Review Questions Flashcards
(34 cards)
What are isotopes and isomers?
- An isotope is an atom with the same number of protons but different number of neutrons
- An atomic nuclei that has the same number of protons and neutrons but with a different energy state
Compare the different types of emission. When would each occur?
Alpha particle emission
- Heavy nuclei/large atomic mass
Beta particle emission
- N:p ratio too high - Too many neutrons
Positron emission
- N:p ratio too low - Too many protons
Gamma radiation emission
- Releases energy from nucleus
The band of stability is above the line on the graph that has a slope of 1. What does this indicate about the number of protons and neutrons for the majority of elements?
- Majority of elements are close to a n:p ratio greater than 1
What affects the activity of a radioactive substance?
the n:p ratio
Compare high- and low-LET radiation. What are some examples of both?
High LET – greater density low linear travel
- Alpha particles
- Protons
- neutrons
Low LET – less likely to be damaging, travels farther through tissue
- Electrons
- Positrons
- Gamma rays
- X-rays
A sample of a radioisotope has 6x10^23 atoms in it, and a half-life of 5 years. What is the activity of the radioisotope in disintegrations per second?
HLV = -ln(0.5)/(5365.25246060)
HLV = 4.4x10^-9
disintigrations/second = 6x10^23x4.4x10^-9
disintigrations/second = 2.64x10^15
Sodium-24 has a half life of 15 hours. If there are 800g of Na-24 initially, how long will it take for 750g of Na-24 to decay?
60 hours
What are some of the major differences between nuclear medicine and x-ray imaging?
- shows function versus anatomy
- treatment and diagnosis
How does PET imaging differ from SPECT imaging? What are the most common radioisotopes used for both of these types of studies?
PET – positron emission tomography
o Positrons
o Radioisotopes have short have lives
o Radioisotopes are cyclotron produced
o Electronic collimation
o Stationary ring detector
o Coincidence detection
SPECT – single photon emission computed tomography
o Gamma ray
o Technetium
o Radioisotopes have long half lives
o Radioisotopes are reactor, generator or cyclotron produced
o Physical collimation
o Rotating detectors
What is a line of response? What are some causes of a false LoR?
- Both annihilation photons escape without interaction with tissue and strike detectors
- Random coincidences – separate emissions strike detectors at same time
- Scatter coincidences – one or both annihilation photons get scattered in tissue
How does the design of the collimator used in PET scans affect the images?
- Parallel – keeps image as it was
- Diverging – minimizes image
- Converging and pinhole – magnifies image
What would the precession frequency be for a hydrogen atom in a 3T magnetic field? The gyromagnetic ratio for hydrogen atoms is approximately 42.6 MHz/T.
127.8 MHz
What is the RF pulse in MRI? Where does it come from and what does it do?
- RF pulse is a radiofrequency pulse – a burst of radio waves
- Rotates the net magnetization into the transverse plane
- Comes from a transmitter coil
What are the different magnetic fields seen in an MRI scan labelled as, and how do they relate to each other?
- Transverse magnetization (T2)
- Longitudinal magnetization (T1)
- They occur simultaneously and independently
What is the difference between T1 and T2 relaxation?
T1 relaxation
o Spin-lattice
o Returning nuclear spin to equilibrium state along its z-axis
T2 relaxation
o Spin-spin
o Decay of magnetization components perpendicular to magnetic field
what is a zipper artifact and what causes it?
- It is caused due to radiofrequency interference from electronics in or near scanner room
What parameters do we alter to produce a T1 weighted, T2 weighted and proton density weighted image in MRI?
T1 Weighted
o Short TR followed by very short TE
o CSF is black
T2 weighted
o Very long TR and Long TE
o CSF is white
Proton Density Weighted
o Related to the number of hydrogen protons instead of magnetic characteristics of the hydrogen nuclei
o Very long TR followed by very short TE
What kinds of tissues would be whiter on a T1-weighted image? What about a T2-weighted one?
- Fat and protein would be whiter on a T1 weighted image
- Water and CSF would appear whiter on a T2 weighted image
how do gradient coils work
- They generate magnetic field in the same direction as B0
- Spatially localize anatomy of interest
- You are preparing a patient for an MRI scan and find out they have a pacemaker that contains ferromagnetic components. What risks could this pose?
- It could stop the pacemaker from working, therefore stopping their heart
What would a sonographer have to do differently if they were imaging the hepatic veins compared to the surface of the liver? How would this change the axial resolution of the image?
- If they were imaging the hepatic veins they would have to compress more to image deeper than the surface of the liver which is very superficial.
- The surface of the liver would have better axial resolution than the hepatic veins due to less compression
How does the acoustic impedance of different tissues affect reflection and transmission of ultrasound waves?
- If the difference in atomic number between the tissues is large it will be reflected as opposed to transmitted
Discuss how the density, compressibility, and stiffness of a medium influence the acoustic velocity of ultrasound waves. Why does sound travel faster in solids compared to liquids and gases?
- As density increases, it will decrease the speed of the sound waves
- As stiffness increases the acoustic velocity increases as the medium resists deformation and transmits the vibrations more efficiently
- As compressibility increases, it reduces the velocity
Calculate the wavelength of a 9 MHz ultrasound wave in soft tissue, given that the acoustic velocity is 1540 m/s. How would the wavelength of a 5 MHz transducer differ?
- Wavelength = 1540 m/s/9x10^6 Hz = 1.711x10^-4 = 0.171 mm
- Wavelength = 1540 m/s/5x10^6 Hz = 3.08x10^-4 = 0.308 mm
