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Fetal MRI: A Developing Technique for the Developing Patient

¹ All authors: Department of Radiology, University of California San Francisco, 505 Parnassus Ave., San Francisco, CA 94143-0628.

View larger version (156K): [in a new window]   Fig. 1A. —Comparison of fetal MRIs obtained during previous 12 years. Oblique sagittal gradient-echo fetal image (TR/TE, 0/6; flip angle, 33.30°) obtained in 1991 shows flow-related enhancement in aneurysm in veins of Galen (asterisk). Anatomic relationships are difficult to see.

View larger version (156K): [in a new window]   Fig. 1B. —Comparison of fetal MRIs obtained during previous 12 years. Axial spoiled gradient-echo T1-weighted fetal image (140/4.2; flip angle, 70°) obtained in 1998 shows flow-related enhancement in aneurysm in veins of Galen (asterisk) and in draining straight sinus (arrow).

View larger version (170K): [in a new window]   Fig. 1C. —Comparison of fetal MRIs obtained during previous 12 years. Sagittal single-shot rapid acquisition T2-weighted image (TR/TEeff, infinite/100) with refocused echoes of same fetus as shown in B shows aneurysm (asterisk) as focal signal void.

View larger version (175K): [in a new window]   Fig. 2A. —Comparison of MRIs with fetal motion. Image degradation by fetal motion during acquisition can usually be overcome by repetition of sequence. Axial single-shot rapid acquisition T2-weighted image (TR/TEeff, infinite/100) with refocused echoes of fetal brain obtained during fetal motion is markedly degraded.

View larger version (176K): [in a new window]   Fig. 2B. —Comparison of MRIs with fetal motion. Image degradation by fetal motion during acquisition can usually be overcome by repetition of sequence. Subsequent axial single-shot rapid acquisition T2-weighted image (infinite/100) with refocused echoes obtained few minutes after degraded image (A) shows that fetus is not moving. This image is of diagnostic quality.

View larger version (127K): [in a new window]   Fig. 3A. —Comparison of fields of view in fetal MRIs. Small field of view is intuitively desirable for fetal MRI but may be detrimental if carried to extremes. Coronal single-shot rapid acquisition T2-weighted images (TR/TEeff, infinite/100) with refocused echoes of fetal brain differ markedly. Image obtained with 14-cm field of view (A) is grainy and degraded by "wrap" artifact (asterisk, A), whereas image obtained with 20-cm field of view (B) is much less grainy and is not degraded by wrap artifact. Absence of corpus callosum can now be seen.

View larger version (165K): [in a new window]   Fig. 3B. —Comparison of fields of view in fetal MRIs. Small field of view is intuitively desirable for fetal MRI but may be detrimental if carried to extremes. Coronal single-shot rapid acquisition T2-weighted images (TR/TEeff, infinite/100) with refocused echoes of fetal brain differ markedly. Image obtained with 14-cm field of view (A) is grainy and degraded by "wrap" artifact (asterisk, A), whereas image obtained with 20-cm field of view (B) is much less grainy and is not degraded by wrap artifact. Absence of corpus callosum can now be seen.

View larger version (147K): [in a new window]   Fig. 4A. —25-gestational-week-old fetus referred for MRI because of mild bilateral ventriculomegaly seen on routine prenatal sonography. Axial single-shot rapid acquisition T2-weighted image (TR/TEeff, infinite/100) with refocused echoes of fetal brain shows mild enlargement of lateral ventricles and focal hyperintensity (arrow) adjacent to frontal horn of left lateral ventricle.

View larger version (143K): [in a new window]   Fig. 4B. —25-gestational-week-old fetus referred for MRI because of mild bilateral ventriculomegaly seen on routine prenatal sonography. Coronal single-shot rapid acquisition T2-weighted image (infinite/100) with refocused echoes obtained through frontal horns confirms periventricular focal hyperintensity (arrow), consistent with parenchymal injury; finding suggests worse postnatal developmental outcome than that expected with isolated mild bilateral ventriculomegaly.

View larger version (180K): [in a new window]   Fig. 5A. —22-gestational-week-old fetus referred for MRI because of suspected agenesis of corpus callosum on routine prenatal sonography. Coronal single-shot rapid acquisition T2-weighted image (TR/TEeff, infinite/100) with refocused echoes shows absence of corpus callosum and abnormal morphology of medial brain surface and continuity of third ventricle (black arrow) with interhemispheric fissure (white arrow).

View larger version (168K): [in a new window]   Fig. 5B. —22-gestational-week-old fetus referred for MRI because of suspected agenesis of corpus callosum on routine prenatal sonography. Midline sagittal single-shot rapid acquisition T2-weighted image (infinite/100) with refocused echoes confirms complete absence of corpus callosum.

View larger version (163K): [in a new window]   Fig. 6. —22-gestational-week-old fetus referred for MRI because routine prenatal sonography raised suspicion of Dandy-Walker syndrome. Sagittal single-shot rapid acquisition T2-weighted image (TR/TEeff, infinite/100) with refocused echoes shows hypogenesis of cerebellar vermis (arrow) with normal corpus callosum and no additional abnormalities. Appearances are consistent with those of Dandy-Walker variant.

