Performance characteristics of the 5-ring GE Discovery MI PET/CT scanner using AAPM TG-126 report.

AIM: To report on the performance characteristics of the 5-ring GE Discovery MI PET/CT systems using the AAPM TG-126 report and compare these results to NEMA NU 2-2012 where applicable. MATERIALS AND METHODS: TG-126 testing was performed on two GE 5-Rings Discovery MI scanners. Tests performed included spatial resolution, PET/CT image-registration accuracy, sensitivity, count rate performance, accuracy of corrections, image contrast, scatter/attenuation correction, and image uniformity. All acquired data were analyzed using scanner console or free software tools as described by TG-126 and the results were then compared to published NEMA NU 2-2012 values. RESULTS: Both scanners gave similar resolution results for TG-126 and NEMA NU 2-2012 and were within manufacturer specifications. Image-registration accuracy between PET and CT using our clinical protocol showed excellent results with values ≤1 mm. Sensitivity using TG-126 was 19.43 cps/kBq while for NEMA the value was 20.73 cps/kBq. The peak noise-equivalent counting rate was 2174 kcps at 63.1 kBq/mL and is not comparable to NEMA NU 2-2012 due to differences in phantoms and methods used to measure and calculate this parameter. The accuracy of corrections for count losses for TG-126 were expressed in SUV values and found to be within 10% of the expected SUV measurement of 1. Image contrast and scatter/attenuation correction using the TG-126 method gave acceptable results. Image uniformity assessment resulted in values within the recommended ± 5% limits. CONCLUSION: These results show that the 5-ring GE Discovery MI PET/CT scanner testing using TG-126 is reproducible and has similar results to NEMA NU 2-2012 tests where applicable. We hope these results start to form the basis to compare PET/CT systems using TG-126.

The potential of biology-guided radiation therapy in thoracic cancer: A preliminary treatment planning study.

Purpose: We investigated the feasibility of biology-guided radiotherapy (BgRT), a technique that utilizes real-time positron emission imaging to minimize tumor motion uncertainties, to spare nearby organs at risk. Methods: Volumetric modulated arc therapy (VMAT), intensity-modulated proton (IMPT) therapy, and BgRT plans were created for a paratracheal node recurrence (case 1; 60 Gy in 10 fractions) and a primary peripheral left upper lobe adenocarcinoma (case 2; 50 Gy in four fractions). Results: For case 1, BgRT produced lower bronchus V40 values compared to VMAT and IMPT. For case 2, total lung V20 was lower in the BgRT case compared to VMAT and IMPT. Conclusions: BgRT has the potential to reduce the radiation dose to proximal critical structures but requires further detailed investigation.

Impact of low injected activity on data driven respiratory gating for PET/CT imaging with continuous bed motion.

Data driven respiratory gating (DDG) in positron emission tomography (PET) imaging extracts respiratory waveforms from the acquired PET data obviating the need for dedicated external devices. DDG performance, however, degrades with decreasing detected number of coincidence counts. In this paper, we assess the clinical impact of reducing injected activity on a new DDG algorithm designed for PET data acquired with continuous bed motion (CBM_DDG) by evaluating CBM_DDG waveforms, tumor quantification, and physician's perception of motion blur in resultant images. Forty patients were imaged on a Siemens mCT scanner in CBM mode. Reduced injected activity was simulated by generating list mode datasets with 50% and 25% of the original data (100%). CBM_DDG waveforms were compared to that of the original data over the range between the aortic arch and the center of the right kidney using the Pearson correlation coefficient (PCC). Tumor quantification was assessed by comparing the maximum standardized uptake value (SUVmax) and peak SUV (SUVpeak) of reconstructed images from the various list mode datasets using elastic motion deblurring (EMDB) reconstruction. Perceived motion blur was assessed by three radiologists of one lesion per patient on a continuous scale from no motion blur (0) to significant motion blur (3). The mean PCC of the 50% and 25% dataset waveforms was 0.74 ± 0.18 and 0.59 ± 0.25, respectively. In comparison to the 100% datasets, the mean SUVmax increased by 2.25% (p = 0.11) for the 50% datasets and by 3.91% (p = 0.16) for the 25% datasets, while SUVpeak changes were within ±0.25%. Radiologist evaluations of motion blur showed negligible changes with average values of 0.21, 0.3, and 0.28 for the 100%, 50%, and 25% datasets. Decreased injected activities degrades the resultant CBM_DDG respiratory waveforms; however this decrease has minimal impact on quantification and perceived image motion blur.

