Oncovision (Spain)

Recent developments in PET instrumentation, including advances in silicon photomultipliers and electronics, are fueling the development of novel PET systems improving flexibility and reducing costs. Among the improvements, ultra-high resolution time-of-flight (TOF) enables the use of limited angle geometry without sacrificing image quality. In this work, we present simulation results for a PET system under development, with ultra-high TOF resolution and depth-of-interaction (DOI). The proposed system is arranged for long axial field-of-view scanning using flat detector panels. We evaluate the performance of the system for varying TOF and DOI resolutions while incorporating geometric corrections during reconstruction. Results demonstrate the promising performance of a 2-panel, 70 ps TOF resolution system with 2.5 mm DOI resolution, as evidenced by traditional and task-based image quality metrics.

Total Body Positron Emission Tomography (TB-PET) scanners provide high-quality images due to the large sensitivity. Our motivation is to design a TB-PET system with up to 70 cm axial coverage that mitigates the parallax error degradation by using a detector concept based on semi-monolithic LYSO crystals. Furthermore, this detector approach allows to simultaneously reach an accurate Coincidence Time Resolution (CTR) to enhance the image quality by means of Time of Flight (TOF) reconstruction algorithms. We have simulated and compared two Positron Emission Tomography (PET) prototypes with about 70 cm but a different number of detector rings (7 vs. 5). The NEMA NU 2 2018 protocol has been implemented. By correcting the parallax error with the Depth of Interaction (DOI) information, the spatial resolution remains homogeneous and below 3 mm in the entire Field of View (FOV), differently from designs based on pixelated crystals. The sensitivity reaches values of 58 and 115 cps/kBq, for the 5 and 7 rings configurations, respectively. The Noise Equivalent Count Rate (NECR) was found at 563 kcps/mL. This value is lower than other systems, most likely due to the requirement to process a larger number of channels to characterize the DOI. Percent contrasts obtained for two different phantoms are in general beyond 80% for the largest spheres, nearly 100% for the 7 rings configuration once TOF is applied during the reconstruction process. In conclusion, although the sensitivity and NECR results for the 5-rings configuration are lower compared to the 7-rings approach, its overall performance is enhanced by the addition of TOF and parallax error correction, improving that of conventional Whole Body PET scanners (axial length: 20 -30 cm) in terms of image quality.

Total-Body Positron Emission Tomography (TB-PET) technology and designs have become very popular in recent years. The advantages of these systems are many, pinpointing the high sensitivity achieved by their long axial FOV and eventually TOF, and the capabilities to simultaneously study the kinetics of multiple organs. Most of TB-PET designs and implementations are based on LYSO crystal pixels without DOI. In this work we present a TB-PET system based on semi-monolithic crystals and, therefore, simultaneously enabling TOF and depth of interaction capabilities. Furthermore, the design named IMAS, makes use of a reduction of signals without compromising performance. We have completed exhaustive simulation studies of the final system geometry, based on 5 rings of 10 cm in the axial direction each, and gaps of about 5 cm, with a total axial length of 71.4 cm. These studies confirm the good performance of the system in terms of spatial resolution, sensitivity and other relevant parameters. Moreover, these days, the full system is being installed at the largest hospital in our region. Very preliminary experimental tests at the lab with the first ring, already predict a spatial resolution of 2.9 mm at the cFOV. We aim to report a full characterization of the scanner during the conference.

