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1.  MR-guided attenuation map for prostate PET-MRI: an intensity and morphologic-based segmentation approach for generating a fiveclass attenuation map in pelvic region.
M. Shirin Shandiz • H. Saligheh Rad • P. Ghafarian • M. Bakhshayesh Karam • Afshin Akbarzadeh • Mohammad Reza Ay
Journal Paper
Ann Nucl Med

 Abstract

PURPOSE: Prostate imaging is one of the major application of hybrid PET/MRI systems. Inaccurate attenuation maps (p-maps) derived by direct segmentation (SEG) in which the cortical bone is ignored and the volume of the air in cavities is underestimated is the main challenge of commercial PET/MRI systems for the quantitative analysis of the p pelvic region. The present study considered the cortical bone and air cavity along with soft tissue, fat, and background air in the p-map of the pelvic region using a method based on SEG. The proposed method uses a dedicated imaging technique that increases the contrast between regions and a hybrid segmentation method to classify MR images based on intensity and morphologic characteristics of tissues, such as symmetry and similarity of bony structures.
PROCEDURES: Ten healthy volunteers underwent MRI and ultra-low dose CT imaging. The dedicated MR imaging technique uses the short echo time (STE) based on the conventional sequencing implemented on a clinical 1.5T MRI scanner. The generation of a p-map comprises the following steps: (1) bias field correction; (2) hybrid segmentation (HSEG), including segmenting images into clusters of cortical bone-air, soft tissue, and fat using https://www.ncbi.nlm.nih.gov/pubmed/?term=MR-guided+attenuation+map+for+prostate+PET-MRI%3A+an+intensity+and+morphdogic-based+segmen... 1/2 12/7/2016 MR-guided attenuation map for prostate PET-MRI: an intensity and morphologic-based segmentation approach for generating a five-class attenuatio...
spatial fuzzy c-means (SFCM), and separation of cortical bone and internal air cavities using morphologic characteristics; (3) the active contour approach for the separation of background air; and (4) the generation of a five-class p-map for cortical bone, internal air cavity, soft tissue, fat tissue, and background air. Validation was done by comparison with segmented CT images.
RESULTS: The Dice and sensitivity metrics of cortical bone structures and internal air cavities were 72 ± 11 and 66 ± 13 and 73 ± 10 and 68 ± 20 %, respectively. High correlation was observed between CT and HSEG-based p-maps (R 2 > 0.99) and the corresponding sinograms (R 2 > 0.98).

2.  New approach for calibration of pixelated scintillation detectors of intraoperative gamma cameras
Afshin Akbarzadeh, Valiallah Saba, Mohammad Reza Ay
Journal Paper
Iranian Journal of Nuclear Medicine and Molecular Imaging, 2017, Vol. 25, No. 1, pp 34-42.

 

Abstract:

Introduction: SURGEOSIGHT is a dedicated intra-operative hand-held gamma camera designed and manufactured by our team to be used for lymphoscintigraphy. Although conventional gamma cameras are widely used, they lack the capability of the sentinel lymph node (SLN) imaging in the operation room. Like conventional gamma cameras it is necessary to calibrate SURGEOSIGHT for linearity distortion, energy and flood correction. Our main objective in this study is to develop and implement three techniques for linearity, energy and uniformity corrections.

Methods: The camera is made up of a pixelated cesium iodide (sodium-activated) (CsI(Na)) scintillation crystal with 1 × 1 mm2 element size along with a Hamamatsu H8500 flat-panel multi-anode (64 channels) photomultiplier tube. All triple corrections required lookup tables (LUTs). To generate all three LUTs, one uncalibrated acquisition is necessary. Linearity distortion correction was based on localization of physical pixels of crystal and thin plate spline interpolation to estimate the amount of distortion. Energy correction LUT was simply a photo-peak map of incoming events which was estimated using self-organizing map technique.

Results: The results showed improvements qualitatively and quantitatively. The extrinsic energy resolution was enhanced from 50% to about 20.6%. Integral uniformity and the differential uniformity, after uniformity correction, in useful field-of-view (UFOV) was measured 9.5% and 4.5%, respectively.

