Phase-aligned multiple spin-echo averaging: a simple way to improve signal-to-noise ratio of in vivo mouse spinal cord diffusion tensor image

Purpose

To improve signal-noise-ratio of in vivo mouse spinal cord diffusion tensor imaging using-phase aligned multiple spin-echo technique.

Material and methods

In vivo mouse spinal cord diffusion tensor imaging maps generated by multiple spin-echo and conventional spin-echo diffusion weighting were examined to demonstrate the efficacy of multiple spin-echo diffusion sequence to improve image quality and throughput. Effects of signal averaging using complex, magnitude and phased images from multiple spin-echo diffusion weighting were also assessed. Bayesian probability theory was used to generate phased images by moving the coherent signals to the real channel to eliminate the effect of phase variation between echoes while preserving the Gaussian noise distribution. Signal averaging of phased multiple spin-echo images potentially solves both the phase incoherence problem and the bias of the elevated Rician noise distribution in magnitude image. The proposed signal averaging with Bayesian phase-aligned multiple spin-echo images approach was compared to the conventional spin-echo data acquired with doubling the scan time. The diffusion tensor imaging parameters were compared in the mouse contusion spinal cord injury. Significance level (p-value) and effect size (Cohen’s d) were reported between the control and contused spinal cord to inspect the sensitivity of each approach in detecting white matter pathology.

Results

Compared to the spin-echo image, the signal-noise-ratio increased to 1.84-fold using the phased image averaging and to 1.30-fold using magnitude image averaging in the spinal cord white matter. Multiple spin-echo phased image averaging showed improved image quality of the mouse spinal cord among the tested methods. Diffusion tensor imaging metrics obtained from multiple spin-echo phased images using three echoes and two averages closely agreed with those derived by spin-echo magnitude data with four averages (two times more in acquisition time). The phased image averaging correctly reflected pathological features in contusion spinal cord injury.

Conclusion

Our in vivo imaging results indicate that averaging the phased multiple spin-echo images yields an 84% signal-noise-ratio increase over the spin-echo images and a 41% gain over the magnitude averaged multiple spin-echo images with equal acquisition time. Current results from the animal model of spinal cord injury suggest that the phased multiple spin-echo images could be used to improve signal-noise-ratio.     

Continuous EEG-fMRI in patients with partial epilepsy and focal interictal slow-wave discharges on EEG

Purpose

To verify whether in patients with partial epilepsy and routine electroenecephalogram (EEG) showing focal interictal slow-wave discharges without spikes combined EEG–functional magnetic resonance imaging (fMRI) would localize the corresponding epileptogenic focus, thus providing reliable information on the epileptic source.

Methods

Eight patients with partial epileptic seizures whose routine scalp EEG recordings on presentation showed focal interictal slow-wave activity underwent EEG–fMRI. EEG data were continuously recorded for 24 min (four concatenated sessions) from 18 scalp electrodes, while fMRI scans were simultaneously acquired with a 1.5-Tesla magnetic resonance imaging (MRI) scanner. After recording sessions and MRI artefact removal, EEG data were analyzed offline. We compared blood oxygen level-dependent (BOLD) signal changes on fMRI with EEG recordings obtained at rest and during activation (with and without focal interictal slow-wave discharges).

Results

In all patients, when the EEG tracing showed the onset of focal slow-wave discharges on a few lateralized electrodes, BOLD-fMRI activation in the corresponding brain area significantly increased. We detected significant concordance between focal EEG interictal slow-wave discharges and focal BOLD activation on fMRI. In patients with lesional epilepsy, the epileptogenic area corresponded to the sites of increased focal BOLD signal.

Conclusions

Even in patients with partial epilepsy whose standard EEGs show focal interictal slow-wave discharges without spikes, EEG–fMRI can visualize related focal BOLD activation thus providing useful information for pre-surgical planning.     

Diffusion-weighted echo-planar imaging of the head and neck using 3-T MRI: Investigation into the usefulness of liquid perfluorocarbon pads and choice of optimal fat suppression method

Purpose

To investigate whether image quality can be improved using liquid perfluorocarbon pads (Sat Pad) and clarify the optimal fat-suppression method among chemical shift selective (CHESS), water excitation (WEX), and short TI inversion recovery (STIR) methods in diffusion-weighted imaging (DWI) of the head and neck using 3-T magnetic resonance imaging. Correlations between results of visual inspection and quantitative analysis were also examined.

