Magnetic Resonance Imaging

MRI acoustic noise-modulated computer animations for patient distraction and entertainment with application in pediatric psychiatric patients Publication date: September 2019 Source: Magnetic Resonance Imaging, Volume 61 Author(s): Refaat E. Gabr, Giovana B. Zunta-Soares, Jair C. Soares, Ponnada A. Narayana Abstract Purpose To reduce patient anxiety caused by the MRI scanner acoustic noise. Material and methods We developed a simple and low-cost system for patient distraction using visual computer animations that were synchronized to the MRI scanner's acoustic noise during the MRI exam. The system was implemented on a 3T MRI system and tested in 28 pediatric patients with bipolar disorder. The patients were randomized to receive noise-synchronized animations in the form of abstract animations in addition to music (n = 13, F/M = 6/7, age = 10.9 ± 2.5 years) or, as a control, receive only music (n = 15, F/M = 7/8, age = 11.6 ± 2.3 years). After completion of the scans, all subjects answered a questionnaire about their scan experience and the perceived scan duration. Results The scan duration with multisensory input (animations and music) was perceived to be ~15% shorter than in the control group (43 min vs. 50 min, P < 0.05). However, the overall scan experience was scored less favorably (3.9 vs. 4.6 in the control group, P < 0.04). Conclusions This simple system provided patient distraction and entertainment leading to perceived shorter scan times, but the provided visualization with abstract animations was not favored by this patient cohort.

Using amide proton transfer to identify cervical squamous carcinoma/adenocarcinoma and evaluate its differentiation grade Publication date: September 2019 Source: Magnetic Resonance Imaging, Volume 61 Author(s): Nan Meng, Jing Wang, Jing Sun, Wenling Liu, Xuejia Wang, Minghuan Yan, Akshay Dwivedi, Dandan Zheng, Kaiyu Wang, Dongming Han Abstract Purpose To explore the possibility of using amide proton transfer-weighted imaging (APTWI) for the identification and diagnosis of cervical squamous carcinoma (CSC), cervical adenocarcinoma (CA) and different levels of CSC. Materials and methods Seventy-six patients with newly diagnosed uterine cervical cancer (UCC) were studied prior to treatment, including 20 with poorly differentiated (Grade 3) CSC, 23 with moderately differentiated (Grade 2) CSC, 17 with well-differentiated (Grade 1) CSC, and 16 with CA (13 with poorly differentiated (Grade 3) CA and 3 with moderately differentiated (Grade 2) CA). Differences in the magnetization transfer ratio at 3.5 ppm (MTRasym (3.5 ppm)) were identified between CSC and CA and between high-level (Grade 3) CSC and low-level (Grade 2 and Grade 1) CSC, as well as among all three grades of CSC differentiation. Receiver operating characteristic (ROC) curve analysis was used to evaluate the diagnostic thresholds and performance of the parameters. Spearman correlation analysis was used to examine the correlation between the MTRasym (3.5 ppm) and histological grade. Results The MTRasym (3.5 ppm) in CA was higher than that in CSC (P = 0.001). The MTRasym (3.5 ppm) in high-level CSC was higher than that in low-level CSC (P = 0.001). The MTRasym (3.5 ppm) was positively correlated with the grade of CSC differentiation (r = 0.498, P = 0.001). The MTRasym (3.5 ppm) in Grade 3 CSC was higher than that in Grade 2 and Grade 1 CSC (P = 0.02/0.01). No significant difference in the MTRasym (3.5 ppm) was found between Grade 2 CSC and Grade 1 CSC (P = 0.173). The area under the ROC curve (AUC) for the MTRasym (3.5 ppm) in distinguishing CSC and CA was 0.779, with a cut-off, sensitivity, and specificity of 2.97%, 60.0% and 82.5%, respectively. The AUC for distinguishing high-/low-level CSC was 0.756, with a cut-off, sensitivity, and specificity of 3.29%, 68.8% and 83.3%, respectively. Conclusion APTWI may be a useful technique for the identification and diagnosis of CSC, CA and different levels of CSC, which may have an important impact on clinical strategies for treating patients with UCC.

