Conventional Gradient Echo Research Articles

Improvement of gadoxetate arterial phase capture with a high spatio‐temporal resolution multiphase three‐dimensional SPGR‐dixon sequence

To determine whether a multiphase method with high spatiotemporal resolution (STR) by means of a combination of parallel imaging, pseudorandom sampling and temporal view sharing improves the capture and intensity of gadoxetate arterial phase images as well as lesion enhancement. Thirty-seven patients were imaged with a conventional spoiled gradient echo acquisition and 48 with a high STR multiphase acquisition after the administration of gadoxetate. Arterial phase capture, image quality, and quality of fat suppression were qualitatively graded. Fourteen lesions in the conventional group and 28 in the high STR multiphase group were imaged, including 34 focal nodular hyperplasias. The ratio of lesion to parenchyma enhancement as well as relative hepatic artery enhancement were calculated. Chi-squared, Mann-Whitney U and student t-tests were used to compare differences. The high STR multiphase acquisition included the arterial phase more frequently than conventional acquisitions (P < 0.001), with the arterial phase missed in 17% (95% CI of 4-28%) of patients with conventional acquisition compared with 2% (95% CI of 0-6%) with the high STR multiphase acquisition. There was no loss of image quality or degree of fat saturation. Additionally, there was increased relative intensity of the hepatic arteries (P < 0.001) as well as lesion enhancement (P = 0.01). The high STR multiphase acquisition resulted in more reliable gadoxetate arterial phase capture compared with a conventional acquisition while preserving image quality with robust fat saturation.

High‐resolution Fourier‐encoded sub‐millisecond echo time musculoskeletal imaging at 3 Tesla and 7 Tesla

The feasibility of imaging musculoskeletal fibrous tissue components, such as menisci, ligaments, and tendons, with a conventional spoiled gradient echo technique is explored in vivo at 3 T and 7 T. To this end, the echo time (TE1 ) of a conventional Fourier-encoded multicontrast three-dimensional SGPR sequence is minimized by using nonselective excitation pulses, highly asymmetric readouts, and a variable TE1 along the phase and slice encoding direction. In addition, a fully sampled second echo image (with TE2 >> TE1 ) can be used to highlight components with short transverse relaxation times in a difference image with positive contrast. Fourier-encoded spoiled gradient echo sequences are able to provide sub-millisecond TE1 of about 800 μs for typical in-plane resolutions of about 0.5 x 0.5 mm(2) . As a result, high-resolution positive contrast images of fibrous tissues can be generated within clinically feasible scan-time of about 2-7 minutes. After optimization, Fourier-encoded spoiled gradient echo provides a highly robust and flexible imaging technique for high-resolution positive contrast imaging of fibrous tissue that can readily be used in the clinical routine.

The value of T2*-weighted gradient-echo MRI for the diagnosis of cerebral venous sinus thrombosis

ObjectivesThe purpose of this study is to compare the various magnetic resonance imaging (MRI) sequences when they are used to visualize and evaluate cerebral venous thrombosis. MethodsEleven patients with cerebral venous thrombosis were retrospectively analyzed using computed tomography, MRI, magnetic resonance angiography (MRA), and conventional angiography. The MR sequence included T1-weighted spin echo (SE) imaging, obtained before and after administration of contrast medium, T2-weighted turbo spin echo (TSE), fluid-attenuated inversion recovery (FLAIR), T2*-weighted conventional gradient-echo (GRE), as well as three-dimensional (3D) venous time-of-flight MRA and conventional angiography. ResultsIn all of our patients, the venous sinus thromboses were most successfully detected during the T2*-weighted GRE sequence. The thrombosis was well visualized with the T1-weighted SE sequence in three of four patients in whom it was in the subacute stage. The T2*-weighted GRE sequence was superior to the T2-weighted TSE, T1-weighted SE, and FLAIR sequences in all patients. Enhanced 3D MR venography showed the thrombosed segment of the venous sinus and well correlated with the conventional angiographic findings. ConclusionsThe T2*-weighted conventional GRE sequences may be the best method for detecting of cerebral venous thrombosis. Therefore, it would seem to be beneficial to integrate a T2*-weighted conventional GRE sequence into the MR protocol to diagnose cerebral venous thrombosis.

