Nuclear Medicine Flashcards
(59 cards)
1
Q
What is nuclear medicine?
A
- Imaging modality focusing on the use of radiopharmaceuticals
- Diagnosis and Treatment
- Based on physiologic function of organs or tissues
2
Q
function vs anatomy
A
The diagnostic information obtained from imaging the distribution of radiopharmaceuticals is functional
3
Q
PET function vs. anatomy
A
- Limited anatomic Information
- Less spatial resolution
- High sensitivity and specificity for molecular processes
4
Q
MRI function vs. anatomy
A
- Excellent soft tissue contrast
- High spatial resolution
- Poor sensitivity for molecular processes
5
Q
what are radiopharmaceuticals
A
- Referred to as radiotracer/tracer
Introduced into the body: - Injection (intravenous, intradermal, intrathecal)
- Inhalation
6
Q
how do radiopharmaceuticals work?
A
- Selected based on ability to localize in organs/tissues
- Undergo radioactive decay to emit gamma rays
- Emissions allow for the detection of the tracer’s presence
7
Q
NM images
A
- Scintillation detectors detect gamma emissions
- Emissions are transformed into images
- Lowest amount of radiotracer used to reduce exposure without compromising image quality
8
Q
nuclear medicine professionals
A
- Radiologist
- Nuclear Medicine Technologist
- Physicist
- Radiochemist
9
Q
radiopharmacy
A
- Naturally occurring radionuclides have very long half-lives
- Limited availability
- High absorbed patient dose
- Radionuclides produced in particle accelerators (cyclotrons) and nuclear generators
10
Q
radionuclide definition
A
radioactive material used to tag the pharmaceutical
11
Q
pharmaceutical definition
A
biologically active compound chosen because of its preferential localization in or function of an organ
12
Q
radionuclides
A
- 11C
- 13N
- 15O
- These elements are the predominant constituents of natural compounds found in the body
- Can replace their stable isotopes in substrates, metabolites, drugs and other biologically active compounds
13
Q
common radionuclides
A
- Commonly used radionuclide, 18F (fluorine), can replace hydroxyl group in many molecules
- Achieved without disrupting any bodily biochemical processes and mechanisms
- Emits positrons
14
Q
isotope production
A
- Radioisotopes and radiotracers need to be produced on the same day as the scan
- Radiochemist produces radioisotope with cyclotron
- Step 2 involves attaching the radioisotope to a biomolecule
15
Q
radiopharmaceutical properties
A
- Easy to produce
- Readily available
- Low cost
- Easily administered
- Concentrate in specific organs or tissues
- Have an activity level that is high enough that only small amounts are needed
- Has the requisite half-life
- Emit gamma radiation suitable for detection by gamma cameras (or positrons suitable for PET scanning)
- Needs to be sterile (regulated as drugs) to be injectable
16
Q
Isotope half life?
A
- Less stable radionuclide = short half life
- Exponential decay
17
Q
what are the most common isotope half life?
A
11C: 20 min
18F: 110 min
18
Q
What are the two modes of imaging in nuclear medicine?
A
- Positron emission tomography - PET scanner
- Single photon emission imaging - gamma camera
19
Q
what is positron emission tomography
A
anti electron radioactivity emitted from an unstable nucleus inside the subject section imaging
20
Q
steps of PET
A
- isotope production
- chemistry, purification and formulation
- imaging and analysis
21
Q
how is signal produced in PET?
A
radionuclide decays into a positron and an isotope
22
Q
annihilation radiation
A
- when a positron combines with an electron
- two 511 keV photons and goes straight out from collision
23
Q
what is coincidence detection?
A
detection of pairs of 511 keV photons by 3D ring of PET detectors
24
Q
18F
A
fluorodeoxyglucose (FDG)
- hydroxyl group (OH) has been replaced with radioactive fluorine (18F) to form FDG
- malignant tumors tend to preferentially metabolize glucose
- FDG can be used to identify sites of malignancy
25
FDG
- measures glucose metabolism
- clinically about 95% of PET scans
- gold standard for oncological imaging
- brain mapping
26
radio[pharmaceutial physiological processes
- receptor/ligand based
- enzyme/substrate based
both get "stuck" at the cell
27
pet sensitivity
- fraction of the annihilation pairs that are detected
- also affected by the number and type of detector
28
true coincidences
- both annihilation photons escape without interaction with tissue and strike detectors
29
random coincidences
- two annihilation photons from separate emissions strike detectors at the same time
- falsely get attributed to a different original event
30
scatter coincidences
- one or both annihilation photons get scattered in tissue
31
PET Scanner Blocks
- basic compartment of a PET scanner
- composed of a scintillation crystal coupled with 4 PMTs
- organized in a row to form detector modules - aligned side by side to form a ring
32
what is LoR?
