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Geometric distortions of diffusion weighted imaging of the head/neck in combined PET/MR: optimization of image acquisition and post-processing correction for oncology applications

Authors:
Adam Espe Hansen at Rigshospitalet
Adam Espe Hansen
Jacob Rasmussen at Rigshospitalet
Jacob Rasmussen
Helle Hjorth Johannesen at Rigshospitalet
Helle Hjorth Johannesen
Astrid M Engberg
Astrid M Engberg
Astrid M Engberg
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Abstract

The combination of PET with Diffusion Weighted Imaging (DWI) is a promising application of PET/MR. DWI geometric accuracy can be compromised in body regions with complex anatomy. Here, we assess DWI head/neck image quality following optimization of acquisition and post-processing. Preliminary data from 10 patients with cancer of the tonsil or base-of-tongue is presented. An integrated PET/MR system (Siemens Biograph mMR) with a 3 T magnet was used. PET was performed as a single-bed, 20 min acquisition, 120 min post injection of 4 MBq/kg [18F]-FDG. MRI included axial T2 weighted STIR, B0 mapping and 2 DWI single-shot EPI measurements (DWI1 and DWI2) with b values 0, 500 and 1000 mm2/s. DWI2 was measured as 3 stacks, each at isocenter to maximize field homogeneity. DWI1/DWI2 had an effective echo spacing 0.375/0.145 ms. For DWI2, distortions were corrected using FSL with FUGUE and Topup algorithms. DWI geometric quality was evaluated in 44×44 mm2 region centred on the tumor, with the STIR image as anatomical reference. Correlation and DICE coefficients between DWI b0 and STIR images were computed, for all DWI image sets. Geometric quality of DWI1 was poor, but improved both by optimization of acquisition (DWI2) and by post-processing. Visually, hyperintensities on the Topup corrected DWI2 images matched closely the STIR images. Also, regions with high FDG uptake and low diffusion had matching shapes. Correlation and DICE coefficients had a large variation for DWI1, and showed an overall increase to a high level >0.6 and 0.8, respectively, following optimization of image acquisition and post-processing correction. Diffusion weighted images of the head/neck with a quality suitable for dual-modality assessment of tumour characteristics on a voxel basis can be obtained following the optimization of acquisition and post-processing.
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Geometric distortions of diffusion weighted imaging of the head/neck in combined PET/MR: optimization of image acquisition and post-processing correction for oncology applicatio
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M E E T I N G A B S T R A C T Open Access
Geometric distortions of diffusion weighted
imaging of the head/neck in combined PET/MR:
optimization of image acquisition and post-
processing correction for oncology applications
Adam E Hansen
1*
, Jacob Rasmussen
2
, Helle H Johannesen
1
, Astrid M Engberg
1
, Flemming L Andersen
1
,
Lena Specht
2
, Andreas Kjaer
1
, Liselotte Højgaard
1
, Thomas Beyer
3
, Barbara M Fischer
1
From PSMR14: 3rd Conference in PET/MR and SPECT/MR
Kos Island, Greece. 19-21 May 2014
1
Dept. of Clinical Physiology,
Nuclear Medicine and PET,
Rigshospitalet, Copenhagen,
Denmark
The combination of PET with Diffusion Weighted Imaging (DWI) is a promising appli-
cation of PET/MR. DWI geometric accuracy can be compromised in body regions with
complex anatomy. Here, we assess DWI head/neck image quality following optimiza-
tion of acquisition and post-processing.
Preliminary data from 10 patients with cancer of the tonsil or base-of-tongue is pre-
sented. An integrated PET/MR system (Siemens Biograph mMR) with a 3 T magnet
was used.
PET was performed as a single-bed, 20 min acquisition, 120 min post injection of
4 MBq/kg [
18
F]-FDG.
MRI included axial T2 weighted STIR, B0 mapping and 2 DWI single-shot EPI mea-
surements (DWI1 and DWI2) with b values 0, 500 and 1000 mm
2
/s. DWI2 was mea-
sured as 3 stacks, each at isocenter to maximize field homogeneity. DWI1/DWI2 had
an effective echo spacing 0.375/0.145 ms. For DWI2, distortions were corrected using
FSL with FUGUE and Topup algorithms.
DWI geometric quality was evaluated in 44×44 mm
2
region centred on the tumor,
with the STIR image as anatomical reference. Correlation and DICE coefficients
between DWI b0 and STIR images were computed, for all DWI image sets.
