Reliability of cerebral blood volume maps as a substitute for diffusion‐weighted imaging in acute ischemic stroke

Purpose:

To assess the reliability of cerebral blood volume (CBV) maps as a substitute for diffusion‐weighted MRI (DWI) in acute ischemic stroke. In acute stroke, DWI is often used to identify irreversibly injured “core” tissue. Some propose using perfusion imaging, specifically CBV maps, in place of DWI. We examined whether CBV maps can reliably subsitute for DWI, and assessed the effect of scan duration on calculated CBV.

Materials and Methods:

We retrospectively identified 58 patients who underwent DWI and MR perfusion imaging within 12 h of stroke onset. CBV in each DWI lesion's center was divided by CBV in the normal‐appearing contralateral hemisphere to yield relative regional CBV (rrCBV). The proportion of lesions with decreased rrCBV was calculated. After using the full scan duration (110 s after contrast injection), rrCBV was recalculated using simulated shorter scans. The effect of scan duration on rrCBV was tested with linear regression.

Results:

Using the full scan duration (110 s), rrCBV was increased in most DWI lesions (62%; 95% confidence interval, 48–74%). rrCBV increased with increasing scan duration (P < 0.001). Even with the shortest duration (39.5 s) rrCBV was increased in 33% of lesions.

Conclusion:

Because DWI lesions may have elevated or decreased CBV, CBV maps cannot reliably substitute for DWI in identifying the infarct core. J. Magn. Reson. Imaging 2012;36:1083–1087. © 2012 Wiley Periodicals, Inc.     

Spatiotemporal dynamics of low frequency fluctuations in BOLD fMRI of the rat

Purpose

To examine spatiotemporal dynamics of low frequency fluctuations in rat cortex.

Materials and Methods

Gradient‐echo echo‐planar imaging images were acquired from anesthetized rats (repetition time = 100 ms). Power spectral analysis was performed to detect different frequency peaks. Functional connectivity maps were obtained for the frequency peaks of interest. The images in the filtered time‐series were displayed as a movie to study spatiotemporal patterns in the data for frequency bands of interest.

Results

High temporal and spectral resolution allowed separation of primary components of physiological noise and visualization of spectral details. Two low frequency peaks with distinct characteristics were observed. Selective visualization of the second low frequency peak revealed waves of activity that typically began in the secondary somatosensory cortex and propagated to the primary motor cortex.

Conclusion

To date, analysis of these fluctuations has focused on the detection of functional networks assuming steady state conditions. These results suggest that detailed examination of the spatiotemporal dynamics of the low frequency fluctuations may provide more insight into brain function, and add a new perspective to the analysis of resting state fMRI data. J. Magn. Reson. Imaging 2009;30:384–393. © 2009 Wiley‐Liss, Inc.     

Perfusion MRI in neuro‐psychiatric systemic lupus erthemathosus

Purpose:

To use perfusion weighted MR to quantify any perfusion abnormalities and to determine their contribution to neuropsychiatric (NP) involvement in systemic lupus erythematosus (SLE).

Materials and methods:

We applied dynamic susceptibility contrast (DSC) perfusion MRI in 15 active NPSLE, 26 inactive NPSLE patients, and 11 control subjects. Cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) maps were reconstructed and regions of interest were compared between groups. In addition, the effect of SLE criteria, NPSLE syndromes, immunological coagulation disorder, and medication on CBF, CBV, and MTT was investigated.

Results:

No significant differences were found between the groups in CBF, CBV, and MTT. No significant influence of SLE criteria or NPSLE syndromes on CBF, CBV, or MTT was found. No significant influence of anti‐cardiolipin antibodies, lupus anti‐coagulant, the presence of anti‐phospholipid syndrome (APS), or medication on CBF, CBV, or MTT was found.

Conclusion:

Our findings suggest CBF, CBV, and MTT in the white and the gray matter in SLE patients is not significantly different from healthy controls or between patients with and without specific symptoms or with and without immunological disorder involving coagulation. J. Magn. Reson. Imaging 2010;32:283–288. © 2010 Wiley‐Liss, Inc.     

Vascular space occupancy (VASO) cerebral blood volume‐weighted MRI identifies hemodynamic impairment in patients with carotid artery disease

Purpose

To assess the role of vascular space occupancy (VASO) magnetic resonance imaging (MRI), a noninvasive cerebral blood volume (CBV)‐weighted technique, for evaluating CBV reactivity in patients with internal carotid artery (ICA) stenosis.

