Sairam Geethanath

Compressive Sensing Could Accelerate 1H MR Metabolic Imaging in the Clinic

PURPOSE To retrospectively evaluate the fidelity of magnetic resonance (MR) spectroscopic imaging data preservation at a range of accelerations by using compressed sensing. MATERIALS AND METHODS The protocols were approved by the institutional review board of the university, and written informed consent to acquire and analyze MR spectroscopic imaging data was obtained from the subjects prior to the acquisitions. This study was HIPAA compliant. Retrospective application of compressed sensing was performed on 10 clinical MR spectroscopic imaging data sets, yielding 600 voxels from six normal brain data sets, 163 voxels from two brain tumor data sets, and 36 voxels from two prostate cancer data sets for analysis. The reconstructions were performed at acceleration factors of two, three, four, five, and 10 and were evaluated by using the root mean square error (RMSE) metric, metabolite maps (choline, creatine, N-acetylaspartate [NAA], and/or citrate), and statistical analysis involving a voxelwise paired t test and one-way analysis of variance for metabolite maps and ratios for comparison of the accelerated reconstruction with the original case. RESULTS The reconstructions showed high fidelity for accelerations up to 10 as determined by the low RMSE (< 0.05). Similar means of the metabolite intensities and hot-spot localization on metabolite maps were observed up to a factor of five, with lack of statistically significant differences compared with the original data. The metabolite ratios of choline to NAA and choline plus creatine to citrate did not show significant differences from the original data for up to an acceleration factor of five in all cases and up to that of 10 for some cases. CONCLUSION A reduction of acquisition time by up to 80%, with negligible loss of information as evaluated with clinically relevant metrics, has been successfully demonstrated for hydrogen 1 MR spectroscopic imaging.

Graphene oxide-Fe3O4 nanoparticle composite with high transverse proton relaxivity value for magnetic resonance imaging

The potential of graphene oxide–Fe3O4 nanoparticle (GO-Fe3O4) composite as an image contrast enhancing material in magnetic resonance imaging has been investigated. Proton relaxivity values were obtained in three different homogeneous dispersions of GO-Fe3O4 composites synthesized by precipitating Fe3O4 nanoparticles in three different reaction mixtures containing 0.01 g, 0.1 g, and 0.2 g of graphene oxide. A noticeable difference in proton relaxivity values was observed between the three cases. A comprehensive structural and magnetic characterization revealed discrete differences in the extent of reduction of the graphene oxide and spacing between the graphene oxide sheets in the three composites. The GO-Fe3O4 composite framework that contained graphene oxide with least extent of reduction of the carboxyl groups and largest spacing between the graphene oxide sheets provided the optimum structure for yielding a very high transverse proton relaxivity value. It was found that the GO-Fe3O4 composites possess...

Substitutional limit of gadolinium in β-tricalcium phosphate and its magnetic resonance imaging characteristics.

To compensate the limitations of bone tissue magnetic resonance imaging (MRI), a series of gadolinium (Gd3+ ) substituted β-Tricalcium phosphate [β-TCP, β-Ca3 (PO4 )2 ] were developed. All the powders were characterized using XRD, Raman spectroscopy, Rietveld refinement of the XRD data and the studies confirmed the Gd3+ occupancy at Ca2+ (1), Ca2+ (2) and Ca2+ (3) lattice sites of β-Ca3 (PO4 )2. HR-TEM analysis revealed the spherical nature of particles with diameter about 100 nm. The Gd3+ doped β-Ca3 (PO4 )2 exhibited non-toxic behaviour to MG-63 cells in vitro and the room temperature magnetic field versus magnetization measurements confirmed its paramagnetic behaviour. MRI analysis revelas that it shorten both T1 and T2 proton relaxation times, thus influencing both r1 and r2 relaxivity values that reach 61.97 mM-1 s-1 and 73.35 mM-1 s-1 .

Application of Region of Interest Compressed Sensing to accelerate magnetic resonance angiography.

