Girth-based administered activity for pediatric 99m Tc-DMSA SPECT.

BACKGROUND: Pediatric molecular imaging requires a balance between administering an activity that will yield sufficient diagnostic image quality while maintaining patient radiation exposure at acceptable levels. In current clinical practice, this balance is arrived at by the current North American Consensus Guidelines in which patient weight is used to recommend the administered activity (AA). PURPOSE: We have previously demonstrated that girth (waist circumference at the level of the kidneys) is better at equalizing image quality than patient weight for pediatric Tc-99m DMSA renal function imaging. However, the correlation between image quality (IQ), AA, and patient girth has not been rigorously and systematically developed. In this work, we generate a series of curves showing the tradeoff between AA and IQ as a function of patient girth, providing the data for standards bodies to develop the next generation of dosing guideline for pediatric DMSA SPECT. METHODS: An anthropomorphic phantom series that included variations in age (5, 10, and 15 years), gender (M, F), local body morphometry (5, 10, 50, 90, and 95th girth percentiles), and kidney size (±15% standard size), was used to generate realistic SPECT projections. A fixed and clinically challenging defect-to-organ volume percentage (0.49% of renal cortex value) was used to model a focal defect with zero uptake (i.e., full local loss of renal function). Task-based IQ assessment methods were used to rigorously measure IQ in terms of renal perfusion defect detectability. This assessment was performed at multiple count levels (corresponding to various AAs) for groups of patients that had similar girths and defect sizes. Receiver-operating characteristics (ROC) analysis was applied; the area under the ROC curve (AUC) was used as a figure-of-merit for task performance. Curves showing the tradeoff between AUC and AA were generated for these groups of phantoms. RESULTS: Overall, the girth-based dosing method suggested different amounts of AA compared to weight-based dosing for the phantoms that had a relatively large body weight but a small girth or phantoms with relatively small bodyweight but large girth. Reductions of AA to 62.9% compared to weight-based dosing guidelines can potentially be realized while maintaining a baseline (AUC = 0.80) IQ for certain 15-year-olds who have a relatively small girth and large defect size. Note that the task-based IQ results are heavily dependent on the simulated defect size for the defect detection task and the appropriate AUC value must be decided by the physicians for this diagnostic task. These results are based purely on simulation and are subject to future clinical validation. CONCLUSIONS: The study provides simulation-based IQ-AA data for a girth-based dosing method for pediatric renal SPECT, suggesting that patient waist circumference at the level of kidneys should be considered in selecting the AA needed to achieve an acceptable IQ. This data may be useful for standards bodies to develop girth-based dosing guidelines.

Joint EANM/SIOPE/RAPNO practice guidelines/SNMMI procedure standards for imaging of paediatric gliomas using PET with radiolabelled amino acids and [18F]FDG: version 1.0.

Positron emission tomography (PET) has been widely used in paediatric oncology. 2-Deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is the most commonly used radiopharmaceutical for PET imaging. For oncological brain imaging, different amino acid PET radiopharmaceuticals have been introduced in the last years. The purpose of this document is to provide imaging specialists and clinicians guidelines for indication, acquisition, and interpretation of [18F]FDG and radiolabelled amino acid PET in paediatric patients affected by brain gliomas. There is no high level of evidence for all recommendations suggested in this paper. These recommendations represent instead the consensus opinion of experienced leaders in the field. Further studies are needed to reach evidence-based recommendations for the applications of [18F]FDG and radiolabelled amino acid PET in paediatric neuro-oncology. These recommendations are not intended to be a substitute for national and international legal or regulatory provisions and should be considered in the context of good practice in nuclear medicine. The present guidelines/standards were developed collaboratively by the EANM and SNMMI with the European Society for Paediatric Oncology (SIOPE) Brain Tumour Group and the Response Assessment in Paediatric Neuro-Oncology (RAPNO) working group. They summarize also the views of the Neuroimaging and Oncology and Theranostics Committees of the EANM and reflect recommendations for which the EANM and other societies cannot be held responsible.

Development and autoregulation of kidney function in children: a retrospective study using 99mTc-MAG3 renography.

