Refer to uploaded videos on Canvas for a summary about radiation, including ionizing radiation and radioactivity.
X-Ray
An x-ray image results from the differential absorption of x-rays.
Differential Absorption: The contrast in x-ray images arises from the varying degrees to which different tissues absorb x-rays.
X-rays that are totally absorbed by a structure:
Stop radiation from reaching the receptor.
Produce bright areas on the image.
Are referred to as radiopaque.
X-rays that penetrate the body and are transmitted with no interaction:
Allow radiation to pass through and blacken the film.
Result in dark areas on the image.
Are referred to as radiolucent; air is radiolucent.
Example:
A radiograph of bony structures results from the differential absorption between bone and soft tissue.
Fluoroscopy
Fluoroscopy is a continuous X-Ray image of the internal structure.
Contrast media is usually used during the exam, barium and iodine compounds.
Contrast media, such as barium and iodine compounds, can be used to help visualize organs by filling them.
Barium is used for the GI tract.
Iodine compounds are used for vascular structures.
Computed Tomography (CT)
CT adds a new dimension to your X-Ray. "Tomo" or "Tomography".
A conventional X-ray image is basically a shadow:
You shine a "light" on one side of the body, and a piece of film on the other side registers the silhouette of the bones
With a CAT scan machine, the X-ray beam moves all around (spirals) the patient, scanning from hundreds of different angles (multiple slices from multiple axis 8,16, 32, 64, 128…)
Magnetic Resonance Imaging (MRI)
Does not involve ionizing radiation.
Advantage: superior ability to differentiate tissues.
Images are constructed from signals from the tissues themselves (as a result of hydrogen atom stimulation).
The human body is up to 75% water. Water = H_2O. There are more Hydrogen atoms than oxygen atoms in the composition of water.
The protons in Hydrogen atoms are affected by magnetic fields.
In the presence of a magnetic field, the protons in your body line up (SPIN) parallel to the direction of the magnetic field that they are sitting in
It takes less energy for a proton to line up with (spin with) the field than against it
The protons within each of the tissues of the body relax at a unique rate after the RF energy is turned off.
This is what allows us to differentiate the tissues on the MR images
How MRI Works:
Atoms spin in random directions, like tops, around their individual magnetic fields. About half the atoms go each way, but there are a few unmatched atoms.
In magnetic field produced by MRI, atoms line up either north or south.
When radio frequency pulse is applied, the unmatched atoms spin the other way.
When the radio frequency is turned off, the extra atoms return to normal position, emitting energy. The energy sends a signal to a computer. The computer uses a mathematical formula to convert the signal into an image.
WARNING! THE MAGNETIC FIELD IN THE MRI SUITE IS ALWAYS ACTIVE!
MRI Safety: Important Patient History.
brain aneurysm clips
cardiac pacemaker
pregnancy
implanted medication pumps
intrauterine device (IUD)
any other surgically implanted or metallic object in the body
tattoos
Nuclear Medicine
Evaluates physiology – not anatomy.
The nuclear part is the radiation part.
PET also looks at physiology but we are able to also see the metabolism of the cells (positron emission tomography).
The radiotracer, injected into a vein, emits gamma radiation as it decays.
A gamma camera scans the radiation area and creates an image.
Cardiac Catheterization
Evaluates blood flow & pressure within the cardiac chambers.