Line of response - line between the 2 annihilations photons
33
detector rings
- to increase z-axis coverage, several rings are combined
- 800-1000 detectors per ring
34
signal detection and processing
- scintillation crystals detect gamma rays
- converts gamma rays into low energy visible photons
- photosensor (PMT) used to convert light to an electrical signal
35
scintillation crystal of PET
LSO:Ce
- high mass density and atomic number
- effective at stopping photons and has a high efficiency of light output
36
collimators PET
- located at the face of the detector, where photons first enter
- filters gamma rays not perpendicular to the detector and removes scatter
- made of material with high Z, like lead
37
how is collimator sensitivity determined?
- determined by the fraction of photons transmitted through the collimator and strike the detector
- depending on the magnification level and sensitivity required, different collimators are used for different exams
38
PET detector module measures what 3 aspects of the signal?
- the time is takes the gamma rays to hit the detector
- position
- energy
39
signal detection and processing
- coincidence unit recognizes the true events generated by the same annihilation event occurring along a specific LoR
40
image reconstruction
- filtered back projection
- iterative reconstruction
41
oncology imaging
- Majority of PET scans are done to diagnose, stage, or restage cancer
- 18F-FDG is the radiopharmaceutical of choice
- PET plays an important role in differentiating benign/malignant processes
- Effectively monitor therapeutic interventions by non-invasively assessing the metabolic response of tissues
42
PET scan colour expression
- shades of grey (hot spot darker)
- colour tables (hot spot red)
- linear colour tables (hot spot light)
43
SPECT
- single photon emission computer tomography
- single photon (gamma ray) is emitted as opposed to positrons
44
Which radionuclide is most used in SPECT?
99m Tc (technetium)
45
what is technetium?
- produced in nuclear generators
- parent - 99 Mo (half life of 66.7 hours)
- daughter - 99Tc (half life of 6 hours)
- isomeric transition yields a gamma photon (140 keV)
46
Technetium as a radiopharmaceutical - tagging
- technetium can be labeled onto a variety of pharmaceuticals
- tagged to macro aggregated albumin: lung scan
- tagged to methyl-diphosphate: bone scans for fractures
47
99mTc MAA
- after IV injection, this substance follows the pathway of blood flow to the lungs, where it is trapped in capillaries
- blood clots prevent distribution beyond the clot
- images show a cold spot
48
SPECT use
- most common for cardiac perfusion, brain, liver, ,tutor and bone studies
- detectors rotate 360 around the patient
- image data can be reconstructed in multiple planes and 3D
- any gamma emitting radionuclides
49
Gamma Camera
- AKA scintillation or Anger camera
- used to image game radiation emitting radioisotopes (scintigraphy)
- original was on detector that rotated around patient
- today systems may have 2 or 3 detector heads - dual head is most common
50
Static/spot view
- snapshot of radiopharmaceutical distribution in the body
- obtained in various orientations around a structure
- low radiopharmaceutical activity levels to minimize patient dose
- images must be acquired for a pre-set amount of time or a minimum umber of counts or radioactive emissions
51
whole body scanning
- sweep images allow the patient and detector to move with respect to each other and produce whole body images
- dual-head camera designed to acquire simultaneous anterior and posterior acquisitions
- used primarily for metastatic tumors, bones or infection imaging
52
dynamic imaging
- acquisition of multiple sequential images at defined intervals or over time
- sequential images are collected and aligned together to show function over time
- a dynamic or "flow" study of a structure is generally used to evaluate blood perfusion in the tissue
53
what are the hybrid imaging systems
SPECT/CT
PET/CT
54
hybrid imaging systems
- provide increased diagnostic accuracy
- misregulation possible due to difference in patient positioning
- hardware approach developed where both SPECT and PET scanners were combined with CT scanners
- Simultaneously acquire PET/SPECT functional images and CT anatomic images
- Both modalities are co-registered or exactly matched in size and position
55
Hybrid imaging
- position of suspected tumors can be recognized more easily
- suspicious metabolically active areas can be identified anatomically
- metabolic and anatomic evaluation after therapy can now be accomplished in one imaging session
56
Radioimmunotherapy
- Antibodies specifically designed to localize on the surface of different types of cancer cells can be tagged with a radioisotope and imaged
- If the antibody successfully localizes on the tumor site, the radioisotope may be replaced with a beta-emitting therapeutic radioisotope
- Current studies are looking to treat non-Hodgkin lymphoma with beta-emitting therapeutic radioisotopes
57
Radiation safety
- differ from safety measures used in general radiography
- radionuclides continuously emit radiation
- TLD badges and rings to monitor exposure to the body and hands
- Designated prep area due to high activity called hot labs
- Isolated ventilation, protective lead and lead glass shielding for vials and syringes, and gloves
58
Patient prep and post care
- Minimal, with most studies requiring no special prep
- All metal objects inside or outside clothing must be removed because they may attenuate photons
- The waiting time between dose administration and imaging varies
- After completion, patient may generally resume normal activity
59
What are the different collimators used in nuclear medicine and how do they affect the image?
parallel - normal
diverging - minimize image
converging - magnify image
pin hole - magnify image and increase spatial resolution