Impact of acquisition time and misregistration with CT on data-driven gated PET.

Objective. Data-driven gating (DDG) can address patient motion issues and enhance PET quantification but suffers from increased image noise from utilization of <100% of PET data. Misregistration between DDG-PET and CT may also occur, altering the potential benefits of gating. Here, the effects of PET acquisition time and CT misregistration were assessed with a combined DDG-PET/DDG-CT technique.Approach. In the primary PET bed with lesions of interest and likely respiratory motion effects, PET acquisition time was extended to 12 min and a low-dose cine CT was acquired to enable DDG-CT. Retrospective reconstructions were created for both non-gated (NG) and DDG-PET using 30 s to 12 min of PET data. Both the standard helical CT and DDG-CT were used for attenuation correction of DDG-PET data. SUVmax, SUVpeak, and CNR were compared for 45 lesions in the liver and lung from 27 cases.Main results. For both NG-PET (p= 0.0041) and DDG-PET (p= 0.0028), only the 30 s acquisition time showed clear SUVmaxbias relative to the 3 min clinical standard. SUVpeakshowed no bias at any change in acquisition time. DDG-PET alone increased SUVmaxby 15 ± 20% (p< 0.0001), then was increased further by an additional 15 ± 29% (p= 0.0007) with DDG-PET/CT. Both 3 min and 6 min DDG-PET had lesion CNR statistically equivalent to 3 min NG-PET, but then increased at 12 min by 28 ± 48% (p= 0.0022). DDG-PET/CT at 6 min had comparable counts to 3 min NG-PET, but significantly increased CNR by 39 ± 46% (p< 0.0001).Significance. 50% counts DDG-PET did not lead to inaccurate or biased SUV-increased SUV resulted from gating. Improved registration from DDG-CT was equally as important as motion correction with DDG-PET for increasing SUV in DDG-PET/CT. Lesion detectability could be significantly improved when DDG-PET used equivalent counts to NG-PET, but only when combined with DDG-CT in DDG-PET/CT.

PET/CT acceptance testing and quality assurance: Executive summary of AAPM Task Group 126 Report.

PURPOSE: A Positron Emission Tomography/Computed Tomography quality assurance program is necessary to ensure that patients receive optimal imaging and care. We summarize the AAPM Task Group (TG) 126 report on acceptance and quality assurance (QA) testing of PET/CT systems. METHODS: TG 126 was charged with developing PET/CT acceptance testing and QA procedures. The TG aimed to develop procedures that would allow for standardized evaluation of existing short-axis cylindrical-bore PET/CT systems in the spirit of NEMA NU 2 standards without requiring specialized phantoms or proprietary software tools. RESULTS: We outline eight performance evaluations using common phantoms and freely available software whereby the clinical physicist monitors each PET/CT system by comparing periodic Follow-Up Measurements to Baseline Measurements acquired during acceptance testing. For each of the eight evaluations, we also summarize the expected testing time and materials necessary and the recommended pass/fail criteria. CONCLUSION: Our report provides a guideline for periodic evaluations of most clinical PET/CT systems that simplifies procedures and requirements outlined by other agencies and will facilitate performance comparisons across vendors, models, and institutions.

Characterization of continuous bed motion effects on patient breathing and respiratory motion correction in PET/CT imaging.

