The Application Of Fetal Magnetic Resonance Hydrography And 3D MR Colonography In Prenatal Diagnosis

As a complementary method of prenatal US screening, fetal MR imaging techniques is very important in detecting fetal structural abnomalities and functional abnomalities. Our study is aim to investigate and evaluate new fetal MRI diagnostic technique and its potential in prenatal diagnosis.Part One Magnetic resonance fetography: evaluation of a single-shot thick-slab turbo spin-echo with heavily T2-weighted imageObjectivesTo evaluate the use of a singl-shot thick-slab turbo spin-echo sequence in fetal magnetic resonance (MR) as an alternative to three-dimensional reconstructions, to evaluate the potential of fetal magnetic resonance fetography (MRF) by compared with multislice T2-weighted sequence.Materials and MethodsFrom april 2006 to february 2008, 169 fetal MR examinations obtained for various indications (18th to 40+3th gestational weeks) on a 1.5 T unit using a phased-array body surface coil after informed consent. Using our conventional protocol, this included thin multislice T2-weighted HASTE and true-FIST sequence and T1-weighted 2D FLASH sequence. A single-shot thick-slab (20~100 mm) turbo spin-echo was added to all MR examinations. MRF was evaluated the relationship of the quality of imaging with gestational age, fetal position, amount of amniotic fluid, and the potential by compared with HASTE sequence images.Results1. All our conventional protocol and singl-shot thick-slab turbo spin-echo were performed. There were not statistical difference between the quality of MRF and gestational age, fetal position, amount of amniotic fluid.2. On images obtained with this method, the whole fetus could be recognized at once. Fetal surface normal structures and fetal extremities were displayed on a single image. In addition, cystic mass, fluid-filled cavities and pathology were recognizable,"shining"through the fetal surface could be depicted. Pathological fluid accumulations could be delineated, as well as maternal cystic mass, fluid-filled cavities and pathology.3. The primary diagnosis was changed in 2.4% of the fetuses with biliary tract or ureter pathological distension. New findings, particularly in limb deformity, mild pathological fluid accumulations and intrauterine adhesious were identified in 8.4% of the fetuses, as well as 33 maternal pathology including cystic mass , fluid-filled cavities and pathology. When fetal pathology was of high water content (61.2% of the fetuses), MRF increased diagnostic confidence. In 13.6% of the fetuses, those with cardiovascular or low water pathology, MRF was not beneficial.4. The fetal cystic mass, fluid-filled cavities and pathology could be visualized clearly independence on gestational age and amount of amniotic fluid. The imaging of fetal vertebral canal and spinal cord and the stomach were distinct and highly correlated with gestational age. The fetal lung and small intestine were recognizable gradually with progress of gestation. The pharynx and tracheobronchial of all fetuses at different gestational age could be visualized clearly, however, degraded by hypamnion greatly, so did fetal extremities and umbilical core. Although the borderline of fetal heart were recognizable gradually with progress of gestation, its anatomy in detail was difficult to be identified. Fetal cardiovascular, large intestine, parenchymal organ and low water pathology could not to be identified independence on gestational age and amount of amniotic fluid.Conclusion1. Because of the amniotic fluid-filled surrounding and the high water content of fetal tissues and pathology, The principle of MRCP can be reversed in fetal imaging to allows a new look at the fetus2. MRF can be repeated to image at different orientations and different view angles quicly, its high quality image will not to be influenced by gestational age, fetal position and amount of amniotic fluid. 3. MRF with thick-slab method offers a global overview of fetal pathology or anatomy that may be captured in one image. The combination of overall appearance and translucency provides a new look at the fetus. It is considered an alternative to 3D reconstructions.4. MRF is considered a valuable adjunct to conventional 2D MR images that highlights fetal extremities, fetal fluid-filled cavities and pathology, pathological fluid accumulations and cystic masses within the fetus.5. The whole fetus obtained high quality with this method are of considerable value to the pediatric surgeons, it can be useful for communicate information to an audience that may not be familiar with sectional anatomy, and thus can contribute to prenatal counseling.Part Two 3D magnetic resonance imaging colonography with T1-weighted 2D fast low-angle shot sequences: evaluation the normal and abnormal gastrointestinal tract in fetusesObjectivesTo determine the MRI characteristics of the normal fetal GI tract in the second and third tremisters and some GI tract malformations, to generated three-dimensional magnetic resonance imaging colonography with T1-weighted 2D fast low-angle shot sequences to understand these characteristics sufficiently with 3D mode.Materials and methods97 fetuses MRI was performed