Serial magnetic resonance diffusion and hemodynamic imaging in a neonatal rabbit model of hypoxic-ischemic encephalopathy

Dynamic changes in relative cerebral blood volume (rCBV) and apparent diffusion coefficient (ADC) were investigated, using high speed magnetic resonance imaging (MRI) in an acute neonatal rabbit model of hypoxic-ischemic encephalopathy (HIE). Serial rCBV imaging used a magnetic susceptibility blood pool contrast agent. Interleaved ADC and rCBV images were acquired with 9 s temporal resolution. Rabbits received unilateral common carotid artery (CCA) ligation followed by hypoxia. rCBV increased bilaterally within 1-2 min after the onset of hypoxia. A biphasic ADC decline was observed: a slowly declining phase (84 +/- 18% of baseline) followed by a rapid, focal drop to 55 +/- 8% of baseline in the ipsilateral cortex, which was paralleled by a rapid focal rCBV drop to 70 +/- 17% of baseline. ADC decline generally began in a small region of ipsilateral cortex and spread over the ipsilateral cortex, ipsilateral subcortical tissue and contralateral cortex. The initial ADC drop usually preceded the initial rCBV drop by approximately 60 s, however at later timepoints rCBV decline sometimes preceded ADC decline. Upon normoxia, rCBV recovered to about baseline values while ADC recovered to baseline or above. This method provides a sensitive means of non-invasively visualizing acute hemodynamic- and metabolic-related changes in HIE with good temporal and spatial resolution.     

Near-infrared frequency-domain optical spectroscopy and magnetic resonance imaging: a combined approach to studying cerebral maturation in neonatal rabbits

The neonatal rabbit brain shows prolonged postnatal development both structurally and physiologically. We use noninvasive near-IR frequency-domain optical spectroscopy (NIRS) and magnetic resonance imaging (MRI) to follow early developmental changes in cerebral oxygenation and anatomy, respectively. Four groups of animals are measured: NIRS in normals, MRI in normals, and both NIRS and MRI with hypoxia-ischemia (HI) (diffusion MRI staging). NIRS and/or MRI are performed from P3 (postnatal day=P) up to P76. NIRS is performed on awake animals with a frequency-domain tissue photometer. Absolute values of oxyhemoglobin concentration ([HbO2]), deoxyhemoglobin concentration ([HbR]), total hemoglobin concentration (HbT), and hemoglobin saturation (StO2) are calculated. The brains of all animals appeared to be maturing as shown in the diffusion tensor MRI. Mean optical coefficients (reduced scattering) remained unchanged in all animals throughout. StO2 increased in all animals (40% at P9 to 65% at P43) and there are no differences between normal, HI controls, and HI brains. The measured increase in StO2 is in agreement with the reported increase in blood flow during the first 2 months of life in rabbits. HbT, which reflects blood volume, peaked at postnatal day P17, as expected since the capillary density increases up to P17 when the microvasculature matures.     

Is there an interaction between cervical length and cervical microbiology in the pathogenesis of preterm labour?

Transvaginal ultrasound of the cervix is increasingly used to estimate cervical length during pregnancy. Initially used to determine a possible need for cervical suture, the technique has been shown to be of value in the prediction of preterm delivery In addition, bacterial vaginosis has been shown to be associated with an increased risk of preterm delivery. We hypothesised that shortening of the cervix and potential cervical pathogens, in particular the presence of bacterial vaginosis, act synergistically in the pathogenesis of premature labour. Three hundred and sixteen women were recruited for prospective longitudinal follow-up, with both transvaginal ultrasound and cervical bacteriology performed at approximately 18 and 28 weeks gestation. A strong correlation was found between a shortened cervix and preterm delivery (p<0.02 at 18 weeks; p<0.001 at 28 weeks). Women with both a short cervix and cervical pathogens had the highest risk of preterm delivery (43%), although not significantly greater than a short cervix with normal cervical flora (31% preterm delivery). In the presence of a normal cervical length, preterm delivery rates in the presence of normal flora and potential cervical pathogens were much lower (9% and 5% respectively).     

Diffusion-weighted interleaved echo-planar imaging with a pair of orthogonal navigator echoes

This work describes a diffusion-weighted (DW) interleaved echo-planar imaging (IEPI) method for use on either conventional whole-body scanners or scanners equipped with highspeed gradient and receiver hardware. In combination with cardiac gating and motion correction with a pair of orthogonal navigator echoes, the presented method is time-efficient, compensates for patient motions, and is less sensitive to image distortions than single-shot methods. The motion-correction scheme consists of correction for constant and linear phase terms found from the orthogonal navigator echoes. The correction for the linear phase term in the phase-encode direction includes gridding the data to the Cartesian grid. The DW IEPI was used to image a phantom rotating about the slice-select direction, and motion correction was performed to eliminate ghost artifacts arising from motion in either the readout- or phase-encoding directions. DW IEPI with motion correction was performed on a normal volunteer and on a patient with a 26-day-old region of ischemia over much of the right hemisphere.