Continuous bed motion (CBM) was recently introduced as an alternative to step-and-shoot (SS) mode for PET/CT data acquisition. In CBM, the patient is continuously advanced into the scanner at a preset speed, whereas in SS, the patient is imaged in overlapping bed positions. Previous investigations have shown that patients preferred CBM over SS for PET data acquisition. In this study, we investigated the effect of CBM versus SS on patient breathing and respiratory motion correction. One hundred patients referred for PET/CT were scanned using a Siemens mCT scanner. Patient respiratory waveforms were recorded using an Anzai system and analyzed using four methods: Methods 1 and 2 measured the coefficient of variation (COV) of the respiratory cycle duration (RCD) and amplitude (RCA). Method 3 measured the respiratory frequency signal prominence (RSP) and method 4 measured the width of the HDChest optimal gate (OG) window when using a 35% duty cycle. Waveform analysis was performed over the abdominothoracic region which exhibited the greatest respiratory motion and the results were compared between CBM and SS. Respiratory motion correction was assessed by comparing the ratios of SUVmax, SUVpeak, and CNR of focal FDG uptake, as well as Radiologists' visual assessment of corresponding image quality of motion corrected and uncorrected images for both acquisition modes. The respiratory waveforms analysis showed that the RCD and RCA COV were 3.7% and 33.3% lower for CBM compared to SS, respectively, while the RSP and OG were 30.5% and 2.0% higher, respectively. Image analysis on the other hand showed that SUVmax, SUVpeak, and CNR were 8.5%, 4.5%, and 3.4% higher for SS compared to CBM, respectively, while the Radiologists' visual comparison showed similar image quality between acquisition modes. However, none of the results showed statistically significant differences between SS and CBM, suggesting that motion correction is not impacted by acquisition mode.

Performance evaluation of the 5-Ring GE Discovery MI PET/CT system using the national electrical manufacturers association NU 2-2012 Standard.

The GE Discovery MI PET/CT system has a modular digital detector design allowing three, four, or five detector block rings that extend the axial field-of-view (FOV) from 15 to 25 cm in 5 cm increments. This study investigated the performance of the 5-ring system and compared it to 3- and 4-ring systems; the GE Discovery IQ system that uses conventional photomultiplier tubes; and the GE Signa PET/MR system that has a reduced transaxial FOV. METHODS: PET performance was evaluated at three different institutions. Spatial resolution, sensitivity, counting rate performance, accuracy, and image quality were measured in accordance with National Electrical Manufacturers Association NU 2-2012 standards. The mean energy resolution, mean timing resolution, and PET/CT subsystem alignment were also measured. Phantoms were used to determine the effects of varying acquisition time and reconstruction parameters on image quality. Retrospective patient scans were reconstructed with various scan durations to evaluate the impact on image quality. RESULTS: Results from all three institutions were similar. Radial/tangential/axial full width at half maximum spatial resolution measurements using the filtered back projection algorithm were 4.3/4.3/5.0 mm, 5.5/4.6/6.5 mm, and 7.4/5.0/6.6 mm at 1, 10, and 20 cm from the center of the FOV, respectively. Measured sensitivity at the center of the FOV (20.84 cps/kBq) was significantly higher than systems with reduced axial FOV. The peak noise-equivalent counting rate was 266.3 kcps at 20.8 kBq/ml, with a corresponding scatter fraction of 40.2%. The correction accuracy for count losses up to the peak noise-equivalent counting rate was 3.6%. For the 10-, 13-, 17-, 22-, 28-, and 37-mm spheres, contrast recoveries in the image quality phantom were measured to be 46.2%, 54.3%, 66.1%, 71.1%, 85.3%, and 89.3%, respectively. The mean energy and timing resolution were 9.55% and 381.7 ps, respectively. Phantom and patient images demonstrated excellent image quality, even at short acquisition times or low injected activity. CONCLUSION: Compared to other PET/CT models, the extended axial FOV improved the overall PET performance of the 5-ring GE Discovery MI scanner. This system offers the potential to reduce scan times or injected activities through increased sensitivity.

Impact of free-breathing CT on quantitative measurements of static and quiescent period-gated PET Images.

