A Comparative Study of 511 keV SPECT and PET Using Separate 370 MBq F-18-FDG Doses on Different Days.

Area of Science:

• Nuclear Medicine
• Medical Imaging
• Oncology

Background:

• Comparative studies of 511 keV SPECT and PET often use a single FDG dose, potentially biasing results.
• Previous methodologies may not accurately reflect the diagnostic capabilities of each modality.

Purpose of the Study:

• To prospectively compare conventional PET and 511 keV SPECT using separate FDG doses on different days.
• To evaluate discrepancies in detecting malignancy in a patient cohort.

Main Methods:

• 23 patients with proven malignancy underwent both PET and SPECT imaging.
• Separate 370 MBq fluorine-18-fluorodeoxyglucose (FDG) doses were administered on different days for each modality.
• Imaging was performed using an ECAT 951/31R PET scanner and a Trionix XLT-20 for SPECT.

Main Results:

• Discrepancies in findings were observed in 52% of patients (12/23).
• PET identified findings exclusively in 8 patients (66% of discrepancies), representing the sole metabolic evidence of disease.
• SPECT detected 71% (37/52) of lesions identified by PET, primarily those larger than 2 cm. Small lesions (<1.2 cm) were missed by both PET and SPECT, as well as CT and MRI in some cases.

Conclusions:

• PET demonstrates superior sensitivity for detecting metabolic evidence of malignancy compared to 511 keV SPECT.
• The study methodology using separate FDG doses minimizes bias and provides a more accurate comparison.
• Both PET and SPECT can miss small or subtle lesions, underscoring the need for multimodal imaging approaches.