Magnetic Resonance Angiography (MRA) is a group of techniques based on Magnetic Resonance Imaging (MRI) to image blood vessels. Compressed Sensing (CS) is a mathematical framework to reconstruct MR images from sparse data to minimize the data acquisition time. Image sparsity is the key in CS to reconstruct MR images. CS technique allows reconstruction from significantly fewer k-space samples as compared to full k-space acquisition, which results in reduced MRI data acquisition time. The images resulting from MRA are sparse in native representation, hence yielding themselves well to CS. Recently our group has proposed a novel CS method called Region of Interest Compressed Sensing (ROICS) as a part of Region of Interest (ROI) weighted CS. This work aims at the implementation of ROICS for the first time on MRA data to reduce MR data acquisition time. It has been demonstrated qualitatively and quantitatively that ROICS outperforms CS at higher acceleration factors. ROICS technique has been applied to 3D angiograms of the brain data acquired at 1.5T. It helps to reduce the MRA data acquisition time and improves the visualization of arteries. ROICS technique has been applied on 4 brain angiogram data sets at different acceleration factors from 2× to 10×. Reconstructed images show ROICS technique performs better than conventional CS technique and is quantified by the comparative Signal to Noise Ratio (SNR) in the ROI.

Graphene oxide-gadolinium (III) oxide nanoparticle composite: a novel MR contrast agent with high longitudinal and transverse relaxivity

Production of bio-compatible contrast agent materials to enhance the sensitivity of the magnetic resonance imaging (MRI) technique is a highly active area in MRI related research. This work illustrates the potential of a new material: graphene oxide-gadolinium (III) oxide nanoparticle (GO-Gd2O3) composite in yielding both transverse (16.3 mM−1 s−1) and longitudinal relaxivity (40 mM−1 s−1) values which are significantly higher than the proton relaxivity values achieved using the gadolinium based contrast agents currently used in MRI. Such high proton relaxivity values can facilitate low dosage of GO-Gd2O3 composite for obtaining both T1 and T2 weighted high signal-to-noise ratio images in MRI.

Gadolinium Doping in Zirconia-Toughened Alumina Systems and Their Structural, Mechanical, and Aging Behavior Repercussions

A series of Gd3+ dopings in zirconia-toughened alumina (ZTA) systems were undertaken to explore the resultant structural, morphological, hydrothermal aging, and mechanical behavior and imaging contrast abilities. The results from the characterization techniques demonstrate the significance of Gd3+ in preserving the structural stability of ZTA systems. ZTA undergoes phase degradation with 10 wt % Gd3+ at 1400 °C, while the 100 wt % Gd3+ yields GdAlO3 even at 1200 °C. Gd3+ doping at the intermediate level preserves the structural stability of ZTA systems until 1400 °C. Gd3+ occupies the ZrO2 lattice, and its gradual accumulation induces tetragonal ZrO2 (t-ZrO2) to cubic ZrO2 (c-ZrO2) phase transition. α-Al2O3 crystallizes at 1200 °C and remains unperturbed except for its reaction with the free Gd3+ ions to yield GdAlO3. Aging studies and mechanical tests signify the impeccable role of Gd3+ in ZTA systems to resist phase degradation. Further, the imaging contrast ability of ZTA systems due to Gd3+ doping is verified from the in vitro magnetic resonance imaging (MRI) tests.

Ultrafine graphene oxide–CoFe2O4 nanoparticle composite as T1 and T2 contrast agent for magnetic resonance imaging

Graphene oxide–CoFe2O4 nanoparticle composites were synthesized using a two step synthesis method in which graphene oxide was initially synthesized followed by precipitation of CoFe2O4 nanoparticles in a reaction mixture containing graphene oxide. Samples were extracted from the reaction mixture at different times at 80 °C. All the extracted samples contained CoFe2O4 nanoparticles formed over the graphene oxide. It was observed that the increase in the reflux time significantly increased the saturation magnetization value for the superparamagnetic nanoparticles in the composite. It was also noticed that the size of the nanoparticles increased with increase in the reflux time. Transverse relaxivity of the water protons increased monotonically with increase in the reflux time. Whereas, the longitudinal relaxivity value initially increased and then decreased with the reflux time. Graphene oxide–CoFe2O4 nanoparticle composites also exhibit biocompatibility towards the MCF-7 cell line.