Measurements of standardized uptake values (SUV) can vary due to many causes, including respiratory motion. Various methodologies have been introduced to correct for motion in PET, with quiescent-period-gated (QPG) PET being the most popular approach. QPG has been shown to improve PET image quantification compared to static-whole-body (SWB) PET. However, to achieve this improvement, QPG PET requires CT attenuation correction data that matches the QPG PET data. In this paper we investigated the effect of using free-breathing CT for attenuation correction of QPG PET on SUVmax and SUVpeak and compared the results to those of SWB PET. 34 lesions in 27 patients were included. All patients were injected with F-18 FDG. 4D-CT datasets representing all possible phases of respiration that could result from a free-breathing CT were acquired. The 4D-CT datasets were used for attenuation correction of the QPG and SWB PET data. Percentage change in the SUVmax and SUVpeak range was calculated for the reconstructions and compared between QPG and SWB PET. The mean percentage change in the lesion SUVmax and SUVpeak ranges were 19.1% (p  = 0.0178) and 25.2% (p  = 0.0002) higher for QPG compared to SWB, respectively. The maximum percent change in SUVmax and SUVpeak ranges were 58.5% and 59.0% for QPG, respectively compared to 46.1% and 45.3% for SWB, respectively. The highest SUVmax and SUVpeak measurements corresponded to the CT phase that matched the QPG phase. Utilizing free-breathing CT for attenuation correction can lead to large changes in quantification due to misalignment with PET data. This misalignment has a large quantitative impact on QPG PET as compared to SWB PET. When interpreting quantitative changes in lesions, it is critical to consider the influences of free-breathing CT-based attenuation correction.

Dose volume histogram-based optimization of image reconstruction parameters for quantitative 90 Y-PET imaging.

PURPOSE: 90 Y-microsphere radioembolization or selective internal radiation therapy is increasingly being used as a treatment option for tumors that are not candidates for surgery and external beam radiation therapy. Recently, volumetric 90 Y-dosimetry techniques have been implemented to explore tumor dose-response on the basis of 3D 90 Y-activity distribution from PET imaging. Despite being a theranostic study, the optimization of quantitative 90 Y-PET image reconstruction still uses the mean activity concentration recovery coefficient (RC) as the objective function, which is more relevant to diagnostic and detection tasks than is to dosimetry. The aim of this study was to optimize 90 Y-PET image reconstruction by minimizing errors in volumetric dosimetry via the dose volume histogram (DVH). We propose a joint optimization of the number of equivalent iterations (the product of the iterations and subsets) and the postreconstruction filtration (FWHM) to improve the accuracy of voxel-level 90 Y dosimetry. METHODS: A modified NEMA IEC phantom was used to emulate clinically relevant 90 Y-PET imaging conditions through various combinations of acquisition durations, activity concentrations, sphere-to-background ratios, and sphere diameters. PET data were acquired in list mode for 300 min in a single-bed position; we then rebinned the list mode PET data to 60, 45, 30, 15, and 5 min per bed, with 10 different realizations. Errors in the DVH were calculated as root mean square errors (RMSE) of the differences in the image-based DVH and the expected DVH. The new optimization approach was tested in a phantom study, and the results were compared with the more commonly used objective function of the mean activity concentration RC. RESULTS: In a wide range of clinically relevant imaging conditions, using 36 equivalent iterations with a 5.2-mm filtration resulted in decreased systematic errors in volumetric 90 Y dosimetry, quantified as image-based DVH, in 90 Y-PET images reconstructed using the ordered subset expectation maximization (OSEM) iterative reconstruction algorithm with time of flight (TOF) and point spread function (PSF) modeling. Our proposed objective function of minimizing errors in DVH, which allows for joint optimization of 90 Y-PET iterations and filtration for volumetric quantification of the 90 Y dose, was shown to be superior to conventional RC-based optimization approaches for image-based absorbed dose quantification. CONCLUSION: Our proposed objective function of minimizing errors in DVH, which allows for joint optimization of iterations and filtration to reduce errors in the PET-based volumetric quantification 90 Y dose, is relevant to dosimetry in therapy procedures. The proposed optimization method using DVH as the objective function could be applied to any imaging modality used to assess voxel-level quantitative information.

