1. 15 February Partial volume correction for liver metastases and lymph nodes1Institute for Medical Image Computing/16SPIE 2010 Partial volume correction for volume estimation of liver metastases and lymph nodes in CT scans using spatial subdivision Frank Heckel 1, Volker Dicken 1, Tilman Bostel 2, Michael Fabel 3, Andreas Kießling 4, Heinz-Otto Peitgen 1 1 Fraunhofer MEVIS, Institute for Medical Image Computing, Bremen, Germany 2 Johannes Gutenberg University, Clinic and Out-patients’ Clinic for Diagnostic and Interventional Radiology, Mainz, Germany 3 Christian-Albrechts-University, Department of Diagnostic Radiology, Kiel, Germany 4 Philipps-University, Department of Diagnostic Radiology, Marburg, Germany

2. 15 February Partial volume correction for liver metastases and lymph nodes2Institute for Medical Image Computing/16SPIE 2010 Overview ›Motivation ›Basic Idea ›Algorithm ›Evaluation ›Open Problems ›Conclusion ›Outlook Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook

3. 15 February Partial volume correction for liver metastases and lymph nodes3Institute for Medical Image Computing/16SPIE 2010 Motivation ›Clinical application: Oncological therapy monitoring »Assessment of tumor growth from consecutive CT scans »RECIST 1.1 1 : Sum of maximum diameters (clinical standard) »Volume is more reliable 2 -Unfortunately: Progress / Response clinically not yet defined -Segmentation needed Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook + 20%Progressive disease - 30%Partial response 1 Eisenhauer, E., Therasse, P., Bogaerts, J., Schwartz, L., Sargent, D., Ford, R., Dancey, J., Arbuck, S., Gwyther, S., Mooney, M., Rubinstein, L., Shankar, L., Dodd, L., Kaplan, R., Lacombe, D., and Verweij, J., “New response evaluation criteria in solid tumours: Revised RECIST guideline (version 1.1),” European journal of cancer 45, 228–247 (2009) 2 Bornemann, L., Dicken, V., Kuhnigk, J.-M., Wormanns, D., Shin, H.-O., Bauknecht, H.-C., Diehl, V., Fabel, M., Meier, S., Kress, O., Krass, S., and Peitgen, H.-O., “OncoTREAT: a software assistant for cancer therapy monitoring,” International Journal of Computer Assisted Radiology and Surgery 1(5), 231–242 (2007)

4. 15 February Partial volume correction for liver metastases and lymph nodes4Institute for Medical Image Computing/16SPIE 2010 Motivation ›Border of tumor not clear Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook Partial volume effect: One voxel represents two or more tissues because of limited spatial resolution of CT Liver tissue Tumor + Liver tissue (partial-volume-voxels) Tumor

5. 15 February Partial volume correction for liver metastases and lymph nodes5Institute for Medical Image Computing/16SPIE 2010 Motivation ›Border of tumor not clear  Threshold for segmentation not clear »Different segmentations by different readers / in different scans »Significant difference in volume Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook 56.61ml (-20%)70.8ml86.46ml (+22.1%) erodedinitialdilated

6. 15 February Partial volume correction for liver metastases and lymph nodes6Institute for Medical Image Computing/16SPIE 2010 Basic Idea ›Weight each partial-volume-voxels based on its value and the values of its influencing tissues and calculate volume by the weighted sum of all voxels ›Challenge: Typically different types of tissue outside the lesion ›Assumptions: »Lesion is ellipsoidal and compact »Partial volume voxels are a mixture of 2 tissues Consider partial volume effect when calculating the tumor’s volume 1.0 0.75 0.5 0.25 0.0 Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook

7. 15 February Partial volume correction for liver metastases and lymph nodes7Institute for Medical Image Computing/16SPIE 2010 Algorithm ›Definition of 5 parts »Calculated by successive erosion / dilation ›Spatial subdivision of the lesion into 3D equiangular parts »To cover different tissues (inside and outside of the lesion) Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook Segmentation Inner partial volume area Outer partial volume area Inner tissue area Outer tissue area Lesion core

8. 15 February Partial volume correction for liver metastases and lymph nodes8Institute for Medical Image Computing/16SPIE 2010 Algorithm Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook ›Calculate weight w for each voxel ›Core and inner tissue  w = 1 ›Outer tissue  w = 0 ›For each segment of the subdivision »Calculate the weight w of each partial volume voxel as a linear combination of: -The value of the partial volume voxel -The average outer tissue value -The average inner tissue value »w is clamped to [0,1]

9. 15 February Partial volume correction for liver metastases and lymph nodes9Institute for Medical Image Computing/16SPIE 2010 Algorithm ›Volume is given by weighted sum of the volume of each voxel in partial volume areas, tissue areas and lesion core ›Calculation time:  2s ›Result: Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook 64.57ml (-12.8%)74.06ml83.18ml (+12.3%) 1.0 0.75 0.5 0.25 0.0 56.61ml (-20%)70.8ml86.46ml (+22.1%) voxel-count: corrected: erodedinitialdilated

10. 15 February Partial volume correction for liver metastases and lymph nodes10Institute for Medical Image Computing/16SPIE 2010 Algorithm ›Special cases: »Average outer partial volume value similar to average outer tissue value  w = 0 (assumption: intended by user) »Lesion too small -Not enough voxels in inner tissue -Use average lesion core value instead »Inner and outer tissue do not represent tissues of partial volume voxels (w > 1) -Use distance to inner tissue instead Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook

11. 15 February Partial volume correction for liver metastases and lymph nodes11Institute for Medical Image Computing/16SPIE 2010 Evaluation ›Phantom: »31 lesions (liver metastases, lymph nodes) »More accurate estimation of the volume: Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook Average difference to real volume in % Standard deviation in %

12. 15 February Partial volume correction for liver metastases and lymph nodes12Institute for Medical Image Computing/16SPIE 2010 Evaluation ›Multi-reader: »132 liver metastases (no rim-enhancing), 2 readers »Significant reduction of inter-observer variability: Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook 3.68ml4.29ml 4.03ml4.08ml = +16.9% = +1.12% voxel-count: corrected: Reader 2Reader 1

13. 15 February Partial volume correction for liver metastases and lymph nodes13Institute for Medical Image Computing/16SPIE 2010 Open Problems ›Rim-enhancing lesions »Rim is not always correctly covered by the inner tissue area ›Separated “islands” might be generated »Because only a voxel’s value is used for calculation, not its position ›Subdivision segments might include different tissue classes ›Calculated volume is inconsistent with the visible segmentation result Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook

14. 15 February Partial volume correction for liver metastases and lymph nodes14Institute for Medical Image Computing/16SPIE 2010 Conclusion ›Algorithm: »Considers different tissues around a lesion »Fast »Not restricted to liver metastases and lymph nodes ›Result of evaluations: »More accurate volume estimation »Significant reduction of inter-observer-variability Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook More robust, reliable and reproducible volume quantification even for complex lesions

15. 15 February Partial volume correction for liver metastases and lymph nodes15Institute for Medical Image Computing/16SPIE 2010 Outlook ›Investigate 5mm phantom results ›Improve subdivision so each segment covers exactly one tissue-class ›Adaptive calculation of the size of partial volume and the tissue areas, to cover rim-enhancing lesions correctly ›Solve “island” issue ›Further evaluations Motivation | Basic Idea | Algorithm | Evaluation | Open Problems | Conclusion | Outlook

16. 15 February Partial volume correction for liver metastases and lymph nodes16Institute for Medical Image Computing/16SPIE 2010 Thanks for your attention! Any Questions? frank.heckel@mevis.fraunhofer.de Thanks to: