Simultaneous Acquisition of Diffusion Tensor and Dynamic Diffusion MRI.

BACKGROUND: Dynamic diffusion magnetic resonance imaging (ddMRI) metrics can assess transient microstructural alterations in tissue diffusivity but requires additional scan time hindering its clinical application. PURPOSE: To determine whether a diffusion gradient table can simultaneously acquire data to estimate dynamic and diffusion tensor imaging (DTI) metrics. STUDY TYPE: Prospective. SUBJECTS: Seven healthy subjects, 39 epilepsy patients (15 female, 31 male, age ± 15). FIELD STRENGTH/SEQUENCE: Two-dimensional diffusion MRI (b = 1000 s/mm2 ) at a field strength of 3 T. Sessions in healthy subjects-standard ddMRI (30 directions), standard DTI (15 and 30 directions), and nested cubes scans (15 and 30 directions). Sessions in epilepsy patients-two 30 direction (standard ddMRI, 10 nested cubes) or two 15 direction scans (standard DTI, 5 nested cubes). ASSESSMENT: Fifteen direction DTI was repeated twice for within-session test-retest measurements in healthy subjects. Bland-Altman analysis computed bias and limits of agreement for DTI metrics using test-retest scans and standard 15 direction vs. 5 nested cubes scans. Intraclass correlation (ICC) analysis compared tensor metrics between 15 direction DTI scans (standard vs. 5 nested cubes) and the coefficients of variation (CoV) of trace and apparent diffusion coefficient (ADC) between 30 direction ddMRI scans (standard vs. 10 nested cubes). STATISTICAL TESTS: Bland-Altman and ICC analysis using a P-value of 0.05 for statistical significance. RESULTS: Correlations of mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were strong and significant in gray (ICC > 0.95) and white matter (ICC > 0.95) between standard vs. nested cubes DTI acquisitions. Correlation of white matter fractional anisotropy was also strong (ICC > 0.95) and significant. ICCs of the CoV of dynamic ADC measured using repeated cubes and nested cubes acquisitions were modest (ICC >0.60), but significant in gray matter. CONCLUSION: A nested cubes diffusion gradient table produces tensor-based and dynamic diffusion measurements in a single acquisition. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 1.

Highly Efficient and Accurate Deep Learning-Based Classification of MRI Contrast on a CPU and GPU.

Classifying MR images based on their contrast mechanism can be useful in image segmentation where additional information from different contrast mechanisms can improve intensity-based segmentation and help separate the class distributions. In addition, automated processing of image type can be beneficial in archive management, image retrieval, and staff training. Different clinics and scanners have their own image labeling scheme, resulting in ambiguity when sorting images. Manual sorting of thousands of images would be a laborious task and prone to error. In this work, we used the power of transfer learning to modify pretrained residual convolution neural networks to classify MRI images based on their contrast mechanisms. Training and validation were performed on a total of 5169 images belonging to 10 different classes and from different MRI vendors and field strengths. Time for training and validation was 36 min. Testing was performed on a different data set with 2474 images. Percentage of correctly classified images (accuracy) was 99.76%. (A deeper version of the residual network was trained for 103 min and showed slightly lower accuracy of 99.68%.) In consideration of model deployment in the real world, performance on a single CPU computer was compared with GPU implementation. Highly accurate classification, training, and testing can be achieved without use of a GPU in a relatively short training time, through proper choice of a convolutional neural network and hyperparameters, making it feasible to improve accuracy by repeated training with cumulative training sets. Techniques to improve accuracy further are discussed and demonstrated. Derived heatmaps indicate areas of image used in decision making and correspond well with expert human perception. The methods used can be easily extended to other classification tasks with minimal changes.

Determining the optimal postlabeling delay for arterial spin labeling using subject-specific estimates of blood velocity in the carotid artery.

