Nucs Flashcards
What is the band of stability?
Happy place atoms go when they have a certain balance of protons and neutrons in the nucleus. Not exactly 1:1, but it’s close.
Depending on the imbalance of neutrons/protons different types of decays occur.
What kind of decay happens when you have lots of neutrons, not enough protons?
Beta minus decay
What is beta minus decay?
Have lots of neutrons, not enough protons
Take one of your neutrons and turn it into a proton - results in the emission of a “beta particle” from the nucleus - basically an electron emitted from the nucleus.
Need to change the charge of a neutron from neutral to positive (neutron is 1/2 negative and 1/2 positive - eject the negative, become all positive).
Need to balance out the energy loss - going from a neutron to proton - emit a massless “neutron” just to balance out the energy.
What is a “beta particle” and why is it ejected?
Ejected in beta minus decay when you have too many neutrons, not enough protons.
Basically an electron that comes from the nucleus.
- Ejected to change the charge of a neutron from neutral to positive (neutrons are basically 1/2 positive and 1/2 negative - eject the negative, then you become all positive).
- Balance out the energy loss - going from a neutron to proton, emit a massless particle called a “neutrino” just to balance out the energy.
What is emitted in beta minus decay?
Beta particle - negative particle
Neutrino - massless, to balance out the energy.
What kind of process is beta minus decay - chemistry term?
Isobaric transition - mass doesn’t change.
The atomic number changed (increased), but the mass of a neutron and proton are about the same - the mass number remained constant.
Is beta minus decay good for imaging?
No, but can cause some damage.
What kind of shielding do you want for a beta emitter?
Plastic b/c it has a low Z.
Lead’s high Z will result in Bremmstahlung x-rays.
What kind of decay happens when you have lots of protons and not enough neutrons?
Beta positive decay
Electron capture
What is Beta Positive Decay?
Too many protons and not enough neutrons.
The “rich guy” - has 1.02 MeV and not problem losing it.
A positively charged proton is converted into a neutral neutron by giving up a “positron” and a neutrino to keep the energy balanced.
Positron travels a very short distance and meets an electron - annihilate each other - results in two 511 keV photons emitted 180 degrees apart from each other.
511 keV is 1/2 of 1.02 MeV
What is Electron Capture?
Too many protons and not enough neutrons
The “poor guy” - don’t have the energy to kick out the positively charged proton to leave - adds a negative to a positive to make a neutral.
Pulls an electron into the neucleus from the K shell
What kind of process is Electron Capture - chemistry term?
Isobaric transition - just like beta minus and beta plus, mass does not change, but atomic number does - lose a proton.
Is Electron capture good for imaging?
Yes, it’s excellent b/c it’s often coupled to a process referred to as “isometric transition” which results in the emission of a characteristic gamma photons that can be imaged under a gamma camera.
After undergoing an isobaric transition (beta emission, positron emission, or electron capture), there is often left over energy - needs to be emitted to achieve final stability.
Isomeric transition - emitting energy and dropping to the ground state.
What is Gamma Emission from Isomeric Transition?
After undergoing isobaric transition (beta emission, positron emission, or electron capture), there is often left over energy - needs to be emitted prior to achieving final stability. Isomeric transition - emitting energy and dropping to the ground state.
Gamma Emimssion - the nucleus will emit its excess energy in the form of a gamma photon. The energy of these photons is variable and depends on the energy differences between the intermediate and final states of the nucleus undergoing isomeric transition. TOTAL energy emission for a given nuclei of a specific nuclide is the same - many times you have more than one intermediate state - with multiple energy gamma photons - why you see multiple peaks for different tracers.
What is Metastable?
In most cases the time spent in the intermediate state is very short. The transition from isobaric to isometric transitions is fast.
Situation where the intermediate state is prolonged - “metastable state”
The main value is the ability to separate out the electron radiation (bad) and the photon radiation (good). By using a nuclide that has already undergone an isobaric (electron emitting) transition - you can only expose the body to useful gamma emissions from the isometric transition.
Mo99 (isobaric transition via beta minus decay - emission of a beta particle (electron)) - Tc99m (hanging out in “metastable” limbo for a couple of hours) - Isometric transmission - emission of 140 keV photons - Tc99
What are the two types of isometric transition?
After undergoing isobaric transition (beta emission, positron emission, or electron capture), there is often left over energy - needs to be emitted prior to achieving final stability. Isomeric transition - emitting energy and dropping to the ground state.