A measurement of the attenuation of radiation from F-18 by a PET/MR scanner.

The attenuation of 511 keV photons by the structure of a PET/MR scanner was measured prior to energizing the magnet. The exposure rate from a source of fluorine-18 was measured in air and, with the source placed at the isocenter of the instrument, at various points outside of the scanner. In an arc from 45 to 135 degrees relative to the long axis of the scanner and at a distance of 1.5 m from the isocenter, the attenuation by the scanner is at least 5.6 half-value layers from the MR component alone and at least 6.6 half-value layers with the PET insert installed. This information could inform better design of the radiation shielding for PET/MR scanners.

Toward a standard for the evaluation of PET-Auto-Segmentation methods following the recommendations of AAPM task group No. 211: Requirements and implementation.

PURPOSE: The aim of this paper is to define the requirements and describe the design and implementation of a standard benchmark tool for evaluation and validation of PET-auto-segmentation (PET-AS) algorithms. This work follows the recommendations of Task Group 211 (TG211) appointed by the American Association of Physicists in Medicine (AAPM). METHODS: The recommendations published in the AAPM TG211 report were used to derive a set of required features and to guide the design and structure of a benchmarking software tool. These items included the selection of appropriate representative data and reference contours obtained from established approaches and the description of available metrics. The benchmark was designed in a way that it could be extendable by inclusion of bespoke segmentation methods, while maintaining its main purpose of being a standard testing platform for newly developed PET-AS methods. An example of implementation of the proposed framework, named PETASset, was built. In this work, a selection of PET-AS methods representing common approaches to PET image segmentation was evaluated within PETASset for the purpose of testing and demonstrating the capabilities of the software as a benchmark platform. RESULTS: A selection of clinical, physical, and simulated phantom data, including "best estimates" reference contours from macroscopic specimens, simulation template, and CT scans was built into the PETASset application database. Specific metrics such as Dice Similarity Coefficient (DSC), Positive Predictive Value (PPV), and Sensitivity (S), were included to allow the user to compare the results of any given PET-AS algorithm to the reference contours. In addition, a tool to generate structured reports on the evaluation of the performance of PET-AS algorithms against the reference contours was built. The variation of the metric agreement values with the reference contours across the PET-AS methods evaluated for demonstration were between 0.51 and 0.83, 0.44 and 0.86, and 0.61 and 1.00 for DSC, PPV, and the S metric, respectively. Examples of agreement limits were provided to show how the software could be used to evaluate a new algorithm against the existing state-of-the art. CONCLUSIONS: PETASset provides a platform that allows standardizing the evaluation and comparison of different PET-AS methods on a wide range of PET datasets. The developed platform will be available to users willing to evaluate their PET-AS methods and contribute with more evaluation datasets.

Challenges in Interpretation of Staging PET/CT in Thoracic Malignancies.

18F-fluorodeoxryglucose (18F-FDG) PET/CT imaging is routinely performed in the evaluation of patients with known or suspected thoracic malignancy. Indications for its use include staging of malignancy, assessment of response to therapy, evaluation of suspected disease recurrence, and evaluation of a solitary pulmonary nodule. In this article, we will discuss specific technical artifacts and also review potential pitfalls in the interpretation of PET/CT in thoracic malignancies including normal variations in physiologic uptake of FDG, benign conditions (such as infection, inflammation, posttreatment changes, and iatrogenic factors) that can result in increased FDG uptake, and malignancies that demonstrate scarce to no FDG uptake.

Classification and evaluation strategies of auto-segmentation approaches for PET: Report of AAPM task group No. 211.

