32-channel Head Research Articles

Design, Implementation, and Evaluation of a Head and Neck MRI RF Array Integrated with a 511 keV Transmission Source for Attenuation Correction in PET/MR.

The goal of this work is to further improve positron emission tomography (PET) attenuation correction and magnetic resonance (MR) sensitivity for head and neck applications of PET/MR. A dedicated 24-channel receive-only array, fully-integrated with a hydraulic system to move a transmission source helically around the patient and radiofrequency (RF) coil array, is designed, implemented, and evaluated. The device enables the calculation of attenuation coefficients from PET measurements at 511 keV including the RF coil and the particular patient. The RF coil design is PET-optimized by minimizing photon attenuation from coil components and housing. The functionality of the presented device is successfully demonstrated by calculating the attenuation map of a water bottle based on PET transmission measurements; results are in excellent agreement with reference values. It is shown that the device itself has marginal influence on the static magnetic field B0 and the radiofrequency transmit field B1 of the 3T PET/MR system. Furthermore, the developed RF array is shown to outperform a standard commercial 16-channel head and neck coil in terms of signal-to-noise ratio (SNR) and parallel imaging performance. In conclusion, the presented hardware enables accurate calculation of attenuation maps for PET/MR systems while improving the SNR of corresponding MR images in a single device without degrading the B0 and B1 homogeneity of the scanner.

Reconstruction of white matter fibre tracts using diffusion kurtosis tensor imaging at 1.5T: Pre-surgical planning in patients with gliomas

Tractography studies for pre-surgical planning of primary brain tumors is typically done using diffusion tensor imaging (DTI), which cannot resolve crossing, kissing or highly angulated fibres. Tractography based on the estimation of the diffusion kurtosis (DK) tensor was recently demonstrated to enable tackling these limitations. However, its use in the clinical context at low 1.5T field has not yet been reported. PurposeTo evaluate if the estimation of whole-brain tractography using the DK tensor is feasible for pre-surgical investigation of patients with brain tumors at 1.5T. MethodsEight healthy subjects and 3 patients with brain tumors were scanned at 1.5T using a 12-channel head coil. Diffusion-weighted images were acquired with repetition/echo times of 5800/107 ms, 82 × 82 resolution, 3 × 3 × 3 mm3 voxel size, b-values of 0, 1000, 2000 s/mm2 and 64 gradient sensitising directions. Whole-brain tractography was estimated using the DK tensor and corticospinal tracts (CST) were isolated using regions-of-interest placed at the cerebral peduncles and motor gyrus. Tract size, DK metrics and CST deviation index (highest curvature point) were compared between healthy subjects and patients. ResultsTract sizes did not differ between groups. The CST deviation index was significantly higher in patients compared to healthy subjects. Fractional anisotropy was significantly lower in patients, with higher mean kurtosis asymmetry index at the highest curvature point in patients. ConclusionsCorticospinal fibre bundles estimated using DK tensor in a 1.5T scanner presented similar properties in patients with brain gliomas as those reported in the literature using DTI-based tractography.

Dynamic Contrast-Enhanced Magnetic Resonance Imaging of Ocular Melanoma as a Tool to Predict Metastatic Potential.

This study explores the capability of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to differentiate tumor characteristics of metastatic and nonmetastatic choroidal melanoma as a potential tool for patient management. A total of 13 patients (69 ± 9 years) with choroidal melanoma were imaged using DCE-MRI on a 3-T MRI system with a 16-channel head coil. The Tofts 2-compartment model was chosen for quantification, and parameters K (the transfer constant from the blood plasma to the extracellular space) and Kep (the transfer constant from the extracellular space to the blood plasma) were calculated and compared. Metastasis was excluded by subsequent clinical work-up or confirmed by histology after targeted biopsy. Six patients were diagnosed with metastatic melanoma and 7 without. All orbital tumors were at least larger than 2 mm. A significant difference was identified in K between patients with (0.73 ± 0.18/min) and without (1.00 ± 0.21/min) metastatic melanoma (P = 0.03), whereas the difference was not significantly shown in Kep (2.58 ± 1.54/min of metastatic patients vs 2.98 ± 1.83/min of nonmetastatic patients, P = 0.67). Dynamic contrast-enhanced magnetic resonance imaging has the potential to differentiate orbital melanomas with metastatic and nonmetastatic spread. Thus, DCE-MRI has the potential to be an in vivo imaging technique to predict early which patients are prone to metastatic disease.

