Ratio of fetal choroid plexus to head size: simple sonographic marker of open spina bifida at 11-13 weeks' gestation.

OBJECTIVES: To measure the ratio of choroid plexus (CP) size to head size in normal fetuses and to compare it to that in fetuses with open spina bifida (OSB) and quantify the subjective sign of a 'dry brain'. METHODS: This was a retrospective study of ultrasound images, obtained during first-trimester screening between 11 and 13 weeks of gestation, from 34 fetuses with OSB and 160 normal fetuses. From the hospital databases, we retrieved images of the fetal head in the transventricular axial plane. We measured the areas of both CPs and the head and calculated the ratio between them. We also measured the longest diameter of each CP and calculated their mean (CP length), and measured the occipitofrontal diameter (OFD) and calculated the ratio of CP length to OFD. Measurements from the OSB fetuses were plotted on crown-rump length (CRL) reference ranges constructed using data from the normal fetuses, and Z-scores were calculated. RESULTS: In the normal fetuses, the CP area increased, while the ratios of CP area to head area and CP length to OFD decreased, with increasing CRL. In 30 of the 34 (88%) fetuses with OSB, both ratios were increased significantly and the CPs filled the entirety of the head, giving the impression of a dry brain. In these cases, the borders of the lateral ventricles could not be identified. CONCLUSIONS: At 11-13 weeks, the majority of fetuses with OSB have reduced fluid in the lateral ventricles such that the CPs fill the head. The dry brain sign is easily visualized during routine first-trimester ultrasound examination while measuring the biparietal diameter, and can be quantified by comparing the size of the CPs to the head size. Until prospective data confirm the usefulness of this sign in screening for OSB, it should be considered as a hint to prompt the examiner to assess thoroughly the posterior fossa and spine. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Exact (spiral + circles) scan region-of-interest cone beam reconstruction via backprojection.

We present a (spiral + circles) scan cone beam reconstruction algorithm in which image reconstruction proceeds via backprojection in the object space. In principle, the algorithm can reconstruct sectional region-of-interest (ROI) in a long object. The approach is a generalization of the cone beam backprojection technique developed by Kudo and Saito in two aspects: the resource-demanding normalization step in the Kudo and Saito's algorithm is eliminated through the technique of data combination that we published earlier, and the elimination of the restriction that the detector be big enough to capture the entire cone beam projection of the ROI. Restricting the projection data to the appropriate angular range required by data combination can be accomplished by a masking process. Because of the simplification resulting from the elimination of the normalization step, the most time-consuming operations of the algorithm can be approximated by the efficient step of line-by-line ramp filtering the cone beam image in the direction of the scan path, plus a correction image. The correction image, which can be computed exactly, is needed because data combination is not properly matched at the mask boundary when ramp filtering is involved. Empirical two-dimensional (2-D) point spread function (PSF) is developed to improve matching with the correction image which is computed with finite samplings. The use of transition region to further improve matching is introduced. The results of testing the algorithm on simulated phantoms are presented.