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.
PET scanners based on monolithic pieces of scintillator can potentially produce superior performance characteristics (high spatial resolution and detection sensitivity, for example) compared to ...conventional PET scanners. Consequently, we initiated development of a preclinical PET system based on a single 7.2 cm long annulus of LYSO, called AnnPET. While this system could facilitate creation of high-quality images, its unique geometry results in optics that can complicate estimation of event positioning in the detector. To address this challenge, we evaluated deep-residual convolutional neural networks (DR-CNN) to estimate the three-dimensional position of annihilation photon interactions. Monte Carlo simulations of the AnnPET scanner were used to replicate the physics, including optics, of the scanner. It was determined that a ten-layer-DR-CNN was most suited to application with AnnPET. The errors between known event positions, and those estimated by this network and those calculated with the commonly used center-of-mass algorithm (COM) were used to assess performance. The mean absolute errors (MAE) for the ten-layer-DR-CNN-based event positions were 0.54 mm, 0.42 mm and 0.45 mm along the
(axial)-,
(transaxial)- and
- (depth-of-interaction) axes, respectively. For COM estimates, the MAEs were 1.22 mm, 1.04 mm and 2.79 mm in the
-,
- and
-directions, respectively. Reconstruction of the network-estimated data with the 3D-FBP algorithm (5 mm source offset) yielded spatial resolutions (full-width-at-half-maximum (FWHM)) of 0.8 mm (radial), 0.7 mm (tangential) and 0.71 mm (axial). Reconstruction of the COM-derived data yielded spatial resolutions (FWHM) of 1.15 mm (radial), 0.96 mm (tangential) and 1.14 mm (axial). These findings demonstrated that use of a ten-layer-DR-CNN with a PET scanner based on a monolithic annulus of scintillator has the potential to produce excellent performance compared to standard analytical methods.
While the performance of most current commercially available PET scanners is sufficient for many standard clinical applications, some specific tasks likely require specialized imaging systems. The ...goal of this project is to explore the capabilities and limitations of a small, high-resolution prototype system for obtaining PET images. The scanner consists of a tandem of detectors. One is a small detector consisting of a 20 × 20 array of 0.7 × 0.7 × mm 3 (pitch 0.8 mm) LYSO elements. The scintillator array is coupled to an array of silicon photomultipliers. The second detector is a 96 × 72 array of 2×2×15 mm 3 (pitch=2.1 mm) LYSO elements coupled to PSPMTs. Separation between the two devices is 180 mm. The detectors are operated in coincidence with each other. Image reconstruction is performed using a limited angle, Maximum Likelihood Expectation Maximization (MLEM) algorithm. Evaluation of the device included measurements of spatial resolution and detection sensitivity as a function of distance. The transaxial radial and tangential spatial resolution of the system ranged from 0.6 mm to 0.9 mm FWHM; axial resolution ranged from 2.7 mm to 4.6 mm FWHM. Detection sensitivity ranged from 0.05 to 0.28%. Spatial resolution and field-of-view vary as a function of distance from the small detector. The tandem detector insert permitted differentiation of the smallest (1 mm diameter) rods in a mini-hot rod phantom. The results indicate that a tandem PET imaging scheme can be potentially employed in applications where high-resolution images over a small region are required.
We describe the design and performance of BRPET, a novel dedicated breast PET (dbPET) scanner designed to maximize visualization of posterior regions of the breast. BRPET uses prone imaging geometry ...and a 12-module detector ring built from pixelated LYSO crystals coupled to position sensitive photomultiplier tubes (PSPMTs). Optical coupling via slanted plastic fiber optic light guides permits partial insertion of the crystals into the exam table’s breast aperture. Image quality testing procedures were adapted from the NEMA NU4-2008 protocol. Two additional phantom tests quantified the posterior extent of the usable volume of view (VoV). BRPET axial, radial, and tangential FWHM spatial resolutions at the isocenter were 1.8, 1.7, and 1.9 mm, respectively. The peak absolute system sensitivity was 0.97% using an energy window of 460–562 keV. The peak noise equivalent counting rate was 5.33 kcps at 21.6 MBq. The scanner VoV extends to within ~6 mm of the plane defining the location of the chest wall. A pilot human study (n = 10) compared the diagnostic performance of FDG-BRPET to that of contrast enhanced MRI (CEMRI), with biopsy as ground truth. Averaged over three expert human observers, the sensitivity/specificity for BRPET was 0.93/1.0, compared to 1.0/0.25 for CEMRI.
A scintillator detector of neutrons and nuclear fragments has been designed, manufactured, and tested on a cosmic-ray stand. The scintillation light is collected with the standard photomultiplier ...(PMT) and six silicon photomultipliers (SiPMs) spaced across the scintillator volume to improve positional sensitivity detector position-sensitive. Data on the detector design and the test results are presented.
The advent of hybrid scanners, combining complementary modalities, has revolutionized the application of advanced imaging technology to clinical practice and biomedical research. In this project, we ...investigated the melding of two complementary, functional imaging methods: positron emission tomography (PET) and electron paramagnetic resonance imaging (EPRI). PET radiotracers can provide important information about cellular parameters, such as glucose metabolism. While EPR probes can provide assessment of tissue microenvironment, measuring oxygenation and pH, for example. Therefore, a combined PET/EPRI scanner promises to provide new insights not attainable with current imagers by simultaneous acquisition of multiple components of tissue microenvironments. To explore the simultaneous acquisition of PET and EPR images, a prototype system was created by combining two existing scanners. Specifically, a silicon photomultiplier (SiPM)-based PET scanner ring designed as a portable scanner was combined with an EPRI scanner designed for the imaging of small animals. The ability of the system to obtain simultaneous images was assessed with a small phantom consisting of four cylinders containing both a PET tracer and EPR spin probe. The resulting images demonstrated the ability to obtain contemporaneous PET and EPR images without cross-modality interference. Given the promising results from this initial investigation, the next step in this project is the construction of the next generation pre-clinical PET/EPRI scanner for multi-parametric assessment of physiologically-important parameters of tissue microenvironments.
