Positron Emission Mammography System Research Articles

Crystal scatter effects in a large-area dual-panel Positron Emission Mammography system.

Positron Emission Mammography (PEM) is a valuable molecular imaging technique for breast studies using pharmaceuticals labeled with positron emitters and dual-panel detectors. PEM scanners normally use large scintillation crystals coupled to sensitive photodetectors. Multiple interactions of the 511 keV annihilation photons in the crystals can result in event mispositioning leading to a negative impact in radiopharmaceutical uptake quantification. In this work, we report the study of crystal scatter effects of a large-area dual-panel PEM system designed with either monolithic or pixelated lutetium yttrium orthosilicate (LYSO) crystals using the Monte Carlo simulation platform GATE. The results show that only a relatively small fraction of coincidences (~20%) arise from events where both coincidence photons undergo single interactions (mostly through photoelectric absorption) in the crystals. Most of the coincidences are events where at least one of the annihilation photons undergoes a chain of Compton scatterings: approximately 79% end up in photoelectric absorption while the rest (<1%) escape the detector. Mean positioning errors, calculated as the distance between first hit and energy weighted (assigned) positions of interaction, were 1.70 mm and 1.92 mm for the monolithic and pixelated crystals, respectively. Reconstructed spatial resolution quantification with a miniDerenzo phantom and a list mode iterative reconstruction algorithm shows that, for both crystal types, 2 mm diameter hot rods were resolved, indicating a relatively small effect in spatial resolution. A drastic reduction in peak-to-valley ratios for the same hot-rod diameters was observed, up to a factor of 14 for the monolithic crystals and 7.5 for the pixelated ones.

Abstract P2-09-01: An Emerging Technology for Breast Cancer Detection - Preliminary Data of Breast Cancer Detection using Novel Low Dose Positron Emission Mammography

Abstract Purpose: To investigate the feasibility of low-dose Positron Emission Mammography (PEM) to identify breast cancer. Materials and Methods: In an REB-approved ongoing clinical trial, which started in December 2019, all newly diagnosed women with breast cancer who had not undergone neoadjuvant chemotherapy and consented to the study were randomly assigned independently of their mammographic breast density, tumor size, and histopathology cancer subtype to perform PEM using a novel organ-targeted PET system(Radialis PET Imager, Radialis Inc., FDA cleared to image and measure the distribution of injected positron-emitting radiopharmaceuticals) with either 1mCi, 2mCi or 5 mCi of 18F-FDG. The PEM images acquired 1 and 4 hours after 18F-FDG administration were reviewed in consensus by two fellowship-trained breast radiologists blinded to cancer location. PEM imaging features of known malignancies and additional PEM findings were recorded and correlated with histopathology as the ground truth. Results: Our cohort comprised 22 women with a median age of 51 years (range 32-85) with 88 completed bilateral sets of images where 23 cancers (18 invasives, and 5 in situ) were present. The median invasive cancer size on surgical pathology was 28 mm (range: 3-120). Out of 18 invasive cancers, the only PEM images that did not visualize cancer (2 invasive lobular cancers and 2 in-situ cancers) were acquired with the lowest dose of 18F-FDG (1 mCi). A total of 6 (27.3%) subjects received 1mCi 18F-FDG with 5 invasive cancers, 7 (31.8%) of patients received 5 mCi 18F-FDG with 7 invasive cancers, and 9 (40.9%) of patients received 5 mCi 18F-FDG with 6 invasive cancers. A total of 3 false-positive images of benign findings were also present. No additional cancers were identified exclusively by PEM. The PEM performance was similar following an additional 3-hour interval for radiotracer uptake. Conclusion: This preliminary data results show the feasibility of invasive breast cancer detection with a decreased 18F-FDG dose, possibly due to the novel PEM system detectors increasing the sensitivity to radiotracer and the perceived spatial resolution by the visual assessment. Larger-scale clinical trials are required to consolidate our preliminary findings. Clinical Relevance: A novel organ-targeted PET system enables the detection of invasive breast cancer using low-dose PEM, potentially emerging as a promising novel imaging tool. Citation Format: Vivianne Freitas, Michael L. Waterston, Ken O. Olsen, Oleksandr Bubon, Shayna Parker, Brandon Baldassi, Borys Komarov, Samira Taeb, Alla Reznik. An Emerging Technology for Breast Cancer Detection - Preliminary Data of Breast Cancer Detection using Novel Low Dose Positron Emission Mammography [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-09-01.