Single-scan R2⁎ measurement with macroscopic field inhomogeneity correction

Accurate quantification of R₂(*) (=1/T₂(*)) is important for many applications in neuroimaging. However, R₂(*) measurements made using conventional multi-echo gradient echo imaging are hampered by macroscopic field inhomogeneities. Several methods for compensation of macroscopic field inhomogeneities have been introduced, most of them requiring increased scan time. In this paper, an R₂(*) estimation process using a modified multi-echo gradient echo sequence that includes bipolar compensation gradients and does not require additional data acquisition time is proposed. A post-processing algorithm based on an excitation-profile weighted signal model is used. The optimal amount of compensation gradients and performance was investigated by numerical simulation and phantom tests. Multi-slice R₂(*) maps were obtained from 11 human volunteers at 3T. Simulation results demonstrated that this method successfully removes the effects of macroscopic field inhomogeneities of up to ± 300μT/m within an error range of ± 8%. ROI analysis revealed R₂(*) values of 30.4 ± 3.0s⁻¹ (substantia nigra), 25.8 ± 2.7s⁻¹ (red nuclei), 23.2 ± 1.0s⁻¹ (genu), 20.8 ± 1.2s⁻¹ (putamen), 34.2 ± 3.4s⁻¹ (globus pallidus), and 21.8 ± 1.4s⁻¹ (splenium) using the proposed method, with statistically significant differences compared to conventional method in the regions of the substantia nigra, red nucleus, genu, putamen, and globus pallidus (p<0.05). Our proposed scheme allows for fast single-scan multi-slice R₂(*) measurement and includes compensation for the effects of macroscopic field inhomogeneity.

A feasible high spatiotemporal resolution breast DCE-MRI protocol for clinical settings

Three dimensional bilateral imaging is the standard for most clinical breast dynamic contrast-enhanced (DCE) MRI protocols. Because of high spatial resolution (sRes) requirement, the typical 1–2 min temporal resolution (tRes) afforded by a conventional full-k-space-sampling gradient echo (GRE) sequence precludes meaningful and accurate pharmacokinetic analysis of DCE time-course data. The commercially available, GRE-based, k-space undersampling and data sharing TWIST (time-resolved angiography with stochastic trajectories) sequence was used in this study to perform DCE-MRI exams on thirty one patients (with 36 suspicious breast lesions) before their biopsies. The TWIST DCE-MRI was immediately followed by a single-frame conventional GRE acquisition. Blinded from each other, three radiologist readers assessed agreements in multiple lesion morphology categories between the last set of TWIST DCE images and the conventional GRE images. Fleiss’ κ test was used to evaluate inter-reader agreement. The TWIST DCE time-course data were subjected to quantitative pharmacokinetic analyses. With a four-channel phased-array breast coil, the TWIST sequence produced DCE images with 20 s or less tRes and ~ 1.0×1.0×1.4 mm3 sRes. There were no significant differences in signal-to-noise (P=.45) and contrast-to-noise (P=.51) ratios between the TWIST and conventional GRE images. The agreements in morphology evaluations between the two image sets were excellent with the intra-reader agreement ranging from 79% for mass margin to 100% for mammographic density and the inter-reader κ value ranging from 0.54 (P<.0001) for lesion size to 1.00 (P<.0001) for background parenchymal enhancement. Quantitative analyses of the DCE time-course data provided higher breast cancer diagnostic accuracy (91% specificity at 100% sensitivity) than the current clinical practice of morphology and qualitative kinetics assessments. The TWIST sequence may be used in clinical settings to acquire high spatiotemporal resolution breast DCE-MRI images for both precise lesion morphology characterization and accurate pharmacokinetic analysis.

