Diffusion tensor imaging of forearm nerves in humans

Purpose:

To implement a diffusion tensor imaging (DTI) protocol for visualization of peripheral nerves in human forearm.

Materials and Methods:

This Health Insurance Portability and Accountability Act (HIPAA)‐compliant study was approved by our Institutional Review Board and written informed consent was obtained from 10 healthy participants. T₁‐ and T₂‐weighted turbo spin echo with fat saturation, short tau inversion recovery (STIR), and DTI sequences with 21 diffusion‐encoding directions were implemented to acquire images of the forearm nerves with an 8 channel knee coil on a 3T MRI scanner. Identification of the nerves was based on T₁‐weighted, T₂‐weighted, STIR, and DTI‐derived fractional anisotropy (FA) images. Maps of the DTI‐derived indices, FA, mean diffusivity (MD), longitudinal diffusivity (λ_//), and radial diffusivity (λ_?) along the length of the nerves were generated.

Results:

DTI‐derived maps delineated the forearm nerves more clearly than images acquired with other sequences. Only ulnar and median nerves were clearly visualized on the DTI‐derived FA maps. No significant differences were observed between the left and right forearms in any of the DTI‐derived measures. Significant variation in the DTI measures was observed along the length of the nerve. Significant differences in the DTI measures were also observed between the median and ulnar nerves.

Conclusion:

DTI is superior in visualizing the median and ulnar nerves in the human forearm. The normative data could potentially help distinguish normal from diseased nerves. J. Magn. Reson. Imaging 2012;36:920–927. © 2012 Wiley Periodicals, Inc.

     

Susceptibility compensated fMRI study using a tailored RF echo planar imaging sequence

Purpose

To implement a method using a tailored radiofrequency (TRF) pulse with a quadratic phase profile to recover susceptibility‐induced signal losses in gradient‐recalled echo‐planar images (EPI).

Materials and Methods

A functional magnetic resonance imaging (fMRI) experiment for compensation of susceptibility artifacts, known as the TRF pulse EPI sequence (TRF‐EPI), was used. TRF pulse compensates the susceptibility effect with a reduced signal‐to‐noise ratio (SNR) to one‐half when the maximum phase distribution is 2π. We demonstrate theoretically that the maximum phase distribution can also be reduced to π rather than 2π, improving the SNR accordingly. An analysis was conducted comparing this newly proposed strategy using a standard RF excitation with a linear phase distribution and a quadratic TRF excitation with a π phase distribution.

Results

Thorough experimental comparisons were also made between the TRF quadratic excitation with a π phase profile and conventional EPI with a standard excitation in human subjects during ventral brain activation.

Conclusion

With reduced maximum phase distribution in the TRF pulse, signals in the susceptibility‐affected areas, such as the orbitofrontal and inferior temporal cortex, were increased, suggesting that the technique could be a useful adjunct to fMRI. J. Magn. Reson. Imaging 2009;29:221–228. © 2008 Wiley‐Liss, Inc.

     

Gd‐EOB‐DTPA‐enhanced MR imaging: Prediction of hepatic fibrosis stages using liver contrast enhancement index and liver‐to‐spleen volumetric ratio

Purpose:

To develop and evaluate a quantitative parameter for staging hepatic fibrosis by contrast enhancement signal intensity and morphological measurements from gadoxetic acid (Gd‐EOB‐DTPA)‐enhanced MR imaging.

Materials and Methods:

MR images were obtained in 93 patients; 75 patients had histopathologically proven hepatic fibrosis and 18 patients who had healthy livers were evaluated. The liver‐to‐muscle signal intensity ratio (SI_post = SIliver/SImuscle), contrast enhancement index (CEI = SIpost/SIpre), and liver‐to‐spleen volumetric ratio (VR = Vliver/Vspleen) were evaluated for staging hepatic fibrosis.

Results:

VR was most strongly correlated with fibrosis stage (7.21; r = ?0.83; P < 0.001). Sensitivity, specificity, and area under the ROC curve demonstrated by linear regression formula generated by VR and CEI in predicting fibrous scores were 100%, 73%, and 0.91, respectively, for the detection of hepatic fibrosis F1 or greater (≥ F1),100%, 87%, and 0.96 for ≥ F2, 74%, 98%, and 0.93 for ≥ F3 and 91%, 100%, and 0.97 for F4.

