Fast spin-echo triple echo dixon: Initial clinical experience with a novel pulse sequence for simultaneous fat-suppressed and nonfat-suppressed T2-weighted spine magnetic resonance imaging

Purpose

To evaluate a prototype fast spin‐echo (FSE) triple‐echo Dixon (FTED) technique for T2‐weighted spine imaging with and without fat suppression compared to conventional T2‐weighted fast recovery (FR) FSE and short‐tau inversion recovery (STIR) imaging.

Materials and Methods

Sixty‐one patients were referred for spine magnetic resonance imaging (MRI) including sagittal FTED (time 2:26), STIR (time 2:42), and T2 FRFSE (time 2:55). Two observers compared STIR and FTED water images and T2 FRFSE and FTED T2 images for overall image quality, fat suppression, anatomic sharpness, motion, cerebrospinal fluid (CSF) flow artifact, susceptibility, and disease depiction.

Results

On FTED images water and fat separation was perfect in 58 (.95) patients. Compared to STIR, the FTED water images demonstrated less motion in 57 (.93) of 61 patients (P < 0.05), better anatomic sharpness in 51 (.84) and patients (P < 0.05), and less CSF flow artifact in 7 (.11) P < 0.05) patients. There was no difference in fat suppression or chemical shift artifact. T2 FRFSE and FTED T2 images showed equivalent motion, CSF flow, and chemical shift artifact. Lesion depiction was equivalent on FTED water and STIR images and FTED T2 and T2 FRFSE images.

Conclusion

FTED efficiently provides both fat‐suppressed and nonfat‐suppressed T2‐weighted spine images with excellent image quality, equal disease depiction, and 56% reduction in scan time compared to conventional STIR and T2 FRFSE. J. Magn. Reson. Imaging 2011;33:390–400. © 2011 Wiley‐Liss, Inc.     

Human cervical spinal cord funiculi: Investigation with magnetic resonance diffusion tensor imaging

Purpose:

To use spinal cord diffusion tensor imaging (DTI) for investigating human cervical funiculi, acquire axial diffusion magnetic resonance imaging (MRI) data with an in‐plane resolution sufficient to delineate subquadrants within the spinal cord, obtain corresponding DTI metrics, and assess potential regional differences.

Materials and Methods:

Healthy volunteers were studied with a 3 T Siemens Trio MRI scanner. DTI data were acquired using a single‐shot spin echo EPI sequence. The spatial resolution allowed for the delineation of regions of interest (ROIs) in the ventral, dorsal, and lateral spinal cord funiculi. ROI‐based and tractography‐based analyses were performed.

Results:

Significant fractional anisotropy (FA) differences were found between ROIs in the dorsal and ventral funiculi (P = 0.0001), dorsal and lateral funiculi (P = 0.015), and lateral and ventral funiculi (P = 0.0002). Transverse diffusivity was significantly different between ROIs in the ventral and dorsal funiculi (P = 0.003) and the ventral and lateral funiculi (P = 0.004). Tractography‐based quantifications revealed DTI parameter regional differences that were generally consistent with the ROI‐based analysis.

Conclusion:

Original contributions are: 1) the use of a tractography‐based method to quantify DTI metrics in the human cervical spinal cord, and 2) reported DTI values in various funiculi at 3 T. J. Magn. Reson. Imaging 2010;31:829–837. ©2010 Wiley‐Liss, Inc.     

Cardiac motion in diffusion-weighted MRI of the liver: artifact and a method of correction

Purpose:

To characterize cardiac motion artifacts in the liver and assess the use of a postprocessing method to mitigate these artifacts in repeat measurements.

Materials and Methods:

Three subjects underwent breathhold diffusion‐weighted (DW) scans consisting of 25 repetitions for three b‐values (0, 500, 1000 sec/mm²). Statistical maps computed from these repetitions were used to assess the distribution and behavior of cardiac motion artifacts in the liver. An objective postprocessing method to reduce the artifacts was compared with radiologist‐defined gold standards.

