Lecture 7 - Diagnostic Imaging Flashcards
What are the 3 principles behind X-rays?
- Electromagnetic waves of short wavelength (photons) are capable of penetrating some thickness of matter
- As X-rays pass through the body they are attenuated by the tissues (the denser the tissue, the more attenuation)
- As X-rays pass through the tissues, they interact with the photographic film behind the body
Magnitude of X-ray wavelengths?
10^(-10) m
In what way do X-rays exit the machine?
They flare out (diverge)
How can we interpret the colors on X-rays?
- Less dense: more black because X-rays can easily get to the photographic film
- More dense: more white because X-rays cannot get through to the photographic film
List air, fat, bone, and water in order of X-ray attenuation.
- Air
- Fat
- Water
- Bone
What is the most often broken bone in the body?
Clavicle
What is the hardest bone to break in the body?
Femur
How to describe subject placement in radiography?
First the side receiving the rays first
Then the side next to the film
Where do you put the part of the body you want to see in radiography? Why?
Closest to the photography film so that it does NOT appear larger because the X-rays diverge as they come out (you want a better representation of the organ)
What are the 2 types of X-ray positioning?
- AP = anterior posterior
2. PA = posterior anterior
How to see structures on an X-ray that are normally not dense enough to show up?
Fill them with contrast agents that will attenuate X-rays more than usual
What contrasting agent should you use to see bowels?
Barium sulfate
What is important to ensure when using contrast agents?
That they are non-toxic
What are the 2 ways of administering barium sulfate? How to pick between the two?
- Oral: to see foregut and midgut
2. Enema: to see large intestine and hindgut
What contrasting agent should you use to see arteries and veins?
Iodine
How is iodine cleared by the body?
Kidneys
When is subtraction angiography used?
When the vessels you are trying to see are around bones or other dense structures
How does subtraction angiography work?
- Images are obtained before the injection of the media
- Contrast is injected and new images are obtained of the vessels
- First set of images are subtracted from the second, producing a solitary image of contrast only
How does ultrasound work?
- Exposing parts of the body to high frequency sound waves
- The waves are reflected back, and interpreted by a computer
- The computer displays a real-time picture
What is the most inexpensive imaging technique?
Ultrasound
What is ultrasound used to see?
Soft tissues
What are 3 great advantages of ultrasound?
- Inexpensive
- Portable
- Very little harm (no radiation)
What are 2 potential physiological effects of ultrasound?
- Increase inflammatory response
2. Heat soft tissue
What are the 8 uses of ultrasound?
- Abdomen and fetus of pregnant women
- Eyes
- Neck
- Soft tissues
- Peripheral musculoskeletal system
- Probes on endoscope to look at esophagus, stomach, and duodenum
- Endocavity ultrasound in women’s genital tract
- Transrectal ultrasound to image prostate
How does a doppler ultrasound work? What is it used for?
Sound waves bounce off moving structures are return and the degree of frequency shift determines whether the object is moving away from or toward the probe, and the speed at which it is traveling.
Enables determination of blood flow (direction and velocity) and can indicate sites of blockage
What does CT scan stand for?
Computer tomography scan
How do CT scans work?
- A patient lies flat on a bed above a photographic film
- An X-ray tube passes around the body, and a series of images are obtained
- A computer carries out a complex mathematical transformation on the multitude of 2D images to produce the final 3D image
What is the directionality of the CT scan image?
- Feet coming out
- Head inside image
Why do we sometimes see black areas in the stomach on a CT scan?
Gas
How do MRIs work?
MRI utilizes magnets which align the free protons in the hydrogen nuclei in water, and then uses radio pulse waves to knock them out of their normal alignment. When they go back they emit a radio pulse wave with a frequency dependent on the amount of water in the tissue which is recorded by a computer
The more the bar magnets move, the more water was in the tissue
When to use a CT scan over an MRI?
When examining tissues of higher density like bone and bowels because it uses ionizing radiation
When to use an MRI over a CT scan?
MRI allows for greater contrast between surrounding tissues so allows for better visualization of tumors and other abnormalities
Which is less harmful: CT scan or MRI?
MRI because it uses non-ionizing radio waves, especially with patients who will need a succession of similar test
Which are less expensive and more widely available: CT scans or MRIs?
CT scans
How does nuclear medicine imaging work?
- A radiotracer is entered into the body and into the organ or area of interest
- There it gives off energy in the form of gamma radiation
- The energy is detected and analyzed and an image is created
Why is nuclear medicine imaging different from other tests?
Because it shows physiologic function rather than traditional anatomy like CT/MRI
When can MRIs not be used?
When the patient has some sort of metal in their body (e.g. pacemaker)
What is a very common radiotracer used in nuclear medicine imaging?
Radioactive glucose that will be taken up by metabolically active tissues
What part of the body is nuclear medicine imaging often used for?
Brain
What 2 combined techniques can pinpoint cancer anatomically?
PET and CT scan
What are PET scans?
A specific kind of nuclear medicine imaging
What does PET stand for?
Positron emission tomography
How do PET scans work?
Imaging modality for detecting positron-emitting radionuclides:
- The proton-rich radionuclide decays and emits a positron
- This positron then encounters an electron causing annihilation of both, producing a pair of photons
- These photons are detected and an image is created
What is the most commonly used PET radionuclide?
Fluorodeoxyglucose (FDG)
What is a positron?
An anti-electron, which is a positively charged particle of antimatter
What does MRI stand for?
Magnetic resonance imaging
