"Black bone" MRI: a partial flip angle technique for radiation reduction in craniofacial imaging

The potential harmful effects of ionising radiation continue to be highlighted. Radiation reduction techniques have largely consisted of low-dose techniques rather than a shift to non-ionising methods of imaging. CT scanning is frequently employed for imaging the craniofacial skeleton despite being one of the key anatomical regions for radiation protection in view of the radiosensitive lens and thyroid gland. We describe a low flip angle gradient echo MRI sequence which provides high image contrast between bone and other tissues but reduces the contrast between individual soft tissues. This permits the "black bone" to be easily distinguished from the uniformity of the soft tissues. While maintaining a repetition time of 8.6 ms and an echo time of 4.2 ms, the flip angle which provided optimised suppression of both fat and water was identified to be 5°. The biometric accuracy of this sequence was confirmed using a phantom to obtain direct anatomical measurements and comparable CT scanning. The average discrepancy between black bone MRI measurements and direct anatomical measurements was 0.32 mm. Black bone MRI therefore has the potential to reduce radiation exposure by replacing CT scanning when imaging the facial skeleton, with particular scope for imaging benign conditions in the young.

Early hyperlactataemia in critically ill children

OBJECTIVE

To examine the relationships between early hyperlactataemia, acidosis, organ failure, and mortality in children admitted to intensive care.

DESIGN

Prospective observational study. Children with lactate levels > 2 mmol/l were eligible for enrolment. Post-operative patients and those with inherited metabolic disease were excluded. Seven hundred and five children admitted to intensive care were screened, and 50 children with hyperlactataemia (incidence 7%), aged 20.3 months (0.1-191) were enrolled and followed up. The Paediatric Risk of Mortality (PRISM) score, Multiorgan System Failure (MOSF) score, length of ICU stay, and outcome were recorded. Data were collected for lactate (mmol/l), pH, and base excess (BE) until 24 h after admission. Data are reported as median (range) and were analysed by the Mann-Whitney, Fisher's Exact, and Kruskal-Wallis tests, and chisquared test for trend.

RESULTS

Overall mortality in the screening group was 70/705 (10%). In the study group (n = 50) median PRISM score was 19 (4-49), median MOSF score 2 (1-4), and observed mortality 32/50 (64%). Median duration of ICU stay was 6 days (2-32) in survivors, and median time until death 3 days (0-13) in nonsurvivors. Eleven nonsurvivors (34%) died within 24 h. In the screening group, hyperlactataemia on admission identified mortality with likelihood ratio = 15. In the study group, neither the admission lactate (3.8 vs 4.6 mmol/l, P = 0.27), pH (7.32 vs 7.30, P = 0.6), nor BE (-7.5 vs -8, P = 0.45) differed significantly between survivors and nonsurvivors. Neither the admission nor peak lactate increased with increasing MOSF score (P = 0.5 and 0.54). The median peak lactate level was 5 mmol/l (2-9.3) in survivors compared to 6.8 mmol/l (2.3-22) in nonsurvivors (P = 0.02), and the cumulative average lactate level was 2.4 mmol/l (1-4.9) in survivors, compared to 4.5 mmol/l (1.6-21) in nonsurvivors (P = 0.0003). Persistent hyperlactataemia 24 h after admission identified mortality with likelihood ratio = 7.

CONCLUSION

Hyperlactataemia on admission to intensive care is associated with a high mortality in children. Nonsurvivors within this group may be distinguished by the peak lactate level, or by persistent hyperlactataemia after 24 h of treatment.

Procalcitonin may help differentiate disseminated herpes simplex viral infection from bacterial sepsis in neonates

Disseminated herpes simplex virus infection is a potentially fatal condition which may be difficult to differentiate from bacterial sepsis. We report the case of a neonate with overwhelming herpes simplex (type 2) viraemia who presented with 'septic shock'.

CONCLUSION

A low procalcitonin level (1.6 ng/ml), inconsistent with bacteraemia, suggests an alternative aetiology and may strengthen the case for antiviral therapy.