A 32-channel coil system for MR vessel wall imaging of intracranial and extracranial arteries at 3T

PurposeTo develop a RF coil system for joint imaging of intracranial and extracranial arterial vessel wall at 3T. Materials and methodThe coil system consists of a 24-channel head coil combined with an 8-channel carotid coil. It is compared with a standard coil configuration (12-channel head coil+4-channel neck coil+8-channel carotid coil) for SNR and g-factors in phantoms and healthy volunteers. The clinical relevance of the proposed coil system is also evaluated in patients. ResultsIn phantom experiments, the SNR of the proposed coil system is 53% higher than the maximum SNR of the standard coil configuration at the center of the phantom which usually corresponds to the intracranial region of the head. The g-factors of the proposed coil system in the sagittal plane are lower than the standard coil configuration (by 10.8% and 26.6% for R=2 and 4 respectively) in the same experiment. In healthy volunteer experiments, 55% of the pixels have SNR above 100 for the proposed coil system, which is 33% more than that of the standard coil configuration. The maximum g-factors in the standard configuration are higher than those from the new coil design by 12% at R=2 and up to 36% at R=4 in the sagittal plane. In patients, in-vivo intracranial and extracranial arterial wall images at an isotropic spatial resolution of 0.6mm can be acquired using the proposed coil system. Plaques are well depicted from the images. ConclusionsThe performance of the proposed coil set is superior to the standard coil configuration, providing high SNR, low g-factor and good spatial coverage needed for simultaneous high resolution imaging of intracranial and extracranial arterial walls. Images acquired in 7.6min using the proposed coil system can achieve an isotropic spatial resolution of 0.6mm and can be used to depict plaques on the intracranial and extracranial arterial walls in patients.

Cold pressor gel test: A safe alternative to the cold pressor test in fMRI.

This study describes a new methodology-the cold pressor gel test (CPGT)-for delivering an accessible experimental pain stimulus, which is reproducible and safe for functional MRI (fMRI). The cold pressor test was modified to put safety precautions into the CPGT. The material used is cool gelled water with a thickening product, which provides a stable temperature at 0.2 °C. Thirteen women with chronic pelvic pain were scanned using a 3 Tesla (T) MR scanner equipped with a 12-channel head coil. Changes in BOLD activation during cold-induced pain were estimated. The results have demonstrated that gel substances maintain a stable temperature during the experiment, resulting in an insignificant variation. Before the experiment, the mean temperature was 0.2 ± 0.11 °C, and at the end it was 0.7 ± 0.15 °C. The time taken by participants to reach the maximum level of pain during the CPGT was 56.92 ± 11.09 s. The pain intensity during the experiments was 6.92 ± 1.66 on the visual analog scale (VAS). The fMRI analysis showed significant BOLD activation in the main brain regions involved in chronic pain processing. The CPGT is an experimental tool to deliver pain that is easily reproducible, particularly in brain functional imaging studies. Moreover, it is cost-effective, safe, and compatible with fMRI. Magn Reson Med 78:1464-1468, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

A robust method for suppressing motion-induced coil sensitivity variations during prospective correction of head motion in fMRI