Conclusion:

The liver‐to‐spleen volumetric ratio and contrast enhancement index were reliable biomarkers for the staging of hepatic fibrosis on Gd‐EOB‐DTPA‐enhanced MR imaging. J. Magn. Reson. Imaging 2012;36:1148–1153. © 2012 Wiley Periodicals, Inc.

     

Statistical representation of mean diffusivity and fractional anisotropy brain maps of normal subjects

Purpose

To create diffusion tensor atlases from echo planar imaging (EPI) images acquired at 3 T in 10 normal subjects.

Materials and Methods

Data from 10 right‐handed healthy adult volunteers (mean age of 31 ± 3 years; eight males) were acquired using a 3.0‐T scanner. Geometric distortion artifacts correction was accomplished by combining parallel acquisition to reduce the distortion as well as postprocessing by registration to a geometrically accurate T2‐weighted fast‐spin‐echo image. This reduced distortions to within a voxel for most of the internal structures of the brain. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) atlases were created by warping images using an iterative optical‐flow–based local deformation algorithm that used two channels of data: ADC and FA.

Results

A three‐dimensional distance measure was used to evaluate the accuracy of the registration algorithm with contours defined on two structures: the corpus callosum and cerebellum. The average three‐dimensional distance value for the nine subjects (with the 10th as the reference) was 0.2 mm for the corpus callosum and 1.2 mm for the cerebellum.

Conclusion

A high‐resolution, diffusion MR atlas with full brain coverage was developed. Additionally, maps of the SD of the diffusion indices were also generated to provide an estimate of the variance within a normal population. Active shape and texture models were also generated for the corpus callosum as an alternate method of representing the variance in morphology and diffusion indices. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.

     

Measuring bone mineral density with fat–water MRI: comparison with computed tomography

Purpose:

To develop a method for measuring bone mineral density (BMD) with MRI, and to validate this method against quantitative computed tomography (QCT).

Materials and Methods:

A mathematical relationship between signal intensities from proton‐density‐weighted in‐phase images generated by multi‐fat‐peak T‐IDEAL MRI and BMD was derived using a set of calibration standards constructed from various concentrations of hydroxyapatite in water. Using these standards, the relationship between hydroxyapatite concentration and MRI signal intensity was examined. A T‐IDEAL protocol was performed on the patella of 5 volunteers and the signal model was used to compute BMD of all voxels of the patella. The BMD data were validated by obtaining QCT scans of the same patella, computing QCT BMD of all voxels, and comparing the MRI and QCT BMD data by performing linear regression analysis on a voxel‐by‐voxel basis.

Results:

A strong linear correlation between hydroxyapatite concentration of the calibration standards and MRI signal intensities was observed (r = 0.98; P < 0.01). In the patella, BMD measurements (N = 28796 voxels) from the MRI signal model were significantly correlated with those from QCT (r = 0.82; P < 0.001; slope = 1.02; and intercept = ?0.26).

Conclusion:

A standardized phantom consisting of hydroxyapatite and water can be used to accurately quantify BMD in vivo using MRI. J. Magn. Reson. Imaging 2013;37:237–242. © 2012 Wiley Periodicals, Inc.

     

Effect of inversion time on delayed-enhancement magnetic resonance imaging with and without phase-sensitive reconstruction

Purpose

To evaluate the consistency and inversion time (TI) independence of phase‐sensitive reconstruction (PSIR) delayed‐enhancement (DE) MRI in a clinical setting.

Materials and Methods

Mid‐ventricular short‐axis DE images were acquired in 25 patients using three TIs: 1) optimized to null viable myocardium, 2) 50 msec less than optimal TI, and 3) 50 msec greater than optimal TI. At each TI, images were acquired with PSIR and without magIR. In each image, percent scar was computed as the ratio of nonviable to total pixels in the left ventricle (LV).

Results

In the magIR images, percent scar was 23% ± 15% (optimal), 11% ± 11% (short), and 22% ± 15% (long). In PSIR images, percent scar was 25% ± 15% (optimal), 22% ± 15% (short), and 22% ± 14% (long). Percent scar was significantly underestimated in magIR images with short TI, but no statistically significant difference in percent scar was observed at the optimal or long TIs.

