming in contact with the magnetic field should be appropriately screened for contraindication. A useful reference for determining MR compatibility is Shellock s Pocket guide to MR Procedur and Metallic Objects.

The following devices are absolutely contraindicated for MR imaging because they are magnetically, electrically, mechanically activated or affected :

a. Pacemakers

b. Neurostimulators

c. Cochlear implants

d. Bone Growth stimulators

e. Implant able drug-infusion pumps

f. implant able cardiac defibrillators

g. implant able pediatric sternum device

h.metallic foreign body in the eye

The following are relative contraindications for MR imaging:


a. Intra-cranial vascular clips

b.Penile implants

c. Shrapnel

d. Halo

e. Coronary stents

f. Pregnancy

















MRI SCAN


If u have ever seen an MRI machine, you know that the basic design used in most is a giant cube.The cube in a typical system might be 7 feet tall by 7feet wide by 10feet long, although new models are rapidly shrinking.

There is a horizontal tube running through the magnet from front to back. This tube is known as the bore of the magnet.

The patient , lying on his or her back, slides into the bore on a special table.Whether or not the patient goes in head first or feet first, as how far in the magnet they will go, is determined by the type of exam to be performed.

MRI scanners vary in size and shape, and newer models have some degree of openness around the sides, but the basic design is the same. Once the body part to be scanned is in the exact center or isocenter of the magnetic field, the scan can begin.

In conjunction with radio wave pulses of energy, the MRI scanner can pick out a very small point inside the patient body and ask it, what type of tissue are you ? The point might be a cube that is half millimeter on each side.

The MRI system goes through the patients body point by point, building up a 2-D or 3-D MAP of tissue typs.

It then integrates all of this information together to create 2-D image or 3-D models.

MRI provides an unparalleled view inside the human body. The level of detail we cn see is extraordinary compared with any other imaging modality.

MRI is the method of choice for the diagnosis of many types of injuries and conditions because of the incredible ability to tailor the exam to particular medical questio being asked.

By changing exam parameters, the MRI system can cause tissues in the body to take on differentappearances.

This is very helpful to the radiologist in determining if something seen is normal or not.

We know that when we do A , normal tissue will look like B , if it doesnt there might be an abnormality.

MRI system can also image flowing blood in virtually any part of the body.

This allows us to perform studies that show the arterial system in the body, but not the tissue around it. In many cases, the MRI system can do this without a contrast injection, which is required in vascular radiology.

Wednesday, April 28, 2010

HOW MRI WORKS

MRI creates a strong magnetic field and the small biological magnets in the human body consisting of protons in the nucleus of the hydrogen atom are magnetized.
Theproton possess fundamental magnetic properties.
  • First, MRIcreates a steady state of magnetism within the human body by placing the body in a steady magnetic field.
  • Second, the MRI stimulates the body with radio waves to change the steady-state orientation of protons.
  • Third, the MRI machine stops the radio waves and registers the body s electromagnetic transmission.
  • Fourth, the tranmitted signal are used to construct internal images of the body by computerized axial tomography.
An MRI image is not a photograph. it is actually a computerized map or image of radio signals emitted by the human body.

Monday, April 26, 2010

The History of MRI

- Sir Joseph Larmor developed the equation that the angular frequency of precession of the nuclear spins being proportional to the strength of the magnetic field


- In the 1930 Isidor Isaac Rabi succeeded in detecting and measuring single states of rotation of atoms and molecules, and in determining the mechanical and magnetic moments of the nuclei.


- Felix Bloch and Edward Purcell developed instruments, whiche could measure the magnetic resonance in bulk material such as liquids and solids ,the both honored with the Nobel Prize for physics in 1952


- In the early of 70 s ,Raymond Damadian demonstrated with his NMR device, there are different T1relaxation times between normal and abnormal tissues of the same type, as well as between different types of normal tissues


-in 1973, Paul Lauterbur described a new imaging technique that he termed Zeugmatography. By utilizing gradients in the magnetic field ,this technique was able to produce a two-dimensional image


Peter mansfield further developed the utilization of gradients in te magnetic field and the mathematically analysis of these signals for a more useful imaging technique .


Paul Lauterbur and Peter Mansfield were awarded with the 2003 Nobel Prize in Medicine.


- In 1975, Richard Ernst introduced 2D NMR usin phase and freuency encoding, and the Fourier Transform . instead of Paul Lauterbur back-projection,he timely switched magnetic field



1977/78 First images could be presented. Across section through a finger by Peter Mansfield and Andrew A. Maudsley. Peter Mansfield also could present the first image through th abdomen.


In 1977, Raymond Damadian completed after 7 years the first MR scanner . In 1978, he founded the FONAR Corporation, which manufactured the first commercial MRI scanner in 1980.Fonar went public in 1981.


1981: schering submitted a patent application for Gd-DTPA dimeglumine.


1982: the first magnetization -transfer imaging by Robert N.Muller.


In 1983, Toshiba obtained approval from the Ministry of ealth and Welfare in japan for the first commercial MRI system.


In 1984, FONAR Corporation receives FDA approval for its first MRI scanner.


1986: Jurgen Hennig, A. Nauerth, and Hartmut Friedburg introduced rapid acquisition with relaxation enhancement imaging. Axel Haase, Jens Frahm, Dieeter Matthaei, Wolfgang Haenicke, and Dietmar K. Merboldt developed the FLASH fast low angle shot sequence.


1988: scherings MAGNEVIST gets its first approval by FDA.


In 1991, fMRI was developed independently by the University of Minnesotas Center for MR Research and Massachusetts General Hospital MR Center.


From 1992 to 1997 Fonar was paid for the infringement of its patents from nearly every one of its competitors in the MRI industry including giant multi-nationals as Toshiba, Siemens, Shimadzu, Philips, and GE.








Sunday, April 25, 2010

what is mri

Magnetic resonance imaging is an imaging technique whiche utilises the phenomenon of nuclear magnetic resonance NMR

Resonance is defined as the amplified response to a stimulus that has the same natural frequency

During MRI scanning, no ionizing radiation is used and the main contributor is the proton NOT th electrons

In MRI there is no beam, photons, attenuation, scatter, or image receptors