A rectilinear scanner is an

imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of an image). Imaging technology is the application of materials and methods to create, preserve, or duplicate images. ...

device, used to capture emission from

radiopharmaceutical Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which ...

s in

nuclear medicine Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...

. The image is created by physically moving a

radiation detector In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing particles, such as those produced by nuc ...

over the surface of a radioactive patient. It has become obsolete in medical imaging, largely replaced by the

gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...

since the late 1960s.

History

One of the first rectilinear scanners was developed by Benedict Cassen in 1950. Before then hand-held detectors had been used to locate radioactive materials in patients, but the Cassen system (designed for

Iodine-131 Iodine-131 (131I, I-131) is an important radioisotope of iodine discovered by Glenn Seaborg and John Livingood in 1938 at the University of California, Berkeley. It has a radioactive decay half-life of about eight days. It is associated with nu ...

) combined a motor driven photomultiplier tube and printing mechanism. Subsequent developments improved the detection systems, movement, display and printing of images.

Components

Cassen's original rectilinear scanner used

calcium tungstate Scheelite is a calcium tungstate mineral with the chemical formula Ca W O4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist K. Scheele (1742-1786). Well-formed crystals are sought by collectors ...

(CaWo₄) crystal as the radiation detector. Later systems used a

Sodium iodide Sodium iodide (chemical formula NaI) is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations (Na+) and iodide anions ...

(NaI) scintillator, as in a gamma camera. The detector must be connected by mechanical or electronic means to an output system. This could be a simple light source over photographic film,

dot matrix printer A dot matrix printer is an impact printer that prints using a fixed number of pins or wires. Typically the pins or wires are arranged in one or several vertical columns. The pins strike an ink-coated ribbon and force contact between the ribbon ...

, oscilloscope or

television screen A display device is an output device for presentation of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people). When the input information that is supplied has an electrical signal the ...

Mechanism

The patient is administered with a radioactive pharmaceutical agent, such as iodine, which will naturally collect in the

thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thy ...

. The detector moves in a raster pattern over studied area of the patient, making a constant count rate. A

collimator A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spati ...

restricts detection to a small area directly below its position so that by the end of the scan emission from the whole study area has been detected. The output method is designed such that positional and detection information is maintained. For example, when using a light source and film the light is moved in tandem with the detector, and the intensity of light produced increases with an increase in activity, producing dark areas on the film. Disadvantages include the very long imaging time (several minutes) due to the need to separately cover each target area, unlike a gamma camera which has a much larger

field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Human ...

, and the motion artefacts this can result in.

References

{{DEFAULTSORT:Rectilinear Scanner 2d nuclear medical imaging Radiology