Material and Methods

This study was approved by our Institutional Review Board and informed consent was waived. DWI was performed on 25 subjects with/without Sat Pad and using three fat-suppression methods (6 patterns). Image quality was evaluated visually (4-point scales and lesion-depiction capability) and by quantitative analysis (signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR)). Two-way repeated-measures analysis of variance (ANOVA) was used to detect significant differences in scores of visual evaluation, SNR, and CNR.

Results

Mean visual evaluation scores were significantly higher with Sat Pad using STIR than without Sat Pad for all fat-suppression methods (P < 0.05). DWI with Sat Pad using STIR tended to be useful for depicting lesions. DWI using STIR showed reduced W-SNR (W: whole area of depicted structure) and CNR (between semispinalis capitis muscle and subcutaneous fat) due to fewer artifacts and uniform fat suppression.

Conclusion

Combining Sat Pad with STIR provides good image quality for visual inspections. When numerous artifacts are present and fat suppression is insufficient, higher SNR and CNR do not always provide good diagnostic image quality.     

Depression recognition using resting-state and event-related fMRI signals

Purpose

This paper aimed to develop a method for depression detection using blood-oxygen-level-dependent (BOLD) response estimated from event-related signals and resting-state functional magnetic resonance imaging (fMRI) signals together.

Materials and Methods

Thirteen patients with unipolar depression and matched healthy subjects were recruited. Resting state data of each subject were collected. Thereafter, event-related paradigm was undertaken using sad facial stimuli. The resting-state fMRI signal was deemed as the baseline of each subject's activity. Coefficient marks were designed to sort and select temporal independent components of event-related signals. Thereafter, stimulus-evoked BOLD response components inside event-related signal were extracted and taken as features to discriminate depressive patients from healthy controls.

Results

Accuracy rate for depression recognition was 77.27% with P value of .017 for whole-brain analysis and 81.82% with P value of .009 for region-of-interest analysis. The effectiveness and the superiority of the proposed method for disease recognition were demonstrated via the performance comparison with three other typical methods.

Conclusions

The proposed model was effective in depression recognition.     

Dynamic magnetic resonance imaging of swallowing and laryngeal motion using parallel imaging at 3 T

Object

To evaluate the feasibility of an optimized MRI protocol based on high field imaging at 3 T in combination with accelerated data acquisition by parallel imaging for the analysis of oropharyngeal and laryngeal function.

Materials and Methods

Fast 2D gradient echo (GRE) MRI with different spatial resolutions (1.7×2.7 and 1.1×1.5 mm²) and image update rates (4 and 10 frames per second) was employed to assess pharyngeal movements and visualize swallowing via tracking of an oral contrast bolus (blueberry juice). In a study with 10 normal volunteers, image quality was semi-quantitatively graded by three independent observers with respect to the delineation of anatomical detail and depiction of oropharynx and larynx function. Additionally, the feasibility of the technique for the visualization of pathological pre- and post-surgical oropharynx and larynx function was evaluated in a patient with inspiratory stridor.

Results

Image grading demonstrated the feasibility of dynamic MRI for the assessment of normal oropharynx and larynx anatomy and function. Superior image quality (P<.05) was found for data acquisition with four frames per second and higher spatial resolution. In the patient, dynamic MRI detected pathological hypermobility of the epiglottis resulting in airway obstruction. Additional post-surgical MRI for one clinical case revealed morphological changes of the epiglottis and improved function, i.e., absence of airway obstruction and normal swallowing.

Conclusion

Results of the volunteer study demonstrated the feasibility of dynamic MRI at 3 T for the visualization of the oropharynx and larynx function during breathing, movements of the tongue and swallowing. Future studies are necessary to evaluate its clinical value compared to existing modalities based on endoscopy or radiographic techniques.     

A preliminary study of blood-oxygen-level-dependent MRI in patients with chronic kidney disease

Background

Blood-oxygen-level-dependent (BOLD) magnetic resonance imaging (MRI) can provide regional measurements of oxygen content using deoxyhemoglobin paramagnetic characteristics. The apparent relaxation rate or R2*(=1/T2*) can be determined from the slope of log (intensity) versus echo time and is directly proportional to the tissue content of deoxyhemoglobin. Thus, as the level of deoxyhemoglobin increases, T2* will decrease, leading to an increase in R2*. Chronic kidney disease (CKD) can affect oxygenation levels in renal parenchyma, which influences the clinical course of the disease. The goal of this study was to detect and assess renal oxygenation levels in CKD using BOLD MRI.

