Positron Emission Mammography Scanner Research Articles

Simulation of the Positron Emission Mammography system based on the Monte Carlo method by considering the effects of Time Of Flight (TOF) and Depth Of Interaction (DOI)

PEM (Positron Emission Mammography) imaging is a molecular imaging technique for early diagnosis and staging of breast cancer. So, it is very important to check the performance of the PAM device in order to improve the image quality. The aim of this work was to investigate the effects of Time Of Flight (TOF) and Depth Of Interaction (DOI) corrections in the PEM system's performance. For this purpose, the commercially available clinical PEM scanner (PEM Flex Solo II, Naviscan) was simulated using GATE software. This system consists of two non-rotating detector heads that are positioned in an opposing fashion on each side of the body part. Each detector head contains 12 sensitive PMTs with a 6 × 2 array. Also, each PMT is coupled by a light guide to 169 crystals with a 13 × 13 array of 2 mm × 2 mm × 13 mm LYSO crystals. The sensitivity parameter and the scattering fraction of the system were investigated according to the NEMA NU4-2008 standard's manual. Then to assessment the effect of TOF, the coincidence time resolution was changed from 900ps to 100ps. The maximum of NECR curve increases by 42.3% for considering the TOF in the simulation. Also, the Phoswich detector with BGO and LYSO crystals was used to investigate the effect of DOI. The results also show that in Phoswich detector with LYSO crystal with a thickness of 5 mm and BGO crystal with a thickness of 9 mm, the maximum NECR curve increases by 54%. The spatial resolution of the system improves from 2.4 mm to 1 mm by considering TOF and DOI. According to these results, considering the TOF and DOI have a significant role in improving the performance of the PEM system.

A dedicated phantom design for positron emission mammography performance evaluation

A standard protocol for performance evaluation of positron emission mammography (PEM) systems has not yet been established. In this work we propose a methodology based on the design of specific phantoms for this imaging modality with component dimensions in accordance with typical breast lesion sizes together with the adaptation of current international protocols designed for clinical and preclinical positron emission tomographs (PET) systems. This methodology was used to evaluate the performance of the Flex Solo II PEM scanner in terms of spatial resolution, uniformity and contrast lesion detectability, recovery coefficients and spill-over ratios. Positron range effects were studied with 18F and 68Ga, which have very different energy spectra. Our results indicate that in-plane spatial resolution of the system is around 3.0 mm and 4.4 mm for 18F and 68Ga, respectively. Lesion detectability tests with sphere diameters between 4 and 10 mm confirmed that the PEM system can resolve all the spheres (hot or cold). Percent contrast values for 18F lie between 6%–38% and 34%–51% for hot- and cold- spheres, respectively; the corresponding intervals for 68Ga are lower, 4%–25% and 32%–44%. Regarding uniformity quantification, the system shows percentage standard deviations within 4.9%–5.7%, while the percent background variability measurements ranged between 6.7% and 10.9% for both radionuclides. Recovery coefficients measured with hot rod diameters between 1.5 and 9 mm, have values between 0.2–1.05 and 0.17–0.69 for 18F and 68Ga, respectively. Spill-over ratios have large values (0.22 in average) for both radionuclides. Our results indicate that the phantoms and the methodology developed in this work can serve as the basis for establishing an image quality protocol for the systematic evaluation of PEM systems, with a potential extension for performance evaluation of dedicated breastPET scanners.

