SimPET is a compact and reliable SiPM-based small animal PET imaging system for hybrid MR imaging and standalone use.
The SimPET series is an advanced silicon photomultiplier (SiPM) based PET insert for truly simultaneous PET/MR imaging with a compact design, low power consumption, and excellent PET detector stability, created by Brightonix Imaging.
The insert is optimized for use with some of the most commonly installed superconducting high-field (>3T) MRI systems, found in many preclinical imaging laboratories around the world. In addition to the insert being used with MRI systems, the PET insert can also be used as a standalone PET imaging system if desired.
Brightonix Imaging has created a state-of-the-art positron emission tomography (PET) insert utilizing their advanced silicon photomultiplier (SiPM) to manufacture a compact insert requiring low power consumption while maintaining excellent PET detector stability. This system has been optimized for use with some of the most commonly installed preclinical MRI systems. The SimPET insert allows for simultaneous PET/MR imaging, but may also be used as a standalone PET imaging system if desired.
There are four (4) different models of SimPET inserts available, they vary in inner/outer diameter and axial field of view. Please refer to the Technical Specifications for complete details. The inserts are ideally suited for mice, rats and other similarly sized animals, depending on the size of the MRI coil used in conjunction with the insert.
The workstation software is intuitive and easy to use. The user is provided with real-time count rate monitoring, FastTomo reconstruction, along with in-line image reconstruction, all with flexible list-mode data acquisition. Calibration procedures for quality control, PET/MR geometry, as well as count rate/activity are all included within the software. Quantification is provided in Bq/ml or standardized uptake value (SUV).
The highly sensitive LSO (lutetium oxyorthosilicate) detectors provide a best-in-class sub-millimeter spatial resolution while maintaining count-rate performance to allow for both low and high-dose imaging applications.
Simultaneous acquisition of both the PET and MR images allows for both spatial and temporal understanding of the PET signal with regards to the anatomical image. MRI is the gold standard in soft tissue imaging, providing not only anatomical reference for the PET signal, but may also in itself provide some additional information with regards to the tissues being imaged. Various image weighting protocol exist to help identify abnormal or pathological tissues, along with the added benefit of using specific and perhaps multi-modal contrast agents to further elucidate the molecular pathway or imaging target of interest.
There are several key benefits of the SimPET inserts:
Exceptional PET performance, optimized for standalone or simultaneous with MR imaging
Highly sensitive detectors provide sub-millimeter spatial resolution
State-of-the-art silicon photomultiplier technology allows for compact design with low power consumption
Acquisition and reconstruction software are intuitive and simple to use
Fully integrated operation with the M7 compact, permanent magnet from Aspect Imaging OR integration with some of the most commonly used high-field (>3T) superconducting preclinical MRI system on the market
Oncology is one of the most common applications of PET in preclinical imaging. Used clinically to detect small metastatic lesions throughout the body, preclinical applications of PET imaging are diverse. PET tracers have been developed to study:
Gene expression of specific molecular targets
PET imaging may be used on any type of tumor model, as the radiotracers are typically injected intravenously for distribution to all areas of the body. Specifically, PET imaging may be used on orthotopic and transgenic/spontaneous tumors, as well as xenografts or metastatic lesions.
The image above shows the effect of tumor associated macrophages on tumor hypoxia and aerobic glycolysis, displayed in values of standard uptake values. A T2-weighted fast spin echo (FSE) image was acquired on the M7, compact, permanent magnet MRI system from Aspect Imaging; PET images were acquired simultaneously with the SimPET-S model.
Neurological applications of PET are commonplace both clinically and preclinically. Preclinical PET tracers have been developed to study:
Biodistribution of a specific target
Cerebral blood flow
Cerebral metabolic rate
Availability of specific receptors in the brain
Plasma membrane transporters
Receptor binding sites
PET imaging has been used to study the pathological processes, response to therapeutics, and resolution of many disease models, including Parkinson’s Disease, Alzheimer’s Disease, Huntington’s Disease, Stroke, Epilepsy, Traumatic Brain Injury, and Neuropsychiatric disorders.