Conclusion

DE‐MRI is a robust imaging technique for clinical use. PSIR provided consistent image quality independently of TI, at least over the range of TIs evaluated in this study. However, neither image quality nor scar appearance in the PSIR images was significantly different from that in the magIR images when TI was at or above the null point of viable myocardium. J. Magn. Reson. Imaging 2005;21:650–655. © 2005 Wiley‐Liss, Inc.

     

Improved fat–water reconstruction algorithm with graphics hardware acceleration

Purpose:

To develop a fast and robust Iterative Decomposition of water and fat with Echo Asymmetry and Least‐squares (IDEAL) reconstruction algorithm using graphics processor unit (GPU) computation.

Materials and Methods:

The fat–water reconstruction was expedited by vectorizing the fat–water parameter estimation, which was implemented on a graphics card to evaluate potential speed increases due to data‐parallelization. In addition, we vectorized and compared Brent's method with golden section search for the optimization of the unknown field inhomogeneity parameter (ψ) in the IDEAL equations. The algorithm was made more robust to fat–water ambiguities using a modified planar extrapolation (MPE) of ψ algorithm. As compared to simple planar extrapolation (PE), the use of an averaging filter in MPE made the reconstruction more robust to neighborhoods poorly fit by a two‐dimensional plane.

Results:

Fat–water reconstruction time was reduced by up to a factor of 11.6 on a GPU as compared to CPU‐only reconstruction. The MPE algorithms incorrectly assigned fewer pixels than PE using careful manual correction as a gold standard (0.7% versus 4.5%; P < 10^?4). Brent's method used fewer iterations than golden section search in the vast majority of pixels (6.8 ± 1.5 versus 9.6 ± 1.6 iterations).

Conclusion:

Data sets acquired on a high field scanner can be quickly and robustly reconstructed using our algorithm. A GPU implementation results in significant time savings, which will become increasingly important with the trend toward high resolution mouse and human imaging. J. Magn. Reson. Imaging 2010; 31: 457–465. © 2010 Wiley‐Liss, Inc.

     

Amide proton transfer MR imaging of prostate cancer: a preliminary study

Purpose:

To evaluate the capability of amide proton transfer (APT) MR imaging for detection of prostate cancer that typically shows a higher tumor cell proliferation rate and cellular density leading to an MRI‐detectable overall elevated mobile protein level in higher grade tumors.

Materials and Methods:

Twelve patients with biopsy‐proven prostate cancer were imaged on a 3 Tesla MR imaging system before prostatectomy. APT‐MR images were acquired by means of a single‐slice single‐shot turbo spin echo sequence with a saturation prepulse preparation using 33 different frequency offsets (?8 to 8 ppm, interval 0.5 ppm). For quantification we used the APT ratio (APTR) based on the asymmetry of the magnetization transfer ratio at 3.5 ppm in respect to the water signal. Tumor and peripheral zone benign regions of interest (ROIs) were delineated based on whole mount pathology slides after prostatectomy.

Results:

APTR in prostate cancer ROIs was 5.8% ± 3.2%, significantly higher than that in the peripheral zone benign regions (0.3% ± 3.2%, P = 0.002).

Conclusion:

APT‐MR imaging is feasible in prostate cancer detection and has the potential to discriminate between cancer and noncancer tissues. J. Magn. Reson. Imaging 2011;33:647–654. © 2011 Wiley‐Liss, Inc.

     

Slice offset frequency and shim adjustment for interactive steady‐state free‐precession (SSFP) imaging

Purpose

To devise a method allowing real‐time optimization of center frequency (CF) and shim for an interactive steady‐state free‐precession (SSFP) sequence by reformatting a previously acquired field map in the same orientation as the interactive acquisition.

Materials and Methods

Field maps were acquired in a rectangular parallel‐piped phantom and a normal volunteer. An SSFP sequence was modified to communicate the current slice offset and rotation to an external program that reformatted the field map into the same plane, calculated the CF and shim offsets, and passed them back to the sequence. CF offsets as a function of position for the phantom were compared with the scanner prescan‐determined offset.

Results

In the phantom, the CF measurements agreed with the scanner‐determined offsets. Bland‐Altman analysis showed a bias of ?14 Hz (field map – prescan) and limits of agreement of ?28 to 0 Hz. In the volunteer there was a qualitative improvement in image quality when using the optimized center frequencies and shims.

