Fetal MRI

1. FETAL MRI
Presenter :Sujan Karki
B.Sc. MIT Final year
National Academy of Medical Sciences(NAMS)
Bir Hospital

2. Contents
• Scanning issues
• Safety of MRI –
• Specific Absorption Rate (Heat Deposition )
• Acoustic Issues
•Timing of MRI - 1st, 2nd and 3rd trimester
• Contrast Issue – Inability to use gadolinium
• Imaging Sequences
• Challenges in fetal imaging
• Fetal MRI indications

3. FETAL MRI : WHEN AND WHY ?
US MADE A DIAGNOSIS
US HAS ABNORMALITY
US IS LIMITED
Better understanding of anatomic features is
needed(surgical planning and prognosis )
MRI Multiplanar Capabilities
Comprehensive visualization
Further information is essential for diagnosis
MRI provides tissue characterization
A diagnosis is required
Oligohydramnios, Obesity, Multiple
fetuses, and late gestational age

5. Scanning Issues

6. Scanning Issues
• Long Scan time
• Repeat Examination
• Motion
1)Maternal Breathing
2)Fetal Motion
a) bulk motion
b) internal motion ( breathing and swallowing)
c) extremity motion

7. Sedation
• Maternal oral administration of 1 mg of flunitrazepam has been
recommended in Europe to reduce fetal movement.
• In some cases mother is sedated using benzodiazepam
• Conventionally pancuronium was injected on fetal muscles avoid the motion
Proper communication with the patient is
the most important sedation .

8. Fasting
• Four hour fasting or overnight fasting causes hypoglycemia which
reduces the fetal MRI
• Avoid caffeine and fizzy drinks which helps in the reduction of patient
motion

9. Coils and Coil Position
• 3T MRI – 32 Channel phased array
coil and a surface coil in abdomen
with 18 elements
• 1.5T uses 6 channel phased array
coil with surface coils in abdomen
with 6 elements
1. Phased array technique
combines multiple coil elements
to provide a large field of view
while maintaining signal.
2. Parallel imaging ????

10. PARALLEL IMAGING

11. Safety in MRI
• Specific absorption rate(heat deposition )
• Increases with field strength, RF power, transmitter-coil type and body size
• 1.5 to 3 T = 4 X SAR
• Multi echo, multi-slice pulse creates higher SAR
• IEC 60601-2-33(ed.3.1) sets limits pertaining to MR
• As 6/30/13,FDA required manufactures to comply wl IEC 60601

12. FDA : SAR LIMITS
Site Dose Time(min)= or> SAR(W/KG)
Whole body Average over 15 >4
Head Average over 10 >3.2
• Maximum limits
• FDA do not define operating mode
• In 2013 ,FDA adopted the IEC limits for MRI manufacturers
• IEC: Normal and First level operating mode

13. IEC/FDA: SAR
Operating mode Whole Body
SAR(W/kg)
Head SAR(W/kg)
Normal 2 3.2
First Level Controlled
(match FDA Limits)
4 3.2
Normal operating mode : no outputs cause physiologic stress
Suitable For: Any patient with impaired heat regulation
Pregnant/neonate patients
First level controlled Mode: under medical supervision

14. RF Deposition in mother and fetus

15. Temperature Rise Limits
Operating Mode Max Rise of Core Temp
Normal 0.5
First Level Controlled 1
Temperature rise is ultimately what we care about

16. Heat loss from mother
• External temp about 20 degree Celsius
• Heat loss mainly through skin
peripheral vasodilation
sweating
• To avoid heating
Good bore ventilation
No blankets
Minimal clothing

17. Heat loss from fetus
• External temperature of 37 degree Celsius
• Heat loss mechanism – conduction and convection
through uterine wall
• Blood flow through placenta
• Exposure duration should be reduced to minimum and only the normal
operation level is to be used …(ICNIRP 2004)
• Particular consideration should be made to restrict the use of controlled
mode as far as possible for imaging …pregnant women…(HPA 2008)