Simulation and evaluation of high-performance cost-effective positron emission mammography scanner

Breast cancer is the main cause of tumor deaths in women, thus several imaging modalities have been introduced recently to better diagnose the disease. New breast cancer cases were estimated to reach up to 246,660 in 2017, and the mortality rate was above 40,000. Early diagnosis is widely approved as being essential for an effective treatment and it also helps to reduce the incidences and mortality rates. Positron Emission Mammography (PEM) is a breast-dedicated imaging device which uses a pair of annihilation gamma photons to detect abnormalities in the breast tissue. PEM device is compact in nature with a reduced field of view to cover the entire breast region, and it employs few detector modules which makes it cost-efficient. To effectively diagnose breast cancer at a very early stage, a device with high spatial resolution and high sensitivity is required. PEM detectors based on semiconductor materials are characterized by an excellent intrinsic spatial resolution but are not cost-effective, whereas detectors based on scintillator crystals are cost-effective but have limited intrinsic resolution to detect small breast lesions. This study focuses on improving the resolution of scintillator detectors by simulating a PEM scanner employing 1 × 1 × 10 mm3 laser processed scintillator crystal. The simulation was done with a GEANT4 application for emission tomography (GATE) software, and performance evaluation tests were carried out according to the National Electrical Manufacturers Association (NEMA) standards. The scanner geometry has 90 mm transaxial field of view (FOV) and 105 mm axial FOV. Evaluation results showed that the scanner has 10.6% system sensitivity, 1.0 mm spatial resolution at the center of the FOV (CFOV) and at 2.5 cm transaxial direction. The resolution at the axial 2.5 cm position is 2.1 mm. NEMA image quality test and Derenzo phantom study showed that the scanner can easily resolve 1 mm in diameter hot rods.

Image improvement method for positron emission mammography

PurposeTo evaluate in clinical use a rapidly converging, efficient iterative deconvolution algorithm (RSEMD) for improving the quantitative accuracy of previously reconstructed breast images by a commercial positron emission mammography (PEM) scanner. Materials and methodsThe RSEMD method was tested on imaging data from clinical Naviscan Flex Solo II PEM scanner. This method was applied to anthropomorphic like breast phantom data and patient breast images previously reconstructed with Naviscan software to determine improvements in image resolution, signal to noise ratio (SNR) and contrast to noise ratio (CNR). ResultsIn all of the patients’ breast studies the improved images proved to have higher resolution, contrast and lower noise as compared with images reconstructed by conventional methods. In general, the values of CNR reached a plateau at an average of 6 iterations with an average improvement factor of about 2 for post-reconstructed Flex Solo II PEM images. Improvements in image resolution after the application of RSEMD have also been demonstrated. ConclusionsA rapidly converging, iterative deconvolution algorithm with a resolution subsets-based approach (RSEMD) that operates on patient DICOM images has been used for quantitative improvement in breast imaging. The RSEMD method can be applied to PEM images to enhance the resolution and contrast in cancer diagnosis to monitor the tumor progression at the earliest stages.

Simulation and evaluation of a high resolution VIP PEM system with a dedicated LM-OSEM algorithm

Over the last two decades there have been a growing number of designs for positron emission tomography (PET) cameras optimized to image the breast. These devices, commonly known as positron emission mammography (PEM) cameras allow much more spatial resolution by putting the photon detectors directly on the breast. PEM cameras have a compact geometry with a restricted field of view (FOV)thus exhibiting higher performance and lower cost than large whole body PET scanners. Typical PEM designs are based on scintillators such as bismuth germanate (BGO), lutetium oxorthosilicate (LSO) orlutetium yttrium orthosicilate (LYSO), and characterized by large parallax error due to deficiency of thedepth of interaction (DOI) information from crystals. In the case of parallel geometry PEM,large parallax error results in poor image resolution along the vertical axis.In the framework of the Voxel Imaging PET (VIP) pathfinder project,we propose a high resolution PEM scanner based on pixelated solid-state CdTe detectors. The pixel PEM device with a millimeter-size pixel pitch provides an excellent spatial resolution inall directions 8 times better than standard commercial devices with a point spread function (PSF) of 1 mm full width at halfmaximum (FWHM) and excellent energy resolution of down to 1.6% FWHM at 511 keV photons at room temperature. The system is capable to detect down to 1 mm diameter hot spheres in warm background.

