16 Channel Collimator
notes: label: Description
content: Imagine you are an expert surgeon, faced with a patient with a brain tumor. You can remove the tumor and cure the patient, but only if you know exactly where the tumor is. What do you do? The development of nuclear reactors after World War II offered a way to attack this problem. These reactors generated a host of radioactive fission products, of many different chemical properties, radiation properties, and half-lives. Some of these quickly found use as tracers for studying physiological processes in the body. Others were put to use irradiating cancer tumors (of known location, to be sure). And in 1952, three doctors in San Francisco reported on a technique for using one of these radioisotopes, iodine-131, to localize small tumors buried deep inside the brain. Their technique also made use of a new method for measuring the radiation from the iodine, the scintillation counter. This is a device superficially like a Geiger-Mueller counter, but using a special crystal that gives off a flash of light when traversed by a gamma ray. The basic idea is simple: make the tumor radioactive with the iodine-131, then move the scintillation counter around the patient’s head, and note where the count rate is greatest. The tumor will be under that point.
label: Description
content: There are several difficulties, though. How do you make the tumor radioactive? Answer: combine the radioactive iodine with the right chemical and get it into the patient’s body. The iodine will then migrate through the body and get to the tumor. But if the whole body is just as radioactive as the tumor, how will you detect the tumor? Answer: choose a chemical that is preferentially absorbed by the tumor. The San Francisco doctors estimated that they could make a tumor four times as radioactive as the brain tissue around it. So far, so good. But simply finding the spot on the skull directly over the tumor is not good enough. The surgeon has to know how far in the tumor is. The solution to this problem is to fit the scintillation counter with a “collimator,” a specially shaped shield that blocks off radiation coming from unwanted directions. The simplest design is a snout made of lead in the form of a truncated cone, with the scintillator crystal at the wide end and, at the narrow end, an opening a couple of centimeters across. If this opening is used to scan the patient’s head, the instrument will “see” the tumor only if it lies on the axis of the cone, in principle. In practice, such a collimator cannot be geometrically perfect, and it lacks sharp definition, so to speak. The solution to this difficulty is to divide up the cone of the collimator into several narrow tapering channels, all converging towards a single point, the “focus,” where a tumor will be detected with maximum efficiency. So equipped, the brain surgeon should now be able to scan the patient’s head all around, and find not only the point directly over the tumor, but how deep it lies beneath that point.
label: Description
content: Our collimator was presented to the Museum by the senior author of the 1952 paper, R. R. Newell of the Radiobiology Department of the Stanford University School of Medicine. The collimator is 6.3 cm long, 7.3 cm in diameter at the wide (scintillator) end, and 3.9 cm wide at the narrow (scanning) end. Its conical interior is divided into 16 channels by narrow lead partitions.
label: Description
content: Reference: R.R.Newell, William Saunders, and Earl Miller, “Multichannel Collimators for Gamma-Ray Scanning with Scintillation Counters,” Nucleonics, Vol. 10, Issue 7: July 1952, pp. 36-40.
label: Location
content: Currently not on view
setName: label: See more items in
content: Medicine and Science: Modern Physics
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: EM.N-08722
label: catalog number
content: N-08722
label: accession number
content: 255575
objectType: label: Object Name
content: Collimator, 16 Channel