DH-Mammo PET: a dual-head positron emission mammography system for breast imaging

Objective. To develop a simultaneous positron emission tomography-Optical (OPET) breast imaging dual-head PET subsystem, called DH-Mammo PET, for accurate, early diagnosis and efficacy assessment of breast cancer with high resolution and sensitivity. Approach. We developed a breast-dedicated PET based on LYSO crystal, silicon photomultiplier array and multi-voltage threshold sampling technique. It consists of two detector heads, each with a detection area of 216 mm × 145.5 mm. The distance between the detector heads is fixed at 120 mm. In order to extract coincidences and correct data, GPU-based software coincidence processing, random, scatter, normalization, gap-filling and attenuation corrections were applied in turn. The images were reconstructed using maximum likelihood expectation maximization with depth of interaction (DOI) modeling. The performance of DH-Mammo PET was evaluated referring to NEMA NU 4–2008, NU 2–2007 and Chinese industry recommended standard YY/T 1835–2022. Besides, several clinical patient images of DH-Mammo PET were compared with those of a whole-body PET/CT. Main results. The energy resolution was 14.5%, and time resolution was < 1.31 ns. Indicated by the 22Na point source imaging, its spatial resolution was 2.60 mm (5.40 mm), 1.00 mm (1.04 mm), and 0.96 mm (0.93 mm) in the X, Y and Z directions, respectively, using the system response matrix with (without) DOI modeling. Indicated by the Derenzo phantom imaging, the spatial resolution was ∼3.0 mm, <1.2 mm, and <1.2 mm in the X, Y and Z directions. The system sensitivity was 6.87%, 4.89% and 3.37% with an energy window of 100–800, 250–750 and 350–650 keV, respectively. The scatter fraction was 26.43%, and the peak NECR was 162.6 kcps at 24.1 MBq for the modified rat-like phantom. As for the recovery coefficients, they ranged from 0.15 to 1.04 for rods between 1 and 5 mm obtained with a NEMA image quality phantom. The spill-over ratio for the air-filled and water-filled chamber was 0.05 and 0.11, respectively. DH-Mammo PET can provide more image details in clinical experiments and fulfil a fast scan with 60–120 s acquisition time. Significance. Good spatial resolution and high sensitivity of DH-Mammo PET would enable fast and accurate PET imaging of the breast. Besides, combining the DH-Mammo PET with the diffuse optical tomography would make full use of tumor metabolic imaging and tissue endogenous optical imaging, which would improve the accuracy of early clinical diagnosis of small lesions of breast cancers.

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.

Development of a mechatronic guidance system for targeted ultrasound-guided biopsy under high-resolution positron emission mammography localization.