A series of small size 22 Na point sources have been simulated using GATE, following the NEMA protocol, and applied to the geometry of a brain dedicated PET so-called MindView. The simulated scanner geometry is currently composed by one ring of 20 detector blocks with a distance of about 330 mm between opposite detectors. Each detector module includes a monolithic LYSO crystal of 50 × 50 × 20 mm 3 and a custom 12 × 12 SiPM array (TSV-type, SensL). The system defines an axial and trans-axial fields of view (FoV) of about 46 mm and 240 mm, respectively. The scintillation light inside the monolithic block was simulated in GEANT4 and is sampled following the readout scheme providing information on each SiPM array row and column (12 + 12). Out of this, three different approaches for the determination of the impact coordinates within the monolithic crystals have been considered. A first approach makes use of the center of gravity (CoG) calculation for the planar XY coordinates but the photon impact depth of interaction (DoI) is not considered. The other methods obtain the XY coordinates using the Raise to Power algorithm (RTP) before CoG calculation, with both discrete (second method) and continuous (third one) DoI information. The data is introduced on the STIR platform for reconstruction using a filtered back projection 3D re-projected algorithm (FBP3DRP). Spatial resolutions ranging in the intervals [2 mm, 3.4 mm], [2.3 mm, 3.3mm] and [2.2 mm, 2.3 mm] have been obtained for the radial, tangential and axial directions, respectively. The points sources were positioned at a radial offset of 100 mm radially out of the center.

To establish an accurate and automatic image segmentation method for extracting the tumor from the healthy tissue using the dedicated 18F-FDG Mammography with Molecular Imaging (MAMMI) Positron Emission Tomography (PET) dynamic images of breast in vivo, the paper presents a novel method using Artificial Neural Network (ANN) combined with time activity curves (TAC) of each voxel as input vector. TACs voxel by voxel were obtained from PET images with average filtering and least-squares fitting algorithm to improve the signal noise ratio (SNR). The data was then normalized and constructed as input feature vectors of the ANN network to train or segment the tumor regions. The initial pilot validation with 2 patient's data of the proposed method using FDG has shown promising results.

Abstract Background: Breast cancer is one of the most common cancers in women. Approximately 232,670 new cases of breast cancer (14% of all new cancer cases) and 40,000 breast cancer deaths (6,8% of all cancer deaths) are expected to occur among US women in 2014. Since 1990, breast cancer death rates have dropped by 34%. Continued progress in the control of breast cancer will require sustained and increased efforts to provide high-quality screening, diagnosis, and treatment Recently, the MAMmography with Molecular Imaging (MAMMI) dedicated breast PET (dbPET) has emerged as an additional imaging tool for breast cancer diagnosis, clarification of complex lesions and therapy follow-up. This study is aimed to determine whether correlations exist between physiological images with 18FDG of pre, post-2-cycles and post Neoadjuvant Chemotherapy, with a predictive value of response. Methods: Twenty-five patients, and three scan points: pre, 2 cycle and post Neoadjuvant Chemotherapy were included in this analysis A prone position high-resolution dedicated breast PET (MAMMI-dbPET) was performed 60 min after administration of 90-120 MBq of 18F-FDG. Maximum standardized uptake value (SUVmax) quantification, volume characterization, positioning in all three space-axes, distances to reference points (proximal breast limit, nipple areola complex) were registered. Results: When treatment was successful, a significant difference was found between pre and post neoadyuvant chemotherapy status and the SUVmax (p < 0.001) of breast tumors. Pre Neoadjuvant (mean SUVmax, 11.4) demonstrated a significantly higher SUVmax than did post 2 cycles tumors (median SUV, 4.7) (p= 0.025). No statistical significant difference was found for SUVmax of post-2 cycles vs. post lesions with a mean SUVmax of 4.7 and 3.9 (p=0.25) respectively. A statistically significant difference was found for volume measurement of pre vs. post-2 cycles vs post Neoadjuvant therapy lesions. A clear qualitative difference by three different observers has been reported among dbPET and MRI volume characterization. A 21% of volume (measurement) discrepancies was found, always with a volume over-estimation by magnetic resonance (structural vs functional imaging). An exquisite -and unexpected- millimetric correlation with post-surgical pathology at the end of neoadjuvant theraphy has been found in dbPET images. Conclusions: dbPET MAMMI has proven to be an excellent tool for quantification, 3D spatial localization and monitoring of neoadjuvant therapy, showing, thanks to its functional nature, earlier and better precision and accuracy than conventional techniques (MRI). Post 2-cycle and Post Neodayuvant Chemotherapy breast cancer tumors consistently display lower 18FDG uptake than pre treatment tumors when treatment is successful. This data suggest that SUVmax measurements of 18FDG-dedicated breast PET can provide valuable information about therapy efficiency. Such an association might be of relevant importance to treatment continuity or adjustement. Citation Format: Michel Herranz, Ines Dominguez, Alvaro Ruibal, Elena Brozos, Sze Yiun Teo, Carmela Rodriguez, Jasper Chaal, Maria Teresa Curiel, Juan Cueva, Beatriz Fernandez, Gabriel G Pavón, Marielle Fortier, Rafael Lopez. Dedicated breast PET (dbPET) a unique functional new tool to accurate quantify response to neoadjuvant therapy in breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-11-11.

