Design and imaging performance of BPET-DBT - a dedicated scanner for breast imaging

A dedicated breast PET (BPET) scanner integrated with digital breast tomosynthesis (DBT) enables three-dimensional functional imaging with quantitative information co-registered to high-resolution anatomical images. With the availability of breast cancer specific PET radiotracers, such a scanner has the potential to improve treatment planning in breast cancer. We recently developed a BPET-DBT scanner utilizing an integrated gantry design to generate intrinsically co-registered BPET-DBT images.

This paper presents the scanner design, characterizes its imaging performance, and reports on our initial human imaging experience to demonstrate scanner's clinical readiness.

The PET component is comprised of two detector heads, providing a 20 × 10 × 10 cm³ scanner field-of-view. The detector provides time-of-flight (TOF) measurement and is comprised of 32×32 LYSO arrays of 1.5 × 1.5 × 15 mm³ crystals coupled to multi-anode PMTs. Custom waveform-sampling electronics ensures high spatial and timing resolution with minimal deadtime. The DBT component is a state-of-the-art system which employs 2D x-ray tube and detector motion for improved contrast and resolution. Phantoms appropriate for breast imaging were imaged to assess spatial resolution, image quantitation, count-rate capability, and co-registration accuracy. First human imaging was performed in volunteers with estrogen-receptor-positive (ER+) breast cancer. A five-minute BPET-DBT scan using ¹⁸F-fluoroestradiol was acquired and compared with a whole-body PET scan.

System timing resolution of 425 ps and energy resolution of 16% were measured. Spatial resolution measurements showed an in-plane (parallel to the detector) resolution of 2 mm and demonstrates the ability to resolve 1.6 mm rods in the micro-deluxe hot rod phantom. TOF reconstruction combined with image-based resolution modeling mitigates artifacts typical in scanners with incomplete angular coverage and enables good out-of-plane (orthogonal to detector) discrimination of the 2.4 mm rods. Count-rate measurements confirm low scanner dead-time, with sufficient count-rate capability for clinical use.

We successfully constructed and tested a BPET scanner and integrated it with DBT. BPET scanner performance was characterized, and imaging capabilities relevant for clinical imaging have been highlighted. Images from a patient with ER+ breast cancer show clear tumor delineation and visualization of heterogeneous uptake, as also seen with WB-PET. This approach offers a promising strategy for improved treatment planning and outcomes in breast cancer care.