Gamma Emission - nucleus emits its excess energy in the form of a gamma photon.
Internal Conversion - The energy you would normally get rid of via gamma emission can be transferred to an electron w/in the atom. Vacancy can lead to a downward cascade from a higher level - and either the transmission of a characteristic x-ray or an Auger electron. Bad b/c you are emitting particles which cause harm, not imageable gamma photons which contribute to the study.
What is Internal Conversion?
Type of isometric transition- left over energy from an isobaric transition (beta emission, positron emission, or electron capture) needs to be emitted.
The energy instead of being emitted via gamma emission, is transferred to an electron w/in the atom. Vacancy can lead to a downward cascade from a higher level - and either the transmission of a characteristic x-ray or an Auger electron. Bad b/c you are emitting particles which cause harm, not imageable gamma photons which contribute to the study.
What is Alpha Decay?
Tends to occur in heavier unstable atoms.
Alpha particles are basically Helium nuclei (2 protons, 2 neutrons). Slow and fat, can’t penetrate a piece of paper, worthless for imaging, but bad in close proximity.
Used in treatment situations - bone cancer mets with Radium 223.
Two types of tracer production?
Bombardment (nuclear reactor or cyclotron) and Fission
What is Bombardment type of tracer production?
Striking target elements with either neutrons (in a nuclear reactor), or with charged particles (alpha particles, protons, or deuterons) in a cyclotron.
Cyclotron has the advantage of producing elements via transmutation, therefore you don’t have any parents to clean up “carrier free”.
Have to clean up the left over parent element.
Difference between bombardment production in nuclear reactor vs cyclotron.
Nuclear Reactor: bombard with neutrons
Cyclotron: bombard with charged particles - usually results in transmutation, so you don’t have to clean up the parent - CARRIER FREE
What is Fission type of tracer production?
Neutrons are fired into large atoms (like Uranium and Plutonium) and split them into pieces - a lot of random stuff being made - I-131, Xenon-133, Strontium-90m, Molybdenum-99, Cesium-137.
The desired isotope also has a bunch of fission products (contaminants) which have to be separated out - can be done with chemistry. Can demonstrate a bunch of different decay methods.
What is Neutron Activation?
Target atoms eat up neutrons to form a new isotope - don’t need to be accelerated.
Products are isotopes of the target atoms, they cannot easily be separated from each other - NOT carrier free.
Neutron rich products tend to decay to beta emission.
Difference between physical, biologic, and effective half life?
Physical - Time necessary for a radionuclide to be reduced to half its existing activity.
Biologic- how long it takes to shit or piss half the tracer out.
Effective- takes both of these into consideration.
How do you calculate effective half life?
1/Effective = 1/Physical + 1/Biologic
If you have a large mismatch with biological and physical half life, effective half life basically becomes the short one.
Xenon: if you breath it out in 15 seconds it doesn’t matter when the physical half life is.
How long do you have to keep radioactive material?
General rule is 10 half lives.
What is activity and what are the units?
Amount of disintegrations per second.
Curie (Ci)- 3.7x 10^10 disintegrations per second.
New SI unit is Becquerel (Bq) which is one disintegration per second.
What is Specific Activity?
Activity per unit of mass (Bq/g).
The longer the half life, the lower the specific activity.
How does half life affect specific activity?
Longer half life = lower specific activity.
Activity per unit of mass (Bq/g).
How does a gamma camera work basically?
Gamma camera takes photons emitted from the radionuclide, turns it into a light pulse, and then takes that light pulse and makes some voltage. The voltage makes a picture.
What is a collimator?
Reduce scatter and allow for correct localization of radionuclide events. Works by discriminating based on direction of travel - can NOT tell the difference in photon energy (that’s done by photon height analyzer).
What tracers is a low energy collimator used for?
1-200 keV
Tc99m, I-123, Xe-133, TI-201
What tracers is a medium energy collimator used for?
200-400 keV
Ga-67, In-111
What tracers is a high energy collimator used for?
> 400 keV
I-131
What is the relationship between sensitivity and resolution with collimators?
Have an inverse relationship.
High sensitivity collimator will allow twice as many counts to be imaged but will degrade the spatial resolution. High sensitivity collimators are important with dynamic imaging (like the flow phase of a bone scan).
