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Bette S, Decker JA, Braun FM, Becker J, Haerting M, Haeckel T, Gebhard M, Risch F, Woźnicki P, Scheurig-Muenkler C, Kroencke TJ, Schwarz F. Optimal Conspicuity of Liver Metastases in Virtual Monochromatic Imaging Reconstructions on a Novel Photon-Counting Detector CT—Effect of keV Settings and BMI. Diagnostics (Basel) 2022; 12:diagnostics12051231. [PMID: 35626387 PMCID: PMC9140684 DOI: 10.3390/diagnostics12051231] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 04/25/2022] [Accepted: 04/26/2022] [Indexed: 11/17/2022] Open
Abstract
In dual-energy CT datasets, the conspicuity of liver metastases can be enhanced by virtual monoenergetic imaging (VMI) reconstructions at low keV levels. Our study investigated whether this effect can be reproduced in photon-counting detector CT (PCD-CT) datasets. We analyzed 100 patients with liver metastases who had undergone contrast-enhanced CT of the abdomen on a PCD-CT (n = 50) or energy-integrating detector CT (EID-CT, single-energy mode, n = 50). PCD-VMI-reconstructions were performed at various keV levels. Identical regions of interest were positioned in metastases, normal liver, and other defined locations assessing image noise, tumor-to-liver ratio (TLR), and contrast-to-noise ratio (CNR). Patients were compared inter-individually. Subgroup analyses were performed according to BMI. On the PCD-CT, noise and CNR peaked at the low end of the keV spectrum. In comparison with the EID-CT, PCD-VMI-reconstructions exhibited lower image noise (at 70 keV) but higher CNR (for ≤70 keV), despite similar CTDIs. Comparing high- and low-BMI patients, CTDI-upregulation was more modest for the PCD-CT but still resulted in similar noise levels and preserved CNR, unlike the EID-CT. In conclusion, PCD-CT VMIs in oncologic patients demonstrated reduced image noise–compared to a standard EID-CT–and improved conspicuity of hypovascularized liver metastases at low keV values. Patients with higher BMIs especially benefited from constant image noise and preservation of lesion conspicuity, despite a more moderate upregulation of CTDI.
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Affiliation(s)
- Stefanie Bette
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Josua A. Decker
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Franziska M. Braun
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Judith Becker
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Mark Haerting
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Thomas Haeckel
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Michael Gebhard
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Franka Risch
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Piotr Woźnicki
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Christian Scheurig-Muenkler
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
| | - Thomas J. Kroencke
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
- Correspondence: ; Tel.: +49-821-400-2441
| | - Florian Schwarz
- Clinic for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Augsburg, Stenglinstr. 2, 86156 Augsburg, Germany; (S.B.); (J.A.D.); (F.M.B.); (J.B.); (M.H.); (T.H.); (M.G.); (F.R.); (P.W.); (C.S.-M.); (F.S.)
- Medical Faculty, Ludwig Maximilian University of Munich, Geschwister-Scholl-Platz 1, 80539 Munich, Germany
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Reimer RP, Gertz RJ, Pennig L, Henze J, Celik E, Lennartz S, Maintz D, Zopfs D, Große Hokamp N. Value of spectral detector computed tomography to differentiate infected from noninfected thoracoabominal fluid collections. Eur J Radiol 2021; 145:110037. [PMID: 34808580 DOI: 10.1016/j.ejrad.2021.110037] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Revised: 11/01/2021] [Accepted: 11/12/2021] [Indexed: 12/28/2022]
Abstract
PURPOSE To investigate the diagnostic value of spectral detector CT (SDCT)-derived virtual non-contrast (VNC), virtual monoenergetic images (VMI) and iodine overlays (IO) for distinguishing infected from noninfected fluid collections (FC) in the chest or abdomen. METHOD This retrospective study included 58 patients with venous phase SDCT with 77 FC. For all included FC, microbiological analysis of aspirated fluid served as reference. For quantitative analysis, wall thickness was measured, and (ROI)-based analysis performed within the fluid, the FC's wall (if any) and the aorta. Two radiologists qualitatively evaluated visibility of wall enhancement, diagnostic confidence regarding infection of fluid collection, confidence of CT-guided drainage catheter placement and visibility of anatomical landmarks in conventional images (CI) and VNC, VMI40keV, IO. RESULTS Wall thickness significantly differed between infected (n = 46) and noninfected (n = 31) FC (3.5 ± 1.8 mm vs. 1.4 ± 1.8 mm, AUC = 0.81; p < 0.05). Fluid attenuation and wall enhancement was significantly higher in infected as compared to noninfected FC in all reconstructions (p < 0.05, respectively). Highest AUC regarding A) attenuation in fluid was yielded in CI and VMI70,80keV (0.75); B) wall enhancement in CI (0.88) followed by iodine concentration (0.86). Contrast-to-noise ratio of wall vs. fluid was highest in VMI40keV (p < 0.05). All assessed qualitative parameters received significantly higher ratings when using spectral reconstructions vs. CI (p for all <0.05), except for visibility of wall enhancement. CONCLUSION Spectral reconstructions improve the assessment of infected from noninfected thoracoabdominal fluid collections and depiction of wall enhancement. Diagnostic performance of the quantitative measurements in spectral reconstructions were comparable with measurements in conventional images.
