Description: Publication date: Available online 19 December 2014 Source: Magnetic Resonance Imaging Author(s): Gordon E. Sarty Progress in the development of portable MRI hinges on the ability to use lightweight mag- nets that have non-uniform magnetic fields. An image encoding method and mathematical procedure for recovering the image from the NMR signal from non-uniform magnets with closed isomagnetic contours is given. Individual frequencies in an NMR signal from an object in a non-uniform magnetic field give rise to integrals of the object along contours of constant magnetic field: generalized projections. With closed isomagnetic field con- tours a simple, cyclic, direct reconstruction of the image from the generalized projections is possible when the magnet and RF transmit coil are held fixed relative to the imaged object while the RF receive coil moves. Numerical simulations, using the Shepp and Logan mathematical phantom, were completed to show that the mathematical method works and to illustrate numerical limitations. The method is numerically verified and exact reconstruction demonstrated for discrete mathematical image phantoms. Correct knowledge of the RF receive field is necessary or severe image distortions will result. The cyclic mathematical reconstruction method presented here will be useful for portable MRI schemes that use non-uniform magnets with closed isomagnetic contours along with me- chanically or electronically moving the RF receive coils.

Description: Publication date: Available online 17 December 2014 Source: Magnetic Resonance Imaging Author(s): Josefina Perlo , Emilia Silletta , Ernesto Danieli , Giorgio Cattaneo , Rodolfo Acosta , Bernhard Blümich , Federico Casanova In this work we evaluate the performance of a 40-mm diameter bore 0.2 T desktop Halbach tomograph to obtain 2D and 3D velocity maps used for studying intra-aneurysmal flow in the presence or absence of nitinol meshed implants with the aim of optimizing the flow diverter efficacy. Phantoms with known spatial velocity distribution were used to determine the performance of the MRI system. Maximum velocities of about 200 mm/s could be measured with a precision of 1 % at a spatial resolution of 0 . 5 × 0 . 5 × 1 mm 3 . This accuracy is suitable to evaluate in vitro intra-aneurysmal flow under different conditions such as variable flow rates, different vessel-aneurysm geometry, as well as the influence of metallic flow diverters on the intra-aneurysmal flow distribution. The information obtained non-invasively with desktop tomographs can be used to complement in vivo studies in order to decide the optimum flow diverter

Description: Publication date: Available online 16 December 2014 Source: Magnetic Resonance Imaging Author(s): Xingju Nie , Eric D. Hamlett , Ann-Charlotte Granholm , Edward S. Hui , Joseph A. Helpern , Jens H. Jensen , Heather A. Boger , Heather R. Collins , Maria F. Falangola Mouse models of Down syndrome (DS) exhibit abnormal brain developmental and neurodegenerative changes similar to those seen in individuals with DS. Although DS mice have been well characterized cognitively and morphologically there are no prior reports utilizing diffusion MRI. In this study we investigated the ability of diffusional kurtosis imaging (DKI) to detect the progressive developmental and neurodegenerative changes in the Ts65Dn (TS) DS mouse model. TS mice displayed higher diffusional kurtosis (DK) in the frontal cortex (FC) compared to normal mice at 2 months of age. At 5 months of age, TS mice had lower radial kurtosis in the striatum (ST), which persisted in the 8-month-old mice. The TS mice exhibited lower DK metrics values in the dorsal hippocampus (HD) at all ages, and the group difference in this region was larger at 8-months. Regression analysis showed that normal mice had a significant age-related increase in DK metrics in FC, ST and HD. On the contrary, the TS mice lacked significant age-related increase in DK metrics in FC and ST. Although preliminary, these results demonstrate that DK metrics can detect TS brain developmental and neurodegenerative abnormalities.

