Mehran Shaghaghi - Academia.edu (original) (raw)

Papers by Mehran Shaghaghi

Magnetic resonance imaging, Jun 1, 2024

Current medical science, Feb 1, 2021

The purpose of this work was to demonstrate the feasibility of neurite orientation dispersion and... more The purpose of this work was to demonstrate the feasibility of neurite orientation dispersion and density imaging (NODDI) in characterizing the brain tissue microstructural changes of middle cerebral artery occlusion (MCAO) in rats at 3T MRI, and to validate NODDI metrics with histology. A multi-shell diffusion MRI protocol was performed on 11 MCAO rats and 10 control rats at different post-operation time points of 0.5, 2, 6, 12, 24 and 72 h. NODDI orientation dispersion index (ODI) and intracellular volume fraction (V ic ) metrics were compared between MCAO group and control group. The evolution of NODDI metrics was characterized and validated by histology. Infarction was consistent with significantly increased ODI and V ic in comparison to control tissues at all time points ( P <0.001). Lesion ODI increased gradually from 0.5 to 72 h, while its V ic showed a more complicated and fluctuated evolution. ODI and V ic were significantly different between hyperacute and acute stroke periods ( P <0.001). The NODDI metrics were found to be consistent with the histological findings. In conclusion, NODDI can reflect microstructural changes of brain tissues in MCAO rats at 3T MRI and the metrics are consistent with histology. This study helps to prepare NODDI for the diagnosis and management of ischemic stroke in translational research and clinical practice.

Frontiers in Neuroscience

BackgroundConventional gadolinium (Gd)-enhanced MRI is currently used for stratifying the lesion ... more BackgroundConventional gadolinium (Gd)-enhanced MRI is currently used for stratifying the lesion activity of multiple sclerosis (MS) despite limited correlation with disability and disease activity. The stratification of MS lesion activity needs further improvement to better support clinics.PurposeTo investigate if the novel proton exchange rate (kex) MRI combined with quantitative susceptibility mapping (QSM) may help to further stratify non-enhanced (Gd-negative) MS lesions.Materials and methodsFrom December 2017 to December 2020, clinically diagnosed relapsing-remitting MS patients who underwent MRI were consecutively enrolled in this IRB-approved retrospective study. The customized MRI protocol covered conventional T2-weighted, T2-fluid-attenuated-inversion-recovery, pre- and post-contrast T1-weighted imaging, and quantitative sequences, including kex MRI based on direct-saturation removed omega plots and QSM. Each MS lesion was evaluated based on its Gd-enhancement as well as i...

Journal of Magnetic Resonance Imaging

Background: Currently available radiological methods do not completely capture the diversity of m... more Background: Currently available radiological methods do not completely capture the diversity of multiple sclerosis (MS) lesion subtypes. This lack of information hampers the understanding of disease progression and potential treatment stratification. For example, inflammation persists in some lesions after gadolinium (Gd) enhancement resolves. Novel metabolic and molecular imaging methods may improve the current assessments of MS pathophysiology. Purpose: To compare the in vivo proton exchange rate (k ex) MRI with Gd-enhanced MRI for characterizing MS lesions. Study Type: Retrospective. Subjects: Sixteen consecutively diagnosed relapsing-remitting multiple sclerosis (RRMS) patients. Field Strength/Sequence: 3.0T MRI with T 2-weighted imaging, postcontrast T 1-weighted imaging, and single-slice chemical exchange saturation transfer imaging.

Biosensors

Quantification of proton exchange rate (kex) is a challenge in MR studies. Current techniques eit... more Quantification of proton exchange rate (kex) is a challenge in MR studies. Current techniques either have low resolutions or are dependent on the estimation of parameters that are not measurable. The Omega plot method, on the other hand, provides a direct way for determining kex independent of the agent concentration. However, it cannot be used for in vivo studies without some modification due to the contributions from the water signal. In vivo tissue proton exchange rate (kex) MRI, based on the direct saturation (DS) removed Omega plot, quantifies the weighted average of kex of the endogenous tissue metabolites. This technique has been successfully employed for imaging the variation in the kex of ex vivo phantoms, as well as in vivo human brains in healthy subjects, and stroke or multiple sclerosis (MS) patients. In this paper, we present a brief review of the methods used for kex imaging with a focus on the development of in vivo kex MRI technique based on the DS-removed Omega plo...

