Timing, Energy, and 3-D Spatial Resolution of the BING PET Detector Module.

We evaluated the 3D spatial, energy, and timing resolution of the Brain (or Breast)-Initiative Next-Generation (BING) PET detector. The BING detector is an array of 1-mm-thick slats of LYSO scintillator with lapped specular-reflective faces (15-mm by 52-mm) that are stacked together and oriented with their long-narrow edges normal to the imaging field of view. Interaction positions are determined from the signals of silicon-photomultiplier (SiPM) arrays placed on the entrance (top) and exit (bottom) faces. The SiPM arrays are offset to determine the slat of interaction (SOI) without requiring any optical light sharing between slats. Maximum likelihood 2D location within the SOI is determined using the sensor signals. Interaction time is determined with a modified first-optical-photon pickoff method. Performance of the BING detector was measured as a function of position using a sideways coincidence-collimated beam. Slats were accurately identified, with an effective tangential detector resolution of 1 mm. Average resolutions (and ranges) are: 0.96 mm (0.85 mm to 1.11 mm) for lateral (axial) detector resolution, 1.6 mm (1.0 mm to 2.1 mm) for depth resolution, 13.6% (12.7% to 16.0%) for energy resolution, and 317 ps (241 ps to 404 ps) for coincidence timing resolution. Initial spatial and timing resolution results demonstrated that the BING detector can be effective in a small field-of view (e.g., brain or breast) PET system.

Designing a compact high performance brain PET scanner-simulation study.

The desire to understand normal and disordered human brain function of upright, moving persons in natural environments motivates the development of the ambulatory micro-dose brain PET imager (AMPET). An ideal system would be light weight but with high sensitivity and spatial resolution, although these requirements are often in conflict with each other. One potential approach to meet the design goals is a compact brain-only imaging device with a head-sized aperture. However, a compact geometry increases parallax error in peripheral lines of response, which increases bias and variance in region of interest (ROI) quantification. Therefore, we performed simulation studies to search for the optimal system configuration and to evaluate the potential improvement in quantification performance over existing scanners. We used the Cramér-Rao variance bound to compare the performance for ROI quantification using different scanner geometries. The results show that while a smaller ring diameter can increase photon detection sensitivity and hence reduce the variance at the center of the field of view, it can also result in higher variance in peripheral regions when the length of detector crystal is 15 mm or more. This variance can be substantially reduced by adding depth-of-interaction (DOI) measurement capability to the detector modules. Our simulation study also shows that the relative performance depends on the size of the ROI, and a large ROI favors a compact geometry even without DOI information. Based on these results, we propose a compact 'helmet' design using detectors with DOI capability. Monte Carlo simulations show the helmet design can achieve four-fold higher sensitivity and resolve smaller features than existing cylindrical brain PET scanners. The simulations also suggest that improving TOF timing resolution from 400 ps to 200 ps also results in noticeable improvement in image quality, indicating better timing resolution is desirable for brain imaging.

Pilot clinical trial of 18F-fluorodeoxyglucose positron-emission mammography in the surgical management of breast cancer.

BACKGROUND: High-resolution positron-emission mammography (PEM) is a new device, which allows the imaging of breast tissue. A prospective study was performed to assess the accuracy of PEM in newly diagnosed breast cancer patients. METHODS: In a prospective multicenter study, 44 women with confirmed breast cancers were imaged with a high-resolution PEM scanner (Naviscan PET Systems, Rockville, MD) with 18F-fluorodeoxyglucose. The images were blindly evaluated and were compared with final pathology. RESULTS: The majority of the index lesions were seen on PEM (89%, 39/44). PEM detected 4 of 5 incidental breast cancers, 3 of which were not seen by any other imaging modalities. Of 19 patients undergoing breast-conserving surgery, PEM correctly predicted 6 of 8 (75%) patients with positive margins and 100% (11/11) with negative margins. CONCLUSION: The current PEM device shows promise in detecting breast malignancies and may assist in the planning of adequate partial mastectomy procedures to better ensure negative margins.

Positron emission mammography: high-resolution biochemical breast imaging.

Positron emission mammography (PEM) provides images of biochemical activity in the breast with spatial resolution matching individual ducts (1.5 mm full-width at half-maximum). This spatial resolution, supported by count efficiency that results in high signal-to-noise ratio, allows confident visualization of intraductal as well as invasive breast cancers. Clinical trials with a full-breast PEM device have shown high clinical accuracy in characterizing lesions identified as suspicious on the basis of conventional imaging or physical examination (sensitivity 93%, specificity 83%, area under the ROC curve of 0.93), with high sensitivity preserved (91%) for intraductal cancers. Increased sensitivity did not come at a cost of reduced specificity. Considering that intraductal cancer represents more than 30% of reported cancers, and is the form of cancer with the highest probability of achieving surgical cure, it is likely that the use of PEM will complement anatomic imaging modalities in the areas of surgical planning, high-risk monitoring, and minimally invasive therapy. The quantitative nature of PET promises to assist researchers interested studying the response of putative cancer precursors (e.g., atypical ductal hyperplasia) to candidate prevention agents.