Effect of distance on sensitivity and resolution
Distance has NO effect on sensitivity (increased distance reduces counts by inverse square, but the increased distance allows for a greater FOV = no change in counts).
Distance DOES affect resolution (septa are no longer able to eliminate photons from oblique angles as distance increases).
Effect of septal length on sensitivity and resolution?
Short septa give a crappy resolution, but better sensitivity
Long septa give excellent spatial resolution, but crappy sensitivity (noisier image).
Effect of hole diameter on sensitivity and resolution?
Wide holes = highly sensitive, low resolution.
Narrow holes = low sensitivity, high resolution.
General trend for high energy and low energy septa?
High energy - want to use long thick septa + wide holes
Lower energy - Short thin septa + narrow holes
What is a converging hole collimator?
Cone Beam - holes are close together on the object side and far apart on the crystal/camera side - magnifies WITHOUT inverting the image (as opposed to a pinhole).
What is a diverging hold collimator?
Holes are far apart on the object side, and close together on crystal/camera side.
Takes a large object and minimizes it - can mage a large part of the body on a small crystal.
Increased area, decreased sensitivity and resolution.
What do photomultiplier tubes do?
Detect the light produced by a photon hitting the scintillation crystal and convert it into an electric signal or measurable magnitude.
More PMTs = more light you can pick up and greater resolution.
PMTs can record two things:
- Location- on X and Y axis
- Signal Intensity - which goes into a pulse height analyzer.
What is the function of a pulse height analyzer?
Discard background information and only look at photons from the tracer you are looking for.
What is the difference between background from a point source vs background from a person?
Compton scatter from a person is a lot closer to the energy you want to image, but really degrades the images.
Set the window that will exclude higher or lower to the desired peak.
What is Downscatter?
High energy photons can spill into the window of a low energy emitter, mainly resulting from Compton scatter effects.
LOWER PHOTON ENERGY TRACERS MUST BE USED FIRST.
How does matrix size affect acquisition time?
Larger matrix has superior resolution, but means longer acquisition time.
What is Star Artifact?
Focal intense energy - septal penetration of the hexagonal collimator holes.
Thyroid bed after a high therapeutic dose (using a medium energy collimator, instead of high).
What are the four parameters measured for gamma camera QC?
Field Uniformity - daily (extrinsic) and weekly (intrinsic) Window Setting - Daily Image Linearity - Weekly Spatial Resolution - Weekly Center of Rotation - Weekly
What is Field Uniformity?
The PMTs can have subtle variability in what voltage they assign to a given photon of light and the crystal isn’t totally uniform, and has subtle variations in thickness.
Want to try and keep these two things as uniform as possible.
A 2-5% non-uniformity is allowed (1% if SPECT).
Tested with a “flood”
What is a “Flood” test?
Test field uniformity- used to see if the camera can produce a uniform image along the entire crystal surface.
Extrinsically - with a collimator
Intrinsically - NO collimator
Use either Na99mTcO4 or Co57 source
Recommended counts for both extrinsic and intrinsic is between 5-10 million.
Recommended counts for extrinsic and intrinsic flood test?
5-10 million counts
How often should extrinsic flood test be done?
WITH collimator - done daily.
Tests the collimator and crystals
How often should intrinsic flood test be done?
WITHOUT collimator - done weekly.
What is the Energy Window test?
Correct window needs to be used prior to each study, so should be done DAILY.
Use a symmetric window centered at the peak energy used in the imaging test.
Source can be a syringe, a vial, or if absolutely necessary the patient.
For Tc you would use a 20% window centered at 140keV.
What is image linearity and spatial resolution test?
Lead bar phantoms with parallel lines placed between collimator and a Co57 sheet.
Done weekly
Resolution is ability to differentiate between two distinct points (can you tell the bars are separate).
Linearity is tested by looking to see if all bars are straight (some distortion at the edges is ok). Bars should NOT look wavy.
What is center of rotation test?
Gamma cameras that are used for SPECT have to be routinely monitored for alignment at the COR (center of rotation).
Done with 5 small Tc99m point sources along the axis of rotation. The axis should be straight with minimal deviation.
WEEKLY.
Why aren’t lead aprons used in NM?
- Thin lead doesn’t stop gamma rays - would have to be a big apron.
- When high energy gamma rays collide with a dense material that is not thick enough to stop them (lead apron) they rapidly slow down and lose energy which turns them into deeply penetrating Bremsstrahlung x-rays which actually makes the dose worse.