Modeling and simulation of Positron Emission Mammography (PEM) based on double-sided CdTe strip detectors

Breast cancer is the most common leading cause of cancer death among women. Positron Emission Tomography (PET) Mammography, also known as Positron Emission Mammography (PEM), is a method for imaging primary breast cancer. Over the past few years, PEMs based on scintillation crystals dramatically increased their importance in diagnosis and treatment of early stage breast cancer. However, these detectors have significant limitations like poor energy resolution resulting with false-negative result (missed cancer), and false-positive result which leads to suspecting cancer and suggests an unnecessary biopsy.In this work, a PEM scanner based on CdTe strip detectors is simulated via the Monte Carlo method and evaluated in terms of its spatial resolution, sensitivity, and image quality. The spatial resolution is found to be ∼ 1 mm in all three directions. The results also show that CdTe strip detectors based PEM scanner can produce high resolution images for early diagnosis of breast cancer.

Performance comparison of dual-head PEM scanner by Monte Carlo simulation

To evaluate the effects of the flat panel dimension on the overall performance qualitatively and quantitatively, the performance of two dual-head Positron Emission Mammography (PEM) cameras with different configurations, the 3×3 modules system and the 1×3 modules system, has been compared, using Monte Carlo simulation based on the Geant4 Application for Tomographic Emission (GATE) open source software. Besides traditional evaluation methods, imaging capability in terms of spatial resolution and lesion detectability have been integrated into the evaluation. Compared with the 3×3 modules system, the 1×3 modules system produces higher spatial resolution along the direction of the 1-module side but lower resolution along the other direction. No significant difference in small and weak lesion visualization has been noted between two systems. In addition, the slight disadvantage in semi-quantification of the 1×3 modules system can be further compensated by other methods such as increasing the imaging time while still in a practically acceptable range.

Analytical Study of the Effect of the System Geometry on Photon Sensitivity and Depth of Interaction of Positron Emission Mammography

Positron emission mammography (PEM) cameras are novel-dedicated PET systems optimized to image the breast. For these cameras it is essential to achieve an optimum trade-off between sensitivity and spatial resolution and therefore the main challenge for the novel cameras is to improve the sensitivity without degrading the spatial resolution. We carry out an analytical study of the effect of the different detector geometries on the photon sensitivity and the angle of incidence of the detected photons which is related to the DOI effect and therefore to the intrinsic spatial resolution. To this end, dual head detectors were compared to box and different polygon-detector configurations. Our results showed that higher sensitivity and uniformity were found for box and polygon-detector configurations compared to dual-head cameras. Thus, the optimal configuration in terms of sensitivity is a PEM scanner based on a polygon of twelve (dodecagon) or more detectors. We have shown that this configuration is clearly superior to dual-head detectors and slightly higher than box, octagon, and hexagon detectors. Nevertheless, DOI effects are increased for this configuration compared to dual head and box scanners and therefore an accurate compensation for this effect is required.

Evaluation of the quantitative accuracy of a commercially available positron emission mammography scanner

