Reducing Radiation Exposure to Paediatric Patients Undergoing [18F]FDG-PET/CT Imaging.

PURPOSE: To investigate the possibility of reducing the injected activity for whole-body [18F]FDG-PET/CT studies of paediatric oncology patients and to assess the usefulness of time-of-flight (TOF) acquisition on PET image quality at reduced count levels. PROCEDURES: Twenty-nine paediatric oncology patients (12F/17M, 3-18 years old (median age 13y), weight 45±20 kg, BMI 19±4 kg/m2), who underwent routine whole-body PET/CT examinations on a Siemens Biograph mCT TrueV system with TOF capability (555ps) were included in this study. The mean injected activity was 156 ± 45 MBq (3.8 ± 0.8 kg/MBq) and scaled to patient weight. The raw data was collected in listmode (LM) format and pre-processed to simulate reduced levels of [18F]FDG activity (75, 50, 35, 20 and 10% of the original counts) by randomly removing events from the original LM data. All data were reconstructed using the vendor-specific e7-tools with standard OSEM only, with OSEM plus resolution recovery (PSF). The reconstructions were repeated with added TOF (TOF) and PSF+TOF. The benefit of TOF together with the reduced count levels was evaluated by calculating the gains in signal-to-noise ratio (SNR) in the liver and contrast-to-noise ratio (CNR) in all PET-positive lesions before and after TOF employed at every simulated reduced count level. Finally, the PSF+TOF images at 50, 75 and 100% of counts were evaluated clinically on a 5-point scale by three nuclear medicine physicians. RESULTS: The visual inspection of the reconstructed images did not reveal significant differences in image quality between 75 and 100% count levels for PSF+TOF. The improvements in SNR and CNR were the greatest for TOF reconstruction and PSF combined. Both SNR and CNR gains did increase linearly with the patients BMI for both OSEM only and PSF reconstruction. These benefits were observed until reducing the counts to 50 and 35% for SNR and CNR, respectively. CONCLUSIONS: The benefit of using TOF was noticeable when using 50% or greater of the counts when evaluating the CNR and SNR. For [18F]FDG-PET/CT, whole-body paediatric imaging the injected activity can be reduced to 75% of the original dose without compromising PET image quality.

High grade primary vesicoureteral reflux in boys: long-term results of a prospective cohort study.

PURPOSE: We evaluated the incidence of new permanent defects in boys with grade 4 or 5 vesicoureteral reflux, identified the risk factors for new permanent defects and reviewed the outcome of different management approaches by assessing the rates of urinary tract infection and new permanent defects. MATERIALS AND METHODS: This prospective cohort study recruited patients from July 1995 to December 2006. Study inclusion criteria were male gender and grade 4 or 5 primary vesicoureteral reflux. Patients were divided into 2 groups by presentation mode, including group 1-prenatal reflux diagnosis and group 2-reflux diagnosed after investigation for urinary tract infection. All patients underwent initial renal (99m)Tc-dimercapto-succinic acid scan evaluation. Continuous antibiotic prophylaxis was given in all patients until at least age 2 years. Surgical correction for reflux was done in 28 patients and 76 were circumcised. Followup included renal (99m)Tc-dimercapto-succinic acid scan with renal ultrasound at age 12 months with repeat (99m)Tc-dimercapto-succinic acid scan at ages 2 and 4 years. RESULTS: Included in our study were 151 patients (206 high grade refluxing renal units) with a median age at diagnosis of 1.9 months (range 1 day to 8.8 years). Median age at first followup was 14 months (range 3 months to 3 years) and at next followup it was 39 months (range 10 months to 11.3 years). There were 52 boys (34%) in group 1 and 99 (66%) in group 2. Baseline perfusion defects on initial renal (99m)Tc-dimercapto-succinic acid scan were identified in 41 of 52 boys (78.8%) in group 1 and in 74 of 99 (74.7%) in group 2. During followup new permanent defects developed in 8 of 52 boys (15%) in group 1 and in 10 of 99 (10%) in group 2. In 18 patients a total of 20 renal units showed new permanent defects, including 13 in kidneys with baseline perfusion defects and 7 in previously normal kidneys (p >0.9). In groups 1 and 2 combined infection developed before and after circumcision in 62 of 137 (45.2%) and 5 of 74 cases (6.7%), respectively (p <0.001). New permanent defects were seen in 4 of 76 circumcised (5.2%) and in 14 of 137 uncircumcised boys (10.2%) (p >0.3). CONCLUSIONS: Baseline perfusion defects were seen on (99m)Tc-dimercapto-succinic acid scan at presentation in 115 of our 151 patients (76%) independent of presentation mode. New permanent defects developed in abnormal and previously normal kidneys, and were associated with urinary tract infection. Being circumcised was associated with fewer urinary tract infections and a lower incidence of observed new permanent defects (5.2% vs 10.2%).