Results:

Signal dropout is pronounced in areas proximal to the heart, such as the left lobe, but also present in the right lobe and in distal liver segments. The dropout worsens with b‐value and leads to overestimation of the diffusivity. By reference to a radiologist‐defined gold standard, a postprocessing correction method is shown to reduce cardiac motion artifact.

Conclusion:

Cardiac motion leads to significant artifacts in liver DW imaging; we propose a postprocessing method that may be used to mitigate the artifact and is advantageous to standard signal averaging in acquisitions with multiple repetitions. J. Magn. Reson. Imaging 2012;318‐327. © 2011 Wiley Periodicals, Inc.     

In vivo DTI assessment of hepatic ischemia reperfusion injury in an experimental rat model

Purpose

To investigate hepatic ischemia reperfusion injury (IRI) using diffusion tensor imaging (DTI).

Materials and Methods

Ten Sprague‐Dawley rats were scanned at 7 Tesla (T) with DTI using b‐value of 1000 s/mm² and 6 gradient directions before, 2 h, and 1 day after 30‐min total hepatic IRI. Apparent diffusion coefficient or mean diffusivity (MD), directional diffusivities and fractional anisotropy (FA) were measured. Seven of the animals were also examined with spin‐echo echo‐planar diffusion‐weighted imaging (DWI) with seven b‐values up to 2000 s/mm² to estimate the true diffusion coefficient (D), blood pseudodiffusion coefficient (D*), and perfusion fraction (f) using a bi‐compartmental model.

Results

MD 2 h after IRI (0.77 ± 0.07 × 10^?3 mm²/s) was significantly lower (P < 0.01) than that before (1.03 ± 0.07 × 10^?3 mm²/s) and 1 day after IRI (1.01 ± 0.05 × 10^?3 mm²/s). Meanwhile, FA 2 h after IRI (0.33 ± 0.03) was significantly higher (P < 0.01) than that before (0.21 ± 0.02) and 1 day after IRI (0.20 ± 0.02). The bi‐compartmental model analysis revealed the transient decrease in D, D* and f 2 h after IRI. Liver histology showed the multifocal cell swelling 3 h after IRI and widespread cell necrosis/apoptosis 1 day after IRI. Sinusoidal narrowing and congestion of erythrocytes were also observed 3 h and 1 day after IRI.

Conclusion

DTI can characterize hepatic IRI by detecting the transient change in both MD and FA. J. Magn. Reson. Imaging 2009;30:890–895. © 2009 Wiley‐Liss, Inc.

     

Fast 3D 1H MRSI of the corticospinal tract in pediatric brain

Purpose

To develop a ¹H magnetic resonance spectroscopic imaging (MRSI) sequence that can be used to image infants/children at 3T and by combining it with diffusion tensor imaging (DTI) tractography, extract relevant metabolic information corresponding to the corticospinal tract (CST).

Materials and Methods

A fast 3D MRSI sequence was developed for pediatric neuroimaging at 3T using spiral k‐space readout and dual band RF pulses (32 × 32 × 8 cm field of view [FOV], 1 cc iso‐resolution, TR/TE = 1500/130, 6:24 minute scan). Using DTI tractography to identify the motor tracts, spectra were extracted from the CSTs and quantified. Initial data from infants/children with suspected motor delay (n = 5) and age‐matched controls (n = 3) were collected and N‐acetylaspartate (NAA) ratios were quantified.

Results

The average signal‐to‐noise ratio of the NAA peak from the studies was ≈22. Metabolite profiles were successfully acquired from the CST by using DTI tractography. Decreased NAA ratios in those with motor delay compared to controls of ≈10% at the CST were observed.

Conclusion

A fast and robust 3D MRSI technique targeted for pediatric neuroimaging has been developed. By combining with DTI tractography, metabolic information from the CSTs can be retrieved and estimated. By combining DTI and 3D MRSI, spectral information from various tracts can be obtained and processed. J. Magn. Reson. Imaging 2009;29:1–6. © 2008 Wiley‐Liss, Inc.     