Conclusion

The proposed method demonstrates how CF and shim can be optimized for any interactively positioned slice, resulting in reduced off‐resonance artifacts. J. Magn. Reson. Imaging 2009;29:1230–1233. © 2009 Wiley‐Liss, Inc.

     

Free-breathing 3D whole-heart black-blood imaging with motion sensitized driven equilibrium

Purpose:

To automatically analyze the time course of collateralization in a rat hindlimb ischemia model based on signal intensity distribution (SID).

Materials and Methods:

Time‐of‐flight magnetic resonance angiograms (TOF‐MRA) were acquired in eight rats at 2, 7, and 21 days after unilateral femoral artery ligation. Analysis was performed on maximum intensity projections filtered with multiscale vessel enhancement filter. Differences in SID between ligated limb and a reference region were monitored over time and compared to manual collateral artery identification.

Results:

The differences in SID correlated well with the number of collateral arteries found with manual quantification. The time courses of ultrasmall (diameter ?0.5 mm) and small (diameter ≈0.5 mm) collateral artery development could be differentiated, revealing that maturation of the collaterals and enlargement of their feeding arteries occurred mainly after the first week postligation.

Conclusion:

SID analysis performed on axial maximum intensity projections is easy to implement, fast, and objective and provides more insight in the time course of arteriogenesis than manual identification. J. Magn. Reson. Imaging 2012;379‐386. © 2011 Wiley Periodicals, Inc.

     

Single-shot half-Fourier RARE sequence with ultra-short inter-echo spacing for lung imaging

Purpose

To improve the image quality of pulmonary magnetic resonance (MR) imaging using an ultra‐short inter‐echo spacing half‐Fourier single shot rapid acquisition with relaxation enhancement (USHA‐RARE) sequence.

Materials and Methods

Pulmonary MR images were acquired by USHA‐RARE sequence with various inter‐echo spacings. The sequence parameters were as follows: repetition time (TR)/effective TE: infinite/39–41 msec; section thickness: 10 mm; acquisition matrix: 128 × 128; field of view: 450 × 450 mm. Inter‐echo spacing varied (2.5 msec, 3.0 msec, 3.5 msec, 4.0 msec, 4.5 msec, 5.0 msec), and the respective phase‐encoding steps were 80, 77, 75, 74, 73, and 72. Signal‐to‐noise ratios (SNRs), the signal ratios between lung and fat (lung‐to‐fat ratio: LFRs), and the signal ratios between the lung and the serratus anterior muscle (lung‐to‐muscle ratio: LMRs) of each inter‐echo spacing were calculated, and statistically evaluated.

Results

The SNRs at inter‐echo spacings of ≤ 3.0 msec were significantly higher than those ≥ 4.0 msec (P < 0.05). The LFRs and LMRs at inter‐echo spacing ≤ 3.0 msec were significantly higher than those ≥ 4.0 msec (P < 0.05).

Conclusion

USHA‐RARE sequence does improve signal intensity from the lung. J. Magn. Reson. Imaging 2004;20:336–339. © 2004 Wiley‐Liss, Inc.

     

MRI signal intensity based B‐Spline nonrigid registration for pre‐ and intraoperative imaging during prostate brachytherapy

Purpose:

To apply an intensity‐based nonrigid registration algorithm to MRI‐guided prostate brachytherapy clinical data and to assess its accuracy.

Materials and Methods:

A nonrigid registration of preoperative MRI to intraoperative MRI images was carried out in 16 cases using a Basis‐Spline algorithm in a retrospective manner. The registration was assessed qualitatively by experts' visual inspection and quantitatively by measuring the Dice similarity coefficient (DSC) for total gland (TG), central gland (CG), and peripheral zone (PZ), the mutual information (MI) metric, and the fiducial registration error (FRE) between corresponding anatomical landmarks for both the nonrigid and a rigid registration method.

Results:

All 16 cases were successfully registered in less than 5 min. After the nonrigid registration, DSC values for TG, CG, PZ were 0.91, 0.89, 0.79, respectively, the MI metric was ?0.19 ± 0.07 and FRE presented a value of 2.3 ± 1.8 mm. All the metrics were significantly better than in the case of rigid registration, as determined by one‐sided t‐tests.