7T GRE-MRI signal compartments are sensitive to dysplastic tissue in focal epilepsy Publication date: September 2019 Source: Magnetic Resonance Imaging, Volume 61 Author(s): Kiran Thapaliya, Javier Urriola, Markus Barth, David C. Reutens, Steffen Bollmann, Viktor Vegh Abstract Ultra-high field magnetic resonance imaging data obtained using a multi-echo gradient echo sequence has been shown to contain information on tissue microstructure. Quantitative assessment of water fraction, relaxation time and frequency shift using multi-compartment signal modelling may help improve our understanding of diseases and disorders affecting the human brain. In this study, we explored tissue microstructure information by analysing voxel compartment water fraction and frequency shifts derived from 7 T multi-echo gradient recalled echo MRI data. We aimed to test whether the parameters of a three compartment model could distinguish the normal cortex from the cortex affected by focal cortical dysplasia. We compartmentalised normal and dysplastic cortical regions in patients diagnosed with focal cortical dysplasia. We found the frequency shift parameter of the shortest T2⁎ signal compartment to be sensitive to regions of dysplastic tissue. We conclude that mathematical modelling of echo time dependent gradient recalled echo MRI signals in patients with focal cortical dysplasia can potentially delineate cortical areas that have undergone microstructural changes in comparison to normal tissue.

Differentiating platinum coated brachytherapy seeds and gold fiducial markers with varying off-resonant frequency offsets Publication date: July 2019 Source: Magnetic Resonance Imaging, Volume 60 Author(s): Evan McNabb, Raimond Wong, Michael D. Noseworthy Abstract Purpose To develop an off-resonant frequency filtered method to selectively differentiate between implanted gold fiducial markers and platinum coated brachytherapy seeds. Materials and methods The magnetic susceptibilities for gold fiducial markers and brachytherapy seeds differ in magnitude and also in their signs, resulting in B0-field inhomogeneity patterns with opposite main lobes. A pulse sequence used to localize brachytherapy seeds with positive contrast, centre-out radial sampling with off-resonance reception (co-RASOR), was used to reconstruct images with a range of off-resonant frequency offsets. The proposed method utilizes two frequency filters to selectively reconstruct maximum intensity projections through band-pass regions where each seed has its maximal localized hyperintensity. Seeds were simulated and then placed in gel and tissue phantoms to validate the technique using orthogonal 2D slices with seeds both parallel and perpendicular to the B0-field. Results Dual-plane 2D co-RASOR sequences were reconstructed off-resonance with applied frequency filters to create two projections displaying each seed, which were then colour-coded to negative and positive frequencies. Phantom validation showed that each seed contains its maximal CNR in opposing frequency regions as predicted. Local maxima can also appear in both negative and positive frequency regions. The relative difference between the signal of each seed and these local maxima ranged from 1.19 to 3.73, and an image threshold was determined in all cases. Tissue validation showed the technique differentiates seeds correctly and is limited by the hyperintensity patterns observed in the co-RASOR method. Conclusions Dual-plane co-RASOR offers sub-millimetre positive contrast from implanted seeds that contain unique off-resonant frequency maxima, which frequency filters can selectively differentiate.

MEGA-PRESS and PRESS measure oxidation of glutathione in a phantom Publication date: July 2019 Source: Magnetic Resonance Imaging, Volume 60 Author(s): Maiken K. Brix, Gerard E. Dwyer, Alexander R. Craven, Renate Grüner, Ralph Noeske, Lars Ersland Abstract Purpose Investigate the possibility of measuring changes in glutathione (GSH) concentration using the MRS PRESS and MEGA-PRESS sequences by tracking the natural oxidation of GSH, and to examine the accuracy of the two methods. Methods 122 GSH edited MEGA-PRESS and PRESS acquisitions were acquired on a "braino" based phantom +3.0 mM GSH during a period of 11 days. All spectra were analyzed in LCModel. (The MEGA-PRESS data were first preprocessed in Matlab). Degradation curves were modeled. A one year follow-up on the same phantom and measurements from a similar phantom without GSH and one pure GSH phantom were also included. Results Both MEGA-PRESS and PRESS showed degradation of the measured GSH signal. Modeling the exponential decay of the GSH signal in MEGA-PRESS and PRESS gave for t = 0; 2.9 i.u. for MEGA-PRESS and 2.3 i.u. for PRESS. As t increased, the GSH concentration converged to zero for MEGA-PRESS but not for PRESS (0.7 i.u.). GSH for the one year follow up were 0.0 i.u. for MEGA-PRESS and 0.6 i.u. for PRESS. Similar phantom without GSH yielded 0.0 i.u. for both MEGA-PRESS and PRESS. Conclusion It is possible to measure changes in GSH concentration in a phantom using both PRESS and MEGA-PRESS techniques, however the PRESS spectrum appears to include oxidized GSH (GSSG). In addition, GSH edited MEGA-PRESS measurement gives more precise values at lower GSH concentrations.

