Exam I Flashcards
What are X-rays?
Photons
discrete packets of energy
Electromagnetic Radiation
Energy (E)=
1/ wavelength
shorter wavelengths= _____ energy
Shorter wavelength= more energy
Examples of high energy wavelengths
***x-rays
gamma rays
Examples of Electric and Magnetic Fields
Radio/TV waves
microwaves
visible light
x-rays
What determines energy and character?
Wavelength
What are some properties of X-rays?
No charge, No mass
Invisible, Cannot feel
Travels in straight line
Travels at speed of light
Penetrates all matter
Ionizations
expose photographis emulsions
You can measure x-rays with an electrometer.
T/F?
False. X-rays have no charge
You can detect Lethal doses of x-rays (photons).
T/F?
False
can fill room and would never know
What are the 3 fates of Ionizations in DNA?
Repair
Cell Death
Mutations
How would you use photons for tumor cells?
Cell Death
X-rays are carcinogenic.
T/F
True!
can cause tumor dvpt
The General public radiation dose limit
1mSv/year
Medical personell radiation dose limit
50 mSv/year
Pregnant medical personell dose limit during gestation
<5 mSv/year
ALARA is used to reduce one’s radiation dose. What does this acronym stand for?
As low as reasonably achievable
_________ distance between personell and radiation source _________ exposure significantly
Increasing distance between personell and radiation sources decreases exposure significantyl
The inverse square law states that the intensity of radiation (xrays/unit area) decreases with the distance from the source.
T/F?
True
The inverse square law states that doubling the distance increases the x-ray intensity to 1/4th (1/2)2
T/F?
False. The inverse square law states that doubling the distance decreases the x-ray intensity to 1/4th
According to the inverse square law, what does tripling the distance do?
Reduces x-ray intensity to 1/9th (1/3)2
What is scatter?
scattered radiation from x-ray that bounced off the patient.
can hit person or ground and scatter around
How can you protect personell against scattered radiation?
Use Shielding!
aprons, gloves, thryoid shield, glasses with lead
What are the effects of scatter?
degrades image and increases personell exposure
Collimation reduces scatter
T/F
True
beams down on small area that want to examine
What is a radiograph?
picture of pattern of x-rays emerging from the patient
Differential absorption is needed to create a radiographic image.
T/F?
True
How are x-rays produced?
when high speed electrons strike metal in an encased x-ray tube
How do you generate X-rays?
Electrons flow from Cathode (-) to Anode (+) through wire filament
A wire filament is made from ______ and has a _____ melting point.
A wire filament is made fromTungsten and has a high melting point.
What happens to the current passing through the filament?
It causes heating and electrons will “boil off”
How are the # of x-rays quantified?
as mAs
The # of X-rays are produced proportional to _________ (mA) and ________ is “on” (s).
The # of X-rays are produced proportional to filament current (mA) and time current is “on” (s).
The number of electrons at the cathode is proportional to mA.
T/F?
True
What does the product of (mA) x (s) determine?
the final # of electrons/ the # of x-rays produced
Will doubling mAs double the amount of x-rays produced?
Yes
What is the Filament Current (mA) limit for most vet machines?
300
The anode (+) is also known as the______.
Target
How is the target quantified?
as kVp
Increasing kVp causing a greater voltage difference than increasing mAs.
T/F?
True
Why is the anode (+) only half the time? How can it be made (+) all the time?
normal alternating current (AC) makes the anode + only half the time.
Electronic trickery can make it + all the time by increasing x-ray yield= “high frequency”
When are x-rays produced at the anode?
when electrons interact/hit tungsten electron shell atoms
X-ray production at the anode is very efficient.
T/F?
False.
it is very ineffient. 99% of electron energy is converted to heat
What 2 x-rays are produced at the anode?
- Characteristic radiation
***2. Bremsstrahlungn (braking or stopping)
What are the two steps in the Bremsstrahlungn (braking or stopping) x-ray production?
- The electrons hit the target and encounters tungsten atoms. Electrons from filament bend around nucleus and “brakes” b/c has large difference in electric charge.
- As electrons slow (brake), it releases energy as an x-ray forms part of the useful x-ray beam
What are the 2 steps in characteristic radiation (collisional interaction) x-ray production?
- Electrons from filaments deposit energy and eject electrons from inner shell. Electron from filament continues at lower energy.
- Outer shell elecron fills inner shell void and energy deposited by electron from filament is released as a characteristic x-ray that is part of the useful x-ray beam.
How are most X-rays produced?
By the Bremsstrahlung (braking or stopping interaction)
What does energy in the x-ray beam depend on?
How close it is to the nucleus
mAs controls?
