Thomas G. Maris | University of Crete (original) (raw)

Papers by Thomas G. Maris

European Journal of Radiology, 2021

PURPOSE The aim of this study is to compare polyacrylamide and agarose gels, as components of a s... more PURPOSE The aim of this study is to compare polyacrylamide and agarose gels, as components of a simple MRI phantom, for the measurements of Apparent Diffusion Coefficient (ADC), T1 and T2 relaxation times. MATERIALS AND METHODS Five (5) test tubes with polyacrylamide gels of different monomer concentrations and six (6) test tubes of different agarose gel concentrations were used as a phantom for ADC, T1 and T2 measurements, which were expressed as 2D color parametric maps, on a 1.5 T clinical MRI system. ADC and T2 maps were calculated utilizing a Weighted Linear (WL) regression fitting algorithm. T1 maps were calculated utilizing a standard non-linear fitting algorithm. RESULTS In agarose gels, ADC measurements are independent of the agarose concentration, whereas the T1 and T2 relaxation times decrease with increasing agarose concentration. On the contrary, in polyacrylamide gels, ADC measurements decrease quadratically while increasing the monomer concentration, whereas the T1 and T2 relaxation times reveal a linear decrease with increasing monomer concentration. CONCLUSION Polyacrylamide gels can serve as a better means for simulating ADC values, as compared with the agarose gels used in this study.

Magnetic Resonance Imaging, May 1, 2017

This study aimed to assess the effect of echo spacing in transverse magnetization (T2) signal dec... more This study aimed to assess the effect of echo spacing in transverse magnetization (T2) signal decay of gel and fat (oil) samples. Additionally, we assess the feasibility of using spin coupling as a determinant of fat content. Methods Phantoms of known T2 values, as well as vegetable oil phantoms, were scanned at 1.5 T scanner with a multi echo FSE sequence of variable echo spacing above and below the empirical threshold of 20ms for echo train signal modulation (6.7, 13.6, 26.8, and 40ms). T2 values were calculated from monoexponential fitting of the data. Relative signal loss between the four acquisitions of different echo spacing was calculated. Results Agreement in the T2 values of water gel phantom was observed in all acquisitions as opposed to fat phantom (oil) samples. Relative differences in signal intensity between two successive sequences of different echo spacing on composite fat/water regions of interest was found to be linearly correlated to fat fraction of the ROI. Conclusion The sample specific degree of signal loss that was observed between different fat samples (vegetable oils) can be attributed to the composition of each sample in J coupled fat components. Hence, spin coupling may be used as a determinant of fat content.

Middle East African Journal of Ophthalmology, 2018

PURPOSE: Posterior staphyloma is an ocular complication associated with high myopia and reflects ... more PURPOSE: Posterior staphyloma is an ocular complication associated with high myopia and reflects degenerative changes on the sclera. Its morphology is associated with chorioretinal atrophy and myopic maculopathy. The purpose of this study was to validate the efficacy of optical coherence tomography (OCT) in providing a simple estimation of the staphyloma pattern. MATERIALS AND METHODS: Observational case-series study of high myopic patients with posterior staphylomas. Patients were examined using the star scan pattern OCT in different radial planes. Three-dimensional (3D) magnetic resonance tomography was also performed to visualize the anatomical characteristics of the posterior pole. 3D-segmentation and curvature analysis were also performed. RESULTS: Eight patients were totally enrolled in this pilot study. Our study pool consisted of 2 wide macular staphylomas, 2 narrow macular staphylomas, and 4 barrel-shaped staphylomas. Our preliminary results revealed that patients displayed mirror-image distortion in the steeper staphyloma axis. In the barrel-shaped subtype, no image distortion was displayed in any plane. CONCLUSION: We estimated the axis of the smaller base curvature by noting the distortion pattern in the different radial axis. The recognition of pathologic axial myopia is important since there is a risk of permanent vision loss from vision to threatening sequelae.

Journal of physics, Dec 1, 2006

Page 1. Gel dosimetry in diagnostic radiology: Measurement of the z-axis geometric efficiency in ... more Page 1. Gel dosimetry in diagnostic radiology: Measurement of the z-axis geometric efficiency in modern MDCT scanners This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2006 J. Phys.: Conf. Ser. 56 272 ...

