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Terms in this set (71)
Describe how X-rays function
X-rays passed through patient
Can only detect 4 densities of tissue
1.) Metal (bright white)
2.) Bones (light grey)
3.) Soft Tissues (dark grey)
4.) Air (black)
All soft tissue looks the same
Things you can see in an X-ray
Joint width and surfaces
Things you can't see in an X-ray
Inside skull (Can't see the brain)
Inside Joints (Can't see tears, Ligaments, Tendons, Menisci, Cartilage)
Infolding of dura mater forming tent like sheath separating the cerebrum from cerebellum
With subarachnoid hemorrhage or subdural hematoma, the ___________may become more dense due to layering of blood
tent of the tentorium cerebelli
Infolding of meninges which lies in the midline, separating the left and right hemispheres
What features of a CT in the head should be evaluated to see if there is a surgical emergency?
If none of the following apply, not likely a surgical Emergency
Brain should look the same on both sides
Quadrigeminial plate cisterns should look like a symmetric smile
Suprasellar cistern should look like a star
Asymmetry can indicate uncal/transentorial herniation, mass or opacification
Size and Position are normal
Advantage of CT over X-ray
Can see fractures otherwise missed (Cervical Spine, pelvis)
Can see the brain (Strokes, bleeds, tumors)
Can see organs (like the lungs and liver) for tumors, trauma, chronic or acute conditions
Problems with CT
1.) Usually requires an IV contrast
Not good for renal patients
2.) Costs more than radiographs
3.) Still can't see structures inside joints
*4.) High radiation dose*
How much radiation is too much chronic exposure?
50 mSv in a single year
Maximum of 100 mSv in a consecutive 5 year period
Fatal acute dose of radiation
Typical radiation dose
Banana equivalent dose = 0.98microSv
When is it appropriate to order contrast for a head CT?
Infections (e.g., meningocephalitis)
How does contrast enhance a head CT?
Breakdown of the blood brain barrier
Within the CNS, contrast will only escape if the BBB is disrupted
What is a PET scan?
Positron emission tomography
Tracts agents with very short half-lives such as fluorine-18 (100 min) or oxygen-15 (2 minutes). These have to be made onsite with a cyclotron. These agents are taken up by tumors, metastases. It is usually combined with a CT, shows abnormal function or abnormal anatomy
What is an MRI?
Magnetic resonance imaging
Doesn't rely on X-rays to see projected shadow of patient
MRI sees tissues based upon subatomic characterics
-Proton Nucleus of hydrogen
How does an MRI generate an image?
Magnetic field divides body into slices
Each slice is divided into 3-dimensional pixels (voxels)
Coil measures signal in each voxel
Computer maps this onto 2D slices with intensities represented in grey scale
Color of High signal in MRI
Color of Intermediate signal on MRI
Color of low signal on MRI
Name of the different resonance imaging in MRI
T1 and T2
T1 resonance in MRI shows _____________ the best
Fat and therefore anatomy
Most normal anatomy is surrounded by fat
T2 resonance in MRI shows _______________ the best
Fluid and therefore pathology
Most pathology contains fluid (edema). Fat suppression makes fluid even more conspicuous
Proton density resonance in MRI shows ______________ the best
Good for meniscal and tendon tears. Used mostly for MRI of joint pain
Advantages to using MRIs
MRI is a stack of slices and more
You get composition of tissue (how fatty/how wet)
fMRI (functional MRI)
Diffusion weighted imaging
Limitations to using MRI
1.) Limited filed of view
Image resolution is related to voxel size
Smaller FOV = smaller voxels
Smaller Voxels = higher resolution
To maximize resolution, try to limit FOV
You can only image at high resolution what is inside the coil
This means you have to have a lot of coils!
2.) MRI is expensive
3.) MRI is time consuming
4.) MRI is restrictive
5.) Uses a high power magnet
Important safety considerations when operating an MRI
Can't bring into the scanner room anything
That is not certified MRI compatible
1.) No pacemakers
2.) No cochlear implants
3.) No Neurostimulators
4.) No fixed metals (quality concerns) or metal than can move
All _____________ looks the same on radiographs
Soft tissue (and bone)
Projection taken with the central ray perpendicular to the mid-sagital plane
Projection taken with the central ray at an angle to any of the body planes. Described by the angle of obliquity and the portion of the body the X-ray beam exits; right or left and posterior or anterior. For example a 45 degree Right Anterior Oblique of the Cervical Spine.