Conclusion: Results substantiated that the correction techniques guarantee uniform and accurate output of the SURGEOSIGHT which is desirable for intra-operative localization of the sentinel lymph nodes in breast cancer and also for imaging of other superficial tumors.

Key words: Uniformity correction; Energy correction; Linearity distortion correction; Self-organizing map; Intra-operative gamma camera

3.  Single STE-MR Acquisition in MR-Based Attenuation Correction of Brain PET Imaging Employing a Fully Automated and Reproducible Level-Set Segmentation Approach
Fathi Kazerooni A. Av MR. Arfaie S Khateri P. Saliaheh Rad H
Journal Paper
Mol Imaging Biol.

 Abstract

Purpose: The aim of this study is to introduce a fully automatic and reproducible short echo-time (STE) magnetic resonance imaging (MRI) segmentation approach for MR-based attenuation correction of positron emission tomography (PET) data in head region. 
Procedures: Single STE-MR imaging was followed by generating attenuation correction maps (μ-maps) through exploiting an automated clustering-based level-set segmentation approach to classify head images into three regions of cortical bone, air, and soft tissue. Quantitative assessment was performed by comparing the STE-derived region classes with the corresponding regions extracted from X-ray computed tomography (CT) images. Results: The proposed segmentation method returned accuracy and specificity values of over 90 % for cortical bone, air, and soft tissue regions. The MR- and CT-derived μ-maps were compared by quantitative histogram analysis.
Conclusions: The results suggest that the proposed automated segmentation approach can reliably discriminate bony structures from the proximal air and soft tissue in single STE-MR images, which is suitable for generating MR-based μ-maps for attenuation correction of PET data 

4.  Neural correlates of audiotactile phonetic processing in early‑blind readers: an fMRI study
Morteza Pishnamazi · Yasaman Nojaba · Habib Ganjgahi · Asie Amousoltani · Mohammad Ali Oghabian
Journal Paper
EXPERIMENTAL BRAIN RESEARCH

 Abstract

Reading is a multisensory function that relies on arbitrary associations between auditory speech sounds and symbols from a second modality. Studies of bimodal phonetic perception have mostly investigated the integration of visual letters and speech sounds. Blind readers perform an analogous task by using tactile Braille letters instead of visual letters. The neural underpinnings of audiotactile phonetic processing have not been studied before. We used functional magnetic resonance imaging to reveal the neural correlates of audiotactile phonetic processing in 16 early-blind Braille readers. Braille letters and corresponding speech sounds were presented in unimodal, and congruent/incongruent bimodal configurations. We also used a behavioral task to measure the speed of blind readers in  dentifying letters presented via tactile and/or auditory modalities. Reaction times for tactile stimuli were faster. The reaction times for bimodal stimuli were equal to those for the slower auditory-only stimuli. fMRI analyses revealed the convergence of unimodal auditory and unimodal tactile responses in areas of the right precentral gyrus and bilateral crus I of the cerebellum. The left and right planum temporale fulfilled the 'max criterion' for bimodal integration, but activities of these areas were not sensitive to the phonetical congruency between sounds and Braille letters. Nevertheless, congruency effects were found in regions of frontal lobe and cerebellum. Our findings suggest that, unlike sighted readers who are assumed to have amodal phonetic representations, blind readers probably process letters and sounds separately. We discuss that this distinction might be due to mal-development of multisensory neural circuits in early blinds or it might be due to inherent differences between Braille and print reading mechanisms. 