British Journal of Radiology, Sep 1, 2021

Objectives:To emerge hypoperfusion of lower limbs in patients with critical limb ischemia (CLI) u... more Objectives:To emerge hypoperfusion of lower limbs in patients with critical limb ischemia (CLI) using Intravoxel Incoherent Motion microperfusion magnetic resonance imaging (IVIM-MRI). Moreover to examine the ability of IVIM-MRI to differentiate patients with severe peripheral arterial disease (PAD) from normal subjects and evaluate the percutaneous transluminal angioplasty (PTA) results in patients with CLI.Methods:Eight patients who presented with CLI and six healthy volunteers were examined. The patients underwent IVIM-MRI of lower extremity before and following PTA. The imaging protocol included sagittal diffusion-weighted (DW) sequences. DW images were analyzed and color parametric maps of the micro-circulation of blood inside the capillary network (D*) were constructed. The studies were evaluated by two observers to define interobserver reproducibility.Results:Technical success was achieved in all patients (8/8). The mean ankle-brachial index increased from 0.35 ± 0.2 to 0.76 ± 0.25 (p < 0.05). Successful revascularization improved IVIM microperfusion. Mean D* increased from 279.88 ± 13.47 10−5 mm2/s to 331.51 ± 31 10−5 mm2/s, following PTA, p < 0.05. Moreover, PAD patients presented lower D* values as compared to healthy individuals (279.88 ± 13.47 10−5 mm2/s vs 332.47 ± 22.95 10−5 mm2/s, p < 0.05, respectively). Good interobserver agreement was obtained with an ICC = 0.84 (95% CI 0.64–0.93).Conclusions:IVIM-MRI can detect differences in microperfusion between patients with PAD and healthy individuals. Moreover, significant restitution of IVIM microperfusion is found following successful PTA.Advances in knowledge:IVIM-MRI is a safe, reproducible and effective modality for evaluation of lower limb hypoperfusion in patients with PAD. It seems also to be a helpful tool to detect changes of tissue perfusion in patients with CLI following revascularization.

Journal of physics, Dec 1, 2006

Journal of Neuro-ophthalmology, Sep 30, 2021

Background: In this study we evaluate the diagnostic accuracy of extraocular muscle volumetry in ... more Background: In this study we evaluate the diagnostic accuracy of extraocular muscle volumetry in detecting thyroid eye disease and to compare the results with simple measurements of maximal medial rectus (MR) diameter. Methods: Cross-sectional study that included 47 eyes of 47 patients with thyroid eye disease and 47 healthy controls. Patients underwent slitlamp examination and imaging consisting of computed tomography scans. Image segmentation and volume measurements were performed by 2 independent researchers. Intraobserver and interobserver reliability testing was also conducted. Results: Total extraocular muscle volume was 7.31 ± 1.88 cm3 and medial volume was 2.38 ± 0.73 cm3 in the study group. In this group, the maximum measured diameter of the MR was 6.67 ± 0.35 mm. MR volume was statistically associated with maximum MR diameter (r = 9.78; P < 0.001). Both MR volume and maximum MR diameter measurements showed good predictive efficacy as shown using receiver operator characteristic curve analysis. Conclusions: Complications of thyroid eye disease are often sight threatening, and timely diagnosis is crucial for the management of the entity and its sequelae. The results of this study imply that simple measurements of maximum MR diameter are sensitive enough to establish diagnosis.

Hellenic Journal οf Radiology, Jun 28, 2019

Optimising T2 relaxation measurements on MS patients utilising a multi-component tissue mimicking... more Optimising T2 relaxation measurements on MS patients utilising a multi-component tissue mimicking phantom and different fitting algorithms in T2 calculations, p. 18-31

Acta Radiologica

Background Persistent type 2 endoleaks (T2EL) require lifelong surveillance to avoid potentially ... more Background Persistent type 2 endoleaks (T2EL) require lifelong surveillance to avoid potentially life-threatening complications. Purpose To evaluate the performance of radiomic features (RF) derived from computed tomography angiography (CTA), for differentiating aggressive from benign T2ELs after endovascular aneurysm repair (EVAR). Material and Methods A prospective study was performed on patients who underwent EVAR from January 2018 to January 2020. Analysis was performed in patients who were diagnosed with T2EL based on the CTA of the first postoperative month and were followed at six months and one year. Patients were divided into two groups according to the change of aneurysm sac dimensions. Segmentation of T2ELs was performed and RF were extracted. Feature selection for subsequent machine-learning analysis was evaluated by means of artificial intelligence. Two support vector machines (SVM) classifiers were developed to predict the aneurysm sac dimension changes at one year, ut...

Hellenic Journal οf Radiology, Sep 27, 2019

T2-based MRI radiomic features for discriminating tumour grading in soft tissues sarcomas, p. 22-31

Poster: "ECR 2018 / C-0661 / Volumetric CT perfusion technique for assessment of PTA outcome... more Poster: "ECR 2018 / C-0661 / Volumetric CT perfusion technique for assessment of PTA outcome in patients with Critical Limb Ischemia: A feasibility study" by: "N. Galanakis1, T. G. Maris2, N. Kontopodis1, E. Kehagias1, C. Ioannou1, N. Kosidekakis1, K. Perisinakis3, A. H. Karantanas1, D. Tsetis1; 1Heraklion/GR, 2Heraklion, Crete/GR, 3Iraklion/GR"