The PEM Flex Solo II (Naviscan, Inc., San Diego, CA) is currently the only commercially available positron emission mammography (PEM) scanner. This scanner does not apply corrections for count rate effects, attenuation, or scatter during image reconstruction, potentially affecting the quantitative accuracy of images. The aim of this work is to measure the overall quantitative accuracy of the PEM Flex system and to determine the individual contributions of error from count rate effects, attenuation, and scatter. Gelatin phantoms were designed to simulate breasts of different thicknesses (4-12 cm) with varying uniform background activity concentration (AC) (0.007-0.5 microCi/cc), cysts, and lesions (2:1, 5:1, and 10:1 lesion-to-background ratios). The overall error was calculated from ROI measurements in the phantoms with a clinically relevant background AC (0.065 microCi/cc). The error due to count rate effects was determined by comparing the overall error at multiple background AC to the error at a very low background AC (0.007 microCi/cc) where count rate effects are considered negligible. A point source and cold gelatin phantoms of different thicknesses were used to assess the errors due to attenuation and scatter. The maximum pixel values of the point source in gelatin and in air were compared to determine the effect of attenuation, while scatter was evaluated by comparing the sum of all pixel values in gelatin and in air. The AC in the uniform background was underestimated in phantoms of all thicknesses, with the exception of the 4-cm-thick phantoms in which the measured AC was within +/- 7% of the true value (0.065 microCi/cc). The degree of underestimation in the uniform background increased with the phantom thickness, up to 34% +/- 6% in the 12 cm phantoms. The AC in all lesions was underestimated by more than that measured in the background (22% for the 2:1 lesions in the 4 cm phantom) and this underestimation increased with increasing thickness and lesion-to-background ratio (85% for the 10:1 lesions in the 12 cm phantoms). The error due to count rate effects reduced the measured AC with respect to its true value. This error increased with increasing background AC (23% +/- 6% at 0.065 microCi/cc to 85% +/- 1% at 0.5 microCi/cc for the 4 cm phantoms) and decreased with increasing phantom thickness (23% +/- 6% for the 4-cm-thick phantoms to 7% +/- 7% for the 12-cm-thick phantoms at 0.065 microCi/cc). Attenuation was a substantial source of error and reduced the measured AC by 51% +/- 10%-77% +/- 4% in the 4-12 cm phantoms, respectively. Scatter increased the total signal measured in images by a relatively constant amount (23% +/- 9%) for all thicknesses. Applying corrections for count rate effects, attenuation, and scatter will be essential for the PEM Flex Solo II to be able to produce quantitatively accurate images.

The ClearPEM breast imaging scanner

We present results on the characterization of the ClearPEM breast imaging scanner. ClearPEM is a dual-head positron emission mammography scanner using APD-based detector modules that are capable of measuring the depth-of-interaction (DOI) with a resolution of 2 mm in LYSO:Ce crystals. The full system comprises 192 detector modules with a total of 6144 LYSO:Ce crystals and 384 32-pixel APD arrays read out by ASICs with 192 input channels. The scanner includes front-end and data acquisition electronics and a robotic gantry for detector placement and rotation. The software implements calibration (energy, time and DOI), normalization and image reconstruction algorithms. In this conference, the scanner main technical characteristics, the calibration strategies and the spectrometric performance in clinical environment were presented as well as the images obtained with point sources and with a microDerenzo phantom. The image resolution was found to be of the order of 1.3 mm FWHM (center of field-of-view) and the DOI capability has shown to have a strong impact on the image sharpness. An assessment of the first clinical experience was also presented at the conference.

WE-A-201B-01: Evaluation of Quantitative Error of a Commercially-Available Positron Emission Mammography Scanner

Purpose: To evaluate the overall quantitative accuracy of, the PEM Flex Solo II (Naviscan Inc., San Diego, CA) positron emission mammographyscanner, and to assess the relative contributions of error from attenuation, scatteredphotons and count‐rate. Method and Materials: The overall error was measured in 4, 6, 8, 10 and 12‐cm thick breast phantoms with uniform background activity (0.07 μCi/cc), simulated lesions (2:1, 5:1 and 10:1 lesion‐to‐background ratios) and cysts. The effect of count‐rate was determined by comparing the overall error to the error at lower background activity concentration (0.007 μCi/cc) for each thickness. The error due to attenuation was measured for each thickness by comparing the maximum pixel values in a point source embedded in non‐radioactive gelatin to the maximum pixel value of the same point source scanned in air. The error due to scatter was determined by comparing the sum of all pixel values in the image volume of the point source in each thickness of gelatin to the sum of all pixel values from the point source in air. Results: The overall background error in 4 to 12‐cm thick phantoms was 0%±7% to −32%±7%, respectively. The minimum error in lesions was −24%±4% for 2:1 lesion‐to‐background ratio in 4‐cm thick phantoms, and increased with phantom thickness and lesion‐to‐background ratio. The error contributed by count‐rate was approximately −24%±9% for 4 to 8‐cm thicknesses, −30%±6% for 10‐cm and −8%±8% for 12‐cm. Attenuation contributed −51%±10% to −77%±5% for 4 to 12‐cm thicknesses, respectively. Scatter contributed 23%±2% for all thicknesses. Conclusion:Images from the PEM Flex Solo II cannot be used for accurate quantitation due in part to the lack of corrections for count‐rate, attenuation and scatter. Even with these corrections, limited angle tomography will be an obstacle to achieving accurate quantitation.

