Numerical Model Development Part I

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2006 SCIENTIFIC SYMPOSIUM OF THE SCIB
The Digital Child Project

• Numerical Model Development Part I Pediatric
  Anatomy
• Albert I. King
• Bioengineering Center
• Wayne State University
• Birmingham, Alabama
• December 13, 2006

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Objectives

• Identify level of detail needed for pediatric FE
  models, focusing on anatomical differences
  between adults and children
• Create appropriate whole body anthropometry for
  3, 6, and 10 year olds using clinical CT and MRI
  data

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Pediatric Anatomy

• Child ? Small Adult
• Anatomical and morphological changes throughout
  maturation
• Example
• Ossification of skeletal structures
• Skull
• Spine

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Pediatric Anatomy
NOT TO SCALE
2 YO 5 YO ADULT
Images from http//www.boneclones.com
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Pediatric Anatomy
Image from http//faculty.washington.edu/chudler/d
ev.html
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Pediatric Anatomy
NOT TO SCALE
Images from http//www.yoursurgery.com/ProcedureDe
tails.cfm?BR4Proc19
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Pediatric Anatomy
NOT TO SCALE
Images from http//faculty.clintoncc.suny.edu/facu
lty/Michael.Gregory/files/ Bio20102/Bio2010220l
ectures/Motor20Systems/infant_skull.jpg and
http//www.uoftbookstore.com/online/prodimg/49090.
jpg
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Pediatric Anatomy
ADULT
3 YO
6 YO
INFANT
NOT TO SCALE
Image altered from Kumaresan, et al. (2000)
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Flowchart
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Timeline
MONTH 2 4 6 8 10 12 14
HIC APPROVAL (MED REC DONE)
OBTAIN DATA (20 COMPLETE)
IDENTIFY LEVEL OF DETAIL
CREATE SURFACE CONTOURS
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HIC Approval

• Institutional Review Board
• Human Investigation Committee of
• Wayne State University
• Approved collection of pediatric image data from
  medical records on September 1, 2006
• Application in process to obtain whole body
  images from pediatric cadavers (nondestructive)

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Data Collection

• MRI data collected from 11 subjects, further MRI
  and CT data in progress in collaboration with the
  Chair of the Radiology Dept.
• Target ages (either gender)
• 2.5-3.5 years
• 5.5-6.5 years
• 9.5-10.5 years

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Data Collection

• MRI data for each subject includes
• Several orientations
• Axial, coronal, sagittal
• Several types
• T1, T2, etc.
• May include contrast
• Some MRAs (blood vessels)

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Segmentation

• Challenges in image processing
• Abnormal anatomy
• Slice orientation
• Image quality
• Slice thickness and resolution
• Noise
• Incomplete structures of interest

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Abnormal anatomy present- reason for scans
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Segmentation

• Solutions - Abnormal anatomy
• Bilateral structures can be reflected
• Removal of pathological tissue formations and
  manual interpolation
• If too abnormal, collect new data from medical
  record
• Pediatric cadavers chosen may have limited
  abnormalities if death due to trauma

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Slice orientation- non-orthogonal
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Segmentation

• Solutions Slice orientation
• Can make structure identification difficult for
  the engineer, consult radiologist
• Translation and/or rotation of structures may be
  necessary for integration into whole body model
  (addressed later)

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Image Quality
3D Doctor
E-Film Lite
3D Slicer
Mimics
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Slice thickness- ranges from 1.8-5.0 mm, usually
4-5 mm
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Segmentation

• Solutions Slice thickness and resolution
• Each subject has numerous image series, choose
  the highest resolution
• Smoothing after surface generated
• If pediatric cadavers become available, we can
  choose finer cuts and higher resolutions with no
  radiation exposure hazard

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Noise
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Segmentation using Mimics without noise removal
Segmentation with noise removed
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Segmentation

• Solutions Noise
• Manual removal with image processing and medical
  image segmentation software packages
• May not affect structure of interest
• Collect new data from the medical record