BACKGROUND: Arterial spin labeling with 3D acquisition requires determining a single postlabeling delay (PLD) value. PLD affects the signal-to-noise ratio (SNR) per unit time as well as quantitative cerebral blood flow (CBF) values due to its bearing on the presence of a vascular signal. PURPOSE: To search for an optimal PLD for pseudocontinuous arterial spin labeling (pCASL) using patient-specific carotid artery blood velocity measurements. STUDY TYPE: Prospective. SUBJECTS: A control group of 11 volunteers with no known pathology. Corroboration was through a separate group of six volunteers and a noncontrol group of five sickle cell disease (SCD) patients. FIELD STRENGTH/SEQUENCE: Pseudocontinuous arterial spin labeling with 3D nonsegmented echo planar imaging acquisition at 3T. ASSESSMENT: A perfusion-based measure was determined over a range of PLDs for each of 11 volunteers. A third-order polynomial was used to find the optimal PLD where the defined measure was maximum. This was plotted against the corresponding carotid artery velocity to determine a relationship between the perfusion measure and velocity. Corroboration was done using a group of six volunteers and a noncontrol group of five patients with SCD. PLD was determined from the carotid artery velocity and derived relationship and compared with optimal PLD obtained from measured perfusion over a range of PLD values. Error between the perfusion measure at predicted and measured optimal PLD was determined. STATISTICAL TESTS: Chi-squared goodness of fit; Pearson correlation; Bland-Altman. RESULTS: Carotid artery velocity was 63.8 ± 6.6 cm/s (53.1 ≤ v ≤ 72.3 cm/s) while optimal PLD was 1374 ± 226.5 msec (1102 ≤ PLD ≤ 1787 msec) across the 11 volunteers. PLD as a function of carotid velocity was determined to be PLD = -31.94. v + 3410 msec (Pearson correlation -0.93). In six volunteers, mean error between the perfusion measure at predicted and measured optimal PLD was 1.35%. Pearson correlation between the perfusion measure at the predicted PLD and the measure obtained experimentally was r = 0.96 (P < 0.001). Bland-Altman revealed a slight bias of 1.3%. For the test case of five SCD patients, the mean error was 1.3%. DATA CONCLUSION: Carotid artery velocity was used to determine optimal PLD for pCASL with 3D acquisition. The derived relationship was used to predict optimal PLD and the associated perfusion measure, which was found to be accurate when compared with its measured counterpart. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:951-960.

Three-dimensional T1 and T2* mapping of human lung parenchyma using interleaved saturation recovery with dual echo ultrashort echo time imaging (ITSR-DUTE).

PURPOSE: To develop and assess a new technique for three-dimensional (3D) full lung T1 and T2* mapping using a single free breathing scan during a clinically feasible time. MATERIALS AND METHODS: A 3D stack of dual-echo ultrashort echo time (UTE) radial acquisition interleaved with and without a WET (water suppression enhanced through T1 effects) saturation pulse was used to map T1 and T2* simultaneously in a single scan. Correction for modulation due to multiple views per segment was derived. Bloch simulations were performed to study saturation pulse excitation profile on lung tissue. Optimization of the saturation delay time (for T1 mapping) and echo time (for T2* mapping) was performed. Monte Carlo simulation was done to predict accuracy and precision of the sequence with signal-to-noise ratio of in vivo images used in the simulation. A phantom study was carried out using the 3D interleaved saturation recovery with dual echo ultrashort echo time imaging (ITSR-DUTE) sequence and reference standard inversion recovery spin echo sequence (IR-SE) to compare accuracy of the sequence. Nine healthy volunteers were imaged and mean (SD) of T1 and T2* in lung parenchyma at 3T were estimated through manually assisted segmentation. 3D lung coverage with a resolution of 2.5 × 2.5 × 6 mm3 was performed and nominal scan time was recorded for the scans. Repeatability was assessed in three of the volunteers. Regional differences in T1/T2* values were also assessed. RESULTS: The phantom study showed accuracy of T1 values to be within 2.3% of values obtained from IR-SE. Mean T1 value in lung parenchyma was 1002 ± 82 ms while T2* was 0.85 ± 0.1 ms. Scan time was ∼10 min for volunteer scans. Mean coefficient of variation (CV) across slices was 0.057 and 0.09, respectively. Regional variation along the gravitational direction and between right and left lung were not significant (P = 0.25 and P = 0.06, respectively) for T1. T2* showed significant variation (P = 0.03) along the gravitational direction. Repeatability for three volunteers was within 0.7% for T1 and 1.9% for T2*. CONCLUSION: 3D T1 and T2* maps of the entire lung can be obtained in a single scan of ∼10 min with a resolution of 2.5 × 2.5 × 6 mm3 . LEVEL OF EVIDENCE: 2 J. Magn. Reson. Imaging 2017;45:1097-1104.