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Affiliation(s)
- Robert Peter Reimer
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany.
| | - Roman Johannes Gertz
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany
| | - Lenhard Pennig
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany
| | - Jörn Henze
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany
| | - Erkan Celik
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany
| | - Simon Lennartz
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany
| | - David Maintz
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany
| | - David Zopfs
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany
| | - Nils Große Hokamp
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Kerpener Str. 62, 50937 Cologne, Germany
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Zopfs D, Lennartz S, Abdullayev N, Lichtenstein T, Laukamp KR, Reimer RP, Kabbasch C, Borggrefe J, Schlamann M, Neuhaus V, Große Hokamp N. Generally applicable window settings of low-keV virtual monoenergetic reconstructions in dual-layer CT-angiography of the head and neck. Quant Imaging Med Surg 2021; 11:3408-3417. [PMID: 34341719 DOI: 10.21037/qims-20-1140] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Accepted: 03/25/2021] [Indexed: 11/06/2022]
Abstract
Background Increased vessel contrast in low-keV virtual monoenergetic images (VMI) in spectral detector CT angiography of the head and neck requires adaption of window settings. Aim of this study was to define generally applicable window settings of low-keV VMI. Methods Two radiologists determined ideal subjective window settings for VMI40-70 keV in 54 patients. To obtain generally applicable window settings, center and width values were modeled against the attenuation of the internal carotid artery (HUICA). This modeling was performed with and without respect to keV. Subsequently, image quality of VMI40-70 keV was assessed using the model-based determined window settings. Results With decreasing keV values, HUICA increased significantly in comparison to conventional images (CI) (P<0.05 for 40-60 keV). No significant differences between modelled and individually recorded window settings were found confirming validity of the obtained models (P values: 0.2-1.0). However, modelling with respect to keV was marginally less precise. Conclusions Window settings of low-keV VMI can be semi-automatically determined in dependency of the ICA attenuation in spectral detector CTA of the head and neck. The reported models are a promising tool to leverage the improved image quality of these images in clinical routine.
