You might be wondering, what the heck is MI-SPECT?
- MI is an abbreviation for Molecular Imaging.
- SPECT is an acronym for Single Photon Emission Computed Tomography.
Prior to 2005, Siemens MI-SPECT was known as the Siemens Nuclear Medicine Group. In May 2005, Siemens acquired CTI of Knoxville, Tennessee. At that time, CTI was becoming a major player in PET imaging; as well as, a growing supplier of biotracers. During the Society of Nuclear Medicine meeting in June 2005, Siemens announced it had developed a Molecular Imaging Division which combined technologies such as Nuclear Medicine, PET, biomarkers, preclinical imaging and cyclotrons. From a service and support perspective, Siemens Molecular Imaging is subdivided into MI-SPECT and MI-PET.
Siemens MI-SPECT headquarters is located 30 miles northwest of downtown Chicago in the nearby suburb of Hoffman Estates, Illinois. Originally, this business operation was founded in 1946 as the Nuclear Chicago Corporation (NCC).
At the age of 25, John Kuranz (and others) started Nuclear Chicago Corporation after completing their work on the Manhattan Project at the University of Chicago. Initially, the company’s primary focus was manufacturing radiation detection equipment, such as Geiger Counters. By 1957, Nuclear Chicago Corporation was widely regarded as building the best Geiger Counter on the market.
So how did a company making Geiger Counters get into medical imaging?
In 1896, French physicist Henri Becquerel began to investigate why uranium salts exhibited phosphorescence. At that time, it was a common belief that uranium salts had healing properties, but Becquerel wanted to uncover why these rocks exhibited a green glow. Initially, he assumed absorbing sunlight was the reason, but he soon discovered something was happening inside the uranium, and that something was radioactivity. PBS produced an excellent documentary about uranium, called "Twisting the Dragon's Tail". The story of Henri Becqueral and uranium are shown at the 6:00 mark of Part 1.
Unfortunately for Becquerel (and others during that time), the only way to study phosphorescence was via visual observation. Obviously, close visual observation of radioactive materials has adverse health effects. A few years later, scientists invented a device called a photomultiplier tube, commonly referred to as a PMT. This device is only slightly larger than a household light bulb (see below); but instead of emitting light, a PMT is extremely sensitive at detecting light. Therefore, one obvious practical application was to use a PMT to measure the phosphorescence of certain radioactive materials. Unfortunately, only very few radioactive materials exhibit phosphorescence.
In 1948, research by physicist Robert Hofstadter discovered a new method of detecting radiation, the scintillation crystal. Hofstadter found that a sodium-iodide crystal doped with thallium had a very special reaction to radiation; specifically, the crystal would emit green light proportional to the energy level of the radiation. The higher the radioactive energy level, the brighter the green light emitted. In short, the crystal would “scintillate” when exposed to radiation.
Hofstadter’s design had one side of a scintillation crystal exposed to the radiation, and the other side coupled to a PMT. In this design, when radiation strikes the crystal and causes it to scintillate, the PMT immediately detects the resultant green light and sends an electrical signal directly proportional to the energy level of the radiation to an amplifier. A scintillation crystal could not only measure the amount of radiation, it could also measure the energy level of the radiation.
In 1957, Hal Anger, an engineer & biophysicist at the University of California Berkley, developed the world’s first useful scintillation camera. Anger took Hofstadter’s idea one step further. First, he dramatically increased the size of the scintillation crystal so that multiple PMTs could be added in a grid pattern. In the example below, there are 59 PMTs placed on top of a scintillation crystal whose dimensions are 21 inches by 15.25 inches. Each PMT is placed inside a Mu Shield to prevent electromagnetic interference. Next, Anger added circuitry that could reliably determine the exact position where each radiation event struck the crystal (see second image below). The result is referred to as an Anger Camera, and it is the core of nuclear medicine imaging. Hal Anger is also credited with inventing the well counter, a device for measuring radioactivity in small samples. Hal Anger is considered the Father of the Nuclear Medicine Camera.
In a scintillation camera, when radiation strikes a sodium-iodine crystal, that crystal emits green light. A “collimator” serves as the camera’s lens – and ensures that only radiation from the patient is channeled to the crystal. Photomultiplier tubes are placed on the non-radiation exposed side of the crystal and detect the green light emitted when the crystal scintillates. Then, using technology developed by Anger, the exact location of each photon can be visualized on a film or a computer screen.
In the PBS documentary, "Twisting the Dragon's Tail", a patient is shown having a Nuclear Medicine scan at the 30:30 mark of Part 2. After being injected with the radioisotope technetium-99m, the patient is scanned on a Siemens MI-SPECT scintillation camera.
Robert Hofstadter invented the scintillation crystal and Hal Anger took that a step further and created the scintillation camera, but how did Siemens get involved?
- In 1957, Hal Anger patented his invention and granted Nuclear Chicago Corporation (NCC) an exclusive license to produce and sell his scintillation cameras.
- In 1962, Nuclear Chicago Corporation delivered the world’s first commercial scintillation camera (based upon Hal Anger’s design) to Ohio State University.
- In 1970, Nuclear Chicago was purchased by G.D. Searle and later renamed Searle Analytic.
- In 1979, Searle Analytic was purchased by Siemens Medical Systems, and became known as the Siemens Nuclear Medicine Group.
- In 2005, the Siemens Nuclear Medicine Group became known as Siemens MI-SPECT.
In case you are wondering what happened to the “exclusive license” to produce and sell Anger’s scintillation cameras…
According to Wikipedia, “Nuclear-Chicago Corporation's exclusivity on marketing the Anger scintillation camera was eventually challenged by the introduction of a competing version of the Anger camera by Picker Corporation. NCC and Anger sued Picker for infringement of the '57 patent, and Picker counterclaimed for invalidity of the '57 patent. Picker also filed a proceeding in the Atomic Energy Commission, challenging the legitimacy of the AEC's release of the patent rights to Anger, and requesting a compulsory license under the '57 patent. The AEC proceeding was decided in favor of Anger and NCC, and the patent infringement lawsuit was eventually settled by the grant of a sublicense agreement to Picker. Other competitors later emerged and further litigation on the '57 patent was initiated. NCC was eventually sold to Siemens Corporation and Siemens continued to develop the technology of the Anger Camera and to market the device worldwide.”
The Institute of Physics has an outstanding overview of Nuclear Medicine on their YouTube channel.
And in closing, Lee Memorial Health Systems in Fort Myers, Florida has several videos on "Going Nuclear."