Gastric Emptying Studies in Pediatrics: A Cincinnati Children's Hospital Experience.

Gastric emptying studies are routinely performed in many nuclear medicine departments; however, there are many different techniques used to perform the procedure across the country. Creating consistency in clinical practice will aid gastroenterologists in diagnosing and treating illnesses associated with abnormalities related to gastric emptying. In 2017, Cincinnati Children's Hospital adopted adult standards for pediatric gastric emptying studies that included a standard meal along with imaging over the course of 4 h. Gastric emptying studies are the second-highest-volume examination performed in the nuclear medicine section at Cincinnati Children's Hospital. Accommodating this volume required changes in the scheduling template, scheduling questionnaire, and epic order sets, as well as identification of specific days and locations for gastric emptying studies. Both protocol standardization and workflow optimization are critically important in creating consistency in patient care. Gastric emptying can be evaluated with solid food, liquid food, or solid and liquid food simultaneously. The methodology of the study is initially determined by the ordering provider but may require special accommodations based on what the patient will tolerate. In coordination with the ordering and interpreting physicians, the nuclear medicine technologists at Cincinnati Children's Hospital have the decision-making ability to deviate from the provider's request as necessary, which helps expedite workflow and eliminates wasted time. Any deviation from the standardized protocol is documented by the nuclear medicine technologist and incorporated into the final report by the interpreting physician, as dietary information is meaningful to the ordering provider. Reference values associated with the standardized or modified protocol are also included in the final report.

Reduced count pediatric whole-body 18F-FDG PET imaging reconstruction with a Bayesian penalized likelihood algorithm.

BACKGROUND: Advanced positron emission tomography (PET) image reconstruction methods promise to allow optimized PET/CT protocols with improved image quality, decreased administered activity and/or acquisition times. OBJECTIVE: To evaluate the impact of reducing counts (simulating reduced acquisition time) in block sequential regularized expectation maximization (BSREM) reconstructed pediatric whole-body 18F-fluorodeoxyglucose (FDG) PET images, and to compare BSERM with ordered-subset expectation maximization (OSEM) reconstructed reduced-count images. MATERIALS AND METHODS: Twenty children (16 male) underwent clinical whole-body 18F-FDG PET/CT examinations using a 25-cm axial field-of-view (FOV) digital PET/CT system at 90 s per bed (s/bed) with BSREM reconstruction (ß=700). Reduced count simulations with varied BSREM ß levels were generated from list-mode data: 60 s/bed, ß=800; 50 s/bed, ß=900; 40 s/bed, ß=1000; and 30 s/bed, ß=1300. In addition, a single OSEM reconstruction was created at 60 s/bed based on prior literature. Qualitative (Likert scores) and quantitative (standardized uptake value [SUV]) analyses were performed to evaluate image quality and quantitation across simulated reconstructions. RESULTS: The mean patient age was 9.0 ± 5.5 (SD) years, mean weight was 38.5 ± 24.5 kg, and mean administered 18F-FDG activity was 4.5 ± 0.7 (SD) MBq/kg. Between BSREM reconstructions, no qualitative measure showed a significant difference versus the 90 s/bed ß=700 standard (all P>0.05). SUVmax values for lesions were significantly lower from 90 s/bed, ß=700 only at a simulated acquisition time of 30 s/bed, ß=1300 (P=0.001). In a side-by-side comparison of BSREM versus OSEM reconstructions, 40 s/bed, ß=1000 images were generally preferred over 60 s/bed TOF OSEM images. CONCLUSION: In children who undergo whole-body 18F-FDG PET/CT on a 25-cm FOV digital PET/CT scanner, reductions in acquisition time or, by corollary, administered radiopharmaceutical activity of >50% from a clinical standard of 90 s/bed may be possible while maintaining diagnostic quality when a BSREM reconstruction algorithm is used.

Simulated Reduced-Count Whole-Body FDG PET: Evaluation in Children and Young Adults Imaged on a Digital PET Scanner.

