Fundamentals of multichannel CT

In the Fall of 1998, four of the largest CT vendors launched what commonly came to be called multislice CT or multidetector row CT. We are currently in a very active developmental phase of this technology [1]. The introduction of this new CT technique was as revolutionary for the field of radiology as the original introduction of CT in 1972 and the introduction of helical CT in 1989. Already in 1992 dual-channel CT was introduced [2]. The dual-channel CT scanners did not get the same attention as the four-channel scanners got 6 years later. One of the cornerstones of multichannel CT (MCCT) is a very fast image-acquisition phase. Total body scanning times have been reduced to less than 30 seconds. This speed is beneficial when large segments of the body have to be scanned or image acquisition has to be fast to catch a dynamic event, such as brain perfusion or CT angiography. Alternatively, the MCCT can be used to produce high milliamperes, which allows scanning through dense areas, such as shoulders or orthopedic hardware. In addition to short acquisition times and high milliamperes, MCCT allows scanning with submillimeter section thickness, which creates ultra high-resolution images. This article discusses the following aspects of the new CT technique: (1) definition of multichannel scanner, (2) detector array design and slice formation for 4- and 16-channel systems, (3) isotropic imaging, (4) pitch, (5) anatomic coverage, (6) the physics behind slice formation, and (7) radiation dose.