Recent and future directions in CT imaging

Abstract

Computed tomography (CT) has made enormous technical advances since its introduction into clinical use. The engineering improvements have in turn led to important clinical applications and large impact in patient care. This paper reviews the technology development trends in CT since its introduction and uses these trends to help illuminate likely future progress. The prediction is that significant further improvements in speed, spatial resolution and dose efficiency can be expected in the next decade.

Figure 1

Speed of CT since its introduction, measured in raw data points measured per second, or in the number of pixels that the measured raw data is used to reconstruct.

Figure 2

Minimum scan time of CT since its introduction. The outlyer in the early 1980’s was the electron beam CT scanner. The two lower recent points are dual source CT systems that whose minimum scan time is approximately half of the gantry rotation time.

Figure 3

Centripetal acceleration at the location of the x-ray tube. The values are calculated for Siemens CT systems since 1976 but are representative of the field.

Figure 4

(A) 2D detector aperture and (B) 1D detector aperture of CT systems. The values are calculated for GE CT systems but are representative of the field.

Figure 5

(A) Diagram of scintillator-photodiode detector. The photodiodes are connected to amplifiers and A/D converters. Multi-detector row CT systems had 2D arrays of detector cells. (B) Diagram of direct conversion detector. In photon counting detectors, each signal electrode is connected to a pulse shaping amplifier and one or more discriminators.

Figure 6

Computer simulation of two small round objects with a center-to-center spacing of two diameters imaged by systems with (A) conventional aperture and (B) high resolution aperture at the same radiation dose, assuming equal x-ray detection efficiency and reconstructed at the resolution limit of the conventional aperture. (C) Performance of a numerical observer to classify whether the object is two disks or one.

Figure 7

Variance in projection (line integral) measurements due to quantum noise and electronic noise as a function of x-ray fluence. As the x-ray fluence decreases the system can become severely limited by electronic noise.

Figure 8

Number of slices per rotation, ignoring the use of reconstruction with less than a full rotation or interpolation in helical reconstruction.

Figure 9

Coronal reformat of images reconstructed with (left) conventional filtered backprojection and (right) model based iterative reconstruction. Images courtesy of J.B. Thibault, R. Senzig, and J. Hsieh.

Figure 9

Coronal reformat of images reconstructed with (left) conventional filtered backprojection and (right) model based iterative reconstruction. Images courtesy of J.B. Thibault, R. Senzig, and J. Hsieh.