Conclusion:

The intensity‐based nonrigid registration method using clinical data was demonstrated to be feasible and showed statistically improved metrics when compare to only rigid registration. The method is a valuable tool to integrate pre‐ and intraoperative images for brachytherapy. J. Magn. Reson. Imaging 2009;30:1052–1058. © 2009 Wiley‐Liss, Inc.

     

Development of a novel optimized breathhold technique for myocardial T2 measurement in thalassemia

Purpose

To develop a reproducible fast spin‐echo (FSE) technique for accurate myocardial T2 measurement with application to iron overload assessment in thalassemia.

Materials and Methods

An FSE sequence was developed to permit acquisition of multiple TE images in one breathhold (BH‐FSE). A dynamic black‐blood scheme was introduced to better cancel blood signal. A nonselective refocusing train was also adopted to suppress stimulated echoes. The optimized technique was tested on phantoms and then applied to 10 normal volunteers and 10 thalassemia patients. Interstudy reproducibility was measured on all the 20 subjects.

Results

The mean difference in T2 values was 1.7% from phantom experiments between BH‐FSE and the conventional spin‐echo (SE) technique. High contrast BH‐FSE images were acquired from human subjects, with minimal stimulated echoes and effective blood suppression (P = 0.0005). The coefficient of variation for interstudy reproducibility was 4.3%. T2 values from thalassemia patients were substantially lower than those from the normal subjects (45.2 ± 26.1 msec vs. 56.9 ± 8.4ms, P = 0.02).

Conclusion

The dynamic black‐blood T2 sequence is a fast reproducible acquisition that compares favorably with conventional techniques, is robust to motion artifacts, and yields high blood‐myocardium contrast. This technique may provide a useful tool in thalassemia and other scenarios requiring myocardial T2 quantification. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.

     

Automated quantification of white matter disease extent at 3 T: comparison with volumetric readings

Purpose:

To develop and validate an algorithm to automatically quantify white matter hyperintensity (WMH) volume.

Materials and Methods:

Images acquired as part of the Dallas Heart Study, a multiethnic, population‐based study of cardiovascular health, were used to develop and validate the algorithm. 3D magnetization prepared rapid acquisition gradient echo (MP‐RAGE) and 2D fluid‐attenuated inversion recovery (FLAIR) images were acquired from 2082 participants. Images from 161 participants (7.7% of the cohort) were used to set an intensity threshold to maximize the agreement between the algorithm and a qualitative rating made by a radiologist. The resulting algorithm was run on the entire cohort and outlier analyses were used to refine the WMH volume measurement. The refined, automatic WMH burden estimate was then compared to manual quantitative measurements of WMH volume in 28 participants distributed across the range of volumes seen in the entire cohort.

Results:

The algorithm showed good agreement with the volumetric readings of a trained analyst: the Spearman's Rank Order Correlation coefficient was r = 0.87. Linear regression analysis showed a good correlation WMHml[automated] = 1.02 × WMHml[manual] ? 0.48. Bland–Altman analysis showed a bias of 0.34 mL and a standard deviation of 2.8 mL over a range of 0.13 to 41 mL.

Conclusion:

We have developed an algorithm that automatically estimates the volume of WMH burden using an MP‐RAGE and a FLAIR image. This provides a tool for evaluating the WMH burden of large populations to investigate the relationship between WMH burden and other health factors. J. Magn. Reson. Imaging 2012;36:305–311. ©2012 Wiley Periodicals, Inc.

     

Brain iron detected by SWI high pass filtered phase calibrated with synchrotron X‐ray fluorescence

Purpose:

To test the ability of susceptibility weighted images (SWI) and high pass filtered phase images to localize and quantify brain iron.

Materials and Methods:

Magnetic resonance (MR) images of human cadaver brain hemispheres were collected using a gradient echo based SWI sequence at 1.5T. For X‐ray fluorescence (XRF) mapping, each brain was cut to obtain slices that reasonably matched the MR images and iron was mapped at the iron K‐edge at 50 or 100 μm resolution. Iron was quantified using XRF calibration foils. Phase and iron XRF were averaged within anatomic regions of one slice, chosen for its range of iron concentrations and nearly perfect anatomic correspondence. X‐ray absorption spectroscopy (XAS) was used to determine if the chemical form of iron was different in regions with poorer correspondence between iron and phase.