Prospective motion correction is a promising candidate solution to suppress the effects of head motion during fMRI, ideally allowing the imaging plane to remain fixed with respect to the moving head. Residual signal artifacts may remain, however, because head motion in relation to a fixed multi-channel receiver coil (with non-uniform sensitivity maps) can potentially introduce unwanted signal variations comparable to the weak fMRI BOLD signal (~1%–4% at 1.5–3.0T). The present work aimed to investigate the magnitude of these residual artifacts, and characterize the regime over which prospective motion correction benefits from adjusting sensitivity maps to reflect relative positional change between the head and the coil. Numerical simulations were used to inform human fMRI experiments. The simulations indicated that for axial imaging within a commonly used 12-channel head coil, 5° of head rotation in-plane produced artifact signal changes of ~3%. Subsequently, six young adults were imaged with and without overt head motions of approximately this extent, with and without prospective motion correction using the Prospective Acquisition CorrEction (PACE) method, and with and without sensitivity map adjustments. Sensitivity map adjustments combined with PACE strongly protected against the artifacts of interest, as indicated by comparing three metrics of data quality (number of activated voxels, Dice coefficient of activation overlap, temporal standard deviation of baseline fMRI timeseries data) across the different experimental conditions. It is concluded that head motion in relation to a fixed multi-channel coil can adversely affect fMRI with prospective motion correction, and that sensitivity map adjustment can mitigate this effect at 3.0T.

Abstract TP91: Vessel Wall Imaging Demonstrates Aneurysm Wall Enhancement in Unruptured Posterior Communicating Artery Aneurysms With Oculomotor Nerve Palsy

Background: In ruptured aneurysms, vessel wall imaging (VWI) shows aneurysm wall enhancement, which may be caused by inflammation of the aneurysm wall. However, whether this inflammation is the cause or the result of aneurysm rupture remains unknown. In this study, we analyzed high-resolution VWI on posterior communicating artery (PComA) aneurysms, seeking to better understand aneurysm wall inflammation. Hypothesis: Oculomotor nerve palsy (ONP) is a warning sign of PComA aneurysm rupture. ONP results from compression of the oculomotor nerve and indicates aneurysm enlargement. Thus, PComA aneurysms with ONP are about to rupture, which makes them perfect cases to research aneurysm wall inflammation. If the inflammation of the aneurysm wall is the cause of aneurysm rupture, VWI may capture images of aneurysm wall enhancement before it ruptures. Methods: PComA aneurysm patients with ONP were examined using a Verio 3.0T scanner with a 12-channel head coil (Siemens Healthcare, Erlangen, Germany). Time-of-flight MRI angiography was performed to localize the aneurysm site. Then, a high-resolution T1-weighted black blood vessel wall sequence was obtained before and after intravenous administration of gadolinium. Each sequence was performed in the axial planes. Additional coronal planes or other planes were obtained if necessary. Patients with ruptured PComA aneurysms were also examined as a positive control, and patients with unruptured PComA aneurysms without ONP were examined as a negative control. Results: Ten patients with PComA aneurysm were examined. VWI of 3 patients with ONP showed aneurysm wall enhancement. Of these 3 patients, 2 were with post-orbital pain, and VWI showed complete enhancement of the aneurysm wall. VWI showed partial enhancement of the aneurysm wall in the other one patient without post-orbital pain. In the positive control group, complete wall enhancement was seen in all 3 ruptured PComA aneurysms (2 with ONP, 1 without ONP). In the negative control group of 4 cases, no aneurysm wall enhancement was seen. Conclusion: VWI demonstrated aneurysm wall enhancement in PComA aneurysms with ONP, which indicates that wall inflammation may occur before aneurysm rupture.

Morphological changes of cerebral cortex in primary open-angle glaucoma patients under magnetic resonance imaging