Silicon photomultipliers (SiPM) are compact, high amplification light detection devices that have recently been incorporated into magnetic field-compatible positron emission tomography (PET) ...scanners. To take full advantage of these devices, it is preferable to cool them below room temperature. Most current methods are limited to the cooling of individual detector modules, increasing complexity and cost of scanners made-up of a large number of modules. In this work we investigated a new method of cooling, immersion of the detector modules in non-electrically conductive, cooled liquid. A small-scale prototype system was constructed to cool a relatively large area SiPM-based, scintillator detector module by immersing it in a circulating bath of mineral oil. Testing demonstrated that the system rapidly decreased and stabilized the temperature of the device. Operation of the detector illustrated the expected benefits of cooling, with no apparent degradation of performance attributable to immersion in fluid.
•Immersion cooling is new, simple and inexpensive method to cool solid state based nuclear medicine scanner.•Method successfully tested on a scaled version of an SiPM-based PET detector module.•Can be scaled up to cool a complete PET scanner.
Recent advances in the development of silicon photomultipliers (SiPM) offer new opportunities for medical imaging applications. Specifically, novel imaging devices for positron emission (PET) and ...single photo-emission computed tomography (SPECT) are becoming feasible. In this investigation, we tested a monolithic array of new generation SiPMs, an SB-8 array from SensL. 8×8 array of 6-mm square SiPMs was studied with two different multiplexing readouts, 4- and 16-channels. SB-8 detector was coupled to various scintillation arrays and resulting prototypes were evaluated. Testing demonstrated that the new device is capable of resolving 1 mm LYSO and 1.5 mm NaI crystals with 16-channel readout and 1.57 mm LYSO and 3 mm NaI crystals with 4-channel readout. Energy resolution of approximately 15% at 511 keV and 19% at 122 keV were obtained with LYSO and NaI crystals, respectively. A timing resolution of 1.52 ns was measured with 1.57 mm LYSO array and the 16-channel readout. It is concluded that new B-series SiPMs from SensL are suitable for use in high spatial resolution nuclear medicine particle detectors.
Purpose
Application of advanced imaging techniques, such as PET and x ray CT, can potentially improve detection of breast cancer. Unfortunately, both modalities have challenges in the detection of ...some lesions. The combination of the two techniques, however, could potentially lead to an overall improvement in diagnostic breast imaging. The purpose of this investigation is to test the basic performance of a new dedicated breast‐PET/CT.
Methods
The PET component consists of a rotating pair of detectors. Its performance was evaluated using the NEMA NU4‐2008 protocols. The CT component utilizes a pulsed x ray source and flat panel detector mounted on the same gantry as the PET scanner. Its performance was assessed using specialized phantoms. The radiation dose to a breast during CT imaging was explored by the measurement of free‐in‐air kerma and air kerma measured at the center of a 16 cm‐diameter PMMA cylinder. Finally, the combined capabilities of the system were demonstrated by imaging of a micro‐hot‐rod phantom.
Results
Overall, performance of the PET component is comparable to many pre‐clinical and other dedicated breast‐PET scanners. Its spatial resolution is 2.2 mm, 5 mm from the center of the scanner using images created with the single‐sliced‐filtered‐backprojection algorithm. Peak NECR is 24.6 kcps; peak sensitivity is 1.36%; the scatter fraction is 27%. Spatial resolution of the CT scanner is 1.1 lp/mm at 10% MTF. The free‐in‐air kerma is 2.33 mGy, while the PMMA‐air kerma is 1.24 mGy. Finally, combined imaging of a micro‐hot‐rod phantom illustrated the potential utility of the dual‐modality images produced by the system.
Conclusion
The basic performance characteristics of a new dedicated breast‐PET/CT scanner are good, demonstrating that its performance is similar to current dedicated PET and CT scanners. The potential value of this system is the capability to produce combined duality‐modality images that could improve detection of breast disease. The next stage in development of this system is testing with more advanced phantoms and human subjects.
Metabolic imaging techniques can potentially improve detection and diagnosis of cancer in women with radiodense and/or fibrocystic breasts. Our group has previously developed a high-resolution ...positron emission tomography imaging and biopsy device (PEM-PET) to detect and guide the biopsy of suspicious breast lesions. Initial testing revealed that the imaging field-of-view (FOV) of the scanner was smaller than the physical size of the detector's active area, which could hinder sampling of breast areas close to the chest wall. The purpose of this work was to utilize segmented, tapered light guides for optically coupling the scintillator arrays to arrays of position-sensitive photomultipliers to increase both the active FOV and identification of individual scintillator elements. Testing of the new system revealed that the optics of these structures made it possible to discern detector elements from the complete active area of the detector face. In the previous system the top and bottom rows and left and right columns were not identifiable. Additionally, use of the new light guides increased the contrast of individual detector elements by up to 129%. Improved element identification led to a spatial resolution increase by approximately 12%. Due to attenuation of light in the light guides the detector energy resolution decreased from 18.5% to 19.1%. Overall, these improvements should increase the field-of-view and spatial resolution of the dedicated breast-PET system.
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