Image-guided needle biopsy of small, detectable lesions is crucial for early-stage diagnosis, treatment planning, and management of breast cancer. High-resolution positron emission mammography (PEM) is a dedicated functional imaging modality that can detect breast cancer independent of breast tissue density, but anatomical context and real-time needle visualization are not yet available to guide biopsy. We propose a mechatronic guidance system integrating an ultrasound (US)-guided core-needle biopsy (CNB) with high-resolution PEM localization to improve the spatial sampling of breast lesions. This paper presents the benchtop testing and phantom studies to evaluate the accuracy of the system and its constituent components for targeted PEM-US-guided biopsy under simulated high-resolution PEM localization. A mechatronic guidance system was developed to operate with the Radialis PEM system and a conventional US system. The system includes a user-operated guidance arm and end-effector biopsy device, integrating a US transducer and CNB gun, with its needle focused on a remote center of motion (RCM). Custom software modules were developed to track, display, and guide the end-effector biopsy device. Registration of the mechatronic guidance system to a simulated PEM detector plate was performed using a landmark-based method. Testing was performed with fiducials positioned in the peripheral and central regions of the simulated detector plate and registration error was quantified. Breast phantom experiments were performed under ideal detection and localization to evaluate for bias in the end-effector biopsy device. The accuracy of the complete mechatronic guidance system to perform targeted breast biopsy was assessed using breast phantoms with simulated lesions. Three-dimensional positioning error was quantified, and principal component analysis assessed for directional trends in 3D space within 95% prediction intervals. Targeted breast biopsies with test phantoms were performed and an overall in-plane needle targeting error was quantified. The mean registration errors were 0.63mm (N=44) and 0.73mm (N=72) in the peripheral and central regions of the simulated PEM detector plate, respectively. A 3D 95% prediction ellipsoid shows an error volume <2.0mm in diameter, centered on the mean registration error. Under ideal detection and localization, targets <1.0mm in diameter can be sampled with 95% confidence. The complete mechatronic guidance system was able to successfully spatially sample simulated breast lesions, 4mm and 6mm in diameter and height (N=20) in known 3D positions in the PEM image coordinate space. The 3D positioning error was 0.85mm (N=20) with 0.64mm in-plane and 0.44mm cross-plane component errors. Targeted breast biopsies resulted in a mean in-plane needle targeting error of 1.08mm (N=15) allowing for targets 1.32mm in radius to be sampled with 95% confidence. We demonstrated the utility of our mechatronic guidance system for targeted breast biopsy under high-resolution PEM localization. Breast phantom studies showed the ability to accurately guide, position, and target breast lesions with the accuracy to spatially sample targets <3.0mm in diameter with 95% confidence. Future work will integrate the developed system with the Radialis PEM system toward combined PEM-US-guided breast biopsy.

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.

Development of an angled Si-PM-based detector unit for positron emission mammography (PEM) system

Positron emission mammography (PEM) systems have higher sensitivity than clinical whole body PET systems because they have a smaller ring diameter. However, the spatial resolution of PEM systems is not high enough to detect early stage breast cancer. To solve this problem, we developed a silicon photomultiplier (Si-PM) based detector unit for the development of a PEM system. Since a Si-PM's channel is small, Si-PM can resolve small scintillator pixels to improve the spatial resolution. Also Si-PM based detectors have inherently high timing resolution and are able to reduce the random coincidence events by reducing the time window. We used 1.5×1.9×15mm LGSO scintillation pixels and arranged them in an 8×24 matrix to form scintillator blocks. Four scintillator blocks were optically coupled to Si-PM arrays with an angled light guide to form a detector unit. Since the light guide has angles of 5.625°, we can arrange 64 scintillator blocks in a nearly circular shape (a regular 64-sided polygon) using 16 detector units. We clearly resolved the pixels of the scintillator blocks in a 2-dimensional position histogram where the averages of the peak-to-valley ratios (P/Vs) were 3.7±0.3 and 5.7±0.8 in the transverse and axial directions, respectively. The average energy resolution was 14.2±2.1% full-width at half-maximum (FWHM). By including the temperature dependent gain control electronics, the photo-peak channel shifts were controlled within ±1.5% with the temperature from 23°C to 28°C. With these results, in addition to the potential high timing performance of Si-PM based detectors, our developed detector unit is promising for the development of a high-resolution PEM system.

Performance Evaluation and Initial Clinical Test of the Positron Emission Mammography System (PEMi)