BACKGROUND: Both the development of kidney function in healthy children and autoregulation ability of kidney function in patients with asymmetric kidneys are important in clinical diagnosis and treatment of kidney-related diseases, but there are however only limited studies. This study aimed to investigate development of kidney function in normal children with healthy symmetric kidneys and autoregulation of the healthy kidney compensating the functional loss of a diseased one in children with asymmetric kidneys. METHODS: Two hundred thirty-seven children (156 male, 81 female) from 0 to 20y (average 4.6y ± 5.1) undergoing 99mTc-MAG3 renography were included, comprising 134 with healthy symmetrically functioning kidneys and 103 with asymmetric kidneys. Clearance was calculated from kidney uptakes at 1-2 min. A developmental model between MAG3 clearance (CL) and patient age in normal group was identified (CL = 84.39Age0.395 ml/min, r = 0.957, p < 0.001). The clearance autoregulation rate in abnormal group with asymmetric kidneys was defined as the ratio of the measured MAG3 clearance and the normal value predicted from the renal developmental model of normal group. RESULTS: No significant difference of MAG3 clearance (p = 0.723) was found between independent abnormal group and normal group. The autoregulation rate of kidney clearance in abnormal group was 94.2% on average, and no significant differences were found between two age groups (p = 0.49), male and female (p = 0.39), and left kidney and right kidney (p = 0.92) but two different grades of asymmetric kidneys (p = 0.02). CONCLUSIONS: The healthy kidney of two asymmetric kidneys can automatically regulate total kidney function up to 94% of two symmetric kidneys in normal children.

Radiation Dose to Pediatric Patients From Radiopharmaceuticals.

Nuclear medicine provides methods and techniques in that has benefited pediatric patients and their referring physicians for over 40 years. Nuclear medicine provides qualitative and quantitative information about overall and regional function of organs, systems, and lesions in the body. This involves applications in many organ systems including the skeleton, the brain, the kidneys and the heart as well as in the diagnosis and treatment of cancer. The practice of nuclear medicine requires the administration of radiopharmaceuticals which expose the patient to very low levels of ionizing radiation. Advanced approaches in the estimation of radiation dose from the internal distribution of radiopharmaceuticals in patients of various sizes and shapes have been developed in the past 20 years. Although there is considerable uncertainty in the estimation of the risk of adverse health effects from radiation at the very low exposure levels typically associated with nuclear medicine, some considers it prudent to be more cautious when applied to children as they are generally considered to be at higher risk than adults. Standard guidelines for administered activities for nuclear medicine procedures in children have been established including the North American consensus guidelines and the Paediatric Dosage Card developed by the European Association of Nuclear Medicine. As we move into the future, these guidelines would likely be reviewed in response to changes in clinical practice, a better understanding of radiation dosimetry as applied to children as well as new clinical applications, new advancements in the field with respect to both instrumentation and image reconstruction and processing.

Residency training for diagnostic imaging physicists should be expanded to include nuclear medicine physics.

The American Board of Radiology offers certification in three specialties of medical physics: Therapeutic Medical Physics, Diagnostic Medical Physics, and Nuclear Medical Physics. Of these specialties, medical nuclear physics has the fewest active diplomates, only a few hundred. The diagnostic medical physics specialty certification incudes a variety of modalities (ultrasound, radiography, computed tomography, and magnetic resonance imaging) yet does not address nuclear medicine imaging or therapy. This separation dates to the beginning of the ABR certification process for medical physicists in 1947; originally there were three certificates available: X-ray and Radium Physics, Medical Nuclear Physics and, as combination of these two, Radiological Physics. Over the span of 75 years since the Medical Nuclear Physics certification was created, much has changed in the scope and proliferation of the nuclear medicine endeavor and the question arises as to the need for change in the preparation process for medical physicists in the field. I offer thanks to our contributors and note that they are writing in the classic style of a debate, the opinions that they argue may or may not reflect their personal views.

Renal 99mTc-DMSA pharmacokinetics in pediatric patients.