2018 IEEE EMBS International Conference on Biomedical & Health Informatics (BHI), 2018

Accurate determination of disease activity by detection of the acute, inflammatory Multiple Scler... more Accurate determination of disease activity by detection of the acute, inflammatory Multiple Sclerosis (MS) lesions, with blood brain barrier disruption and contrast enhancement is critical for clinicians because it affects diagnosis and treatment. In this work, a new Dynamic Contrast Enhanced (DCE) protocol was investigated in conjunction with different pharmacokinetic (PK) models in order to define a well-designed workflow for DCE MRI analysis of acute, active MS lesions. This time extended protocol, achieved to double the perfusion time by extending the overall MRI acquisition less than two minutes. Four patients with early relapsing remitting multiple sclerosis were analyzed with two different DCE protocols and three PK models. The statistical comparison of the different approaches, including biomarkers and metrics of goodness of fit, showed that extension of the DCE imaging time, the so called ‘Snaps’ protocol, combined with the extended Tofts model PK analysis, achieved the characterization of 15% more pixels into acute, active MS lesions in terms of fitting low enhancement pixels, and resulted in more accurate detection of the active lesion area. To this end, a novel DCE acquisition framework is presented herein that achieved to double the perfusion time by loading the protocol duration less than two minutes, and as a result a better characterization of active MS lesions in terms of fitting accuracy and size of the lesion was achieved.

2018 IEEE EMBS International Conference on Biomedical & Health Informatics (BHI), 2018

The present study aims 1. to automatically classify the heterogeneously perfused tumors using dyn... more The present study aims 1. to automatically classify the heterogeneously perfused tumors using dynamic contrast-enhanced (DCE) MRI data from two patients diagnosed with malignant peripheral nerve sheath tumor (MPNST), 2. to compare the differences between the two cases, and 3. to detect the possible presence of hypoxia. A pattern recognition (PR) algorithm has been applied to the data resulting in the identification of areas with different perfusion. The algorithm was proven to be robust since the intensity curves of the PR classified pixels had similar shapes with the curves of the PR identified patterns and were in line with the theoretically expected enhancement patterns of the DCE time-signal curves.

2016 IEEE International Conference on Imaging Systems and Techniques (IST), 2016

The vascular microenvironment of tumors is a key determinant of the tumor pathophysiology. Hypoxi... more The vascular microenvironment of tumors is a key determinant of the tumor pathophysiology. Hypoxia, i.e. lack of sufficient oxygen supply, might affect significantly the treatment efficacy of solid tumors making it an important imaging biomarker. The ability to characterize oxygen perfusion of the tumor can provide prognostic information about the tumor progression and risk of metastases. In this work, Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE-MRI), a non-invasive method, has been used for the detection of tumor hypoxic areas on neck sarcoma data. Data analysis was performed using a pattern recognition (PR) technique able to automatically identify potential tumor hypoxic regions along with a well-established pharmacokinetic (PK) model for computing perfusion parameters. The paper presents a novel method for the initialization of the PR technique through realistic assumptions in order to overcome instability issues found in random initialization. To this end, the PR technique was initialized using two novel approaches based on the wash-in part of the dynamic acquisition and the ktrans map derived from the PK analysis. The results, from these different implementations show high correlation between them and consistently lead to the separation of the tumor area into well-perfused, hypoxic and necrotic regions.

2019 IEEE 19th International Conference on Bioinformatics and Bioengineering (BIBE), 2019

Radiomics-based studies have created an unprecedented momentum in computational medical imaging o... more Radiomics-based studies have created an unprecedented momentum in computational medical imaging over the last years by significantly advancing and empowering correlational and predictive quantitative studies in numerous clinical applications. An important element of this exciting field of research especially in oncology is multi-scale texture analysis since it can effectively describe tissue heterogeneity, which is highly informative for clinical diagnosis and prognosis. There are however, several concerns regarding the plethora of radiomics features used in the literature especially regarding their performance consistency across studies. Since many studies use software packages that yield multi-scale texture features it makes sense to investigate the scale-space performance of texture candidate biomarkers under the hypothesis that significant texture markers may have a more persistent scale-space performance. To this end, this study proposes a methodology for the extraction of Gabor multi-scale and orientation texture DCE-MRI radiomics for predicting breast cancer complete response to neoadjuvant therapy. More specifically, a Gabor filter bank was created using four different orientations and ten different scales and then firstorder and second-order texture features were extracted for each scale-orientation data representation. The performance of all these features was evaluated under a generalized repeated cross-validation framework in a scale-space fashion using extreme gradient boosting classifiers.

