fast, free-breathing, and motion minimized techniques for

Michael S. Gee, MD, PhD

Chief of Pediatric Imaging Massachusetts General Hospital Associate Professor of Radiology Massachusetts General Hospital

Fast, free-breathing, and motion minimized techniques for pediatric

body MRI

Disclosures

Research agreements with Siemens Medical Solutions and GE Healthcare

Overview

o  Issues related to MRI sedation in children

o  Current and emerging strategies to decrease respiratory motion artifacts in free-breathing abdominal MRI

Issues with sedation for pediatric MRI

o  Longer wait times for limited GA timeslots

o  Increased exam and recovery time

o  Increased cost

o  Low risk of laryngospasm/aspiration

o  Potential long-term neurologic effects

TL Slovis, Pediatr Radiol (2011) RT Wilder, Anesthesiology (2009)

Studies suggesting potential long term effects of sedation/anesthesia

on young children •  2011 study from Mayo comparing 350 children

with GA exposure before 2yo with matched nonexposed controls showed that repeated exposures (but not single) had higher risk of developing LD and IEP (RP Flick, Pediatrics 2011)

•  2013 study of 8 fetal and neonatal macaques showed large inc in CNS apoptosis compared with ctrls when exposed to 5 hrs of propofol anes (C Creeley, Br J Anaes (2013)

NEJM Perspective states “we believe that parents and care providers should be made aware of the potential risks that anesthetics pose to the developing brain…. parents should consider carefully how urgently surgery (or MRI?) is needed, particularly in children under 3 years of age.”

BA Rappaport, N Engl J Med (2015)

Recent data suggesting lower anesthetic risk to children

  PANDA study of 105 sibling pairs within 3yrs of age

  One sibling had single anesthetic exposure for inguinal hernia repair < 36 mos of age, otherwise healthy

  All received inhaled anesthetic for 20-240 minutes (median 80 mins)

  No significant differences in global cognitive function, memory/learning, or behavior observed in exposed group

LS Sun, JAMA (2016)

General techniques to reduce respiratory motion artifacts in body MRI

1.  Suspend respiration (BH)

2.  Respiratory triggering (bellows, nav)

3.  Decrease motion artifact conspicuity (e.g sat bands, PE direction)

4.  Signal averaging (inc NEX)

5.  Single shot techniques

Fast free-breathing MRI techniques would benefit multiple

pediatric populations •  ER patients (e.g.

appendicitis, seizure)

•  Genetic syndromes

•  History of cancer

•  Abdominal lesions detected on US

Benefits of rapid free-breathing MRI protocols

1.  Allow children to undergo MRI awake using DVD goggles or other AV distraction techniques without interruption

2.  Decrease sedation meds and need for intubation/ventilation for children requiring anesthesia

Radial-based T2-weighted imaging

(PROPELLER, BLADE, MultiVane)

Cartesian sampling

Radial sampling

•  Radial k-space sampling

•  Oversamples center of k-space with relative peripheral k-space undersampling

•  Disperses artifact along the phase encoding direction (radially).

•  Motion correction option (prospective phase correction)

Radial T2-weighted sequences reduce respiration motion phase-encoding artifact

compared with Cartesian technique

Rad

ial

Car

tesi

an

Motion correction for radial T2-weighted imaging can make image quality worse

when resp motion is significant

  Low resolution blade reconstruction with rigid body translation/rotation

  In-plane motion lead to correction to wrong blade

  Thru-plane motion not corrected (2D multislice)

Philips Healthcare Courtesy of John Kirsch, PhD

Coronal acquisition of radial T2-weighted sequences can have more motion artifacts from

thru-plane respiration and bowel peristalsis

Comparable acquisition times for resp triggered radial and Cartesian T2-weighted images in the abdomen

Age range 1-8 years: Cartesian: 4.89 + 2.49 mins (range 2.61-7.63 mins) Radial: 4.33 + 1.40 mins (range 2.67-6.67 mins)