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Some structures are incomplete due to Field of
View In this case, the brain Often a problem in
junction between thorax and abdomen (liver often
incomplete in both)
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Segmentation

• Solutions- Incomplete structures
• Manual interpolation
• Collect new data for that body part from medical
  record
• Could be solved if pediatric cadavers become
  available

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Scaling

• Combine body parts from different subjects to
  create a whole body model which is average
  sized
• Preserve developmental anatomy
• Scaling child to child of similar maturation
  level (NOT adult to child)
• Geometric scaling only (based on Irwin, et al.
  1997)

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Scaling

• Average child anthropometry by age determined
  from Snyder, et al. (1977)
• External measurements only, no data available on
  relationship between external landmarks and
  internal landmarks (noted by Reed, et al. at
  UMTRI, 2005, 2006)

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Scaling

• Snyder data provided
• Heights
• Breadths
• Circumferences
• of external landmarks
• Age ranges of interest
• 2.0-3.5, 5.5-6.5, and 9.5-10.5 years

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Head Dimensions
in the sagittal and coronal planes
Image altered from http//ovrt.nist.gov/projects/a
nthrokids/
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Thorax Dimensions in the coronal plane
Sagittal plane data also available
Image altered from http//ovrt.nist.gov/projects/a
nthrokids/
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Scaling

• Challenges
• All anthropometric data cannot be applied to each
  subjects scans
• For example, this abdomen MRI precludes measuring
  chest breadth at axilla

Breadth at Axilla
Natural Waist Breadth
Waist Breadth
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Scaling

• Solutions- Scaling
• Scale using all available external measurements
• When finished, check realism of complete body in
  terms of proportion
• Use whole body images from pediatric cadavers to
  determine relationships between internal and
  external geometries

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Positioning

• Complete 3D solid model must be properly
  positioned for use in analysis
• Translation of entire model
• Rotation of joints
• Automotive seating postures to be based on Reed,
  et al. (2005, 2006)
• Data not available for three year olds

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Positioning

• Challenge
• Snyders seated anthropometries not
  representative of automotive seating postures
• Sources of such seating postures for children
  incomplete

Image altered from http//ovrt.nist.gov/projects/a
nthrokids/
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Positioning
Positions of the extremities not reported
Data available for 6 YO and 10 YO, including head
angle and positions relative to H-point
Image altered from Reed, et al. (2005)
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Positioning

• Solutions- Positioning
• Extrapolation
• From Reed, et al. data
• May perform small study at WSU
• Will not be representative of the population

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Proposed Positioning Study
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Discussion and Conclusions

• In creating accurate pediatric 3D model surfaces
• Pediatric medical images of a lower quality than
  adult due to standard procedures
• Issues can be overcome will the use of a
  combination of software and manual editing

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Discussion and Conclusions

• In the absence of an average sized pediatric
  cadaver, geometric scaling between subjects of
  similar maturation levels will be necessary
• Positioning of the 3D model involves sparse data
  sets, but reasonable postures can be achieved
  with additional experimental information

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Future Work

• Collect more MRI and CT data, especially CT in
  regions of partial ossification
• Continue work to procure whole body images of
  pediatric cadavers
• Determine appropriate scaling method and
  calculate component locations (joint centers)

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Future Work

• Evaluate open source and commercial image
  processing/segmentation software
• Evaluate different segmentation methods using
  known partially ossified structures
• Create segmentation protocol appropriate for
  pediatric anatomy

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Thank You
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INFANT 1-3 YO 3-6 YO 11-14 YO ADULT
Image altered from Yoganandan, et al. (1999)
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Pelvic Dimensions in the coronal plane
Image altered from http//ovrt.nist.gov/projects/a
nthrokids/
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Positioning

• Automotive seating postures to be based on Reed,
  et al. (2005, 2006)
• Data not available for three year old

Posture Variable Sitter-Selected (Degrees) ATD Standard (Degrees)
Neck Angle 3.5 3.3
Thorax Angle 10.0 9.8
Abdomen Angle 45 34.7
Pelvis Angle 47.6 43.5
Average age 8.4 years