Geometric quality of DWI1 was poor, but improved both by optimization of acquisi-
tion (DWI2) and by post-processing. Visually, hyperintensities on the Topup corrected
DWI2 images matched closely the STIR images. Also, regions with high FDG uptake
and low diffusion had matching shapes. Correlation and DICE coefficients had a large
variation for DWI1, and showed an overall increase to a high level >0.6 and 0.8,
respectively, following optimization of image acquisition and post-processing
correction.
Diffusion weighted images of the head/neck with a quality suitable for dual-modality
assessment of tumour characteristics on a voxel basis can be obtained following the
optimization of acquisition and post-processing.
Hansen et al.EJNMMI Physics 2014, 1(Suppl 1):A76
http://www.ejnmmiphys.com/content/1/S1/A76
© 2014 Hansen et al; licensee Springer This is an Open Access article distributed under the terms of the Creative Commons Attribution
License (http ://creativecommons.org /licenses/b y/4.0), which permits unrestricted use, d istribution, and reproduc tion in any mediu m,
provided the or iginal work is properly cite d.
Authors’details
1
Dept. of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, Copenhagen, Denmark.
2
Dept. of Oncology,
Section of Radiotherapy, Rigshospitalet, Copenhagen, Denmark.
3
Centre for Medical Physics and Biomedical
Engineering, Medical University Vienna, Austria.
Published: 29 July 2014
doi:10.1186/2197-7364-1-S1-A76
Cite this article as: Hansen et al.: Geometric distortions of diffusion weighted imaging of the head/neck in
combined PET/MR: optimization of image acquisition and post-processing correction for oncology applications.
EJNMMI Physics 2014 1(Suppl 1):A76.
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Hansen et al.EJNMMI Physics 2014, 1(Suppl 1):A76
http://www.ejnmmiphys.com/content/1/S1/A76
Page 2 of 2
... Distortions may also be corrected with post-processing techniques, e.g., based on B 0 -field mapping [20]. Such techniques have frequently been utilized for brain fMRI [21] but only very little in context of oncology [8,22]. Therefore, both PSF modelling for PET image reconstruction and distortion correction of DWI can potentially improve PET/MR image quality and, thus, be expected to provide a robust basis for a voxelwise combination of the modalities. ...
... EPI distortions were corrected using the algorithm FMRIB's Utility for Geometrically Unwarping EPIs (FUGUE) of the FSL software package (Analysis Group, FMRIB where FMRIB is Oxford Centre for Functional MRI of the Brain) [22]. FUGUE reduces artefacts by using a computed B 0 -field map based on two collected gradient echo images and a corresponding phase map. ...
... The current study also demonstrated that performing EPI distortion correction by FUGUE on the optimized DWI protocol further reduced geometric distortions significantly. Distortion correction with B 0 -field mapping are commonly applied for fMRI [20], but only recently for oncology studies [8,22,28,29]. However, with the increasing interest in preserving spatial accuracy, e.g. for radiotherapy purposes, distortion correction of EPI could become even more important [30]. ...
Preparing data for multiparametric PET/MR imaging: Influence of PET point spread function modelling and EPI distortion correction on the spatial correlation of [18F]FDG-PET and diffusion-weighted MRI in head and neck cancer
Article
Full-text available
  • May 2019
  • PHYS MEDICA
Purpose: Multiparametric imaging holds great potential for characterization of disease heterogeneity. For integrated PET/MR imaging, the combination of 18F-flourodeoxyglucose (FDG) PET and diffusion weighted imaging (DWI) has been suggested for the assessment of tumor heterogeneity. However, PET image resolution is limited and DWI is prone to image distortions. The aim of this study was to assess the influence of PET point spread function (PSF) modelling and DWI distortion correction on the voxelwise correlation between FDG-PET and DWI. Methods: Data were collected from 11 patients with head and neck cancer, each undergoing PET/MR imaging twice. PET reconstructions with and without PSF modelling and DWI with and without distortion correction were derived. Tumor SUV was compared between PET reconstructions by linear regression. Geometric distortions of DWI with and without distortion correction were quantified by voxelwise correlation coefficients to an undistorted anatomical reference. The influence of PSF modelling and DWI distortion correction on a multiparametric analysis was assessed as a change of the voxelwise correlation coefficient between FDG-PET and DWI measured in tumors. Results: The inclusion of PSF modelling in the PET reconstruction affected tumor quantification by a 10-20% increase in SUV. Distortion correction reduced DWI geometric distortions significantly. The impact of PET PSF modelling on the spatial correlation with DWI was insignificant. However, distortion correction of DWI had a significant effect on the spatial correlation with PET. Conclusions: Proper preparation of the imaging modalities is important for a correct analysis and interpretation of multiparametric PET/MR imaging of head and neck cancer.