Cerebral Cortex, 2021

In order to inform the debate whether cortical areas related to action observation provide a prag... more In order to inform the debate whether cortical areas related to action observation provide a pragmatic or a semantic representation of goal-directed actions, we performed 2 functional magnetic resonance imaging (fMRI) experiments in humans. The first experiment, involving observation of aimless arm movements, resulted in activation of most of the components known to support action execution and action observation. Given the absence of a target/goal in this experiment and the activation of parieto-premotor cortical areas, which were associated in the past with direction, amplitude, and velocity of movement of biological effectors, our findings suggest that during action observation we could be monitoring movement kinematics. With the second, double dissociation fMRI experiment, we revealed the components of the observation-related cortical network affected by 1) actions that have the same target/goal but different reaching and grasping kinematics and 2) actions that have very similar...

Poster: "ECR 2003 / C-1075 / Development of a comprehensive quantitative MRI (qMRI) protocol... more Poster: "ECR 2003 / C-1075 / Development of a comprehensive quantitative MRI (qMRI) protocol: In vivo assessment of tissue minerals" by: "T. Maris1, E. Chryssou1, O. Papakonstantinou2, N. Papanikolaou3, P. Prassopoulos4, N. Gourtsoyiannis3; 1Iraklion/GR, 2Athens/GR, 3Heraklion/GR, 4Alexandroupolis/GR"

2018 IEEE International Conference on Imaging Systems and Techniques (IST), 2018

Quantitative MRI plays a central role in the precision management of cancer. Regarding breast can... more Quantitative MRI plays a central role in the precision management of cancer. Regarding breast cancer (BRCA) patients, DCE-MRI imaging biomarkers (IBs) have shown promising results both in clinical trials and clinical practice. The advancements in the field of radiomics offer more opportunities for defining disease-specific imaging biomarkers for screening, diagnosis and therapy assessment. In this paper we present a study investigating the role of radiomics in predicting breast-cancer therapy response in the neoadjuvant setting. A temporal radiomics approach is proposed for predicting breast cancer therapy response in the neoadjuvant setting on a public cohort of 35 patients with histologically-proven breast cancer of stage II/III with DCEMRI data available before treatment, after the first cycle and before the end of treatment. The results based on 57 radiomics features indicate that neoadjuvant chemotherapy (NAC) treatment outcome can be predicted both at baseline and right after the first NAC cycle. Our analyses, found that the best predictors were the median and size-zone non-uniformity normalized calculated from the wavelet decomposition of level 2 of the baseline and the first follow-up exam, achieving an AUROC of 80.80% and 81.34% respectively. These encouraging preliminary results call for more relevant research investigating the role of temporal radiomics in predicting NAC outcome towards more personalized therapy planning.

European Journal of Radiology, 2021

PURPOSE To investigate and histopathologically validate the role of model selection in the design... more PURPOSE To investigate and histopathologically validate the role of model selection in the design of novel parametric meta-maps towards the discrimination of low from high-grade soft tissue sarcomas (STSs) using multiple Diffusion Weighted Imaging (DWI) models. METHODS DWI data of 28 patients were quantified using the mono-exponential, bi-exponential, stretched-exponential and the diffusion kurtosis model. Akaike Weights (AW) were calculated from the corrected Akaike Information Criteria (AICc) to select the most suitable model for every pixel within the tumor volume. Pseudo-colorized classification maps were then generated to depict model suitability, hypothesizing that every single model underpins different tissue properties and cannot solely characterize the whole tumor. Single model parametric maps were turned into meta-maps using the classification map and a histological validation of the model suitability results was conducted on several subregions of different tumors. Several histogram metrics were calculated from all derived maps before and after model selection, statistical analysis was conducted using the Mann-Whitney U test, p-values were adjusted for multiple comparisons and performance of all statistically significant metrics was evaluated using the Receiver Operator Characteristic (ROC) analysis. RESULTS The histologic analysis on several tumor subregions confirmed model suitability results on these areas. Only 3 histogram metrics, all derived from the meta-maps, were found to be statistically significant in differentiating low from high-grade STSs with an AUC higher than 89 %. CONCLUSION Embedding model selection in the design of the diffusion parametric maps yields to histogram metrics of high discriminatory power in grading STSs.

Magnetic Resonance Materials in Physics, Biology and Medicine, 2021

To propose a new method of simulating the BOLD contrast using a dynamic, easy to construct and op... more To propose a new method of simulating the BOLD contrast using a dynamic, easy to construct and operate, low-cost physical phantom. A structure of thin pipelines passing through a gel volume was used to simulate blood vessels in human tissue. Quantitative T2*, R2* measurements were used to study the signal change of the phantom. BOLD fMRI experiments and analysis were performed to evaluate its potential use as an fMRI simulator. Experimental T2*, R2* measurements showed similar behavior with published references. BOLD contrast was successfully achieved with the proposed method. In addition, there were several proposed parameters, like the angle of the phantom relative to B0, which can easily adjust the signal change and the activation area. Coefficients of variation showed good reproducibility within a month period. Statistical t maps were produced with in-house software for the BOLD measurements. T2*maps and BOLD images confirm the potential use of this phantom as an fMRI simulator and also as a tool for studying sensitivity and specificity of BOLD sequences/algorithms.