A new polygon positron emission mammography imaging system (PEMi) was developed in 2009 by the Institute of High Energy Physics, Chinese Academy of Sciences. PEMi is constructed in a polygon structure with lutetium yttrium orthosilicate crystal arrays mounted on a position-sensitive photomultiplier. The system consists of 64 blocks and each block is arranged in $16 \times 16$ crystal arrays with a pixel size of $1.9~\times 1.9~ \times 15$ mm. The diameter of the detector ring is 166 mm, and the axial length is 128 mm. The transaxial field of view of PEMi is 110 mm. The goal of the initial study was to test PEMi’s performance and the clinical imaging ability with a small group of selected subjects. The detectors have a measured intrinsic spatial resolution averaging 1.67 mm. The axial and tangential resolution remained under 2.5-mm full width at half maximum within the central 5-cm diameter of the field of view. The hot rods with a diameter of 1.7 mm can be clearly identified, and the structure of the region containing 1.35-mm diameter rods can also be observed. Using a 6-ns coincidence timing window and a ${\hbox {360}} \sim {\hbox {660}}$ -keV energy window, the peak sensitivity of the tomograph is 6.88%. The noise-equivalent count rate peak is 110 $\thinspace$ 766 cps for a breast-like cylindrical phantom of 100 mm in diameter at an activity concentration of $0.03~\hbox{MBq}/{\rm cc}$ . The recovery coefficients ranged from 0.21 to 0.85 for rods between 1 mm and 5 mm in the image-quality phantom. The reconstructed image resolution achieved an improvement compared with whole-body positron emission tomography (PET), which might reduce the lower threshold on detectable lesion size. Example patient images demonstrate that PEMi is clinically feasible. And more detailed structure information was obtained with PEMi than with the whole-body PET imaging.

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.

Sci-Fri AM: Imaging - 02: High resolution detectors for PET mammography.

With high specificity for malignant breast lesions, dedicated-breast molecular imaging systems such as positron emission mammography (PEM) have potential to improve the sensitivity of cancer in women with radio-dense breasts and to reduce the false-positive rate of breast screening when used as a diagnostic adjunct. For high signal-to-noise ratio and to minimize the patient dose, scintillation detectors in a PEM system must have high annihilation photon detection efficiency. This efficiency can be increased by accepting annihilation photons from wider incident angles and by using depth-of-interaction (DOI) measurement within a scintillation crystal to minimize parallax blurring. We have developed a dual-ended readout block (DERB) detector that uses asymmetry of signals from photodetectors on either end of a scintillation array to measure DOI and uses Anger Logic with light sharing to identify interacting crystal elements while minimizing the number of photodetectors required. A prototype DERB detector was constructed from two arrays of silicon photomultipliers (SiPM), two glass optical diffusers, and an array of LYSO scintillation crystals. Assembled, each of the 2 × 2 SiPM arrays detect photons that are dispersed via the optical light diffusers originating from either end of 3 × 3 scintillation crystal elements. We evaluated the ability of the detector to identify the crystal index, resolve DOI, and discriminate energy. The DERB detector was able to clearly identify interacting crystal elements, to measure DOI with ̃5mm resolution in 2mm × 2mm × 20mm crystals, and to achieve an average energy resolution of ̃20%. The DERB detector characteristics suggest that it can be used to reduce the parallax effect in PEM systems without increasing the number of required photodetectors. Further investigation is warranted to improve performance with high optical photon detection efficiency photodetectors.

Investigating the limit of detectability of a positron emission mammography device: a phantom study.

