Methods and apparatus for weighting of computed tomography data

• US 6,754,299 B2
• Filed: 08/02/2002
• Issued: 06/22/2004
• Est. Priority Date: 08/02/2002
• Status: Expired due to Term

• Current Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Original Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Inventors: Patch, Sarah K.
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US10/211,206
• Publication Number:
  US 20040022365A1
• Time in Patent Office: 690 Days
• Field of Search: 378/4, 378/8, 378/15, 378/901
• US Class Current: 378/15
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4085 Cone-beams
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

A method for reconstructing an image of an object utilizing a computed tomographic (CT) imaging system is provided. The CT system includes a radiation source and a multislice detector array on a rotating gantry, with the radiation source configured to project a beam of radiation through an object and towards. the multislice detector array. The multislice detector array is configured to sense attenuation of the radiation passing through the object. The method for reconstructing an image includes helically scanning an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles, generating a plurality of cone angle dependent weights that are inversely correlated to an absolute value of a cone angle, and weighting the projection data using the cone angle dependent weights.

Claims

1. A method for reconstructing an image of an object utilizing a computed tomographic (CT) imaging system having a radiation source and a multislice detector array on a rotating gantry, the radiation source configured to project a beam of radiation through an object and towards the multislice detector array, the multislice detector array configured to sense attenuation of the radiation passing through the object, said method comprising:

scanning an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles;

generating a plurality of cone angle dependent weights that are a function of a conjugate ray; and

weighting the projection data using the cone angle dependent weights.

2. A method in accordance with claim 1 wherein said weighting the projection data comprises weighting measured data and extrapolated data.

3. A method in accordance with claim 2 further comprising weighting the measured data more heavily than the extrapolated data.

4. A method in accordance with claim 1 wherein said scanning an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles further comprises helically scanning an object with a normalized pitch p such that:

5. A method in accordance with claim 1 wherein said generating a plurality of cone angle dependent weights comprises generating a plurality of cone angle dependent weights in accordance with:

$w_q<br><br>\left(\mathrm{\alpha <br><br>},\mathrm{\beta <br><br>},\mathrm{\gamma <br><br>}\right)=\frac{2<br><br>g^q}{\left(g^q+g_c^q\right)}$

where;

g=max(0,((π

/2+Γ

_ω

)−

|β

|))|tan α

_c|;

g_c=max(0,((π

/2+Γ

_ω

)−

|β

_c|))|tan α

|;

q≧

1;

α

is a cone beam angle;

β

is a gantry angle;

γ

is a fan beam angle;

α

_c is a cone beam angle of a conjugate ray;

β

_c=β

+π

−

2γ

;

γ

_c=−

γ

;

Γ

is a hardware-defined cone angle for the CT system;

Γ

_ω

is a user-defined fan angle for a fan-beam geometry; and

Γ

_ω

≧

Γ

.

6. A method in accordance with claim 1 wherein said scanning an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles further comprises helically scanning an object with a normalized pitch p such that:

7. A computed tomographic (CT) imaging system for reconstructing an image of an object, said computed tomographic (CT) imaging system comprises a radiation source and a multislice detector array on a rotating gantry, said radiation source configured to project a beam of radiation through an object and towards said multislice detector array, said multislice detector array configured to sense attenuation of said radiation passing through the object;

said imaging system configured to;

scan an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles;

generate a plurality of cone angle dependent weights that are a function of a conjugate ray; and

weight the projection data using the cone angle dependent weights.

8. An imaging system in accordance with claim 7 wherein said scanning an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles further comprises helically scanning an object with a normalized pitch p such that:

9. An imaging system in accordance with claim 7 wherein said scanning an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles further comprises helically scanning an object with a normalized pitch p such that:

10. An imaging system in accordance with claim 7 wherein said generating a plurality of cone angle dependent weights comprises generating a plurality of cone angle dependent weights in accordance with:

$w_q<br><br>\left(\mathrm{\alpha <br><br>},\mathrm{\beta <br><br>},\mathrm{\gamma <br><br>}\right)=\frac{2<br><br>g^q}{\left(g^q+g_c^q\right)}$

where;

g=max(0,((π

/2+Γ

_ω

)−

|β

|))|tan α

_c|;

g_c=max(0,((π

/2+Γ

_ω

)−

|β

_c|))|tan α

|;

q≧

1;

α

is a cone beam angle;

β

is a gantry angle;

γ

is a fan beam angle;

α

_c is a cone beam angle of a conjugate ray;

β

_c=β

+π

−

2γ

;

γ

_c=−

γ

;

Γ

is a hardware-defined cone angle for the CT system;

Γ

_ω

is a user-defined fan angle for a fan-beam geometry; and

Γ

_ω

≧

Γ

.