European Journal of Radiology, 2021

PURPOSE The aim of this study is to compare polyacrylamide and agarose gels, as components of a s... more PURPOSE The aim of this study is to compare polyacrylamide and agarose gels, as components of a simple MRI phantom, for the measurements of Apparent Diffusion Coefficient (ADC), T1 and T2 relaxation times. MATERIALS AND METHODS Five (5) test tubes with polyacrylamide gels of different monomer concentrations and six (6) test tubes of different agarose gel concentrations were used as a phantom for ADC, T1 and T2 measurements, which were expressed as 2D color parametric maps, on a 1.5 T clinical MRI system. ADC and T2 maps were calculated utilizing a Weighted Linear (WL) regression fitting algorithm. T1 maps were calculated utilizing a standard non-linear fitting algorithm. RESULTS In agarose gels, ADC measurements are independent of the agarose concentration, whereas the T1 and T2 relaxation times decrease with increasing agarose concentration. On the contrary, in polyacrylamide gels, ADC measurements decrease quadratically while increasing the monomer concentration, whereas the T1 and T2 relaxation times reveal a linear decrease with increasing monomer concentration. CONCLUSION Polyacrylamide gels can serve as a better means for simulating ADC values, as compared with the agarose gels used in this study.

Magnetic Resonance Imaging, May 1, 2017

This study aimed to assess the effect of echo spacing in transverse magnetization (T2) signal dec... more This study aimed to assess the effect of echo spacing in transverse magnetization (T2) signal decay of gel and fat (oil) samples. Additionally, we assess the feasibility of using spin coupling as a determinant of fat content. Methods Phantoms of known T2 values, as well as vegetable oil phantoms, were scanned at 1.5 T scanner with a multi echo FSE sequence of variable echo spacing above and below the empirical threshold of 20ms for echo train signal modulation (6.7, 13.6, 26.8, and 40ms). T2 values were calculated from monoexponential fitting of the data. Relative signal loss between the four acquisitions of different echo spacing was calculated. Results Agreement in the T2 values of water gel phantom was observed in all acquisitions as opposed to fat phantom (oil) samples. Relative differences in signal intensity between two successive sequences of different echo spacing on composite fat/water regions of interest was found to be linearly correlated to fat fraction of the ROI. Conclusion The sample specific degree of signal loss that was observed between different fat samples (vegetable oils) can be attributed to the composition of each sample in J coupled fat components. Hence, spin coupling may be used as a determinant of fat content.

Middle East African Journal of Ophthalmology, 2018

PURPOSE: Posterior staphyloma is an ocular complication associated with high myopia and reflects ... more PURPOSE: Posterior staphyloma is an ocular complication associated with high myopia and reflects degenerative changes on the sclera. Its morphology is associated with chorioretinal atrophy and myopic maculopathy. The purpose of this study was to validate the efficacy of optical coherence tomography (OCT) in providing a simple estimation of the staphyloma pattern. MATERIALS AND METHODS: Observational case-series study of high myopic patients with posterior staphylomas. Patients were examined using the star scan pattern OCT in different radial planes. Three-dimensional (3D) magnetic resonance tomography was also performed to visualize the anatomical characteristics of the posterior pole. 3D-segmentation and curvature analysis were also performed. RESULTS: Eight patients were totally enrolled in this pilot study. Our study pool consisted of 2 wide macular staphylomas, 2 narrow macular staphylomas, and 4 barrel-shaped staphylomas. Our preliminary results revealed that patients displayed mirror-image distortion in the steeper staphyloma axis. In the barrel-shaped subtype, no image distortion was displayed in any plane. CONCLUSION: We estimated the axis of the smaller base curvature by noting the distortion pattern in the different radial axis. The recognition of pathologic axial myopia is important since there is a risk of permanent vision loss from vision to threatening sequelae.

Journal of physics, Dec 1, 2006

Page 1. Gel dosimetry in diagnostic radiology: Measurement of the z-axis geometric efficiency in ... more Page 1. Gel dosimetry in diagnostic radiology: Measurement of the z-axis geometric efficiency in modern MDCT scanners This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2006 J. Phys.: Conf. Ser. 56 272 ...

