Keith R. Duncan

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.

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.

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.

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.

The changes in magnetic resonance properties of the fetal lungs: a first result and a potential tool for the non‐invasive in utero demonstration of fetal lung maturation

Objective To measure magnetic resonance parameters T1 and T2 of the fetal lungs and investigate the relationship of these parameters to changes in volume and gestation.

IN VIVO RELAXATION TIME MEASUREMENTS IN THE HUMAN PLACENTA USING ECHO PLANAR IMAGING AT 0.5 T

This paper presents the first in vivo measurements of the nuclear magnetic resonance relaxation times T1 and T2 at 0.5 T in the human placenta from 20 weeks gestational age until term, in both normal and compromised pregnancies. T1 measurements were performed by using both an inversion recovery sequence and the Look-Locher echo planar imaging (EPI) sequence on a total of 41 women with normal pregnancies and 11 women with compromised pregnancies. T2 measurements were performed by using a spin-echo EPI sequence on 36 women with normal pregnancies and 14 women with compromised pregnancies. In normal pregnancies, both the T1 values measured with the inversion recovery sequence and the T2 values were found to decrease with gestational age, the linear regression results gave T1 = -9.1t + 1538 r2 = 0.23 p = 0.03. T2 = -4.0t + 338 r2=0.47 p =410(-6) where t is the gestational age in weeks, and T1 and T2 are the relaxation times in milliseconds. T1 values measured very rapidly with the Look-Locher EPI sequence, but, therefore, with a much lower signal-to-noise ratio, showed no significant trends. The T1 values measured in the abnormal group were significantly lower than those measured in the normal group. Four out of eight patients with compromised pregnancies had placental T1 values lying outside the 90% confidence limits for the normal population based about the regression line, significantly more than expected by chance (p = 0.005). Ten out of fourteen of the T2 measurements in the abnormal group were below the regression line established for the normal group, with 4 lying below the 90% confidence interval, although these trends were only just significant (p = 0.06 and p = 0.03).

Demonstration of changes in fetal liver erythropoiesis using echo-planar magnetic resonance imaging

This study investigated the variation in magnetic resonance characteristics of the fetal liver during a time of changing erythropoietic function. Echo-planar imaging was carried out in 25 normal pregnant women at 20 and 26 wk gestation. The signal intensity from regions of the fetal liver, background image, and maternal back muscle and the highest signal intensity from the maternal spinal cord were measured and compared with the signal intensity of amniotic fluid. Data are expressed as ratios, in arbitrary units (median pixel values; interquartile range shown in parentheses), and analyzed with the use of Wilcoxons signed-rank test. At 20 wk, the signal intensity ratio of liver to amniotic fluid was 0.309 (0.231-0.365). At 26 wk, the ratio was 0.544 (0.429-0.616). The change was highly significant (P < 0.0001). No change in the signal intensity ratios of amniotic fluid compared with other measured parameters was noted. These data are consistent with known changes in fetal liver erythropoiesis occurring between 20 and 26 wk gestation and have potential use in early noninvasive physiological assessment of the fetus.

Multilevel modeling of fetal and placental growth using echo-planar magnetic resonance imaging.

Objective: To quantify longitudinal increses in fetal, fetal liver, and fetal brain volume using echo-planar magnetic resonance imaging and to quantify the results using appropriate statistical modeling. Methods: Fifty-six singleton fetuses were studied using echo-planar (snap-shot) magnetic resonance imaging, between 19 weeks and term. They were assessed at a variety of different gestations and on a different number of occasions, thereby requiring multilevel statistical modeling to analyze the pattern of fetal growth. Results: Fetal volume varied according to the following equation: square root (√) [fetal volume] = -37.71 + 2.17·gestational age (GA) - 0.004·GA2. The equation for fetal liver volume was √[fetal liver volume] = 9.47 + 0.56·GA - 0.02·GA2, for fetal brain volume was √[fetal brain volume] = 15.50 + 0.69·GA - 0.014·GA2, and for placental volume √[placental volume] = 28.54 + 0.95·GA - 0.039·GA2, where GA is the gestational age in weeks -30. Conclusion: The assessment of fetal, fetal organ, and placental volume was feasible using echo-planar magnetic resonance imaging from 20 weeks to term. Multilevel statistical modeling can be applied to analyze sets of data with different measurements on different occasions. This information is useful clinically to assess abnormal fetal growth.

Estimation of fetal lung volume using enhanced 3-dimensional ultrasound: a new method and first result

54* 19 U/mL during menses’. This cyclical variation confirmed in 12 healthy ovulatory women3 may be due to a breakdown in blood/tissue barriers during menstruation; however no rise was demonstrated during withdrawal bleeds in 10 patients on the combined oral contraceptive pill in the same study, suggesting other mechanisms such as increased tissue synthesis of CAI 25 or retrograde menstruation with peritoneal absorption of CA125. In view of the above data, I feel that the sensitivity and specificity of this screening test for endometriosis may be improved by obtaining the CAI25 samples at a specific point in the menstrual cycle.