99mTc-DMSA is one of the most commonly used pediatric nuclear medicine imaging agents. Nevertheless, there are no pharmacokinetic (PK) models for 99mTc-DMSA in children, and currently available pediatric dose estimates for 99mTc-DMSA use pediatric S values with PK data derived from adults. Furthermore, the adult PK data were collected in the mid-70's using quantification techniques and instrumentation available at the time. Using pediatric imaging data for DMSA, we have obtained kinetic parameters for DMSA that differ from those applicable to adults. METHODS: We obtained patient data from a retrospective re-evaluation of clinically collected pediatric SPECT images of 99mTc-DMSA in 54 pediatric patients from Boston's Children Hospital (BCH), ranging in age from 1 to 16 years old. These were supplemented by prospective data from twenty-three pediatric patients (age range: 4 months to 6 years old). RESULTS: In pediatric patients, the plateau phase in fractional kidney uptake occurs at a fractional uptake value closer to 0.3 than the value of 0.5 reported by the International Commission on Radiological Protection (ICRP) for adult patients. This leads to a 27% lower time-integrated activity coefficient in pediatric patients than in adults. Over the age range examined, no age dependency in uptake fraction at the clinical imaging time was observed. Female pediatric patients had a 17% higher fractional kidney uptake at the clinical imaging time than males (P < 0.001). CONCLUSIONS: Pediatric 99mTc-DMSA kinetics differ from those reported for adults and should be considered in pediatric patient dosimetry. Alternatively, the differences obtained in this study could reflect improved quantification methods and the need to re-examine DMSA kinetics in adults.

PET/computed tomography in inpatients: part 1, international survey.

PURPOSE: The purposes of this study are to (1) identify patterns of inpatient PET/computed tomography (CT) use in and outside of the USA and (2) characterize inpatient PET/CT use by location and indication. MATERIALS AND METHODS: The study was deemed exempt by the Institutional Review Board. A survey link through REDCap was emailed to the Society of Nuclear Medicine and Molecular Imaging (SNMMI) members and PET Centers of Excellence members and posted on the SNMMI website. Data were collected from May 2018 to August 2018. Analyses were conducted using SAS Software 9.4 with the NPAR1WAY procedure. Differences were evaluated using the Kruskal-Wallis test with statistical significance defined as P ≤ 0.05. RESULTS: A total of 124 people responded to the survey, 71.8% (89/124) in the USA, and 26.6% (33/124) outside the USA [1.6% (2/124) no response]. 81.5% (101/124) read inpatient PET/CTs. Median percent of inpatient PET/CTs was 8.0% (range 0-100). Use of inpatient PET/CT was different (P < 0.0001) in the USA (5%, range 0-80%) versus outside USA (17.7%, range 0-100%). Use of inpatient PET/CT was different by institution type: median percent of inpatient PET/CTs in community teaching hospitals was 4.5% (range 0-50) versus 1.1% (range 0-20) in community nonteaching, 10% (range 0-80) in academic medical centers, and 20.0% (range 6.3-40) in government-affiliated institutions (P = 0.0001). CONCLUSIONS: Most US and non-US respondents read inpatients PET/CTs. Non-US respondents read a higher percentage of inpatient PET/CTs than US respondents. Respondents in government-affiliated institutions read the highest percent of inpatient PET/CTs and community nonteaching institutions the least. Results of this survey may help physicians evaluate whether their practice of providing inpatient PET/CT fits with current practice patterns.

Celebrating eighty years of radionuclide therapy and the work of Saul Hertz.

