Rachel J. Moore

Fetal brain activity demonstrated by functional magnetic resonance imaging

Functional magnetic resonance imaging was used to study fetal brain activity. This activity was in response to an auditory stimulus.

Fetal Brain Activity in Response to a Visual Stimulus

Previous studies have demonstrated the use of functional magnetic resonance imaging (fMRI) to assess fetal brain activity. To extend these studies, a fetal fMRI experiment using a visual stimulus has been performed at 0.5 T. This used a block fMRI paradigm with a bright, constant‐intensity light source being shone at the maternal abdomen for 8 sec followed by 16 sec of darkness. This was repeated typically 40 times on nine subjects all of whom were greater than 36 weeks gestational age. Of these, one could not be analysed due to motion, three did not show significant activation, and five showed significant activation (P < 0.0085). In all cases, activation was localised within the frontal cortex. Exact localisation was difficult but this may correspond to the frontal eye fields and dorsolateral prefontal cortex. In no cases was significant activation present within the occipital region as would have been expected and was observed in 2/8 adult subjects. Hum. Brain Mapping 20:239–245, 2003.

Antral motility measurements by magnetic resonance imaging

Magnetic resonance imaging has been recently proposed as a promising, noninvasive technique to assess the motility of the gastric antrum. However, so far the reproducibility and dependence on test meal composition has not been evaluated. In this study, snapshot echo‐planar magnetic resonance imaging was used to measure the frequency, propagation speed and percentage occlusion of antral contractions in 28 healthy volunteers. They were fed either liquid (n=12), mixed liquid/solid (n=8) or mixed viscous/solid (n=8) nutrient (1350 kJ) test meals, and a total of 208 motility measurements were performed. No effect of meal type on antral motility parameters was observed. Antral contraction frequency was 3.0 ± 0.2 min−1 (mean ± SD, n=164), propagation speed was 1.6 ± 0.2 mm s−1 (n=164) and the percentage occlusion was 58 ± 14% (n=76). Overall, 21% of measurements did not provide useful antral motility data, because, in the supine position, the antrum was not filled by the test meal. Simple methods to overcome this and reduce scanning time to a minimum are proposed. The results show that the noninvasive magnetic resonance imaging evaluation of antral motility is accurate and reproducible and has potential to become a standard tool for such investigations.

Non-invasive mapping of placental perfusion

BACKGROUND We aim to develop a clinical technique for the non-invasive measurement of placental perfusion, to enable early detection of intrauterine growth restriction (IUGR). Pregnancies with this complication are characterised by low placental perfusion. METHODS We measured placental perfusion by means of perfusion-sensitive echoplanar imaging (EPI); a rapid method of making magnetic resonance images. Perfusion measurements were done on six healthy volunteers with normal pregnancies and nine with pregnancies complicated by IUGR. Perfusion maps were created to assess the relation between placental perfusion and fetal size at birth. FINDINGS Pregnancies complicated by IUGR differed significantly from normal pregnancies in patterns of perfusion within the placenta (p<0.0001, ANOVA). Subsequent analysis showed that the proportion of placentas with low perfusion rates was higher in the IUGR group than in the normal group. A significant correlation between areas of reduced placental perfusion and fetal size was demonstrated (p=0.041, Spearmans rank correlation). INTERPRETATION Non-invasive imaging of placental perfusion by means of EPI has potential as a clinical tool in assessing the dynamics of placental perfusion.

Antenatal determination of fetal brain activity in response to an acoustic stimulus using functional magnetic resonance imaging.

Functional magnetic resonance imaging (fMRI) is now a well‐established technique for directly identifying adult brain activity. This study builds on earlier pilot work that showed that fMRI could provide direct evidence of fetal brain cortical activation in response to an auditory stimulus. The new work presented here aims to assess the sensitivity of this technique in a larger sample group. This article includes a specific discussion of the methodology required for fetal fMRI. Sixteen pregnant subjects were scanned between 37 and 41 weeks gestation, 12 had an auditory stimulus applied to the maternal abdomen (study group) and 4 had an auditory stimulus applied to the mothers ears (control group). Two of twelve (2/12) study‐group patients experienced back pain so that the experiment was abandoned; 4/12 showed significant activation (P < 0.005) in one or both of the temporal lobes; 1/12 showed significant activation in the frontal lobe. A susceptibility artifact at the interface between the maternal bowel and the fetus affected 3/12 data sets. No significant activation was found in 3/4 of the control cases, and 1/4 could not be analyzed due to a susceptibility artifact. Hum. Brain Mapping 12:94–99, 2001.

