Registration of micro-PET and high-resolution MR images of mice for monitoring photodynamic therapy

Abstract

We are investigating imaging techniques to study the rapid biochemical and physiological response of tumors to photodynamic therapy (PDT). Positron emission tomography (PET) can provide physiological and functional images of cancers. While MRI can provide high resolution anatomical images and generate serial, noninvasive, in vivo observations of morphological changes. In this study, we investigate image registration methods to combine MRI and micro-PET (µPET) images for improved tumor monitoring. We acquired high resolution MR and PET 18 Ffluorodeoxyglucose (FDG) images from mice with RIF-1 tumors. We used rigid body registration with three translations and three angular variables. We used normalized mutual information as the similarity measure. To assess the quality of registration, we performed slice by slice review of both image volumes, manually segmented feature organs such as the left and right kidneys and the bladder in each slice, and computed the distance between corresponding centroids of the organs. We also used visual inspection techniques such as color overlay displays. Over 40 volume registration experiments were performed with MR and µPET images acquired from three C3H mice. The color overlays showed that the MR images and the PET images matched well. The distance between corresponding centroids of organs was 1.5 ± 0.4 mm which is about 2 pixels of µPET. In conclusion, registration of high resolution MR and µPET images of mice may be useful to combine anatomical and functional information that could be used for the potential application in photodynamic therapy.

High‐field magnetic resonance imaging of the response of human prostate cancer to Pc 4‐based photodynamic therapy in an animal model

“…In our previous study, we used both MRI and positron emission tomography (PET) to image C3H mice bearing RIF-1 tumors after PDT [31,32]. PET with 18 F-fluorodeoxyglucose (FDG) provided metabolic information of the tumors.…”

MR/PET quantification tools: Registration, segmentation, classification, and MR‐based attenuation correction

“…The voxel size was 1.0 × 1.0 × 1.6 mm 3 . We registered the CT to the corresponding MR images using the registration methods [22][23][24][25][26][27][28] that have been evaluated in our laboratory. On the CT images, we used a threshold method to obtain the skull and the results provide the ground truth of the skull for the evaluation of the MR image segmentation.…”

“…(1) We first register the MR images with the preliminary reconstruction of PET data using the mutual informationbased registration methods developed in our lab. [22][23][24][25][26][27][28] (2) The skull tissue is segmented on the MR images using our segmentation method as described below. (WM), and cerebrospinal fluid (CSF).…”

In vivo small animal imaging for early assessment of therapeutic efficacy of photodynamic therapy for prostate cancer

“…We found that the tumor FDG uptake decreased immediately after PDT. [11][12][13] In this study, we focus on small animal MR imaging and analysis methods for monitoring the efficacy of prostate PDT in vivo. To the best of our knowledge, this is the first report on in vivo imaging for Pc 4-based PDT for prostate cancer.…”

“…10 In a previous study, we used both MRI and positron emission tomography (PET) to image C3H mice bearing RIF-1 tumors after PDT. [11][12][13] PET with 18 F-fluorodeoxyglucose (FDG) provided metabolic information of the tumors. High-resolution MRI provided anatomical and morphological changes of the lesions.…”