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Purpose: Positron emission tomography (PET) with ¹⁵O-labeled water (H₂ ¹⁵O) facilitates the visualization and quantification of blood flow in clinical investigations and also in small animals. The quantification of blood flow requires an input function, which is generally obtained by measuring radioactivity in arterial blood withdrawn during PET scanning. However, this approach is not always feasible, because abundant blood sampling may affect the physiological process being measured. The purpose of the present study was to develop and cross-validate two methods, namely, a blood- and an image-based method for obtaining the input function for blood flow studies from rat H₂ ¹⁵O PET.Methods: The study material consisted of two separate groups of rats. Group 1 rats were imaged twice by a high-resolution research tomograph PET camera at resting condition for a test-retest study (n = 4), and group 2 rats were imaged with and without adenosine infusion for a rest-stress study (n = 4). In group 1, radioactivity concentration in arterial blood was measured with a new flow-through detector during imaging and a blood-based input function was obtained. The image-based input function was estimated using time-activity curves from the left ventricle and myocardial regions. To validate the two input function methods, myocardial blood flow (MBF) and cerebral blood flow (CBF) were computed, and the methods were tested for reproducibility (test-retest study) and changes (rest-stress study).Results: The blood- and image-based input functions were similar, and the corresponding CBF values differed only by -6.9 ± 8.1%. In the test-retest study, both MBF and CBF showed good reproducibility, and in the rest-stress study, adenosine significantly increased both MBF (P = 0.035) and CBF (P = 0.029), compared with the resting condition.Conclusion: It is possible both to measure the input function from rat arteria femoralis during H₂ ¹⁵O PET imaging and to estimate the input function from rat H₂ ¹⁵O PET images, thereby facilitating the assessment of blood flow in organs visible in PET images. [ABSTRACT FROM AUTHOR]

Purpose: Positron emission tomography (PET) with O-labeled water (HO) facilitates the visualization and quantification of blood flow in clinical investigations and also in small animals. The quantification of blood flow requires an input function, which is generally obtained by measuring radioactivity in arterial blood withdrawn during PET scanning. However, this approach is not always feasible, because abundant blood sampling may affect the physiological process being measured. The purpose of the present study was to develop and cross-validate two methods, namely, a blood- and an image-based method for obtaining the input function for blood flow studies from rat HO PET. Methods: The study material consisted of two separate groups of rats. Group 1 rats were imaged twice by a high-resolution research tomograph PET camera at resting condition for a test-retest study ( n = 4), and group 2 rats were imaged with and without adenosine infusion for a rest-stress study ( n = 4). In group 1, radioactivity concentration in arterial blood was measured with a new flow-through detector during imaging and a blood-based input function was obtained. The image-based input function was estimated using time-activity curves from the left ventricle and myocardial regions. To validate the two input function methods, myocardial blood flow (MBF) and cerebral blood flow (CBF) were computed, and the methods were tested for reproducibility (test-retest study) and changes (rest-stress study). Results: The blood- and image-based input functions were similar, and the corresponding CBF values differed only by −6.9 ± 8.1%. In the test-retest study, both MBF and CBF showed good reproducibility, and in the rest-stress study, adenosine significantly increased both MBF ( P = 0.035) and CBF ( P = 0.029), compared with the resting condition. Conclusion: It is possible both to measure the input function from rat arteria femoralis during HO PET imaging and to estimate the input function from rat HO PET images, thereby facilitating the assessment of blood flow in organs visible in PET images. [ABSTRACT FROM AUTHOR]

Purpose: The aim of the study was to compare (68)Ga-chloride with 2-[(18)F]fluoro-2-deoxy-D: -glucose (FDG) for the imaging of pancreatic xenografts.Procedures: Rats with subcutaneous human pancreatic adenocarcinoma xenografts were evaluated in vivo by dynamic positron emission tomography (PET) and ex vivo by measuring radioactivity of excised tissues and by digital autoradiography of tumor cryosections.Results: Both tracers were capable of delineating all subcutaneous tumors from surrounding tissues by PET. The standardized uptake values of tumors by PET were 0.9 +/- 0.3 (mean +/- SD) for (68)Ga-chloride (n = 13) and 1.8 +/- 1.2 for FDG (n = 11). Ex vivo studies showed tumor-to-muscle ratio of 4.0 +/- 0.3 for (68)Ga-chloride (n = 4) and 7.9 +/- 3.2 for FDG (n = 4).Conclusions: (68)Ga-chloride delineated subcutaneously implanted pancreatic adenocarcinoma xenografts by PET, but the uptake was lower than FDG. Further studies to clarify the value of (68)Ga-chloride for PET imaging of tumors are warranted. [ABSTRACT FROM AUTHOR]