Image quality evaluation of real low-dose dedicated breast PET

Introduction: High-resolution dedicated breast positron emission tomography (dbPET) has been developed for the detection of early-stage breast cancers. Since ring-shaped dbPETs have highly sensitive detectors and do not use X-ray computed tomography to perform attenuation correction, they are expected to greatly reduce the radiation dose to patients. We previously evaluated the dose reduction related to the use of dbPET based on phantom tests and clinical cases and the results revealed that by employing 25% of the standard ¹⁸F-2-fluorodeoxy-D-glucose (¹⁸F-FDG) dose, it is possible to obtain a clinically acceptable image quality, while 12.5% of the standard dose results in an image quality that is still sufficient for the detection of lesions [1]. However, in the previous study, only the examination of simulated dose reduction was considered for clinical cases. Therefore, based on the previous results, the clinical feasibility was evaluated by comparing the dbPET images with real low dose FDG and the images with full dose FDG.

Methods: Nine women (median age and age range: 49 and 41–60 years) who had no history of breast cancer and were previously scanned by dbPET injected with a clinical ¹⁸F-FDG dose (3 MBq/kg) within the last 3 years, were included in this study. They were injected with 50% of the clinical dose FDG and scanned with dbPET for 10 min for each breast, 60 and 90 min after ¹⁸F-FDG injection. The dbPET images of the right breast were evaluated to rule out the effects of FDG in the myocardium located outside the field-of-view to the left breast. To investigate the effect of the scan start time and acquisition time on image quality, list-mode data was divided into 1,3,5,7-min (and 10-min with 50% of injected FDG) from the start of acquisition and reconstructed respectively (Fig. 1). Subsequently, the reconstructed images were compared visually and quantitatively for the following PET parameters: the mean standardized uptake value (SUV_mean) and coefficient of variation (CV) of the mammary grand.

Results: The contrast between fat and the mammary gland on dbPET images acquired for 7-min with 50% dose of injected FDG was similar to that of the image with 100% dose, and the smoothness was higher (Fig. 2). There was no significant difference in image quality depending on the scan start time for images with 50% dose of FDG. There was also no difference between the 7-min and 10-min acquisition times with the 50% dose of FDG (Fig. 2). SUV_mean of the mammary gland were lower with 50% dose, however, the CVs were approximately similar (Fig. 3).

Conclusions: The quality of dbPET images with 50% FDG dose was high enough to be suitable for clinical application. It is better to start the scan 90 min after injection, as the contrast between the lesion and the normal mammary gland will be clearer.

Reference

1. Satoh Y, Sekine T, Omiya Y, Onishi H, Motosugi U. Reduction of the fluorine-18-labeled fluorodeoxyglucose dose for clinically dedicated breast positron emission tomography. EJNMMI Phys. 2019 Nov 29; 6(1): 21.

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