In vivo intravoxel incoherent motion measurements in the human placenta using echo-planar imaging at 0.5 T

This paper presents the first in vivo measurements of intravoxel incoherent motion in the human placenta, obtained using the pulsed gradient spin echo (PGSE) sequence. The aims of this study were two‐fold. The first was to provide an initial estimate of the values of the IVIM parameters in this organ, which are currently unknown. The second aim was then to use these results to optimize the sequence timings for future studies. The moving blood fraction (f), diffusion coefficient (D), and pseudo‐diffusion coefficient (D*) were measured. The average value of f was 26 ± 6 % (mean ± SD), D was 1.7 ± 0.5 × 10−3 mm2/sec, and D* was 57 ± 41 × 10−3 mm2/sec. For the optimized values of b, the expected percentage uncertainty in the fitted values of f, D, and D* for the placenta were σf/f = 14.9%, σD/D = 14.3%, σD*/D* = 44.9%, for an image signal‐to‐noise of 20:1, and a total imaging time of 800 sec. Magn Reson Med 43:295–302, 2000.

In vivo diffusion measurements as an indication of fetal lung maturation using echo planar imaging at 0.5T.

The aim of this study was twofold: First, to establish the normal range of fetal lung diffusion values measured during healthy pregnancy; and second, to determine whether fetal lung diffusion could be used as an indication of fetal lung maturity. The apparent diffusion coefficient (ADC), averaged over all 26 subjects with an average gestational age of 29 ± 6 weeks (mean ± sd), was found to be 2.0 ± 0.6 × 10−9 m2/sec (mean ± sd), but a trend was found indicating that ADC increased with gestational age at the rate of 0.07 × 10−9 m2/sec per week (P = 4 × 10−5). To determine the usefulness of this data in predicting lung maturity, a simple three‐compartment model was proposed which was comprised of intra‐lung amniotic fluid, intra‐tissue water, and vascular blood. The relative proportions of each compartment were taken from the literature, and exchange between the compartments was assumed to be minimal. This model predicted the in vivo data reasonably well, and indicated that MR measurements of fetal lung diffusion are a marker for the degree of vascularization of the terminal tubules. Magn Reson Med 45:247–253, 2001.

Fetal brain activity and hemodynamic response to a vibroacoustic stimulus

Previous studies have demonstrated the practicality of using functional magnetic resonance imaging (fMRI) techniques to assess fetal brain activity. The purpose of this study was to compare the fetal hemodynamic response to that of the adult. Seventeen pregnant subjects, all of whom were at more than 36 weeks gestation were scanned while the fetus was exposed to a vibroacoustic stimulus. Thirteen adult subjects were scanned with an equivalent acoustic stimulus. Of the fetal subjects, two could not be analyzed due to technical problems, eight did not show significant activation, and seven showed significant activation. In all cases, activation was localized within the temporal region. Measures of fetal hemodynamic responses revealed an average time to peak (ttp) of 7.36 ± 0.94 sec and an average percentage change of 2.67 ± 0.93%. In contrast, activation was detected in 5 of 13 adults with an average ttp of 6.54 ± 0.54 sec and an average percentage change of 1.02 ± 0.40%. The measurement of changes in the fetal hemodynamic response may be important in assessing compromised pregnancies. Hum. Brain Mapping 22:118–123, 2004.

A comparison of fetal organ measurements by echo‐planar magnetic resonance imaging and ultrasound

Objectives  To compare fetal organ size measured using echo‐planar magnetic resonance imaging and 2D ultrasound. To determine the relative accuracy with which each technique can predict fetal growth restriction.

The Investigation of Placental Relaxation and Estimation of Placental Perfusion Using Echo-planar Magnetic Resonance Imaging

Echo-planar imaging (EPI) is a form of magnetic resonance imaging (MRI) which acquires images in milliseconds rather than minutes as with conventional MRI. The images produced using EPI are affected by the physiological environment in which the hydrogen atoms producing the signals are found, a process referred to as relaxation. Also by producing images a matter of milliseconds apart, quantification of perfusion within the tissue being imaged is feasible. The objective of this study was to investigate T1 and T2 relaxation times along with perfusion in placentae from normal pregnancies at different gestations and also to compare these to pregnancies complicated by abnormal placental function. A cross-sectional study of normal and compromised pregnancies from 20 weeks to term and a longitudinal study of normal pregnancy were performed. Placental T1, T2 relaxation times, and perfusion were measured using echo-planar magnetic resonance imaging. Placental T1 and T2 relaxation times decreased in normal pregnancy (P<0.001). Relaxation times in pregnancies associated with placental pathology appeared to be reduced for that gestation although the numbers were too small to allow any statistical validation. No differences in placental perfusion with gestation or between normal and compromised pregnancy were demonstrated using this technique. This is the first demonstration of placental magnetic resonance relaxation and perfusion measurements in normal pregnancy using echo-planar magnetic resonance imaging. In the future it may be possible to identify compromised pregnancies by differences in placental T1 and T2 relaxation times, using this novel non-invasive technique.