Development of ClearPEM-Sonic — A multimodal positron emission mammograph and ultrasound scanner

Breast cancer is one of the most frequent causes of premature death amongst women. To enhance the chances for complete recovery, the tumor shall be detected at an early stage. It is therefore necessary to develop efficient diagnostic means with high spatial resolution. In this focus, we developed a positron emission tomograph coupled to an ultrasound elastography system, dedicated to mammography: the ClearPEM-Sonic. ClearPEM, the first mammography PET developed by the Crystal Clear Collaboration, is based on LYSO:Ce crystals read out on two extraction faces with avalanche photodiodes. For the ClearPEM-Sonic, the crystal properties were improved with regard to the first prototype. The light yield of the crystals increased by 25% to 17500 photons/MeV, with a depth of interaction precision of 2 mm. The main objective of the ClearPEM-Sonic project is to improve diagnostic accuracy by combining metabolic information obtained with ClearPEM with 3D morphologic and anatomic information obtained with an ultrasound imaging system, the SuperSonic Imagine Aixplorer. It provides both conventional 3D B-mode information and a quantified 3D elasticity measurement of the tissue. The main challenge of combining both modalities is, aside from the mechanical integration, the fusion of both images to achieve an excellent mapping precision. The breast is immobilized with a conical contention system integrated in the patient bed. A removable arm is used to bring the US transducer in any required position. The exact location of the US image can be calculated by recording the transducer position with a high-precision tracking system. The information from all modalities is transferred to dedicated software for image treatment and fusion. We present images acquired on phantoms that confirm a PEM spatial resolution close to 1.6 mm and fusion precision better than 2 mm.