Detection of iron-labeled single cells by MR imaging based on intermolecular double quantum coherences at 14 T

To evaluate the efficiency and feasibility of intermolecular multiple quantum coherence (iMQC) magnetic resonance (MR) imaging for single cell detection, we obtained intermolecular double quantum coherence (iDQC) and conventional gradient echo (GE) images of macrophage cells labeled by contrast agents in gel. The iDQC images obtained with echo-planar readout visualized the labeled cells effectively and with a higher contrast than seen in conventional GE images, especially at low planar resolutions and with thick slices. This implies that iDQC imaging with contrast agents could be a good alternative to conventional MR imaging for detecting labeled single cells or cell tracking under favorable conditions.

Efficacy of positive contrast imaging techniques for molecular MRI of tumor angiogenesis

Superparamagnetic iron oxide particles (SPIOs) are promising contrast agents for molecular MRI. To improve the in vivo detection of iron-based contrast media, positive contrast imaging techniques have been developed. Here, the efficacy of two positive contrast techniques, white marker and susceptibility gradient mapping (SGM), were evaluated for molecular MRI of tumor angiogenesis and compared with conventional negative contrast gradient echo (GE) imaging. In vitro, cylindrical phantoms containing varying iron oxide concentrations were used to measure the response of positive contrast techniques. In vivo, tumor bearing mice were used as a model for tumor angiogenesis. Mice were injected with unlabeled SPIOs (n = 5) or SPIOs labeled with cyclic NGR peptide (cNGR) (n = 5), which homes specifically to angiogenic microvessels. Pre- and post-contrast GE and white marker images were acquired. Subsequently, SGM images and R(2)(*) maps were calculated. For image analysis, the contrast-to-noise ratio (CNR) and the percentage of enhanced voxels (EVs) in the tumor rim and core were calculated. In vitro, the linear increases in MRI signal response for increasing iron oxide concentration were much stronger for SGM than white marker. In vivo, the CNR of GE, white marker and SGM imaging was 5.7, 1.2 and 6.2, respectively, with equal acquisition times. Significant differences in the percentage of EVs between the tumor rim and core were found using R(2)(*) mapping, GE and SGM (p < 0.05). The two contrast agents had significantly different percentages of EVs by R(2)(*) mapping and SGM in the rim (p < 0.001). The in vivo efficacy of white marker and SGM was evaluated for molecular MRI relative to GE imaging and R(2)(*) mapping. Only SGM, and not white marker, can be used to transfer the negative contrast from targeted SPIOs in a positive contrast signal without loss of CNR.

Delayed contrast-enhanced cardiac MRI at an open 1.0T MR-system comparison of conventional segmented 3D gradient echo and phase-sensitive inversion recovery sequences: initial results

Background Delayed contrast enhanced (DE) cardiac MR imaging (cMRI) has become the gold standard for the in vivo detection and quantification of myocardial infarcts (MI). Up to now, cMRI had to be performed in a closed bore environment due to technical constraints of the existing open low-field MR scanners. The introduction of an open 1.0T MR-system with high gradient performance has paved the way for cardiac imaging, which may be beneficial in critically ill and claustrophobic patients as well as during stress examinations and MR-guided interventions. The aim of this study was to evaluate image quality, scar/myocardium-contrast and assess feasibility of delayed contrast enhanced cMRI using a 1) breath hold (BH) 3 dimensional (3D) Inversion Recovery (IR), 2) BH phase-sensitive IR (PSIR), and 3) a respiratory triggered (RT) PSIR sequence at an open MR-system. Methods 41 patients (11 female, 30 male; age 57+/-15 years) with known or suspected MI underwent viability imaging 10 min after i.v. application of Gd-DTPA (0.2 mmol/kg BW) at an open MRI system (Panorama HFO 1.0 Tesla, Philips Healthcare, Best, Netherlands). DE cMRI with complete coverage of the left-ventricular myocardium in short-axis (SA) slices was acquired using three different sequences and approaches: 1) A conventional k-space segmented 3D T1-weighted inversion-recovery-prepared gradient-echo sequence (in-plane resolution 1.33x1.33 mm2, slice thickness 5 mm) was performed. The inversion delay time TI was iteratively adjusted to null the signal from normal myocardium. Additionally, a fast multislice single-shot 3D PSIR sequence was performed in 2) BH technique (in-plane resolution 1.51x1.71 mm2, slice thickness 10 mm, SENSE factor 2 and 3) respiratory triggered (in-plane resolution 1.8x1.8 mm2, slice thickness 10 mm). Image quality of DE was rated on a 4-point grading scale. Contrast (C=SIscar/SImyo) was calculated and area of DE was assessed in % of LV mass. Results There was no statistical significant difference in image quality using BH 3D IR, BH PSIR and RT PSIR (3.71 +/-0.46; 3.27+/-0.61, 3.36+/-0.87, p<0.05), respectively. No infarcts were missed and agreement between the three approaches regarding infarct extent (BH 3D IR 5.47+/-9.08% vs. BH PSIR 5.26+/-8.89% vs. RT PSIR 5.59+/-8.85%, p< 0.05) was high. Contrast for 3D BH IR, BH PSIR and RT PSIR was 10.4+/-3.3 and 11.8+/-3.0, and 12.6+/-1.9, respectively. Conclusions Delayed contrast enhanced cMRI is feasible at an open 1.0T MRI system in a clinical setting and offers excellent image quality. Respiratory triggered PSIR findings correlate well with breath hold 3D IR and PSIR sequences for the detection and extent of myocardial infarcts.