To observe the morphology changes of cerebral cortex in primary open-angle glaucoma (POAG) patients, and to explore the damage mechanism in the central nerve system. 30 patients, 19 males and 11 females (age ranged from 26 to 82 years old), who were diagnosed with POAG in the department of ophthalmology at Huashan Hospital of Fudan University from February 2011 to December 2012 were enrolled. Meanwhile, additional 30 age- and sex- matched patients were collected as controls. All subjects underwent a complete ophthalmic evaluation. As for magnetic resonance imaging (MRI), we adopted the scans of T1WI, T2WI and fluid attenuated inversion recovery (FLAIR) on a Siemens Magneton Verio 3T MRI machine with a 12-channel head coil. Subjects with space occupying or vascular lesion in brain imaging were excluded from the study. The three-dimensional magnetization prepared rapid acquisition gradient echo sequence (3D-MPRAGE) was used to acquire the volume data of whole brain of all subjects. SPM8 and VBM8 toolbox were used to analyze the image data. Voxel-based analysis was done for whole brain grey matter images. Compared with the control group, the volume of grey matter from several brain regions of the POAG patients decreased. These structures included left lingual gyrus (t=3.207, P=0.002), left medial frontal gyrus (t=2.912, P=0.004), right superior frontal gyrus (t=2.745, P=0.005), left middle temporal gyrus (t=2.958, P=0.003), right precuneus (t=3.291, P=0.001), right postcentral gyrus (t=3.306, P=0.001), left inferior parietal lobule(t=2.716, P=0.006), left parahippocampa gyrus (t=2.815, P=0.005). The results were assessed with comparative t-test to perform statistical analysis. When t>2.479, P<0.01, the difference between the two groups was considered statistically significant. The volume of grey matter in POAG patients' brain decreased in several regions. It is illustrated that POAG is a syndrome, which causes damages in the brain of POAG patients at multi-aspects and multi-levels. The damages contained not only injuries in the visual pathway, but also morphological and functional changes in many other brain regions.

SU-D-303-05: Optimal Protocols and Analysis Strategies for Intravoxel Incoherent Motion MRI

Purpose: Intravoxel Incoherent Motion (IVIM) MRI can saperate perfusion and diffusion components of the tissues. Previous studies showed that non-Gaussian diffusion effect may influence the quantifications of perfusion. This study aimed to propose optimal protocols and analysis strategies for the perfusion measurement of normal brain tissues. Methods: An Non-Gaussian IVIM model was used to generate IVIM signals. There were three conditions of b-values: (1) 0–500 (2) 0–1000 (3) 0–2500. SNR of 250 was set. For analysis, the Gaussian and the Non-Gaussian models were used for both full-fitting and asymptotic methods. The mean errors and coefficient of variation were calculated. The MR imaging were applied by using a 3.0T scanner with a 12-channel phase array head coil. The diffusion images ware obtained with the following parameters: b values (0, 5, 10, 20, 30, 50, 70, 100, 200, 400, 600, 800, 1000, 1500, 2000, 2500 s/mm2), repetition time/echo time, 2,500/67 milliseconds; flip angle, 90 degrees; pixel size, 3.4375 x 3.4375 mm2 ; matrix, 64x 64; slice thickness,5 mm; 22 slices, gap= 6 mm; bandwidth, 1594 Hz. Results: Compared with the full-fitting methods, the asymptotic methods provided better precision for IVIM analysis. However, the asymptotic methods were sensitive to the weighting of perfusion component. To minimize the effect of perfusion component, the minimum of the b-value set for asymptotic methods should be larger than 500 and 767 for 5% and 1% residual perfusion component, respectively. In addition, the Gaussian models were sensitive to the non-Gaussian effects. For a general normal kurtosis (K=0.8), the Gaussian model methods were not valid with large b-values. However, the Non-Gaussian methods were sensitive to SNR. The experiment showed similar results with the simulation. Conclusion: The asymptotic Non-Gaussian methods is recommanded for IVIM analysis if appropriate SNR was available. The b-values should be set as 0–2500.