=mA + time
of x-rays produced
kVp controls?
energy of x rays produced
What is wrong with this radiograph?
Underexposed= too light
Either the kVp or the mAs is too low
What is wrong with this radiograph?
Overexposed or too dark
kVp or mAs is too high
How do you fix an underexposed (too light) radiograph?
Increase mAs (more x-rays and time)
or
Increase kVp (higher energy)
To correct underexposure, by how much can you increase mAs?
double
To correct underexposure, by how much should you increase kVp and why?
only ~15-20%
more energy can get through patient, it is equivalent to doubling mAs
Which radiographic image is high contrast? Which is low contrast?
Left- high contrast (black & white, few grays)
Right- low contrast (many grays, few black & white)
Which type of contrast image has a high mAs and low kVp?
What part of the body is this good for?
high contrast image
The abdomen!
Which imaging technique is good for the thorax?
Low contrast
low mAs, high kVp
Photoelectric effect is desirable in radiographic imaging. As it ________, kVp_________
As photoelectric effect decreases, kVp increases
Photoelectric effect is dependent on ________. This allows increased distinction between tissues. If you have differences in tissues then you will have differences in x-ray _________.
Photoelectric effect is dependent on atomic number. This allows increased distinction between tissues. If you have differences in tissues then you will have differences in x-ray absorption. For example, imaging of the abdomen relies on fat so must maximize the effect to distinguish betwen tissues.
Compton scattering is also desirable in radipgraphic imaging.
T/F?
False
Compton scattering is atomic number ________ meaning there is ____ distinction between tissues. As it ________, kvP ________.
Compton scattering is atomic number independent meaning there is less distinction between tissues. As it increases, kvP increases.
Absorption is similar between tissues so the contrast is reduced and now relying on the p for contrast!
Which body parts is compton scattering best used for?
Thorax
Low contrast= _____ scale
- X-rays are _____ penetrable
- More ____ Interactions
- Absorption is _______
Low contrast= long scale
x- rays are more penetrable
more Compton interactions
Absoprtion is more uniform
High contrast= ______ scale
- X-rays are _____ penetrable
- More ____ Interactions
- Absorption _______
High contrast= short scale
X-rays are less penetrable
More Photoelectric Interactions
Absorption either occurs or not
What provides contrast in the Thorax? Will you need to maximize this contrast further?
Air
No. already have subject contrast due to air in lungs
What provides contrast in the abdomen? Will you need to maximize this contrast further?
Fat.
Yes. use low kVp and high mAs photoelectric effects
This radiograph is________.
What should you do to correct it?
Overexposed
Either decrease mAs by 1/2 or decrease kVp by 15%.
This rad was made using 5mAs and 100kVp. What technique should you use to try to correct this?
Can increase kVp by ~15% from 100 to 120kVp.
What 2 things are needed to make an image with radiograpy?
Absorption and transmission
What problems does scatter cause?
Degradation of image
and
Increases personell dose
When do we need to use a grid while taking radiographs?
When the patient is thicker than 10cm b/c they create more scatter.
Grids intercept scatter from the patient before it reaches the film
Grids are composed of alternating strips of ______ and _____.
lead and aluminum
must be lined up properly
When using a grid you need to use 2-3x more photons or a higher mAs due to absorption of the primary beam by lead.
T/F
True
Where do you position the grid?
Between the patient and cassette.
What 2 main methods do you use to record an image (converting x-ray pattern exiting patient into a visible image)?
- Analog conversion (film/screen systems)
- Digital Conversion
>90% blackness is due to light vs x-rays.
T/F?
True
X-ray film is much more sensitive to light
What is a digital radiograph?
Converting a recorded map of x ray transmission through a patient to a digital file into a digital image
What is a digital image?
Map of x-ray transmission converted to digital matrix
Digital radiograph is composed of pixels, each with an assigned shade of gray. In order to see a lesion on the image, the pixels must be _______ than the lesion.
Digital radiograph is composed of pixels, each with an assigned shade of gray. In order to see a lesion on the image, the pixels must be smaller than the lesion.
Pixels must be _______ and there must be a large number of ______ shades to obtain good contrast resolution.
Pixels must be small and there must be a large number of gray shades to obtain good contrast resolution
An image plate in a cassette like- housing similar to film-screen is characteristic of….?
Computed radiography
In order to view the radigraphic image from Computed Radiography (CR), cassettes must be processed in a place reader for 90seconds.
T/F?
True!
Besides flat panel, what other type of Direct Digital Radiography is there?
CCD (charge coupled device)
How does the CCD radiography system work?
the CCD chip converts light to electrical charge
The image quality is a function of light collection, lens and pixels in a camera chip
What are the 2 kinds of flat panel direct digital radiograpy systems?