March 2021 will mark the eightieth anniversary of targeted radionuclide therapy, recognizing the first use of radioactive iodine to treat thyroid disease by Dr. Saul Hertz on March 31, 1941. The breakthrough of Dr. Hertz and collaborator physicist Arthur Roberts was made possible by rapid developments in the fields of physics and medicine in the early twentieth century. Although diseases of the thyroid gland had been described for centuries, the role of iodine in thyroid physiology had been elucidated only in the prior few decades. After the discovery of radioactivity by Henri Becquerel in 1897, rapid advancements in the field, including artificial production of radioactive isotopes, were made in the subsequent decades. Finally, the diagnostic and therapeutic use of radioactive iodine was based on the tracer principal that was developed by George de Hevesy. In the context of these advancements, Hertz was able to conceive the potential of using of radioactive iodine to treat thyroid diseases. Working with Dr. Roberts, he obtained the experimental data and implemented it in the clinical setting. Radioiodine therapy continues to be a mainstay of therapy for hyperthyroidism and thyroid cancer. However, Hertz struggled to gain recognition for his accomplishments and to continue his work and, with his early death in 1950, his contributions have often been overlooked until recently. The work of Hertz and others provided a foundation for the introduction of other radionuclide therapies and for the development of the concept of theranostics.

DeepAMO: a multi-slice, multi-view anthropomorphic model observer for visual detection tasks performed on volume images.

Purpose: We propose a deep learning-based anthropomorphic model observer (DeepAMO) for image quality evaluation of multi-orientation, multi-slice image sets with respect to a clinically realistic 3D defect detection task. Approach: The DeepAMO is developed based on a hypothetical model of the decision process of a human reader performing a detection task using a 3D volume. The DeepAMO is comprised of three sequential stages: defect segmentation, defect confirmation (DC), and rating value inference. The input to the DeepAMO is a composite image, typical of that used to view 3D volumes in clinical practice. The output is a rating value designed to reproduce a human observer's defect detection performance. In stages 2 and 3, we propose: (1) a projection-based DC block that confirms defect presence in two 2D orthogonal orientations and (2) a calibration method that "learns" the mapping from the features of stage 2 to the distribution of observer ratings from the human observer rating data (thus modeling inter- or intraobserver variability) using a mixture density network. We implemented and evaluated the DeepAMO in the context of Tc 99 m -DMSA SPECT imaging. A human observer study was conducted, with two medical imaging physics graduate students serving as observers. A 5 × 2 -fold cross-validation experiment was conducted to test the statistical equivalence in defect detection performance between the DeepAMO and the human observer. We also compared the performance of the DeepAMO to an unoptimized implementation of a scanning linear discriminant observer (SLDO). Results: The results show that the DeepAMO's and human observer's performances on unseen images were statistically equivalent with a margin of difference ( Δ AUC ) of 0.0426 at p < 0.05 , using 288 training images. A limited implementation of an SLDO had a substantially higher AUC (0.99) compared to the DeepAMO and human observer. Conclusion: The results show that the DeepAMO has the potential to reproduce the absolute performance, and not just the relative ranking of human observers on a clinically realistic defect detection task, and that building conceptual components of the human reading process into deep learning-based models can allow training of these models in settings where limited training images are available.

Dosimetric considerations of 99mTc-MDP uptake within the epiphyseal plates of the long bones of pediatric patients.

Skeletal scintigraphy is most performed in pediatric patients using the radiopharmaceutical 99mTc labelled methylene diphosphonate (99mTc-MDP). Reference biokinetic models for 99mTc-MDP indicate 50% of the administered activity is uniformly localized to the interior bone surfaces (trabecular and cortical regions), yet imaging data clearly show some preferential uptake to the epiphyseal growth plates of the long bones. To explore the dosimetric consequences of these regional activity concentrations, we have modified mesh-type computational phantoms of the International Commission on Radiological Protection (ICRP) reference pediatric series to explicitly include geometric models of the epiphyseal growth plates (2 mm in thickness) within the left/right, distal/proximal ends of the humeri, radii, ulnae, femora, tibia, and fibulae. Bone mineral activity from the ICRP Publication 128 biokinetic model for 99mTc-MDP (ICRP 2015) was then partitioned to the growth plates at values of 0.5%, 4.4%, 8.3%, 12.2%, 16.1%, and 20%. Radiation transport simulations were performed to compute 99mTc S-values and organ dose coefficients to the soft tissues and to bone site-specific regions of spongiosa. As the percentage of bone activity assigned to the growth plates was increased (from 0.5% to 20%), absorbed doses to the soft tissue organs, active bone marrow, bone endosteum (BE), as well as the detriment-weighted dose, were shown to decrease from their nominal values (no substantial growth plate activity), while epiphyseal plate self-doses increased. In the 15 year old male phantom, moving from 0.5% to 20% relative bone activity within the epiphyseal plates resulted in a 15% reduction in active marrow (AM) and BE dose, a 10% reduction in mean soft tissue and detriment-weighted dose, and a 6.3-fold increase in epiphyseal plate self-dose. In the newborn female phantom, we observed a 18% decrease in AM and BE dose, a 10% decrease in mean soft tissue dose, a 15% decrease in detriment-weighted dose, and 12.8-fold increase in epiphyseal plate self-dose. Increases (to 3 mm) and decreases (to 1 mm) in the assumed growth plate thickness of our models were shown to impact only the growth plate self-dose. Future work in differential quantification of 99mTc-MDP activity-growth plates versus other bone surfaces-is required to provide clinically realistic data on activity partitioning as a function of patient age, and perhaps skeletal site. The phantom series presented here may be used to develop more optimized age-related guidance on 99mTc-MDP administered activities to children.