PURPOSE: The purpose of this educational report is to provide an overview of the present state-of-the-art PET auto-segmentation (PET-AS) algorithms and their respective validation, with an emphasis on providing the user with help in understanding the challenges and pitfalls associated with selecting and implementing a PET-AS algorithm for a particular application. APPROACH: A brief description of the different types of PET-AS algorithms is provided using a classification based on method complexity and type. The advantages and the limitations of the current PET-AS algorithms are highlighted based on current publications and existing comparison studies. A review of the available image datasets and contour evaluation metrics in terms of their applicability for establishing a standardized evaluation of PET-AS algorithms is provided. The performance requirements for the algorithms and their dependence on the application, the radiotracer used and the evaluation criteria are described and discussed. Finally, a procedure for algorithm acceptance and implementation, as well as the complementary role of manual and auto-segmentation are addressed. FINDINGS: A large number of PET-AS algorithms have been developed within the last 20 years. Many of the proposed algorithms are based on either fixed or adaptively selected thresholds. More recently, numerous papers have proposed the use of more advanced image analysis paradigms to perform semi-automated delineation of the PET images. However, the level of algorithm validation is variable and for most published algorithms is either insufficient or inconsistent which prevents recommending a single algorithm. This is compounded by the fact that realistic image configurations with low signal-to-noise ratios (SNR) and heterogeneous tracer distributions have rarely been used. Large variations in the evaluation methods used in the literature point to the need for a standardized evaluation protocol. CONCLUSIONS: Available comparison studies suggest that PET-AS algorithms relying on advanced image analysis paradigms provide generally more accurate segmentation than approaches based on PET activity thresholds, particularly for realistic configurations. However, this may not be the case for simple shape lesions in situations with a narrower range of parameters, where simpler methods may also perform well. Recent algorithms which employ some type of consensus or automatic selection between several PET-AS methods have potential to overcome the limitations of the individual methods when appropriately trained. In either case, accuracy evaluation is required for each different PET scanner and scanning and image reconstruction protocol. For the simpler, less robust approaches, adaptation to scanning conditions, tumor type, and tumor location by optimization of parameters is necessary. The results from the method evaluation stage can be used to estimate the contouring uncertainty. All PET-AS contours should be critically verified by a physician. A standard test, i.e., a benchmark dedicated to evaluating both existing and future PET-AS algorithms needs to be designed, to aid clinicians in evaluating and selecting PET-AS algorithms and to establish performance limits for their acceptance for clinical use. The initial steps toward designing and building such a standard are undertaken by the task group members.

Qualitative and quantitative comparison of gated blood pool single photon emission computed tomography using low-energy high-resolution and SMARTZOOM collimation.

OBJECTIVE: The aim of this study was to assess the feasibility of IQ-SPECT gated blood pool (MUGA) under conditions of decreased scan time (ST). PATIENTS AND METHODS: Ten patients underwent routine 26-min, two-view planar, followed by LEHR and IQ-SPECT MUGA, on a Siemens dual-head Symbia scanner. Six 'back and forth' 4-min SPECT scans were summed into 4-, 8-, 12-, 16-, 20-, and 24-min equivalent scans, and reconstructed iteratively (IQ-SPECT and LEHR) and with FBP (LEHR). Uniformity, contrast, and wall motion were scored on a five-point scale. Linear regressions of left ventricular (LV) ejection fraction (EF) were performed between FBP, Flash 3D, and IQ-SPECT versus planar and Flash 3D and IQ-SPECT versus FBP. Agreement tables between Flash 3D and IQ-SPECT versus FBP LV EF were generated using a normal versus cardiotoxicity threshold of 50%. RESULTS: IQ-SPECT had the best scores for all STs, and 4, 8, and 16 min IQ-SPECT were judged to be similar to 24-min LEHR FBP, Flash 3D, and planar, respectively. The average LV EF correlation coefficients were 0.69, 0.71, and 0.63 between IQ-SPECT, Flash 3D, and FBP versus planar, respectively; 0.70 between IQ-SPECT and FBP; and 0.88 between Flash 3D and FBP, and all were statistically significant (P<0.05), except for 16-min FBP LEHR versus planar. Agreement tables showed diagnostic equivalence of IQ-SPECT, Flash 3D, and FBP. CONCLUSION: These preliminary results suggest that IQ-SPECT is equivalent to LEHR Flash 3D and FBP for MUGA SPECT, and better at reduced ST. A larger patient population study is necessary for a more definitive assessment.

Characterizing proton-activated materials to develop PET-mediated proton range verification markers.

