X-rays and MRIs
X-rays are waves of electromagnetic energy. They behave in much the same way as light rays, but at much shorter wavelengths. When directed at a target, X-rays can often pass through the substance uninterrupted, especially when it is of low density.
Higher density targets (like the human body) will reflect or absorb the X-rays. They do this because there is less space between the atoms for the short waves to pass through. X-rays are one of the most common radiology procedures. X-rays produce a still picture of bones and organs.
Since Rontgen's discovery that X-rays can identify bone structures, X-rays have been developed for their use in medical imaging. Radiology is a specialized field of medicine that employs radiography and other techniques for diagnostic imaging. X-rays are especially useful in the detection of pathology of the skeletal system, but are also useful for detecting some disease processes in soft tissue.
Diagnostic imaging techniques help narrow the causes of an injury or illness and ensure that the diagnosis is accurate. These techniques include X-rays, computed tomography (CT) scans, and magnetic resonance imaging (MRI).
These imaging tools let your doctor see inside your body to get a picture of your bones, organs, muscles, tendons, nerves, and cartilage. Your doctor uses these tools to determine if there are any abnormalities.
X-rays (radiographs) are the most common and widely available diagnostic imaging technique. Even if you also need more sophisticated tests, you will probably get an X-ray first.
The X-ray or radiograph is produced by the transmission of energy. A beam of high-energy photons is passed through the body, some of which are attenuated or blocked when they strike subatomic particles.
The higher the atomic weight of the substance through which the photons are passing, the “denser” it appears to photons, and the more likely they are to be blocked, or attenuated. In decreasing order of density, the principal densities visible in a radiograph are metal, bone, water (including soft tissues such as muscle), fat, and air.
Risks of X-Ray
There is very little risk with having one X-ray test. However, with repeated tests there is a risk that the X-rays may damage some cells in the body, possibly leading to cancer in the future. The dose of X-ray radiation is always kept to the minimum needed to get a good picture of the particular body part being checked.
Also, radiographers who take the X-ray pictures always wear lead aprons or go behind a protective screen when the X-rays are fired to avoid repeated exposure to X-rays.
Pregnant women, if possible, should not have an X-ray test as there is a small risk that X-rays may cause an abnormality to the unborn child. This is why women are asked before having an X-ray if they are, or might be, pregnant.
What is MRI?
MRI Stands for Magnetic Resonance Imaging. MRI is a way of getting pictures of various parts of your body without the use of X-rays. Unlike X-rays and computed tomographic (CT) scans, which use radiation, a MRI uses powerful magnets and radio waves. A radio wave antenna is used to send signals to the body and then receive signals back. These returning signals are converted into pictures by a computer attached to the scanner. Pictures of almost any part of your body can be obtained at almost any particular angle.
Is MRI safe?
MRI is quite safe in the majority of patients. Certain patients may not be able to have an MRI. These include people who get nervous in small spaces (claustrophobic) and those with implanted medical devices such as aneurysm clips in the brain, heart pacemakers and cochlear (inner ear) implants. Also, people with pieces of metal close to or in an important organ (such as the eye) may not be scanned. There are a few additional safety considerations and some exceptions based on individual circumstances.
Also, certain metal objects that we common have on our persons like watches, credit cards, hair pins, writing pens, etc. may be damaged by the MRI scanner or may be pulled away from our bodies if we go into an MRI room. Also, metal can sometimes cause poor pictures if it is close to the part being scanned. For these reasons, patients are asked to remove these objects before entering the MRI scanner
Why the MRI test is performed?
Combining MRIs with other imaging methods can often help the doctor make a more definitive diagnosis. MRI images taken after a special dye (contrast) is delivered into the body may provide additional information about the blood vessels.
An abdominal MRI provides detailed pictures of the belly area from many different views. It is often used to clarify findings from previous x-rays or CT scans. The pad on the patient’s abdomen helps make the pictures clearer.
This test may be used to diagnose or evaluate:
- Abnormal growths and tumors
- Blood flow
- Blood vessels
- Lymph nodes
- Organ function
- MRI can distinguish tumors from normal tissues and can help the doctor determine the tumor's size, severity, and spread. This is called staging.
Advantages & Disadvantages
Advantages of MRI include diagnosing:
- Strokes in their earliest stages
- Brain and pituitary tumors
- Spine, or joint infections
- Visualizing torn ligaments in the wrist, knee, and ankle
- Visualizing shoulder injuries
- Herniated discs in the spine
MRI also has disadvantages. These include:
- People with pacemakers cannot have MRIs.
- Patient who are morbidly obese may not fit into an MRI system.
- Claustrophobic patients often cannot make it through a MRI. These patients may require sedatives or an Open MRI which is an MRI system that is not completely closed around the patient.
- The MRI machine makes a tremendous amount of noise during a scan. The noise sounds like a continual, rapid hammering. The noise is due to the rising electrical current in the wires of the gradient magnets being opposed by the main magnetic field. The stronger the main field, the louder the gradient noise. Patients are given earplugs or stereo headphones to muffle the noise.
- MRI scans require patients to hold still for extended periods of time. MRI exams can range in length from 20 minutes to 90 minutes or more.
- MRI systems are very expensive. Therefore the exams are also very expensive.
- Lastly, people with kidney disease, dialysis patients, or people who didn't know they had kidney disease are at high risk to develop an incurable condition called Nephrogenic Systemic Fibrosis (NSF) from the MRI dye injection gadolinium. NSF causes a hardening or stiffening of the skin and joints.
Preparation for MRI test
Before your MRI test, tell your health professional and the MRI technologist if you:
- Are allergic to any medicines
- If you are or might be pregnant
- If you wear any jewelry, eyeglasses, hearing aids, hairpins, removable dental work or other objects that may interfere with the procedure
- Had recent surgery on a blood vessel. In some cases you may not be able to have the MRI test.
- Have any other health conditions, such as kidney problems that may prevent you from having an MRI using contrast material.
- Wear any medication patches. The MRI may cause a burn at the patch site.
- For an MRI of the abdomen, you may be asked to not eat or drink for several hours before the test.