What is Inverse-Geometry CT?

Inverse-geometry computed tomography (IGCT) systems are being developed to provide improved volumetric imaging. In conventional multislice CT systems, x-rays are emitted from a small area and irradiate a large-area detector. In an IGCT system, x-ray sources are distributed over a large area, with each beam irradiating a small-area detector. Therefore, in the inverse geometry, a series of narrow x-ray beams are switched on and off while the gantry rotates. In conventional CT geometry, cone-beam and scatter artifacts increase with the imaged volume thickness. An inverse geometry may be less susceptible to scatter effects, because only a fraction of the field of view is irradiated at one time. The distributed source in the inverse geometrypotentially improves sampling, leading to reduced cone-beam artifacts. In the inverse geometry, the tube current may be adjusted separately for each source location, which potentially reduces dose. Multiple IGCT prototypes have been constructed and tested on phantoms. A gantry-based IGCT system with one-second gantry rotation was developed, and images of phantoms and small animals were successfully acquired. Clinical feasibility with acceptable noise levels and scan times has not yet been shown. Overall, results from prototype systems suggest that the inverse geometry will enable imaging of a thick volume (∼16 cm) while potentially reducing cone-beam artifacts, scatter effects, and radiation dose. The magnitude of these benefits will depend on the specific IGCT implementation and need to be quantified relative to comparable multislice scanners.

PMID: 21601552

Schoenhagen Paul

Cardiovascular Imaging
Imaging Institute and
Heart&Vascular Institite
Cleveland Clinic
Cleveland, OH
Posted in Computed Tomography and tagged , , , , , .

2 Comments

  1. See also:

    Inverse-geometry volumetric CT system with multiple detector arrays for wide field-of-view imaging.
    Mazin SR, Star-Lack J, Bennett NR, Pelc NJ.
    Med Phys. 2007 Jun;34(6):2133-42.
    PMID: 17654916

  2. This is really interesting technology. Every time Paul posts a paper thick with physics it makes me spend at least half an hour google-ing for easy to grasp explanations of things.

    Something very cool I read from a doctoral thesis that was posted online is: “Instead of using a single x-ray source and a large detector array, the MS-IGCT system employs a distributed source array and a smaller detector array. Since the source and detector array have the same extent in the axial direction, acquired projection data satisfy the data sufficiency condition for an exact reconstruction, and therefore image artifacts inherent in 3rd cone beam CT system can be reduced. In addition, the smaller size of the detector array can reduce the detected scatter radiation, and the radiation dose to the patient can be optimized by adjusting the x-ray flux of each source independently.”… Independent correction for the attenuation of each source. Brilliant!

    Some people keep thinking outside the box!

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