doi:10.2967/jnmt.107.040402
Journal of Nuclear Medicine Technology Volume 35, Number 4, 2007 237-241
© 2007 by Society of Nuclear Medicine
Reconstruction Parameters for 111In-Pentetreotide SPECT: Variability with Respect to Body Weight and Body Region
Arianna Massaro1,
Silvia Cittadin1,
Francesca Rossi2,
Lucia Rampin1,
Elena Banti1,
Otello Nibale3 and
Domenico Rubello1
1 PET Unit, Nuclear Medicine Service, S. Maria della Misericordia Hospital, Rovigo, Italy; 2 Technician and Nursing Service, S. Maria della Misericordia Hospital, Rovigo, Italy; and 3 Medical Physic Service, S. Maria della Misericordia Hospital, Rovigo, Italy
Correspondence: For correspondence or reprints contact: Arianna Massaro, CNMT, Nuclear Medicine Service, PET Unit, "S. Maria della Misericordia Rovigo" Hospital, Istituto Oncologico Veneto (IOV)-IRCCS, Viale Tre Martiri, 140, 45100, Rovigo, Italy. E-mail: rubello.domenico{at}azisanrovigo.it
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ABSTRACT
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This study, which was based on a large series of consecutive patients imaged by 111In-pentetreotide SPECT for a neuroendocrine tumor, evaluated variability in reconstruction parameters in relation to patient body weight and the body region imaged, looking for the possibility of standardizing such parameters. Methods: One hundred twenty-four patients underwent 111In-pentetreotide scintigraphy: 4- and 24-h whole-body and planar scans and a 24-h SPECT examination. All patients were injected with 140–150 MBq of 111In-pentetreotide at least 1 wk after somatostatin analogs had been discontinued. SPECT images were systematically acquired at the levels of the head, chest, and abdomen. SPECT was performed using a dual-head 
-camera with medium-energy collimators, step-and-shoot method, no circular orbit, a 64 x 64 matrix, and 30 s per view for a total of 64 views. Two reconstruction procedures were compared: the iterative method using 10 iterations and the filtered backprojection method using a Butterworth filter with different cutoffs and orders. Results: Optimal SPECT images were obtained by applying the Butterworth filter. The reconstruction parameters could be standardized for the head and chest but were more variable for the abdomen, mainly because 111In-pentetreotide is physiologically trapped in different intestinal areas and varies over time, especially in the liver, spleen, bowel, and urinary tract. Conclusion: Filtered backprojection using a Butterworth filter appears adequate for standardizing the reconstruction parameters for 111In-pentetreotide SPECT of the head and chest. Processing of abdominal images is more operator-dependent. A 150-MBq dose of 111In-pentetreotide is recommended when planning multiple SPECT acquisitions in the same patient.
Key Words: 111In-pentetreotide; SPECT; reconstruction parameters; standardization; neuroendocrine tumors
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INTRODUCTION
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In recent years, SPECT has gained an important role in scintigraphic evaluations because it is accurate and allows precise localization of the depth of radioactive lesions. At present, SPECT studies using radiotracers labeled with 99mTc-pertechnetate are well standardized, mainly because the radioisotope is characterized by optimal energy and high-statistic count rates for acquisitions with currently available -cameras (1,2). In contrast, the choice of reconstruction parameters for medium-energy radioisotopes such as 111In is more difficult, mainly because they are characterized by a relatively low-statistic count rate (3,4).
This study, which was based on a large series of consecutive patients imaged by 111In-pentetreotide SPECT for a neuroendocrine tumor, evaluated variability in reconstruction parameters in relation to patient body weight and the body region imaged, looking for the possibility of standardizing such parameters.
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MATERIALS AND METHODS
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At our center from January 2005 to December 2006, 124 consecutive patients affected by a clinically and biochemically proven neuroendocrine tumor were enrolled in the study. All patients were injected with 140–150 MBq of 111In-pentetreotide at least 1 wk after somatostatin analogs had been discontinued and underwent 4- and 24-h whole-body and spot planar imaging. Moreover, a 24-h SPECT acquisition of the head, chest, and abdomen was also systematically obtained.
The SPECT images were acquired on a dual-head -camera (E-CAM; Siemens) using medium-energy collimators, a step-and-shoot acquisition protocol with no circular orbit, a 64 x 64 matrix, and 30 s per view for a total of 64 views. Two different reconstruction procedures were compared: first, an iterative method using ordered-subset expectation maximization (OSEM) with 10 iterations, like the method used in some previous studies on 99mTc-technetium–labeled compounds (5); and second, filtered backprojection using a conventional technique previously described (6), with application and comparison of a variety of commercially available filters.
Scintigraphic images were examined in a masked fashion by 2 skilled nuclear medicine physicians. In cases of discrepancy, the diagnosis was reached by consensus.
Among the different reconstruction protocols used, we found the Butterworth filter to be most satisfactory in regard to spatial resolution, contrast, and image definition, producing a global improvement in image quality. Different orders and cutoffs were applied using this filter.
The patients were divided into 2 groups according to body weight (49 patients weighed more than 70 kg; 65 weighed 70 kg or less), and the SPECT images of the 3 body regions (head, chest, and abdomen) of each patient were compared.
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RESULTS
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Table 1 summarizes our results, and Figures 1–3
show examples of head, chest, and abdominal images obtained using the iterative and filtered backprojection methods. Image shape seemed slightly smoother with the iterative method, whereas the global quality of SPECT images was better defined with filtered backprojection with the Butterworth filter.
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ABSTRACT
INTRODUCTION
