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Download Tools for Successful Pediatric MRI
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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 • • • • 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 • • • • • • 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 • • • • 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 • • • • • • 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 • • • • • 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 • • • • 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 • • • • 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 • • • • • • 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