Submillimeter diffusion tensor imaging and late gadolinium enhancement cardiovascular magnetic resonance of chronic myocardial infarction.

BACKGROUND: Knowledge of the three-dimensional (3D) infarct structure and fiber orientation remodeling is essential for complete understanding of infarct pathophysiology and post-infarction electromechanical functioning of the heart. Accurate imaging of infarct microstructure necessitates imaging techniques that produce high image spatial resolution and high signal-to-noise ratio (SNR). The aim of this study is to provide detailed reconstruction of 3D chronic infarcts in order to characterize the infarct microstructural remodeling in porcine and human hearts. METHODS: We employed a customized diffusion tensor imaging (DTI) technique in conjunction with late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) on a 3T clinical scanner to image, at submillimeter resolution, myofiber orientation and scar structure in eight chronically infarcted porcine hearts ex vivo. Systematic quantification of local microstructure was performed and the chronic infarct remodeling was characterized at different levels of wall thickness and scar transmurality. Further, a human heart with myocardial infarction was imaged using the same DTI sequence. RESULTS: The SNR of non-diffusion-weighted images was >100 in the infarcted and control hearts. Mean diffusivity and fractional anisotropy (FA) demonstrated a 43% increase, and a 35% decrease respectively, inside the scar tissue. Despite this, the majority of the scar showed anisotropic structure with FA higher than an isotropic liquid. The analysis revealed that the primary eigenvector orientation at the infarcted wall on average followed the pattern of original fiber orientation (imbrication angle mean: 1.96 ± 11.03° vs. 0.84 ± 1.47°, p = 0.61, and inclination angle range: 111.0 ± 10.7° vs. 112.5 ± 6.8°, p = 0.61, infarcted/control wall), but at a higher transmural gradient of inclination angle that increased with scar transmurality (r = 0.36) and the inverse of wall thickness (r = 0.59). Further, the infarcted wall exhibited a significant increase in both the proportion of left-handed epicardial eigenvectors, and in the angle incoherency. The infarcted human heart demonstrated preservation of primary eigenvector orientation at the thinned region of infarct, consistent with the findings in the porcine hearts. CONCLUSIONS: The application of high-resolution DTI and LGE-CMR revealed the detailed organization of anisotropic infarct structure at a chronic state. This information enhances our understanding of chronic post-infarction remodeling in large animal and human hearts.

Structural and Functional Correlates of Myocardial T1 Mapping in 321 Patients With Hypertrophic Cardiomyopathy.

OBJECTIVE: The aim of this study was to evaluate the structural and functional correlates of T1 mapping in 321 patients with hypertrophic cardiomyopathy (HCM). METHODS: Three hundred twenty-one patients with HCM who underwent cardiac magnetic resonance from 2003 to 2013 were retrospectively identified from our institution's HCM registry. Left ventricular volume, function, late gadolinium enhancement (LGE), and Look-Locker T1 time were quantified. T1 time was normalized to blood pool to calculate T1 ratio. Correlations between LGE%, T1 ratio, and structural and functional features were performed using Pearson correlation coefficient. RESULTS: Late gadolinium enhancement showed stronger correlation with left ventricular mass index (r = 0.41, P < 0.001) compared with T1 ratio (r = -0.17, P = 0.004). Both LGE% and T1 ratio correlated with ejection fraction (r = -0.18 and P = 0.002 vs r = 0.21 and P < 0.001, respectively). E/e' showed correlation with LGE% but not with T1 ratio. CONCLUSIONS: Late gadolinium enhancement was more strongly correlated with the phenotypic expression of HCM compared with T1 ratio.

Long T2 suppression in native lung 3-D imaging using k-space reordered inversion recovery dual-echo ultrashort echo time MRI.