Performance Evaluation of a PEM Scanner Using the NEMA NU 4—2008 Small Animal PET Standards

The recently published NEMA NU 4-2008 Standards has been specially designed for evaluating the performance of small animal PET scanners used in preclinical applications. In this paper, we report on the NU 4 performance of a clinical positron emission mammography (PEM) system. Since there are no PEM specific performance test protocols available, and the NU 2 protocol (intended for whole-body PET scanners) cannot be applied without modification due to the compact design of the PEM scanner, we decided to evaluate the NU 4 Standards as an alternative. We obtained the following results: Trans-axial spatial resolution 1.8 mm FWHM for high resolution reconstruction mode and 2.4 mm FWHM for standard resolution reconstruction mode with no significant variation within the field of view. The total system sensitivity was 0.16 cps/Bq. In image quality testing, the uniformity was found to be 3.9% STD at the standard resolution mode and 5.6% at the high resolution mode when measured with a 34 mm paddle separation. The NEMA NU 4-2008 Standards were found to be a practicable tool to evaluate the performance of the PEM scanner after some modifications to address the specifics of its detector configuration. Furthermore, the PEM scanner's in-plane spatial resolution was comparable to other small animal PET scanners with good image quality.

Preliminary simulation studies on a cylindrical PEM scanner using GATE

In this paper, we investigate the performance of a cylindrical positron emission mammography (PEM) by simulation, in order to estimate its feasibility before implementation. A well-developed simulation package, Geant4 Application for Tomographic Emission (GATE), is used to simulate the scanner geometry and physical processes. The simulated PEM scanner is composed of 64 blocks axially arranged in 4 rings with an axial field-of-view (AFOV) of 12.8 cm and 16.6 cm in diameter. For each block, there is a 16×16 array of 2 mm×2 mm×15 mm lutetium yttrium oxyorthosilicate (LYSO) crystals. In the simulated measurements, the spatial resolution is at the center of the FOV of 1.73±0.07 mm (radial) and 1.81±0.08 mm (tangential), but of 4.83±0.09 mm (radial) and 4.37±0.07 mm (tangential) while 5 cm off the center. The central point source sensitivity (ACS) is 4.04% (1.50 Mcps/mCi) at an energy window of 350–650 keV. Moreover, the capillary and cylindrical sources are simulated coupled to breast phantoms for the scatter fraction (SF) and Noise Equivalent Count Rate (NECR) test. For a breast phantom with a 350–650 keV energy window, SF may reach the highest 32.95%, while NECR is degraded down to the lowest 255.71 kcps/mCi. Finally, we model a breast phantom embedded with two spheres of different activities. The reconstructed image gives good results despite a bit of difference in image contrast. Further, the image quality will be improved by scatter and random correction. All these test results indicate the feasibility of this PEM system for breast cancer detection.