Quantification of holmium‐166 loaded microspheres: Estimating high local concentrations using a conventional multiple gradient echo sequence with S0‐fitting

To provide a best estimate of the R 2* value and hence of the local concentration of highly paramagnetic holmium-166 loaded microspheres (HoMS) in voxels for which R 2* cannot be characterized by conventional fitting of multigradient echo (MGE) data because of fast signal decay due to high local concentrations. A postprocessing method, S(0)-fitting, was implemented in a conventional R 2* fitting method that is used for quantification of HoMS. S(0)-fitting incorporates the estimated initial amplitude of the free induction decay (FID) curve, S(0), of neighboring voxels into the fitting procedure for voxels for which the conventional algorithm failed. The method was applied to HoMS in vitro and ex vivo in a rabbit liver. The performance of the S(0)-fitting method was evaluated by comparing results qualitatively and quantitatively with results obtained with quantitative ultrashort TE imaging (qUTE). Applying S(0)-fitting provided a best estimate for R 2* up to a value of about 2300 s(-1) compared with a maximum value of about 1000 s(-1) that could be characterized using conventional fitting. A good agreement was observed both qualitatively and quantitatively for in vitro experiments as well as for ex vivo rabbit liver experiments between results obtained with S(0)-fitting and results obtained with qUTE imaging. S(0)-fitting is a postprocessing method that can provide a best estimate of high R 2* values that cannot be characterized by conventional relaxometry. The method can be applied to conventional MGE datasets and was shown to be beneficial for quantification of high local concentrations of holmium-loaded microspheres.

In vivo proton electron double resonance imaging of mice With fast spin echo pulse sequence

To develop and evaluate a two-dimensional (2D) fast spin echo (FSE) pulse sequence for enhancing temporal resolution and reducing tissue heating for in vivo proton electron double resonance imaging (PEDRI) of mice. A four-compartment phantom containing 2 mM TEMPONE was imaged at 20.1 mT using 2D FSE-PEDRI and regular gradient echo (GRE)-PEDRI pulse sequences. Control mice were infused with TEMPONE over ~1 min followed by time-course imaging using the 2D FSE-PEDRI sequence at intervals of 10-30 s between image acquisitions. The average signal intensity from the time-course images was analyzed using a first-order kinetics model. Phantom experiments demonstrated that EPR power deposition can be greatly reduced using the FSE-PEDRI pulse sequence compared with the conventional gradient echo pulse sequence. High temporal resolution was achieved at ~4 s per image acquisition using the FSE-PEDRI sequence with a good image SNR in the range of 233-266 in the phantom study. The TEMPONE half-life measured in vivo was ~72 s. Thus, the FSE-PEDRI pulse sequence enables fast in vivo functional imaging of free radical probes in small animals greatly reducing EPR irradiation time with decreased power deposition and provides increased temporal resolution.

High spatial and temporal resolution breast DCE-MRI: A feasibility study.