TH-CD-207-06: Development of a Wide-View Retinotopic Mapping to Quantify Age Effects On Visual Cortex

Purpose: Neural degeneration in normal aging can lead to functional changes in the visual cortex. However, the visual stimuli used in previous studies only covered a narrow, central visual field. The goals of this study were to 1) establish a practical, low-cost visual screen system inside a clinical MRI system; 2) investigate effects of normal aging with the wide-view to include central and peripheral visual areas. Methods: Five elderly (60.6±3.4 y.o.) and five young (26.6±3.0 y.o.) normal volunteers were scanned at 3T. Visual stimulations (checkerboard animations) were projected to a customized plastic screen inside the magnet bore. Retinotopic BOLD fMRI was performed using the posterior half of a 12-channel head coil to image the occipital lobe without obstructing subjects’ vision to achieve visual simulation from 0∼90° of the visual field. MRI data were processed in Freesurfer for a two-sample unpaired group analysis with significance level p<0.05. Results: Boundaries of complete visual cortex areas were delineated with retinotopic fMRI and the wide-view stimulus system. With a small ring stimulus in the central visual field, older subjects showed significantly reduced neural activity (p<0.05) compared to younger subjects in the central vision region of the primary visual cortex. However, with the ring-stimulus expanded to the periphery (visual angle 45°∼90°), older subjects had significantly more activation (p<0.05) in central visual cortex areas than young subjects but significantly weaker responses (p<0.05) in periphery visual cortex areas. Conclusion: Our results demonstrated that wide-view retinotopic mapping could be used to quantify age-related changes in the visual cortex. Central visual areas of healthy older subjects exhibited weaker BOLD activity for central stimulation and stronger signal for periphery stimulation, indicating potential central vision loss and neural reorganization with age. Future studies will correlate fMRI with visual field tests to investigate neural alterations in glaucoma patients.

Corticospinal MRI tractography in space-occupying brain lesions by diffusion tensor and kurtosis imaging methods.

Recently, DKI-based tractography has been developed, showing improved crossing-fiber resolution in comparison to deterministic DTI-based tractography in healthy subjects. In this work, DTI and DKI-based tractography methods were compared regarding the assessment of the corticospinal tract in patients presenting space-occupying brain lesions near cortical motor areas. Nine patients (4 males) aged 23 to 62 years old, with space-occupying brain lesions (e.g. tumors) were studied for pre-surgical planning using a 1.5T MRI scanner and a 12-channel head coil. In 5 patients diffusion data was acquired along 64 directions and in 4 patients along 32 directions both with b-values 0, 1000 and 2000 s/mm2. Corticospinal tracts were estimated using deterministic DTI and DKI methods and also using probabilistic DTI. The superior cerebellar peduncles and the motor cortical areas, ipsilateral and contralateral to the lesions, were used as seed regions-of-interest for fiber tracking. Tracts courses and volumes were documented and compared between methods. Results showed that it was possible to estimate fiber tracts using deterministic DTI and DKI methods in 8/9 patients, and using the probabilistic DTI method in all patients. Overall, it was observed that DKI-based tractography showed more voluminous fiber tracts than when using deterministic DTI. The DKI method also showed curvilinear fibers mainly above lesions margins, which were not visible with deterministic DTI in 5 patients. Similar tracts were observed when using probabilistic DTI in 3 of those patients. Results suggest that the DKI method contribute with additional information about the corticospinal tract course in comparison with the DTI method, especially with subcortical lesions and near lesions’ margins. Therefore, this study suggests that DKI-based tractography could be useful in MRI and hybrid PET-MRI pre-surgical planning protocols for improved corticospinal tract evaluation.

Combining phase and magnitude information for contrast agent quantification in dynamic contrast-enhanced MRI using statistical modeling.

The purpose of this study was to investigate, using simulations, a method for improved contrast agent (CA) quantification in DCE-MRI. We developed a maximum likelihood estimator that combines the phase signal in the DCE-MRI image series with an additional CA estimate, e.g. the estimate obtained from magnitude data. A number of simulations were performed to investigate the ability of the estimator to reduce bias and noise in CA estimates. Noise levels ranging from that of a body coil to that of a dedicated head coil were investigated at both 1.5T and 3T. Using the proposed method, the root mean squared error in the bolus peak was reduced from 2.24 to 0.11 mM in the vessels and 0.16 to 0.08 mM in the tumor rim for a noise level equivalent of a 12-channel head coil at 3T. No improvements were seen for tissues with small CA uptake, such as white matter. Phase information reduces errors in the estimated CA concentrations. A larger phase response from higher field strengths or higher CA concentrations yielded better results. Issues such as background phase drift need to be addressed before this method can be applied in vivo.