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Affiliation(s)
- David Zopfs
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
| | - Simon Lennartz
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany.,Department of Radiology, Massachusetts General Hospital, Boston, MA, USA
| | - Nuran Abdullayev
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
| | - Thorsten Lichtenstein
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
| | - Kai Roman Laukamp
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
| | - Robert Peter Reimer
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
| | - Christoph Kabbasch
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
| | - Jan Borggrefe
- Department of Radiology, Neuroradiology and Nuclear Medicine, Johannes Wesling University Hospital, Ruhr University Bochum, Bochum, Germany
| | - Marc Schlamann
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
| | - Victor Neuhaus
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
| | - Nils Große Hokamp
- Department of Diagnostic and Interventional Radiology, Faculty of Medicine and University Hospital Cologne, University Cologne, Cologne, Germany
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Virtual monoenergetic images from spectral detector computed tomography facilitate washout assessment in arterially hyper-enhancing liver lesions. Eur Radiol 2020; 31:3468-3477. [PMID: 33180163 PMCID: PMC8043945 DOI: 10.1007/s00330-020-07379-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 08/20/2020] [Accepted: 10/06/2020] [Indexed: 02/07/2023]
Abstract
Objectives To investigate whether the increased soft tissue contrast of virtual monoenergetic images (VMIs) obtained from a spectral detector computed tomography (SDCT) system improves washout assessment of arterially hyper-enhancing liver lesions. Methods Fifty-nine arterially hyper-enhancing lesions in 31 patients (age 65 ± 9 years, M/W 20/11) were included in this IRB-approved study. All patients underwent multi-phase SDCT for HCC screening. MRI, CEUS or biopsy within 3 months served as standard of reference to classify lesions as LiRADS 3 or 4/5. VMIs and conventional images (CIs) were reconstructed. Visual analysis was performed on 40, 60, and 80 kiloelectronvolt (keV) and CIs by 3 radiologists. Presence and visibility of washout were assessed; image quality and confidence of washout evaluation were evaluated on 5-point Likert scales. Signal-to-noise ratio (SNR), lesion-to-liver contrast-to-noise ratio (CNR) (|HUlesion–HUliver|/SDliver) and washout (|HUlesion–HUliver|) were calculated. Statistical assessment was performed using ANOVA and Wilcoxon test. Results On subjective lesion analysis, the highest level of diagnostic confidence and highest sensitivity for the detection of lesion washout were found for 40-keV VMIs (40 keV vs. CI, 81.3 vs. 71.3%). Image quality parameters were significantly better in low-kiloelectronvolt VMIs than in CIs (p < 0.05; e.g. SNRliver: 40 keV vs. CIs, 12.5 ± 4.1 vs. 5.6 ± 1.6). In LiRADS 4/5 lesions, CNR and quantitative washout values were significantly higher in 40-keV VMIs compared to CIs (p < 0.05; e.g. CNR and washout in 40 keV vs. CIs, 2.3 ± 1.6 vs. 0.8 ± 0.5 and 29.0 ± 19.1 vs. 12.9 ± 6.9 HU, respectively). Conclusion By increasing lesion contrast, low-kiloelectronvolt VMIs obtained from SDCT improve washout assessment of hyper-enhancing liver lesions with respect to washout visibility and diagnostic confidence. Key Points • Low-kiloelectronvolt virtual monoenergetic images from spectral detector CT facilitate washout assessment in arterially hyper-enhancing liver lesions. • Image quality and quantitative washout parameters as well as subjective washout visibility and diagnostic confidence benefit from low-kiloelectronvolt virtual monoenergetic images. Electronic supplementary material The online version of this article (10.1007/s00330-020-07379-3) contains supplementary material, which is available to authorized users.
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Al-Baldawi Y, Große Hokamp N, Haneder S, Steinhauser S, Püsken M, Persigehl T, Maintz D, Wybranski C. Virtual mono-energetic images and iterative image reconstruction: abdominal vessel imaging in the era of spectral detector CT. Clin Radiol 2020; 75:641.e9-641.e18. [PMID: 32362502 DOI: 10.1016/j.crad.2020.03.036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Accepted: 03/27/2020] [Indexed: 12/29/2022]
Abstract
AIM To compare the quality of virtual mono-energetic (VMI) and polychromatic images reconstructed with hybrid iterative (PCIHIR) or model-based reconstruction (PCIMBR) derived from dual-layer spectral detector computed tomography (SDCT) in arterial phase images to visualise the aorta and abdominal main branches. MATERIAL AND METHODS A retrospective review of 50 patients with abdominal arterial phase scans was undertaken. Attenuation, intraluminal noise, and signal-/contrast-to-noise ratio (S-/CNR) were assessed in the PCIHIR, PCIMBR and VMI40keV, VMI70keV, and VMI100keV images. Contrast, noise, and visualization of soft-plaque, and macro-/micro-calcifications were scored in a blinded reading by two radiologists. RESULTS VMI40keV yielded highest S-/CNR (p≤0.001). VMI70keV and PCIMBR showed comparable SNR (p≥0.999) and yielded higher SNR than PCIHIR. VMI70keV yielded higher CNR than PCIHIR (p<0.001) and PCIMBR (p<0.045). VMI100keV yielded lowest CNR (p≤0.001) and SNR (p≥0.104). In the subjective analysis, VMI40keV outperformed PCIMBR for contrast and noise, PCIMBR scored better than VMI70keV, and the latter scored better than PCIHIR for these categories (all p<0.001). PCIMBR was superior for depiction of soft-plaque and micro-calcifications (p<0.001). VMI100keV visualized micro-calcifications second best (p<0.001) and matched PCIMBR for the depiction of macro-calcifications (p>0.999), while VMI40keV scored second best for depiction of soft-plaque (p<0.020). CONCLUSIONS VMI40keV and VMI70keV yield better S-/CNR than PCIHIR and PCIMBR; however, PCIMBR visualized arteriosclerotic plaques best, followed by VMI40keV for depiction of soft-plaque and VMI100keV for macro- and micro-calcification. Based on the present findings, PCIMBR on conventional CT and VMI40keV supplemented by VMI100keV on SDCT are recommended for the diagnostic assessment of abdominal arteries.
