The energy spectrum of X-ray photons after passage through an absorber contains information about its elemental composition. Thus, tissue characterisation becomes feasible provided that absorption characteristics can be measured or differentiated. Dual-energy CT uses two X-ray spectra enabling material differentiation by analysing material-dependent photo-electric and Compton effects. Elemental concentrations can thereby be determined using three-material decomposition algorithms. In comparison to dual-energy CT used in clinical practice, recently developed energy-sensitive photon-counting detectors sample the material-specific attenuation curves at multiple energy levels and within narrow energy bands; the latter allows the detection of element-specific, k-edge discontinuities of the photo-electric cross section. Multi-energy CT imaging therefore is able to concurrently identify multiple materials with increased accuracy. These specific data on material distribution provide information beyond morphological CT, and approach functional imaging. This article reviews the principles of dual- and multi-energy CT imaging, hardware approaches and clinical applications.

Objectives

The effect of preterm birth on growth of the corpus callosum is detectable by 6 weeks after delivery in preterm infants born at gestations of 23 to 33 weeks. Reduced growth of the corpus callosum in weeks 2 to 6, places these infants at elevated risks of later psychomotor delay and cerebral palsy.

Objective: A bedside method for assessing the effectiveness of strategies to improve cerebral development in very premature infants is desirable. The aim of this study was to compare the growth trajectory of the corpus callosum on cranial ultrasound in very premature infants and compare it with the growth rate seen antenatally. Methods: We recruited 100 very low birth weight infants admitted to a single regional Level III neonatal intensive care unit from November 1998 to November 2000. Sixty-four (32 boys) infants, mean gestational age 28 weeks (range 23-33 weeks), had cranial ultrasound images of the corpus callosum adequate for measurement obtained in the first week of life and at term equivalent. The length of corpus callosum was identified as the most reproducible measurement in a subgroup of 16 infants. The growth rate of the corpus callosum was compared in the 64 study infants to the expected growth rate of 0.20-0.27 mm/day from antenatal data; and correlated with clinical outcome at two years of age in 55 infants using Mental Development Index and Psychomotor Development Index. Results: The average growth rate of the corpus callosum was half the rate expected from antenatal data. Mean growth rates were similar for all age ranges (p = 0.4); 0.12 mm/day (0.07-0.17) for the 9 infants born at 23-25 weeks' gestation; 0.11 mm/day (0.06-0.18) for the 35 infants born at 26-29 weeks; 0.11 mm/day (0.05-0.29) for the 20 born at 30-33 weeks. Growth rate of the corpus callosum was greater in infants who had antenatal steroids (p = 0.02) or who were born IUGR (p = 0.04). There was no correlation with gender, PROM, multiple birth; or BPD or indomethicin postnatally. There was poor correlation with mental and psychomotor outcome. Conclusion: Measurement of the length of the corpus callosum at cranial ultrasound is reproducible. The length of corpus callosum grows at a much lower rate postnatally than in utero among very premature infants.

Clinical management of neonates with Trisomy 18 depends on a knowledge of life expectancy. True estimates of potential life span are required for genetic counselling purposes when parents interpret the genetic threat, not only in terms of the mathematical odds involved, but also in terms of the quality and length of life of an affected infant, should such be born. This paper reports the findings from a study to generate life tables for Trisomy 18. This study is a total population study over 10 years based on a primary population of 2.2 million. Forty‐eight cases of Trisomy 18 were identified, five at amniocentesis. Four of the 43 clinical cases (9%) were mosaics. The median life expectancy for live‐born infants was five days (range one hour to 18 months). Mean age at death was 48 days. Life tables, by sex and by sub‐types (associated congenital abnormalities) are presented. The annual incidence is 14 per 100,000 total births, with a prevalence estimate of 0.06 per 100,000 total population.