5.  T-1 correlates age: A short-TE MR relaxometry study in vivo on human cortical bone free water at 1.5 T
Atena Akbari , Shahrokh Abbasi-Rad , Hamidreza Saligheh Rad
Journal Paper
BONE

 Abstract

Large pores of human cortical bone (>30 mu m) are filled with fluids, essentially consisting of water, suggesting that cortical bone free water can be considered as a reliable surrogate measure of cortical bone porosity and hence quality. Signal from such pores can be reliably captured using Short Echo Time (STE) pulse sequence with echo-time in the range of 1-1.5 msec (which should be judiciously selected correspond to T-2* value of free water molecules). Furthermore, it is well-known that cortical bone T-1-relaxivity is a function of its geometry, suggesting that cortical bone free water increases with age. In this work, we quantified cortical bone free water longitudinal relaxation time (T-1) by a Dual-TR technique using STE pulse sequence. In the sequel, we investigated relationship between STE-derived
cortical bone free water T-1-values and age in a group of healthy volunteers (thirty subjects covering the age range of 20-70 years) at 1.5 T. Preliminary results showed that cortical bone free water T-1 highly correlates with age (r(2) = 0.73, p < 0.0001), representing cortical bone free water T-1 as a reliable indicator of cortical bone porosity and age-related deterioration. It can be concluded that STEMRI can be utilized as proper alternative in quantifying cortical bone porosity parameters in-vivo, with the advantages of widespread clinical availability and being cost-effective, (c) 2015 Elsevier Inc. All rights reserved.
 

6.  Monte Carlo-based assessment of the trade-off between spatial resolution, field-of-view and scattered radiation in the variable resolution X-ray CT scanner
Hossein Arabi , Ali Reza Kamali Asl , Mohammad Reza Ay , Habib Zaidi
Journal Paper
PHYSICA MEDICA-EUROPEAN JOURNAL OF MEDICAL PHYSICS

 Abstract

Objective: The purpose of this work is to evaluate the impact of optimization of magnification on performance parameters of the variable resolution X-ray (VRX) CT scanner. MethodsA realistic model based on an actual VRX CT scanner was implemented in the GATE Monte Carlo simulation platform. To evaluate the influence of system magnification, spatial resolution, fieldof- view (FOV) and scatter-to-primary ratio of the scanner were estimated for both fixed and optimum object magnification at each detector rotation angle. Comparison and inference between these
performance parameters were performed angle by angle to determine appropriate object position at each opening half angle.
Results: Optimization of magnification resulted in a trade-off between spatial resolution and FOV of the scanner at opening half angles of 90 degrees-12 degrees, where the spatial resolution increased up to 50% and the scatter-to-primary ratio decreased from 4.8% to 3.8% at a detector angle of about 90 degrees for the same FOV and X-ray energy spectrum. The disadvantage of magnification optimization at these angles is the significant reduction of the FOV (up to 50%). Moreover, magnification optimization was definitely beneficial for opening half angles below 12 degrees improving the spatial resolution from 7.5 cy/mm to 20 cy/mm. Meanwhile, the FOV increased by more than 50% at these angles.

7.  Monte Carlo-based assessment of the trade-off between spatial resolution, field-of-view and scattered radiation in the variable resolution X-ray CT scanner
Hossein Arabi , Ali Reza Kamali Asl , Mohammad Reza Ay , Habib Zaidi
Journal Paper
Physica Medica

 Abstract

The purpose of this work is to evaluate the impact of optimization of magnification on performance parameters of the variable resolution X-ray (VRX) CT scanner. A realistic model based on an actual VRX CT scanner was implemented in the GATE Monte Carlo simulation platform. To evaluate the influence of system magnification, spatial resolution, field-of-view (FOV) and scatter-to-primary ratio of the scanner were estimated for both fixed and optimum object magnification at each detector rotation angle. Comparison and inference between these performance parameters were performed angle by angle to determine appropriate object position at each opening half angle.
Optimization of magnification resulted in a trade-off between spatial resolution and FOV of the scanner at opening half angles of 90°-12°, where the spatial resolution increased up to 50% and the scatter-to-primary ratio decreased from 4.8% to 3.8% at a detector angle of about 90° for the same FOV and X-ray energy spectrum. The disadvantage of magnification optimization at these angles is the significant reduction of the FOV (up to 50%). Moreover, magnification optimization was definitely beneficial for opening half angles below 12° improving the spatial resolution from 7.5 cy/mm to 20 cy/mm. Meanwhile, the FOV increased by more than 50% at these angles.