Description: Publication date: Available online 16 December 2014 Source: Magnetic Resonance Imaging Author(s): Dongik Cha , Chan Kyo Kim , Sung Yoon Park , Jung Jae Park , Byung Kwan Park Purpose To investigate the usefulness of multiparametric MR imaging (mp-MRI) at 3 T for evaluating suspected soft tissue lesion in the prostate bed after radical prostatectomy (RP). Materials and Methods Forty-three patients with biochemical recurrence (BCR) who received RP underwent mp-MRI at 3 T with a phased-array coil, including T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI) and dynamic contrast-enhanced imaging (DCE-MRI) and were enrolled in this study. All patients with BCR had a suspected soft tissue lesion in the prostate bed, followed by transrectal ultrasound-guided biopsy. As a control group, 14 consecutive patients without BCR who received RP were also enrolled. Two experienced radiologists independently analyzed four different imaging datasets. Results For predicting local recurrence, the specificity, accuracy and area under the curve for both readers were significantly greater on all combined imaging datasets than on T2WI alone (P 〈 0.05). The sensitivity of all combined imaging datasets in both readers was not statistically different with T2WI alone (P > 0.05), except for combined T2WI and DWI. Inter-reader agreements for the four different imaging datasets were moderate. Conclusion DCE-MRI or DWI in combination with T2WI at 3 T with a phased-array coil appears to be more useful than T2WI alone in evaluating suspected soft tissue lesion of the prostate bed after RP.

Description: Publication date: Available online 16 December 2014 Source: Magnetic Resonance Imaging Author(s): Simon Konstandin , Philipp Krämer , Matthias Günther , Lothar R. Schad A method for uniform k-space sampling of 3D ultra-short echo time (UTE) techniques with anisotropic resolution in one direction is introduced to increase signal-to-noise ratio (SNR). State-of-the-art acquisition schemes for sodium MRI with radial (projection reconstruction) and twisting (twisted projection imaging (TPI)) trajectories are investigated regarding SNR efficiency, blurring behavior under T 2 ⁎ decay, and measurement time in case of anisotropic field-of-view and resolution. 3D radial and twisting trajectories are redistributed in k-space for UTE sodium MRI with homogeneous noise distribution and optimal SNR efficiency, if T 2 ⁎ decay can be neglected. Simulations based on Voronoi tessellations and phantom simulations/measurements were performed to calculate SNR efficiency. Point-spread functions were simulated to demonstrate the influence of T 2 ⁎ decay on SNR and resolution. Phantom simulations/ measurements and in vivo measurements confirm the SNR gain obtained by simulations based on Voronoi cells. An increase in SNR of up to 21 % at an anisotropy factor of 10 could be theoretically achieved by TPI with projection adaption compared to the same sequence but without redistribution of projections in k-space. Sodium MRI with anisotropic resolution and uniform k-space sampling is demonstrated by in vivo measurements of human intervertebral disks and heart at 3 Tesla. The SNR gain can be invested in a measurement time reduction of up to 32 %, which is important especially for sodium MRI.

Description: Publication date: Available online 15 December 2014 Source: Magnetic Resonance Imaging Author(s): Maciej Piskunowicz , Lucie Hofmann , Emilie Zuercher , Isabelle Bassi , Bastien Milani , Matthias Stuber , Krzysztof Narkiewicz , Bruno Vogt , Michel Burnier , Menno Pruijm Objectives To assess inter-observer variability of renal blood oxygenation level-dependent MRI (BOLD-MRI) using a new method of analysis, called the concentric objects (CO) technique, in comparison with the classical ROI (region of interest)-based technique. Methods MR imaging (3 T) was performed before and after furosemide in 10 chronic kidney disease (CKD) patients (mean eGFR 43 ± 24 ml/min/1.73 m 2 ) and 10 healthy volunteers (eGFR 101 ± 28 ml/min1.73 m 2 ), and R2* maps determined on four coronal slices. In the CO-technique, R2* values were based on a semi-automatic procedure that divided each kidney in six equal layers, whereas in the ROI-technique, all circles (ROIs) were placed manually in the cortex and medulla. The mean R2*values as assessed by two independent investigators were compared. Results With the CO-technique, inter-observer variability was 0.7-1.9% across all layers in non-CKD, versus 1.6-3.8% in CKD. With the ROI-technique, median variability for cortical and medullary R2* values was 3.6 and 6.8% in non-CKD, versus 4.7 and 12.5% in CKD; similar results were observed after furosemide. Conclusion The CO-technique offers a new, investigator-independent, highly reproducible alternative to the ROI-based technique to estimate renal tissue oxygenation in CKD.

