Transcript Tools for Successful Pediatric MRI

Pediatric MRI
Tools to reduce
frustration and improve
image quality
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Advances
• CT volumes have plateau’ed or decreased
• Faster gradients, better coils and technologic
enhancements have improved pediatric MRI
• Greatest contribution:
• Fetal MRI
• Dynamic CE- body and MSK
• MR urography
• MRCP
• MR enterography
• MR elastography
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Challenges
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Motion: physiologic and voluntary
Size
Geometry
Environment
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion: Solutions
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Sedation
Improve patient comfort
Immobilization
Distraction
Limit time on table
Motion reduction technology
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion: Sedation
Strain. Pediatric Radiology 2001
• Girls: 4 and under
• Boys: 6 and under
• Exceptions:
• Developmentally delayed
• Attention Deficit
• Involuntary spasms
• Pain
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion: Improve comfort
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Empty bladder
Positioning
Create a friendly environment
Do not separate from parent
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion: Immobilization
• Bundling of newborns
• Incubator
• Tie shoes together and use velcro over knees
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion: Distraction
Strain. Pediatric Radiology 2001
• Headphones
• Video Goggles- 18% reduction sedation*
• Parent or child life worker in room
CinemaVision- Resonance Technologies
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion: Limit Table Time
• Technologist:
• Be prepared and be one step ahead
• Radiologist:
• Protocol ahead
• Fast screen then tailor
• Minimize scan planes and
sequences
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion: Limit Table Time
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Limit number of excitations/signals averaged
Thicken slices and inter-slice gap
Watch phase oversampling
Move arms out of imaging field
Choose single over dual echo
Limit z axis
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion: Limit Table Time
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion Reduction Technology
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3D to replace two or three planes
Parallel imaging
Radial k-space filling
Respiratory compensation
Ultrafast imaging; half fourier transformation
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion Reduction Technology:
Parallel Imaging
• Align coil elements in phase direction
• Build in phase “cushion” on RECT FOV to avoid
aliasing
320 X 230
JR Reid MD, FRCPC
320 X 320
Core Fellow Lectures 2014
Motion Reduction Technology:
Radial k-space filling
• Blade (Propeller)
• “Periodically rotated overlapping parallel
lines with enhanced reconstruction”
• Increases time by factor /2
• Significant reduction in ghosting,
and other artifacts
• Significant subjective improvement in
sharpness, SNR, overall image quality
Hirokawa AJR Oct 2008
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion Reduction Technology:
BLADE
Reduced motion from bowel
Sag FSE T2
JR Reid MD, FRCPC
Sag FSE T2 with BLADE
Core Fellow Lectures 2014
Motion Reduction Technology:
BLADE
Ax FSE T2
Ax FSE T2 with BLADE
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion Reduction Technology:
Respiratory Triggering
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Respiratory trigger (PACE)
Not as effective as BLADE
Higher resolution with thinner slices
Need patient co-operation, slower and regular
respirations
Hirokawa AJR Oct 2008
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Motion Reduction Technology:
Breath hold
• Requires patient co-operation (children tend to
move more with breath hold)
• Can be used during anesthesia with
hyperventilation followed by sustained apnea
• Quiet breathing more reliable in awake patient
Ax STIR BH
JR Reid MD, FRCPC
Ax HASTE
Core Fellow Lectures 2014
Size
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Size: Challenges
• Too small
• Too big
• Physiologic (contrast bolus timing):
• Rapid circulation time
• Small blood volume
• Rapid respiratory rates
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Size Variability
• Difficult to write standard pediatric protocols
because of variability in size of patients/parts
• Based on:
• Age?
• Weight?
• Girth?
• BMI?
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Size: Solutions
• Versatility: be aware of the greatest detriments
to SNR:
• Coil
• FOV
• Matrix
• NEX
• BLADE
•  field
strength (3T)
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Coil Selection
• Smallest to completely cover the anatomy
• Channel elements : Align elements correctly for
IPAT
• Multiple elements
• Transmit: receive vs.
receive only
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Size: Too Big
• Diffuse Disease: Some conditions require
subtotal whole body imaging eg. Klippel
Trenaunay Syndrome or NF1
• Elusive presentation:
eg. child with a limp
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Size Variability: Solutions
• Whole body ultrafast imaging: sacrifice detail
• Screen and tailor on the fly: requires close
monitoring and versatility
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Ultrafast: Single Shot
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Large FOV STIR and Tailor
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Geometry
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Fat Suppression
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Chemical
Inversion recovery
Opposed Phase
Water excitation
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Chemical (Shift) Fat Saturation
• Saturation pulse at fat resonance
frequency
• ↓ SNR and ↑ imaging time
• Poor fat sat:
• Field inhomogeneities: surface
coils, large FOV, interfaces and
changes in geometry
• Lower field strength
• Radiofrequency ↕ (< or > 90)
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Inversion Recovery
• Depends on the difference in
T1 relaxation times between
water and fat
• Fat recovers more quickly
than water to 180 pulse
• Image at the TI (null point)
• Excellent T1 and T2 contrast
• Not affected by field
inhomogeneities
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Inversion Recovery
• Disadvantages:
• Lower SNR (not all protons have time to
saturate
• Suppresses everything with similar T1: some
hemorrhage, mucoid or proteinaceous
material, melanin etc.
• May not suppress fat that is not white fat or
buried in a lesion with slightly different T1
properties
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Opposed Phase
• Differences in precessional
frequencies of fat and water
and phase shift created in
recovery from 90 excitation
pulse
• Opposed phase: vectors
are 180 apart so subtract
• In phase: vectors are 360
apart (aligned with the same
orientation) so add
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Opposed Phase
• Advantages:
• Fast
• Sensitive to small amounts of fat in structures
• Insensitive to field inhomogeneities
• Disadvantages:
• Only suppresses fat within structures, not adipose
• Gadolinium can increase suppression and
paradoxically decrease enhancement
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Water Excitation
• On GRE or FSE
• Great for MSK
• Double echo to separate fat and water and then
align them to achieve pure water and pure fat
• 3T: 20º and 90º pulses; 1.5T: 30º and 90º
• DESS: double echo steady state optimizes cartilage
(1st pulse) and synovium/water (2nd pulse)
• Better SNR than STIR
• Field heterogeneities a problem at 3T
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Environment
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Environment
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Friendly staff comfortable with children
No sense of urgency or intolerance
Temperature: blankets, room temperature
Lighting: subdued
Familiarity: Music or movies
Education: Teaching materials, child life,
telephone contact
• REWARDS
JR Reid MD, FRCPC
Core Fellow Lectures 2014
JR Reid MD, FRCPC
Core Fellow Lectures 2014
Thank you
JR Reid MD, FRCPC
Core Fellow Lectures 2014