8.  Development of Gold-Coated Magnetic Nanoparticles as a Potential MRI Contrast Agent
Ali Reza Montazerabadi, Mohammad Ali Oghabian*, Rasoul Irajirad, Samad Muhammadnejad, Davoud Ahmadvand, Hamid Delavari H and Seyed Rabie Mahdavi
Journal Paper
NANO

 Abstract

Gold-coated superparamagnetic iron oxide nanoparticles (SPIONs) coated with methylpolyethylene glycol (mPEG) are synthesized and investigated as a magnetic resonance (MR) imaging contrast agent. The synthesized mPEG-core@shells are characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS), vibrating sample magnetometry (VSM), zeta-potential analysis and X-ray diffraction (XRD). In addition, the transverse relaxivity of the mPEG-core@shells is measured using a 3T MRI scanner. The cytotoxicity of the mPEG-core@shells is tested in the LNCaP cell line using an 3-(4,5-Dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay. The results show that the mPEG-core@shell particles are semispherical with hydrodynamic size of similar to 65 nm and a transverse relaxivity of 162.3 mM(-1) S-1. The mPEG-core@shell particles demonstrate good stability in biological media without any significant in vitro cytotoxicity under high cellular uptake conditions. Finally, in vivo imaging shows that mPEG-core@shells are a potential contrast agent for use in early-stage detection.

9.  Effect of Functional Group and Surface Charge of PEG and Dextran-Coated USPIO as a Contrast Agent in MRI on Relaxivity Constant
Nastaran Najafian • Saeed Shanehsazzadeh • Farzaneh Hajesmaeelzadeh • Afsaneh Lahooti • Cordula Gruettner • Mohammad Ali Oghabian
Journal Paper
APPLIED MAGNETIC RESONANCE

 Abstract

The challenges in molecular imaging are focused on the development of novel contrast agents with much lower relaxation times. Ultrasmall superparamagnetic iron oxide nanoparticles known as USPIOhave been used for a variety of applications such as imaging of cancer, apoptosis, and hyperthermia providing higher signal changes based on weighted susceptibility effects. Although many studies had been performed on USPIO there is still a lack of data on the effects of the physicochemical properties of these nanoparticles (NP) such as hydrodynamic size, surface charge and type of functional groups, which may alter the relaxivity of these NPs. The aim of this study was to evaluate the effect of different functional groups and surface charges of PEGylated and dextran-coated NPs on their magnetic properties. All relaxometry studies were performed using a 3-T magnetic resonance imaging. Our results showed that the impact of charge on magnetic properties is much higher than that of coating thickness. In this respect, particles with positive surface charges showed higher r (2)/r (1) ratios.

10.  Rapid microwave-assisted synthesis of PVP-coated ultrasmall gadolinium oxide nanoparticles for magnetic resonance imaging
Parisa Vahdatkhah , Hamid Reza Madaah Hosseini , Azin Khodaei , Ali Reza Montazerabadi , Rasoul Irajirad , Mohamad Ali Oghabian , Hamid Delavari H.
Journal Paper
Chemical Physics

 Abstract

Synthesis of polyvinyl pyrrolidone (PVP) coated ultrasmall Gd203 nanoparticles (NPs) with enhanced T-1-weighted signal intensity and r(2)/r(1) ratio close to unity is performed by a microwave-assisted polyol process. PVP coated Gd(2)0(3)NPs with spherical shape and uniform size of 2.5 +/- 0.5 nm have been synthesized below 5 min and structure and morphology confirmed by HRTEM, XRD and FTIR. The longitudinal (r(1)) and transversal relaxation (r(2)) of Gd(2)0(3)NPs is measured by a 3 T MRI scanner. The results showed considerable increasing of relaxivity for Gd(2)0(3)NPs in comparison to gadolinium chelates which are commonly used for clinical magnetic resonance imaging. In addition, a mechanism for Gd(2)0(3)NPs formation and in situ surface modification of PVP-grafted Gd(2)0(3)NPs is proposed. (C) 2015 Elsevier B.V. All rights reserved.                                                            

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