How should a ring badge be worn?
On dominant hand, index finger, label in towards source (usually means towards the palm), under a glove (to avoid contamination).
What is a well counter?
Basically a small gamma camera with PMT. HOle in the block of NaI crystal into which the sample is placed (so it’s surrounding the sample)
Great efficiency, but can be overwhelmed. If sample exceeds 5000 counts per second (a lot less than a micro curie), it will be under reported.
Limitation of a well counter?
Great efficiency, but can be overwhelmed. If sample exceeds 5000 counts per second (a lot less than a micro curie), it will be under reported.
What is “dead time” in a Geiger-Muller Counter?
GM counters are very sensitive but also vulnerable to being overloaded by a large dose of radiation. Then you have “dead time” before it can respond again.
Max dose it can handle is about 100 mR/h
Can NOT provide info on radiation type.
What is the maximum dose a Geiger-Muller counter can handle?
100 mR/h.
What is an ionization chamber?
Same concept as a Geiger-Muller Counter but when higher doses are expected. Don’t have dead time problem.
Can detect exposure rates from 0.1 to 100 R/h (GM counter is 100mR/h) - unit change.
Dose calibrator is ionization chamber.
Exposure rates detected with ionization chamber?
0.1 to 100 R/h
GM is 100 mR/h - unit change.
Differences between a Geiger-Muller Counter and Ionizing Chamber?
GM Counter - Very sensitive, great for low-level radioactive survey, terrible for very high radiation fields (“dead time”)
Ionizing Chamber - lower sensitivity, stable across a wide voltage range - excellent for accurate estimates (or exposure).
What are the types of personal dosimeters?
Pocket ionization detector
Solid state dosimeter
Film badge
Optically stimulated dosimeter
Thermo-luminescent dosimeter
What should the constancy measurement be for a dose calibrator and when should it be checked?
Should be within 5% of computed activity. Checked with reference sources - checked DAILY.
What is linearity for a dose calibrator and when should it be checked?
Accurate readout for activities over the whole range of potentially encountered activities - checked with a large activity of Tc (around 200 mCi) and decaying it down to less than the smallest activity you would measure for use.
Or use a Calicheck or LIneator kit (contains sheets of varied thickness of lead, simulating decay over time).
QUARTERLY.
What is Accuracy for a dose calibrator and when should it be checked?
Standard measurements of radiotracers measured and compared to what the activity should be
At installation of the device and annually.
What is Geometry for a dose calibrator and when should it be checked?
Correction for different positioning and size (different volumes of liquids) of the sample (performed at installation and any time you move the device).
Where are the rules and regulations for NM found?
Code of Federal Regulations (CFR)
Part 19- Inspections
Part 20- Radiation protection
Part 35- Human use of radioisotopes
The NRC is the governing body that has been charged with the task of enforcing all the directives.
Activity greater than what for Tc99m, TI-201, In-111, Ga-67, and I-131 is considered a major spill?
Greater than 100 mCi of Tc-99m is considered
Greater than 100 mCi of TI-201 is considered
Greater than 10 mCi of In-111 is considered to represent
Greater than 10 mCi of Ga-67 is considered to represent
Greater than 1 mCi of I-131 is considered to constitute
What do you do for a major spill vs a minor spill?
Minor spill = You clean it up
Major Spill = Don’t clean it up, call the radiation safety officer.
Activity of Tc-99m to be considered a major spill?
100 mCi
Activity of Tl-201 to be considered a major spill?
100 mCi
Activity of In-111 to be considered to represent a major spill?
10 mCi
Activity of Ga-67 to be considered to represent a major spill?
10 mCi
Activity of I-131 to be considered a major spill?
I-131
What do you do during a minor spill?
- Protect the patient- address the patient first if in distress, then address the spill.
- Confine the spill/limit the spread - don’t let people come in and track it all over the place.
- Clean up the spill - use gloves and wear shoes
- Survey cleanup items - anything used in the clean up needs to be surveyed or presumed contaminated (held until they decay to safe levels - rule is 10 half lives).
- Survey cleanup people - surveyed by the radiation safety officer.
What do you do for a major spill?
- Clear area
- Cover spill with absorbent paper. Do NOT clean it up.
- Clearly indicate boundaries of spill area. Limit movement of contaminated persons.