Physical systems can store information and their informational properties are governed by the law... more Physical systems can store information and their informational properties are governed by the laws of information. In particular, the amount of information that a physical system can convey is limited by the number of its degrees of freedom and their distinguishable states. Here we explore the properties of the physical systems with absolutely one degree of freedom. The central point in these systems is the tight limitation on their information capacity. Discussing the implications of this limitation we demonstrate that such systems exhibit a number of features, such as randomness, no-cloning, and non-commutativity, which are peculiarities attributed to quantum mechanics (QM). After demonstrating many astonishing parallels to quantum behavior, we postulate an interpretation of quantum physics as the physics of systems with a single degree of freedom. We then show how a number of other quantum conundrum can be understood by considering the informational properties of the systems and ...

Quantitative Imaging in Medicine and Surgery

Background: Proton exchange rate (k ex) magnetic resonance imaging (MRI) has recently been develo... more Background: Proton exchange rate (k ex) magnetic resonance imaging (MRI) has recently been developed, with preliminary results demonstrating its potential for evaluating reactive oxygen species. This prospective cohort study investigated the k ex in different stroke stages and its correlation with stroke severity and prognosis. Methods: In all, 96 ischemic stroke patients were included in the study. Patients were divided into 3 groups based on stroke phase (acute, subacute, and chronic). A spin echo-echo planar imaging sequence with presaturation powers of 1.5, 2.5, and 3.5 μT was implemented to obtain Z-spectra, and k ex maps were constructed from direct saturation-removed omega plots. Relative k ex (rk ex) and the relative apparent diffusion coefficient (rADC) were calculated as the ratio of k ex or ADC in the infarcts to values in contralateral tissue, respectively. Correlations between both k ex and rk ex and National Institute of Health Stroke Scale (NIHSS) scores were evaluated. Receiver operating characteristic (ROC) analysis was used to evaluate the performance of k ex , rk ex , rADC, and lesion volume for predicting acute stroke outcome. Results: The k ex was significantly higher in ischemic lesions than in contralateral tissue at all stages. In addition, the k ex of acute lesions was higher than that of subacute and chronic lesions [mean (± SD) 935.1±81.5 vs. 881.4±55.7 and 866.9±76.7 s-1 , respectively; P<0.05 and P<0.01, respectively]. The difference in k ex between subacute and chronic lesions was not significant. In acute stroke, there was a limited correlation between a lesion's k ex and NIHSS score (R 2 =0.16; P=0.01) and between rk ex and NIHSS score (R 2 =0.28; P=0.001). Acute stroke patients with poor prognosis had significantly higher lesion k ex and rk ex than did those with good prognosis (k ex : 991.1±78.2 vs. 893.1±55.1 s-1 , P<0.001; rk ex : 1.28±0.09 vs. 1.15±0.06, P<0.001). In ROC analyses, k ex and rk ex showed favorable predictive performance for acute stroke outcome, with areas under the curve (AUC) of 0.837 and 0.880, respectively, which were slightly but not significantly higher than the AUCs for lesion volume (0.730) and rADC (0.673). Conclusions: This study indicates that k ex MRI is promising for the diagnosis and management of ischemic stroke because it can reflect the oxidative stress of lesions and predict prognosis.

The relationship between language and consciousness has been debated since ancient times, but the... more The relationship between language and consciousness has been debated since ancient times, but the details have never been fully articulated. Certainly, there are animals that possess the same essential auditory and vocal systems as humans, but acquiring language is seemingly uniquely human. In this essay, we investigate the relationship between language and consciousness by demonstrating how language usage implies the self-awareness of the user. We show that the self-awareness faculty encompasses the language faculty and how this self-awareness, that is uniquely human, enables us to create social realities through utilizing the social character of the language. We conclude that it is self-awareness that empowers humans to form collective intentionality and to structure societies. Establishing the relationship between self-awareness, language and society sheds light on connections between philosophy of mind, philosophy of language and philosophy of society

Simultaneous observation of the wave-like and particle-like aspects of the photon in the double-s... more Simultaneous observation of the wave-like and particle-like aspects of the photon in the double-slit experiment is unallowed. The underlying reason behind this limitation is not understood. In this paper, we explain this unique behavior by considering the communicational properties of the photons. Photons have three independently adjustable properties (energy, direction, and spin) that can be used to communicate messages. The double-slit experiment setup fixes two of these properties and confines the single photon’s capacity for conveying messages to no more than one message. With such a low communication capacity, information theory dictates that measurements associated only with one proposition can obtain consistent results, and a second measurement associated with an independent proposition must necessarily lead to randomness. In the double-slit example, these are the wave or particle properties of the photon. The interpretation we offer is based on the formalism of information t...