Materials and Methods

VASO reactivity, defined as a signal change in response to hypercapnic stimulus (4‐second exhale, 14‐second breath‐hold), was measured in the left and right ICA flow territories in patients (n = 10) with varying degrees of unilateral and bilateral ICA stenosis and in healthy volunteers (n = 10).

Results

Percent VASO reactivity was more negative (P < 0.01) bilaterally in patients (ipsilateral: ?3.6 ± 1.5%; contralateral: ?3.4 ± 1.2%) compared with age‐matched controls (left: ?1.9 ± 0.6%; right: ?1.9 ± 0.8%). Owing to the nature of the VASO contrast mechanism, this more negative VASO reactivity was attributed to autoregulatory CBV effects in patients. A postbreath‐hold overshoot, which was absent in healthy volunteers, was observed unilaterally in a subset of patients.

Conclusion

More negative VASO reactivity was observed in patients with ICA stenosis and may be a marker of autoregulatory effects. Furthermore, the postbreath‐hold overshoot observed in patients is consistent with compensatory microvascular vasoconstriction and may be a marker of hemodynamic impairment. Based on the results of this feasibility study, VASO should be useful for identifying CBV adjustments in patients with steno‐occlusive disease of the ICA. J. Magn. Reson. Imaging 2009;29:718–724. © 2009 Wiley‐Liss, Inc.

     

Pharmacological modulation of the BOLD response: a study of acetazolamide and glyceryl trinitrate in humans

Purpose:

To examine the effect of acetazolamide, known to increase cerebral blood flow (CBF) and glyceryl trinitrate (GTN), known to increase cerebral blood volume (CBV) on the blood oxygenation level‐dependent (BOLD) response in humans using 3 T magnetic resonance imaging (MRI), and to evaluate how pharmacological agents may modulate cerebral hemodynamic and thereby possibly the BOLD signal.

Materials and Methods:

Six subjects were randomly allocated to receive acetazolamide, GTN, or placebo in a double‐blind three‐way crossover controlled study. Before, during, and after drug administration we recorded the BOLD response during visual stimulation with reversing checkerboard.

Results:

We found that acetazolamide caused significant depression of the BOLD response (P = 0.0066). The maximum decrease occurred at 5 minutes after infusion and was 51.9% (95% confidence interval [CI], 22.03–81.76). GTN did not influence the BOLD response (P = 0.55).

Conclusion:

The BOLD response is decreased during increased CBF by acetazolamide, suggesting an inverse relationship between global CBF and the BOLD response. GTN does not change the BOLD response. This indicates that GTN exerts an effect on the large vessels only and that CBV changes in the microvascular system are necessary to alter the BOLD response. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Detecting blood oxygen level‐dependent (BOLD) contrast in the breast

Purpose:

To develop a robust technique for detecting blood oxygenation level‐dependent (BOLD) contrast in the human breast and to evaluate the signal in healthy and malignant breast.

Materials and Methods:

The design of this study focused on determining the optimal pulse sequence and stimulus for detecting BOLD contrast in the breast. For this study a single‐shot fast spin echo (SSFSE) sequence was compared to a gradient echo (GRE) pulse sequence. Also, several hyperoxic stimuli were tested on 15 healthy volunteers to determine the best stimulus for inducing BOLD contrast in the breast: air interleaved with carbogen (95% O₂, 5% CO₂), air interleaved with oxygen, and oxygen interleaved with carbogen. The stimulus with the most consistent results among the healthy population was tested on three breast cancer patients.

Results:

An SSFSE pulse sequence produced improved BOLD contrast results in the breast compared to a GRE pulse sequence. Oxygen interleaved with carbogen yielded the most consistent results in the healthy population. BOLD contrast in healthy glandular breast tissue positively correlates with carbogen and malignant tissue mostly negatively correlates to carbogen.

Conclusion:

BOLD contrast can consistently be detected in the breast using a robust protocol. This methodology may be used in the future as a noninvasive method for evaluating tumor oxygenation. J. Magn. Reson. Imaging 2010;32:120–129. © 2010 Wiley‐Liss, Inc.     