- Shield source if possible
- Notify the Radiation Safety Officer immediately
- Decontaminate persons
What do you do if a spill gets on your clothes?
Take them off - will be held by the RSO until decayed to safe levels.
What do you do if a spill gets on your skin?
Wash with soap and water (don’t scrub so hard you break your skin).
What do you do if there is a Xenon leak?
Without alarming the patient, instruct all individuals to leave room as quickly as possible. Close the door.
Wipe test does NOT work on xenon contamination.
What is the annual dose limit to the public?
100 mrem
What is the dose limit per hour in an “unrestricted area”?
Not greater than 2 mrem per hour
What is a “restricted area”?
Any place that receives a dose greater than 2 mrem/h
What area has a sign that says “Radiation Area”?
Any place you could get 0.005 rem (0.05 mSv) in 1 hour at 30 cm.
What area has a sign that says “High Radiation Area”?
Any place you could get 0.1 mrem (1 mSv) in 1 hour at 30 cm.
What area has a sign that says “Very High Area”?
Any place you could get 500 rads (5 gray) in 1 hour at 1 meter
What are the occupational exposure dose limits?
Total body dose per year = 5 rem (50 mSv)
Dose to the ocular lens per year = 2 rem (20 mSv)
Total equivalent organ dose (skin is also an organ) per year = 50 rem (500 mSv)
Total equivalent extremity dose per year = 50 rem (500 mSv)
Total dose to embryo/fetus over entire 9 months - 0.5 rem (5 mSv)
Occupational limit for total body dose per year?
5 rem (50 mSv)
Occupational limit for dose to the ocular lens per year?
2 rem (20 mSv)
Occupational total equivalent organ dose (skin is also an organ) per year?
50 rem (500 mSv)
Occupational total equivalent extremity dose per year?
50 rem (500 mSv)
Occupational dose to embryo/fetus over entire 9 months?
0.5 rem (5 mSv)
Unit conversions in NM
1 rad = 1 rem
1 rad - 0.01 Gy
1 mSv = 100 mrem = 0.1 rem
What is 10 CFR part 19?
Notices, instructions, and reports to worker
What is 10 CFR part 20?
Standards for protection against radiation
What is 10 CFR part 35?
Medical use of by-product material.
What is the limit of variation from dose via the NRC?
20%
What constitutes a medical event?
- Wrong drug, wrong route, wrong patient, or wrong dose (more than 20%) OR patient receives a dose to a part of the body other than the intended treatment site that exceeds by 50% or more the dose expected by proper administration and prescription.
- Have to harm the patient - dose >5 rem or single organ dose >50 rem
5 rem = 0.05 Sv = 50 mSv
Doses considered a recordable event?
Whole body dose <5 rem
Single organ dose <50 rem
Doses considered a diagnostic medical event?
Whole body dose >5 rem
Single organ dose >50 rem
What do you have to do after a medical event?
Call the doctor who ordered it, the patient, and NRC/State and explain what happened and if anything needs to be done about it.
How long do you have to keep a log of recordable events?
5 years.
Also have to perform an institutional review.
Difference between a reportable and recordable event?
Whole body dose > or < 5 rem
Single organ dose > or < 50 rem
Greater = reportable event Less = recordable event
What do you have to do after a reportable event?
Call NRC w/in 24 hours
Write NRC letter w/in 15 days
Present your testicles to the NRC for castration (w/in 30 days)
Notify referring doctor w/in 24 hours
Notify the patient (or let referring do it)
What must be done within 3 hours of receipt of a package?
3 working hours
Survey package with GM counter at the surface and 1 meter from the package.
Wipe of all surfaces of the package (>6600 dpm/300 cm2 is not allowed)
Keep package in controlled area.
What is the limit of a wipe of a package?
> 6600 dpm/300 cm2
What is a White 1 package?
No special handling, surface dose rate <0.5 mrem/hr, 1 meter 0 mrem/hr
What is a Yellow 2 package?
Special handing required, surface dose rate <50 mrem/hr, 1 meter < 1 mrem/hr
What is a Yellow 3 package?
Special handing required, surface dose rate <200 mrem/hr, 1 meter <10 mrem/hr
What is the “Transport Index”?
Measured max dose at 1 meter. This is an actual dose rate measured at 1 meter (not an allowable dose rate), at the time of shipping.
What is Radioactive Label 1 Transport Index?
