- Positron emission tomography (PET) takes advantage of the fact that a positron is annihilated whenever it encounters an electron. The combined mass and energy of the two annihilated particles is carried away by two gamma rays. What additional fact accounts for the ability of PET to form a reasonably clear image without the use of lead collimators? Explain how this fact is used by PET scanners.
- Oxygen-15 labeled carbon monoxide binds irreversibly to hemoglobin and can therefore be used to make an image of the distribution of red blood cells in the brain. What property of oxygen-15 labeled water makes it useful for making an image of blood flow in the brain. (Hint: oxgyen-15 labeled butanol gives an even more accurate image of blood flow in the brain because this property applies even more to it than it does to oxygen-15 labeled water).
- Have the subject close the right eye while looking at the alternating checkerboard.
- Have the subject close the left eye while looking at the alternating checkerboard.
- Place the alternating checkerboard entirely to the left of the subject's visual fixation point.
- Place the alternating checkerboard entirely to the right of the subject's visual fixation point.
- Do both A and C simultaneously.
- Do both A and D simultaneously.
- Do both B and C simultaneously.
- Do both B and D simultaneously.
Looking at an alternating checkerboard pattern causes increased blood flow in the occipital lobe along the calcarine cortex that can be identified by PET (when compared to a resting state without a checkerboard pattern). For each of the following stimuli, indicate whether it should produce a response in primary visual cortex that is limited to the left occipital lobe.
- Explain in your own words what is meant by the terms T1 and T2. Indicate how these are related to contrast between gray matter and white matter in MR images.
- MRI is viewed by many as the method of choice for imaging the anatomic structure of the soft tissues within the cranium. Explain, using on your knowledge of the underlying physics of the MRI signal detection process, why this is the case.
- How do the lesion and electrocorticography methods differ fundamentally from brain imaging? Prior to imaging, the maps of language systems in the brain were very different from those today. Name a psychiatric disorder that has been studied with imaging. What did the imaging studies reveal about that disorder? Can you think of any alternative interpretations?
- What are similarities and differences between optical intrinsic signal imaging and other measures of hemodynamic responses?
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