Test-retest stability analysis of resting brain activity revealed by blood oxygen level-dependent functional MRI

Purpose:

To assess test–retest stability of four functional magnetic resonance imaging (fMRI)‐derived resting brain activity metrics: the seed‐region‐based functional connectivity (SRFC), independent component analysis (ICA)‐derived network‐based FC (NTFC), regional homogeneity (ReHo), and the amplitude of low frequency fluctuation (ALFF).

Methods:

Simulations were used to assess the sensitivity of SRFC, ReHo, and ALFF to noise interference. Repeat resting blood oxygen level‐dependent (BOLD) fMRI were acquired from 32 healthy subjects. The intraclass correlation coefficient (ICC) was used to assess the stability of the four metrics.

Results:

Random noise yielded small random SRFC, small but consistent ReHo and ALFF. A neighborhood size greater than 20 voxels should be used for calculating ReHo in order to reduce the noise interference. Both the anterior cingulate cortex (ACC) and posterior cingulate cortex (PCC)‐based SRFC were reproducible in more spatially extended regions than ICA NTFC. The two regional spontaneous brain activity (SBA) measures, ReHo and ALFF, showed test–retest reproducibility in almost the whole gray matter.

Conclusion:

SRFC, ReHo, and ALFF are robust to random noise interference. The neighborhood size for calculating ReHo should be larger than 20 voxels. ICC > 0.5 and cluster size > 11 should be used to assess the ICC maps for ACC/PCC SRFC, ReHo, and ALFF. BOLD fMRI‐based SBA can be reliably measured using ACC/PCC SRFC, ReHo, and ALFF after 2 months. J. Magn. Reson. Imaging 2012;36:344–354. ©2012 Wiley Periodicals, Inc.     

Breathhold‐regulated blood oxygenation level‐dependent (BOLD) MRI of human brain at 3 tesla

Purpose:

To investigate the cerebrovascular response to repeated breathhold challenges using blood oxygenation level‐dependent (BOLD) MRI at 3T and compare the results with previous data at 1.5T.

Materials and Methods:

Six normal volunteers and six patients with brain tumors were recruited for this 3T study. For the normal group, BOLD MRI during repeated breathholds of different durations (five to 30 seconds) were acquired. Maximum signal change, full‐width at half‐maximum (FWHM) and onset time (defined as the time to the first half‐maximum) were determined by curve fitting. The fractional activation volume was also calculated. Patients performed a 10‐ or 15‐second breathhold paradigm according to individual capability.

Results:

Significant BOLD signal increases in the gray matter for a breathhold period as short as 5 seconds at 3T, instead of 10 seconds at 1.5T. The fractional activation volume vs. breathhold duration reached a plateau of 49.54 ± 7.26% at 15 seconds at 3T, which was higher and shorter than that at 1.5T. The maximum signal changes were significantly larger (a 69% increase) at 3T than at 1.5T. In the patient group, there were BOLD signal increases in gray matter but not in tumor bulk or perifocal edema, which agreed with the results previously found at 1.5T.

Conclusion:

BOLD MRI at 3T is more sensitive for detecting breathhold‐regulated signal changes than at 1.5T, which allows a shorter and more feasible breathhold paradigm for clinical applications in patients with brain tumors. J. Magn. Reson. Imaging 2010;31:78–84. © 2009 Wiley‐Liss, Inc.     

Artifact‐reduced two‐dimensional cine steady state free precession for myocardial blood‐ oxygen‐level‐dependent imaging

Purpose:

To minimize image artifacts in long TR cardiac phase‐resolved steady state free precession (SSFP) based blood‐oxygen‐level‐dependent (BOLD) imaging.

Materials and Methods:

Nine healthy dogs (four male, five female, 20–25 kg) were studied in a clinical 1.5 Tesla MRI scanner to investigate the effect of temporal resolution, readout bandwidth, and motion compensation on long repetition time (TR) SSFP images. Breath‐held 2D SSFP cine sequences with various temporal resolutions (10–204 ms), bandwidths (239–930 Hz/pixel), with and without first‐order motion compensation were prescribed in the basal, mid‐ventricular, and apical along the short axis. Preliminary myocardial BOLD studies in dogs with controllable coronary stenosis were performed to assess the benefits of artifact‐reduction strategies.

Results:

Shortening the readout time by means of increasing readout bandwidth had no observable reduction in image artifacts. However, increasing the temporal resolution in the presence of first‐order motion compensation led to significant reduction in image artifacts. Preliminary studies demonstrated that BOLD signal changes can be reliably detected throughout the cardiac cycle.

