ISSN:0899-3459    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

The development of ultrafast sequences has revolutionized fetal magnetic imaging (MRI). Fetal anatomy can be characterize precisely by MRI. This is particularly true for evaluation of the central nervous system, for which magnetic resonance (MR) evaluation is superior to ultrasound evaluation. MR allows analysis of development of the cerebrum as well as posterior fossa structures. Awareness of the normal sequence of maturation as well as the approximate timing of development of key structures is useful for evaluating the developing fetus. MRI also permits evaluation of the oropharynx, lungs, diaphragm, and intra-abdominal and retroperitoneal structures. Occasionally, beautiful depiction of smaller structures, including extremities and details of the face and neck may be obtained, but this is dependent on the orientation of the fetus and the plane of imaging as well as the section thickness. MRI is useful in assignment of fetal gender as well as in evaluation of the chorionicity of twin gestations. This report illustrates the normal appearance of the developing fetus as seen on fast sequences during the second and third trimesters.

ISSN:0899-3459    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Fetal thoracic abnormalities are increasingly being detected using prenatal ultrasound. Prenatal magnetic resonance imaging is an important adjunct in evaluation of fetal chest lesions. It can help differentiate different masses and is most helpful in evaluation of large or atypical masses. It also is very important in planning in utero interventional procedures, delivery, and immediate postnatal surgery.

ISSN:0899-3459    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Ultrasound is the screening modality of choice for fetal imaging. However, there are circumstances in which an alternate imaging modality is needed for additional information regarding fetal anatomy or pathology. Fast magnetic resonance imaging (MRI) is increasingly being used as a correlative imaging modality in pregnancy because it uses no ionizing radiation, provides excellent soft-tissue contrast, and has multiple planes for reconstruction and a large field of view. However, sonographic evaluation of the fetus still is important to select the appropriate fetuses for magnetic resonance (MR) examination and to guide the protocol of the examination. Performance of high-quality sonographic and MR examinations as well as interpretation by individuals familiar with prenatal diagnosis are important factors for optimal parental counseling. MRI frequently adds additional information beyond that available with ultrasound. This information commonly changes patient counseling and, at times, patient management.

ISSN:0899-3459    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Prenatal magnetic resonance imaging (MRI) has several advantages over obstetric ultrasound, including a larger field of view, superior soft-tissue contrast, more precise volumetric measurements, and greater accuracy in the demonstration of intracranial abnormalities. Prenatal MRI has been shown to positively and incrementally influence management in a substantial proportion of patients being considered for fetal intervention. Despite these findings, precise indications for prenatal MRI in the setting of fetal surgery are not yet established, because both prenatal MRI and fetal surgery are relatively new techniques that remain in evolution. Conditions in which prenatal MRI appears to contribute to fetal surgical planning and postoperative evaluation are described in this review. These conditions include congenital diaphragmatic hernia, cystic adenomatoid malformation, sacrococcygeal teratoma, complicated twin pregnancies, upper airway obstruction, and myelomeningocele.

ISSN:0899-3459    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Recent and past work using echo-planar imaging (EPI) in pregnancy has allowed important anatomic and physiological information to be obtained, giving advantages over conventional radiological methods such as ultrasound. EPI is a quick, convenient method of measuring organ volumes. The volumetric estimates throughout gestation correlate well with known fetal weight at these gestations. Relaxation time measurements also can be made in the placenta and lungs. By combining the changes in relaxation and volume with gestation in the future, it may be possible to develop an “index of maturity.” This could be used to accurately reflect lung maturation. T1 and T2 parameters in the placenta decreased with gestational age and with abnormal placentation. EPI can be used to assess perfusion in the placenta and flow in the uterine arteries because of its rapid acquisition times. These techniques have been applied to assess perfusion within the fetal brain.

ISSN:0899-3459    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

New hardware and software allow for increased magnetic resonance imaging (MRI) speed. This speed is crucial for MRI of the fetus, where motion degrades image quality. Single-shot sequences such as echo-planar and single-shot fast spin echo now are practical with most clinical scanners. This article reviews and illustrates the physics of fast magnetic resonance sequences.

ISSN:0899-3459    

出版商:OVID    

年代:2001

数据来源: OVID