Measured max dose at 1 meter. This is an actual dose rate measured at 1 meter (not an allowable dose rate), at the time of shipping.
White 1 - There is no T.I. b/c the rate at 1 meter will be so low
What is Radioactive Label 2 Transport Index?
Measured max dose at 1 meter. This is an actual dose rate measured at 1 meter (not an allowable dose rate), at the time of shipping.
Yellow 2 - The T.I. is <1.0 mR per hour
What is Radioactive Label 3 Transport Index?
Measured max dose at 1 meter. This is an actual dose rate measured at 1 meter (not an allowable dose rate), at the time of shipping.
Yellow 3 - The T.I. is >1.0 mR per hour
What dose/hr is a “radiation area”?
5 mRem/hr (0.05 mSv)
What dose/hr is a “high radiation area”?
100 mRem/hr
What is a “common carrier”?
A truck that carries regular packages and radioactive material - the T.I .should not exceed 10 mR/hour
Surface rate should not be more than 200 mRem
What is “multiple packages”?
Those shipped together, the sum should NOT exceed 50 mR
Half life of Mo99 vs Tc99m
Mo99 = 67 hours
Tc99m = 6 hours
How does a Mo99/Tc99m generator work?
Mo’s half life is longer than Tc, so it can be made and shipped as a generator. Mo adheres to the aluminum column tightly and can be washed off with saline across the column.
When it comes out, the Tc is stuck to Na (Na99mTcO4).
It’s in a +7 valence state and must be reduced to be used - accomplished with stannous ions.
What valence does Tc99 come out of the reactor as?
+7 valence - must be reduced - accomplished with stannous ions.
How do you test purity in Tc99?
Mo in the sample is called “break through”.
Look for different photo peaks of the radionuclides. Sample is placed behind a lead shield. Mo is assayed for first - high energy photons of Mo (like 740 keV) will NOT be attenuated by the shield, but the 140 keV Tc photons will.
No more than 0.15 micro Ci of Mo per 1 mCi of Tc at the time of administration.
If ratio is less than 0.038 at the time of elution, the material will be suitable for injection for at least 12 hours.
For Tc purity, a ratio of what at the time of elution will be suitable for injection for at least 12 hours
Ratio of less than 0.038 at the time of elution
What is chemical purity with Tc-99?
The column is made of Aluminum oxide- can wash off, clump up with Tc and show up as liver activity, or cause sulfur colloid aggregation and show up in the lungs on liver spleen scan.
The test for purity is performed with pH paper. Allowed amount is <10 microgram Al per 1 ml
How can aluminum contamination of Tc be shown?
Liver spleen scan + LUNG
Tc scan + LIVER ACTIVITY
What is Radiochemical Purity with Tc?
Tc comes out of the generator as Na99mTcO4. So to use it for anything useful it needs to be reduced (accomplished by adding it to SnCl2).
Thin layer chromatography is used to assess for purity.
How is Na99mTcO4 reduced when it comes out of the generator?
Adding it to SnCl2.
Limits for free Tc?
95% Na99mTcO4
92% for 99mTc sulfur colloid (MAA)
91% for all other Tc radiopharmaceuticals
When you check the radiochemical purity of 99mTc-MAA you are checking for what?
Free pertechnetate
Is testing for chemical purity mandatory?
Not mandatory in NRC states
When must the 99Mo and 99mTc ratio be known?
At time of ADMINISTRATION, not elution
When checking for radionuclide purity (Mo breakthrough) when is assayed first?
Mo assay first
Is 99mTc carrier free?
Technically no b/c of the presence of 99mTc which is technically a radionuclide (but essentially stable since it’s half life is 200,000 years).
What causes free Tc?
Lack of stannous ions (reducing agents) or accidental air injection into the vial or syringe (which oxidizes).
Shown as gastric uptake, salivary glands, and thyroid
How is free Tc shown?
Gastric, salivary glands, and thyroid uptake.
What is radionuclide purity? How is it tested? What is the limit?
How much Mo in the Tc
Tested in a dose calibrator with lead shields
0.15 Mci of Mo per 1 milliCi of Tc
What is chemical purity? How is it tested? What is the limit?
How much Al in the Tc
Tested with pH paper
<10 micrograms Al per 1 ml
What is radiochemical purity? How is it tested? What is the limit?