74 Background: The typical 1-2 min low temporal resolution (tRes) of conventional gradient-echo (GRE) breast dynamic contrast-enhanced (DCE) MRI precludes accurate quantitative pharmacokinetic (PK) analysis. The commercially available GRE-based TWIST (time-resolved angiography with stochastic trajectories) sequence employs an alternative k-space sampling scheme to provide high spatial and temporal resolution for dynamic imaging, originally intended for time-resolved MR angiography. Here we sought to evaluate the feasibility of breast DCE-MRI with the TWIST sequence, using both tumor morphology and quantitative PK analyses. Methods: 22 patients with 25 mammography-detected suspicious lesions underwent TWIST DCE-MRI on a 3T Siemens system prior to biopsy. The axial bilateral images were acquired with 20 s tRes and 1.0x1.0x1.4 mm3 spatial resolution (sRes). Immediately after TWIST DCE-MRI, a single DCE image set was acquired in 68 s using a conventional GRE sequence with the same sRes. Blinded to pathology, 3 radiologists compared lesion morphology assessments from the last TWIST DCE and the conventional images, and gave MRI BIRADS scores based on morphology and qualitative kinetic curve analyses. The TWIST DCE lesion signal time-courses were also subjected to Shutter-Speed Model PK analysis. Results: Normal parenchyma S/N ratios were not statistically different between TWIST and conventional GRE images. All readers indicated 88% [95% CI: (68%, 97%)] agreement in morphology evaluation between the TWIST and conventional DCE images. The degree of inter-reader agreement was substantial (κ = 0.75), as was the agreement in BIRADS scores (κ = 0.76). Pathology revealed 8 malignant and 17 benign lesions. Based on MRI BIRADS scores, all 3 readers attained 100% sensitivity and 82% specificity. With PK analysis, a Ktrans (contrast agent plasma/interstitium transfer rate constant) cut-off value of 0.1 min-1 further improved specificity to 94%. Conclusions: TWIST breast DCE-MRI provides both high tRes and sRes for accurate quantitative PK analysis and morphology evaluation, respectively. Utilizing TWIST for clinical breast DCE-MRI with quantitative PK analysis is feasible and may improve MRI interpretation.

High-resolution TOF MR angiography at 4.7 Tesla for volumetric and morphologic evaluation of coiled aneurysm neck remnants in a rat model

Detection of morphologic and volumetric changes in aneurysm necks is important when evaluating the effects of endovascular devices for aneurysm occlusion. To optimize high-resolution 3D-TOF MRA at 4.7 T in order to achieve the best aneurysm-to-background contrast in experimental rat aneurysms, and to quantify the volume of the aneurysm neck by imaging. Saccular aneurysms in the abdominal aorta of rats were coiled with platinum coils. Tissue relaxation times were measured, and used in a mathematical simulation. To optimize 3D-TOF angiography, imaging parameters were varied within the range obtained from the simulations. Tissue contrast and contrast-to-noise ratio were measured from MR images. TOF images were compared to conventional spin echo and gradient echo images and to endoscopic and histological analyses. Parameters yielding the best aneurysm-to-background contrast and contrast-to-noise ratio were determined. The agreement between the results from in vivo imaging and simulation was good. The optimized 3D-TOF MRA sequence (TR/TE/FA = 60 ms/6.6 ms/20°) had an isotropic voxel size of 117 µm, which enabled measurement of the aneurysm neck volume. High-resolution 3D-TOF angiography enables non-invasive quantification of changes in neck remnants of endovascularly coiled experimental aneurysms. In this model innovations like bioactive coils can be accurately tested for their efficacy for aneurysm occlusion.