Impact of blood flow on diffusion coefficients of the human kidney: A time‐resolved ECG‐triggered diffusion‐tensor imaging (DTI) study at 3T

Purpose:

To evaluate the impact of renal blood flow on apparent diffusion coefficients (ADC) and fractional anisotropy (FA) using time‐resolved electrocardiogram (ECG)‐triggered diffusion‐tensor imaging (DTI) of the human kidneys.

Materials and Methods:

DTI was performed in eight healthy volunteers (mean age 29.1 ± 3.2) using a single slice coronal echoplanar imaging (EPI) sequence (3 b‐values: 0, 50, and 300 s/mm²) at the timepoint of minimum (20 msec after R wave) and maximum renal blood flow (200 msec after R wave) at 3T. Following 2D motion correction, region of interest (ROI)‐based analysis of cortical and medullary ADC‐ and FA‐values was performed.

Results:

ADC‐values of the renal cortex at maximum blood flow (2.6 ± 0.19 × 10^?3 mm²/s) were significantly higher than at minimum blood flow (2.2 ± 0.11 × 10^?3 mm²/s) (P < 0.001), while medullary ADC‐values did not differ significantly (maximum blood flow: 2.2 ± 0.18 × 10^?3 mm²/s; minimum blood flow: 2.15 ± 0.14 × 10^?3 mm²/s). FA‐values of the renal medulla were significantly greater at maximal blood (0.53 ± 0.05) than at minimal blood flow (0.47 ± 0.05) (P < 0.01). In contrast, cortical FA‐values were comparable at different timepoints of the cardiac cycle.

Conclusion:

ADC‐values in the renal cortex as well as FA‐values in the renal medulla are influenced by renal blood flow. This impact has to be considered when interpreting renal ADC‐ and FA‐values. J. Magn. Reson. Imaging 2013;37:233–236. © 2012 Wiley Periodicals, Inc.

     

New MR imaging methods for metallic implants in the knee: artifact correction and clinical impact

Purpose:

To evaluate two magnetic resonance imaging (MRI) techniques, slice encoding for metal artifact correction (SEMAC) and multiacquisition variable‐resonance image combination (MAVRIC), for their ability to correct for artifacts in postoperative knees with metal.

Materials and Methods:

A total of 25 knees were imaged in this study. Fourteen total knee replacements (TKRs) in volunteers were scanned with SEMAC, MAVRIC, and 2D fast spin‐echo (FSE) to measure artifact extent and implant rotation. The ability of the sequences to measure implant rotation and dimensions was compared in a TKR knee model. Eleven patients with a variety of metallic hardware were imaged with SEMAC and FSE to compare artifact extent and subsequent patient management was recorded.

Results:

SEMAC and MAVRIC significantly reduced artifact extent compared to FSE (P < 0.0001) and were similar to each other (P = 0.58), allowing accurate measurement of implant dimensions and rotation. The TKRs were properly aligned in the volunteers. Clinical imaging with SEMAC in symptomatic knees significantly reduced artifact (P < 0.05) and showed findings that were on the majority confirmed by subsequent noninvasive or invasive patient studies.

Conclusion:

SEMAC and MAVRIC correct for metal artifact, noninvasively providing high‐resolution images with superb bone and soft tissue contrast. J. Magn. Reson. Imaging 2011;33:1121–1127. © 2011 Wiley‐Liss, Inc.     

Diffusion tensor imaging of kidneys with respiratory triggering: Optimization of parameters to demonstrate anisotropic structures on fraction anisotropy maps

Purpose

To demonstrate the feasibility of diffusion tensor imaging (DTI) of kidneys with respiratory triggering, and determine the optimal imaging parameters for fraction anisotropy (FA) maps.

Materials and Methods

DTI of kidneys from 16 healthy volunteers was performed using a 1.5T scanner. Five different sequences with different parameters including respiration‐triggered acquisition or multiple breath‐holding, slice thicknesses of 3 or 5 mm, and different numbers of signal averaging and b values were compared. FA and apparent diffusion coefficients (ADCs) of the cortex and medulla were measured. Measurement error within the same and repeated examination was examined using within‐individual standard deviation (Sw).