Radiograph taken wile in flexion
Stress view radiograph
Typically taken of joints held in a stressed position. Test of stability
Extension of the radiograph
Joint is radiographed while in extension
HBL, HRL, HCR, or CTL Radiograph
Horizontal beam lateral, Horizontal ray lateral, Horizontal Central ray, or Cross table lateral. Used to obtain a lateral projection usually when patients are unable to move
Patient lying down. Further described by the downside body surface: dorsal (backside down), ventral (frontside down), or lateral (left or right side down).
Occipito-mental, an imagery positioning line extending from the menti (chin) to the occiput (particularly the external occiputal protuberance)
Cranial or Cephalad
Tube angulation toward the head
Tube angulation toward the feet
For joints you need a minimum of ______________ views
____________________ is the name of the radiographic technique to overcome the 2-D
For x-ray tomography, structures in the ________________ are in focus, whereas structures outside of the _______________ are not in focus
Focal plane, Focal plane
One of the biggest problems with X-ray tomography
High radiation exposures
The first computed tomography was the _____________________
EMI brain scanner (EMI = electrical and musical industries)
How was the EMI brain scanner an improvement from X-rays?
It was able to measure different densities (hounsfield units), now making it possible to see through the skull into the brain
CAT scan uses ______________________________ to make the image
Sutures on a CT look ______________
The ___________________ is most susceptible to fill with blood following a basal skull fracture
______________________ of the choroid plexuses is a common CT finding in adults
A __________________________, might cause a loss of the grey-white matter differentiation in the brain.
___________________ are small infarcts within the deep cerebral white matter
Characteristic finding on a CT of an alcoholic
Characteristic finding on a CT for hydrocephalus
Characteristic findings on a CT of Alzheimers
Enlarged ventricles, small medial temporal lobe
Characteristics findings on a CT of Hypoxia
Cerebral edema, swelling of the brain
What is the average background radiation exposure to each person every year?
Radiation that we are exposed to everyday
Cosmic rays, Radon-222, Potassium-40
Radiation exposure from a chest radiograph
0.6mSv (1 week of background radiation)
Radiation exposure from a chest CT
7.0 mSv (3 years of background radiation)
What was Albert Stevens famous for?
He was injected with plutonium in 1945 without his knowledge or consent after a gastric ulcer was misdiagnosed as terminal cancer
What is iodine-131?
A highly radioactive isotope of iodine, synthesized from the fission of Uranium-235
What are the medical uses of iodine-131?
Iodine is highly used in the thyroid gland to make thyroid hormone, and is shuttled to the Iodine. Iodine-131 is radioactive and emits beta particles, and is therefore useful for treating thyroid cancer. Not useful however when fallout from a nuclear reactor. It can also be used as an X-ray contrast dye
What is technetium? How can it be used medically?
Naturally occurring element (like iodine). It is the first element to be artificially produced.
It has a short half life (6 hours, 94% gone after 24). Emits gamma rays (which passes out of the patient without accumulation). It emits a good amount of energy for a gamma camera.
Dense stuff in an MRI
Pathology in an MRI that would have fluid
Edema (soft tissue and bone)
Compare a T1 and T2 radiograph
T1 shows fat better (good for anatomy)
T2 shos fluid better (good for pathology)
Patients that are not good candidates for MRI
Time Consuming: If they can't lie still (sneezing/coughing) then don't bother
Restrictive: Patients that can't lie flat (CHF), patients that are claustrophobic, patients with electronic implants, patients with unsecured metal in their body
Problem with a pacemaker in MRI
Might drain the battery, fire erratically, scramble electronics, or reprogram it.
Issues with metal and MRI
Metal that is fixed is NOT a safety issue (fine for MRI): e.g. fillings in teeth, braces. They are quality concerns
Need to worry about metal that is NOT fixed: e.g. former grinders/metal morkers, older style aneurysm clips
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