When it comes to mammography screening for women with dense breast tissue, radiologists have long looked for alternatives to established modalities like MRI and ultrasound. In a paper in Radiology: Imaging Cancer, researchers put a new twist on an older technology, positron emission mammography (PEM).
Molecular imaging technologies like PEM have been investigated for years as potential adjuncts to conventional mammography due to the challenges X-ray imaging has with dense breast tissue.
- These technologies have carried different names – PEM, breast-specific gamma imaging, molecular breast imaging – but in the end all have fallen short due to the higher radiation dose they deliver compared to mammography.
But Canadian startup Radialis has developed a new version of PEM with its Radialis PET Imager that drastically cuts radiation dose by targeting specific organs, enabling clinicians to use far lower doses of radiopharmaceuticals. The company received clearance for the system in 2022.
- Radialis touts its system as having high spatial resolution and a small field of view thanks to digital detectors with thousands of silicon sensors that can be placed next to the target organ; this makes it well-suited for imaging specific organs like the breast.
In the new paper, Canadian researchers tested the Radialis system as an adjunct to X-ray mammography in a pilot study of 25 women recently diagnosed with breast cancer.
- They wanted to see if PEM performed as well as breast MRI, but with fewer false positives and a radiation dose closer to screening mammography.
Women underwent PEM at three FDG dose levels – 37, 74, or 185 MBq (for comparison, standard whole-body PET uses 370 MBq, a level that translates to a radiation exposure of 6.2-7.1 mSv). Researchers found …
- PEM had sensitivity of 87% across all FDG dose levels (MRI was 100%)
- The sample size was too small to detect statistically significant differences in sensitivity between dose levels
- PEM had specificity of 95%
- PEM detected 96% of known index malignant lesions (24 of 25), with the one miss occurring in a patient at the 37MBq level
- PEM’s radiation dose ranged from 0.62-1.42 mSv, versus 0.44 mSv for a two-view screening digital mammogram
The Takeaway
The findings show that PEM with the Radialis system is a feasible adjunctive breast imaging modality at a radiation dose that’s mostly acceptable relative to X-ray-based mammography. But (as always) additional studies with larger patient populations are needed.