Indirect & Direct Digital Detectors
With high contrast images bones are _______ and gas is _______
With high contrast images bones are white and gas is dark
With low contrast images, bones are_______ and gas is ______
With low contrast images, bones are gray gas is gray
In film the exposure latitude is narrow. What is exposure latitude?
The extent to which a film, image plate of flat panel can be over or underexposed to radiation and still get a good image
Digital Exposure Latitude also has a narrow margin of error.
T/F?
False!
With digital, you do not hve to be that precise with mAs and kVp.
Which images were taken with Analog, which with digital?
A B C taken with analog, D E F taken with digital all with different exposures
Since Detail is slightly better with film images, what happens if a digital image is underexposed or has low exposure?
The image looks grainy and has more “noise”= loose detail
There is also a limit to plate overexposure in digital imaging. What happens if the digital image is overexposed?
the plate becomes ‘saturated’ and the anatome ‘disappears’.
The computer cannot compensate anymore so everywhere that is overexposed appears black
Explain Contrast optimization with application of additionaly processing that ‘normalizes’ the image
Dark regions are made lighter and lighter regions made darker
= smooth ‘wide latitude’ radiograph
What are components of the basic PACS?
Device, Network, Image Archive ‘server’, Work stations, Communication protocol (DICOM), redundancy/disaster recovery
Which image describes helical mode?
B
A is single slice mode
How could you use IV contrast medium for CT to evaluate brain tumors?
Brain tumors alter the BBB. If you give IV iodinated substance the substance will show up as a different opacity in the image because with a tumor it will leak out
How does the MRI work?
Very Strong Magnetism!
The only hazard with the MRI is ionizing radiation.
T/F?
False!
There is no radiation hazard with MRI. Only the dangers of flying objects from the strong magnetism
What proton sequence does this MRI image depict?
PD (proton density)
the magnet “hears” all protons from bone, fat, CSF
Which proton sequence does this MRI image depict?
T2
2 signals (water and fat)
free water & tissue water, fat
Which proton sequence does this MRI image depict?
T1
1 signal
protons in fat, high signal
Which proton sequence does this MRI image depict?
FLAIR
nulls signal from fat
Most lesions, such as this infarct, result in increased _______. Which proton sequence was used in this MRI image?
tissue water
T2
FLAIR stands for _________________ and nulls signal from ________.
FLAIR stands for fluid attenuated inversion recovery and nulls signal from free fluid
helps see lesions better in the tissue b/c does NOT null tissue fluid
STIR stands for _____________ and nulls signal from __________
STIR stands for Short Tau Inversion Recovery and nulls signal from fat
right image rids fat from medullary cavity and makes lesion more obvious
What is Gadolinium and with which proton sequence can you use it with?
IV Contrast medium for MRI. Paramagnetic compound that speeds up proton relaxation. Used to detect defective BBB or inflammation
Only used with T1
What kind of image is this?
CT
bones are white
What type of MR image is this?
T2 weighted
fat and water signals
How would you define superimposition?
a structure that appears in an unexpected location and misinterpreted as a lesion.
Ex: looks like a lytic lesion on ischium, but just overlying anal sac
Does this right lateral view depict a lung nodule or due to metastases or is this a product of superimposition?
The VD view shows NO “lung nodule” it was superimposition from a tick
What type of summation does this rad of swiss cheese depict?
Negative summation
the overlapping areas are more radiolucent
Which vessel is an example of the silhouette sign in the thoracic cavity? Which vessels can be seen?
Coronoary artery cannot be seen on myocardium
Pulmonary arteries CAN be seen on the lungs
What vessel is depicted by the arrows in the image?
Pulmnary artery
Cannot say coronary artery b/c remember it has the same opacity as the mediastinum. If the coronary artery were mineralized you could say that.
In which positional view can you see the heart with a pleural effusion? When it is surrounded by fluid or the lungs?
Can see heart when surrounded by lungs in VD view when there is a pleural effusion.
Cannot see when surrounded by fluid b/c of the silhouette
What is the ONLY way to name radiographs?
First Word= point of entry
2nd word= point of exit
You can look at a radiograph and tell which it was taken.
T/F?
FALSE!
You think you can but you can’t!
Is this the correct orientation of the radiograph?
No.
Cranial should be oriented to the left (patellar left)
This cat has fluid in peritoneal space that resulted in reduced visualization of abnormal organ. This is an example of…….?
Silhouette Sign
What technique do you use to see the urethral and perienal region?
pull pelvic limbs cranially
Why is it good to look at the urethra in male dogs?
Good to look for calculi in the urethra. The os penis narrows further down and calculi like to lodge through here in the urethra
What shape does the cat spleen look liek radiographically?
Small triangle