How much free Tc
Tested with thin layer chromotography
95% Na99mTcO4
92% for 99mTc sulfur colloid (MAA)
91% for all other Tc radiopharmaceutcals
What is Equilibrium?
Concentration of parent and daughter isotopes are equal
What is transient equilibrium?
Type of equilibrium occurs when the half life of the daughter is shorter than the parent (but not by a lot).
Mo-99 generator making Tc-99.
A transient equilibrium occurs after 4 half lives (usually)
What is an example of transient equilibrium?
Mo-99 generator making Tc-99
When does transient equilibrium usually occur?
After 4 half lives
What is Secular equilibrium?
Occurs when the half life of the daughter is way way way shorter than the parent.
What is Critical Organ?
Organ that limits the dose of the radiopharmaceutical due to the increased susceptibility of the critical organ for cancer.
May or may not be the “target organ”.
Organ that the tracer is going to spend the most time in.
Gallium - bowel RBC - heart head damaged RBCs - spleen MAG3 and DTPA - bladder DMSA - kidney Free Tc - thyroid MIBG - bladder (or thyroid if not blocked)
What is the Target Organ?
Organ you want the tracer to accumulate in. Organ of interest.
With which tracers is the spleen the critical organ?
Octreotide
Damaged RBCs
With which tracers is the liver the critical organ?
Indium
I-131 MIBG
Sulfur Colloid
With which tracers is the gallbladder wall the critical organ?
HIDA
With which tracers is the stomach the critical organ?
Pertechnetate
With which tracers is the renal cortex the critical organ?
Thallium
DMSA
With which tracers is the proximal colon the critical organ?
Sulfur colloid (oral) Sestamibi
With which tracers is the distal colon the critical organ?
Gallium
With which tracers is the bladder the critical organ?
MAG3
DTPA
I-123 MIBG
MDP
Difference between SPECT and PET?
SPECT - single photon system
PET - uses two photons (from a positron annihilation event)
Type of reconstruction used in SPECT?
Iterative Reconstruction
What is sensitivity of SPECT dependent on?
Depth dependent - radiation from different tissue origins attenuated to different degrees.
PET is not dependent on depth
What is the big advantage of SPECT over planar?
Improved contrast from overlapping structures
What is Tuning Fork Artifact?
180 orbit with point source, should look like a point source.
If error with the center of rotation (misregistration error) then it will look like a tuning fork (two lines in one direction and one line in the other) - same appearance can be sen with motion.
Difference between SPECT and PET detectors?
SPECT has a few cameras rotating around the patient.
PET has a set of complete rings/detectors surrounding the patient
Difference in energy of SPECT vs PET?
SPECT is set up to detect medium-ish energy photons. NaI systems
PET- very high energy photons (511) - thicker robust crystals (Bismuth Germinate (BGO), Lutetium Oxyorthosilicate (LSO), or Lutetium Ytrium Oxyorthosilicate - LYSO.
What are the inherent limitations to PET?
Crystal Thickness (number of detectors) - need thick crystals to contain the high energy 511 photons = decreased spatial resolution. - PRIMARY LIMITING FACTOR that degrades spatial resolution of PET. Smaller crystal = more detectors = better spatial resolution.
Positron Range- positron travels a little bit prior to annihilation event- always a little off. How off depends on the energy of the photon.
Angulation- some extra kinetic energy at the annihilation that can wobble the takeoff - 1-3 degrees.
Scatter- try to reduce with coincidence detection.
What are the three types of events detected by PET?
True.
Scatter- one of the photons has a compton interaction and is defelcted, but still hits the detector w/in the coincident time window- just not the calculated location.
Random Coincidence- two photons, from different annihilation reactions just so happen to land w/in the same coincident window - creating the false calculation that they occured from the same event.
Increases with the dose of the administered activity.
What type of detected event increases with dose administered activity?
Random Coincidence.
How do you reject scatter in PET?
Incident time and photon energy.
If the photon undergoes scatter it will lose energy.
Difference between 2D and 3D PET systems
2D systems = use lead (or tungsten) septa to block unwanted scatter radiation - also decreasing your sensitivity for un-scattered photons
3D systems = do NOT use septa - large increase in sensitivity and allows for you to decrease amount of tracer you are giving. Need faster coincidence detector.
Seen in CNS and PEDs imaging.
Disadvantages of 3D PET?