View larger version (175K): [in a new window]   Fig. 7. —24-gestational-week-old monochorionic twin fetus with periventricular white matter injury. In utero endoscopic laser ablation of placental vascular connections was performed 2 weeks before scanning for treatment of twin–twin transfusion syndrome. Findings on concurrently obtained sonogram of brain (not shown) were unremarkable, but autopsy confirmed coagulative necrosis of periventricular white matter. Coronal single-shot rapid acquisition T2-weighted image (TR/TEeff, infinite/100) with refocused echoes shows twin pregnancy. Difference in size of fetuses is consistent with twin–twin transfusion syndrome. Area of increased T2 signal intensity (arrow) is seen adjacent to frontal horn of left lateral ventricle in smaller fetus (i.e., donor twin) with focal ventricular dilatation.

View larger version (187K): [in a new window]   Fig. 8A. —23-gestational-week-old fetus with subependymal heterotopia, subsequently confirmed at autopsy, referred for possible inferior vermian agenesis seen on routine prenatal sonography. Other images (not shown) confirmed normal vermis. Axial single-shot rapid acquisition T2-weighted image (TR/TEeff, infinite/100) with refocused echoes of fetal brain shows nodule of decreased signal (arrow) along right lateral ventricle.

View larger version (168K): [in a new window]   Fig. 8B. —23-gestational-week-old fetus with subependymal heterotopia, subsequently confirmed at autopsy, referred for possible inferior vermian agenesis seen on routine prenatal sonography. Other images (not shown) confirmed normal vermis. Coronal single-shot rapid acquisition T2-weighted image (infinite/100) with refocused echoes confirms subependymal nodule (arrow).

View larger version (184K): [in a new window]   Fig. 9A. —33-gestational-week-old fetus with bilateral open lip schizencephaly referred for MRI after routine sonography suggested possible holoprosencephaly. Coronal single-shot rapid acquisition T2-weighted image (TR/TEeff, infinite/100) with refocused echoes shows bifrontal clefts (arrows) extending from ventricles to subarachnoid space. Clefts are lined with areas of low signal intensity. Septum pellucidum is absent.

View larger version (160K): [in a new window]   Fig. 9B. —33-gestational-week-old fetus with bilateral open lip schizencephaly referred for MRI after routine sonography suggested possible holoprosencephaly. Axial T2-weighted single-shot rapid acquisition image (infinite/100) with refocused echoes shows abnormal gyral pattern (arrow) adjacent to clefts.

View larger version (120K): [in a new window]   Fig. 10A. —29-gestational-week-old fetus without congenital diaphragmatic hernia. Coronal spoiled gradient-echo T1-weighted image (TR/TE, 140/4.2; flip angle, 70°) shows normal chest and abdomen. Liver (arrow) is of high T1 signal intensity.

View larger version (135K): [in a new window]   Fig. 10B. —29-gestational-week-old fetus without congenital diaphragmatic hernia. Coronal T2-weighted single-shot rapid acquisition image (TR/TEeff, infinite/100) with refocused echoes shows lungs (white arrows) as high signal intensity. Fluid is visible in stomach (black arrow).

View larger version (123K): [in a new window]   Fig. 11. —Fetus with left-sided congenital diaphragmatic hernia. Coronal spoiled gradient-echo T1-weighted image (TR/TE, 140/4.2; flip angle, 70°) shows upward herniation of left hepatic lobe (arrow). Prognosis is worse than that for patient with congenital diaphragmatic hernia, but left hepatic lobe remains in abdomen.

View larger version (175K): [in a new window]   Fig. 12. —Typical fetal extralobar sequestration. Axial T2-weighted single-shot rapid acquisition image (TR/TEeff, infinite/100) with relaxation enhancement shows fetal chest sequestration (black asterisk) as large left-sided triangular mass of increased signal intensity relative to displaced and compressed normal lungs (arrows). Lungs and heart (white asterisk) are displaced to right.

View larger version (138K): [in a new window]   Fig. 13. —Fetus with right-sided congenital cystic adenomatoid malformation. Coronal T2-weighted single-shot rapid acquisition image (TR/TEeff, infinite/100) with refocused echoes shows chest with right-sided congenital cystic adenomatoid malformation (black arrow). Heart (H) and left lung (L) are displaced to left. Macrocyst (white arrow) is visible in lesion.

View larger version (171K): [in a new window]   Fig. 14A. —Fetus with right-sided bronchial atresia. Axial T2-weighted single-shot rapid acquisition image (TR/TEeff, infinite/100) with refocused echoes shows that right lung (asterisk) is grossly overexpanded and heart and left lung (arrow) are displaced to left.

View larger version (149K): [in a new window]   Fig. 14B. —Fetus with right-sided bronchial atresia. Sagittal T2-weighted single-shot rapid acquisition image (infinite/100) with refocused echoes shows dilatation of proximal right airways (thick black arrow) below level of obstruction. Diaphragm (white arrow) is inverted because of overexpansion of right lung. Ascites (thin black arrow) visible in abdomen indicates development of hydrops fetalis.

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