18. Exposure to RF
• Edward et.al (2013) : performed on animal models and found CNS is most
vulnerable
• 2 degree rise over 2hrs may cause neural tube defects and cranio-facial defects
• Any pulse sequence developed must not cause a body temperature rise above
0.5 degree Celsius for normal mode , 1 degree Celsius for controlled mode and
greater than 1 degree Celsius in experimental mode .
• Manufacturer estimates the SAR value for each pulse sequence
• Hand et.al –typically body coil with 1.5 T and 3T
fetus – 40-70% of maximum mom SAR

19. Acoustic Noise
• About 30% reduction in dB intensity provided by fetal surroundings
• Protocols involving rapid gradients creates higher noises
• EPI produces loudest sound reaches up to 120 dB
• Bakers et.al conducted a study on 18 patients and 16 passed a hearing test so
Acoustic damage from MRI is appeared to be theoretical concern rather
than a real concern

20. Timing of MRI – 1st ,2nd and 3rd trimester
• Yip et.al conducted a study in chicks embryo at 1.5 T
MRI
• At different developmental stages
• Increased abnormalities and mortality rates in six days
embryos after exposure
• ACR white paper --- pregnant patient can be accepted
to undergo MRI at any stage of pregnancy
considering the risk-benefit ratio .

21. Contrast Issues
Contrast Administered to mother
Appears in fetal bladder
Excreted into the amniotic fluid
Swallowed by fetus
? Reabsorbed from the GI tract
Cross placenta

22. Patient preparation
• Maternal 4 hrs. fasting prior exam – reduces bowl peristalsis and prevent postprandial
fetal motion
• Patient should empty bladder just before examination
• Written consent is advisable
• Explain the mother about procedure and indication and assure her that she is the part of
examination
• Check the indications and if possible ask radiologist to stay in console room ??????

23. Patient positioning
• Feet first supine
• Left lateral decubitus

24. Scout
images
• Planned orthogonal to maternal pelvis
• Large FOV
• Overview and Orientation
• Fetal lie in relation with mother …to confirm which side is which
• Always use last sequence to plan for new sequence

25. T2 Weighted/HASTE(single shot FSE/TSE)
• Single Shot ? ??? Breath hold
• 3 orthogonal plane
• Alter TE ???
• 140 for excellent grey-white discrimination
• Can reduce TE with increase in GE age of >30
• TE of 90ms for body imaging
• use of T2 HASTE, the foundation of fetal
imaging, produced no significant temperature
increase in the fetal brain or amniotic fluid of a
pig model.
• And in a pregnant model, in normal mode at 1.5
T and 3.0T, the calculated temperature increase
and SAR limits were found to be within a safe
range

26. TRUE FISP(BFFE/FIESTA)
• provides images with T2/T1 contrast weighting
with high temporal resolution
• useful in demonstrating vasculature and fluid-
filled cavities like heart chambers, umbilical
cord
• obtained in a wide field of view, allowing
visualization of the maternal abdominal anatomy
and the uterus/placenta
• similar image quality to SSFSE for brain
imaging in the second trimester; however,
axonal migration in the third trimester is best
depicted with SSFSE

27. Fetogropahy
• Thick slab MRCP sequence
• 3D visualization/Global
Visualization
• Heavily T2 weighted
• 20-50 mm slice thickness

28. T1 FLASH/VIBE(FSGR/T1 FFE)
• LONGER TO ACQUIRE(15-30s)
• MATERNAL BREATH HOLD
• PRONE TO FETSL MOTION

29. EPI
• FAST ACQUISTION ( 4s for whole head )
• HIGH SENSITIVITY FOR HEMMOHRAGE
• Helps for the evaluation for
developments
• CAN EPI BE USED FOR SKELETAL
EVLUATION ????

