Search

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. [ABSTRACT FROM AUTHOR]

Purpose: In the current clinical practice, administered activity (AA) for pediatric molecular imaging is often based on the North American expert consensus guidelines or the European Association of Nuclear Medicine dosage card, both of which were developed based on the best clinical practice. These guidelines were not formulated using a rigorous evaluation of diagnostic image quality (IQ) relative to AA. In the guidelines, AA is determined by a weight‐based scaling of the adult AA, along with minimum and maximum AA constraints. In this study, we use task‐based IQ assessment methods to rigorously evaluate the efficacy of weight‐based scaling in equalizing IQ using a population of pediatric patients of different ages and body weights. Methods: A previously developed projection image database was used. We measured task‐based IQ, with respect to the detection of a renal functional defect at six different AA levels (AA relative to the AA obtained from the guidelines). IQ was assessed using an anthropomorphic model observer. Receiver‐operating characteristics (ROC) analysis was applied; the area under the ROC curve (AUC) served as a figure‐of‐merit for task performance. In addition, we investigated patient girth (circumference) as a potential improved predictor of the IQ. Results: The data demonstrate a monotonic and modestly saturating increase in AUC with increasing AA, indicating that defect detectability was limited by quantum noise and the effects of object variability were modest over the range of AA levels studied. The AA for a given value of the AUC increased with increasing age. The AUC vs AA plots for all the patient ages indicate that, for the current guidelines, the newborn and 10‐ and 15‐yr phantoms had similar IQ for the same AA suggested by the North American expert consensus guidelines, but the 5‐ and 1‐yr phantoms had lower IQ. The results also showed that girth has a stronger correlation with the needed AA to provide a constant AUC for 99mTc‐DMSA renal SPECT. Conclusions: The results suggest that (a) weight‐based scaling is not sufficient to equalize task‐based IQ for patients of different weights in pediatric 99mTc‐DMSA renal SPECT; and (b) patient girth should be considered instead of weight in developing new administration guidelines for pediatric patients. [ABSTRACT FROM AUTHOR]

Introduction: Although vesicoureteral reflux (VUR) associated with bacteriuria may cause renal scarring, sterile VUR is thought not to cause renal injury. However, in many infants with high grade reflux, renal scarring is found even though bacteriuria is not present. In this study, we sought to determine the incidence of renal abnormality as assessed by DMSA renal scan in infants with high grade VUR but without a prior history of urinary tract infection. Methods: We retrospectively reviewed the results of Tc-99m DMSA renal scan performed during the first six months of life on infants with VUR detected during an evaluation of hydronephrosis identified prenatally or for sibling screening. Correlation was made with renal ultrasonography. We excluded infants with a history of urinary tract infection, evidence of ureteropelvic junction or bladder outlet obstruction as documented on intravenous pyelogram or voiding cystourethrogram (VCUG). All renal nuclear scans were reviewed by one radiologist (LC) while the corresponding sonograms were reviewed independently by another (CB). Of the 34 infants (28 boys and 6 girls) who met the criteria, VUR was bilateral in 25 and unilateral in 9. Thirty-eight of the 59 refluxing renal units had grade IV or V, 18 grade II or III and 3 grade I reflux. Median age at time of the DMSA renal scan was 2.2 months (range 0.5-5.8). Results: DMSA renal scan identified parenchymal abnormalities in 65% (22) of the patients and 39% (23) of the refluxing renal units. The majority of these patients were male (19 compared to 3 female) and had bilateral VUR (15 compared to 7 unilateral cases). Differential uptake [is less than] 40% and cortical defects were seen in 10 refluxing units, differential uptake [is less than] 40% without cortical defects in 7 and cortical defects alone in 6. Of the 23 refluxing renal units with DMSA abnormalities, 20 were associated with Grade IV or V and 3 with Grade II or III. Interestingly, only 42% of the patients with an abnormal DMSA scan had sonographic evidence of a parenchymal abnormality. Conclusions: We observed that of those children with high grade reflux in whom we had obtained DMSA renal scans, the majority had decreased differential function, cortical defects or both. Furthermore, not all those with renal parenchymal defects were identified by renal ultrasonography. These findings suggest that many infants with high grade VUR may have evidence of renal injury in the absence of bacteriuria and that DMSA renal scans, rather than renal sonograms alone, are useful in the follow-up care of these patients in assessing the detrimental effects of VUR on the kidneys., Hiep T. Nguyen, MD, Leonard Connolly, MD, Carol Barnewolt, MD, Patti L. Ephraim, S. Ted Treves, MD, Craig A Peters, MD, FAAP and Stuart B, Bauer, MD, FAAP. Department of [...]