OBJECTIVE: Long T2 species can interfere with visualization of short T2 tissue imaging. For example, visualization of lung parenchyma can be hindered by breathing artifacts primarily from fat in the chest wall. The purpose of this work was to design and evaluate a scheme for long T2 species suppression in lung parenchyma imaging using 3-D inversion recovery double-echo ultrashort echo time imaging with a k-space reordering scheme for artifact suppression. MATERIALS AND METHODS: A hyperbolic secant (HS) pulse was evaluated for different tissues (T1/T2). Bloch simulations were performed with the inversion pulse followed by segmented UTE acquisition. Point spread function (PSF) was simulated for a standard interleaved acquisition order and a modulo 2 forward-reverse acquisition order. Phantom and in vivo images (eight volunteers) were acquired with both acquisition orders. Contrast to noise ratio (CNR) was evaluated in in vivo images prior to and after introduction of the long T2 suppression scheme. RESULTS: The PSF as well as phantom and in vivo images demonstrated reduction in artifacts arising from k-space modulation after using the reordering scheme. CNR measured between lung and fat and lung and muscle increased from -114 and -148.5 to +12.5 and 2.8 after use of the IR-DUTE sequence. Paired t test between the CNRs obtained from UTE and IR-DUTE showed significant positive change (p < 0.001 for lung-fat CNR and p = 0.03 for lung-muscle CNR). CONCLUSION: Full 3-D lung parenchyma imaging with improved positive contrast between lung and other long T2 tissue types can be achieved robustly in a clinically feasible time using IR-DUTE with image subtraction when segmented radial acquisition with k-space reordering is employed.

Evaluation of optimized breath-hold and free-breathing 3D ultrashort echo time contrast agent-free MRI of the human lung.

PURPOSE: To evaluate an optimized stack of radials ultrashort echo time (UTE) 3D magnetic resonance imaging (MRI) sequence for breath-hold and free-breathing imaging of the human lung. MATERIALS AND METHODS: A 3D stack of ultrashort echo time radials trajectory was optimized for coronal and axial lower-resolution breath-hold and higher-resolution free-breathing scans using Bloch simulations. The sequence was evaluated in 10 volunteers, without the use of contrast agents. Signal-to-noise ratio (SNR) mean and 95% confidence interval (CI) were determined from separate signal and noise images in a semiautomated fashion. The four scanning schemes were evaluated for significant differences in image quality using Student's t-test. Ten clinical patients were scanned with the sequence and findings were compared with concomitant computed tomography (CT) in nine patients. Breath-hold 3D spokes images were compared with 3D stack of radials in five volunteers. A Mann-Whitney U-test was performed to test significance in both cases. RESULTS: Breath-hold imaging of the entire lung in volunteers was performed with SNR (mean = 42.5 [CI]: 35.5-49.5; mean = 34.3 [CI]: 28.6-40) in lung parenchyma for coronal and axial scans, respectively, which can be used as a quick scout scan. Longer respiratory triggered free-breathing scan enabled high-resolution UTE scanning with mean SNR of 14.2 ([CI]: 12.9-15.5) and 9.2 ([CI]: 8.2-10.2) for coronal and axial scans, respectively. Axial free-breathing scans showed significantly higher image quality (P = 0.008) than the three other scanning schemes. The mean score for comparison with CT was 1.67 (score 0: n = 0; 1: n = 3; 2: n = 6). There was no significant difference between CT and MRI (P = 0.25). 3D stack of radials images were significantly better than 3D spokes images (P < 0.001). CONCLUSION: The optimized 3D stack of radials trajectory was shown to provide high-quality MR images of the lung parenchyma without the use of MRI contrast agents. The sequence may offer the possibility of breath-hold imaging and provides greater flexibility in trading off slice thickness and parallel imaging for scan time.

Optimized three-dimensional sodium imaging of the human heart on a clinical 3T scanner.

PURPOSE: Optimization of sequence and sequence parameters to allow three-dimensional (3D) sodium imaging of the entire human heart in vivo in a clinically reasonable time. THEORY AND METHODS: A stack of spirals pulse sequence was optimized for cardiac imaging by considering factors such as spoiling, nutation angles, repetition time, echo time, T1/T2 relaxation, off-resonance, data acquisition window, motion, and segmented k-space acquisition. Simulations based on Bloch equations as well as the exact trajectory used for data acquisition provided the basis for choice of parameter combinations for sodium imaging. Sodium phantom scanning was used to validate the choice of parameters and for corroboration with simulations. In vivo cardiac imaging in six volunteers was also performed with an optimized sequence. RESULTS: Phantom studies showed good correlation with simulation results. Images obtained from human volunteers showed that the heart can be imaged with a nominal resolution of 5 × 5 × 10 mm(3) and with a signal-to-noise ratio >15 (in the septum) in about 6-10 minutes. Long axis views of the reformatted human heart show true 3D imaging capability. CONCLUSION: Optimization of the sequence and its parameters allowed in vivo 3D sodium imaging of the entire human heart in a clinically reasonable time.