Hepatobiliary scintigraphy with SPECT in infancy.

UNLABELLED: Hepatobiliary scintigraphy (HBS) is an important investigation for the diagnosis of biliary atresia (BA) and its differentiation from causes of conjugated hyperbilirubinemia that do not require surgical intervention. Delayed imaging at 24 hours and phenobarbitone augmentation for 5 days has been required to achieve high sensitivity and specificity with current techniques. This study explores whether adding single photon emission computed tomography (SPECT) performs as well as existing methods without requiring delayed 24-hour imaging and whether the phenobarbitone premedication is necessary in all cases. METHODS: A retrospective analysis of 105 HBS studies on 94 patients was performed. HBS included SPECT at 4 to 6 hours postinjection when no tracer was seen in the gastrointestinal tract in the first 60 minutes. This was done in 80 patients. RESULTS: Gastrointestinal activity was seen in 14 patients within 60 minutes. For 4- to 6-hour studies, standard HBS and HBS with SPECT data showed a sensitivity of 100% for the diagnosis of BA. The specificity, accuracy, and positive likelihood ratios (PLR) were 67%, 75%, and 3 (confidence interval [CI]=2.03-4.16) for planar imaging at 4 to 6 hours and 90%, 93%, and 10 (CI=4.42-19) for 4- to 6-hour planar and SPECT imaging. When the 11 patients who had phenobarbitone stimulation were included, the results improved to 97%, 98%, and 30 (CI=7.06-80). CONCLUSION: The addition of SPECT 4 to 6 hours postinjection of tracer significantly improves the diagnostic accuracy of hepatobiliary scintigraphy compared with planar imaging alone. This accuracy is as good as HBS performed after phenobarbitone stimulation. The combined technique of HBS with SPECT and phenobarbitone has the highest accuracy. Delayed imaging at 24 hours is usually not necessary.

Nephrotoxicity with cyclooxygenase 2 inhibitor use in children.

The nephrotoxic potential of anti-inflammatory drugs alone and in compound preparations has been known for over fifty years. Nephrotoxicity associated with selective cyclooxygenase 2 (COX-2) inhibitor use is reported in adult patients but not in children. We present here the first report of reversible acute renal failure associated with the COX-2 inhibitor rofecoxib (Vioxx) in three children. Patient 1, an 18 month old girl with neonatal Bartter syndrome, developed acute renal failure with a peak creatinine of 1.9 mg/dl (164 micromol/l) and severe hyperkalemic metabolic acidosis. Patient 2, a 14 year old boy with a history of rheumatic fever, developed acute renal failure with a peak creatinine of 2.7 mg/dl (240 micromol/l). While patient 3, a healthy 14 year old girl, developed acute renal failure and tubulointerstitial nephritis confirmed on renal biopsy with a peak creatinine of 3.3 mg/dl (287 micromol/L). All children had been taking non-selective non-steroidal anti-inflammatory drugs (NSAID's) immediately prior to rofecoxib use. Renal function returned to normal within one week in all three patients and has remained normal at follow-up. This paper highlights the nephrotoxic risk of COX-2 inhibitor use in the pediatric population.