Methods

Fifteen healthy subjects and 11 patients with CKD underwent a renal scan using multigradient-recalled-echo sequence with eight echoes. R2* (1/s) of the renal cortex and medulla was measured on BOLD images. Of the 11 patients, nine had biopsy-proven chronic glomerulonephritis, and two had a similar diagnosis based on clinical symptoms and investigations.

Results

Mean medullary R2* (MR2*) and cortex R2* (CR2*) levels were significantly higher in patients (22 kidneys, MR2*=24.79±4.84 s⁻¹, CR2*=18.97±2.72 s⁻¹) than in controls (30 kidneys, MR2*=19.98±1.19 s⁻¹, CR2*=16.03±1.23 s⁻¹) (P<.01), and MR2* was increased more than CR2*. Medullary to cortical R2* ratios (MCR2*) of patients were significantly increased when compared with those of controls (P<.01). In the patient group, estimated glomerular filtration rate levels were greater than or equal to 60 ml/min/1.73 m² in six patients (12 kidneys), whose MR2* and CR2* were also significantly higher than those of controls (P<.01). Serum creatinine levels were normal in seven patients (14 kidneys), whose MR2*, CR2* and MCR2* were also higher than those of controls (P<.01).

Conclusions

BOLD MRI can be used to evaluate changes in renal oxygenation in CKD, suggesting that it has the potential to be an excellent noninvasive tool for the evaluation of renal function.     

Changes in cerebral activity after decreased upper-limb hypertonus: an EMG-fMRI study

Objective

Whereas several studies have used functional magnetic resonance imaging (fMRI) to investigate motor recovery, whether therapy to decrease post-stroke hypertonus alters central motor patterns remains unclear. In this study, we used continuous electromyography (EMG)-fMRI to investigate possible changes in movement-related brain activation in patients receiving Botulinum toxin (BoNT-A) for hand-muscle hypertonus after chronic stroke.

Methods

We studied eight stroke patients all of whom had hemiparesis and associated upper-limb hypertonus. All patients underwent an fMRI-EMG recording and clinical-neurological assessment before BoNT-A and 5 weeks thereafter. The handgrip motor task during imaging was fixed across both patients and controls. The movements were metronome paced, movement amplitude and force were controlled with a plastic orthosis, dynamometer and EMG recording. An age-matched control group was recruited from among healthy volunteers underwent the same fMRI-EMG recording.

Results

Before BoNT-A, while patients moved the paretic hand, fMRI detected wide bilateral activation in the sensorymotor areas (SM1), in the supplementary motor area (SMA) and cerebellum. After BoNT-A blood oxygenation level-dependent (BOLD) activation decreased in ipsilateral and contralateral motor areas and became more lateralized. BOLD activation decreased also in ipsilateral cerebellar regions and in the SMA.

Conclusion

Changes in peripheral upper-limb hypertonus after BoNT-A were associated to an improvement in active movements and more lateralized and focalized activation of motor areas. The clinical and EMG-fMRI coregistration technique we used to study hand-muscle hypertonus in patients receiving BoNT-A after chronic stroke should be useful in future studies seeking improved strategies for post-stroke neurorehabilitation.     

A next-generation,flow-diverting implant used to treat brain aneurysms: in vitro evaluation of magnetic field interactions,heating and artifacts at 3-T

Background and Purpose

Fine-mesh braided, stent-like structures (flow diverters) have been proposed for treatment of brain aneurysms. To date, the safety of performing magnetic resonance imaging (MRI) in patients with these implants is unknown. Therefore, the purpose of this study was to evaluate MRI issues at 3-T for a new flow-diverting implant used to treat brain aneurysms.