Pediatric Solid Gastric Emptying Scintigraphy: Normative Value Guidelines and Nonstandard Meal Alternatives.

INTRODUCTION: Adult standards for gastric emptying scintigraphy, including the type of meal and range of normative values for percent gastric emptying, are routinely used in pediatric practice, but to date have not been validated. The purpose of this study is to determine whether the use of adult criteria for gastric emptying scintigraphy is valid for children and whether alternative nonstandard meals can also be offered based on these criteria. METHODS: This retrospective study analyzed patients (n = 1,151 total) who underwent solid-phase gastric emptying scintigraphy. Patients were stratified into normal and delayed gastric emptying cohorts based on adult criteria, i.e., with normal gastric emptying defined as ≤10% gastric retention at 4 hours. Patients were further stratified based on the type of meal, namely complete or partial adult standard meals or alternative cheese-based meals. Percent gastric retention values at 1, 2, 3, and 4 hours were compared. RESULTS: The median (95% upper reference limit) percentage gastric retention values for the complete standard meal were 72% (93%) at 1 hour, 39% (65%) at 2 hours, 15% (33%) at 3 hours, and 6% (10 %) at 4 hours. By comparison, the values for cheese-based meals were 60% (87%) at 1 hour, 29% (61%) at 2 hours, 10% (30%) at 3 hours, and 5% (10%) at 4 hours. Consumption of at least 50% of the standard meal yielded similar retention percentages; 68% (89%) at 1 hour, 32% (57%) at 2 hours, 10% (29%) at 3 hours, and 5% (10%) at 4 hours. There were no significant age- or sex-specific differences using the adult criteria. DISCUSSION: The adult normative standards for gastric emptying scintigraphy are applicable for use in the pediatric population. These same standards can be also be applied to nonstandard meal options, including cheese-based alternative meals and partial standard meals.

Body morphometry appropriate computational phantoms for dose and risk optimization in pediatric renal imaging with Tc-99m DMSA and Tc-99m MAG3.

Current guidelines for administered activity (AA) in pediatric nuclear medicine imaging studies are based on a 2016 harmonization of the 2010 North American Consensus guidelines and the 2007 European Association of Nuclear Medicine pediatric dosage card. These guidelines assign AA scaled to patient body mass, with further constraints on maximum and minimum values of radiopharmaceutical activity. These guidelines, however, are not formulated based upon a rigor-ous evaluation of diagnostic image quality. In a recent study of the renal cortex imaging agent 99mTc-DMSA (Li Y et al 2019), body mass-based dosing guidelines were shown to not give the same level of image quality for patients of differing body mass. Their data suggest that patient girth at the level of the kidneys may be a better morphometric parameter to consider when selecting AA for renal nuclear medicine imaging. The objective of the present work was thus to develop a dedicated series of computational phantoms to support image quality and organ dose studies in pediatric renal imaging using 99mTc-DMSA or 99mTc-MAG3. The final library consists of 50 male and female phantoms of ages 0 to 15 years, with percentile variations (5th to 95th) in waist circumference (WC) at each age. For each phantom, nominal values of kidney volume, length, and depth were incorporated into the phantom design. Organ absorbed doses, detriment-weighted doses, and stochastic risks were assessed using ICRP reference biokinetic models for both agents. In Monte Carlo radiation transport simulations, organ doses for these agents yielded detriment-weighted dose coefficients (mSv/MBq) that were in general larger than current ICRP values of the effective dose coefficients (age and WC-averaged ratios of eDW/e were 1.40 for the male phantoms and 1.49 for the female phantoms). Values of risk index (ratio of radiation-induced to natural background cancer incidence risk x 100) varied between 0.062 (newborns) to 0.108 (15-year-olds) for 99mTc-DMSA and between 0.026 (newborns) to 0.122 (15-year-olds) for 99mTc-MAG3. Using tallies of photon exit fluence as a rough surrogate for uniform image quality, our study demonstrated that through body region-of-interest optimization of AA, there is the potential for further dose and risk reductions of between factors of 1.5 to 3.0 beyond simple weight-based dosing guidance.