between 18 and 40 gestational weeks after informed consent. T1-weighted (T1-W) fast gradient-echo (2D Flash) and T2-weighted (T2-W) HASTE and true-FIST sequences were obtained on a 1.5-T unit in frontal and sagittal or transverse planes. We generated 3D MR colonography images from the 2D FLASH data sets using maximum intensity projection (MIP), multiple planner reconstraction (MPR) and volume-rendering (VR) algorithm at a computer workstation. On 3D MR colonography images, In the fetuses with a normal GI tract, appearance and signal characteristics of the stomach, the duodenum, the proximal small intestine, the distal small intestine were analysed. Signal, situation, diameter, shape , haustral pattern of each segment of the colon and the rectum were assessed. The MRI characteristics of some fetal GI tract malformations was determined.Results1. In all 76 normal and 21 abnormal cases confirmed by the postnatal course or pathological examination, T2-W imaging, 2D FLASH T1-W imaging, and 3D MR colonography were performed. and 3D MR colonography provides excellent delineation of the meconium-filled parts of the colon to be similar to postnatal X-ray barium enem imaging.2. GI normal patterns (n=76): The stomach always was recognizable as a filled with T2-hyperintense and T1-hypointense amniotic fluid structure in the left upper abdomen from 18GW onward. the oesophagus and duodenum were revealed occasionally. The intestinal content showed proximal small intestines predominantly in the left abdominal moiety to change T1-W signal intensities from intermediate to low and T2-W signal intensities from intermediate to high gradually with gestational age and meconial progression, on the contrary, distal small intestines predominantly in the right lower abdomen to change T1- weighted signal intensities from intermediate to high and T2-weighted signal intensities from intermediate to low. The rectum always was seen in all cases and exhibited meconium-like high signal on T1-W images and low signal on T2-W images from 18GW onward. It was close to the posterior bladder wall whatever the fetal gender with its cul-de-sac below the bladder neck obviously. The colon had a same signal. meconium accumulate in the fetal colon from distal to proximal. Around 25 GW, the whole colon is usually meconium-filled. There were highly correlationbetween diameter of large intestine and gestational age(p<0.01).The diameters of colon and rectum increased progressively with gestational age, with maximum to 21mm. A mean diameter of large intestine was 16.6mm. Location of the ascending colon was down with gestational age from the same to lower level of proctosigmoid borderline. The descending colon fixed to left lower abdomen. Proctosigmoid fixed close to median line and higher than that of adult. The sigmoid was variable. The colonic haustra was recognizable by 22GW.3. GI tract abnormalities (n=21): esophageal atresia (n=1) demonstrated an empty stomach and polyhydramnios; duodenal atresia(n=2) was represented as polyhydramnios and the"doubble bubble"sign; proximal jejunum atresia (n=1) demonstrated small bowel dilatation above the atresia with fluid-like signal; colon atresia (n=2) demonstrated dilated colon with different signal and a microcolon distal to the atresia; anal atresia (n=1) didn't show the meconium-filled rectum that should be close to the posterior bladder wall; cloacal malformation (n=1) showed as a dilated bowel with a meconial-like signal behind the superior surface of the urinary bladder but without rectum that should be close to the posterior bladder wall; VACTERL association (n=1) including proximal jejunum atresia, sigmoid atresia without anorectum; left-sided CDH (n=6) and gastroschisis (n=2) and acromphalus(n=4) showed abnormal location of bowel with normal size and signal.Conclusion1. T1-weighted 2D fast low-angle shot sequences can generate high-quality fetal 3D MR colonography images similar to those obtained after X-ray barium enema.2. Using"natural"contrast media such as amniotic fluid and meconium in the fetal GI tract, MRI offers an unique capability of imaging the anatomy and development of fetal GI tract in the second and third tremisters, imaging the physiological process of meconium migration.3. The MRI pattern of GI tract abnormalities is guided by demonstration of abnormal bowel size, abnormal bowel signal, and abnormal bowel location. Abnormal rectum size, signal and location are usually an importante information of anorectal malformation. Our experience is beginning in the field of fetal GI tract disorders, and some fetal GI tract discoders of MR investigations are not yet determined. Nevertheless, MRI seems to be informative in the diagnosis of severe malformations.4. Used as a complementary method of multislice T1-W imaging, 3D MR colonography images provides complete visualization of fetal GI tract. It is useful to evaluate morphology and auxanology characteristics of normal and abnormal fetal gastrointestinal tract. The 3D images of fetal gastrointestinal tract malformations are easy to be understood at family counseling and at conferences with neonatologists and pediatric surgeons. It was useful for surgical simulation and treatment planning before birth.