CHAPTER 12 RAD 1126 Flashcards
ATTENUATION
Refers to the absorption of x ray as it passes through the patients body reducing the number of x rays that reaches the IR
ALL INTERACTIONS ie. Compton, photoelectric, coherent
within the patient causes some degree of absorption
Differential Absorption (subject contrast)
This is the ratio between the absorption of one tissue and the adjacent nearby tissue
( This is the variation in how different tissues absorb x rays, it creates contrast in the image to help distinguish one tissue from another
Differential Absorption
The subtle differences in x-ray attenuation between various tissues in a body part is termed
BONE AND SOFT TISSUES
are two extremes of tissues in how they attenuate the beam providing a high contrast (1.50)
SUBJECT CONTRAST
It is the difference in shades of gray on an x ray image ( Brightness) DIFFERENT TISSUES LIKE BONES AND SOFT TISSUES absorbs x rays differently creating subject contrast
BONE- MORE PE AND COMPTON INTERACTIONS IN BONE
There are more photoelectric and Compton interactions in bone, leading to a much highter attenuation factor of 90%
Bones will appear white to a high contrast due to photoelectric/compton interaction
Soft tissues absorbs fewer x rays appear darker compare to bone
PHOTOELECTRIC/COMPTON RATIO
SUBJECT CONTRAST IN A RADIOGRAPH IS DIRECTLY PROPORTIONAL TO PHOTOELECTRIC/COMPTON RATIO
HIGH CONTRAST
Better differentiation in tissues
Because of pathology (disease) the soft-tissue absorbs more radiation (has more interactions) and the contrast ratio drops (1.13). This reduces the overall contrast, making the soft tissue lighter and closer to how the bone appears)- low contrast hard to dfferentiate between tissues
When there’s a health problem (pathology) in soft tissue, that tissue absorbs more X-rays. This means it interacts more with the X-ray beam, which causes the differences between soft tissue and bone to become less clear.
As a result, the contrast ratio drops (to 1.13), making the soft tissue appear lighter on the X-ray image and more similar in appearance to bone. This reduces the overall contrast, making it harder to distinguish between soft tissue and bone.
Three attenuation properties causing various subject contrast:
- Thickness of Tissue
- Physical Density of Tissue
- Atomic number of tissue ( most impact) a higher atomic number tissue will attenuate more x rays than a lower atomic number material
Tissue Thickness
Every 4cm of tissue thickness is added, and the attenuation of the x-ray beam is doubled. Changes in the part thickness may cause the subject contrast to either increase or decrease
Thicker tissues absorb more X-rays
For every 4cm of tissue that is added,
the attenuation of the x-ray beam doubles, changes in thicker or thinner tissue can change contrast on image making it clear or hard to see
Thicker tissue absorbs more X-rays. As the thickness of the tissue increases, more X-rays are attenuated (weakened or absorbed) by the tissue, which means fewer X-rays reach the image receptor. This results in lighter areas on the X-ray image where the tissue is thick, while thinner areas allow more X-rays to pass through, resulting in darker areas on the image
ATTENUATION IN TISSUE THICKNESS
ATTENUATION DOUBLES EVERY 4CM OF ADDED TISSUE THICKNESS
TISSUE DENSITY
Density is the Degree of darkness or lightness in an area of an image
HIGH DENSITY- MORE BLACK AND WHITE -ABSORBS MORE X RAYS, eg. bone
LOW DENSITY- MORE GRAYS- ABSORBS FEWER X RAYS- has few molecules packed together so they do not absorb much x ray eg.lungs, Air, fat
DENSITY
In this sense, it describes how dark or light a particular area appears on the X-ray film or digital image. Darker areas indicate that more X-rays have passed through the tissue (meaning the tissue is less dense, like air or fat), while lighter areas indicate that fewer X-rays have passed through (meaning the tissue is denser, like bone).
What is tissue density? Tissue density may be defined as the concentration of atoms or molecules w/in a tissue. Both photoelectric and compton interactions will double if the number of atoms is doubled. Overall density differences in the body are small so it requires extreme differences in tissue density to result in high subject contrast
Tissue density is about how many atoms or molecules are packed into a piece of tissue. If you double the number of atoms in the tissue, the interactions with X-rays (photoelectric and Compton) also double. However, in the body, the differences in density between tissues are usually small. Because of this, you need really big differences in density between different tissues to see clear differences in the X-ray image (high subject contrast)
3 MAJOR TISSUE CATOGARIES BASED ON TD ARE
SOFT TISSUES, AIR IN LUNGS, FAT
FAT/AIR
FAT SHOWS UP DARKER- LESS ATTENUATION than soft tissue and bone
AIR- has very little attenuation- VERY DARK
EG. Chest x ray, shows difference between air in lungs and the soft tissue- will absorb 1000 more radiation
TISSUE ATOMIC NUMBER
A high atomic number indicates an atom with more electrons in it’s shells. As atomic number increases, the (exponential) likelihood of interactions increases. Overall differences ie such as those between muscles and connective tissues are so small we normally cannot distinguish between the two. But much bigger differences exist between soft tissue and bone/contrast media.
High Atomic Number: This means the atom has more electrons, making it more likely to interact with x-rays.
More Interactions: As the atomic number goes up, the chance that x-rays will interact with that material increases a lot.
Small Differences: The differences in density between muscles and connective tissue are usually too small for us to see clearly in an x-ray image.
Bigger Differences: However, there are much bigger differences between soft tissues (like muscles) and denser tissues (like bones or contrast media), which makes them easier to see on an x-ray.
In short, higher atomic numbers lead to more x-ray interactions, which helps create clearer images of different tissues
BARIUM 56, CALCIUM 20
ATOMIC NUMBER
BONE
HAS CALCIUM- HAS A HIGH ATOMIC NUMBER SO IT ABSORBS MORE X RAYS, BONE-HIGH CONTRAST/WHITE
CONTRAST AGENTS
IODINE - Z53
BARIUM- BA56
AKA POSITIVE CONTRAST MEDIA
INCREASE SUBJECT CONTRAST
-PHOTOELECTRIC EFFECT- APPEAR BRIGHTER
-THEY HAVE HIGH ATOMIC # SUCH AS BARIUM
-USED IN BARIUM ENEMA
-HELP TO MAKE IMAGE SHOW UP BETTER
-BRINGS BINDING ENERGY TISSUE CLOSER TO X-RAY
Contrast agents (positive contrast media) can be introduced into cavities to provide increased subject contrast. These pharmaceuticals have a high atomic number such as barium #56. The contrast brings up the binding energy of the tissue closer to the x-ray energy causing more photoelectric effect and appearing bright.
Contrast Agents: These are special substances (like barium) that are used in medical imaging to help make certain areas of the body show up better on x-rays.
High Atomic Number: Barium has a high atomic number (#56), which means it has many electrons. This helps it interact more with x-rays.
Better Images: When contrast agents are used, they make the tissues in the area denser. This increases the chances of x-rays being absorbed (photoelectric effect), making those areas appear bright on the x-ray image.
In short, contrast agents help improve the visibility of certain body parts by increasing the difference between how much x-rays are absorbed in those areas.
USING BARIAM ENEMA AS A CONTRAST AGENT
Barium Enema: This is a medical procedure where a liquid containing barium is introduced into the rectum and colon.
Purpose: The barium helps to highlight the lower gastrointestinal (GI) tract during x-ray imaging.
How it Works: Because barium is a contrast agent with a high atomic number, it absorbs x-rays well. This makes the outlines of the intestines show up clearly on the x-ray images, allowing doctors to see any abnormalities, such as tumors or inflammation
