Abstract
1509
Objectives 123I-MIBG scintigraphy with CT imaging provides anatomic and functional information with good sensitivity and specificity for detection of pheochromocytoma and paraganglioma (PPGL). It is known that physiological uptake in adrenal glands can sometimes give false-positive results or obscure small lesions. The purpose of this retrospective study was to evaluate the diagnostic performance of quantitative analysis of 123I-MIBG-SPECT/CT in patients with suspected PPGL, comparing with that of visual assessment.
Methods We analyzed 74 consecutive patients who were clinically suspected of having PPGL and underwent 123I-MIBG SPECT/CT scan between September 2009 and October 2015. Patients got an intravenous injection of 111 to 222 MBq 123I-MIBG, and SPECT/CT was performed at 6-h and/or 24-h post-injection, in addition to obtaining planar images at 6-h and 24-h post-injection. A low-dose unenhanced CT was used for attenuation correction. On SPECT images, we measured standardized uptake values (SUVs) of retroperitoneal tumors including PPGLs and physiological uptake of normal organs using a newly-developed software. ROC analysis was performed to assess the diagnostic performance of this technique in differentiating PPGLs from others. In addition, planar images, 6-h SPECT/CT images and 24-h SPECT/CT images were evaluated separately by visual assessment in terms of the presence or absence of PPGL using a 5-point grading scale (0 = definitely negative, 1 = probably negative, 2 = equivocal, 3 = probably positive, and 4 = definitely positive). Lesions determined to be grade 3 or 4 were considered positive, and the diagnostic performance of visual analysis was also assessed by ROC analysis.
Results The mean ± standard deviation of SUVmax of PPGLs was 9.97 ± 3.86 for 6-h SPECT/CT, which was significantly higher (p < 0.05) than that of other retroperitoneal lesions (3.85 ± 1.51) and normal adrenal (3.80 ± 1.08). The SUVmax of physiological uptake in parotid glands, submandibular glands, thyroid, heart, and liver at 6-h post-injection were 6.04 ± 3.48, 3.87 ± 2.74, 7.85 ± 3.57, 6.82 ± 2.61, and 12.3 ± 3.80, respectively. When applying 6.57 as the optimal cut-off value, the sensitivity, specificity, and accuracy of quantitative assessment for 6-h SPECT/CT in differentiating PPGLs from others were 80.0%, 98.6% and 95.3%, respectively, with the area under the curve (AUC) of 0.901 on a lesion basis (n = 85). On a patient basis (n = 42), the AUCs of quantitative assessment were 0.882 for 6-h SPECT/CT and 0.835 for 24-h SPECT/CT, whereas those of visual assessment were 0.813 for planar, 0.779 for 6-h SPECT/CT and 0.952 for 24-h SPECT/CT. The sensitivity of quantitative assessment was comparable or a little lower than that of visual assessment, whereas the specificity tended to be higher, regardless of 6h-SPECT/CT or 24-h SPECT/CT. When 24-h SPECT/CT images were assessed quantitatively, there were 3 false-positive cases, in which all patients had undergone hemodialysis.
Conclusions Quantitative approach in 123I-MIBG SPECT/CT was clinically feasible, and it demonstrated reasonably high diagnostic performance in differentiating PPGLs from other retroperitoneal pathology or physiological uptake in adrenal gland.
Diagnostic Accuracy of Each Method by Patient (n = 42)
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