Results

FAs of the renal cortex were lower than the medulla (mean value of a sequence ranging 0.148–0.224, 0.433–0.476) and the ADCs of the cortex were higher than the medulla (2.26–2.69 × 10^?3 mm²/s, 1.77–2.19 × 10^?3 mm²/s) in all sequences (P < 0.001). The renal cortex–medulla difference was the largest, with respiratory trigger‐ ing including a 3‐mm slice thickness, three signal averages,and a b‐value = 0, 200, or 400 s/mm² (P < 0.001). Sw tended to be smaller in the sequence with a b‐value of 400 s/mm².

Conclusion

DTI of kidneys with respiratory triggering is feasible with excellent cortex–medulla differentiation. J. Magn. Reson. Imaging 2009;29:736–744. © 2009 Wiley‐Liss, Inc.

     

Effects of formalin fixation on magnetic resonance indices in multiple sclerosis cortical gray matter

Purpose

To characterize and evaluate functional and anatomic changes of visual pathway lesions during hyperbaric oxygen (HBO) treatment with blood‐oxygenation‐level‐dependent functional MRI (BOLD‐fMRI) and diffusion tensor imaging (DTI).

Materials and Methods

Sixteen patients with visual pathway lesions received HBO treatment. Both BOLD‐fMRI and DTI were performed before and after the treatment, while 12 healthy subjects were also studied with 2 examinations as control. The t‐tests were used for the comparison of number of activated voxels (AVs) and fractional anisotropy (FA) between the two groups, and within the patient group before and after HBO treatment. Visual acuity of the patient group before and after the treatment was compared using Wilcoxon signed‐rank test.

Results

Before the treatment, both AVs (P < 0.01) and FA (P < 0.05) in the bilateral cortexes of occipital lobes were significantly less in the patient group than in the control group. After the treatment, both AVs (P < 0.05) and FA (P < 0.05) were significantly increased. Moreover, The FA of 6 patients with lesions in the optical nerve was greater than the FA of the other 10 patients with lesions in the optic radiation (P < 0.05).

Conclusion

BOLD‐fMRI combined with DTI was useful for the characterization and evaluation of anatomic and functional changes of visual pathway lesions and their development during HBO treatment. J. Magn. Reson. Imaging 2010;31:1054–1060. © 2010 Wiley‐Liss, Inc.     

Relationships of brain white matter microstructure with clinical and MR measures in relapsing‐remitting multiple sclerosis

Purpose:

To assess the relationships of microstructural damage in the cerebral white matter (WM), as measured by diffusion tensor imaging (DTI), with clinical parameters and magnetic resonance imaging (MRI) measures of focal tissue damage in patients with multiple sclerosis (MS).

Materials and Methods:

Forty‐five relapsing‐remitting (RR) MS patients (12 male, 33 female; median age = 29 years, Expanded Disability Status Scale (EDSS) = 1.5, disease duration = 3 years) were studied. T2‐lesion masks were created and voxelwise DTI analyses performed with Tract‐Based Spatial Statistics (TBSS).

Results:

T2‐lesion volume (T2‐LV) was significantly (P < 0.05, corrected) correlated with fractional anisotropy (FA) in both lesions and normal‐appearing WM (NAWM). Relationships (P = 0.08, corrected) between increasing EDSS score and decreasing FA were found in the splenium of the corpus callosum (sCC) and along the pyramidal tract (PY). All FA associations were driven by changes in the perpendicular (to primary tract direction) diffusivity. No significant global and voxelwise FA changes were found over a 2‐year follow‐up.

Conclusion:

FA changes related to clinical disability in RR‐MS patients with minor clinical disability are localized to specific WM tracts such as the sCC and PY and are driven by changes in perpendicular diffusivity both within lesions and NAWM. Longitudinal DTI measurements do not seem able to chart the early disease course in the WM of MS patients. Imaging 2010; 31:309–316. © 2010 Wiley‐Liss, Inc.     