Reduced scan time three-dimensional FLAIR using modulated inversion and repetition time.

BACKGROUND: The purpose of this study is to design and evaluate a new reduced scan time three-dimensional (3D) FLuid Attenuated Inversion Recovery (FLAIR) sequence. METHODS: The 3D FLAIR sequence was modified so that the repetition time was modulated in a predetermined smooth manner (3D mFLAIR). Inversion times were adjusted accordingly to maintain cerebrospinal fluid (CSF) suppression. Simulations were performed to determine SNR for gray matter (GM), white matter (WM), and CSF. Fourteen volunteers were imaged using the modified and product sequence. SNR measurements were performed in GM, WM, and CSF. Mean value and the 95% confidence interval ([CI]) were assessed. Scan time for the 3D FLAIR and 3D mFLAIR sequences was measured. RESULTS: There was no statistically significant difference in the SNR measured in GM (P value = 0.5; mean SNR = 42.8 [CI]: 38.2-45.5 versus 42.2 [CI]: 38.3-46.1 for 3D FLAIR and 3D mFLAIR, respectively) and WM (P value = 0.25; mean SNR = 32.1 [CI]: 30.3-33.8 versus 32.9 [CI]: 31.1-34.7). Scan time reduction greater than 30% was achieved for the given parameter set with the 3D mFLAIR sequence. CONCLUSION: Scan time for 3D FLAIR can be effectively reduced by modulating repetition and inversion time in a predetermined manner while maintaining the SNR and CNR of a constant TR sequence.

Part 1 - Coronary angiography with gadofosveset trisodium: a prospective feasibility study evaluating injection techniques for steady-state imaging.

BACKGROUND: The purpose of this study was to define an optimal injection protocol for 5-10 min duration navigator-based coronary MR angiography using an intravascular gadolinium-based contrast agent (GBCA), which is better suited for steady-state coronary MR angiography than conventional GBCAs. METHODS: Using projections from pharmacokinetic models of the intravascular concentration of gadofosveset, a dual-injection protocol was formulated and tested on 14 healthy human subjects. Modified Look-Locker inversion recovery (MOLLI) sequences were used for T1 mapping at 3 Tesla to evaluate the concentration of tracer in the aorta over the scanning interval. RESULTS: Pharmacokinetic models for a bolus plus slow infusion technique at a 5, 10, and 15 min steady state intravascular concentration was compared to single bolus curves. The 70 %/30 % bolus/slow infusion technique resulted in the highest intravascular concentration over a 5 min scan duration. Similarly, the 60 %/40 % bolus/slow infusion technique was projected to be ideal for image acquisition duration of 5-10 min. These models were confirmed with T1 maps on normal volunteers. Arterial-venous mixing of contrast was achieved within 90 s of the beginning of the bolus. CONCLUSIONS: Gadofosveset injection is optimized for the lowest intravascular T1 time for 5-10 min duration MR angiography by bolus injection of 60-70 % of the total dose followed by slow infusion of the remainder of the total dose. This protocol achieves rapid and prolonged steady state intravascular concentrations of the GBCA that may be useful for prolonged image acquisition, such as required for navigator-based coronary MR angiography at 3 Tesla. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01130545 NCT01130545 , registered as of May 25, 2010.

Axial scan orientation and the tibial tubercle-trochlear groove distance: error analysis and correction.

OBJECTIVE: The tibial tubercle (TT)-trochlear groove (TG) distance is an important metric in the assessment of patellofemoral dysfunction and is routinely measured on axial MRI and CT. This study examines error in measurements of the TT-TG distance related to variance in axial MRI scan orientation. SUBJECTS AND METHODS: Isotropic 3D turbo spin-echo MRI of the extended knee was performed in 12 healthy subjects. The z-axis of the scanner defines the perpendicular to a routine axial plane, and the anatomic axial plane is parallel to the knee joint. Isotropic MRI was reformatted into routine and anatomic axial planes and in axial planes simulating 5° of femoral adduction and abduction relative to the anatomic plane. A method for correcting the TT-TG distance to account for variable axial scan orientation is presented. RESULTS: Five degrees of simulated femoral abduction is associated with a mean increase in the TT-TG distance of 38% (SD = 17%), whereas 5° of simulated femoral adduction is associated with a mean decrease in the TT-TG distance of 51% (SD = 39%). The average deviation of the routine axial plane from the anatomic axial plane was 5.0° abduction (SD = 2.3°). The simplest correction method reduced the mean discrepancy in the observed TT-TG distance by 68% and 72% in simulated femoral abduction and adduction, respectively. CONCLUSION: The TT-TG distance is sensitive to small changes in femoral alignment and should be interpreted with caution if axial image acquisition is not standardized. Knowing the vertical separation of the TT from the TG facilitates a simplified correction of the TT-TG distance, which is as effective as more complex corrections.