Conclusion:

Artifact‐reduction methods used in this study provide significant improvement in image quality compared with conventional long TR SSFP BOLD MRI. It is envisioned that the methods proposed here may enable reliable detection of myocardial oxygenation changes throughout the cardiac cycle with long TR SSFP‐based myocardial BOLD MRI. J. Magn. Reson. Imaging 2010;31:863–871. ©2010 Wiley‐Liss, Inc.     

Comparison between intensity normalization techniques for dynamic susceptibility contrast (DSC)-MRI estimates of cerebral blood volume (CBV) in human gliomas

Purpose:

To compare “standardization,” “Gaussian normalization,” and “Z‐score normalization” intensity transformation techniques in dynamic susceptibility contrast magnetic resonance imaging (DSC‐MRI) estimates of cerebral blood volume (CBV) in human gliomas. DSC‐MRI is a well‐established biomarker for CBV in brain tumors; however, DSC‐MRI estimates of CBV are semiquantitative. The use of image intensity transformation algorithms provides a mechanism for obtaining quantitatively similar CBV maps with the same intensity scaling.

Materials and Methods:

The coefficient of variance (CV) in normal‐appearing white matter and relative contrast between tumor regions and normal tissue was compared between the three CBV transformations across five different MR scanners in 96 patients with gliomas.

Results:

The results suggest all normalization techniques improved variability and relative tumor contrast of CBV measurements compared with nonnormalized CBV maps. The results suggest Gaussian normalization of CBV maps provided slightly lower CV in normal white matter and provided slightly higher tumor contrast for glioblastomas (WHO grade IV) compared with other techniques.

Conclusion:

The results suggest Gaussian normalization of leakage‐corrected CBV maps may be the best choice for image intensity correction for use in large‐scale, multicenter clinical trials where MR scanners and protocols vary widely due to ease of implementation, lowest variability, and highest tumor to normal tissue contrast. J. Magn. Reson. Imaging 2012;35:1472–1477. © 2012 Wiley Periodicals, Inc.     

T1-weighted functional imaging based on a contrast agent in presurgical mapping

Purpose

To assess the applicability of T1‐weighted images in the presence of a contrast agent for functional mapping free of susceptibility artifacts, in comparison to the blood oxygenation level‐dependent (BOLD) imaging.

Materials and Methods

Six patients and five control subjects were scanned using BOLD and T1‐weighted functional imaging, in the presence of a Gd‐DTPA contrast‐agent (TOFICA). In the control group, low‐ and high‐resolution BOLD images were performed. Functional stimuli included motor and language activations.

Results

Both BOLD and TOFICA methods resulted in activations in the expected anatomical regions. The TOFICA mapping gave less distributed and with higher percent signal changes in comparison with the BOLD images. Gd‐DTPA remained almost constant in the blood for at least 15 min post injection. In one patient with surgical clips, no signal was detected in the left cerebral hemisphere using BOLD imaging, but activation could be mapped using the TOFICA method.

Conclusion

T1‐weighted imaging in the presence of a contrast agent can be used for functional mapping. This method is insensitive to susceptibility artifacts, and is therefore advantageous in the evaluation of presurgical cases and in areas of the brain close to cavities in which the BOLD method cannot reliably be applied. J. Magn. Reson. Imaging 2008;28:1245–1250. © 2008 Wiley‐Liss, Inc.     

Perfusion parameters derived from bolus‐tracking perfusion imaging are immune to tracer recirculation

Purpose:

To investigate the impact of tracer recirculation on estimates of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT).

Materials and Methods:

The theoretical model used to derive CBF, CBV, and MTT was examined. CBF and CBV estimates with and without tracer recirculation were compared in computer simulations to examine the effects of tracer recirculation.

Results:

The equations used to derive CBF, CBV, and MTT assume that the arterial input function and tissue tracer signals define the input and output signals, respectively, of a linear time‐invariant system. As a result of the principle of superposition, these perfusion parameters are immune to tracer recirculation, which was confirmed by computer simulation. However, limited acquisition durations can lead to CBV and CBF errors of up to 50%.

Conclusion:

Tracer recirculation does not impact estimation of CBF, CBV, or MTT. However, previous approaches used to remove recirculation effects may be beneficial when used to compensate for limited acquisition durations in which the passage of the bolus is not adequately captured. J. Magn. Reson. Imaging 2010;31:753–756. © 2010 Wiley‐Liss, Inc.     