The Tofts model in frequency domain: fast and robust determination of pharmacokinetic maps for dynamic contrast enhancement MRI

Dynamic contrast enhancement magnetic resonance imaging (DCE-MRI) is a well-established method for non-invasive detection and therapeutic monitoring of pathologies through administration of intravenous contrast agent. Quantification of pharmacokinetic (PK) maps can be achieved through application of compartmental models relevant to the pathophysiology of the tissue under interrogation. The determination of PK parameters involves fitting of time-concentration data to these models. In this work, the Tofts model in frequency domain (TM-FD) is applied to a weakly vascularized tissue such as the breast. It is derived as a convolution-free model from the conventional Tofts model in the time domain (TM-TD). This reduces the dimensionality of the curve-fitting problem from two to one. The approaches of TM-FD and TM-TD were applied to two kinds of in silico phantoms and six in vivo breast DCE data sets with and without the addition of noise. The results showed that computational time taken to estimate PK maps using TM-FD was 16-25% less than with TM-TD. Normalized root mean square error (NRMSE) calculation and Pearson correlation analyses were performed to validate robustness and accuracy of the TM-FD and TM-TD approaches. These compared with ground truth values in the case of phantom studies for four different temporal resolutions. Results showed that NRMSE values for TM-FD were significantly lower than those of TM-TD as validated by a paired t-test along with reduced computational time. This approach therefore enables online evaluation of PK maps by radiologists in a clinical setting, aiding in the evaluation of 3D and/or increased coverage of the tissue of interest.

Lanthanide phosphate (LnPO4) rods as bio-probes: A systematic investigation on structural, optical, magnetic, and biological characteristics: LANTHANIDE PHOSPHATE (LnPO4) RODS AS BIO-PROBES

The proposed work involves an exclusive study on the synthesis protocol, crystal structure analysis, and imaging contrast features of unique lanthanide phosphates (LnPO4 ). XRD and Raman spectra affirmed the ability of the proposed synthesis technique to achieve unique LnPO4 devoid of impurities. The crystal structure analysis confirms the P121/c1 space setting of NdPO4 , EuPO4 , GdPO4 , and TbPO4 that all uniformly crystallizes in monoclinic unit cell. In a similar manner, the tetragonal crystal setting of DyPO4 , ErPO4 , HoPO4 , and YbPO4 that unvaryingly possess the I41/amd space setting is confirmed. Under the same synthesis conditions, the monoclinic (Eu) and tetragonal (Ho) lanthanide phosphates displayed uniform rod-like morphologies. Absorption and luminescence properties of unique LnPO4 were determined. In vitro biological studies demonstrated low toxicity levels of LnPO4 and clearly distinguished fluorescence of TbPO4 and EuPO4 in Y79, retinoblastoma cell lines. The paramagnetic response of GdPO4 , NdPO4 , DyPO4 , TbPO4 , and HoPO4 facilitated excellent magnetic resonance imaging (MRI) contrast features. Meanwhile, GdPO4 , DyPO4 , HoPO4 , and YbPO4 possessing higher X-ray absorption coefficient than clinical contrast Omnipaque™ exhibited high computed tomography (CT) efficiency.

Association of freezing of gait with nigral iron accumulation in patients with Parkinson's disease

BACKGROUND AND PURPOSE The objective of this work was to investigate whether patients with and without freezing of gait (FOG) in Parkinsons disease (PD) have differences in iron accumulation in substantia nigra using R2* relaxometry. MATERIALS AND METHODS This study included seventeen PD patients with FOG [FOG (+)], equal number of age and gender matched patients without FOG [FOG (-)] and 34 healthy controls (HC). T2* images were obtained from a 3-Tesla MRI system using multi-echo sequence. R2* values were extracted from Substantia Nigra (SN) and red nucleus and were compared among the three groups and correlated with clinical findings. RESULTS R2* values were increased in PD group as a whole compared to HC in rostral and caudal segments of Substantia Nigra pars compacta (SNc) and in Substantia Nigra pars reticulata (SNr) but not in red nucleus. Within PD subgroups, FOG (+) group had increased iron accumulation in SNc compared to FOG (-) and HC. FOG score positively correlated with R2* values in the caudal region of SNc in FOG (+) group. CONCLUSIONS Our study reveals higher nigral iron content in FOG (+) compared to FOG (-) and HCs. In addition, we observed positive correlation of FOG score with iron accumulation in SNc. Results of this study emphasize possible role of higher nigral iron content in the pathogenesis of FOG in PD.