Dead Time - possibly overwhelm (and temporarily paralyze) the detectors
More Random Events - increased sensitivity can lead to more detections and a resulting low level background noise.
Scatter - no septa = more scatter. Need good coincidence detection.
How can you reduce PET “dead time”?
Use crystals with faster scintillation times - LSO or can add more PMTs.
What is Time of Flight PET?
Annihilation event in anterior - one photon will take longer to travel due to longer distance - use quick detection which helps estimate the actual point of annihilation.
Results in improved spatial resolution and image contrast.
What does TOF PET do to SUV vs standard PET?
SUV measurements are higher.
Why is CT performed for PET-CT?
- See where things are
2. Attenuation correction
What is attenuation correction?
Correction for different levels of attenuation a photon might undergo as it tries to get out of the body to the detector
How do you tell the difference between the corrected and uncorrected attenuation images?
Look at the skin - hot
Lungs - hot
Calculation of SUV?
SUV = (Tissue radioactivity concentration at time point 1 x patient weight)/(injected dose activity)
How does SUV vary with fat vs skinny people?
Fat has low FDG uptake - more accurate to use patient’s lean body mass instead of weight.
SUV in fat people are overestimated - more sugar for the tumor.
How is SUV different in fat people?
Overestimated - more sugar for the tumor.
How does FDG uptake change with time?
Longer you wait between FDG administration and imaging the more FDG uptake you get.
Rapid uptake in first 2 hours, then goes up slower.
Delayed imaging will show higher FDG values - need to scan at same time each scan.
How does high glucose level change SUV?
High glucose = low SUV
more non-labeled glucose floating around - less FDG the tumor can drink.
How does smaller lesion change SUV?
Smaller = partial volume effects = lower SUV
How does dose extravasation change SUV?
= lower SUV
How does iterative reconstruction change SUV?
More iterations = higher SUV
What is truncation artifact in PET?
Lesion outside the CT FOV but inside the PET FOV.
Lesion appears artificially HOT at the margin and artificially cold outside of the CT FOV.
Appear hotter than they really are from attenuation over-correction. Outside CT FOV but seen on PET scanner may seem artifically cold b/c they reviewed litter or no attenuation correction.
Diet prior to FDG PET?
Fasting for 4 hours.
Minimize cardiac activity with 12 hour fast and a low carb/high protein and fat diet for 24 hours.
What causes muscle uptake in FDG PET?
Exercise (discourage for 24-48 hours prior to exam)
Eating or insulin use
Drugs to prevent brown fat uptake?
Propanolol and diazepam (valium)
What is a Blank scan for PET QA?
DAILY
PET equivalent of the uniformity scan. Helps keep the attenuation correction data accurate. Done with nothing in the FOV. Use the system transmission radiation source. “Zeroing” the scanner
When should a blank scan be done for PET QA?
Daily
What is a Normalization scan for PET QA?
MONTHLY
Corrects for discrepancies in the thousands of detector elements. Scan a calibrated position source placed in the FOV. Scan serves to “normalize” the detection lines.
If bad, see horizontal linear streaks in the images.
When should normalization scan for PET QA?
MONTHLY
What is Bucket Setup for PET QA?
A power surge or sudden power loss can imbalance the bucket setup/tube balancing.
Dark block rotating on the sinogram.
Energy and physical half life of Tc-99m
Low energy - 140
6 hours
Energy and half life of I-123
Low energy - 159
13 hours
Energy and half life of Xenon - 133
Low energy - 81
125 hours - biologic half life about 30 seconds.
Energy and half life of Thallium-201
What is it an analog of?
Analog of Potassium
Low energy - 135 (2%), 167 (8%), use 71 201Hg daughter x-rays
73 hours
Energy and half life of Indium-111
Medium energy - 173 (89%) and 247 (94%)
67 hours
What is Ga-67 an analog of and what are the energy and physical half life?
Analog of Iron
Multiple energies - 93 (40%), 184 (20%), 300 (20%), 393 (5%)
78 hours
Energy and half life of Iodine-131
High energy - 365
8 days
Energy and half life of F-18
High energy - 511
110 min
Half life of treatment radionuclide Strontium 89?
50.5 DAYS (14 days in bone)
Half life of treatment radionuclide Samarium 153?
46 hours
Half life of treatment radionuclide Yttrium 90?
64 hours
Half life of treatment radionuclide Radium 223?
11.4 DAYS
