The terms first-generation through fourth-generation scanners are used to represent the developments in technology that relate the configuration of the x-ray tube to the detectors. The first-generation scanners, which are no longer in use, had a thin x-ray beam pass linearly over the patient in a 180° arc, followed by a single detector on the opposite side.2 Scanning time was very lengthy. Second-generation scanners used multiple detectors and a fan-shaped x-ray beam that continued to pass linearly across the patient before rotating. Scan times improved but were still very long.
Third-generation scanners represented a significant advance in technology, and scan times were greatly reduced. This design incorporates a fan-shaped beam and a detector array, and both move in a circle within the gantry. With the use of a rotating detector, all of the readings that make up a view can be recorded at the same time.1 Third-generation scanners are the most common conventional models in use today.
Fourth-generation scanners have a detector array that is fixed and positioned in a complete circle within the gantry. The x-ray tube produces a fan-shaped beam that rotates around the patient. Scan times are theoretically shorter than with third-generation scanners, but few fourth-generation scanners have been installed. 2
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.