Acoustic noise reduction in MRI using Silent Scan: an initial experience.

Acoustic noise during magnetic resonance imaging (MRI) is the main source for patient discomfort and leads to verbal communication problems, difficulties in sedation, and hearing impairment. Silent Scan technology uses less changes in gradient excitation levels, which is directly related to noise levels. Here, we report our preliminary experience with this technique in neuroimaging with regard to subjective and objective noise levels and image quality. Ten patients underwent routine brain MRI with 3 Tesla MR750w system and 12-channel head coil. T1-weighted gradient echo (BRAVO) and Silenz pulse sequence (TE=0, 3D radial center-out k-space filling and data sampling with relatively small gradient steps) were performed. Patients rated subjective sound impression for both sequences on a 6-point scale. Objective sound level measurements were performed with a dedicated device in gantry at different operation modes. Image quality was subjectively assessed in consensus by two radiologists on a 3-point scale. Readers rated image quality as fully diagnostic in all patients. Measured mean noise was reduced significantly with Silenz sequence (68.8 dB vs. 104.65 dB with BRAVO, P = 0.024) corresponding to 34.3% reduction in sound intensity and 99,97% reduction in sound pressure. No significant difference was observed between Silenz sound levels and ambient sounds (i.e., background noise in the scanner room, 68.8 dB vs. 68.73 dB, P = 0.5). The patients' subjective sound level score was lower for Silenz compared with conventional sequence (1.1 vs. 2.3, P = 0.003). T1-weighted Silent Scan is a promising technique for acoustic noise reduction and improved patient comfort.

Evaluation of a 32-channel versus a 12-channel head coil for high-resolution post-contrast MRI in giant cell arteritis (GCA) at 3 T

The aim of this study was to evaluate the diagnostic value of a 32-channel head coil for the characterization of mural inflammation patterns in the superficial cranial arteries in patients with giant cell arteritis (GCA) compared to a standard 12-channel coil at 3T MRI.55 patients with suspected GCA underwent high resolution T1-weighted post-contrast MRI at 3T to detect inflammation related vessel wall enhancement using both coils. To account for different time delays between contrast agent injection and sequence acquisition, the patients were divided into two cohorts: 27 patients were examined with the 32-channel coil first and 28 patients with the 12-channel coil first. Images were evaluated by two blinded readers with regard to image quality, artifact level and arteries’ inflammation according to a standardized ranking scale; furthermore signal-to-noise ratio (SNR) measurements were performed at three locations.Identification of arteries’ inflammation was achieved with both coils with excellent inter-observer agreement (κ=0.89 for 12-channel and κ=0.96 for 32-channel coil). Regarding image grading, the inter-observer variability was moderate for the 12-channel (κ=0.5) and substantial for the 32-channel coil (κ=0.63). Significantly higher SNR and improved image quality (p<0.01) were obtained with the 32-channel coil in either coil order.Image quality for depiction of the superficial cranial arteries was superior for the 32-channel coil. For standardized GCA diagnosis, the 12-channel coil was sufficient.

Analysis of intensity and sensitivity of single- and multiple-channel RF head coilsin 3.0-T MRI system

BackgroundHigh-resolution anatomical and functional images can be acquired using high- andultrahigh-field magnetic resonance imaging (MRI) systems. An increase in the mainmagnetic field strength results in high resolution but suffers from thedisadvantage of field nonuniformity in the radio frequency (RF). To overcome thisRF field inhomogeneity, parallel RF transmission system and sensitivity encodingare widely used.FindingsOur experimental results showed that the best signal intensity was in transmit andreceive mode head coil, except for the T2-weighted fast field echo (FFE). The bestsignal-to-noise ratio (SNR) was in the 32-channel head coil.ConclusionIn general, multiple-channel coils have been known as more efficient materials interms of SNR. However, they may not be as important in experiments where intensityis an important factor. Therefore, a suitable coil should be selected using apulse sequence.

