Fetal Imaging Flashcards
(27 cards)
What is ultrasound used for?
Primary screening modality for obstetric and foetal imaging
What are the advantages of fetal imaging?
- Low cost
- Easy access
- Quicker
What are the advantages of fetal imaging?
- Reduced FOV
- Lower spatial resolution
- Poor soft tissue contrast
- Operator dependent
What is Foetal MRI?
Complementary tool
What are the safety features of foetal imaging?
- Operate within radiological safety guidelines
- Avoid first trimester
- Screen for metal
- Issues with claustrophobia and high BMI
- Minimise heating effects: operate sequences with low SAR (specific absorption rates)
- Minimise noise e.g. add soft tone
- No reported detrimental effects to fetus
What are the features of foetal MR imaging?
- Relatively new technique (1980’s)
- Motion is a major problem
- Initial studies paralysed fetus
- Maternal sedation
Why is foetal MR imaging relatively new technique?
- Complementary to ultraound
- Improve detection rate of abnormalities
- Improve characterisation of known abnormalities
What are the optimal brain sequences essential for optimal clinical scan?
- 3 planes T2 (fast spin echo)
- Axial T1-weighted
- Axial Diffusion weighted (ischaemia)
- T2 GRE (haemorrhage)
What are the body sequences essential for optimal clinical scan?
- T2 (fast spin echo)
- T1 (meconium in the rectum)
- T2 GRE (good for spine)
- T2 TRUFFI (good for spine and placenta)
What are essentials for optimal clinical scan?
- Always have all clinical and ultrasound data available
- Experienced interpreter
- Understanding of relevant pregnancy termination laws
What are the features of foetal motion?
- Single slice fast acquisition - no artefacts unless movement, very quick
- Fetus move in and out of plane during acquisition
- Incomplete coverage of brain and rotated views may make interpretation difficult
What does snap shot image with volume reconstruction (SVR) provide?
- High signal to noise
- High resolution
- 3D volumetric dataset of brain in presence of foetal motion
What does reconstruction allow for?
Non-rotated views with full brain coverage
optimal for clinical interpretation
What are the CNS imaging indications?
- Ventriculomegaly
- Agenesis of corpus callosum
- Cerebellar anomalies
- Congenital infection
- Neural tube defect
What is the consequence of CNS imaging indications?
- Complications of twin pregnancies
2. Acute maternal hypoxic event or illness
When is ventriculomegaly observed?
- 1% pregnancies atrial diameter > 10mm on ultrasound
2. More frequent in males
What are the current practice for ventriculomegaly?
- Detailed fetal ultrasound
- Maternal TORCH screen
- Fetal MRI
- Consider Amniocentesis
MRI in ventriculomegaly
- Most common indication for MR referral
- Detection any obvious cause for ventriculomegaly
- haemorrhage/obstruction - Identification additional anomalies
- Inform further investigations
- Helps on outcome predicition and counselling
When does isolated ventriculomegaly cause neurodevelopmental impairment?
Atrial > 15mm up to 75%
What are the causes of ventriculomegaly?
- Ventricular dilation with evidence of germinal matrix haemorrhage
- Haemorrhage involves basal ganglia
- Posterior limb of internal capsule
Agenesis of corpus callosum
Incidence 0.5 -70 per 10,000
Variable outcome (approx. 30% moderate /severe)
Exclude other abnormalities as outcome worse (increased detection with MRI 22.5%)
Agenesis of corpus callosum
Chromosomal abnormalities in approx. 17% ( More common when other anomalies)
May be referred from US with ventriculomegaly
Occasionally as a parenchymal cyst
Gender of fetus important to exclude possible Aicardi syndrome (females)
What are the cortical anomalies?
- MRI able to assess cortical maturation
- May have early abnormal folding
- Delayed or absent folding
- Markedly abnormal appearance to cortex posteriorly
- Very low signal thickened and abnormally shaped
- Probably early polymicogyria
What are the cerebellar anomalies?
Large cisterna magna Cerebellar hypoplasia Vermis +/- hemispheres Rhomboencephalosynapsis Cerebellar haemorrhage