Comparison of k‐t SENSE/k‐t BLAST with conventional SENSE applied to BOLD fMRI

Purpose:

To compare k‐t BLAST (broad‐use linear‐acquisition speedup technique)/k‐t SENSE (sensitivity encoding) with conventional SENSE applied to a simple fMRI paradigm.

Materials and Methods:

Blood oxygen level‐dependent (BOLD) functional magnetic resonance imaging (fMRI) was performed at 3 T using a displaced ultra‐fast low‐angle refocused echo (UFLARE) pulse sequence with a visual stimulus in a block paradigm. Conventional SENSE and k‐t BLAST/k‐t SENSE data were acquired. Also, k‐t BLAST/k‐t SENSE was simulated at different undersampling factors from fully sampled data after removal of lines of k‐space data. Analysis was performed using SPM5.

Results:

Sensitivity to the BOLD response in k‐t BLAST/k‐t SENSE was comparable with that of SENSE in images acquired at an undersampling factor of 2.3. Simulated k‐t BLAST/k‐t SENSE yielded reliable detection of activation‐induced BOLD contrast at undersampling factors of 5 or less. Sensitivity increased significantly when training data were included in k‐space before Fourier transformation (known as “plug‐in”).

Conclusion:

k‐t BLAST/k‐t SENSE performs at least as well as conventional SENSE for BOLD fMRI at a modest undersampling factor. Results suggest that sufficient sensitivity to BOLD contrast may be achievable at higher undersampling factors with k‐t BLAST/k‐t SENSE than with conventional parallel imaging approaches, offering particular advantages at the highest magnetic field strengths. J. Magn. Reson. Imaging 2010;32:235–241. © 2010 Wiley‐Liss, Inc.     

Evaluation of pressure‐driven brain infusions in nonhuman primates by intra‐operative 7 tesla MRI

Purpose:

To characterize the effects of pressure‐driven brain infusions using high field intra‐operative MRI. Understanding these effects is critical for upcoming neurodegeneration and oncology trials using convection‐enhanced delivery (CED) to achieve large drug distributions with minimal off‐target exposure.

Materials and Methods:

High‐resolution T2‐weighted and diffusion‐tensor images were acquired serially on a 7 Tesla MRI scanner during six CED infusions in nonhuman primates. The images were used to evaluate the size, distribution, diffusivity, and temporal dynamics of the infusions.

Results:

The infusion distribution had high contrast in the T2‐weighted images. Diffusion tensor images showed the infusion increased diffusivity, reduced tortuosity, and reduced anisotropy. These results suggested CED caused an increase in the extracellular space.

Conclusion:

High‐field intra‐operative MRI can be used to monitor the distribution of infusate and changes in the geometry of the brain's porous matrix. These techniques could be used to optimize the effectiveness of pressure‐driven drug delivery to the brain. J. Magn. Reson. Imaging 2012; 36:1339–1346. © 2012 Wiley Periodicals, Inc.     

Multiband accelerated spin‐echo echo planar imaging with reduced peak RF power using time‐shifted RF pulses

Purpose:

To evaluate an alternative method for generating multibanded radiofrequency (RF) pulses for use in multiband slice‐accelerated imaging with slice‐GRAPPA unaliasing, substantially reducing the required peak power without bandwidth compromises. This allows much higher accelerations for spin‐echo methods such as SE‐fMRI and diffusion‐weighted MRI where multibanded slice acceleration has been limited by available peak power.

Theory and Methods:

Multibanded “time‐shifted” RF pulses were generated by inserting temporal shifts between the applications of RF energy for individual bands, avoiding worst‐case constructive interferences. Slice profiles and images in phantoms and human subjects were acquired at 3 T.

Results:

For typical sinc pulses, time‐shifted multibanded RF pulses were generated with little increase in required peak power compared to single‐banded pulses. Slice profile quality was improved by allowing for higher pulse bandwidths, and image quality was improved by allowing for optimum flip angles to be achieved.

Conclusion:

A simple approach has been demonstrated that significantly alleviates the restrictions imposed on achievable slice acceleration factors in multiband spin‐echo imaging due to the power requirements of multibanded RF pulses. This solution will allow for increased accelerations in diffusion‐weighted MRI applications where data acquisition times are normally very long and the ability to accelerate is extremely valuable. Magn Reson Med 69:1261–1267, 2013 Wiley Periodicals, Inc.     