British Journal of Radiology, Sep 1, 2021

Objectives:To emerge hypoperfusion of lower limbs in patients with critical limb ischemia (CLI) u... more Objectives:To emerge hypoperfusion of lower limbs in patients with critical limb ischemia (CLI) using Intravoxel Incoherent Motion microperfusion magnetic resonance imaging (IVIM-MRI). Moreover to examine the ability of IVIM-MRI to differentiate patients with severe peripheral arterial disease (PAD) from normal subjects and evaluate the percutaneous transluminal angioplasty (PTA) results in patients with CLI.Methods:Eight patients who presented with CLI and six healthy volunteers were examined. The patients underwent IVIM-MRI of lower extremity before and following PTA. The imaging protocol included sagittal diffusion-weighted (DW) sequences. DW images were analyzed and color parametric maps of the micro-circulation of blood inside the capillary network (D*) were constructed. The studies were evaluated by two observers to define interobserver reproducibility.Results:Technical success was achieved in all patients (8/8). The mean ankle-brachial index increased from 0.35 ± 0.2 to 0.76 ± 0.25 (p < 0.05). Successful revascularization improved IVIM microperfusion. Mean D* increased from 279.88 ± 13.47 10−5 mm2/s to 331.51 ± 31 10−5 mm2/s, following PTA, p < 0.05. Moreover, PAD patients presented lower D* values as compared to healthy individuals (279.88 ± 13.47 10−5 mm2/s vs 332.47 ± 22.95 10−5 mm2/s, p < 0.05, respectively). Good interobserver agreement was obtained with an ICC = 0.84 (95% CI 0.64–0.93).Conclusions:IVIM-MRI can detect differences in microperfusion between patients with PAD and healthy individuals. Moreover, significant restitution of IVIM microperfusion is found following successful PTA.Advances in knowledge:IVIM-MRI is a safe, reproducible and effective modality for evaluation of lower limb hypoperfusion in patients with PAD. It seems also to be a helpful tool to detect changes of tissue perfusion in patients with CLI following revascularization.

Journal of physics, Dec 1, 2006

Journal of Neuro-ophthalmology, Sep 30, 2021

Background: In this study we evaluate the diagnostic accuracy of extraocular muscle volumetry in ... more Background: In this study we evaluate the diagnostic accuracy of extraocular muscle volumetry in detecting thyroid eye disease and to compare the results with simple measurements of maximal medial rectus (MR) diameter. Methods: Cross-sectional study that included 47 eyes of 47 patients with thyroid eye disease and 47 healthy controls. Patients underwent slitlamp examination and imaging consisting of computed tomography scans. Image segmentation and volume measurements were performed by 2 independent researchers. Intraobserver and interobserver reliability testing was also conducted. Results: Total extraocular muscle volume was 7.31 ± 1.88 cm3 and medial volume was 2.38 ± 0.73 cm3 in the study group. In this group, the maximum measured diameter of the MR was 6.67 ± 0.35 mm. MR volume was statistically associated with maximum MR diameter (r = 9.78; P < 0.001). Both MR volume and maximum MR diameter measurements showed good predictive efficacy as shown using receiver operator characteristic curve analysis. Conclusions: Complications of thyroid eye disease are often sight threatening, and timely diagnosis is crucial for the management of the entity and its sequelae. The results of this study imply that simple measurements of maximum MR diameter are sensitive enough to establish diagnosis.

Hellenic Journal οf Radiology, Jun 28, 2019

Optimising T2 relaxation measurements on MS patients utilising a multi-component tissue mimicking... more Optimising T2 relaxation measurements on MS patients utilising a multi-component tissue mimicking phantom and different fitting algorithms in T2 calculations, p. 18-31

Acta Radiologica

Background Persistent type 2 endoleaks (T2EL) require lifelong surveillance to avoid potentially ... more Background Persistent type 2 endoleaks (T2EL) require lifelong surveillance to avoid potentially life-threatening complications. Purpose To evaluate the performance of radiomic features (RF) derived from computed tomography angiography (CTA), for differentiating aggressive from benign T2ELs after endovascular aneurysm repair (EVAR). Material and Methods A prospective study was performed on patients who underwent EVAR from January 2018 to January 2020. Analysis was performed in patients who were diagnosed with T2EL based on the CTA of the first postoperative month and were followed at six months and one year. Patients were divided into two groups according to the change of aneurysm sac dimensions. Segmentation of T2ELs was performed and RF were extracted. Feature selection for subsequent machine-learning analysis was evaluated by means of artificial intelligence. Two support vector machines (SVM) classifiers were developed to predict the aneurysm sac dimension changes at one year, ut...

Hellenic Journal οf Radiology, Sep 27, 2019

T2-based MRI radiomic features for discriminating tumour grading in soft tissues sarcomas, p. 22-31

Poster: "ECR 2018 / C-0661 / Volumetric CT perfusion technique for assessment of PTA outcome... more Poster: "ECR 2018 / C-0661 / Volumetric CT perfusion technique for assessment of PTA outcome in patients with Critical Limb Ischemia: A feasibility study" by: "N. Galanakis1, T. G. Maris2, N. Kontopodis1, E. Kehagias1, C. Ioannou1, N. Kosidekakis1, K. Perisinakis3, A. H. Karantanas1, D. Tsetis1; 1Heraklion/GR, 2Heraklion, Crete/GR, 3Iraklion/GR"

