Establishing diagnostic reference levels for pediatric fluoroscopic examinations in a tertiary hospital.

BACKGROUND: Diagnostic reference levels (DRLs) identify unusually high patient radiation exposures and are required for dose optimisation. DRLs for pediatric fluoroscopic examinations are not widely determined in Australia. OBJECTIVE: Our objectives were to establish DRLs for pediatric fluoroscopic examinations in a South Australian tertiary hospital and compare these to previously published data and to explore relationships between patient dose area product (DAP), age and fluoroscopy times. MATERIALS AND METHODS: Dose data from 365 pediatric patients undergoing 5 fluoroscopic examinations were retrospectively collected for a 3-year period commencing January 2018 to develop local DRLs. Relationships between DAP, age and fluoroscopy time were explored using scatterplots, Spearman's correlation, and regression analyses. RESULTS: Local DRLs were significantly lower than data published previously, possibly reflecting technological and procedural advancements. Each 1-year increase in patient age was associated with a 0.77 µGy·m2 increase in DAP for barium meal and follow-through studies (95% confidence interval [CI]=0.055, 1.48) (P=0.04), and a 1.37 µGy·m2 increase in DAP for barium swallow studies (95% CI=0.61, 2.12) (P<0.001). A low correlation was demonstrated between DAP and fluoroscopy time for micturating cystourethrography studies (r=0.35, 95% CI=0.15, 0.51, P<0.001) and barium meal and follow-through studies (r=0.37, 95% CI= -0.011, 0.65, P=0.05). Age and fluoroscopy time were not significantly related. CONCLUSION: This study provides updated Australian pediatric fluoroscopic DRLs, with the intention of promoting a national database for benchmarking pediatric doses. The local DRLs can be used for dose comparisons and optimisation between facilities.

A USPIO doped gel phantom for R2* relaxometry.

OBJECTIVE: This work describes a phantom containing regions of controlled R2* (1/T2*) values to provide a stable reference object for testing implementations of R2* relaxometry commonly used for liver and heart iron assessments. MATERIALS AND METHODS: A carrageenan-strengthened gadolinium DTPA doped agarose gel was used to enclose nine gels additionally doped with ultra-small superparamagnetic iron oxide. R2* values were determined at 1.5 T using multi-echo GRE sequences and exponential regression of pixel values from a region of interest against echo time using non-linear regression algorithms. We measured R2*, R2 and R1 values and the inter-scan and inter-operator reproducibility. RESULTS: The phantom reliably demonstrated R2* values in seven steps between 22.4 s-1 (SE 1.98) and 441.9 s-1 (SE 6.76), with an R2* relaxivity (r2*) of 792 (SE 5.6) mM-1 s-1. The doped gels displayed a concentration-dependent R2' component of R2* phantom, indicating superparamagnetic enhancement effects. We observed no significant change in relaxivity (r2*) over 12 months, and estimate a useful life of 3 years. Detailed descriptions of the production process and calculators are been provided as Online Resources. CONCLUSION: The phantom provides a durable test object with controlled R2* relaxation behaviour, useful for a range of R2* relaxometry reference work.

Early and progressive circadian abnormalities in Huntington's disease sheep are unmasked by social environment.

Insidious changes in behaviour herald the onset of progressive neurodegenerative disorders such as Huntington's disease (HD), sometimes years before overt symptoms are seen. Sleep and circadian disturbances are particularly disruptive symptoms in patients with neurological disorders, but they are difficult to measure in humans. Here we studied circadian behaviour in transgenic HD sheep expressing the full-length human huntingtin protein with an expanded CAG repeat mutation in the juvenile range. Young HD sheep with no other symptoms exhibited circadian behavioural abnormalities that worsened with age. The most obvious change was a disturbed evening behaviour reminiscent of 'sundowning' that is seen in some patients with dementia. There were no structural abnormalities seen with magnetic resonance imaging, even in 5-year-old HD sheep. Interestingly, detection of the circadian abnormalities depended upon their social grouping. Abnormalities emerged in sheep kept in an 'HD-only' flock, whereas the behaviour of HD sheep kept mixed with normal sheep was relatively normal. Sleep-wake abnormalities in HD patients are also likely to be hidden, and may precede overt symptoms by many years. Sleep disruption has deleterious effects, even in normal people. The knock-on effects of sleep-wake disturbance may exacerbate, or even cause symptoms such as irritability and depression that are common in early stage HD patients. HD sheep will be useful models for probing the mechanisms underlying circadian behavioural disorder in HD.