Conventional proton beam range verification using positron emission tomography (PET) relies on tissue activation alone and therefore requires particle therapy PET whose installation can represent a large financial burden for many centers. Previously, we showed the feasibility of developing patient implantable markers using high proton cross-section materials ((18)O, Cu, and (68)Zn) for in vivo proton range verification using conventional PET scanners. In this technical note, we characterize those materials to test their usability in more clinically relevant conditions. Two phantoms made of low-density balsa wood (~0.1 g cm(-3)) and beef (~1.0 g cm(-3)) were embedded with Cu or (68)Zn foils of several volumes (10-50 mm(3)). The metal foils were positioned at several depths in the dose fall-off region, which had been determined from our previous study. The phantoms were then irradiated with different proton doses (1-5 Gy). After irradiation, the phantoms with the embedded foils were moved to a diagnostic PET scanner and imaged. The acquired data were reconstructed with 20-40 min of scan time using various delay times (30-150 min) to determine the maximum contrast-to-noise ratio. The resultant PET/computed tomography (CT) fusion images of the activated foils were then examined and the foils' PET signal strength/visibility was scored on a 5 point scale by 13 radiologists experienced in nuclear medicine. For both phantoms, the visibility of activated foils increased in proportion to the foil volume, dose, and PET scan time. A linear model was constructed with visibility scores as the response variable and all other factors (marker material, phantom material, dose, and PET scan time) as covariates. Using the linear model, volumes of foils that provided adequate visibility (score 3) were determined for each dose and PET scan time. The foil volumes that were determined will be used as a guideline in developing practical implantable markers.

AAPM/SNMMI Joint Task Force: report on the current state of nuclear medicine physics training.

The American Association of Physicists in Medicine (AAPM) and the Society of Nuclear Medicine and Molecular Imaging (SNMMI) recognized the need for a review of the current state of nuclear  medicine physics training and the need to explore pathways for improving nuclear medicine physics training opportunities. For these reasons, the two organizations formed a joint AAPM/SNMMI Ad Hoc Task Force on Nuclear Medicine Physics  Training. The mission of this task force was to assemble a representative group of stakeholders to:• Estimate the demand for board-certified nuclear medicine physicists in the next 5-10 years,• Identify the critical issues related to supplying an adequate number of physicists who have received the appropriate level of training in nuclear medicine physics, and• Identify approaches that may be considered to facilitate the training of nuclear medicine physicists.As a result, a task force was appointed and chaired by an active member of both organizations that included representation from the AAPM, SNMMI, the American Board of Radiology (ABR), the American Board of Science in Nuclear Medicine (ABSNM), and the Commission for the Accreditation of Medical Physics Educational Programs (CAMPEP). The Task Force first met at the AAPM Annual Meeting in Charlotte in July 2012 and has met regularly face-to-face, online, and by conference calls. This manuscript reports the findings of the Task Force, as well as recommendations to achieve the stated mission.

Metastases to the breast from extramammary malignancies - PET/CT findings.

Detection of incidental malignant lesions in the breast has a significant clinical impact not only on healthy individuals but also on patients with known malignant disease. This review describes a spectrum of metastatic breast lesions incidentally detected by FDG PET-CT at staging that may be misinterpreted as second primary malignancy. The common non-mammary malignancies that metastasize to the breast include melanoma, hematopoietic malignancies and epithelial cancers. We present the FDG PET-CT features of incidental non-mammary metastases to the breast that may help distinguish primary breast cancer from metastatic disease and aid in the management of patients with a known malignancy.

Benign breast lesions detected by positron emission tomography-computed tomography.

(18)F-fluorodeoxyglucose positron emission computed tomography (FDG PET-CT) is widely used in the initial staging and response evaluation of patients with malignancy. This review describes a spectrum of benign breast findings incidentally detected by FDG PET-CT at staging that may be misinterpreted as malignancy. We describe the pattern of distribution and intensity of FDG uptake in a spectrum of benign breast diseases with their corresponding typical morphological imaging characteristics to help the nuclear medicine physician and/or general radiologist identify benign lesions, avoiding unnecessary breast imaging work-up and biopsies.