30. Spin echo based EPI and GRE Based EPI

31. Diffusion Imaging
• Longer to acquire (20-
30s)
• T2 SHINE THROUGH
• Apparent coefficient
diffusion(ADC) maps

32. Dynamic Sequences
• Swallowing
• Bulk fetal motion
•Fetal Cardiac
Assessment
• Fetal akinesia
•Movement disorders

33. Challenges to imaging and quality
Fetal Motion
During slice acquisition
Sleep-wake phase
Multiple pregnancies
Maternal comfort
Time constrains
Maternal breathing and movements
Dependance on diaphragmatic excursion
Effect dependent on fetal position
Limit to comfort time

34. FETAL MOTION

35. Maternal Breathing and Movements

36. Multiple Pregnancies

37. MOVEMENTS BETWEEN THE SEQUENCES
RADIOLOGIST PRESENCE
DURING THE ACQUISTION ??

38. Indications of fetal MRI
• CNS (38%)
• Lung/Thoracic (34%) Congenital Diaphragmatic Hernia most common
• In 29.3% post referral diagnosis changed completely
• In 28% additional findings were discovered
• In 42% referral diagnosis was concordant with post referral diagnosis.

39. 28% extra pathological findings by fetal MRI

40. Indications and reasons of performing fetal MRI at
1.5T and 3T
Indications Reasons
Indication for 3 T
Brain Intraparenchymal Resolution
Bones Sensitivity for susceptibility effects
Gestational Age >18 weeks,
cartilage(joints), abdominal organs
Resolution
Angiography Background Suppression
Indication at 1.5 T
Polyhydramnios Less sensitive to moving fluids`
Maternal sensitivity to heat Less warming
Large maternal habitus Less sensitive to artefacts

41. Ventriculomegaly, Callosal Agenesis, Chiari malformation

42. Tumors and Masses
• The most common
reported tumors
diagnosed in-utero are
teratomas,
glioblastomas, lipomas,
choroid plexus tumors,
and
craniopharyngiomas

43. Diaphragmatic Hernia
• Congenital diaphragmatic hernia is a
developmental defect in the
posterolateral diaphragm with herniation
of abdominal viscera into the thorax.
• The cause is unknown, but one third of
cases are associated with chromosomal
or additional anatomic abnormalities and
have a mortality rate of 76%
• The sonographic diagnosis of congenital
diaphragmatic hernia and the evaluation
of liver position can be difficult because
lung and liver are of similar echogenicity

44. Biometric measurements

45. Monochorionic twin pregnancy complications

46. Esophageal Atresia
• Esophageal atresia is
a birth defect in
which part of a
baby's
esophagus (the tube
that connects the
mouth to the
stomach) does not
develop properly.

47. Placenta, Umbilical Cord and fetal Presentation
Evaluation of the placenta is a part
of the second and third trimester
examination
Multiplanar imaging allows clear and
detailed placental position and size
The umbilical cord and its insertion
can be imaged

48. Meningocele ,Myelomeningocele

49. Omphalocoele
• a condition in which
there is a skin or
membrane covered
herniation of
abdominal contents
into the base of the
umbilical cord.

50. Placenta Previa & Placenta Accreta

51. Other maternal indications
• Appendicitis -100% sensitivity and 94% specificity
• Intestinal Bowl Diseases- 91% sensitivity and 71%
specificity.
• Diverticulitis- 86-94% sensitivity and 88-92% specificity .
• Pulmonary Embolism

52. Limitations of fetal MRI
• reduced signal to noise ratio (especially prior to 18 weeks gestation)
• maternal weight/size exceeds table recommendations/MRI caliber
• claustrophobia
• implanted ferromagnetic devices

53. References
• T2-Weighted Fast MR Imaging with True FISP Versus HASTE
Comparative Efficacy in the Evaluation of Normal Fetal Brain Maturation
Hsiao-Wen Chung1 , Cheng-Yu Chen2, Robert A. Zimmerman3
• Fetal magnetic resonance imaging: jumping from 1.5 to 3 tesla
(preliminary experience) Teresa Victoria & Diego Jaramillo & Timothy Paul
Leslie Roberts.
• MRI Fetal Imaging –A Literature Review Lisa Roorda, BSc., M.R.T. (R.)
Red River College MRI Technologist Student, Winnipeg, Manitoba.
• Techniques, terminology, and indications for MRI in pregnancy Ray O.
Bahado-Singh, MD