Three-year follow-up of human transplanted kidneys by diffusion-weighted MRI and blood oxygenation level-dependent imaging

Purpose:

To prospectively determine the 3‐year stability and potential changes of functional parameters in renal allograft recipients obtained from diffusion‐weighted imaging (DWI) and blood oxygenation level‐dependent (BOLD) MRI.

Materials and Methods:

Nine renal allograft recipients underwent DWI and BOLD‐MRI twice, once 7 ± 3 months after transplantation, and again 32 ± 2 months after the first MRI. DWI yielded an apparent diffusion coefficient (ADC) and the perfusion contribution (F_P). BOLD imaging yielded R2*, providing an estimation of renal oxygenation. Coefficients of variation between (CV_b) and within subjects (CV_w) were calculated.

Results:

The parameters were stable after 32 months in eight of the nine patients, who had well‐functioning allografts. Mean diffusion values were very similar in the first and second scan. CV_w and CV_b for ADC values were less than 3.5% and 5.9%, respectively, in cortex and medulla, but were higher for F_P (15%–18%). CV_w and CV_b of R2* were also low (medulla: CV_w = 10.8%, CV_b = 11.4%; cortex: CV_w and CV_b = 7.2%). R2* increased significantly (P = 0.035) in cortex but not in medulla, suggesting reduced cortical oxygen content. One subject with decreased glomerular filtration rate demonstrated strongly altered parameters.

Conclusion:

In the absence of graft dysfunction, DWI and BOLD imaging yield consistent results over 3 years in stable human renal allograft recipients. J. Magn. Reson. Imaging 2012;35:1133‐1138. © 2011 Wiley Periodicals, Inc.     

Comparison of ferucarbotran‐enhanced fluid‐attenuated inversion‐recovery echo‐planar,T2‐weighted turbo spin‐echo,T2*‐weighted gradient‐echo,and diffusion‐weighted echo‐planar imaging for detection of malignant liver lesions

Purpose:

To compare the diagnostic accuracy of superparamagnetic iron oxide (SPIO)‐enhanced fluid‐attenuated inversion‐recovery echo‐planar imaging (FLAIR EPI) for malignant liver tumors with that of T2‐weighted turbo spin‐echo (TSE), T2*‐weighted gradient‐echo (GRE), and diffusion‐weighted echo‐planar imaging (DW EPI).

Materials and Methods:

SPIO‐enhanced magnetic resonance imaging (MRI) that included FLAIR EPI, T2‐weighted TSE, T2*‐weighted GRE, and DW EPI sequences was performed using a 3 T system in 54 consecutive patients who underwent surgical exploration with intraoperative ultrasonography. A total of 88 malignant liver tumors were evaluated. Images were reviewed independently by two blinded observers who used a 5‐point confidence scale to identify lesions. Results were correlated with results of histopathologic findings and surgical exploration with intraoperative ultrasonography. The accuracy of each MRI sequence was measured with jackknife alternative free‐response receiver operating characteristic analysis. The sensitivity of each observer with each MRI sequence was compared with McNemar's test.

Results:

Accuracy values were significantly higher with FLAIR EPI sequence (0.93) than with T2*‐weighted GRE (0.80) or DW EPI sequences (0.80) (P < 0.05). Sensitivity was significantly higher with the FLAIR EPI sequence than with any of the other sequences.

Conclusion:

SPIO‐enhanced FLAIR EPI sequence was more accurate in the diagnosis of malignant liver tumors than T2*‐weighted GRE and DW EPI sequences. SPIO‐enhanced FLAIR EPI sequence is helpful for the detection of malignant liver tumors. J. Magn. Reson. Imaging 2010;31:607–616. ©2010 Wiley‐Liss, Inc.     

Visualization of cerebral microbleeds with dual‐echo T2*‐weighted magnetic resonance imaging at 7.0 T

Purpose:

To assess the visualization of cerebral microbleeds with dual echo T2*‐weighted imaging at 7.0 T magnetic resonance imaging (MRI).

Materials and Methods:

Ten consecutive participants (eight men, two women, mean age 54 ± 12 years) with vascular disease or risk factors from the second manifestations of arterial disease (SMART) study were included. Dual‐echo T2*‐weighted scans (echo time: 2.5/15.0 msec) were made for all participants at 7.0 T MRI. The number of visible microbleeds and the diameter of the microbleeds were recorded on minimal intensity projection images of both echoes.