Fast high resolution whole brain T2* weighted imaging using echo planar imaging at 7 T

Magnetic susceptibility based (T2* weighted) contrast in MRI at high magnetic field strength is of great value in research on brain structure and cortical architecture, but its use is hampered by the low signal-to-noise ratio (SNR) efficiency of the conventional spoiled gradient echo sequence (GRE) leading to long scan times even for a limited number of slices. In this work, we show that high resolution (0.5mm isotropic) T2* weighted images of the whole brain can be obtained in 6min by utilizing the high SNR efficiency of echo-planar imaging (EPI). A volumetric (3D) EPI protocol is presented and compared to conventional 3D GRE images acquired with the same resolution, amount of T2* weighting, and imaging duration. Spatial coverage in 3D EPI was increased by a factor of 4.5 compared to 3D GRE, while also the SNR was increased by a factor of 2. Image contrast for both magnitude and phase between gray and white matter was similar for both sequences, with enhanced conspicuity of anatomic details in the 3D EPI images due to the increased SNR. Even at 7T, image blurring and distortion is limited if the EPI train length remains short (not longer than the T2* of the imaged tissue). 3D EPI provides steps (speed, whole brain coverage, and high isotropic resolution) that are necessary to utilize the benefits of high field MRI in research that employs T2* weighted imaging.

Direct imaging and quantification of carotid plaque calcification

Carotid plaque calcification normally appears as a signal void with clinical MR sequences. Here, we describe the use of an adiabatic inversion recovery prepared two-dimensional ultrashort echo time sequence to image and characterize carotid plaque calcification using a clinical 3-T scanner. T(1), T 2*, and free water content were measured for seven carotid samples, and the results were compared with micro-CT imaging. Conventional gradient echo and fast spin echo images were also acquired for comparison. Correlations between T(1), T 2*, free water concentration, and mineral density were performed. There was a close correspondence between inversion recovery prepared two-dimensional ultrashort echo time morphologic and micro-CT appearances. Carotid plaque calcification varied significantly from sample to sample, with T(1) s ranging from 94 ± 19 to 328 ± 21 msec, T 2*s ranging from 0.31 ± 0.12 to 2.15 ± 0.25 msec, and free water concentration ranging from 5.7 ± 2.3% to 16.8 ± 3.4%. There was a significant positive correlation between T(1)(R = 0.709; P < 0.074), T 2* (R = 0.816; P < 0.025), and free water concentration, a negative correlation between T(1) (R = 0.773; P < 0.042), T 2* (R = 0.948; P < 0.001) and CT measured mineral density, and a negative correlation between free water concentration (R = 0.936; P < 0.002) and mineral density.

Improving contrast to noise ratio of resonance frequency contrast images (phase images) using balanced steady-state free precession

Recent MRI studies have exploited subtle magnetic susceptibility differences between brain tissues to improve anatomical contrast and resolution. These susceptibility differences lead to resonance frequency shifts which can be visualized by reconstructing the signal phase in conventional gradient echo (GRE) acquisition techniques. In this work, a method is proposed to improve the contrast to noise ratio per unit time (CNR efficiency) of anatomical MRI based on resonance frequency contrast. The method, based on the balanced steady-state free precession (bSSFP) MRI acquisition technique, was evaluated in its ability to generate contrast between gray and white matter in human brain at 3T and 7T. The results show substantially improved CNR efficiency of bSSFP phase images (2.85±0.21 times at 3T and 1.71±0.11 times at 7T) compared to the GRE data in a limited spatial area. This limited spatial coverage is attributed to the sensitivity of bSSFP to macroscopic B0 inhomogeneities. With this CNR improvement, high resolution bSSFP phase images (resolution=0.3×0.3×2mm3, acquisition time=10min) acquired at 3T had sufficient CNR to allow the visualization of cortical laminar structures in invivo human primary visual cortex. Practical application of the proposed method may require improvement of B0 homogeneity and stability by additional preparatory scans and/or compensation schemes such as respiration and drift compensation. Without these additions, the CNR benefits of the method may be limited to studies at low field or limited regions of interest.