11. An imaging system in accordance with claim 7 wherein said weighting the projection data comprises weighting measured data and extrapolated data.

12. An imaging system in accordance with claim 11 further comprising weighting the measured data more heavily than the extrapolated data.

13. A computer for collecting computed tomography (CT) scan data, said computer programmed to:

scan an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles;

generate a plurality of cone angle dependent weights that are a function of a conjugate ray; and

weight the projection data using the cone angle dependent weights.

14. A computer in accordance with claim 13 wherein to scan an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles said computer configured to helically scan an object with a normalized pitch p such that:

15. A computer in accordance with claim 13 wherein to generate a plurality of cone angle dependent weights said computer configured to generate a plurality of cone angle dependent weights in accordance with:

$w_q<br><br>\left(\mathrm{\alpha <br><br>},\mathrm{\beta <br><br>},\mathrm{\gamma <br><br>}\right)=\frac{2<br><br>g^q}{\left(g^q+g_c^q\right)}$

where;

g=max(0,((π

/2+Γ

_ω

)−

|β

|))|tan α

_c|;

g_c=max(0,((π

/2+Γ

_ω

)−

|β

_c|))|tan α

|;

q≧

1;

α

is a cone beam angle;

β

is a gantry angle;

γ

is a fan beam angle;

α

_c is a cone beam angle of a conjugate ray;

β

_c=β

+π

−

2γ

;

γ

_c=−

γ

;

Γ

is a hardware-defined cone angle for the CT system;

Γ

_ω

is a user-defined fan angle for a fan-beam geometry; and

Γ

<sub>ω

≧

Γ

.</sub>

16. A computer in accordance with claim 13 wherein to generate a plurality of cone angle dependent weights said computer configured to generate a plurality of cone angle dependent weights in accordance with:

$w<br><br>\left(\mathrm{\alpha <br><br>},\mathrm{\beta <br><br>},\mathrm{\gamma <br><br>}\right)=\frac{\left[{P<br><br>\left(\mathrm{\beta <br><br>},\mathrm{\gamma <br><br>}\right)}^p<br><br>{\left(\cot <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}\right)}^{2<br><br>\mathrm{\alpha <br><br>}}\right]}{\left[{P<br><br>\left(\mathrm{\beta <br><br>},\mathrm{\gamma <br><br>}\right)}^p<br><br>{\left(\cot <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}\right)}^{2<br><br>a}+{P<br><br>\left({\mathrm{\beta <br><br>}}_c,{\mathrm{\gamma <br><br>}}_c\right)}^p<br><br>{\left(\cot <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\alpha <br><br>}}_c\right)}^{2<br><br>a}\right]}$

where;

α

≧

0;

p=helical pitch, normalized to a number of detector rows;

P(β

,γ

)^p is a function for Parker'"'"'s partial scan weights;

α

is a cone beam angle;

β

is a gantry angle;

γ

is a fan angle;

α

_c is a cone beam angle of a conjugate ray;

β

_c=+π

−

2γ

; and

γ

_c=−

γ

.

17. A computer in accordance with claim 13 wherein to weight the projection data said computer programmed to weight measured data and extrapolated data.

18. A computer in accordance with claim 17 wherein to weight measured data and extrapolated data said computer programmed to weight the measured data more heavily than the extrapolated data.

19. A computer in accordance with claim 13 wherein to scan an object with a computed tomographic imaging system to acquire a plurality of views of projection data at a plurality of gantry angles and a plurality of cone angles said computer configured to helically scan an object with a normalized pitch p such that: