Functional Imaging Division
Introduction
In the imaging of cancer, the evaluation of its functional aspects is becoming increasingly important. The Functional Imaging Division is actively investigating this clinically significant issue using mainly 2 kinds of imaging modalities, namely, radionuclide imaging and magnetic resonance imaging.
Radionuclide imaging—clinical PET-
FDG-PET is a useful tool to detect malignant lesions such as lung cancer (64). The detectability of malignant lesions can be altered by altering the conditions of image reconstruction. Since lymph node (LN) metastasis is the most important prognostic factor in most malignancies, it is clinically important to accurately diagnose LN metastasis. However, the conditions of image reconstruction are not often optimized for the detection of small lesions such as LN metastases. Since the detectability of LN metastases from colorectal cancer using FDG PET was not so good, optimization of the conditions of image reconstruction was investigated. Increasing the iteration number enhanced the contrast between small lesions and the background, resulting in improved detectability of LN metastases. Statistical analysis also showed that the image data effectively detected small lesions such as LN metastases. The detectability of LN metastases was improved by selecting a statistically significantly high-activity area in the image. This study received the Excellent Presentation Award at the 41st Meeting of The Japan Health Physics Society (Tokyo, June 2007). Dr. Kazumasa Inoue, a research resident of this Division, was presented the Research Encouraging Award by The Japanese Society of Nuclear Medicine Technology for a series of studies regarding technical improvements in the methods of processing the PET image data.
Radionuclide imaging-experimental-
NanoSPECT/CT is a combined SPECT/CT scanner with excellent resolution and high sensitivity for the imaging of small animals such as mice and rats. Using this scanner, the heterogeneous distribution of liposomes, including In-111, in the S180 tumors implanted into mice could be depicted, thereby indicating that liposomes were mainly accumulated in the marginal area of the tumor. Since evaluation of tumor heterogeneity is important for the selection of the optimal treatment regimen for the tumor, this result will promote further studies on the evaluation of the functional heterogeneity inside the tumor.
This scanner could clearly differentiate the intracerebral distribution of 2 kinds of I-125-labeled compounds, namely iomazenil and iodometamphetamine, despite the fact that these compounds emit gamma rays with an energy as low as 28 keV. Since I-125 is one of the most commonly used radionuclides in the field of experimental oncology, precise in vivo imaging of I-125-labeled compounds is considerably useful.
A planar positron imaging system (PPIS) is a unique imaging system that is used for imaging of positron emitters. Although this device cannot provide sectional images of the entire body unlike PET, it can show images with excellent resolution inside the field of view. Moreover, PPIS is so compact that it can be easily combined with other devices. In our institute, PPIS is installed into the proton beam therapy equipment. When a proton beam irradiates a patient’s body, positron emitters are generated in the irradiated area by a photonuclear reaction. The accuracy of proton beam therapy can be evaluated by visualizing the distribution of positron emitters using PPIS (127).
Magnetic resonance imaging
Magnetic resonance imaging (MRI) can visualize various kinds of cancer lesions by utilizing the contrast that is provided by some tissue parameters, including relaxation times and apparent diffusion coefficients (96). MRI can also provide accurate diagnostic criteria for assessing newly developed therapeutic strategies for cancers by demonstration of the anatomical and functional changes in the cancer lesions. Presently, some newly developed therapeutic strategies have to be tested in appropriate animal models in laboratories before they are applied clinically. MRI is expected to be a useful tool for such preclinical studies. In early 2007, a whole-body MR scanner operating at 3 Tesla was installed at the Research Center for Innovative Oncology. A high static magnetic field and high-performance gradient coil systems allow high spatial resolution images with an acceptable signal-to-noise ratio to be obtained even in a small field-of-view. In order to further increase the sensitivity of the MR signals to enable the imaging of small animals, highly sensitive RF coils were constructed. Using this sophisticated imaging system, the heterogeneous distribution of MR signal intensities within the lesion was clearly visualized in both sarcoma 180 and colon 26 tumor models. These heterogeneous signals might represent the difference in the tissue compositions within the tumor. In vivo MR imaging for tumor-bearing small animals using a clinical whole-body MR scanner is a useful technique in terms of ‘translational research’ in the field of cancer research. Human cancer patients can be examined using the same imaging equipment with the same imaging parameters as in animal cancer models; hence, it is easy to interpret these imaging findings in human subjects on the basis of the same criteria as in the animal models without being concerned about the differences in the MR imaging conditions.
Other research fields
Optical imaging is another attractive real time imaging modality that can visualize the molecular process inside a living body. The application of this imaging strategy to surgery is promising.
Image-guided surgery using invisible near-infrared fluorescent light is technically feasible for sentinel LN mapping (97).
Tomographic imaging is useful to gauge the depth of the lesion. However, it often requires more time and effort as compared to planar imaging. When 2 planar images are obtained from slightly different directions and are observed stereoscopically, 3-dimensional visualization becomes possible. Since a rough estimate of the depth of a lesion can be obtained by this method, it is useful to check the location of sentinel LN in breast cancer (98).
Diagnostic reports are generally written to clearly explain the results of imaging tests. If they are provided in an electronic form, they can be easily reused. It was revealed that the structuring of these diagnostic reports is useful for their secondary utilization (99). This scientific paper was selected for the Best Paper Award at Medinfo 2007 (Sydney, Australia, August 2007).
Reversible phosphorylation of proteins plays an essential role in regulating various cellular events. In the lens of the eye, a 50-kDa phosphatase belonging to the PP-2C family and an 18-kDa phosphatase belonging to the low molecular weight tyrosine phosphatase family were the 2 major phosphatases. It would be attractive to study the visualization of such a process. For this study, Izumi O Umeda, PhD, the section head of this division, was presented the 45th Research Encouraging Award by The Japanese Society for Cataract Research.
● H. Fujii ●
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