Cartesian Radial

Young children with fast/shallow/irregular respiration can lead to problems with

respiratory triggering

Modifying the radial blade coverage can improve image quality and may allow true free

breathing T2-weighted imaging without triggering Triggered BLADE 4:30 FB BLADE (6 blades) 1:40

TR range 3500-5000 TR 4500

FB BLADE (12 blades) 3:04

TR 4500

FB BLADE (18 blades)

TR 4500

4:28

Less motion More blurring

Improving spatial overlap can improve quality of T2 radial imaging without triggering

Triggered BLADE 4:30 FB BLADE (iPAT3) 1:40

TR range 3500-5000 TR 4500 AT 3:04

TR 4500

FB BLADE (iPAT2) 2:10

TR 4500

Free-breathing radial hybrid 3D multiphase post-contrast imaging

H Chandarana, Invest Radiol (2011)

•  “Stack of stars” volumetric technique: radial k-space acquisition in plane, Cartesian in slice direction

•  Continuous imaging leads to dispersion of motion artifacts and view sharing

•  Higher number of blades (>500) and narrower blade width compared with T2

Free-breathing radial post-contrast imaging with temporal-resolved

subframes

PRE ART

PV AVE

Splenic capillary malformation in child with Megalencephaly-capillary malformation-

polymicrogyria (MCAP) syndrome imaged with multiphase Star VIBE

T2 FS Star VIBE (60 secs) Star VIBE (3 mins)

Hybrid radial compressed sensing (GRASP) post-contrast imaging

  Continuous passage of radial lines through center of k-space

  K-space data sorted into undersampled datasets based on cardiac and respiratory motion states

  Compressed sensing used to reconstruct datasets to remove radial undersampling artifact

L Feng, H Chandarana et al, Magn Res Med (2016)

Compressed sensing allows significant MR acceleration by reconstructing

diagnostic images from sparse data

Image compression: high sampling rate and discarding low coefficients Compressed sensing: low sampling rate in incoherent manner, then reconstruct to remove incoherence L Feng, J Magn Reson Imaging (2017)

Free-breathing GRASP 3min

Free-breathing Radial post-contrast imaging with GRASP Reconstruction

Reconstruction #1



Reconstruction #2



Reconstruction #3



Reconstruction #4



Reconstruction #5

Courtesy of Hersh Chandarana, NYU

6-year-old female free breathing MRI

Spatial resolution 1.0x1.0x1.0 mm3, frame rate ~4.1 s

Soft-gated Locally Low Rank Parallel Imaging

Un-gated Locally Low Rank Parallel Imaging

Radial, variable density k-space sampling with CS and navigator motion soft-gating

Courtesy of Shreyas Vasanawala, Stanford

Accelerated free breathing DWI using simultaneous multislice (SMS)acquisition combined with parallel

imaging

•  MB RF pulse excites multiple k-space lines simultaneously

•  PI + controlled aliasing gradients allow slice info to be separated by coil sensitivity

•  Accelerates imaging thru TR reduction and higher PI factors B Bilgic, Magn Reson Med 2012

BA Poser, Magn Reson Med 2014 M Barth, Magn Reson Med 2016

6 year old with TSC: SMS DWI of kidneys

T2 single shot

Radial post-contrast

DWI SMS DWI

Standard ADC SMS ADC

2.55 x 10-3 2.53 x 10-3

TR 4100 TA 3:03

TR 2200 TA 1:42

Accelerated SMS DWI in 1 year old girl with medulloblastoma (40% shorter AT) for DTI

Standard DWI

(3:05)

SMS DWI

(1:46)

Courtesy of Camilo Jaimes, MD

Conclusions •  MRI is an increasingly utilized in

young children with thoracoabdominal pathology

•  Anesthetic medications for pediatric MRI should be reserved for cases that are medically indicated

•  New acceleration and motion correction MR techniques allow free-breathing abdominal MRI in children and should decrease MR scan times and sedation requirements

fast, free-breathing, and motion minimized techniques for

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