Liver methylene fraction by dual- and triple-echo gradient-echo imaging at 3.0T: Correlation with proton MR spectroscopy and estimation of robustness after SPIO administration

Purpose

To assess the systematic errors in liver methylene fraction (LMF) resulting from fat–fat interference effects with dual‐ and triple‐echo gradient‐recalled‐echo Dual/Triple GRE) sequences and to test the robustness of these sequences after iron overloading.

Materials and Methods

Forty type‐2 diabetic patients underwent LMF measurement by 3.0T ¹H magnetic resonance spectroscopy (corrected for T1 and T2 decays) as the reference standard and liver fat fraction (%Fat) measurement by four Dual/Triple GRE sequences with 20° and 60° flip angle (α), corrected for T1 recovery. The same four sequences were repeated in eight patients after ferumoxide injection. Corrections for systematic errors were determined from the linear regressions (spectroscopy LMF values over Dual/Triple GRE %Fat values). Robustness was tested using Wilcoxon's signed‐rank test.

Results

Fat–fat interference effects produced a ～10% relative systematic error and T2* decay produced a 1.9%–4.2% absolute systematic error in LMF. When comparing before and after ferumoxide, dual‐echo imaging with α = 20° and α = 60°, even when corrected, showed absolute differences of 7.23% [2.81%–10.25%] (P = 0.0117) and 5.65% [1.89%–8.216.8%] (P = 0.0117), respectively; compared to only 1.17% [0.08%–2.83%] (P = 0.0251) and 1.15% [0.37%–2.73%] (P = 0.2626) with triple‐echo imaging and α = 20° and α = 60°, respectively.

Conclusion

Triple‐echo imaging with α = 60° corrected for both T1 recovery and fat–fat interference effects is robust after superparamagnetic iron oxide (SPIO) administration and can reliably quantify LMF. J. Magn. Reson. Imaging 2011;33:119–127. © 2010 Wiley‐Liss, Inc.     

Diffusion tensor imaging of liver fibrosis in an experimental model

Purpose

To characterize changes in diffusion properties of liver using diffusion tensor imaging (DTI) in an experimental model of liver fibrosis.

Materials and Methods

Liver fibrosis was induced in Sprague–Dawley rats (n = 12) by repetitive dosing of carbon tetrachloride (CCl₄). The animals were examined with a respiratory‐gated single‐shot spin‐echo echo‐planar DTI protocol at 7 T before, 2 weeks after, and 4 weeks after CCl₄ insult. Apparent diffusion coefficient (ADC), directional diffusivities (ADC_// and ADC_?), and fractional anisotropy (FA) were measured. Liver histology was performed with hematoxylin‐eosin staining and Masson's trichrome staining.

Results

Significant decrease (P < 0.01) in ADC was found at 2 weeks (0.86 ± 0.09 × 10^?3 mm²/s) and 4 weeks (0.74 ± 0.09 × 10^?3 mm²/s) following CCl₄ insult, as compared with that before insult (0.97 ± 0.08 × 10^?3 mm²/s). Meanwhile, FA at 2 weeks (0.18 ± 0.03) after CCl₄ insult was significantly lower (P < 0.01) than that before insult (0.26 ± 0.05), and subsequently normalized at 4 weeks (0.26 ± 0.07) after the insult. Histology showed collagen deposition, presence of intracellular fat vacuoles, and cell necrosis/apoptosis in livers with CCl₄ insult.

Conclusion

DTI detected the progressive changes in water diffusivities and diffusion anisotropy of liver tissue in this liver fibrosis model. ADC and FA are potentially valuable in detecting liver fibrosis at early stages and monitoring its progression. Future human studies are warranted to further verify the applicability of DTI in characterizing liver fibrosis and to determine its role in clinical settings. J. Magn. Reson. Imaging 2010;32:1141–1148. © 2010 Wiley‐Liss, Inc.

     

Monitoring of acute axonal injury in the swine spinal cord with EAE by diffusion tensor imaging

Purpose

To evaluate the ability of diffusion tensor imaging (DTI) to detect and monitor acute axonal injury in swine spinal cord with acute experimental allergic encephalomyelitis (EAE).