Description: Publication date: Available online 15 December 2014 Source: Magnetic Resonance Imaging Author(s): S.B. Bulumulla , E. Fiveland , K.J. Park , T.K. Foo , C.J. Hardy As the number of coils increases in multi-channel MRI receiver-coil arrays, RF cables and connectors become increasingly bulky and heavy, degrading patient comfort and slowing workflow. Inductive coupling of signals provides an attractive “wireless” approach, with the potential to reduce coil weight and cost while simplifying patient setup. In this work, multi-channel inductively coupled anterior arrays were developed and characterized for 1.5 T imaging. These comprised MR receiver coils inductively (or “wirelessly”) linked to secondary or “sniffer” coils whose outputs were transmitted via preamps to the MR system cabinet. The induced currents in the imaging coils were blocked by passive diode circuits during RF transmit. The imaging arrays were totally passive, obviating the need to deliver power to the coils, and providing lightweight, untethered signal reception with easily positioned coils. Single-shot fast spin echo images were acquired from 5 volunteers using a 7-element inductively coupled coil array and a conventionally cabled 7-element coil array of identical geometry, with the inductively-coupled array showing a relative signal-to-noise ratio of 0.86 +/− 0.07. The concept was extended to a larger 9-element coil array to demonstrate the effect of coil element size on signal transfer and RF-transmit blocking.

Description: Publication date: Available online 15 December 2014 Source: Magnetic Resonance Imaging Author(s): David A. Lawrence , Adam T. Lipman , Sumeet K. Gupta , Nicholas C. Nacey The case reported is of a 47-year-old man with an undetected ferromagnetic metallic intraocular foreign body in the right eye who underwent elective MR examinations for chronic neck and low back pain. The patient underwent the MR scans and subsequently developed blurred vision in his right eye caused by a hyphema associated with an anterior chamber metallic foreign body. Case reports of orbital injuries in patients with intraocular metallic foreign bodies undergoing MRI are rare, with only one prior report in the radiology literature. While the incidence of intraocular foreign bodies causing injury in patients undergoing MRI is likely rare even among patients with foreign bodies, this case demonstrates that complications from an IMFB can potentially have a subtle presentation. Our case also illustrates potential limitations of pre-MRI safety questionnaires, particularly pertaining to a patient's understanding of the thoroughness of foreign body removal.

Description: Publication date: Available online 15 December 2014 Source: Magnetic Resonance Imaging Author(s): Jiafei Zhao , Qin Lv , Yanghui Li , Mingjun Yang , Weiguo Liu , Lei Yao , Shenglong Wang , Yi Zhang , Yongchen Song In this work, magnetic resonance imaging (MRI) was employed to observe the in-situ formation and dissociation of methane hydrates in porous media. Methane hydrate was formed in a high-pressure cell with controlled temperature, and then the hydrate was dissociated by thermal injection. The process was photographed by the MRI, and the pressure was recorded. The images confirmed that the direct visual observation was achieved; these were then employed to provide detailed information of the nucleation, growth, and decomposition of the hydrate. Moreover, the saturation of methane hydrate during the dissociation was obtained from the MRI intensity data. Our results showed that the hydrate saturation initially decreased rapidly, and then slowed down; this finding is in line with predictions based only on pressure. The study clearly showed that MRI is a useful technique to investigate the process of methane hydrate formation and dissociation in porous media.

Description: Publication date: January 2015 Source: Magnetic Resonance Imaging, Volume 33, Issue 1 Author(s): Hironori Shimizu , Hiroyoshi Isoda , Tsuyoshi Ohno , Rikiya Yamashita , Seiya Kawahara , Akihiro Furuta , Koji Fujimoto , Aki Kido , Hiroshi Kusahara , Kaori Togashi Purpose To compare and evaluate images of non-contrast enhanced magnetic resonance (MR) portography and hepatic venography acquired with two different fat suppression methods, the chemical shift selective (CHESS) method and short tau inversion recovery (STIR) method. Materials and methods Twenty-two healthy volunteers were examined using respiratory-triggered three-dimensional true steady-state free-precession with two time-spatial labeling inversion pulses. The CHESS or STIR methods were used for fat suppression. The relative signal-to-noise ratio and contrast-to-noise ratio (CNR) were quantified, and the quality of visualization was scored. Results Image acquisition was successfully conducted in all volunteers. The STIR method significantly improved the CNRs of MR portography and hepatic venography. The image quality scores of main portal vein and right portal vein were higher with the STIR method, but there were no significant differences. The image quality scores of right hepatic vein, middle hepatic vein, and left hepatic vein (LHV) were all higher, and the visualization of LHV was significantly better (p 〈 0.05). Conclusion The STIR method contributes to further suppression of the background signal and improves visualization of the portal and hepatic veins. The results support using non-contrast-enhanced MR portography and hepatic venography in clinical practice.