Mapping of cognitive functions in chronic intractable epilepsy: Role of fMRI

Background:Functional magnetic resonance imaging (fMRI), a non-invasive technique with high spatial resolution and blood oxygen level dependent (BOLD) contrast, has been applied to localize and map cognitive functions in the clinical condition of chronic intractable epilepsy.Purpose:fMRI was used to map the language and memory network in patients of chronic intractable epilepsy pre- and post-surgery.Materials and Methods:After obtaining approval from the institutional ethics committee, six patients with intractable epilepsy with an equal number of age-matched controls were recruited in the study. A 1.5 T MR scanner with 12-channel head coil, integrated with audio-visual fMRI accessories was used. Echo planar imaging sequence was used for BOLD studies. There were two sessions in TLE (pre- and post-surgery).Results:In TLE patients, BOLD activation increased post-surgery in comparison of pre-surgery in inferior frontal gyrus (IFG), middle frontal gyrus (MFG), and superior temporal gyrus (STG), during semantic lexical, judgment, comprehension, and semantic memory tasks.Conclusion:Functional MRI is useful to study the basic concepts related to language and memory lateralization in TLE and guide surgeons for preservation of important brain areas during ATLR. This will help in understanding future directions for the diagnosis and treatment of such disease.

A study on the measurement of the core body temperature change after radiofrequency ablation (RFA) through MR temperature mapping

This study examined the change in the heat generated during radiofrequency ablation (RFA) using a self-manufactured phantom and used magnetic resonance imaging (MRI) to analyze the change in the temperature of the core body and the tissues surrounding the phantom. In this experiment, the image and the phase image were obtained simultaneously from a gradient echo-based sequence using 1.5-Tesla MRI equipment and a 12-channel head coil. The temperature mapping technique was used to calculate the change in temperature. The regions of interest (ROIs) (ROI 1 - ROI 6) were set with a focus on the area where the RFA was performed, according to the temperature distribution, before monitoring the temperature change for one hour in time intervals of five minutes. The results showed that the temperature change in the ROI with time was largest in the ROI 1 and smallest in the ROI 5. In addition, after the RFA procedure, the temperature decreased from the initial value to 0 °C in one hour. The temperature changes in the core body and the surrounding tissues were confirmed by MRI temperature mapping, which is a noninvasive method.

A comparison of five standard methods for evaluating image intensity uniformity in partially parallel imaging MRI

To investigate the utility of five different standard measurement methods for determining image uniformity for partially parallel imaging (PPI) acquisitions in terms of consistency across a variety of pulse sequences and reconstruction strategies. Images were produced with a phantom using a 12-channel head matrix coil in a 3T MRI system (TIM TRIO, Siemens Medical Solutions, Erlangen, Germany). Images produced using echo-planar, fast spin echo, gradient echo, and balanced steady state free precession pulse sequences were evaluated. Two different PPI reconstruction methods were investigated, generalized autocalibrating partially parallel acquisition algorithm (GRAPPA) and modified sensitivity-encoding (mSENSE) with acceleration factors (R) of 2, 3, and 4. Additionally images were acquired with conventional, two-dimensional Fourier imaging methods (R=1). Five measurement methods of uniformity, recommended by the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA) were considered. The methods investigated were (1) an ACR method and a (2) NEMA method for calculating the peak deviation nonuniformity, (3) a modification of a NEMA method used to produce a gray scale uniformity map, (4) determining the normalized absolute average deviation uniformity, and (5) a NEMA method that focused on 17 areas of the image to measure uniformity. Changes in uniformity as a function of reconstruction method at the same R-value were also investigated. Two-way analysis of variance (ANOVA) was used to determine whether R-value or reconstruction method had a greater influence on signal intensity uniformity measurements for partially parallel MRI. Two of the methods studied had consistently negative slopes when signal intensity uniformity was plotted against R-value. The results obtained comparing mSENSE against GRAPPA found no consistent difference between GRAPPA and mSENSE with regard to signal intensity uniformity. The results of the two-way ANOVA analysis suggest that R-value and pulse sequence type produce the largest influences on uniformity and PPI reconstruction method had relatively little effect. Two of the methods of measuring signal intensity uniformity, described by the (NEMA) MRI standards, consistently indicated a decrease in uniformity with an increase in R-value. Other methods investigated did not demonstrate consistent results for evaluating signal uniformity in MR images obtained by partially parallel methods. However, because the spatial distribution of noise affects uniformity, it is recommended that additional uniformity quality metrics be investigated for partially parallel MR images.

