The immense value of PET for studying normal brain function was highlighted by several path-breaking investigations. Phelps , for instance, was one of the first to show in striking detail how different parts of the brain are activated when performing mental tasks such as hearing, reading, talking, thinking, etc. The first PET scanners had a small number of radiation sensors to build the image, and they could do only a slice at a time. The slices were also very thick.
Autoradiography was used along with gas radiotracers in , initializing the beginning of brain imaging. The first safe radiotracer to be used in humans was 2-deoxyglucose DG , developed by Louis Sokoloff.
It competitively inhibits a portion of the glycolytic pathway, making it a useful molecule to measure the use of glucose in the brain, which directly translates to brain activity.
Initially this molecules was radio labeled with 14 C but in Sokoloff along with Dr. Alfred Wolf and Joanna Fowler they synthesized 2-fluorodeoxy-D-glucose FDG , which is radiolabelled with 18 F and is one of the mostly widely used radiotracers today.
Other less commonly used radiolabels in PET are 13 N, 15 O, and 82 Rb, with lifetimes below 10 minutes except for 15 O which has a lifetime comparable to 18 F. The scintiscanner was the first instrument used to create images for the detection of radioactivity within the body.
It was invented in by Benedict Cassen and would tap to create dots in a paper; later improved in by Dr. Other substances may be used for PET scanning, depending on the purpose of the scan. If blood flow and perfusion of an organ or tissue is of interest, the radionuclide may be a type of radioactive oxygen, carbon, nitrogen, or gallium.
The radionuclide is administered into a vein through an intravenous IV line. Next, the PET scanner slowly moves over the part of the body being examined. Positrons are emitted by the breakdown of the radionuclide. Gamma rays called annihilation photons are created when positrons collide with electrons near the decay event.
The scanner then detects the annihilation photons, which arrive at the detectors in coincidence at degrees apart from one another. A computer analyzes those gamma rays and uses the information to create an image map of the organ or tissue being studied. The amount of the radionuclide collected in the tissue affects how brightly the tissue appears on the image, and indicates the level of organ or tissue function.
PET may also be used to evaluate the function of organs, such as the heart or brain. The most common use of PET is in the detection of cancer and the evaluation of cancer treatment. To diagnose dementias conditions that involve deterioration of mental function , such as Alzheimer's disease, as well as other neurological conditions such as:.
Parkinson's disease. A progressive disease of the nervous system in which a fine tremor, muscle weakness, and a peculiar type of gait are seen. Huntington's disease. A hereditary disease of the nervous system which causes increasing dementia, bizarre involuntary movements, and abnormal posture. This is useful since PET scans are best for the spatial distribution of metabolic or biochemical activity in the body, and CT scans are best for anatomical imaging.
This is because PET scans can display changes in processes at a cellular level, whereas a CT scan reveals glimpses at tissues and organs. Until the invention of the PET-CT , medical doctors were frustrated for years, attempting to match two different scans from the PET or CT scanners and studying them in order to determine the exact location of a tumor, for example.
How did the solution develop?
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