The effects of computed tomography image characteristics and knot spacing on the spatial accuracy of B-spline deformable image registration in the head and neck geometry

Radiation Oncology

Harm Meertens²  Nanna M Sijtsema²  Aart A van ’t Veld²  Roel GJ Kierkels²  Charlotte L Brouwer¹ 

[1] Department of Radiation Oncology, University Medical Center Groningen, PO Box 30001, Groningen 9700 RB, The Netherlands;University of Groningen, University Medical Center Groningen, Department of Radiation Oncology, Groningen, the Netherlands

关键词: Computed tomography;    Head-and-neck;    Contrast-to-noise ratio;    B-spline knot spacing;    Spatial accuracy;    B-spline transformation model;    Deformable image registration;   

Others  :  1151986
DOI  :  10.1186/1748-717X-9-169

 received in 2013-12-02, accepted in 2014-07-18,  发布年份 2014

【 摘 要 】

Objectives

To explore the effects of computed tomography (CT) image characteristics and B-spline knot spacing (BKS) on the spatial accuracy of a B-spline deformable image registration (DIR) in the head-and-neck geometry.

Methods

The effect of image feature content, image contrast, noise, and BKS on the spatial accuracy of a B-spline DIR was studied. Phantom images were created with varying feature content and varying contrast-to-noise ratio (CNR), and deformed using a known smooth B-spline deformation. Subsequently, the deformed images were repeatedly registered with the original images using different BKSs. The quality of the DIR was expressed as the mean residual displacement (MRD) between the known imposed deformation and the result of the B-spline DIR.

Finally, for three patients, head-and-neck planning CT scans were deformed with a realistic deformation field derived from a rescan CT of the same patient, resulting in a simulated deformed image and an a-priori known deformation field. Hence, a B-spline DIR was performed between the simulated image and the planning CT at different BKSs. Similar to the phantom cases, the DIR accuracy was evaluated by means of MRD.

Results

In total, 162 phantom registrations were performed with varying CNR and BKSs. MRD-values < 1.0 mm were observed with a BKS between 10–20 mm for image contrast ≥ ± 250 HU and noise < ± 200 HU. Decreasing the image feature content resulted in increased MRD-values at all BKSs. Using BKS = 15 mm for the three clinical cases resulted in an average MRD < 1.0 mm.

Conclusions

For synthetically generated phantoms and three real CT cases the highest DIR accuracy was obtained for a BKS between 10–20 mm. The accuracy decreased with decreasing image feature content, decreasing image contrast, and higher noise levels. Our results indicate that DIR accuracy in clinical CT images (typical noise levels < ± 100 HU) will not be effected by the amount of image noise.

【 授权许可】

   
2014 Brouwer et al.; licensee BioMed Central Ltd.

【 图 表 】

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