Methods

The Surpass NeuroEndoGraft (Surpass Medical, Ltd., Tel Aviv, Israel) underwent evaluation for magnetic field interactions, MRI-related heating and artifacts using standardized techniques. Magnetic field interactions were assessed for this implant with regard to translational attraction (i.e., using the deflection angle technique) and torque (qualitative assessment method). MRI-related heating was evaluated by placing the implant in a gelled-saline-filled, head/torso phantom and performing MRI using a transmit/receive radiofrequency body coil at a whole-body-averaged specific absorption rate of 2.9 W/kg for 15 min. Artifacts were characterized using T1-weighted, spin echo (SE) and gradient echo (GRE) pulse sequences.

Results

The Surpass NeuroEndoGraft exhibited minor magnetic field interactions (21° deflection angle and no torque), which were acceptable from a safety consideration. Heating was not substantial, with the highest temperature change being 2.3°C (background temperature rise without the implant was 1.5°C). Artifacts may create issues if the area of interest is in the same area or close to this implant.

Conclusions

The findings demonstrated that it would be acceptable for patients with this next-generation, flow-diverting implant to undergo MRI at 3-T or less.     

Fast volumetric spatial-spectral MR imaging of hyperpolarized C-labeled compounds using multiple echo 3D bSSFP

Purpose

The goal of this work was to develop a fast 3D chemical shift imaging technique for the noninvasive measurement of hyperpolarized ¹³C-labeled substrates and metabolic products at low concentration.

Materials and Methods

Multiple echo 3D balanced steady state magnetic resonance imaging (ME-3DbSSFP) was performed in vitro on a syringe containing hyperpolarized [1,3,3-2H3; 1-¹³C]2-hydroxyethylpropionate (HEP) adjacent to a ¹³C-enriched acetate phantom, and in vivo on a rat before and after intravenous injection of hyperpolarized HEP at 1.5 T. Chemical shift images of the hyperpolarized HEP were derived from the multiple echo data by Fourier transformation along the echoes on a voxel by voxel basis for each slice of the 3D data set.

Results

ME-3DbSSFP imaging was able to provide chemical shift images of hyperpolarized HEP in vitro, and in a rat with isotropic 7-mm spatial resolution, 93 Hz spectral resolution and 16-s temporal resolution for a period greater than 45 s.

Conclusion

Multiple echo 3D bSSFP imaging can provide chemical shift images of hyperpolarized ¹³C-labeled compounds in vivo with relatively high spatial resolution and moderate spectral resolution. The increased signal-to-noise ratio of this 3D technique will enable the detection of hyperpolarized ¹³C-labeled metabolites at lower concentrations as compared to a 2D technique.     

Fractional amplitude of low-frequency fluctuation changes in monkeys with spinal cord injury: A resting-state fMRI study

Purpose

Although functional magnetic resonance imaging (fMRI) has revealed that spinal cord injury (SCI) causes anomalous changes in task-induced brain activation, its effect during the resting state remains unclear. The aim of this study is to explore the changes of the brain resting-state function in non-human primates with unilateral SCI.

Materials and methods

Eleven adult female rhesus monkeys were subjected to resting-state fMRI: five with unilateral thoracic SCI and six healthy monkeys, to obtain the fractional amplitude of low-frequency fluctuations (fALFF) of the blood oxygenation level-dependent (BOLD) contrast signal to determine the influence of SCI on the cerebral resting-state function.

Results

The SCI-induced fALFF vary significantly in several encephalic regions, including the left cerebellum, the left thalamus, the right lateral geniculate nucleus, the right superior parietal lobule, and the posterior cingulate gyrus.

Conclusion

Analysis of the resting-state fMRI provides evidence of abnormal spontaneous brain activations in primates with SCI, which may help us understand the pathophysiologic mechanisms underlying the changes in neural plasticity in the central nervous system after SCI.     

3D high-resolution contrast enhanced MRI of carotid atheroma — a technical update

Objective

Development of a fast 3D high-resolution magnetic resonance imaging (MRI) protocol for improved carotid artery plaque imaging.

Methods

Two patients with carotid atherosclerosis disease underwent 3D high-resolution MRI which included time-of-flight and T₁-weighted variable flip angle, fast-spin-echo (FSE) imaging, pre- and post-intravenous gadolinium-based contrast agent administration.

Results

Good quality images with intrinsic blood suppression were obtained pre- and post-contrast administration using a 3D FSE sequence. The plaque burden, lipid core volume, hemorrhage volume and fibrous cap thickness were well determined.

Conclusions

3D high-resolution MR imaging of carotid plaque using TOF and 3D FSE can achieve high isotropic resolution, large coverage, and excellent image quality within a short acquisition time.     

High-resolution intracranial MRA at 7T using autocalibrating parallel imaging: initial experience in vascular disease patients

Purpose

Greater spatial resolution in intracranial three-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA) is possible at higher field strengths, due to the increased contrast-to-noise ratio (CNR) from the higher signal-to-noise ratio and the improved background suppression. However, at very high fields, spatial resolution is limited in practice by the acquisition time required for sequential phase encoding. In this study, we applied parallel imaging to 7T TOF MRA studies of normal volunteers and patients with vascular disease, in order to obtain very high resolution (0.12 mm³) images within a reasonable scan time.

Materials and Methods

Custom parallel imaging acquisition and reconstruction methods were developed for 7T MRA, based on generalized autocalibrating partially parallel acquisition (GRAPPA). The techniques were compared and applied to studies of seven normal volunteers and three patients with cerebrovascular disease.

Results

The technique produced high resolution studies free from discernible reconstruction artifacts in all subjects and provided excellent depiction of vascular pathology in patients.

Conclusions

7T TOF MRA with parallel imaging is a valuable noninvasive angiographic technique that can attain very high spatial resolution.     

A new vascular coupling device: Assessment of MRI issues at 3-tesla

Objective

Vascular grafting frequently involves a time-consuming operation. A new vascular coupling device (VCD) made from metallic material was recently developed that may be advantageous because of the reduced operative time and decreased patient risks. Because of the metal, there are safety concerns related to MRI. Therefore, the purpose of this investigation was to use standardized testing techniques to evaluate MRI issues for this VCD in association with a 3-Tesla MR system.

Methods

The VCD (corlife oHG, Hannover, Germany) was evaluated for magnetic field interactions (translational attraction and torque), MRI-related heating, and artifacts at 3-Tesla. MRI-related heating was assessed with the VCD in a gelled-saline-filled phantom with MRI performed at a whole body averaged SAR of 2.9-W/kg for 15-min. Artifacts were assessed using T1-weighted, spin echo, and gradient echo pulse sequences.

Results

The VCD exhibited minor magnetic field interactions and minimal heating (maximum temperature elevation, 1.8 °C). Artifacts were relatively small in relation to the size and shape of this implant. The lumen of the VCD could not be visualized using the gradient echo pulse sequence.

Conclusions

The metallic VCD that underwent evaluation is MR conditional for a patient undergoing an MRI procedure at 3-Tesla or less.     

Detection of bone metastases using diffusion weighted magnetic resonance imaging: comparison with C-methionine PET and bone scintigraphy

Purpose

We evaluated the ability of diffusion-weighted imaging (DWI) to detect bone metastasis by comparing the results obtained using this modality with those obtained using ¹¹C-methionine (MET) positron emission tomography (PET) and bone scintigraphy.

Materials and methods

This retrospective study involved 29 patients with bone metastasis. DWI was obtained using a single-shot echo planar imaging (EPI) sequence with fat suppression using a short inversion time inversion recovery sequence. The detection capabilities of DWI for bone metastases were compared with those of whole body MET PET (in 19 patients) and 99mTc-methylene diphosphonate bone scintigraphy (in 15 patients).

Results

Among the 19 patients who were diagnosed using DWI and PET, the PET identified 39 bone metastases, while the DWI identified 60 metastases out of 69 metastases revealed with conventional magnetic resonance imaging (MRI). Among the 15 patients who were diagnosed using DWI and bone scintigraphy, the bone scintigraphy identified 18 bone metastases, while the DWI identified 72 metastases out of 78 metastases revealed with conventional MRI. The overall bone metastasis detection rates were 56.5% for PET, 23.1% for bone scintigraphy and 92.3% for DWI.

Conclusion

DWI is a very sensitive method for detecting bone metastasis and is superior to MET PET and bone scintigraphy in terms of its detection capabilities.     

Unfolding the long-term pathophysiological processes following an acute inflammatory demyelinating lesion of multiple sclerosis

Background

Acute symptomatic inflammation is a main feature of multiple sclerosis but pathophysiological processes underlying total or partial recovery are poorly understood.

Objective

To characterize in vivo these processes at molecular, structural and functional levels using multimodal MR methods.

