Radiation Dose and Image Quality in Pediatric Neck CT.

BACKGROUND AND PURPOSE: Optimization of pediatric neck CT protocols is of critical importance in order to maintain good diagnostic image quality while reducing the radiation burden. Our aim was to evaluate the image quality of pediatric neck CT studies before and after the implementation of a low radiation dose protocol. MATERIALS AND METHODS: We retrospectively reviewed 179 pediatric neck CT studies, 75 before and 104 after the implementation of low-dose protocols, performed in children 0-16 years of age. The 2 cohorts were divided into 3 age groups, 0-4, 5-9, and 10-16 years. The signal-to-noise ratio was calculated using the axial image through the true vocal folds. Three neuroradiologists assessed the image quality of the same CT scan using a 5-point scoring system. We compared the CT dose index volume, dose-length product, image-quality ratings, and SNR of studies conducted at baseline and with low-dose protocols. RESULTS: Image-quality ratings were lower in the low-dose than in the baseline cohort in children 10-16 years of age, but not in children 0-4 and 5-9 years of age. The SNR was lower in the low-dose cohort than in the baseline cohort in children 0-4 and 10-16 years of age, but not in children 5-9 years of age. Despite the decrease in image-quality scores in older children, 97% of the studies (73/75) in the baseline cohort and 96% of studies (100/104) in the low-dose cohort were considered of sufficient image quality. CONCLUSIONS: Images acquired with the low-dose CT protocols were deemed to be of sufficient quality for making a clinical diagnosis. Our initial results suggest that there may be an opportunity for further radiation dose reduction without compromising diagnostic image quality using iterative reconstruction algorithms.

Development of High Signal Intensity within the Globus Pallidus and Dentate Nucleus following Multiple Administrations of Gadobenate Dimeglumine.

BACKGROUND AND PURPOSE: Previous studies have evaluated various gadolinium based contrast agents and their association with gadolinium retention, however, there is a discrepancy in the literature concerning the linear agent gadobenate dimeglumine. Our aim was to determine whether an association exists between the administration of gadobenate dimeglumine and the development of intrinsic T1-weighted signal in the dentate nucleus and globus pallidus. MATERIALS AND METHODS: In this single-center, retrospective study, the signal intensity of the globus pallidus, dentate nucleus, thalamus, and middle cerebellar peduncle was measured on unenhanced T1-weighted images in 29 adult patients who had undergone multiple contrast MRIs using exclusively gadobenate dimeglumine (mean, 10.1 ± 3.23 doses; range, 6-18 doses). Two neuroradiologists, blinded to the number of prior gadolinium-based contrast agent administrations, separately placed ROIs within the globi pallidi, thalami, dentate nuclei, and middle cerebellar peduncles on the last MR imaging examinations. The correlations between the globus pallidus:thalamus and the dentate nucleus:middle cerebellar peduncle signal intensity ratios with the number of gadolinium-based contrast agent administrations and cumulative dose were tested with either 1-tailed Pearson or Spearman correlations. A priori, P < .05 was considered statistically significant. RESULTS: Both the globus pallidus:thalamus and dentate nucleus:middle cerebellar peduncle ratios showed significant correlation with the number of gadolinium-based contrast agent administrations (r = 0.39, P = .017, and r = 0.58, P = .001, respectively). Additionally, the globus pallidus:thalamus and dentate nucleus:middle cerebellar peduncle ratios showed significant correlation with the cumulative dose of gadobenate dimeglumine (r = 0.48, P = .004, and r = 0.43, P = .009, respectively). Dentate nucleus hyperintensity was qualitatively present on the last MR imaging in 79.3%-86.2% of patients and in all patients who had received >10 doses. CONCLUSIONS: At high cumulative doses (commonly experienced by patients, for example, with neoplastic disease), gadobenate dimeglumine is associated with an increase in the globus pallidus:thalamus and dentate nucleus:middle cerebellar peduncles signal intensity ratios.

Effects of ovariectomy on the neuroendocrine axes regulating reproduction and energy balance in young cynomolgus macaques.

Degeneration of the ovary in middle-aged women results in castrate levels of ovarian steroids and increased gonadotropin secretion from the anterior pituitary gland. Ageing in women is also accompanied by significant changes in energy homeostasis. We have observed alterations in hypothalamic morphology and gene expression in older women, including hypertrophy and increased gene expression of neurokinin B (NKB) neurones, elevated levels of gonadotropin releasing-hormone (GnRH) mRNA and decreased numbers of neurones expressing pro-opiomelanocortin (POMC) mRNA. To determine if loss of ovarian steroids could produce comparable changes in gene expression in young primates, we measured the effects of ovariectomy on NKB, GnRH and POMC gene expression in young cynomolgus monkeys. We also measured serum leptin and body weight to examine the consequences of ovariectomy on energy balance. NKB neurones in the infundibular nucleus of ovariectomized monkeys were larger, more numerous and displayed increased levels of NKB mRNA compared to those of intact controls. Moreover, ovariectomy increased the number of neurones expressing GnRH gene transcripts and elevated serum luteinizing hormone. By contrast, several parameters related to energy balance, including POMC gene expression, serum leptin and body weights, were unchanged by ovariectomy. Thus, the rise in NKB and GnRH gene expression in older women was simulated by ovariectomy in monkeys, but the changes in POMC gene expression and energy balance were not. This study provides strong support for the hypothesis that ovarian failure contributes to the increased NKB and GnRH gene expression observed in postmenopausal women.