Quantitative Imaging in Medicine and Surgery, 2021

Background: The non-invasive characterization of glioma metabolites would greatly assist the mana... more Background: The non-invasive characterization of glioma metabolites would greatly assist the management of glioma patients in the clinical setting. This study investigated the applicability of intra-subject inter-metabolite correlation analyses for differentiating glioma malignancy and proliferation. Methods: A total of 17 negative controls (NCs), 39 low-grade gliomas (LGGs) patients, and 25 highgrade gliomas (HGGs) subjects were included in this retrospective study. Amide proton transfer (APT) and magnetization transfer contrast (MTC) imaging contrasts, as well as total choline/total creatine (tCho/tCr) and total N-acetylaspartate/total creatine (tNAA/tCr) ratios quantified from magnetic resonance spectroscopic imaging (MRSI) were co-registered voxel-wise and used to produce three intra-subject inter-metabolite correlation coefficients (IMCCs), namely, R APT vs. MTC , R APT vs. tCho/tCr , and R MTC vs. tNAA/tCr. The correlation between the IMCCs and tumor grade and Ki-67 labeling index (LI) for tumor proliferation were explored. The differences in the IMCCs between the three groups were compared with one-way analysis of variance (ANOVA). Finally, regression analysis was used to build a combined model with multiple IMCCs to improve the diagnostic performance for tumor grades based on receiver operator characteristic curves. Results: Compared with the NCs, gliomas showed stronger inter-metabolic correlations. R APT vs. MTC was significantly different among the three groups (NC vs. LGGs vs. HGGs: −0.18±0.38 vs. −0.40±0.34 vs. −0.70±0.29, P<0.0001). No significant differences were detected in R MTC vs. tNAA/tCr among the three groups. R APT vs. MTC and R APT vs. tCho/tCr correlated significantly with tumor grade (R=−0.41, P=0.001 and R=0.448, P<0.001, respectively). However, only R APT vs. MTC was mildly correlated with Ki-67 (R=−0.33, P=0.02). R APT vs. MTC and R APT vs. tCho/tCr achieved areas under the curve (AUCs) of 0.754 and 0.71, respectively, for differentiating NCs from gliomas; and 0.77 and 0.78, respectively, for differentiating LGGs from HGGs. The combined multi-IMCCs model improved the correlation with the Ki-67 LI (R=0.46, P=0.0008) and the tumor-grade stratification with AUC increased to 0.85 (sensitivity: 80.0%, specificity: 79.5%). Conclusions: This study demonstrated that glioma patients showed stronger inter-metabolite correlations than control subjects, and the IMCCs were significantly correlated with glioma grade and proliferation. The multi-IMCCs combined model further improved the performance of clinical diagnosis.

Bulletin of the American Physical Society, 2012

European Spine Journal, 2021

Purpose Z-spectral MRI data were analyzed to produce multiparametric metabolic and microenvironme... more Purpose Z-spectral MRI data were analyzed to produce multiparametric metabolic and microenvironmental contrasts for identifying intervertebral discs with/without pain symptom and sore pain. Methods Z-spectra data were collected from the lumbar discs of 26 patients with non-specific chronic low bck pain (CLBP) and 21 asymptomatic controls (AC) with a chemical exchange saturation transfer (CEST). Data were fitted to quantify the CEST effects from glycosaminoglycan, amide proton transfer (APT), nuclear Overhauser enhancement (NOE), semi-solid magnetization transfer contrast effects, and the direct saturation of water. Multiparametric maps were computed from the fitted peak amplitudes, and the average values were calculated from all five lumber discs. Those parameters were compared between the CLBP and AC groups and between the subgroups with and without (Nsore) sore pain. Results The discs in symptomatic patients have lower water content, collagen-bound water and collagen than the disc...