A new positron emission mammography (PEM) device (PEM Flex Solo II, Naviscan Inc., San Diego, CA) has recently been introduced and its performance characteristics have been documented. However, no systematic assessment of its limit of detectability has been evaluated. The aim of this work is to investigate the limit of detectability of this new PEM system using a novel, customized breast phantom. Two sets of F-18 infused gelatin breast phantoms of varying thicknesses (2, 4, 6, and 8 cm) were constructed with and without (blank) small, shell-less contrast objects (2 mm thick disks) of varying diameters (3-14.5 mm) [volumes: 0.15-3.3 cc] and activity concentration to background ratio (ACR) (2.7-58). For the phantom set with contrast objects, the disks were placed centrally inside the phantoms and both phantom sets were imaged for a period of 10 min on the PEM device. In addition, scans for the 2 and 6 cm phantoms were repeated at different times (0, 90, and 150 min) post phantom construction to evaluate the impact of total activity concentration (count density) on lesion detectability. Each object from each phantom scan was then segmented and placed randomly in a corresponding blank phantom image. The resulting individual images were presented blindly to seven physician observers (two nuclear medicine and five breast imaging radiologists) and scored in a binary fashion (1-correctly identified object, 0-incorrect). The sensitivity, specificity, and accuracy of lesion detectability were calculated and plots of sensitivity versus ACR and lesion diameters for different phantom thicknesses and count density were generated. The overall (mean) detection sensitivity across all variables was 0.68 (95% CI: [0.64, 0.72]) with a corresponding specificity of 0.93 [0.87, 0.98], and diagnostic accuracy of 0.72 [0.70, 0.75]. The smallest detectable object varied strongly as a function of ACR, as sensitivity ranged from 0.36 [0.29, 0.44] for the smallest lesion size (3 mm) to 0.80 [0.75, 0.84] for the largest (14.5 mm). The detectability performance of this PEM system demonstrated its ability to resolve small objects with low activity concentration ratios which may assist in the identification of early stage breast cancer. The results of this investigation can be used to correlate lesion detectability with tumor size, ACR, count rate, and breast thickness.

SU-E-I-183: Variation in Lesion Detectability of a Positron Emission Mammography (PEM) System as a Function of Breast Thickness

Purpose: In a previous study the lesion detectability of a PEM system was evaluated using 2 and 4 cm thick phantoms (Shkumat N et al. J Nucl Med 51(Suppl 2):130P, 2010). In this work we extend that analysis to thicker (6 and 8 cm) phantoms that more accurately represent patient breast sizes. Methods: Gelatin breast phantoms with and without (blank) disk shaped (2mm thick) contrast objects (lesions) with varying diameters (3–14.5 mm) and activity concentrations ratios (ACR) to background (2.7–58) were constructed with two thicknesses (6 and 8 cm). All phantoms were imaged with the standard clinical protocol of 10 minutes. Each lesion was then segmented from the resulting images and inserted randomly into the corresponding blank phantom image. The resulting image sets (120 in total) were read by 7 physicians and scored (1 — correctly identified, 0 incorrect). From these results, the sensitivity, specificity, and accuracy of lesion detectability were calculated and correlated with lesion size, ACR and phantom thickness and compared to the same metrics in the thinner (2 and 4 cm) phantoms. Results: The overall sensitivity across all ACR and lesion diameters decreased from 0.77(95% CI: [0.74, 0.80]) in the 2 and 4 cm phantoms to 0.55(95% CI: [0.49, 0.62]) in the 6 and 8 cm phantoms. More specifically sensitivity decreased from 0.52 to 0.10 and 0.93 to 0.67 for the 3 and 14.5mm diameter respectively, and 0.27 to 0.05 and 1 to 0.86 for ACR of 3 and 58 respectively. Conclusions: There was significant degradation of detactability performance with thicker phantom suggesting that women with larger breasts would benefit the least from PEM exams. We anticipate a sensitivity improvement when using spheroidal lesions rather than the disks used in this investigation.

Positron emission mammography using Pr:LuAG scintillator – Fusion of optical material study and systems engineering

The breast cancer is one of the most frequent cause of death among female cancer patients. However, when discovered at the early stage, the probability of recovery is very high. Therefore, the development of positron emission mammography (PEM) to detect the breast cancer at the early stage with high efficiency is demanding. As the diameter of the scanner part is small, a scintillator with faster response is required. As the recently developed Pr:LuAG has almost twice as short scintillation decay time than that of Ce:LSO, the Pr:LuAG scintillator was employed in our recently developed PEM system. One camera unit consisted of 20 × 64 scintillator pixels optically coupled with three H8500-03 multi anode photomultipliers. The Pr:LuAG pixel size is 2.1 × 2.1 × 15 mm 3 and the BaSO 4 was used as a reflector. Four planar cameras are placed at both sides. Therefore, eight cameras were installed at both sides of the instrument. The spatial resolution was evaluated to be 1.1 mm using the 22Na point source. Fluorodeoxyglucose with 18F hotspot image was also detected using the breast phantom.

