A method of image registration for small animal, multi-modality imaging

Abstract

Many research institutions have a full suite of preclinical tomographic scanners to answer biomedical questions in vivo. Routine multi-modality imaging requires robust registration of images generated by various tomographs. We have implemented a hardware registration method for preclinical imaging that is similar to that used in the combined positron emission tomography (PET)/computed tomography (CT) scanners in the clinic. We designed an imaging chamber which can be rigidly and reproducibly mounted on separate microPET and microCT scanners. We have also designed a three-dimensional grid phantom with 1288 lines that is used to generate the spatial transformation matrix from software registration using a 15-parameter perspective model. The imaging chamber works in combination with the registration phantom synergistically to achieve the image registration goal. We verified that the average registration error between two imaging modalities is 0.335 mm using an in vivo mouse bone scan. This paper also estimates the impact of image misalignment on PET quantitation using attenuation corrections generated from misregistered images. Our technique is expected to produce PET quantitation errors of less than 5%. The methods presented are robust and appropriate for routine use in high throughput animal imaging facilities.

Figure 1

(a) Photograph of imaging chamber (inset shows the removable bed). Photographs of imaging chamber on PET (b) and CT (c) scanners.

Figure 2

Transverse (a), coronal (b) and sagittal (c) CT images of the grid phantom overlaid with a mouse study in the imaging chamber.

Figure 3

Comparison of 6- versus 15-parameter registration model (red and blue dots, respectively) as determined from software alignment of the grid phantom. Insets show enlarged area indicated.

Figure 4

Coronal (a) and sagittal (b) images of dots before (black) and after (red) the second registration, with overlay of CT mouse image aligned using the automatically generated spatial transformation matrix. Inset shows enlarged area indicated.

Figure 5

Profiles of microPET quantitation error across the different chambers of the simulated mouse-sized phantom for increasing offset from the registered transmission image. The correct emission profiles (perfect and smoothed) are shown in black above the error profiles for reference and are not on the same scale as the error profiles.