Human Studies

The clustering algorithm has been applied to a range of FDG-PET studies and three examples (two patients with brain tumor and one patient with a lung cancer) are presented in this chapter. FDG-PET was chosen to assess the clustering algorithm because it is commonly used in clinical oncologic PET studies. All oncological PET studies were performed at the Department of PET and Nuclear Medicine, Royal Prince Alfred Hospital, Sydney, Australia. Ethical permissions were obtained from the Institutional Review Board.

Dynamic neurologic FDG-PET studies were performed on an ECAT 951R whole-body PET tomograph (CTI/Siemens, Knoxville, TN). Throughout the study the patient's eyes were patched and ears were plugged. The patients received 400 MBq of FDG, infused at a constant rate over a 3-min period using an automated injection pump. At least 30 min prior to the study, patient's hands and forearms were placed into hot water baths preheated to 44 °C to promote arterio-venous shunting. Blood samples were taken at approximately 30 sec for the first 6 min, and at approximately 8, 10, 15, 30, and 40 min, and at the end of emission data acquisition. A dynamic sequence of 22 frames was acquired for 60 min following radiotracer administration according to the following schedule: 6 x 10 sec, 4 x 30 sec, 1 x 2 min, 11 x 5 min. Data were attenuation corrected with a postinjection transmission method [103]. Images were reconstructed on a 128 x 128 matrix using FBP with a Shepp and Logan filter cut-off at 0.5 of the Nyquist frequency.

The dynamic lung FDG-PET study was commenced after intravenous injection of 487 MBq of FDG. Emission data were acquired on an ECAT 951R whole-body PET tomograph (CTI/Siemens, Knoxville, TN) over 60 min (22 frames, 6 x 10 sec, 4 x 30 sec, 1 x 2 min, and 11 x 5 min). Twenty one arterial blood samples were taken from the pulmonary artery using a Grandjean catheter to provide an input function for kinetic modeling.

The patient details are as follows:

Patient 1: The FDG-PET scan was done in a female patient, 6 months after resection of a malignant primary brain tumor in the right parieto-occipital lobe. The scan was done to determine if there was evidence for tumor recurrence. A partly necrotic hypermetabolic lesion was found in the right parieto-occipital lobe that was consistent with tumor recurrence.

Patient 2: A 40-year-old woman had a glioma in the right mesial temporal lobe. The FDG-PET scan was performed at 6 months after tumor resection. A large hypermetabolic lesion was identified in the right mesial temporal lobe that was consistent with tumor recurrence.

Patient 3: A 67-year-old man had an aggressive mesothelioma in the left lung. In the PET images, separate foci of increased FDG uptake were seen in the contralateral lymph nodes as well as in the peripheral left lung.

As they are unnecessary for clustering and the subsequent analysis, low count areas such as the background (where the voxel values should be zero theoretically) and streaks (which are due to reconstruction errors) were excluded by zeroing voxels whose summed activity was below 5% of the mean pixel intensity of the integrated dynamic images. A3 x 3 closing followed by a 3 x 3 erosion operation was then applied to fill any "gap" inside the intracranial/body region to which cluster analysis was applied. Parametric images of the physiological parameter, K, which is defined as the value of + fcjj) [104], were generated by fitting all voxels inside the intracranial/body region using Patlak graphical approach [105]. The resultant parametric images obtained for the raw dynamic images and dynamic images after cluster analysis were assessed visually. Compartmental model fitting using the three-compartment FDG model [104] was also performed on the tissue TACs extracted manually and by cluster analysis to investigate whether there is any disagreement between the parameter estimates.

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