Dose Optimization of Hybrid Imaging.

Hybrid imaging combines the functional and molecular imaging of positron emission computed tomography and single-photon emission computed tomography with the anatomical information available from computed tomography and magnetic resonance imaging. As a result, the clinical utility of positron emission computed tomography/computed tomography and single-photon emission computed tomography/computed tomography has been clearly established in the past 17 y. In addition, the use of positron emission computed tomography/magnetic resonance, which was introduced to the clinic in the past decade, has continued to grow. These multimodality approaches to medical imaging have substantial dosimetric aspects associated with their practice in both adults and children. For positron emission computed tomography/computed tomography and single-photon emission computed tomography/computed tomography, one must consider the radiation dose delivered from both the radiopharmaceutical and the computed tomography portion of the hybrid scan. Whether the computed tomography is to be used solely for attenuation correction, anatomical correlation of patient, or full diagnosis must be taken into account when deciding on the computed tomography acquisition parameters. Even after 17 y, the most appropriate approach to the acquisition of these modalities is not fully established. When appropriately used, positron emission computed tomography/magnetic resonance provides the opportunity for notable dose reduction. In addition to the elimination of the radiation dose from the computed tomography, one may consider the higher sensitivity of the positron emission computed tomography component relative to that used in positron emission computed tomography/computed tomography and the longer acquisition time to reduce the amount of administered activity of the radiopharmaceutical. However, one must realize that magnetic resonance presents a different set of safety concerns outside of those associated with ionizing radiation. As with all medical procedures, the benefits as well as the potential risks of the procedure need to be evaluated in the context of choosing the most appropriate procedure to be performed and the optimization of acquisition protocol to assure high-quality clinical information with the least potential for risk possible.

Re-evaluation of pediatric 18F-FDG dosimetry: Cristy-Eckerman versus UF/NCI hybrid computational phantoms.

Because of the concerns associated with radiation exposure at a young age, there is an increased interest in pediatric absorbed dose estimates for imaging agents. Almost all reported pediatric absorbed dose estimates, however, have been determined using adult pharmacokinetic data with radionuclide S values that take into account the anatomical differences between adults and children based upon the older Cristy-Eckerman (C-E) stylized phantoms. In this work, we use pediatric model-derived pharmacokinetics to compare absorbed dose and effective dose estimates for 18F-FDG in pediatric patients using S values generated from two different geometries of computational phantoms. Time-integrated activity coefficients of 18F-FDG in brain, lungs, heart wall, kidneys and liver, retrospectively, calculated from 35 pediatric patients at the Boston's Children Hospital were used. The absorbed dose calculation was performed in accordance with the Medical Internal Radiation Dose method using S values generated from the University of Florida/National Cancer Institute (UF/NCI) hybrid phantoms, as well as those from C-E stylized computational phantoms. The effective dose was computed using tissue-weighting factors from ICRP Publication 60 and ICRP Publication 103 for the C-E and UF/NCI, respectively. Substantial differences in the absorbed dose estimates between UF/NCI hybrid pediatric phantoms and the C-E stylized phantoms were found for the lungs, ovaries, red bone marrow and urinary bladder wall. Large discrepancies in the calculated dose values were observed in the bone marrow; ranging between -26% to +199%. The effective doses computed by the UF/NCI hybrid phantom S values were slightly different than those seen using the C-E stylized phantoms with percent differences of -0.7%, 2.9% and 2.5% for a newborn, 1 year old and 5 year old, respectively. Differences in anatomical modeling features among computational phantoms used to perform Monte Carlo-based photon and electron transport simulations for 18F, and very likely for other radionuclides, impact internal organ dosimetry computations for pediatric nuclear medicine studies.

