University of North Carolina

Comparison of Human and M-rep Kidneys Comparison of Human and M-rep Kidneys Segmented from CT ImagesSegmented from CT Images

James Chen, Gregg Tracton, James Chen, Gregg Tracton, Manjari Rao, Sarang Joshi, Manjari Rao, Sarang Joshi,

Steve Pizer, Joshua Stough, and Steve Pizer, Joshua Stough, and Ed Chaney Ed Chaney

University of North Carolina University of North Carolina Chapel HillChapel Hill

MethodsMethods

Target ImagesTarget Images: 12 planning CT images from : 12 planning CT images from archives (24 kidneys)archives (24 kidneys)

Human (A and B) segmentationHuman (A and B) segmentation: Careful : Careful slice-by-slice pixel painting (voxel-based)slice-by-slice pixel painting (voxel-based)

Computer segmentationComputer segmentation: Deformable m-reps : Deformable m-reps (yields smooth surface)(yields smooth surface)

Comparison metrics reported hereComparison metrics reported here: Volume : Volume overlap and mean surface separationoverlap and mean surface separation

University of North Carolina

The median volume overlap is measured by the overlap volume The median volume overlap is measured by the overlap volume divided by the union of the two volumes being compared.divided by the union of the two volumes being compared.

Image ChallengesImage Challenges

Poor contrast (no contrast agent)Poor contrast (no contrast agent)

Crowded soft tissue environmentCrowded soft tissue environment

Image ChallengesImage Challenges

Motion artifactsMotion artifacts

Image ChallengesImage Challenges

Image variability near renal pelvis Image variability near renal pelvis

Three human segmentations of renal pelvisThree human segmentations of renal pelvis

Three Stages of M-rep Three Stages of M-rep SegmentationSegmentation

Similarity + elongationSimilarity + elongation Atom deformationAtom deformation Boundary displacementBoundary displacement

Implied surface after each scale of segmentationImplied surface after each scale of segmentation

University of North Carolina

Result after Final StageResult after Final Stage

Limitations of ComparisonLimitations of Comparison

Segmented structures represented as Segmented structures represented as collections of whole 2 mmcollections of whole 2 mm3 3 voxelsvoxels Conversion of m-rep surfaces to voxels Conversion of m-rep surfaces to voxels introduces a bias that favors humansintroduces a bias that favors humans Sensitivity of distance ~ 2 mmSensitivity of distance ~ 2 mm Best possible volume overlap is ~ 95% Best possible volume overlap is ~ 95%

Results: Volume OverlapResults: Volume Overlap

Human A to Human B: Human A to Human B: 90%-96% 90%-96% M-rep to Human A or B: M-rep to Human A or B: 85%-95% 85%-95%

University of North Carolina

Case

Human volume overlap

0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

Human A vs B volume overlapHuman A vs B volume overlap

Kidney NumberKidney Number

University of North Carolina

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1V

olu

me

Ove

rlap

(%

)

First Atom Boundary

M-rep vs Human A volume overlapM-rep vs Human A volume overlap

CaseCase

University of North Carolina

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Case

Ave

rag

e D

ista

nce

(cm

)A

fter

Bo

un

dar

y S

tag

e

abacbc

Results: Average Surface SeparationResults: Average Surface Separation

Human A to Human B: Within one voxelHuman A to Human B: Within one voxel

M-rep to Human A or B: Within one voxelM-rep to Human A or B: Within one voxel**

**with one exceptionwith one exception

University of North Carolina

ImageImage

ImageImage

HumanHuman

HumanHuman

M-repM-rep

M-repM-rep

Outlier CaseOutlier Case

Who is right (Human or M-rep)?Who is right (Human or M-rep)?

QuickTime™ and a decompressor

are needed to see this picture.

Movie LoopMovie Loop

ConclusionsConclusions

In this study m-reps compared In this study m-reps compared with humans A and B as well as with humans A and B as well as

A compared with B. A compared with B.

University of North Carolina

Sunset at Portsmouth IslandSunset at Portsmouth Island