Materials and Methods

Magnetic resonance imaging of the cervical spinal cord was performed in vivo at different time points through the onset and progression of EAE using a 3 Tesla clinical scanner. The DTI parameters were calculated in four separate regions of interest at the C2/C3 level. The quantitative DTI‐pathology and DTI‐clinical correlations were verified.

Results

In the monophasic acute course of EAE onset and progression, axial diffusivity (AD) decrease correlates with acute axonal injury (r = ?0.84; P < 0.001). By contrast, radial diffusivity does not change and no demyelination in histopathology was detected. Moreover, a clear correlation between clinical disease and axial diffusivity was found in two swine EAE models (r = ?0.86; P < 0.001 and r = ?0.92; P < 0.001).

Conclusion

AD corresponds with axonal injury in the absence of demyelination and may be a useful noninvasive tool to investigate the underlying pathogenic processes of multiple sclerosis and to monitor the effects of experimental treatments for axonal injury. J. Magn. Reson. Imaging 2009;30:277–285. © 2009 Wiley‐Liss, Inc.

     

Diffusion tensor imaging of the median nerve in healthy and carpal tunnel syndrome subjects

Purpose

To determine if diffusion tensor imaging (DTI) of the median nerve could allow identification of patients with carpal tunnel syndrome (CTS).

Materials and Methods

A total of 13 healthy subjects and 9 CTS patients were scanned on a 3T magnetic resonance imaging (MRI) scanner. The MRI protocol included a DTI sequence from which the fractional anisotropy (FA), apparent diffusion coefficient (ADC), and the parallel and radial diffusivities could be extracted. Those parameters were quantified at different locations along the median nerve (proximal to the carpal tunnel, within the carpal tunnel, and distal to the carpal tunnel).

Results

At the carpal tunnel, the FA, radial diffusivity, and ADC differed significantly between healthy subjects and CTS patients (P < 0.0002). This highly significant difference between the two groups was due to an opposite trend of changes in the DTI indices between the proximal to the carpal tunnel and within the carpal tunnel locations. In healthy subjects the FA increased (+20%, P < 0.001) and the radial diffusivity and ADC decreased (by ?15% and ?8%, respectively, P < 0.05) between the proximal to the carpal tunnel and within the carpal tunnel locations. In CTS subjects the FA decreased (by ?21%, P < 0.05) and the radial diffusivity increased (by +23%, P < 0.01) between the proximal to the carpal tunnel and within the carpal tunnel locations.

Conclusion

DTI enables visualization and characterization of the median nerve in healthy subjects and CTS patients. DTI indices show clear‐cut discrimination between the two groups and in fact enables the of use DTI in the diagnosis of CTS. J. Magn. Reson. Imaging 2009;29:657–662. © 2009 Wiley‐Liss, Inc.

     

Cross-sectional and in-plane coronary vessel wall imaging using a local inversion prepulse and spiral read-out: a comparison between 1.5 and 3 Tesla

Purpose:

To compare cross‐sectional and in‐plane coronary vessel wall imaging using a spiral readout at 1.5 and 3 Tesla (T).

Materials and Methods:

Free‐breathing coronary vessel wall imaging using a local inversion technique and spiral readout was implemented. Images were acquired in ten healthy adult subjects on a 3T clinical scanner using a 32‐element cardiac coil and repeated on a 1.5T clinical scanner using a 5‐element coil.

Results:

Cross‐sectional and in‐plane spiral vessel wall imaging was performed at both 1.5 and 3T. In cross‐sectional images, artifact scores were superior at 1.5T (P < 0.05) but no significant difference was found in image quality scores compared with 3T. Image quality (P < 0.01) and artifact scores (P < 0.01) were found to be superior for in‐plane images at 1.5T. Vessel wall sharpness in the in‐plane orientation was also found to be higher at 1.5T (P < 0.03).

Conclusion:

Although excellent in‐plane coronary vessel wall images can be acquired at 3T, the overall robustness may be affected by off‐resonance blurring due to increased B0 inhomogeneity compared with 1.5T. J. Magn. Reson. Imaging 2012;35:969–975. © 2011 Wiley Periodicals, Inc.     

Imaging age‐related cognitive decline: A comparison of diffusion tensor and magnetization transfer MRI

Purpose

To determine which MR technique was the most sensitive to age‐related white matter damage. We compared both diffusion tensor imaging (DTI) and magnetization transfer (MT) maps to determine which technique correlated most strongly with cognitive function in a middle‐aged and elderly community population.

Materials and Methods

In all, 64 healthy subjects (aged 50–90) underwent MRI and neuropsychology. Histograms were generated for white matter mean diffusivity (MD), fractional anisotropy (FA), and MT ratio (MTR). White matter hyperintensity volume (WMH) and brain volume were also determined. Composite neuropsychological scores were derived for 4 cognitive domains (executive function, working memory, episodic memory, and information processing speed).

Results

All MRI parameters correlated with age (FA r = 0.726, P < 0.001; MD r = ?0.619 P < 0.001, MTR r = ?0.566, P < 0.001, WMH r = 0.511, P < 0.001). All MRI parameters correlated with cognition, but DTI, and particularly FA, correlated most strongly. Adding DTI parameters explained more variance in cognition than WMH alone; the increase was greatest with FA, which alone explained 45%, 33%, and 25% of the variance in cognition for information processing speed, episodic memory, and executive function, respectively.

Conclusion

DTI appears the most sensitive imaging parameter to determine age‐related white matter damage. The stronger relationship with FA suggests that axonal damage is important in age‐related cognitive decline. J. Magn. Reson. Imaging 2009;29:23–30. © 2008 Wiley‐Liss, Inc.

     

Impact of nonrigid motion correction technique on pixel-wise pharmacokinetic analysis of free-breathing pulmonary dynamic contrast-enhanced MR imaging

Purpose:

To investigates the impact of nonrigid motion correction on pixel‐wise pharmacokinetic analysis of free‐breathing DCE‐MRI in patients with solitary pulmonary nodules (SPNs). Misalignment of focal lesions due to respiratory motion in free‐breathing dynamic contrast‐enhanced MRI (DCE‐MRI) precludes obtaining reliable time–intensity curves, which are crucial for pharmacokinetic analysis for tissue characterization.

Materials and Methods:

Single‐slice 2D DCE‐MRI was obtained in 15 patients. Misalignments of SPNs were corrected using nonrigid B‐spline image registration. Pixel‐wise pharmacokinetic parameters K^trans, v_e, and k_ep were estimated from both original and motion‐corrected DCE‐MRI by fitting the two‐compartment pharmacokinetic model to the time–intensity curve obtained in each pixel. The “goodness‐of‐fit” was tested with χ²‐test in pixel‐by‐pixel basis to evaluate the reliability of the parameters. The percentages of reliable pixels within the SPNs were compared between the original and motion‐corrected DCE‐MRI. In addition, the parameters obtained from benign and malignant SPNs were compared.

Results:

The percentage of reliable pixels in the motion‐corrected DCE‐MRI was significantly larger than the original DCE‐MRI (P = 4 × 10^?7). Both K^trans and k_ep derived from the motion‐corrected DCE‐MRI showed significant differences between benign and malignant SPNs (P = 0.024, 0.015).

Conclusion:

The study demonstrated the impact of nonrigid motion correction technique on pixel‐wise pharmacokinetic analysis of free‐breathing DCE‐MRI in SPNs. J. Magn. Reson. Imaging 2011;33:968–973. © 2011 Wiley‐Liss, Inc.

     

A new approach towards improved visualization of myocardial edema using T2-weighted imaging: a cardiovascular magnetic resonance (CMR) study

Purpose:

To compare T2‐weighted cardiovascular magnetic resonance (CMR) imaging with AASPIR (asymmetric adiabatic spectral inversion recovery) and STIR (short T1 inversion recovery) for myocardial signal intensity, image quality, and fat suppression.