SU-FF-J-25: Quality Control Procedure for the PET-Guided Interventions

Objectives: Positron Emission Mammography (PEM) with F18-FDG has been useful in breast cancer diagnosis and characterization [1]. Clinical PEM scanners produce high resolution (2mm) PET images of immobilized breasts in 5–10 minutes. This allows the PEM scanner to guide breast interventions, with the help of a localization accessory including software for procedure planning and hardware for needle support. We report the development of a quality control procedure to test the performance of the accessory in a clinical setting on a daily basis. Materials and Methods: A quality control procedure was designed to evaluate the functionality of the Stereo Navigator accessory to the PEM Flex PET Scanner (Naviscan PET Systems, Inc., San Diego, CA). During the procedure, 1 microCurie point source was placed in the field of view of the PEM scanner. PEM scan of the point source was performed. The software was used to select the point source as a target and guide a radioactive rod containing 0.1 microCurie/cm of Germanium-68 toward the source. A distance of less than 5mm from the tip of the rod to the point source was considered acceptable. A second PEM image was acquired, and regions of interest were used to verify the activities of the sources. To test the validity of the procedure, failures were introduced such as incompatible hardware/software and incorrect calibration rod activity. Time to perform the procedure was recorded. Results: The procedure detects clinically-relevant failures and can be performed by a trained user in less than 5 minutes. Conclusions: The quality control procedure for the localization accessory to the PEM scanner can be performed in clinically acceptable time.

The Clear-PEM Electronics System

The Clear-PEM detector system is a compact positron emission mammography scanner with about 12000 channels aiming at high sensitivity and good spatial resolution. Front-end, Trigger, and Data Acquisition electronics are crucial components of this system. The on-detector front-end is implemented as a data-driven synchronous system that identifies and selects the analog signals whose energy is above a predefined threshold. The off-detector trigger logic uses digitized front-end data streams to compute pulse amplitudes and timing. Based on this information it generates a coincidence trigger signal that is used to initiate the conditioning and transfer of the relevant data to the data acquisition computer. To minimize dead-time, the data acquisition electronics makes extensive use of pipeline processing structures and derandomizer memories with multievent capacity. The system operates at 100-MHz clock frequency, and is capable of sustaining a data acquisition rate of 1 million events per second with an efficiency above 95%, at a total single photon background rate of 10 MHz. The basic component of the front-end system is a low-noise amplifier-multiplexer chip presently under development. The off-detector system is designed around a dual-bus crate backplane for fast intercommunication between the system boards. The trigger and data acquisition logic is implemented in large FPGAs with 4 million gates. Monte Carlo simulation results evaluating the trigger performance, as well as results of hardware simulations are presented, showing the correctness of the design and the implementation approach

Performance Simulation Studies of the Clear-PEM DAQ/Trigger System

The Clear-PEM detector is a positron emission mammography scanner based on a high-granularity avalanche photodiode readout with 12 288 channels. The front-end sub-system is instrumented with low-noise 192:2 channel amplifier-multiplexer ASICs and free-running sampling ADCs. The off-detector trigger, implemented in a FPGA based architecture, computes the pulses amplitude and timing required for coincidence validation from the front-end data streams. A high-level C++ simulation tool was developed for data acquisition performance analysis and validated at bit-level against FPGA VHDL testbenches. In this work, simulation studies concerning the performance of the on-line/off-line energy and time extraction algorithms and the foreseen detector energy and time resolution are presented. Time calibration and trigger efficiency are also discussed

Pilot clinical trial of 18F-fluorodeoxyglucose positron-emission mammography in the surgical management of breast cancer

Background High-resolution positron-emission mammography (PEM) is a new device, which allows the imaging of breast tissue. A prospective study was performed to assess the accuracy of PEM in newly diagnosed breast cancer patients. Methods In a prospective multicenter study, 44 women with confirmed breast cancers were imaged with a high-resolution PEM scanner (Naviscan PET Systems, Rockville, MD) with 18F-fluorodeoxyglucose. The images were blindly evaluated and were compared with final pathology. Results The majority of the index lesions were seen on PEM (89%, 39/44). PEM detected 4 of 5 incidental breast cancers, 3 of which were not seen by any other imaging modalities. Of 19 patients undergoing breast-conserving surgery, PEM correctly predicted 6 of 8 (75%) patients with positive margins and 100% (11/11) with negative margins. Conclusion The current PEM device shows promise in detecting breast malignancies and may assist in the planning of adequate partial mastectomy procedures to better ensure negative margins.

