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TU‐D‐332‐08: Gd‐DTPA DCE‐MRI Assisted Image‐Guided PO2 Measurements in Rodent Tumor Xenografts
Author(s) -
Huang M,
Zhang M,
Chang J,
Le C,
Zanzonico P,
Humm J,
Koutcher J,
Ling C
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2962599
Subject(s) - fiducial marker , nuclear medicine , magnetic resonance imaging , image registration , medicine , gadolinium , voxel , biomedical engineering , materials science , radiology , artificial intelligence , computer science , image (mathematics) , metallurgy
Purpose: To optimize the correlation between interstitial pO 2 readings and PET‐derived18F ‐ FMISO / 18F ‐ FDG concentrations in tumors using co‐registered Gd‐DTPA DCE‐MRI to distinguish viable and necrotic tumor cells. Method and Materials: Nude rats with Dunning R3327‐AT xenografts were positioned in a custom‐fabricated mold and imaged by (1) T2‐weighted MRI imaging; (2) DCE‐MRI following IV injection of gadopentetate dimeglumine; (3) microPET for 1/2 hr post‐IV injection of18F ‐ FDG or18F ‐ FMISO . The MRI and PET images were used to direct intra‐tumoral pO 2 measurements using an image‐guided robot system. PET‐ and MRI‐visible fiducial markers were used to register the respective image and robot coordinate systems. pO 2 was measured at 0.5‐mm increments along different tracks within the tumor using an OxyLite™ 4000 Oxygen probe advanced by the robot, providing point‐to‐point correspondence between the pO 2 measurement and image‐voxel intensity. Measurement points in the necrotic region and those outside tumor region, identified by DCE‐MRI and T2‐weighted MRI, were excluded from the correlation analysis. Necrotic tissue was identified as having ( I ( t ) − I 0 ) / I 0 < 0.1 at t=2 min after contrast injection, where I 0 and I(t) are MR image intensities before injection and at time t. Results: The registration error between images and the robot is <0.3mm. For three FMISO studies with 539 measurements and 21 tracks, the correlation between interstitial pO 2 readings and18F ‐ FMISO intensities was not improved — r = − 0.71 ± 0.14 ( mean ± SD ) vs r = − 0.73 ± 0.16 ( p = 0.50 ) . Four animals were studied using18F ‐ FDG with 423 measurements and 20 tracks. The negative correlation improved significantly (p =0.00118) — r = − 0.36 ± 0.35 vs r = − 0.65 ± 0.24 — if only viable‐tumor points were considered. Conclusion: The negative correlation between18F ‐ FDG voxel intensities and intra‐tumoral pO 2 was improved when DCE‐MRI was used to exclude necrotic tissue pO 2 s. Exclusion of necrotic points did not improve the correlation for18F ‐ FMISO , however.