Materials and Methods:

Forty consecutive patients (47 ± 16 years old) referred by cardiologists for CMR‐based myocardial tissue characterization were scanned with both STIR and AASPIR T2‐weighted imaging approaches. Signal intensity of left ventricular myocardium was normalized to a region of interest generating a signal‐to‐noise ratio (SNR). In six patients with regional edema on STIR the contrast‐to‐noise ratio (CNR) was assessed. Two independent observers used a scoring system to evaluate image quality and artifact suppression. Six healthy volunteers (three males, 32 ± 7 years) were recruited to compare fat suppression between AASPIR and STIR.

Results:

SNR of AASPIR was greater than STIR for basal (128 ± 44 vs. 83 ± 40, P < 0.001), mid‐ (144 ± 65 vs. 96 ± 39, P < 0.01), and apical (145 ± 59 vs. 105 ± 35, P < 0.05) myocardium. Improved image quality and greater suppression of artifacts was demonstrated with AASPIR. In patients with regional edema, CNR increased by 49% with AASPIR, while SNR of pericardial fat did not differ (44 ± 39 vs. 33 ± 30, P > 0.05).

Conclusion:

Our findings support the implementation of an AASPIR‐based approach for T2‐weighted imaging due to improved pericardial fat suppression, image quality, and artifact suppression with greater CNR and SNR. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Respiratory motion compensated MR cholangiopancreatography at 3.0 Tesla

Purpose:

To reduce irregular respiratory motion‐induced artifacts in free‐breathing prospective navigator‐triggered three‐dimensional (3D) MR cholangiopancreatography (MRCP).

Materials and Methods:

A reference respiration model was estimated from the first‐five respiration periods during the initial navigator scan. With the navigator information acquired before and after triggering, the un‐acquired diaphragm position during the actual imaging was interpolated using the amplitude‐scaled reference model. Craniocaudal translational motion during imaging was retrospectively corrected using the estimated diaphragm position. T2‐weighted 3D MRCP data were acquired from 17 healthy volunteers. For quantitative analysis, contrast‐to‐noise ratio (CNR) and relative contrast (RC) of the biliary tree and gallbladder were compared using the paired t‐test.

Results:

The CNR and RC of the biliary tree and gallbladder were significantly higher (P < 0.05) in the maximum intensity projection images after motion compensation.

Conclusion:

The proposed algorithm can be an effective tool to reduce the irregular respiratory motion‐induced artifacts in 3D MRCP imaging. J. Magn. Reson. Imaging 2010;32:726–732. © 2010 Wiley‐Liss, Inc.     

High B‐value apparent diffusion‐weighted images from CURVE‐ball DTI

Purpose

To investigate the utility of a proposed clinical diffusion imaging scheme for rapidly generating multiple b‐value diffusion contrast in brain magnetic resonance imaging (MRI) with high signal‐to‐noise ratio (SNR).

Materials and Methods

Our strategy for efficient image acquisition relies on the invariance property of the diffusion tensor eigenvectors to b‐value. A simple addition to the conventional diffusion tensor MR imaging (DTI) data acquisition scheme used for tractography yields diffusion‐weighted images at twice and three times the conventional b‐value. An example from a neurosurgical brain tumor is shown. Apparent diffusion‐weighted (ADW) images were calculated for b‐values 800, 1600, and 2400 s/mm², and a map of excess diffusive kurtosis was computed from the three ADWs.

Results

High b‐value ADW images demonstrated decreased contrast between normal gray and white matter, while the heterogeneity and contrast of the lesion was emphasized relative to conventional b‐value data. Kurtosis maps indicated the deviation from Gaussian diffusive behavior.

Conclusion

DTI data with multiple b‐values and good SNR can be acquired in clinically reasonable times. High b‐value ADW images show increased contrast and add information to conventional DWI. Ambiguity in conventional b‐value images over whether hyperintense signal results from abnormally low diffusion, or abnormally long T₂, is better resolved in high b‐value images. J. Magn. Reson. Imaging 2009;30:243–248. © 2009 Wiley‐Liss, Inc.