MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS

1. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS Without reference, identify principles relating to Magnetic Resonance Imaging with at least 70 percent accuracy.

2. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • What is Magnetic Resonance Imaging (MRI) • MRI uses a computer and the physical properties of magnetic fields and radio waves to produce high quality sectional images of the inside of the body • MRI produces images of the anatomy without the use of radiation found in x-ray or CT scanning • It is the fastest and safest way to get the clearest pictures of the human anatomy • MRI can see right through bone to image structures, tissues, organs, and fluids such as blood • To date, MRI has been particularly valuable in scanning the brain and spine • Through brain and spine scans, MRI can detect multiple sclerosis in its earliest stages, tumors, brain and spine disease, and fluid in the skull • Heart scans can show plaque build-up in arteries • It can detect cancer and other diseases in the kidneys, ovaries, uterus and liver

3. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • Brief History of MRI • MRI utilizes a physics phenomenon discovered in the 1930s called nuclear magnetic resonance (NMR) in which magnetic fields and radio waves, both harmless, cause atoms to give off tiny radio signals • It wasn't until 1970, however, that Raymond Damadian, a medical doctor and research scientist, discovered the basis for using magnetic resonance as a tool for medical diagnosis • The "nuclear" was dropped off in the late 1970's because of the negative connotations associated with the word • The future of MRI seems limited only by our imaginations • This technology, comparatively speaking, is still in its infancy • It has been in widespread use about 20 years (compared with over 100 years for x-rays) • "Magnetic" • Magnetic fields • The strength of the magnetic field relates to the pull or force from the magnet and measures in units called gauss or tesla • 10,000 gauss equals 1 tesla • The main magnetic field of a 1.5T magnet is about 30,000 times the strength of the earth's magnetic field, which is approximately 0.5 gauss

4. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • The strongest magnetic field permitted in MRI of humans is 1.5 tesla (1.5T) • Low field magnet less than 0.5T • Mid-field magnet: between 0.5 and 1.0T • High-field magnet: between 0.75 and 1.5T • The strength of electromagnets used to pick up cars in junkyards is about the field strength of MRI machines (1.5 to 2.0 Tesla) • The scientific community uses MRI with a field strength as high as 4.0T for non-human testing

5. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • Three types of magnetic properties of matter • Diamagnetic substances have a negative interaction or negative magnetic susceptibility inside a magnetic field • Paramagnetic substances also exhibit no magnetic properties outside a magnetic field • In the magnetic field, these substances exhibit a slight positive interaction • Ferromagnetic materials generally contain iron, nickel, or cobalt • These materials have a large positive magnetic susceptibility and have the ability to remain magnetized when removed from a magnetic field

6. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • Magnet types available for use in MRI • Super-conducting magnets • The most common • Made from coils of wire producing a horizontal field • Use liquid helium to keep the magnet wire at 4 degrees Kelvin (-268.8 Celsius) where there is no resistance • Keep the coil and the liquid helium in a large dewar or jacket • This dewar is typically surrounded by liquid nitrogen (77.4Kelvin) dewar that acts as a thermal buffer between the room temperature (293K) and the liquid helium • It can also be a helium-only design with a refrigeration system to keep the helium boil off at a minimum • Resistive magnets • Constructed from a coil of wire • The more turns to the coil, and the more current in the coil, the higher the magnetic field • Resistive magnets are similar to superconductors • Air-cooled resistive magnets have a greater resistance to current and create weaker magnetic fields • The magnets are lower in cost to construct than a super-conducting magnet, but require huge amounts of electricity (up to 50kw) to operate because of the natural resistance of the wire

7. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • Permanent magnets • Sometimes referred to as a vertical field magnet • Made from two ferromagnetic plates forming a north and south pole • The patient lies on a scanning table between these two plates • No need for electricity or cryogenic liquids to maintain the magnetic fields • Are the weakest magnetic fields • The major drawback is that these magnets are extremely heavy - many tons in weight at the 0.4T level • "Resonance" • The "resonance" part of MRI • The MRI machine applies an RF (radio frequency) pulse that is specific only to hydrogen • The system directs the pulse toward the examination area of the body • The pulse causes the protons in that area to absorb the energy required, making them spin in a different direction • The RF pulse forces the protons to spin at a particular frequency, in a particular direction • The Larmour frequency is the specific frequency of resonance • Base the calculation on the image of the particular tissue and the strength of the main magnetic field

8. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • RF Coils • RF coils are the "antenna" of the MRI system that broadcasts the RF signal to the patient and/or receives the return signal • There are several varieties of coils • Receive-only, in which case the coil is used as a receiver • Transmit-only, in which case the coil is used as a transmitter • Transceiver, transmitter-receiver • Detect the weak MR signals in the presence of background RF signals from local television and radio stations • MRI scanners are normally enclosed in a copper or stainless steel shield known as a Faraday shield to filter out extraneous noise • Use gradient coils are used to produce deliberate variations in the main magnetic field • There are usually three sets of gradient coils, one for each direction (x, y and z-axis) • The variation in the magnetic field permits localization of image slices as well as phase encoding and frequency encoding

9. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • How it works • The physics involved are extremely complex • Patients undergoing scans of their brain, heart or other body parts lie flat on a scanning table in a magnet field created by a large magnet • Millions of negatively and positively charged atoms compose the human body • The hydrogen nucleus (a single proton) is abundant in the body due to the high water content of non- bony tissues • The protons in the patient's tissues align themselves along the direction of the magnetic field when placed within a MRI scanner • This is a physical phenomenon known as gyroscopic precession • Excitation occurs by applying short RF pulses causing the hydrogen protons to absorb energy making them spin perpendicular to the magnetic field • The radio frequency power produced matches that of many small radio stations (15-20 kW) • Relaxation occurs when the radio signal stops, the protons relax back into alignment with the magnetic field releasing energy signals, which the RF coil receives and acts as an antenna

10. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • The receiver coils record these changes in excitation and relaxation and then a sophisticated super-computer mathematically reconstructs them into 2D and 3D images that vividly represent conditions of health, disease or injury • Transfer the constructed images onto film • The science is different from x-ray • MRI is the absorption and emission of energy in the form of radio waves within the electromagnetic spectrum, whereas radiographs (x-ray) are the absorption of x-ray energy • Perform scans for multiple body parts without repositioning the patient. The entire procedure takes 15 to 45 minutes • How safe is MRI • It is a non-invasive procedure of which there are no significant biological hazards demonstrated because of exposure to patients from the magnetic fields or radio frequency pulses used in magnetic resonance imaging • More of an annoyance than a safety problem is the ability of the magnetic field of a MRI machine to erase the information contained on the magnetic strip on ATM and credit cards. This may occur a short distance inside of the scanner room of a MRI machine

11. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • The magnetic field can pull certain metal objects like watches, hairpins, writing pens, phones, pagers, etc., away from the body when entering an MRI room • It is strong enough to pull heavy-duty floor buffers and mop buckets into the bore of the magnet, pull stretchers across the room and turn oxygen bottles into flying projectiles • Important patient considerations • Patients with various medical implant devices should avoid MRI • The MRI magnetic field attracts ferromagnetic (metallic iron) objects • Do not scan patients with cardiac pacemakers • Cerebral aneurysm clip: most patients who have had surgical repair of a cerebral (brain) aneurysm cannot have MRI scans (the clip might move and bleeding could occur) • The magnetic field can damage implanted electromagnetic devices: medication or insulin pumps, bio-stimulators, and neuro-stimulators; therefore, do not scan patients with these devices • Prosthetic heart valve: Most are safe but check with physician and staff • Do not scan patients with magnetically activated or supported implants (cochlea implant, some dental and ocular implants) • The patient and staff should address other devices not noted

12. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • Metal workers or individuals exposed to ocular metallic injuries or having metallic foreign objects in soft tissue should be examined before undergoing MR • Patients with ferromagnetic shrapnel or bullet fragments should be imaged with another modality (most bullet fragments are non-ferromagnetic) • If the patient's scan is to include a contrast medium, any known allergies should be discussed with the physician prior to the test. (Gadolinium is used as a contrast to enhance images of patients undergoing MRI) • Advantages • Unlike MRI, some imaging studies require the patient to change position during the examination • The MRI is able to generate images in the sagittal (left/right), coronal (front/back), axial (head/toe), and oblique (slanted) planes without moving the patient • MRI is able to produce vivid complex images in 256 levels of gray characterizing relationships between vertebrae, intervertebral discs, the spinal cord, and nerve roots • May also eliminate the need for painful diagnostic procedures with serious side effects such as: • Myelography • Arthrography

13. MAGNETIC RESONANCE IMAGING CLINICAL APPLICATIONS • Soft tissue differentiation is excellent giving display and boundary contrast between anatomical structures with unprecedented clarity • Its high sensitivity to early pathological changes makes early detection possible • Disadvantages • MRI is not usually recommended for pregnant patients, particularly in the 1st Trimester • Large units and high magnetic fields produce a banging noise that is often frightening to patients • Because patients must lie quietly inside a narrow tube, MRI may raise anxiety levels in the patients, especially those with claustrophobia • It has a longer scanning time than CT, which makes it more sensitive to motion artifacts • Higher cost compared to a regular x-ray or CT scan • CT scan is better at looking at the bones than MRIFIXED