COMBINED RING RECONSTRUCTION METHOD FOR OVERLAPPED DUAL SLICES IN MEDICAL IMAGING
Publication Date: 2005-Mar-24
The IP.com Prior Art Database
In an embodiment, a combined ring reconstruction method for overlapped dual slices in medical imaging includes advancing a table by a substantially smaller distance for example, by about 3 mm so that the Z region or slice of the patient recorded in one ring overlaps the slice recorded in the complementary ring after the table is advanced. The raw data are then combined for the two rings on adjacent slices.
FIELD OF THE INVENTION
 This invention relates generally, to methods for ring construction, and more particularly, to a combined ring reconstruction method for overlapped dual slices in medical imaging.
BACKGROUND OF THE INVENTION
 Generally, an EBT scanner collects X-ray data on two detector rings that partially surround the patient. For example, each ring may have several Cadmium Tungstate crystal detectors and cover about 216 degrees at a radius of about 675 mm. These rings lie in a plane normal to the direction of the patient table (the Z axis). The ring closest to the electron beam source is denoted as ring 1, the ring furthest from the electron source is ring 2. Rings 1 and 2 are separated by a 0.2 mm septum.
 For example, X-rays are generated by a 1 Amp, 140 kV electron beam striking a circular tungsten target below the patient that covers 210 degrees with a 900 mm radius. X-rays from the target are collimated by a circular brass radiation collimator. The target and detector rings are not in the same plane and hence a fan of collimated x-rays from the target is not parallel to the detector rings, but intersects the detectors along an arc, with the center of the arc closest to the electron source.
 One example of a configuration of the scanner includes a dual 1.5 mm collimation, wherein the X-ray beam is collimated to a Z width of 3 mm (measured at the center of the patient) and the septum between the two detector rings is centered on the X-ray fan so that rings 1 and 2 record data for two adjacent 1.5 mm slices. Dual 1.5 mm collimation is important because it provides the thinnest slices available to the scanner with the greatest resolution in the Z direction. Because the intersection of the X-rays with the detectors is not parallel to the septum or the detectors, the pattern of X-rays is different on the two detector rings. Ring 1 intersects the top of the arc and hence for Ring 1 the signal is enhanced for detectors near the center of the fan but depleted for detectors near the edges. Ring 2 has a roughly even distribution of x-rays for all of the detectors in the fan.
 A single sweep of the beam around the target ring provides data for both detector rings that may be reconstructed into two images, one image for each ring. These images represent two 1.5 mm thick slices through the patient separated by 1.5 mm.
 One of the most clinically important scans for the e-Speed scanner is called an electron beam angiography (EBA) where the heart is scanned using dual 1.5 mm collimation. The scanner is triggered on the R-wave of the heart's ECG signal to perform a sequence of four to six 50 ms sweeps. The patient table is advanced 3 mm before the scanner is triggered again on the next heartbeat. The two detector rings allow imaging two Z levels of the heart during each sequence of...