2018 IEEE EMBS International Conference on Biomedical & Health Informatics (BHI), 2018

Accurate determination of disease activity by detection of the acute, inflammatory Multiple Scler... more Accurate determination of disease activity by detection of the acute, inflammatory Multiple Sclerosis (MS) lesions, with blood brain barrier disruption and contrast enhancement is critical for clinicians because it affects diagnosis and treatment. In this work, a new Dynamic Contrast Enhanced (DCE) protocol was investigated in conjunction with different pharmacokinetic (PK) models in order to define a well-designed workflow for DCE MRI analysis of acute, active MS lesions. This time extended protocol, achieved to double the perfusion time by extending the overall MRI acquisition less than two minutes. Four patients with early relapsing remitting multiple sclerosis were analyzed with two different DCE protocols and three PK models. The statistical comparison of the different approaches, including biomarkers and metrics of goodness of fit, showed that extension of the DCE imaging time, the so called ‘Snaps’ protocol, combined with the extended Tofts model PK analysis, achieved the characterization of 15% more pixels into acute, active MS lesions in terms of fitting low enhancement pixels, and resulted in more accurate detection of the active lesion area. To this end, a novel DCE acquisition framework is presented herein that achieved to double the perfusion time by loading the protocol duration less than two minutes, and as a result a better characterization of active MS lesions in terms of fitting accuracy and size of the lesion was achieved.

2018 IEEE EMBS International Conference on Biomedical & Health Informatics (BHI), 2018

The present study aims 1. to automatically classify the heterogeneously perfused tumors using dyn... more The present study aims 1. to automatically classify the heterogeneously perfused tumors using dynamic contrast-enhanced (DCE) MRI data from two patients diagnosed with malignant peripheral nerve sheath tumor (MPNST), 2. to compare the differences between the two cases, and 3. to detect the possible presence of hypoxia. A pattern recognition (PR) algorithm has been applied to the data resulting in the identification of areas with different perfusion. The algorithm was proven to be robust since the intensity curves of the PR classified pixels had similar shapes with the curves of the PR identified patterns and were in line with the theoretically expected enhancement patterns of the DCE time-signal curves.

2016 IEEE International Conference on Imaging Systems and Techniques (IST), 2016

The vascular microenvironment of tumors is a key determinant of the tumor pathophysiology. Hypoxi... more The vascular microenvironment of tumors is a key determinant of the tumor pathophysiology. Hypoxia, i.e. lack of sufficient oxygen supply, might affect significantly the treatment efficacy of solid tumors making it an important imaging biomarker. The ability to characterize oxygen perfusion of the tumor can provide prognostic information about the tumor progression and risk of metastases. In this work, Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE-MRI), a non-invasive method, has been used for the detection of tumor hypoxic areas on neck sarcoma data. Data analysis was performed using a pattern recognition (PR) technique able to automatically identify potential tumor hypoxic regions along with a well-established pharmacokinetic (PK) model for computing perfusion parameters. The paper presents a novel method for the initialization of the PR technique through realistic assumptions in order to overcome instability issues found in random initialization. To this end, the PR technique was initialized using two novel approaches based on the wash-in part of the dynamic acquisition and the ktrans map derived from the PK analysis. The results, from these different implementations show high correlation between them and consistently lead to the separation of the tumor area into well-perfused, hypoxic and necrotic regions.

2019 IEEE 19th International Conference on Bioinformatics and Bioengineering (BIBE), 2019

Radiomics-based studies have created an unprecedented momentum in computational medical imaging o... more Radiomics-based studies have created an unprecedented momentum in computational medical imaging over the last years by significantly advancing and empowering correlational and predictive quantitative studies in numerous clinical applications. An important element of this exciting field of research especially in oncology is multi-scale texture analysis since it can effectively describe tissue heterogeneity, which is highly informative for clinical diagnosis and prognosis. There are however, several concerns regarding the plethora of radiomics features used in the literature especially regarding their performance consistency across studies. Since many studies use software packages that yield multi-scale texture features it makes sense to investigate the scale-space performance of texture candidate biomarkers under the hypothesis that significant texture markers may have a more persistent scale-space performance. To this end, this study proposes a methodology for the extraction of Gabor multi-scale and orientation texture DCE-MRI radiomics for predicting breast cancer complete response to neoadjuvant therapy. More specifically, a Gabor filter bank was created using four different orientations and ten different scales and then firstorder and second-order texture features were extracted for each scale-orientation data representation. The performance of all these features was evaluated under a generalized repeated cross-validation framework in a scale-space fashion using extreme gradient boosting classifiers.

Cerebral Cortex, 2021

In order to inform the debate whether cortical areas related to action observation provide a prag... more In order to inform the debate whether cortical areas related to action observation provide a pragmatic or a semantic representation of goal-directed actions, we performed 2 functional magnetic resonance imaging (fMRI) experiments in humans. The first experiment, involving observation of aimless arm movements, resulted in activation of most of the components known to support action execution and action observation. Given the absence of a target/goal in this experiment and the activation of parieto-premotor cortical areas, which were associated in the past with direction, amplitude, and velocity of movement of biological effectors, our findings suggest that during action observation we could be monitoring movement kinematics. With the second, double dissociation fMRI experiment, we revealed the components of the observation-related cortical network affected by 1) actions that have the same target/goal but different reaching and grasping kinematics and 2) actions that have very similar...