Defining internal target volume using positron emission tomography for radiation therapy planning of moving lung tumors.

Substantial disagreement exists over appropriate PET segmentation techniques for non-small cell lung cancer. Currently, no segmentation algorithm explicitly considers tumor motion in determining tumor borders. We developed an automatic PET segmentation model as a function of target volume, motion extent, and source-to-background ratio (the VMSBR model). The purpose of this work was to apply the VMSBR model and six other segmentation algorithms to a sample of lung tumors. PET and 4D CT were performed in the same imaging session for 23 patients (24 tumors) for radiation therapy planning. Internal target volumes (ITVs) were autosegmented on maximum intensity projection (MIP) of cine CT. ITVs were delineated on PET using the following methods: 15%, 35%, and 42% of maximum activity concentration, standardized uptake value (SUV) of 2.5 g/mL, 15% of mean activity concentration plus background, a linear function of mean SUV, and the VMSBR model. Predicted threshold values from each method were compared to measured optimal threshold values, and resulting volume magnitudes were compared to cine-CT-derived ITV. Correlation between predicted and measured threshold values ranged from slopes of 0.29 for the simplest single-threshold techniques to 0.90 for the VMSBR technique. R2 values ranged from 0.07 for the simplest single-threshold techniques to 0.86 for the VMSBR technique. The VMSBR segmentation technique that included volume, motion, and source-to-background ratio, produced accurate ITVs in patients when compared with cine-CT-derived ITV.

Investigating the use of nonattenuation corrected PET images for the attenuation correction of PET data.

PURPOSE: The aim of this study is to investigate the feasibility of using the nonattenuated PET images (PET-NAC) as a means for the AC of PET data. METHODS: A three-step iterative segmentation process is proposed. In step 1, a patient's body contour is segmented from the PET-NAC using an active contour algorithm. Voxels inside the contour are then assigned a value of 0.096 cm(-1) to represent the attenuation coefficient of soft tissue at 511 keV. This segmented attenuation map is then used to correct for attenuation the raw PET data and the resulting PET images are used as the input to Step 2 of the process. In step 2, the lung region is segmented using an optimal thresholding approach and the corresponding voxels are assigned a value of 0.024 cm(-1) representing the attenuation coefficients of lung tissue at 511 keV. The updated attenuation map is then used for a second time to correct for attenuation the raw PET data, and the resulting PET images are used as the input to step 3. The purpose of Step 3 is to delineate parts of the heart and liver in the lung contour using a region growing approach since these parts were unavoidably excluded in the lung contour in step 2. These parts are then corrected by using a value of 0.096 cm(-1) in the attenuation map. Finally the attenuation coefficients of the bed are included based on CT images to eliminate the impact of the couch on the accuracy of AC. The final attenuation map is then used to AC the raw PET data and generates the final PET image, which we name iterative AC PET (PET-IAC). To assess the proposed segmentation approach, a phantom and 14 patients (with a total of 55 lesions including bone) were scanned on a GE Discovery-RX PET∕CT scanner. PET-IAC images were generated using the proposed process and compared to those of CT-AC PET (PET-CTAC). Visual inspection, lesion SUV, and voxel by voxel histograms between PET-IAC and PET-CTAC for phantom and patient studies were performed to assess the accuracy of image quantification. RESULTS: Visual inspection showed a small difference in lung parenchyma between the PET-IAC and PET-CTAC. Tumor SUV based on PET-IAC were on average different by 3%±9% (6%±7%) compared to the SUVs from the PET-CTAC in the phantom (patient) studies. For bone lesions only, the average difference was 3%±6%. The histogram comparing PET-CTAC and PET-IAC resulted in an average regression line of y=(1.08±0.07)x+(0.00007±0.0013), with R2=0.978±0.0057. CONCLUSIONS: Preliminary results suggest that PET-NAC for the AC of PET images is feasible. Such an approach can potentially be used for dedicated PET or PET∕MR hybrid systems while minimizing scan time or potential image artifacts, respectively.