Paper Topic:

`How CT works` A history of the 1st - 5th generation CT gantries.

Computerized tomography (CT ) has also been known as Computerised axial tomography (CAT , Computerised transaxial tomography (CTAT , and digital axial tomography (DAT . Tomography is taken from the Greek word `tomos , meaning section (wikipedia .org . Since the technology involved the computer , hence the name . If we consider very briefly about the history , Housefield demonstrated the CT in 1972 , while the first whole body was done in 1975 (Moss , 1993 . In 1979 , Hounsefield , and Cormack received the Nobel Prize for their work on the CT machine (Fullreton 1994 . The Spiral CT came up in 1979

, and the multislice CT was introduced in 1991 (Siemens .com , Rydberg , 2003

Over the last 10-15 years , the rapid advance of CT machinery from a single slice to now multislice scanners has been mindblowing . A number of advances in hardware and software has made this possible . In particular the development of the slip rings to allow the gantry to rotate continuously in one direction (Rydberg , 2003 . The development to x ray tubes to bear the heat produced so that large exposure times are possible , even upto 60 sec . cheaper , more stable solid state conductors and multidetector arrays , improved computer power and hardware to handle and store the large amount of data produced , and the improvement of the software to allow rapid postprocessing (Claudia , 2000

In less than 4 years after the introduction of the first EMI machine in 1972 (Wikipedia .org , CT evolved through four generations of scanners This rapid evolution was due primarily to improvements in the mechanical design for the scanners , which yielded shorter scan times and therefore better control of patient motion

The principle advantage of CT imaging over other x ray imaging is improved contrast resolution , no superimposition of tissue , less scatter radiation , 3-dimesional imaging , and bone mineral assay (Claudia , 2000 The principle limitations are spatial resolution , radiation dose to the patient , and artifacts (Claudia , 2000

Basics about computerized tomography

CT involves the transmission of x rays through the patient . Here the radiograph is obtained with a moving source image receptor assembly . The development of the CT required the emergence of the digital computer and special mathematics . The basic approach is the translation of an object through a collimated x ray beam , and to detect an image projection . A computer generated matrix of a section of the object is produced by back projection reconstruction through a special sequence of computerized algorithms Moss , 1993

Basic Parts of the CT machine

Every CT machine has three distinguishing components - the operating console , the computer and the gantry . The operating console performs two major functions- imaging control with preselected technique and image viewing and manipulation . The CT computer has no distinguishing features . It may be inbuilt into the console . The gantry is special to the CT . it houses the x ray source , the detector assembly , and the high volatge generator (Siemens .com . The patient aperture of a CT gantry has a maximum diameter of approximately 70 cm . and the gantry can be tilted either way approximately 30 degrees...

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