Chapter 13 Flashcards
Define functional and molecular imaging
Functional Imaging:
Refers to studies that map changes in tumor or normal tissue function that are based on the interaction of many biochemical or physiological states.
Molecular Imaging:
Studies of single molecules that may be nb in experimental or clinical oncology.
Ct scans are based on a measurement of ___. The grey scale image created by a CT scan is expressed in units called ____ Units. This provides _____(anatomic, functional, molecular - pick one) info only.
x-ray attenuation
Houndsfeld
Anatomic
Nuclear medicine uses radioactive agents that emit high energy photons. The most commonly used one is ____. Whose half life is ____ hours. This molecule is attached to biologic compounds and transformed into scintillation. Which are used to detect bone mets by binding to _____.
How does it bind to the bone?
How long after injection do you evaluate the patient?
What can cause false + result?
TC-99 m (technesium) 6h MDP (methylene diphosphonate) Binds bone matrix dt ostoblast activity caused by mets. 3h+ Infection, fracture, arthritis
What is SPECT?
single photon emission computed tomography
combines nuc med and CT for a 3D image
What does PET stand for? How does it work?
What are 2 disadvantages/limitations for its usefulness?
Positron emission tomography
Positrons excite electrons producing two 511 kev photons in exact opposite directions. These are detected by emission scan.
Disadvantages:
- PET nucleotides have short t1/2
- To make radionucleotides, need cyclotron which is $$$
The most common tracer for PET scanning is FDG.
What is FDG and how does it help/work?
Name 2 other nucleotides used in pet scanning and their uses.
18F-fluorodeoxyglucose
FDG is metabolized in the cell (phosphorylated) which traps it in the cell. It cannot be further metabolized, therefore concentration of FDG trapped in cell correlates w/ rate of glucose phosphorylation (or metabolism). Tumors use more glucose than normal cells, so it can be used to localize and image tumors.
Carbon-11, Fluorine-18, Iodine-122, 124, Iron-52, Nitrogen-13, Oxygen-15, Copper-64
How does an MR work?
On which T1 or 2 is fluid white?
With which one do we use contrast?
Patient placed in large magnetic field w/in a scanner. Protons oscillate or precess at a known frequency. A pulse is given changing magnetic field. When pulse is turned off, precession slowly returns to normal.
T1 - fluid black. T2 - fluid white.
Contrast used w/ T1.
Uses - brain and sc
How does an ultrasound work/make an image?
U/S is based on reflection of high frequency sound waves by tissue interference
Optical imaging relies on fluorescence, reflectance or bioilluminescence as contrast to provide images of molecules in vivo?
What is the major limitation of optical imaging?
Only works in small animals (mice) or superficial targets bc short penetration of depth of light in tissue
ex: GFPs
Describe characteristics of tumor vasculature that make them different from normal vessels.
Spatial heterogeneity
Abnormal AV shunts
Transient flow
Leaky vessels
Measurement of blood flow in a tumor can be a useful marker for hypoxia.
Name 2 ways we can measure blood flow in a tumor.
Tracer studies that measure tracer that is injected and measurements are made w/ CT or MR to measure flow in and clearance from area.
Perfusion measurements using MRI w/ contrast (gradient echo-MRI)
Doppler ultrasound bc signal is related to flow
Why is using carbon labeled thymidine a good way to use PET to evaluate DNA synthesis?
Thymidine is the only base NOT used in RNA so you get rid of the RNA background signal.
Problem is that its degraded quickly, and often before too much is incorporated into DNA.
PET imaging can also be used for gene labeling studies and for evaluating apoptosis in vivo.
What marker of apoptosis on the cell surface can be imaged in vivo? (we’ve discussed this before)
Phosphatidylserine is only flipped to the o/s of the cell membrane in EARLY apoptosis.
It is labeled by ANNEXIN V which can be seen w/ PET etc based on how it is labeled