Results:

The first echo image shows dark microbleeds against a homogeneous, more hyperintense signal of the brain tissue without contrast for veins and basal ganglia. In eight patients microbleeds were observed, with a total of 104 microbleeds. Of these, 88 (84.6%) were visible on the first and 102 (98.0%) on the second echo. The mean diameter of the microbleeds was 1.24 mm for the first echo and 2.34 mm for the second echo.

Conclusion:

T2*‐weighted imaging at two echo times at 7.0 T combines the advantages of the first and second echo. Microbleeds visible on the first echo show large contrast with the surrounding tissue, even in the presence of paramagnetic ferritin. The second echo enables visualization of smaller microbleeds than the first echo. J. Magn. Reson. Imaging 2010;32:52–59. © 2010 Wiley‐Liss, Inc.     

Novel application of T1‐weighted BLADE sequences with fat suppression compared to TSE in contrast‐enhanced T1‐weighted imaging of the neck: Cutting‐edge images?

Purpose:

To evaluate if the use of BLADE sequences might overcome some limitations of magnetic resonance imaging (MRI) in the extracranial head and neck, which is a diagnostically challenging area with a variety of artifacts and a broad spectrum of potential lesions.

Materials and Methods:

After informed consent and Institutional Review Board approval, two different BLADE sequences with (BLADE IR) and without inversion pulse (BLADE) were compared to turbo‐spin echo (TSE) with fat saturation for coronal T1‐weighted postcontrast imaging of the extracranial head and neck region in 40 individuals of a routine patient collective. Visual evaluation of image sharpness, motion artifacts, vessel pulsation, contrast of anatomic structures, contrast of pathologies to surrounding tissue as well as BLADE‐specific artifacts was performed by two experienced, independent readers. Statistical evaluation was done by using the Wilcoxon test.

Results:

Both BLADE and BLADE IR were significantly superior to TSE regarding pulsation artifacts and delineation of thoracic structures. TSE provided better results concerning contrast muscle/fat tissue and contrast lymph nodes/fat. More important, it showed significantly better contrast of several lesions, facilitating the detection of patient pathology.

Conclusion:

T1‐weighted coronal imaging of the extracranial head and neck region is demanding. T1‐weighted BLADE sequences still have drawbacks in anatomical contrast and lesion detection but offer possibilities to achieve reasonable image quality in difficult cases with a variety of artifacts. J. Magn. Reson. Imaging 2013;37:660—668. © 2012 Wiley Periodicals, Inc.     

Assessment of fast dynamic imaging and the use of Gd‐EOB‐DTPA for MR‐guided liver interventions

Purpose:

1) To analyze and compare fast dynamic imaging sequences to biopsy suspect liver lesions. 2) To evaluate the additional use of hepatocyte‐specific contrast agent compared to the nonenhanced fast dynamic scans and diagnostic liver imaging.

Materials and Methods:

Image acquisition was performed using a 1T open‐configured scanner suitable for interventional purposes. Transversal postcontrast T1‐weighted (T1w) fat‐saturated 3D high‐resolution examination (THRIVE) images were acquired >20 minutes postintravenous application of gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd‐EOB‐DTPA). A single slice, crossing the level of the lesion, was acquired using intermediate‐weighted steady‐state free‐precession (bTFE), T1w‐gradient echo and spin echo (T1FFE/TSE), T2w‐spin echo (sshTSE) sequences. T1w imaging was acquired prior and after contrast media application. Diagnostic and fast dynamic images were compared based on a 10‐point rating scale. In addition, the liver‐to‐lesion‐contrast ratio was measured.

Results:

A total of 39 malignant lesions with a mean diameter of 13 mm (5–30 mm) in 39 patients were included. Concerning a test of noninferiority, there was no significant difference between rating score values of fast dynamic imaging employing contrast‐enhanced T1FFE‐sequences compared to diagnostic THRIVE (P = 0.001). Calculated liver‐to‐lesion contrast also showed no difference for either imaging sequence (P = 1.0). All other sequences tested showed significant inferiority (P ≤ 0.001).

Conclusion:

T1w Gd‐EOB‐DTPA contrast‐enhanced fast dynamic GRE imaging significantly improves the contrast behavior of malignant liver lesions comparable to diagnostic imaging and is best suited for liver intervention, especially at 1T open magnetic resonance imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.