WE‐B‐204C‐01: Postron Emission Mammography

Specialized positron emission tomography (PET) systems dedicated to imaging breast cancer have been proposed and developed since the mid‐1990s. The term positron emission mammography (PEM) has been applied to this specialized area of PET scanners and scanning.While progress has been made in reversing a long increasing trend of breast cancer deaths in the U.S. and elsewhere, there is still a relatively high incidence of breast cancer diagnosis and mortality: an estimated 192,000 cases, and 40,000 deaths in the U.S. in 2009. This is the second leading cause of cancer deaths in women in the U.S. Screening X‐ray mammography has played an important role in reversing the trend of increasing deaths, and is the primary imaging modality for breast cancer screening. A limitation of screening and diagnostic mammography is its lack of specificity to malignant disease, resulting in many false positives. A number of imaging methods are used to further investigate equivocal mammography findings, including ultrasound, magnetic resonance imaging (MRI), scintigraphy, and PEM.PET is a functional imaging modality used routinely in oncology to image hyper‐metabolic lesions, including breast cancers. However, the spatial resolution of whole‐body PET (WB‐PET) scanners limits their usefulness in early breast cancer because lesion sizes at diagnosis tend to be smaller than can be reliably imaged with WB‐PET. Dedicated PEM systems focus on improved spatial resolution for imaging early breast cancer, and its functional nature is seen to complement the morphological information provided by mammography. One proposed use of PEM is to improve specificity in diagnosing suspicious but equivocal findings in mammography. PEM has also been suggested for identifying multi‐focal, multi‐centric, or bilateral disease for purposes of planning surgical treatment, for guiding and monitoring therapies, and for better identification of ductal carcinoma in situ.This lecture will provide a brief history of PEM development, give the current status of PEM, compare PEM to WB‐PET and mammography, and discuss clinical applications and operations.Learning Objectives:1. At the end of this lecture, attendees should be able to2. Understand the differences between whole‐body PET and PEM3. Understand the differences between mammography and PEM4. List possible clinical applications/indications for PEM5. Describe clinical operation and requirements of PEM scanning

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.

An Amorphous Selenium Based Positron Emission Mammography Camera with Avalanche Gain

Early diagnosis of breast cancer is crucial for effective treatment, and the need exists for greater detection ability and specificity than possible by screening x-ray mammography (currently the primary imaging technique for the detection of breast lesions). Positron Emission Tomography (PET) using the radiotracer 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) offers a noninvasive, highly sensitive method for the diagnosis of breast cancer. Images from PET contain unique metabolic information that is not available from anatomical imaging techniques. We propose a Positron Emission Mammography (PEM) imaging system that maintains the established high specificity of FDG PET while providing improved collection efficiency for the radiotracer signal and the potential for images with better spatial resolution. This PEM system will enable detection of lesions that are considerably smaller than those that can be visualized using whole body PET imaging. The compact dual-head PEM camera will be based on an amorphous selenium (a-Se) avalanche photodetector and the scintillator lutetium oxyorthosilicate (LSO). The camera promises high collection efficiency by combining the fast scintillation light decay and high light yield of LSO with the excellent quantum efficiency, large avalanche gain, and rapid response time of a-Se. We have measured the gain and readout time of an 8 microm a-Se layer and demonstrated the feasibility of the proposed PEM camera.

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.

Monte Carlo simulation using DETECT2000 of a multilayered scintillation block and fit to experimental data

The authors have used DETECT2000, a Monte Carlo simulation program of the light photon transport inside a scintillation block, to improve the performance of their next positron emission mammography system. The scintillation blocks of the system are composed of two arrays of crystals that are held together by an interconnecting layer. First, they used previously acquired experimental data on the block to find good simulated surface parameters for the scintillation block. They have found that the surface of the crystals are smooth and have good reflectivity. After a set of parameters was found to replicate the behavior of the block, the model geometry was modified in order to increase the block's performance. The DETECT2000 simulations determined that the removal of the interconnecting layer would yield the best results. The experimental results on a modified block yielded excellent results, showing the power of Monte Carlo simulations.