We employed deuterium nuclear magnetic resonance spectroscopy (2 H-NMR) to investigate the effect... more We employed deuterium nuclear magnetic resonance spectroscopy (2 H-NMR) to investigate the effect of sterol structure on lipid membrane organization. Cholesterol is the major sterol component of mammalian cell plasma membranes. It strongly affects the properties of phospholipid membranes. For example, incorporating cholesterol in liquid crystalline membranes increases lipid acyl chain order, and induces the liquid ordered phase which is considered to have biological importance. We first measured the chain ordering in pure bilayers of 1-cholesterylhemisuccinoyl-2-palmitoyl(d31)-snglycero-3-phosphocholine (CholPC), a sterol-modified phospholipid with a cholesterol moiety covalently attached to the phospholipid glycerol backbone in place of one of the lipid acyl chains. We then compared CholPC's chain ordering with that of 1-palmitoyl-2palmitoyl-d31-sn-glycero-3-phosphocholine (DPPC-d31)/cholesterol and found that constrainded cholesterol's ability to order adjacent acyl chains is greatly reduced. Several sterols, broadly similar in structure to cholesterol but with specific chemical modifications, are prevalent in plant or fungal cell plasma membranes. We used 2 H-NMR to study the influence of sterol structure on its effectiveness in modifying the acyl chain order of a 1-palmitoyl(d31)-2-oleoyl-sn-glycero-3-phosphocholine (POPC-d31) membrane. Spectra of POPC-d31 multilamellar vesicles containing campesterol, βsitosterol, brassicasterol or stigmasterol were taken at 25 o C for sterol concentrations up to 45 mol% and compared to previous observations obtained using cholesterol, 7dehydrocholesterol (7-DHC) or ergosterol. Among the sterol structural modifications we compared, the C22 double bond reduced the sterol's ordering ability the most, followed by a C24 ethyl or methyl substituent. Finally we used 2 H-NMR to study the effect of sterol structure on the propensity of sterols to induce phase separation in equimolar DPPC/POPC/sterol membranes containing 7-DHC, brassicasterol or stigmasterol. The results were compared to previous observations obtained for membranes containing cholesterol or ergosterol, which highlighted the significance of sterol structure on phase separation promoting properties. Such comparative studies are prerequisites to establishing the underlying principles of sterol/phospholipid interactions.

In this thesis I address two di erent topics in quantum theory. The rst one is the long discussed... more In this thesis I address two di erent topics in quantum theory. The rst one is the long discussed Schrodinger's cat problem, and the issues related to having a macroscopic superposition state. I show that the quantum theory provides full explanation to the problem. In the second part, I discuss the time measurement related issues in quantum mechanics. Since there does not exist any time operator in quantum mechanics generally, time is not directly measurable. Therefore we should devise other methods to register time. We study di erent time-energy relations and will nd that accurate clocks have high energy uncertainties. If we use accurate clocks in quantum systems to observe their time evolutions, their high energy uncertainties interfere with system's normal evolution and slows it down. I also provide a formal proof to a previously suggested limiting accuracy relation on the measurements of the time-of-arrival experiments.

Journal of Neuroscience Methods, 2020

Pediatrics (2)-Upper limb: Obstetric brachial plexus palsy and rehabilitation of the upper limb (... more Pediatrics (2)-Upper limb: Obstetric brachial plexus palsy and rehabilitation of the upper limb (SOFMER-SFERHE session)