How we read pediatric PET/CT: indications and strategies for image acquisition, interpretation and reporting.

PET/CT plays an important role in the diagnosis, staging and management of many pediatric malignancies. The techniques for performing PET/CT examinations in children have evolved, with increasing attention focused on reducing patient exposure to ionizing radiation dose whenever possible and minimizing scan duration and sedation times, with a goal toward optimizing the overall patient experience. This review outlines our approach to performing PET/CT, including a discussion of the indications for a PET/CT exam, approaches for optimizing the exam protocol, and a review of different approaches for acquiring the CT portion of the PET/CT exam. Strategies for PACS integration, image display, interpretation and reporting are also provided. Most practices will develop a strategy for performing PET/CT that best meets their respective needs. The purpose of this article is to provide a comprehensive overview for radiologists who are new to pediatric PET/CT, and also to provide experienced PET/CT practitioners with an update on state-of-the art CT techniques that we have incorporated into our protocols and that have enabled us to make considerable improvements to our PET/CT practice.

Stomach frame-count-based attenuation correction of dynamic posterior view gastric emptying scintigraphy with continuous acquisition in children.

BACKGROUND: When performing dynamic gastric emptying scintigraphy with continuous acquisition in children, a single posterior view acquisition is preferred because it allows the young patient to more easily interact with a parent or technologist even though this method tends toward overestimating gastric emptying. OBJECTIVES: The objective of our study was to develop a new attenuation correction (AC) method to improve the accuracy of the time activity curve and the measurement of residual gastric emptying from 1-h posterior images of gastric emptying scintigraphy with continuous acquisition. MATERIALS AND METHODS: We developed a frame-count-based AC for gastric emptying scintigraphy from the posterior view (posterior AC method). We retrospectively reviewed 122 gastric emptying studies performed in children using conjugated posterior and anterior views, and evaluated the statistical differences between posterior only (without AC) and posterior AC using the geometric mean method as a reference standard. RESULTS: The residual values obtained using posterior AC were not significantly different (P=0.813) compared to those using the geometric mean while the values using the posterior only were significantly different (P<0.001) from the geometric mean. CONCLUSION: The proposed method can replace the geometric mean method to estimate gastric emptying residual fraction using patient-friendly posterior view without a significant difference in 1-h gastric emptying scintigraphy with continuous acquisition.

Operational and Dosimetric Aspects of Pediatric PET/CT.

No consistent guidelines exist for the acquisition of a CT scan as part of pediatric PET/CT. Given that children may be more vulnerable to the effects of ionizing radiation, it is necessary to develop methods that provide diagnostic-quality imaging when needed, in the shortest time and with the lowest patient radiation exposure. This article describes the basics of CT dosimetry and PET/CT acquisition in children. We describe the variability in pediatric PET/CT techniques, based on a survey of 19 PET/CT pediatric institutions in North America. The results of the survey demonstrated that, although most institutions used automatic tube current modulation, there remained a large variation of practice, on the order of a factor of 2-3, across sites, pointing to the need for guidelines. We introduce the approach developed at our institution for using a multiseries PET/CT acquisition technique that combines diagnostic-quality CT in the essential portion of the field of view and a low-dose technique to image the remainder of the body. This approach leads to a reduction in radiation dose to the patient while combining the PET and the diagnostic CT into a single acquisition. The standardization of pediatric PET/CT provides an opportunity for a reduction in the radiation dose to these patients while maintaining an appropriate level of diagnostic image quality.