Results:

Iron XRF maps, SWI, and high pass filtered phase data in nine brain slices from five subjects were visually very similar, particularly in high iron regions. The chemical form of iron could not explain poor matches. The correlation between the concentration of iron and phase in the cadaver brain was estimated as c_Fe [μg/g tissue] = 850Δ? + 110.

Conclusion:

The phase shift Δ? was found to vary linearly with iron concentration with the best correspondence found in regions with high iron content. J. Magn. Reson. Imaging 2010;31:1346–1354. © 2010 Wiley‐Liss, Inc.

     

Impact of motion on T1 mapping acquired with inversion recovery fast spin echo and rapid spoiled gradient recalled‐echo pulse sequences for delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) in volunteers

Purpose:

To evaluate the impact of motion on T1 values acquired by using either inversion‐recovery fast spin echo (IR‐FSE) or three‐dimensional (3D) spoiled gradient recalled‐echo (SPGR) sequences for delayed gadolinium‐enhanced magnetic resonance imaging of cartilage (dGEMRIC) in volunteers.

Materials and Methods:

Single‐slice IR‐FSE and 3D SPGR sequences were applied to perform dGEMRIC in five healthy volunteers. A mutual information‐based approach was used to correct for image misregistration. Displacements were expressed as averaged Euclidean distances and angles. Averages of differences in goodness of fit (Δχ²) tests and averages of relative differences in T1 values (ΔT1) before and after motion correction were computed.

Results:

Maximum Euclidean distance was 3.5 mm and 1.2 mm for IR‐FSE and SPGR respectively. Mean ± SD of Δχ² were 10.18 ± 8.4 for IR‐FSE and ?1.37 ± 5.5 for SPGR. Mean ± SD of ΔT1 were 0.008 ± 0.0048 for IR‐FSE and ?0.002 ± 0.019 for FSPGR. Pairwise comparison of Δχ² values showed a significant difference for IR‐FSE, but not for 3D‐SPGR. Significantly greater variability in T1 values was also noted for IR‐FSE than for 3D‐SPGR.

Conclusion:

Involuntary motion has a significant influence on T1 values acquired with IR‐FSE, but not with 3D‐SPGR in healthy volunteers. J. Magn. Reson. Imaging 2010;32:394–398. © 2010 Wiley‐Liss, Inc.

     

Reproducibility of hepatic fat fraction measurement by magnetic resonance imaging

Purpose:

To evaluate the reproducibility of magnetic resonance imaging (MRI)‐determined hepatic fat fraction (%) across imaging sites with different magnet types and field strength. Reproducibility among MRI platforms is unclear, even though evaluating hepatic fat fractions (FFs) using MRI‐based methods is accurate against MR spectroscopy.

Materials and Methods:

Overweight subjects were recruited to undergo eight MRI examinations at five imaging centers with a range of magnet manufacturers and field strengths (1.5 and 3 T). FFs were estimated in liver and in fat‐emulsion phantoms using three methods: 1) dual‐echo images without correction (nominally out‐of‐phase [OP] and in‐phase [IP]); 2) dual‐dual‐echo images (two sequences) with T2* correction (nominally OP/IP and IP/IP); and 3) six‐echo images with spectral model and T2* correction, at sequential alternating OP and IP echo times (Methods 1, 2, and 3, respectively).

Results:

Ten subjects were recruited. For Methods 1, 2, and 3, respectively, hepatic FF ranged from ?2.5 to 27.0, 1.9 to 29.6, and 1.3 to 34.4%. Intraclass correlation coefficients were 0.85, 0.89, and 0.91 for each method, and within‐subject coefficients of variation were 18.5, 9.9, and 10.3%, respectively. Mean phantom FFs derived by Methods 2 and 3 were comparable to the known FF for each phantom. Method 1 underestimated phantom FF.

Conclusion:

Methods 2 and 3 accurately assess FF. Strong reproducibility across magnet type and strength render them suitable for use in multicenter trials and longitudinal assessments. J. Magn. Reson. Imaging 2013;37:1359–1370. © 2012 Wiley Periodicals, Inc.

     

Resovist enhanced MR imaging of the liver: Does quantitative assessment help in focal lesion classification and characterization?

Purpose:

To improve characterization of focal liver lesions by a prospective quantitative analysis of percentage signal intensity change, in dynamic and late phases after slow (0.5 mL/s) Resovist administration.