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Affiliation(s)
- Y Al-Baldawi
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Cologne, Germany.
| | - N Große Hokamp
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Cologne, Germany
| | - S Haneder
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Cologne, Germany
| | - S Steinhauser
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Medical Statistics and Computational Biology, Cologne, Germany
| | - M Püsken
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Cologne, Germany
| | - T Persigehl
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Cologne, Germany
| | - D Maintz
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Cologne, Germany
| | - C Wybranski
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Cologne, Germany
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D'Angelo T, Cicero G, Mazziotti S, Ascenti G, Albrecht MH, Martin SS, Othman AE, Vogl TJ, Wichmann JL. Dual energy computed tomography virtual monoenergetic imaging: technique and clinical applications. Br J Radiol 2019; 92:20180546. [PMID: 30919651 DOI: 10.1259/bjr.20180546] [Citation(s) in RCA: 73] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Dual energy CT (DECT) has evolved into a commonly applied imaging technique in clinical routine due to its unique post-processing opportunities for improved evaluation of all body areas. Reconstruction of virtual monoenergetic imaging (VMI) series has shown beneficial effects for both non-contrast and contrast-enhanced DECT due to the flexibility to calculate low-keV VMI reconstructions to increase contrast and iodine attenuation, or to compute high-keV VMI reconstructions to reduce beam-hardening artefacts. The goal of this review article is to explain the technical background of VMI and noise-optimized VMI+ algorithms and to give an overview of useful clinical applications of the VMI technique in DECT of various body regions.
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Affiliation(s)
- Tommaso D'Angelo
- 1 Department of Biomedical Sciences and Morphological and Functional Imaging, Policlinico G. Martino - University Hospital Messina , Messina , Italy.,2 Department of Diagnostic and Interventional Radiology, Division of Experimental Imaging, University Hospital Frankfurt , Frankfurt , Germany
| | - Giuseppe Cicero
- 1 Department of Biomedical Sciences and Morphological and Functional Imaging, Policlinico G. Martino - University Hospital Messina , Messina , Italy
| | - Silvio Mazziotti
- 1 Department of Biomedical Sciences and Morphological and Functional Imaging, Policlinico G. Martino - University Hospital Messina , Messina , Italy
| | - Giorgio Ascenti
- 1 Department of Biomedical Sciences and Morphological and Functional Imaging, Policlinico G. Martino - University Hospital Messina , Messina , Italy
| | - Moritz H Albrecht
- 2 Department of Diagnostic and Interventional Radiology, Division of Experimental Imaging, University Hospital Frankfurt , Frankfurt , Germany
| | - Simon S Martin
- 2 Department of Diagnostic and Interventional Radiology, Division of Experimental Imaging, University Hospital Frankfurt , Frankfurt , Germany
| | - Ahmed E Othman
- 3 Department of Diagnostic and Interventional Radiology, Eberhard Karls University Tübingen , Tübingen , Germany
| | - Thomas J Vogl
- 2 Department of Diagnostic and Interventional Radiology, Division of Experimental Imaging, University Hospital Frankfurt , Frankfurt , Germany
| | - Julian L Wichmann
- 2 Department of Diagnostic and Interventional Radiology, Division of Experimental Imaging, University Hospital Frankfurt , Frankfurt , Germany
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