Fetal mri

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 3 rd 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

4. Scanning Issues

5. 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

6. 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 .

7. 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

8. 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 Phased array technique combines multiple coil elements to provide a large field of view while maintaining signal. Parallel imaging ????

9. PARALLEL IMAGING

10. 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

11. 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

12. 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

13. RF Deposition in mother and fetus

14. 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

15. 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

16. 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)

17. 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

18. 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

19. Timing of MRI – 1 st ,2 nd and 3 rd 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 .

20. 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

21. 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 ??????

22. Patient positioning Feet first supine Left lateral decubitus

23. 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

24. 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

25. 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 

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

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

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

29. Spin echo based EPI and GRE Based EPI

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

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

32. 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

33. FETAL MOTION

34. Maternal Breathing and Movements

35. Multiple Pregnancies

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

37. 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.

38. 28% extra pathological findings by fetal MRI

39. 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

40. Ventriculomegaly, Callosal Agenesis, Chiari malformation

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

42. 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

43. Biometric measurements

44. M onochorionic twin pregnancy complications

45. 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. 

46. 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

47. Meningocele ,Myelomeningocele

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

49. Placenta Previa & Placenta Accreta

50. 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

51. 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

52. References T2-Weighted Fast MR Imaging with True FISP Versus HASTE Comparative Efficacy in the Evaluation of Normal Fetal Brain Maturation Hsiao-Wen Chung 1  , Cheng-Yu Chen 2 , Robert A. Zimmerman 3 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