Ultrafast MR Imaging of the Fetus: Why, How and What?

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1 Ultrafast MR Imaging of the Fetus: Why, How and What? 長庚紀念醫院放射線診斷科 黃敏政醫師

2 THE FETUS AS A PATIENT pediatrician sonographer experiments obstetrician The developing fetus is susceptible to a wide variety of genetic, developmental and acquired abnormalities and insults.

3 Options of Management DO NOTHING EVALUATE PROGNOSIS PRECIPITATE BIRTH FETAL SURGERY EARLY PLANNING OF POSTNATAL CARE TERMINATION EARLY AND ACCURATE DIAGNOSIS

4 Fetal Surgery

5 FETAL DIAGNOSIS Biochemical study Amniotic fluid analysis Chromosomal and genetic study Imaging study

6 Ultrasonography US is the screening imaging modality of choice: Low cost Wide availability Superb safety profile Real time capability Often provides adequate information

7 GA 25 weeks

8 Ultrasonography Evaluation of fetal anatomy, esp. CNS can be limited by: Reverberation artifacts Poor penetration through ossified skull Maternal bowel gas, obesity Oligohydramnios Poor acoustic access to fetal head deep in pelvis Difficulty in obtaining multiplanar views Dependence on operator, equipment, time dedicated to the scan Interpreter s knowledge of neurological diseases

9 WHY PERFORMING FETAL MRI?

10 Fetal MRI Fast imaging acquisition (<1 sec / slice) Better SNR Superior spatial and soft tissue resolution (developing cortex and sulcation pattern) Multiplanar capabilities (both up-side and down-side hemispheres of the brain) Large FOV Simultaneous visualization of fetal and maternal structures

11 Fast Imaging Acquisition HASTE (half-fourier Acquisition Single-shot Turbo spin-echo) True FISP (Fast Imaging with Steady-state free Precession) [FIESTA, bffe) Turbo FLASH (Fast Low- Angle Shot) [FSPGR, TFE]

12 Safety of Fetal MRI No evidence in the literature to indicate adverse effect of fetal MRI SAR (specific absorption rate: rate at which energy is deposited into the body) of fast MR imaging sequences well within limits specified by the FDA (US) and the British National Radiological Protection Board.

13 Safety of Fetal MRI American College of Radiology white paper on the safety of MRI published in 2002: Pregnant patients can be accepted to undergo MR scans at any stage of pregnancy if, in the determination of a Level Two MR Personnel-designated attending radiologist, the risk-benefit ratio to the patient warrants that the study be performed. MRI not performed during organogenesis or before 18 th GA

14 Fetal MRI Indications Cerebral anomalies detected by US whose prognosis depends on associated anomalies undetectable by US (CC, VM, PF, intracranial cyst, micro-, macrocrania) Fetuses at risk for CNS lesions even with a normal US (familial history, viral infection, complicated multiple pregnancies, fetal cardiac rhabdomyomas) Limitations of US Obstetric / Non-obstetric

15 HOW TO PERFORM FETAL MRI?

16 QUESTIONS TO BE ASKED Is US satisfactory for diagnosis? Is high-quality US available for comparison? Is a recent US available for comparison? Informed consent (safety; risk of increased anxiety caused by unexpected findings)?

17 HOW TO PERFORM FETAL MRI? Patient positioning: supine, feet entering the magnet Monitoring the examination: clinical questions, fetal anatomy, orthogonal planes, appropriate protocols

18 Technique of Fetal MRI Image acquired in axial, coronal and sagittal planes orthogonal to fetal brain T2WI: HASTE; true FISP T2*WI: Echo-planar imaging (EPI) T1: FLASH sec acquisition min examination NO medication including CM NO sedation

19 FLASH EPI-FID HASTE DIFFUSION IMAGING truefisp

20 WHAT INFORMATION CAN FETAL MRI PROVIDE?

21 Brain Development Detection of Structural Abnormalities

22 Brain Development 19 weeks

23 Brain Development 22 weeks

24 Brain Development 26 weeks

25 Brain Development 32 weeks

26 Brain Development Detection of Structural Abnormalities

27 Fetal Imaging - MRI Destructive Processes Cortical Infarction Hypoxic Ischemic Periventricular Leukomalacia Germinal Matrix Hemorrhage Infection Metabolic Diseases Coronal T2 37 week fetus Coronal T2 25 week fetus Cortical Infarctions

28 Periventricular Leukomalacia, fetus referred for Ventriculomegaly Coronal T2 32 week fetus Coronal T2 6 week infant

29 Germinal Matrix Hemorrhage with Subarachnoid Hemorrhage Sagittal T2 EPI Axial T2 EPI Echo planar imaging is better for susceptibility of blood products compared with HASTE (Turbo Spin Echo)

30 INTRACRANIAL HEMORRHAGE

31 28 weeks, Schizencephaly 23 weeks, In utero insult

32 GRAY MATETR HETEROTOPIA Fetal Infant

33 ARACHNOID CYST +

34 POLYMICROGYRIA

35 SEPTAL OR CALLOSAL ANOMALIES

36 AGENESIS OF CORPUS CALLOSUM

37 NORMAL POSTERIOR FOSSA GA 22 wks

38 DANDY-WALKER MALFORMATION + PARTIAL AGENESIS OF CORPUS CALLOSUM

39 CHIARI II MALFORMATION

40 ENCEPHALOCELE true FISP HASTE

41 Intracranial/extracranial masses

42 Fetal Imaging MRI 28 weeks, Teratoma

43 Vascular Abnormalities MRA and MRV To study conditions of the brain and size of the heart (hydrocephalus, cardiac failure) Encephalomalacia has negative impact on prognosis

44 Arteriovenous Malformations Vein of Galen Axial T2 32 week fetus Sagittal 2D Phase Contrast MRA Gradient Echo T1 Coronal MIP MRA

45 UTERINE MASS, OLIGOHYDRAMNIOS

46 Fetal Imaging - MRI Twins = 1.5% pregnancies Mortality = 4-6x single Morbidity = 2x single Conjoint Encephalocele Fetal Demise

47 TWINS: HOLOPROSENCEPHALY

48 FMR changes Patient Counseling & Management 46% (24/52) of pregnancies managed differently Simon EM et al. MR imaging of fetal CNS anomalies in utero. Am J Neuroradiol 2000;21(9): % (10/18) additional findings to US; altered counseling in 39% (7/18) Levine et al. Fetal central nervous system anomalies: MR imaging augments sonographic diagnosis. Radiology 1997;204(3): Major new findings (in addition to US) in 31.7 % (46/145) of cases Change in either diagnosis or patient counseling in 49.6 % (72/145) of cases Change in patient management in 18.6 % (27/145) of cases Levine D et al. Fast MR imaging of fetal central nervous system abnormalities. Radiology 2003;229:51-61

49 Hidden Risks Incidental findings Discrepancy between diagnostic capability prognostic implications Findings of uncertain significance Conditions with unclear natural history

50 Pitfalls subtle Cortical Anomaly True lesion but suboptimally imaged? Developing lesion, but not yet visualized by the current examination?

51 Molecular and Functional Perspectives Diffusion Tensor Imaging, Fiber Tractography Functional Imaging 4-Dimensional Imaging (VGH Prof. Guo WY) Better Resolution with lower SAR

52 Conclusion Advances in development of fast MR imaging sequences allow detailed examination of the frequently moving fetus. US remains the primary screening imaging modality CONFIRMS & expands on US suspicions TECHNICALLY good images PLUS expertise of NEURORADIOLOGIST in interpreting the images Emerging ETHICAL issues

53 Thank you for you attention!