SiPMs-based gamma ray detectors have shown a significant development impulse in recent years due to a number of advantages, namely: good time response, small size, magnetic field immunity and low cost. We have designed a special SiPM array formed by 12×12 SiPMs of 3×3 mm2 active area (FB-30035, SensL) that covers a total photosensor area of 5×5 cm2 for gamma ray detection in PET scanners. When thick crystals are considered, pile-up events increase with the scintillation material volume leading to a loss of events and spatial distortions in the image.

The LM-EM algorithm has the advantage to calculate the emission probabilities needed for the reconstruction process on the fly, without the need of a pre-calculated system matrix. The reconstruction time for this algorithm strongly depends on the used backprojector and the available statistics. This algorithm when implemented in systems using monolithic crystals to detect gamma radiation allows one to extensively exploit the virtual pixilation feature, not available for systems based on pixilated crystals. In this work we present a backprojector for LM-EM, the TOR method, which achieves a tradeoff between computational efficiency and image quality. Its temporal subset algorithm optimization (LM-OS) has also been implemented in order to achieve real-time reconstructions. To evaluate the performances of LM-OS algorithm with the TOR method backprojector and only with one iteration on the datasets, studies based on the system spatial resolution, uniformity, and contrast coefficients were carried out and they were compared with those obtained with LM-EM and MLEM algorithms using twelve iteration. Finally, a study on reconstruction time using LM-OS has been performed with breast patients data.

MAMMI is a dedicated breast positron emission tomograph (PET) based on monolythic LYSO crystals, with a transaxial field of view (FOV) of 170 mm. It has been upgraded by adding a second ring of detectors that extends the axial FOV from 40 mm to 94.4 mm, in order to improve its sensitivity and reduce the acquisition time. In this work we present the performance evaluation of the dual ring MAMMI breast PET and a discussion about the contribution of the addition of a second ring of detectors, the compensation of the detector blur and the increase of the scintillator thickness. Experimental measurements suggested on NEMA NU 4-2008 and NEMA NU 2-2007 have been conveniently adapted to the dimensions of the MAMMI. The addition of the second ring of detectors leads to a rise of the sensitivity from 1.8% to 3.6%. The spatial resolution at one-fourth of the axial FOV (1.5 mm axial, 1.6 mm tangential, 1.7 mm radial) is slightly better than that measured at the axial center (1.9 mm axial, 1.8 mm tangential and radial), because of the 14 mm gap in between detection rings. The results obtained after the evaluation reflect a substantial performance improvement, specially in the absolute sensitivity, because of the changes introduced in the MAMMI PET.

In this work we describe a procedure to reduce the number of signals detected by an array of 256 Silicon Photomultipliers (SiPMs) using a resistor network to divide the signal charge into few readout channels. Several configurations were modeled, and the pulsed signal at the readout contacts were simulated. These simulation results were experimentally tested on a specifically designed and manufactured set of printed circuit boards. Three network configurations were modeled. The modeling provided encouraging results for all three configurations. The measurements on the prototypes constructed for this study, however, provided useful position-sensitivity for only one of the network configurations. The lack of input signal amplification into the networks, the SiPM dark current, as well as the complexity of an eight layers board with parasitic capacitances, could have caused the degradation of resolving the impact photon position. This is hard to overcome with external printed circuit boards and components.