Methods

A neuroimaging 3-year follow-up (Weeks 0, 3, 11, 29, 59 and 169) was conducted on a 41-year-old woman presenting at baseline with a large acute demyelinating lesion of multiple sclerosis. Conventional magnetic resonance imaging (MRI), magnetization transfer imaging, diffusion-weighted imaging, functional MRI and magnetic resonance spectroscopy were conducted at 1.5 T.

Results

Patient presenting with subacute left hemiplegia recovered progressively (expended disability status scale 7 to 5.5). The MR exploration demonstrated structural functional and metabolic impairments at baseline. Despite restoration of the blood brain barrier integrity, high lactate levels persisted for several weeks concomitant with glial activation. Slow and progressive structural and metabolic restorations occurred from baseline to W169 (lesion volume −64%; apparent diffusion coefficient −14.7%, magnetization transfer ratio +14%, choline −51%, lipids −78%, N-acetylaspartate +77%) while functionality of the motor system recovered.

Conclusions

Multimodal MRI/MRS evidenced long-term dynamics recovery processes involving tissue repair, glial activation, recovery of neuronal function and functional systems. This may impact on customized rehabilitation strategies generally focused on the first months following the onset of symptoms.     

Informatics methods to enable sharing of quantitative imaging research data

Introduction

The National Cancer Institute Quantitative Research Network (QIN) is a collaborative research network whose goal is to share data, algorithms and research tools to accelerate quantitative imaging research. A challenge is the variability in tools and analysis platforms used in quantitative imaging. Our goal was to understand the extent of this variation and to develop an approach to enable sharing data and to promote reuse of quantitative imaging data in the community.

Methods

We performed a survey of the current tools in use by the QIN member sites for representation and storage of their QIN research data including images, image meta-data and clinical data. We identified existing systems and standards for data sharing and their gaps for the QIN use case. We then proposed a system architecture to enable data sharing and collaborative experimentation within the QIN.

Results

There are a variety of tools currently used by each QIN institution. We developed a general information system architecture to support the QIN goals. We also describe the remaining architecture gaps we are developing to enable members to share research images and image meta-data across the network.

Conclusions

As a research network, the QIN will stimulate quantitative imaging research by pooling data, algorithms and research tools. However, there are gaps in current functional requirements that will need to be met by future informatics development. Special attention must be given to the technical requirements needed to translate these methods into the clinical research workflow to enable validation and qualification of these novel imaging biomarkers.     

Optimal techniques for magnetic resonance imaging of the liver using a respiratory navigator-gated three-dimensional spoiled gradient-recalled echo sequence

Purpose

To optimize the navigator-gating technique for the acquisition of high-quality three-dimensional spoiled gradient-recalled echo (3D SPGR) images of the liver during free breathing.

Materials and methods

Ten healthy volunteers underwent 3D SPGR magnetic resonance imaging of the liver using a conventional navigator-gated 3D SPGR (cNAV-3D-SPGR) sequence or an enhanced navigator-gated 3D SPGR (eNAV-3D-SPGR) sequence. No exogenous contrast agent was used. A 20-ms wait period was inserted between the 3D SPGR acquisition component and navigator component of the eNAV-3D-SPGR sequence to allow T1 recovery. Visual evaluation and calculation of the signal-to-noise ratio were performed to compare image quality between the imaging techniques.

Result

The eNAV-3D-SPGR sequence provided better noise properties than the cNAV-3D-SPGR sequence visually and quantitatively. Navigator gating with an acceptance window of 2 mm effectively inhibited respiratory motion artifacts. The widening of the window to 6 mm shortened the acquisition time but increased motion artifacts, resulting in degradation of overall image quality. Neither slice tracking nor incorporation of short breath holding successfully compensated for the widening of the window.

Conclusion

The eNAV-3D-SPGR sequence with an acceptance window of 2 mm provides high-quality 3D SPGR images of the liver.     

Focal fat deposition at liver MRI with gadobenate dimeglumine and gadoxetic acid: Quantitative and qualitative analysis

Objective

To evaluate the image findings of focal fat deposition (FFD) in the liver on gadobenate dimeglumine (Gd-BOPTA)- and gadoxetic acid (Gd-EOB-DTPA)-enhanced MRI, particularly during the hepatobiliary phase (HBP), and the relationship between relative enhancement (RE) and fat signal fraction (FSF) of FFD.