Non-contrast-enhanced magnetic resonance imaging for visualization and quantification of endovascular aortic prosthesis, their endoleaks and aneurysm sacs at 1.5 T Publication date: July 2019 Source: Magnetic Resonance Imaging, Volume 60 Author(s): Mona Salehi Ravesh, Patrick Langguth, Julian Andreas Pfarr, Jasper Schupp, Jens Trentmann, Ioannis Koktzoglou, Robert R. Edelman, Joachim Graessner, Andreas Greiser, David Hautemann, Anja Hennemuth, Marcus Both, Olav Jansen, Jan-Bernd Hövener, Jost Philipp Schäfer Abstract Purpose After an endovascular aortic aneurysm repair (EVAR), a follow-up at 1, 6 and every 12 months is recommended for remainder of the patient's life. The diagnostic standard methods for diagnosing endoleaks and visualization of aneurysms in EVAR-patients are: invasive digital subtraction angiography (DSA), contrast enhanced (CE) computed tomographic angiography (CE-CTA), and magnetic resonance angiography (CE-MRA). These techniques, however, require the use of iodine- or gadolinium-based contrast agents with rare, but possibly life threatening side effects such as renal impairment, thyrotoxicosis and allergic reactions, nephrogenic systemic fibrosis, and cerebral gadolinium deposition. The aim of this prospective study was to compare a non-contrast-enhanced MRI protocol (consist of four MRI methods) with DSA and CE-CTA for visualization and quantification of endovascular aortic prosthesis, their endoleaks and aneurysms. Material and methods Eight patients (mean age 76.8 ± 4.9 years, 63% male), whose thoracic, abdominal, or iliac aneurysms were treated with different endovascular prosthesis and suffered from type I–V endoleaks, were examined on a 1.5 Tesla MR system. Quiescent-interval slice selective MR angiography (QISS-MRA), 4-dimensional (4D)-flow MRI, T1- and T2-mapping, as well as DSA and CE-CTA were used for the visualization and quantification of endoprosthesis, endoleaks, and aneurysms in these patients. Results QISS-MRA provided good visualization of endoleaks and comparable quantification of aneurysm size with respect to CE-CTA and DSA. The 4D-flow MRI provided additional information about the wall shear stress, which could not be determined using DSA. In contrast to CE-CTA, T1- and T2-mapping provided detailed information about heterogeneous areas within an aneurysm sac. Conclusions Compared to DSA and CE-CTA, the proposed MRI methods provide improved anatomical and functional information for various types of endoprostheses and endoleaks. In addition, hemodynamic parameters of the aorta and information on the content of aneurysm sac are provided as well. Within the frame of personalized medicine, the personalized diagnosis enabled by this non-CE MRI protocol is the foundation for a personalized and successful treatment.

Assessment of transplant renal artery stenosis with diffusion-weighted imaging: A preliminary study Publication date: July 2019 Source: Magnetic Resonance Imaging, Volume 60 Author(s): Min Fan, Xuefeng Ni, Yanjun Li, Jinsong Chen, Dongrui Cheng, Donghong Shi, Xiaozhou He, Jiqiu Wen Abstract Objective To characterize capillary perfusion and tissue diffusion changes in transplant renal artery stenosis (TRAS) with diffusion-weighted imaging (DWI). Materials & methods We retrospectively identified 30 patients with non-contrast enhanced magnetic resonance angiography-proven TRAS. Another 20 kidney transplant recipients without TRAS were prospectively recruited to serve as control group. DWI parameters were compared among various groups with one-way analysis of variance and post hoc Tukey test. Additionally, DWI parameters were compared in 7 severe TRAS patients before and after successful angioplasty using paired Student t-test. Receiver-operating characteristic (ROC) curves were generated to evaluate the diagnostic performance of various DWI parameters. Results All DWI parameters of renal cortex and medulla were not statistically different between normal allografts and allografts with mild TRAS. Nonetheless, cortical total apparent diffusion coefficient (ADCT) of allografts with moderate TRAS was significantly decreased compared with normal allografts. All cortical and medullary DWI parameters were significantly reduced in severe TRAS compared with normal allografts. ROC curve analysis indicated ADCT could identify severe TRAS with 93.8% sensitivity, 82.4% specificity and an area under the curve of 0.930. ADCT increased significantly after successful angioplasty while it showed no significant change in a patient with unsuccessful angioplasty. Conclusion DWI is a robust technique that revealed no tissue diffusion and perfusion impairment in mild TRAS. ADCT has good sensitivity and specificity for identifying patients with severe TRAS. DWI is potentially an alternative radiologic biomarker for assessing microstructural and perfusion alterations in TRAS. DWI is useful in detecting renal functional recovery following successful angioplasty.