Aberrant cortico–subcortical functional connectivity among women with poor motor control: Toward uncovering the substrate of hyperkinetic perseveration

ObjectiveHyperkinetic perseveration (HKP) refers to perseverative repetition of rudimentary motor output. Although HKP is known to be associated with brain injuries and certain neurodegenerative disorders (primarily those involving the frontal lobes and the basal ganglia), an increased tendency to exhibit HKP is also commonly associated with apparently normal aging (i.e., in the absence of known neuropathology). The purpose of the present study was to examine anomalies in brain functioning associated with HKP tendencies in a non-injured brain. MethodThe present study examined functional MRI connectivity patterns associated with HKP in a sample of 24 “young” (ages 25–35 years) and 20 “old” (ages 65–75 years) healthy community dwelling women. Participants performed a motor learning task (the Push-Turn-Taptap task: PTT) known to elicit HKP. On a separate day, participants were scanned on a Siemens 3T Trio MR scanner with a 12-channel head coil, while performing a block-design motor sequence learning task that was designed to be a scanner analog for the PTT task. Cortico–subcortical connectivity patterns involving two subcortical regions of interest (putamen and thalamus) and three cortical regions (sensory-motor cortex, Brodmann Area 6, inferior frontal gyrus) were examined. ResultsOlder participants exhibited a higher rate of HKP compared to younger participants. Age-related HKP was associated with hemispheric asymmetry marked by a relatively stronger right-hemisphere cortico–subcortical connectivity involving the sensory-motor cortex and, to a lesser extent, Brodmann Area 6. These patterns were distinct from connectivity patterns associated with aging alone. ConclusionsHKP is related to anomalies involving frontal–subcortical circuits. Future research should examine specific components of the basal-ganglia circuitry.

Improvement of SNR and acquisition acceleration using a 32-channel head coil compared to a 12-channel head coil at 3T

Magnetic resonance imaging (MRI) techniques continue to improve in manifold ways. Besides field strength and sequence optimization, technical advances in coil design and sensitivity yield to increase the signal detection and therefore improve image quality. To evaluate the performance of signal-to-noise ratio (SNR) and parallel acquisition technique (PAT) acceleration of a dedicated 32-channel head coil compared with a standard 12-channel head coil. In a clinical 3T setting, spatial resolved SNR values for unaccelerated imaging and PAT with acceleration factors of 2-6 of a 32-channel head coil were evaluated in relation to a 12-channel head coil. SNR was determined quantitatively using proton-density-weighted in-vivo examinations in five healthy volunteers. Quantitative SNR maps for unaccelerated and PAT imaging were calculated using unfiltered MR raw data. Up to three-fold higher SNR values were achieved with the 32-channel head coil, which diminished towards the center to an increase of 40% compared with the 12-channel head coil. When using PAT, the 32-channel head coil resulted in a lower spatial-dependent quantitative noise enhancement, varying between 0% at R = 2 and 33% at R = 5. The 32-channel head coil provided superior SNR both with and without PAT compared with a 12-channel head coil, especially close to the brain surface. Using PAT, the unavoidable noise enhancement is diminished up to acceleration factors of 6 for the 32-channel head coil. Therefore, the 32-channel head coil is considered as a preferable tool for high-resolution neuroradiological imaging.