Subjects and Methods

Twenty-one patients with 27 FFDs (mean diameter, 21.9 mm), which showed low signal intensity on opposed-phase compared with in-phase MRI, were retrospectively evaluated. RE of the liver (RE_liver) and FFD (RE_FFD) and liver-to-lesion contrast-to-noise ratio (CNR) of FFD were measured on dynamic phases and HBP images with fat-saturated in-phase gradient-echo sequence. The FSF of each FFD was measured on in- and opposed-phase dual gradient-echo images. We qualitatively analyzed imaging findings of FFDs, including signal intensity, shape, margin, and homogeneity on HBP images, and enhancement pattern during dynamic phases. The correlations between RE_FFD and FSF and between CNR and FSF on HBP images were evaluated using Pearson’s correlation tests and a simple linear regression model.

Results

There were no significant differences between RE_FFD and RE_liver in dynamic phases and HBP, regardless of contrast agents (p ≥ 0.075). On HBP images, CNR (p = 0.008) but not RE_FFD (p = 0.122) was significantly correlated with FSF of FFDs (mean FSF, 19%). On HBP images, 21 of the 27 (77.8%) FFDs were hypointense, and 17 (63%) were homogeneous. Of the 21 hypointense FFDs, 12 (57.1%) had an ovoid shape and 11 (52.4%) were well margined. Although the 27 FFDs showed various enhancement patterns, 17 (63%) showed no enhancement.

Conclusion

Most FFDs appeared as hypointense lesions on Gd-BOPTA- and Gd-EOB-DTPA-enhanced MRI during HBP, with various enhancement patterns during dynamic contrast-enhanced phases. RE_FFD on HBP images was not significantly correlated with FSF of low grade FFDs.     

Microimaging of hairless rat skin by magnetic resonance at 900 MHz

Purpose

Quantitative imaging of the rat skin was performed using magnetic resonance imaging (MRI) at 900 MHz.

Materials and methods

A number of imaging techniques utilized for multiple contrast included magnetization transfer contrast, spin-lattice relaxation constant (T1-weighting), combination of T2-weighting with magnetic field inhomogeneity (T2*-weighting), magnetization transfer weighting and diffusion tensor weighting. These were used to obtain 2D slices and 3D multislice-multiecho images with high magnetic resonance contrast. These 2D and 3D imaging techniques were combined to achieve high-resolution MRI.

Results

Oil–water phantom showed distinct fat-water contrast. The dermis and epidermis, including the stratum corneum remnants, of nude rat skin were distinct due to their proton magnetic resonance as a result of proton interactions with the skin interstitial tissue. Combined details obtained from high-resolution, high-quality ex vivo skin images with different multicontrast characteristics generated better differentiation of skin layers, sublayers and significant correlation (r²=0.4927 for MRI area, r²=0.3068 for histology area; P<.0148) of MR data with co-registered histological areas of the epidermis as well as the hair follicle.

Conclusion

The multiple contrast approach provided a noninvasive ex vivo MRI visualization with semi-quantitative assessment of the major skin structures including the stratum corneum remnants, epidermis, hair, papillary dermis, reticular dermis and hypodermis.     

Intracranial microvascular imaging at 7 T MRI with transceiver RF coils

Purpose

To investigate intracranial microvascular images with transceiver radio-frequency (RF) coils at ultra-high field 7 T magnetic resonance imaging (MRI).

Materials and methods

We designed several types of RF coils for the study of 7 T magnetic resonance angiography and analyzed quantitatively each coil's performance in terms of the signal-to-noise ratio (SNR) profiles to evaluate the usefulness of RF coils for microvascular imaging applications. We also obtained the microvascular images with different resolutions and parallel imaging technique.

Results

The overlapped 6-channel (ch) transceiver coil exhibited the highest performance for angiographic imaging. Although other multi-channel coils, such as 4- or 8-ch, were also suitable for fast imaging, these coils performed poorly in homogeneity or SNR for angiographic imaging. Furthermore, the 8-ch coil was poor in SNR at the center of the brain, while it had the highest SNR at the periphery.

Conclusion

The present study has demonstrated that the overlapped 6-ch coil with large-size loop coils provided the best performance for microvascular imaging or angiography with the ultra-high-field 7 T MRI, mainly because of its long penetration depth together with high SNR.