Materials and Methods:

Seventy‐three patients were submitted on clinical indication to MR examination with Resovist. Signal intensity of 92 detected focal lesions (5–80 mm) were measured with regions of interest and normalized to paravertebral muscle in arterial, portal, equilibrium and T1/T2 late phases, by two observers in conference. Five values of percentage variations per patient were obtained and statistically evaluated.

Results:

The enhancement obtained on dynamic study is more suitable in hemangiomas and focal nodular hyperplasias than in adenomas and hepatocellular carcinomas. To discriminate benign versus malignant lesions on late‐phase‐T2‐weighted images, a cutoff = ?26%, allowed sensitivity and specificity values of 97.4% and 97.7%, respectively. Area under the receiver operating characteristic (ROC) curve was 0.99. To differentiate hemangioma versus all other focal liver lesions, on late‐phase‐T1‐weighted images, a cutoff = +40% permitted sensitivity and specificity values of 90.5% and 98.0%, respectively. Area under the ROC curve was 0.98.

Conclusion:

Late phase quantitative evaluation after slow Resovist administration, allows to differentiate malignant from benign hepatic masses and hemangiomas from all the others focal liver lesions, on T2‐/T1‐weighted acquisitions, respectively. J. Magn. Reson. Imaging 2009;30:1012–1020. © 2009 Wiley‐Liss, Inc.

     

Cortical calcification in sturge–weber syndrome on MRI‐SWI: Relation to brain perfusion status and seizure severity

Purpose:

To determine the relationship between calcified cortex and perfusion status of white matter and seizure severity in patients with Sturge–Weber Syndrome (SWS), a sporadic neurocutaneous disorder characterized by a leptomeningeal angioma, progressive brain ischemia, and a high incidence of seizures using susceptibility weighted imaging (SWI) and dynamic susceptibility contrast‐enhanced perfusion weighted imaging (DSC‐PWI).

Materials and Methods:

Fifteen children (ages: 0.9–10 years) with unilateral SWS prospectively underwent magnetic resonance imaging (MRI). The degree of cortical calcification was assessed using SWI while perfusion status was quantified using DSC‐PWI images (asymmetries of various perfusion parameters). Comparisons between calcification, perfusion status, and seizure variables were performed.

Results:

Patients with severely calcified cortex demonstrated significantly lower perfusion in the ipsilateral white matter (mean asymmetry: ?0.52 ± 0.22) as compared to patients with only mildly calcified cortex or no calcification (mean asymmetry: 0.08 ± 0.25). Patients with severely calcified cortex also suffered from a higher seizure burden (a composite measure of seizure frequency and epilepsy duration; P = 0.01) and a trend for earlier seizure onset and longer epilepsy duration.

Conclusion:

Severe calcification in the affected hemisphere is related to severely decreased perfusion in underlying white matter and is associated with more severe epilepsy in SWS patients. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.

     

Left ventricle segmentation using graph searching on intensity and gradient and a priori knowledge (lvGIGA) for short‐axis cardiac magnetic resonance imaging

Purpose

To develop and evaluate an automated left ventricle (LV) segmentation algorithm using Graph searching based on Intensity and Gradient information and A priori knowledge (lvGIGA).

Materials and Methods

The lvGIGA algorithm was implemented with coil sensitivity correction and polar coordinate transformation. Graph searching and expansion were applied for extracting myocardial endocardial and epicardial borders. LV blood and myocardium intensities were estimated for accurate partial volume calculation of blood volume and myocardial mass. Cardiac cine SSFP images were acquired from 38 patients. The lvGIGA algorithm was used to measure blood volume, myocardial mass, and ejection fraction, and compared with clinical manual tracing and the commercial MASS software.

Results

The success rate for segmenting both endocardial and epicardial borders was 95.6% slices for lvGIGA and 37.8% for MASS (excluding basal slices that required manual enclosure of ventricle blood). The lvGIGA segmentation result agreed well with manual tracing, within ?2.9 ± 4.4 mL, 2.1 ± 2.2%, and ?9.6 ± 13.0 g, for blood volume, ejection fraction, and myocardial mass, respectively.

Conclusion

The lvGIGA algorithm substantially improves the robustness of LV segmentation automation over the commercial MASS software, agrees well with clinical manual tracing, and may be a useful tool for clinical practice. J. Magn. Reson. Imaging 2008;28:1393–1401. © 2008 Wiley‐Liss, Inc.