Quantitative Imaging in Medicine and Surgery, 2019

Background: To implement omega plot method for in vivo mapping of proton exchange rates in human ... more Background: To implement omega plot method for in vivo mapping of proton exchange rates in human brain by taking into account the water direct saturation (DS) effect and multiple saturation transfer exchanging species in vivo. Methods: Four Z-spectra were collected with chemical exchange saturation transfer (CEST) saturation power =1, 2, 3 & 4 μT. Water DS was estimated by fitting the Z-spectrum to a linear combination of multiple Lorentzian components and its contribution to the signal was subsequently removed. Exchange rate maps were derived by the omega plot, consisting of fitting the inverse of the signal intensity, M z /(M 0 −M z), as a function of 1/(γB 1) 2. Results: The exchange rate values quantified with the DS removed omega plot were significantly higher in the GM region than in the WM region (616±29 vs. 575±20 s −1 , P<0.001). Phantom studies confirmed that the exchange rates from DS-removed plots varied linearly with pH (R 2 =0.998) for the pH range of 6.2 to 7.4, whereas exchange rates from conventional omega plots failed to show such linearity in the entire physiological pH range. Conclusions: The calculated exchange rate with DS-corrected omega plot is a weighted average for all saturation transfer exchanging proton species which contribute to Z-spectral signal. The healthy brain exchange rate map provided by DS-removed omega plots may serve as a baseline for detecting any pathological changes.

Langmuir : the ACS journal of surfaces and colloids, Jan 19, 2017

We report here the first exploration of the nature of the hydrophobic region of bilayer membranes... more We report here the first exploration of the nature of the hydrophobic region of bilayer membranes formed from sterol-modified phospholipids [Huang, Z.; Szoka, F. C., Sterol-Modified Phospholipids: Cholesterol and Phospholipid Chimeras with Improved Biomembrane Properties. J. Am. Chem. Soc. 2008, 130 (46), 15702-15712] & [Ding, J.; Starling, A. P.; East, J. M.; Lee, A. G., Binding Sites for Cholesterol on Ca(2+)-ATPase Studied by Using a Cholesterol-Containing Phospholipid. Biochemistry 1994, 33 (16), 4974-4979]. Using H NMR spectroscopy, we present our results for the phase behavior and acyl chain ordering of multilamellar vesicles (MLVs) of a sterol-modified phospholipid, 1-cholesterylhemisuccinoyl-2-palmitoyl(d)-sn-glycero-3-phosphocholine (hereafter referred to as CholPPC-d). We compared our results with the conformational order induced by cholesterol at various concentrations in 1-palmitoyl,2-palmitoyl(d)-sn-glycero-3-phosphocholine (DPPC-d)/cholesterol membranes. On the basis o...

Langmuir : the ACS journal of surfaces and colloids, Aug 2, 2016

The effect of a series of phytosterols on lipid chain ordering in 1-palmitoyl((2)H31)-2-oleoyl-sn... more The effect of a series of phytosterols on lipid chain ordering in 1-palmitoyl((2)H31)-2-oleoyl-sn-glycero-3-phosphocholine (POPC-d31) multibilayer vesicles was examined by (2)H NMR spectroscopy at 25 °C. These results, along with existing data for other sterols, indicate that the ordering power of sterols in POPC-d31 depends on subtle aspects of sterol structure. Cholesterol, 7-dehydrocholesterol (7-DHC), campesterol, β-sitosterol, ergosterol, brassicasterol, and stigmasterol all increase the lipid chain order as sterol concentration is increased. However, saturation of the ordering occurs at different sterol concentrations for ergosterol (as previously reported), brassicasterol, β-sitosterol, and stigmasterol. Here our interest lies in finding which part of the sterol structure is responsible for the observed saturation of the palmitoyl chain order as a function of sterol concentration. In particular, we propose that the saturation of the ordering of POPC-d31/brassicasterol and POP...

NeuroImage, Jan 31, 2015

Here we present the application of neurite orientation dispersion and density imaging (NODDI) to ... more Here we present the application of neurite orientation dispersion and density imaging (NODDI) to the healthy spinal cord in vivo. NODDI provides maps such as the intra-neurite tissue volume fraction (vin), the orientation dispersion index (ODI) and the isotropic volume fraction (viso), and here we investigate their potential for spinal cord imaging. We scanned five healthy volunteers, four of whom twice, on a 3T MRI system with a ZOOM-EPI sequence. In accordance to the published NODDI protocol, multiple b-shells were acquired at cervical level and both NODDI and diffusion tensor imaging (DTI) metrics were obtained and analysed to: i) characterise differences in grey and white matter (GM/WM); ii) assess the scan-rescan reproducibility of NODDI; iii) investigate the relationship between NODDI and DTI; and iv) compare the quality of fit of NODDI and DTI. Our results demonstrated that: i) anatomical features can be identified in NODDI maps, such as clear contrast between GM and WM in OD...