BACKGROUND. Digital PET scanners with increased sensitivity may allow shorter scan acquisition times or reductions in administered radiopharmaceutical activities. OBJECTIVE. The purpose of this study was to evaluate in children and young adults the impact of shorter simulated acquisition times on the quality of whole-body FDG PET images obtained using a digital PET/CT system. METHODS. This retrospective study included 27 children and young adults (nine male and 18 female patients) who underwent clinically indicated whole-body FDG PET/CT examinations performed using a 25-cm axial FOV PET/CT system at 90 s per bed position (expressed hereafter as seconds per bed). Raw list-mode data were reprocessed to simulate acquisition times of 60, 55, 50, 45, 40, and 30 s/bed. Three radiologists independently reviewed reconstructed images and assigned Likert scores for lesion conspicuity, normal structure conspicuity, image quality, and image noise. A separate observer recorded the SUVmax, SUVmean, and SD of the SUV (SUVSD) for liver, thigh, and the most FDG-avid lesion. The SUVSD/SUVmean (the SUVSD divided by the SUVmean) was calculated as a surrogate of image noise. ANOVA, the Friedman test, and the Dunn test were used to compare qualitative measures (combining reader scores) and SUV measurements. RESULTS. The mean patient age was 10.8 ± 8.3 (SD) years, mean BMI was 18.7 ± 2.9, and mean administered FDG activity was 4.44 ± 0.37 MBq/kg (0.12 ± 0.01 mCi/kg). No qualitative measure showed a significant difference versus 90 s/bed for the simulated acquisition at 60 s/bed (all p > .05). Significant differences (all p < .05) versus 90 s/bed were observed for lesion conspicuity at at most 40 s/bed, conspicuity of normal structures and overall image quality at at most 45 s/bed, and image noise at at most 55 s/bed. SUVmean was not significantly different from 90 s/bed for any site for any reduced-count simulation (all p > .05). SUVSD/SUVmean and SUVmax showed gradual increases with decreasing acquisition times and were significantly different from 90 s/bed only for liver at 60 s/bed (for SUVmax: 1.00 ± 0.00 vs 1.05 ± 0.03, p = .02; for SUVSD/SUVmean: 0.09 ± 0.02 vs 0.11 ± 0.02, p = .04). CONCLUSION. Favorable findings for the simulated acquisition at 60 s/bed suggest that, in children and young adults who undergo imaging performed using a 25-cm FOV digital PET scanner, acquisition time or administered FDG activity may be decreased by approximately 33% from the clinical standard without significantly impacting image quality. CLINICAL IMPACT. A 25-cm axial FOV digital scanner may allow FDG PET/CT examinations to be performed with reduced radiation exposure or faster scan acquisition times.

Nuclear Medicine Procedures in Children: Special Considerations.

Nuclear medicine imaging in children is best accomplished when a child-friendly environment is provided for patients and parents. An approach that minimizes patient anxiety and fear is described. International guidelines for administered activity should be used to minimize absorbed radiation doses from radiopharmaceuticals. CT exposure parameters may be reduced to pediatric best practice for diagnostic CT and further reduced when CT images are needed only for localization purposes.

Pre-medication to block [(18)F]FDG uptake in the brown adipose tissue of pediatric and adolescent patients.

BACKGROUND: Radiopharmaceutical uptake of [(18)F]2-deoxy-2-glucose (FDG) in brown adipose tissue is noted on 15-20% of positron emission tomography (PET) scans in children and adolescents. One report suggests that moderate-dose oral diazepam can partly or completely block FDG uptake in brown adipose tissue. OBJECTIVE: To determine whether [(18)F]FDG uptake in brown adipose tissue can be adequately blocked by pre-medication other than moderate-dose oral diazepam. MATERIALS AND METHODS: One hundred and eighteen [(18)F]FDG PET body imaging studies were performed in 69 pediatric patients with a variety of solid tumors. The mean age at the time of imaging was 12.9 years (range 1.2-22.6 years), and 33 studies were performed in patients younger than 10 years old. Seventy-six were performed in boys and 42 in girls. Patients were imaged using a dedicated PET camera. Pre-medication was given in 88 studies: 45 received intravenous fentanyl (0.75-1.0 mug/kg), 34 received low-dose oral diazepam (0.06 mg/kg) and 9 received moderate-dose oral diazepam (0.10 mg/kg). Thirty patients received no pre-medication, 7 of whom were known to have received opiates for pain during the 12 h before the study. Six body regions in the neck and chest were reviewed for [(18)F]FDG uptake in brown adipose tissue. Uptake of FDG in brown fat was visually graded: 0 for no FDG uptake, 1 for low-grade uptake, 2 for moderate uptake, and 3 for intense uptake. Visual grades 2 and 3 were considered to interfere potentially with image interpretation in the neck and chest. Data were analyzed by multivariate regression using a Poisson distribution. RESULTS: [(18)F]FDG uptake in brown adipose tissue was most often seen in the lateral neck region and superior and lateral to the lungs (in 36 and 39 studies, respectively). Uptake was also seen near the costovertebral junctions (15 studies), in the superior and central neck in 7 studies and in the anterior mediastinum in 2. Brown adipose tissue uptake was thought to interfere potentially with image interpretation (visual grades 2 and 3) in 19 studies-in 6 of 23 (26.1%) studies after no pre-medication and no opiates for pain, in 10 of 34 (29.4%) after low-dose oral diazepam, in 0 of 9 (0%) after moderate-dose oral diazepam, in 3 of 45 (6.7%) after intravenous fentanyl, and in 0 of 7 (0%) after opiates prescribed for pain. Intravenous fentanyl reduced the grade of brown adipose tissue compared to no drug (P=0.0039) and low-dose diazepam (P=0.0024). Low-dose diazepam had no effect when compared to no drug (P=0.984). There were inadequate data for statistical testing of moderate-dose valium and opiates prescribed for pain. Children younger than 10 years had lower uptake grades (P=0.019) than those older than 10 years. SUMMARY: The frequency of interfering [(18)F]FDG uptake in brown adipose tissue is reduced by intravenous fentanyl pre-medication, which appears to be an effective alternative to the existing standard pre-medication, moderate-dose oral diazepam.