Poster: "ECR 2003 / C-1075 / Development of a comprehensive quantitative MRI (qMRI) protocol... more Poster: "ECR 2003 / C-1075 / Development of a comprehensive quantitative MRI (qMRI) protocol: In vivo assessment of tissue minerals" by: "T. Maris1, E. Chryssou1, O. Papakonstantinou2, N. Papanikolaou3, P. Prassopoulos4, N. Gourtsoyiannis3; 1Iraklion/GR, 2Athens/GR, 3Heraklion/GR, 4Alexandroupolis/GR"

2018 IEEE International Conference on Imaging Systems and Techniques (IST), 2018

Quantitative MRI plays a central role in the precision management of cancer. Regarding breast can... more Quantitative MRI plays a central role in the precision management of cancer. Regarding breast cancer (BRCA) patients, DCE-MRI imaging biomarkers (IBs) have shown promising results both in clinical trials and clinical practice. The advancements in the field of radiomics offer more opportunities for defining disease-specific imaging biomarkers for screening, diagnosis and therapy assessment. In this paper we present a study investigating the role of radiomics in predicting breast-cancer therapy response in the neoadjuvant setting. A temporal radiomics approach is proposed for predicting breast cancer therapy response in the neoadjuvant setting on a public cohort of 35 patients with histologically-proven breast cancer of stage II/III with DCEMRI data available before treatment, after the first cycle and before the end of treatment. The results based on 57 radiomics features indicate that neoadjuvant chemotherapy (NAC) treatment outcome can be predicted both at baseline and right after the first NAC cycle. Our analyses, found that the best predictors were the median and size-zone non-uniformity normalized calculated from the wavelet decomposition of level 2 of the baseline and the first follow-up exam, achieving an AUROC of 80.80% and 81.34% respectively. These encouraging preliminary results call for more relevant research investigating the role of temporal radiomics in predicting NAC outcome towards more personalized therapy planning.

European Journal of Radiology, 2021

PURPOSE To investigate and histopathologically validate the role of model selection in the design... more PURPOSE To investigate and histopathologically validate the role of model selection in the design of novel parametric meta-maps towards the discrimination of low from high-grade soft tissue sarcomas (STSs) using multiple Diffusion Weighted Imaging (DWI) models. METHODS DWI data of 28 patients were quantified using the mono-exponential, bi-exponential, stretched-exponential and the diffusion kurtosis model. Akaike Weights (AW) were calculated from the corrected Akaike Information Criteria (AICc) to select the most suitable model for every pixel within the tumor volume. Pseudo-colorized classification maps were then generated to depict model suitability, hypothesizing that every single model underpins different tissue properties and cannot solely characterize the whole tumor. Single model parametric maps were turned into meta-maps using the classification map and a histological validation of the model suitability results was conducted on several subregions of different tumors. Several histogram metrics were calculated from all derived maps before and after model selection, statistical analysis was conducted using the Mann-Whitney U test, p-values were adjusted for multiple comparisons and performance of all statistically significant metrics was evaluated using the Receiver Operator Characteristic (ROC) analysis. RESULTS The histologic analysis on several tumor subregions confirmed model suitability results on these areas. Only 3 histogram metrics, all derived from the meta-maps, were found to be statistically significant in differentiating low from high-grade STSs with an AUC higher than 89 %. CONCLUSION Embedding model selection in the design of the diffusion parametric maps yields to histogram metrics of high discriminatory power in grading STSs.

Magnetic Resonance Materials in Physics, Biology and Medicine, 2021

To propose a new method of simulating the BOLD contrast using a dynamic, easy to construct and op... more To propose a new method of simulating the BOLD contrast using a dynamic, easy to construct and operate, low-cost physical phantom. A structure of thin pipelines passing through a gel volume was used to simulate blood vessels in human tissue. Quantitative T2*, R2* measurements were used to study the signal change of the phantom. BOLD fMRI experiments and analysis were performed to evaluate its potential use as an fMRI simulator. Experimental T2*, R2* measurements showed similar behavior with published references. BOLD contrast was successfully achieved with the proposed method. In addition, there were several proposed parameters, like the angle of the phantom relative to B0, which can easily adjust the signal change and the activation area. Coefficients of variation showed good reproducibility within a month period. Statistical t maps were produced with in-house software for the BOLD measurements. T2*maps and BOLD images confirm the potential use of this phantom as an fMRI simulator and also as a tool for studying sensitivity and specificity of BOLD sequences/algorithms.