Comparison of scintillators for positron emission mammography (PEM) systems

Positron emission mammography (PEM) has promise as an effective method for the detection of breast lesions. Perhaps the most significant design feature of a PEM system is the choice of scintillator material. In this investigation we compared three scintillators for use in PEM: NaI(Tl), gadolinium oxyorthosilicate (GSO), and lutetium-gadolinium oxyorthosilicate (LGSO). The PEM systems consisted of two 30/spl times/30 arrays of pixelated scintillators (3/spl times/3/spl times/10 mm/sup 3/ for GSO and LGSO and 3/spl times/3/spl times/19 mm/sup 3/ for NaI(Tl)) coupled to arrays of square position-sensitive photomultiplier tubes. The Compton scatter fraction, system energy resolution, spatial resolution, spatial resolution uniformity, and detection sensitivity were compared. Compton scatter fractions for the systems were comparable, between 8% and 9%. The NaI(Tl) system produced the best system energy resolution (18.2%), the GSO system had the worst system energy resolution (28.7%). Spatial resolution for each system was relatively uniform across the face of the detectors, though the magnitude was dependent upon scintillator material. The NaI(Tl) system produced the lowest mean resolution (3.54/spl plusmn/0.05 mm for horizontal profiles and 3.51/spl plusmn/0.04 mm for vertical profiles), while the LGSO system produced the greatest mean spatial resolution (3.19/spl plusmn/0.04 mm for horizontal profiles and 3.20/spl plusmn/0.03 mm for vertical profiles). Detection sensitivity varied among the three systems: NaI(Tl)=217.7 c/s/kBq/ml, GSO=383.9 c/s/kBq/ml and LGSO=646.9 c/s/kBq/ml. Imaging of a simulated breast containing various sized spheres demonstrated that the LGSO system produced the greatest detectability for small spheres (as gauged by the contrast-to-noise ratio), while the NaI(Tl) system had the worst detectability. These differences were due mainly to the lower sensitivity of the NaI(Tl) system compared to the LGSO and GSO imagers. This investigation demonstrated the very important connection between scintillator selection and performance of PEM systems.

Corrections for the effects of accidental coincidences, Compton scatter, and object size in positron emission mammography (PEM) imaging

Positron emission mammography (PEM) has begun to show promise as an effective method for the detection of breast lesions. Due to its utilization of tumor-avid radiopharmaceuticals labeled with positron-emitting radionuclides, this technique may be especially useful in imaging of women with radiodense or fibrocystic breasts. While the use of these radiotracers affords PEM unique capabilities, it also introduces some limitations. Specifically, acceptance of accidental and Compton-scattered coincidence events can decrease lesion detectability. The authors studied the effect of accidental coincidence events on PEM images produced by the presence of /sup 18/F-Fluorodeoxyglucose in the organs of a subject using an anthropomorphic phantom. A delayed-coincidence technique was tested as a method for correcting PEM images for the occurrence of accidental events. Also, a Compton scatter correction algorithm designed specifically for PEM was developed and tested using a compressed breast phantom. Finally, the effect of object size on image counts and a correction for this effect were explored. The imager used in this study consisted of two PEM detector heads mounted 20 cm apart on a Lorad biopsy apparatus. The results demonstrated that a majority of the accidental coincidence events (/spl sim/80%) detected by this system were produced by radiotracer uptake in the adipose and muscle tissue of the torso. The presence of accidental coincidence events was shown to reduce lesion detectability. Much of this effect was eliminated by correction of the images utilizing estimates of accidental-coincidence contamination acquired with delayed coincidence circuitry built into the PEM system. The Compton scatter fraction for this system was /spl sim/14%. Utilization of a new scatter correction algorithm reduced the scatter fraction to /spl sim/1.5%. Finally, reduction of count recovery due to object size was measured and a correction to the data applied. Application of correction techniques for accidental coincidences, Compton scatter, and count loss due to image size increased target-to-background contrast ratios to approximately the maximum level theoretically achievable with this PEM system.