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... Both image acquisition and postprocessing were optimized to minimize distortions. The visually judged correspondence of DWI and 18 F-FDG PET was overall good, as seen in the figures (25). After this FUGUE correction was implemented, no patient had to be excluded because of signal drop out (Supplemental Fig. 1). ...
Feasibility of Multiparametric Imaging with PET/MR in Head and Neck Squamous Cell Carcinoma
Article
  • Sep 2016
Purpose: The purpose of this study was to investigate and assess the correlation and the reproducibility of multiparametric imaging in head and neck cancer patients. Material and methods: Twenty-one patients were included in this prospective scan-rescan study. All patients were scanned twice on an integrated Positron Emission Tomography and Magnetic Resonance imaging scanner (PET/MR). Gross tumor volumes (GTV) were defined on T2-weighted MR images (GTVT2) and volumes of interest were defined on diffusion-weighted magnetic resonance imaging and FDG PET (VOIDWI, VOIPET). Overlap between volumes was assessed as a percent-wise overlap. FDG uptake and diffusion were measured using standardized uptake value (SUV) and apparent diffusion coefficient(ADC) and correlation was tested across and within patients and as a voxel-by-voxel analysis. Results: Seventeen patients were available for correlation analysis and 12 patients were available for assessment of tumor overlap. The median tumor overlap between VOIDWI and VOIPET was 82%( VOIDWI in VOIPET) and 62%( VOIPET in VOIDWI) on scan 1 and scan 2, respectively. Across patients, the correlation between SUV and ADC was weak and non-significant. However, in individual patients a weak but significant correlation was identified on a voxel-by-voxel basis. Conclusion: In multiparametric imaging with the integrated PET/MR, the VOIs from DWI and FDG PET were both within the target volume for radiotherapy and overlapped substantially although not completely. No correlation between FDG uptake and DWI could be found across patients, but within individual patients a statistically significant, but weak, voxel-by-voxel correlation was found. The findings suggest that information on glucose uptake and diffusion coefficient carries complementary information of interest which may be relevant for radiotherapy treatment planning.
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Intratumor heterogeneity is biomarker specific and challenges the association with heterogeneity in multimodal functional imaging in head and neck squamous cell carcinoma
Article
  • Mar 2021
  • EUR J RADIOL
Rationale Tumor biopsy cannot detect heterogeneity and an association between heterogeneity in functional imaging and molecular biology will have an impact on both diagnostics and treatment possibilities. Purpose Multiparametric imaging can provide 3D information on functional aspects of a tumor and may be suitable for predicting intratumor heterogeneity. Here, we investigate the correlation between intratumor heterogeneity assessed with multiparametric imaging and multiple-biopsy immunohistochemistry. Methods In this prospective study, patients with primary or recurrent head and neck squamous cell carcinoma (HNSCC) underwent PET/MRI scanning prior to surgery. Tumors were removed en bloc and six core biopsies were used for immunohistochemical (IHC) staining with a predefined list of biomarkers: p40, p53, EGFR, Ki-67, GLUT1, VEGF, Bcl-2, CAIX, PD-L1. Intratumor heterogeneity of each IHC biomarker was quantified by calculating the coefficient of variation (CV) in tumor proportion score among the six core biopsies within each tumor lesion. The heterogeneity in the imaging biomarkers was assessed by calculating CV in ¹⁸F-fluorodeoxyglucose (FDG)-uptake, diffusion and perfusion. Concordance of the two variance measures was quantified using Spearman’s rank correlation Results Twenty-eight patients with a total of 33 lesions were included. There was considerable heterogeneity in most of the IHC biomarkers especially in GLUT1, PD-L1, Ki-67, CAIX and p53, however we only observed a correlation between the heterogeneity in GLUT1 and p53 and between Ki-67 and EGFR. Heterogeneity in FDG uptake and diffusion correlated with heterogeneity in cell density. Conclusion Considerable heterogeneity of IHC biomarkers was found, however, only few and weak correlations between the studied IHC markers were observed. The studied functional imaging biomarkers showed weak associations with heterogeneity in some of the IHC biomarkers. Thus, biological heterogeneity is not a general tumor characteristic but depends on the specific biomarker or imaging modality.
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