The recent COVID-19 pandemic has brought to the forefront the importance of PET imaging in immunological and infectious disease research. A survey of the literature shows that preclinical PET imaging has been shown to be invaluable in studying the following:
Understanding disease progression and pathogenesis
Diagnosis of disease, by targeting the specific pathogenic agent
Studying therapeutic efficacy of target compounds
Optimizing treatment regimes and studying the resolution of infections
Understanding the host’s immune response to infection
Studying the efficacy of vaccines
Infectious diseases and immunology are not limited to the study of viruses, but rather go well beyond these specific agents to look at models of bacterial, viral, parasite, and prion infections. The only limitation to this type of work is in the PET tracers available to investigate both the infectious agent as well as the host’s response.
Dynamic PET imaging is often used to study the kinetics of a newly developed PET tracer, or to investigate target concentrations, or biodistribution. Time-activity curves are often prepared along with assessments of radiotracer accumulation and biodistribution kinetic modeling.
The above set of images shows a dynamic scan acquired with the SimPET-X insert, having an axial field of view of 11cm. A mouse was injected, via the tail vein, with 331µCi [18F]-fluorodeoxygluocose (FDG).
A variety of bone diseases may be studied using PET imaging, these include but are not limited to osteoporosis, osteomalacia, rickets, or rheumatoid arthritis.
A wide variety of other diseases, including metabolic disorders, can also be studied using PET imaging.
There is truly no limit on the application of PET in preclinical imaging, it is merely dependent on the development of specific and relevant PET tracers.
The above image shows increased metabolic activity in the rear paws in the mouse model of arthritis. These images were acquired using the SimPET-S insert along with the M7, compact, permanent magnet from Aspect Imaging, following an i.v. injection of 300µCi of [18F]- fluorodeoxygluocose (FDG). The K/BxN model is a commonly used mouse model to study arthritic disease. The gradient echo (GRE) MR image, acquired on the M7 system, provides the anatomical context for the PET images.
The spatial resolution, at the center of the field of view, based on the 3D OSEM reconstruction was found to be 0.7mm without a warm background and 1.45mm with a warm background.
In the hot rod phantom image, seen below, the 0.75mm diameter rods were resolved with incorporation of the point spread function.
In the image above a hot rod phantom was imaged, rods with diameters of 0.75, 1.0, 1.35, 2.0, and 2.4mm were included. Reconstruction was completed using a 3D OSEM algorithm. The point spread function has been incorporated in a, while it was not incorporated in b.
The sensitivity of the SimPET-S was found to be 4.21% (energy window = 250-750 keV) in this study. Additional studies have found the sensitivity of the SimPET-X model, within the same energy window, to be greatly improved, measured at 8.14%. The SimPET-X model is designed for use in some of the most commonly used high-field (>3T) superconducting magnets designed for pre-clinical imaging.
Above, is the NEMA sensitivity plots, measured at the transaxial center, for both the SimPET-S (gold) and SimPET-X (blue) inserts; measured with an energy window of 250-750 keV.
The NEC rate of the SimPET-S was found to be 151 kcps at 38.4 MBq, using the same energy window as the sensitivity testing (250-750 keV); while the NEC rate of the SimPET-X was found to be 348 kcps at 26.2 MBq, measured in additional studies. The SimPET-X model is designed for use in some of the most commonly used high-field (>3T) superconducting magnets designed for pre-clinical imaging.
The above is the NEMA Count Rate Performance measurements made for the SimPET-S model insert
The above is the NEMA Count Rate Performance measurements made for the SimPET-X model insert
There were no remarkable differences in signal to noise ratio (SNR) and uniformity of the MR images and PET count rates when using different PET conditions and MRI pulse sequences.
The image above demonstrates the compatibility of the SimPET insert with the M7 system from Aspect Imaging. Various MRI pulse sequences including T2-weigheted Fast Spin Echo (T2WFSE), T1-weighted Spin Echo (T1WSE), and a 3D Gradient Echo (3DGRE).
When used with the M7, the compact permanent magnet from Aspect Imaging, the SimPET-S insert is placed within the bore of the magnet from one side, while the animal handling system with the RF coil is inserted from the other side of the magnet fitting within the PET insert.
The image above shows the SimPET-S insert positioned to enter into the M7 MRI system from Aspect Imaging. The animal handling system with RF coil enters the M7 from the opposite side.
The diagram above shows the configuration of the SimPET-S insert positioned within the bore of the M7 MRI system from Aspect imaging.