In conventional CT, rotation of the x-ray tube and detectors around the patient entwines the detector cables around the gantry, limiting rotation to 360 degrees. Consequently, the gantry must be returned to the starting position (and the patient advanced) before acquisition of the next slice("step-and-shoot" imaging), resulting in a set of disconnected images. Spiral CT introduces slip-ring technology, which enables continuous rotation of the gantry. This, in combination with x-ray tubes that can remain on for extended periods, allows for uninterrupted imaging that traces a spiral path around the patient. The resulting volumetric data set can be manipulated to increase image resolution.
The first and most significant innovation----(single-slice) spiral CT----
revolutionized CT scanning by allowing uninterrupted imaging and production of a volumetric data set
Gantry housing x-ray tube and
detectors rotate uninterrupted
around the patient while patient
continuously advanced through
gantry
Continuous Volume of Data Spiral
pattern of volumetric data acquired
Gantry containing x-ray tube and
detectors returned to starting position
after one 360-degree rotation, patient
advanced fixed distance through
gantry.
Set of Disconnected Data Series of contiguous 2-D axial images of
specified thickness are required.
In single-slice CT, emitted x-rays are detected by a single row of detectors, yielding one slice per gantry rotation. The first generation of multislice CT scanners, introduced in 1992, was designed with two rows of detectors, capturing two slices per gantry rotation. However, this technology languished in an imaging community not yet fully comfortable with single-slice scanning. The second generation of multislice scanners was introduced in 1998. These scanners, equipped with multiple rows of detectors, can capture four slices per gantry rotation.
The second–and most recent–innovation in CT technology is the addition of multiple detectors to spiral CT scanners
Radiation penetrating through patient
is registered by four rows of detectors
Spiral path traced around patient yields four slices per gantry rotation
Radiation penetrating through patient
is registered by one row of detectors
Spiral path traced around patient yields one slice per gantry rotation