Clinical Imaging Characteristics of the Positron Emission Mammography Camera: PEM Flex Solo II

Abstract

We evaluated a commercial positron emission mammography (PEM) camera, the PEM Flex Solo II. This system comprises two 6 · 16.4 cm detectors that scan together covering up to a 24 · 16.4 cm field of view (FOV). There are no specific standards for testing this detector configuration. We performed several tests important to breast imaging, and we propose tests that should be included in standardized testing of PEM systems. Methods: We measured spatial resolution, uniformity, countingrate linearity, recovery coefficients, and quantification accuracy using the system's software. Image linearity and coefficient of variation at the edge of the FOV were also characterized. Anecdotal examples of clinical patient data are presented. Results: The spatial resolution was 2.4 mm in full width at half maximum for image planes parallel to the detector faces. The background variability was approximately 5%, and quantification accuracy and recovery coefficients varied within the FOV. Positioning linearity began at approximately 13 mm from the edge of the detector housing. The coefficient of variation was significantly higher close to the edge of the FOV because of limited sensitivity in these image planes. Conclusion: A reconstructed spatial resolution of 2.4 mm represented a significant improvement over conventional whole-body PET scanners and should reduce the lower threshold on lesion size and tracer uptake for detection in the breast. Limited-angle tomography and a lack of data corrections result in spatially variable quantitative results. PEM acquisition geometry limits sampling statistics at the chest-wall edge of the camera, resulting in high variance in that portion of the image. Example patient images demonstrate that lesions can be detected at the chest-wall edge despite variance artifacts, and fine structure is visualized routinely throughout the FOV in the focal plane. The PEM Flex camera should enable the functional imaging of breast cancer earlier in the disease process than whole-body PET. Posi tron emission mammography (PEM) is a technique using 2 annihilation-photon detectors and limited-angle tomographic reconstruction to image radiotracer distributions within the breast. Because of their smaller size and closer proximity to the source, dedicated PEM cameras can provide better spatial resolution and count sensitivity than whole-body PET (WB PET). PEM is undergoing clinical trials and has been suggested for breast cancer detection, characterization, treatment planning, and assessment of response to therapy. PEM, like WB PET, provides functional imaging information. Radiographic mammography, ultrasound, and MRI primarily provide anatomic information. PEM can thus provide complementary information to conventional breast imaging modalities. Screening mammography is believed to be an important factor in recent declines in breast cancer mortality (1). Despite the successes of earlier detection by mammography, however, breast cancer is the second-leading cause of cancer-related deaths in North American women. This stat...

A Molecular Approach to Breast Imaging

“…It is a stationary flat detector-based PEM scanner using limited-angle tomosynthetic reconstruction with an in-plane spatial resolution of 2.4 mm, a marked improvement over whole-body PET/CT (;5-7 mm) (9). Because images are obtained in the same projections as mammography with minimal breast compression, correlation of imaging findings can be performed with direct coregistration possible using the earlier integrated PEM-I design.…”

Positron Emission Mammography Image Interpretation for Reduced Image Count Levels

“…The PEM Flex scanner is a limited-angle tomosynthesis system yielding 12 image slices, 16.3 · 24.0 cm with 1.2-mm pixel size (18,19). Slice thickness is one-twelfth of the distance between the 2 detectors, which is adjusted for each patient to immobilize the breast with mild compression.…”

“…Recommendations for 18 F-FDG injected activity have been established for WB PET in the United States at 370-740 MBq (14). Equivalent guidelines have yet to be established for PEM scanning.…”

Modeling and simulation of Positron Emission Mammography (PEM) based on double-sided CdTe strip detectors

“…There are several different geometric designs such as rectangular geometry (four detector plates surrounding the breast [12]), ring geometry [13], and coplanar geometry [11]. The coplanar detector geometry based on scintillation crystals is the most used, since it provides great spatial resolution in plane 1 down to 2 mm full width at half maximum (FWHM) [11] and high contrast images with 4 mm minimum detectable lesion size for 10:1 tumor to normal tissue ratio [14]. The detector heads are positioned in opposing fashion on either side of the body part and move in parallel across the paddles during a scan [11].…”

“…This is a consequence of the partial volume effect [18] that produces a loss of intensity and a smearing of the activity distribution around those high uptake regions whose volume is smaller than twice the detector resolution. In the particular case of coplanar scanners, it implies a resolution a factor of 4 worse than the inplane spatial resolution: a large parallax error results in a dramatic deterioration of the resolution up to 8 mm FWHM along the vertical axis [14]. Obviously, all these pose constraints on the minimum detectable tumor size and on the correct assessment of malignancy of small lesions which are probably the two most important factors to determine the effectiveness of any breast cancer treatment [17].…”