Simultaneous Multiparametric PET/MRI with Silicon Photomultiplier PET and Ultra-High-Field MRI for Small-Animal Imaging.

UNLABELLED: Visualization of biologic processes at molecular and cellular levels has revolutionized the understanding and treatment of human diseases. However, no single biomedical imaging modality provides complete information, resulting in the emergence of multimodal approaches. Combining state-of-the-art PET and MRI technologies without loss of system performance and overall image quality can provide opportunities for new scientific and clinical innovations. Here, we present a multiparametric PET/MR imager based on a small-animal dedicated, high-performance, silicon photomultiplier (SiPM) PET system and a 7-T MR scanner. METHODS: A SiPM-based PET insert that has the peak sensitivity of 3.4% and center volumetric resolution of 1.92/0.53 mm(3) (filtered backprojection/ordered-subset expectation maximization) was developed. The SiPM PET insert was placed between the mouse body transceiver coil and gradient coil of a 7-T small-animal MRI scanner for simultaneous PET/MRI. Mutual interference between the MRI and SiPM PET systems was evaluated using various MR pulse sequences. A cylindric corn oil phantom was scanned to assess the effects of the SiPM PET on the MR image acquisition. To assess the influence of MRI on the PET imaging functions, several PET performance indicators including scintillation pulse shape, flood image quality, energy spectrum, counting rate, and phantom image quality were evaluated with and without the application of MR pulse sequences. Simultaneous mouse PET/MRI studies were also performed to demonstrate the potential and usefulness of the multiparametric PET/MRI in preclinical applications. RESULTS: Excellent performance and stability of the PET system were demonstrated, and the PET/MRI combination did not result in significant image quality degradation of either modality. Finally, simultaneous PET/MRI studies in mice demonstrated the feasibility of the developed system for evaluating the biochemical and cellular changes in a brain tumor model and facilitating the development of new multimodal imaging probes. CONCLUSION: We developed a multiparametric imager with high physical performance and good system stability and demonstrated its feasibility for small-animal experiments, suggesting its usefulness for investigating in vivo molecular interactions of metabolites, and cross-validation studies of both PET and MRI.

Comparison of conventional and sensor-based electronic stethoscopes in detecting cardiac murmurs of dogs.

BACKGROUND AND OBJECTIVE: Cardiac auscultation is one of the most important parts of the cardiological examination traditionally performed with acoustic stethoscopes. The aim of this study was to compare the sensitivities and the diagnostic capabilities of traditional and electronic stethoscopes in detecting canine heart murmurs. MATERIALS AND METHODS: The study was performed on 21 dogs referred for cardiologic examination with suspected heart murmurs. Six out of these dogs had cardiac murmurs bilaterally. Cardiac auscultation was performed independently by a final-year veterinary student (AB=I1) and by an experienced clinician (KV=I2), both using a traditional and a Welch Allyn Meditron electronic sensor-based stethoscope. Final diagnoses were established by echocardiography and by digital phonocardiography. RESULTS: Correct detection of a murmur was made by I1 with a traditional stethoscope in 20/27 (74.0%) of the suspected murmurs (p=0.30, kappa[κ] =0.2) and with the electronic stethoscope in 26/27 (96.3%), respectively (p=0.0013, κ=0.75). I2 correctly detected the murmurs with the traditional stethoscope in 25/27 (92.6%) cases (p=0.0013, κ=0.75) and with the electronic stethoscope in all 27/27 (100%) cases (p=0.00012, κ=1). Agreements of murmur intensity gradings between traditional and electronic stethoscopes were highly significant (I1: p=6.9´10⁻8; κ=0.79), (I2: p=5.2´10⁻¹¹; κ=0.92). When grading the murmurs with the traditional stethoscope, there was a significant agreement between I1 and I2 (p=2.9´10⁻7; κ=0.79), being even higher with the electronic stethoscope (p=1.1´10⁻¹¹; κ=0.92). CONCLUSION: The electronic stethoscope was more sensitive than the traditional one in detecting and grading cardiac murmurs being especially useful for I1 with less experience. However, it can be suggested to use a traditional and an electronic stethoscopes simultaneously to optimally utilize their advantages.