Demonstration of striatopallidal iron deposition in chorea-acanthocytosis by susceptibility-weighted imaging

Chorea-acanthocytosis (ChAc) is a rare hereditary disorder characterized by involuntary choreiform movements and erythrocytic acanthocytosis [1]. MRI commonly shows a T2-signal increase in the atrophic striatum, which reveals neuronal loss with gliosis on autopsy. Increased brain iron levels are seen in various neurodegenerative diseases [2–5] and can be easily detected by newer MR imaging technologies, such as susceptibility-weighted imaging (SWI) [2, 3]. We attempted to visualize areas of degenerative change according to abnormal iron deposition in ChAc by using SWI. A 35-year-old woman presented with exacerbation of orolingual dyskinesia, dysarthria and cognitive decline during the course of 3 years. There was no family history of similar neurological disorders. Neurological examination revealed orofaciolingual dyskinesia and intermittent choreiform movements of the head and neck. There was involuntary tongue protrusion and self-mutilating behaviour affecting the tongue and lips. Also, her speech was dysarthric. Muscle power and bulk, and sensory function were all intact. She could walk without difficulty. Hyporeflexia was present in the lower limbs. On laboratory examination, the serum creatine kinase (CK) level was elevated at 345 IU/l (normal range 5–217 IU/l). Serum lipids and lipoprotein electrophoresis were normal. There were no abnormal findings in the nerve conduction study, including electromyography, muscle CT and EEG. Cardiomyopathy, cardiac arrhythmia and hepatosplenomegaly were absent. Genetic tests for Huntington’s disease, DRPLA, and spinocerebellar ataxia 1, 2, 3 and 17 were all negative. Peripheral blood smear revealed 20% acanthocytes confirmed by scanning electron microscopy (Fig. 1a). Brain MR imaging (3.0-T MR system, Verio, Siemens, Germany) revealed the bilateral atrophic putamina and head of caudate nuclei with increased signal intensity on T2-weighted (Fig. 1b) and iso-signal intensity on T1-weighted imaging. SWI (TR = 28 ms, TE = 20 ms, flip angle = 20 slice thickness = 2 mm) showed a paramagnetic dark signal in both striata (Fig. 1c), the corresponding area to T2 hyperintensity. Also, dark condensed stripes were observed in the lateral pallidum (arrows, Fig. 1d). Such a paramagnetic signal was not prominent in conventional gradient echo sequences (Fig. 1e). No evidence of calcification or hemorrhage was observed on brain CT (Fig. 1f). Genetic screening for VPS13A gene or Western blot for chorein was not available. The clinical presentation of this patient most likely fits with ChAc. However, correct clinical diagnosis is difficult due to symptom overlap with McLeod syndrome (MLS) [1]. Although neither mutations of the XK gene nor Kell antigen expression was looked for in this patient, the diagnosis of MLS is unlikely based on the lack of J.-H. Lee (&) Department of Neurology, Medical Research Institute, Pusan National University Yangsan Hospital, Beomo-ri, Mulgum-eup, Yangsan-si, Gyeongsangnam-do 626-770, South Korea e-mail: jhlee.neuro@pusan.ac.kr

A Concept for Magnetic Resonance Visualization of Surgical Textile Implants

To develop a method for visualizing surgical textile implant (STI) with superparamagnetic iron oxides (SPIO), using magnetic resonance imaging (MRI). Therefore, positive-contrast inversion-recovery with on-resonant water suppression (IRON) was applied and its properties were evaluated in vitro. STI with different concentrations of SPIO integrated into the base material were produced. Imaging was performed on a clinical 1.5 Tesla scanner, using conventional balanced gradient echo sequences (SSFP), T2*-weighted sequences, and IRON-imaging. In vitro experiments were conducted in an agarose phantom. On MR-images, contrast-to-noise-ratios, and the dimensions of the implant were assessed. Conventional MRI exhibited SPIO-loaded STI as signal voids. Using IRON, the mesh was clearly exhibited hyperintensely with suppression of on-resonant background signals with a distinct differentiation to other sources of off-resonances. Concentrations of approximately 9 mg/g led to best positive contrast and highest contrast-to-noise-ratios using IRON. Depending on B0-orientation, phase encoding direction and the STI's SPIO-load, the IRON-signal showed a characteristic pattern and an overestimation of STI size up to 4.6 mm. The integration of SPIOs into the base material combined with IRON is a feasible approach to visualize STI with MRI. This method could help to identify mesh-related problems in time and to reduce the need for surgical revision.