Development of a positron emission mammography scanner for breast cancer detection

Positron Emission Mammography(PEM) is a relatively new nuclear medicine imaging technique for the detection and staging of breast cancer.PEM tries to overcome the limitations of existing whole body clinical PETscanners by means of a breast-dedicated design. We have designed a novel PEMscanner prototype, called YAP-PEM, based on a pair of opposing detector heads made up of a 6 cm ×6 cm YAP:Ce scintillation matrix and position sensitive photo-detectors. This thesis work is dedicated to the detector development for the construction of the PEMscanner. The utilization of three different types of PSPMT have been evaluated: the R8520-00-C12, the well known R2486 and a very early version of the new H8500 “Flat Panel” PSPMT, all from Hamamatsu. These tubes have been fully characterized in terms of their imaging performance in the identification of small scintillation pixels. The H8500 confirmed the good expected performance and represents a noticeable advance in position sensitive photo-detection, in particular for its shape and size, that allows it to be tiled over large areas, as demanded by current and future application. The adopted final solution is based on an array of position sensitive PMTs, model R8520-00-C12, because of the size of the used YAP:Ce matrix that better fits with this solution. A complete signal processing and acquisition platform has been also developed for the utilization of an array of nine of these PS-PMTs. The first detector head composed of the YAP:Ce matrix and nine R8520 has been assembled, optimized and characterized. In the thesis the calibration procedures and evaluation results for the chosen detector solution for the PEM system are described. The work is completed by a full Monte Carlo simulation. Various parameters have been considered here; in particular the acquisition geometry and the tumor size. The Monte Carlo simulation on YAP-PEM indicates that our system could be able to detect very small tumors, down to 5 mm in diameter for a tumor-to-background uptake ratio of 10:1. An experimental study on a dual head system, based on the small animal YAP-(S)PET scanner, has been simulated, so as to validate the Monte Carlo code. The results obtained support that the YAP-PEM scanner under development could be a valuable tool for breast cancer investigation, showing excellent performance, similar or better than that of other existing (or in development) Positron Emission Mammography systems.

Detector development for a novel Positron Emission Mammography scanner based on YAP:Ce crystals

A prototype for positron emission mammography is under development within a collaboration of the Departments of Physics of Pisa and Ferrara. The device will be composed of two opposing detectors (parallel plane geometry). The active part of the detector head is constituted by a matrix of scintillators with a small pixel size (2×2 mm 2). We have evaluated the possibility to use an array of Position Sensitive PhotoMultiplier Tube (PSPMT mod R8520-C12 from Hamamatsu) for the readout of the scintillation matrix. Two different crystal-PMT coupling techniques have been explored: the results for each method are reported in this work. The overall performance, in terms of efficiency and pixel identification of the final prototype of the detector head are also presented. For future applications the new H8500 (also called the ‘flat panel’ PMT) has been studied and compared to the R8520 in terms of the imaging performance and other considerations such as cost and geometry. The imaging performance of these tubes is characterized in terms of the pixel image resolution and the peak-to-valley ratio.

Image properties of list-mode likelihood reconstruction for a rectangular positron emission mammograph with DOI measurements

A positron emission mammography scanner is under development at our Laboratory. The tomograph has a rectangular geometry consisting of four banks of detector modules. For each detector, the system can measure the depth of interaction information inside the crystal. The rectangular geometry leads to irregular radial and angular sampling and spatially variant sensitivity that are different from conventional PET systems. Therefore, it is of importance to study the image properties of the reconstructions. We adapted the theoretical analysis that we had developed for conventional PET systems to the list mode likelihood reconstruction for this tomograph. The local impulse response and covariance of the reconstruction can be easily computed using FFT. These theoretical results are also used with computer observer models to compute the signal-to-noise ratio for lesion detection. The analysis reveals the spatially variant resolution and noise properties of the list mode likelihood reconstruction. The theoretical predictions are in good agreement with Monte Carlo results.