Compressed sensing reconstruction of 7 Tesla 23Na multi-channel breast data using 1H MRI constraint Publication date: July 2019 Source: Magnetic Resonance Imaging, Volume 60 Author(s): Sebastian Lachner, Olgica Zaric, Matthias Utzschneider, Lenka Minarikova, Štefan Zbýň, Bernhard Hensel, Siegfried Trattnig, Michael Uder, Armin M. Nagel Abstract Purpose To reduce acquisition time and to improve image quality in sodium magnetic resonance imaging (23Na MRI) using an iterative reconstruction algorithm for multi-channel data sets based on compressed sensing (CS) with anatomical 1H prior knowledge. Methods An iterative reconstruction for 23Na MRI with multi-channel receiver coils is presented. Based on CS it utilizes a second order total variation (TV(2)), adopted by anatomical weighting factors (AnaWeTV(2)) obtained from a high-resolution 1H image. A support region is included as additional regularization. Simulated and measured 23Na multi-channel data sets (n = 3) of the female breast acquired at 7 T with different undersampling factors (USF = 1.8/3.6/7.2/14.4) were reconstructed and compared to a conventional gridding reconstruction. The structural similarity was used to assess image quality of the reconstructed simulated data sets and to optimize the weighting factors for the CS reconstruction. Results Compared with a conventional TV(2), the AnaWeTV(2) reconstruction leads to an improved image quality due to preserving of known structure and reduced partial volume effects. An additional incorporated support region shows further improvements for high USFs. Since the decrease in image quality with higher USFs is less pronounced compared to a conventional gridding reconstruction, proposed algorithm is beneficial especially for higher USFs. Acquisition time can be reduced by a factor of 4 (USF = 7.2), while image quality is still similar to a nearly fully sampled (USF = 1.8) gridding reconstructed data set. Conclusion Especially for high USFs, the proposed algorithm allows improved image quality for multi-channel 23Na MRI data sets.

Demonstration of full tensor current density imaging using ultra-low field MRI Publication date: July 2019 Source: Magnetic Resonance Imaging, Volume 60 Author(s): P. Hömmen, J.-H. Storm, N. Höfner, R. Körber Abstract Direct imaging of impressed dc currents inside the head can provide valuable conductivity information, possibly improving electro-magnetic neuroimaging. Ultra-low field magnetic resonance imaging (ULF MRI) at μT Larmor fields can be utilized for current density imaging (CDI). Here, a measurable impact of the magnetic field BJ, generated by the impressed current density J, on the MR signal is probed using specialized sequences. In contrast to high-field MRI, the full tensor of BJ can be derived without rotation of the subject in the scanner, due to a larger flexibility in the sequence design. We present an ULF MRI setup based on a superconducting quantum interference device (SQUID), which is operating at a noise level of 380 aT Hz−1/2 and capable of switching all imaging fields within a pulse sequence. Thereby, the system enables zero-field encoding, where the full tensor of BJ is probed in the absence of other magnetic fields. 3D CDI is demonstrated on phantoms with different geometries carrying currents of approximately 2 mA corresponding to current densities between 0.45 and 8 A/m2. By comparison to an in vivo acquired head image, we provide insights to necessary improvements in signal-to-noise ratio.

Accelerated positive contrast MRI of interventional devices using parallel compressed sensing imaging Publication date: July 2019 Source: Magnetic Resonance Imaging, Volume 60 Author(s): Samira Vafay Eslahi, Jim Ji Abstract Susceptibility-based magnetic resonance imaging (MRI) method can image small MR-compatible devices with positive contrast. However, the relatively long data acquisition time required by the method hinders its practical applications. This study presents a parallel compressive sensing technique with a modified fast spin echo to accelerate data acquisition for the susceptibility-based positive contrast MRI. The method integrates the generalized autocalibrating partially parallel acquisitions and the compressive sensing techniques in the reconstruction algorithm. MR imaging data acquired from several phantoms containing interventional devices such as biopsy needles, stent, and brachytherapy seeds, used for validating the proposed technique. The results show that it can speed up data acquisition by a factor of about five while preserving the quality of the positive contrast images.

Alexandros Sfakianakis
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alsfakia@gmail.com