### Abstract

We present a cone-beam image reconstruction algorithm for helical CT scanning with a tilted gantry and N-PI data acquisition. When the gantry is tilted, the effective source trajectory in the patient's reference frame lies on an elliptical cylinder, rather than on a circular cylinder as in the standard helical scanning mode. The aim of this work is to provide a means of reconstructing an image object directly from cone-beam projection data without transforming the image object into a virtual object and without rebinning projection data acquired for a real object into the projection data of the virtual object. This task has been accomplished by the application of an exact reconstruction algorithm, which utilizes an important geometrical property of the elliptical helical trajectory: the existence of generalized N-PI lines for a given image point. Based on this property, a mathematically exact image reconstruction scheme via filtering the backprojection image of differentiated projection data (FBPD) is applied to solve the reconstruction problem. Due to the gantry tilt, the required detector size is different from that of the standard helical trajectory (nontilted). A systematic analysis of the required detector size is presented. For an N-PI data acquisition scheme, an image may be reconstructed using data from an N-PI window, an (N-2)-PI window, and so on. Although the images reconstructed using an N-PI (N > 1) window are noisier than the images reconstructed from a 1-PI window, a weighted-average scheme over reconstructed images is presented to generate a final image with significantly lower noise variance than that in the 1-PI data acquisition scheme. The image reconstruction algorithm was numerically validated using a mathematical phantom.

Original language | English (US) |
---|---|

Article number | 015004 |

Journal | Optical Engineering |

Volume | 46 |

Issue number | 1 |

DOIs | |

State | Published - Jan 2007 |

Externally published | Yes |

### Fingerprint

### Keywords

- Cone beam
- Helix
- N-PI
- Tilt gantry

### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics

### Cite this

*Optical Engineering*,

*46*(1), [015004]. https://doi.org/10.1117/1.2431801

**Helical cone-beam computed tomography image reconstruction algorithm for a tilted gantry with N-PI data acquisition.** / Leng, Shuai; Zhuang, Tingliang; Nett, Brian E.; Chen, Guang Hong.

Research output: Contribution to journal › Article

*Optical Engineering*, vol. 46, no. 1, 015004. https://doi.org/10.1117/1.2431801

}

TY - JOUR

T1 - Helical cone-beam computed tomography image reconstruction algorithm for a tilted gantry with N-PI data acquisition

AU - Leng, Shuai

AU - Zhuang, Tingliang

AU - Nett, Brian E.

AU - Chen, Guang Hong

PY - 2007/1

Y1 - 2007/1

N2 - We present a cone-beam image reconstruction algorithm for helical CT scanning with a tilted gantry and N-PI data acquisition. When the gantry is tilted, the effective source trajectory in the patient's reference frame lies on an elliptical cylinder, rather than on a circular cylinder as in the standard helical scanning mode. The aim of this work is to provide a means of reconstructing an image object directly from cone-beam projection data without transforming the image object into a virtual object and without rebinning projection data acquired for a real object into the projection data of the virtual object. This task has been accomplished by the application of an exact reconstruction algorithm, which utilizes an important geometrical property of the elliptical helical trajectory: the existence of generalized N-PI lines for a given image point. Based on this property, a mathematically exact image reconstruction scheme via filtering the backprojection image of differentiated projection data (FBPD) is applied to solve the reconstruction problem. Due to the gantry tilt, the required detector size is different from that of the standard helical trajectory (nontilted). A systematic analysis of the required detector size is presented. For an N-PI data acquisition scheme, an image may be reconstructed using data from an N-PI window, an (N-2)-PI window, and so on. Although the images reconstructed using an N-PI (N > 1) window are noisier than the images reconstructed from a 1-PI window, a weighted-average scheme over reconstructed images is presented to generate a final image with significantly lower noise variance than that in the 1-PI data acquisition scheme. The image reconstruction algorithm was numerically validated using a mathematical phantom.

AB - We present a cone-beam image reconstruction algorithm for helical CT scanning with a tilted gantry and N-PI data acquisition. When the gantry is tilted, the effective source trajectory in the patient's reference frame lies on an elliptical cylinder, rather than on a circular cylinder as in the standard helical scanning mode. The aim of this work is to provide a means of reconstructing an image object directly from cone-beam projection data without transforming the image object into a virtual object and without rebinning projection data acquired for a real object into the projection data of the virtual object. This task has been accomplished by the application of an exact reconstruction algorithm, which utilizes an important geometrical property of the elliptical helical trajectory: the existence of generalized N-PI lines for a given image point. Based on this property, a mathematically exact image reconstruction scheme via filtering the backprojection image of differentiated projection data (FBPD) is applied to solve the reconstruction problem. Due to the gantry tilt, the required detector size is different from that of the standard helical trajectory (nontilted). A systematic analysis of the required detector size is presented. For an N-PI data acquisition scheme, an image may be reconstructed using data from an N-PI window, an (N-2)-PI window, and so on. Although the images reconstructed using an N-PI (N > 1) window are noisier than the images reconstructed from a 1-PI window, a weighted-average scheme over reconstructed images is presented to generate a final image with significantly lower noise variance than that in the 1-PI data acquisition scheme. The image reconstruction algorithm was numerically validated using a mathematical phantom.

KW - Cone beam

KW - Helix

KW - N-PI

KW - Tilt gantry

UR - http://www.scopus.com/inward/record.url?scp=34247210698&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=34247210698&partnerID=8YFLogxK

U2 - 10.1117/1.2431801

DO - 10.1117/1.2431801

M3 - Article

AN - SCOPUS:34247210698

VL - 46

JO - Optical Engineering

JF - Optical Engineering

SN - 0091-3286

IS - 1

M1 - 015004

ER -