Quantification of Calcifications in Endarterectomy Samples by Means of High-Resolution Ultra-Short Echo Time Imaging

Magnetic resonance imaging (MRI) has proven its value for noninvasive assessment and classification of atherosclerotic lesions. MRI provides excellent access to soft tissue information, but its capability for assessing calcified segments of the lesion remains limited. The aim of this study was to investigate the ultra-short echo time (UTE) sequence for accurate quantification of the plaque volumes and qualitative assessment of the calcium density. Images of 35 endarterectomy samples were acquired by a high-resolution UTE sequence (TE = 50 micros) technique and compared with the conventional gradient echo (fast field echo) approach, volume computed tomography, and histology. The UTE technique yielded accurate quantification of the volume of the calcification as well as enabled qualitative assessment of the calcium density according to the resulting relative signal intensity. In comparison, the fast field echo technique yielded an average overestimation of the lesion size by about 35% and the low signal intensity did not allow a clear delineation of the different calcium densities. The presented data provide evidence that incorporation of the UTE technique in today's MRI protocols for plaque classification holds the potential to add the missing important information on calcium volume and density solely based on MRI data.

Susceptibility gradient quantization by MRI signal response mapping (SIRMA) to dephaser

Susceptibility effects are a very efficient source of contrast in magnetic resonance imaging. However, detection is hampered by the fact the induced contrast is negative. In this work, the SIgnal Response MApping (SIRMA) to dephaser method is proposed to map susceptibility gradient to improve visualization. In conventional gradient echo acquisitions, the echo formation of susceptibility affected spins is shifted in k-space, the shift being proportional to the susceptibility gradient. Susceptibility gradients map can be produced by measuring this induced shifts. The SIRMA method measures these shifts from a series of dephased images collected with additional incremental dephasers. These additional dephasers correspond either to a slice refocusing gradient offset or to a reconstruction window off-centering. The signal intensity profile as a function of the additional dephaser was determined on a pixel-by-pixel basis from the ensemble of dephased images. Susceptibility affected voxels presented a signal response profile maximum shifted compared to nonaffected voxels ones. Shift magnitude and sign were measured for each pixel to determine susceptibility gradients and produce a susceptibility gradient map. In vitro experiments demonstrated the ability of the method to map gradient inhomogeneities induced by a cylinder. Quantization accuracy was evaluated comparing SIRMA images and simulations performed on the well-characterized air filled cylinder model. Performances of the SIRMA method, evaluated in vitro on cylinders filled with various superparamagnetic iron oxide SPIO concentrations, showed limited influence of acquisition parameters. Robustness of the method was then assessed in vivo after an infusion of SPIO-loaded nanocapsules into the rat brain using a convection-enhanced drug delivery approach. The region of massive susceptibility gradient induced by the SPIO-loaded nanocapsules was clearly delineated on SIRMA maps and images were compared to T2* weighted images, Susceptibility Gradient Map (SGM), and histological Perl's staining slice. The potential for quantitative evaluation of SPIO distribution volume was demonstrated. The proposed method is a promising technique for a wide range of applications especially in molecular or cellular imaging with respect to its quantitative nature and its computational simplicity.

Design and use of variable flip angle schedules in transient balanced SSFP subtractive imaging

In subtractive imaging modalities, the differential longitudinal magnetization decays with time, necessitating signal-efficient scanning methods. Balanced steady-state free precession pulse sequences offer greater signal strength than conventional spoiled gradient echo sequences, even during the transient approach to steady state. Although traditional balanced steady-state free precession requires that each excitation pulse use the same flip angle, operating in the transient regimen permits the application of variable flip angle schedules that can be tailored to optimize certain signal characteristics. A computationally efficient technique is presented to generate variable flip angle schedules efficiently for any optimization metric. The validity of the technique is shown using two phantoms, and its potential is demonstrated in vivo with a variable angle schedule to increase the signal-to-noise ratio (SNR) in myocardial tissue. Using variable flip angles, the mean SNR improvement in subtractive imaging of myocardial tissue was 18.2% compared to conventional, constant flip angle, balanced steady-state free precession (P = 0.0078).