Modified Look-Locker T1 evaluation using Bloch simulations: human and phantom validation.

Modified Look-Locker imaging is frequently used for T(1) mapping of the myocardium. However, the specific effect of various MRI parameters (e.g., encoding scheme, modifications of flip angle, heart rate, T(2), and inversion times) on the accuracy of T(1) measurement has not been studied through Bloch simulations. In this work, modified Look-Locker imaging was characterized through a numerical solution for Bloch equations. MRI sequence parameters that may affect T(1) accuracy were systematically varied in the simulation. For validation, phantoms were constructed with various T(2) and T(1) times and compared with Bloch equation simulations. Human volunteers were also evaluated with various pulse sequences parameters to assess the validity of the numerical simulations. There was close agreement between simulated T(1) times and T(1) times measured in phantoms and volunteers. Lower T(2) times (i.e., <30 ms) resulted in errors greater than 5% for T(1) determination. Increasing maximum inversion time value improved T(1) accuracy particularly for precontrast myocardial T(1). Balanced steady-state free precession k space centric encoding improved accuracy for short T(1) times (post gadolinium), but linear encoding provided improved accuracy for precontrast T(1) values. Lower flip angles are preferred if the signal-to-noise ratio is sufficiently high. Bloch simulations for modified Look-Locker imaging provide an accurate method to comprehensively quantify the effect of pulse sequence parameters on T(1) accuracy. As an alternative to otherwise lengthy phantom studies or human studies, such simulations may be useful to optimize the modified Look-Locker imaging sequence and compare differences in T(1)-derived measurements from different scanners or institutions.

Modified look-locker inversion recovery T1 mapping indices: assessment of accuracy and reproducibility between magnetic resonance scanners.

BACKGROUND: Cardiovascular magnetic resonance (CMR) T1 mapping indices, such as T1 time and partition coefficient (λ), have shown potential to assess diffuse myocardial fibrosis. The purpose of this study was to investigate how scanner and field strength variation affect the accuracy and precision/reproducibility of T1 mapping indices. METHODS: CMR studies were performed on two 1.5T and three 3T scanners. Eight phantoms were made to mimic the T1/T2 of pre- and post-contrast myocardium and blood at 1.5T and 3T. T1 mapping using MOLLI was performed with simulated heart rate of 40-100 bpm. Inversion recovery spin echo (IR-SE) was the reference standard for T1 determination. Accuracy was defined as the percent error between MOLLI and IR-SE, and scan/re-scan reproducibility was defined as the relative percent mean difference between repeat MOLLI scans. Partition coefficient was estimated by ΔR1myocardium phantom/ΔR1blood phantom. Generalized linear mixed model was used to compare the accuracy and precision/reproducibility of T1 and λ across field strength, scanners, and protocols. RESULTS: Field strength significantly affected MOLLI T1 accuracy (6.3% error for 1.5T vs. 10.8% error for 3T, p<0.001) but not λ accuracy (8.8% error for 1.5T vs. 8.0% error for 3T, p=0.11). Partition coefficients of MOLLI were not different between two 1.5T scanners (47.2% vs. 47.9%, p=0.13), and showed only slight variation across three 3T scanners (49.2% vs. 49.8% vs. 49.9%, p=0.016). Partition coefficient also had significantly lower percent error for precision (better scan/re-scan reproducibility) than measurement of individual T1 values (3.6% for λ vs. 4.3%-4.8% for T1 values, approximately, for pre/post blood and myocardium values). CONCLUSION: Based on phantom studies, T1 errors using MOLLI ranged from 6-14% across various MR scanners while errors for partition coefficient were less (6-10%). Compared with absolute T1 times, partition coefficient showed less variability across platforms and field strengths as well as higher precision.

T1 Mapping in cardiomyopathy at cardiac MR: comparison with endomyocardial biopsy.

PURPOSE: To determine the utility of cardiac magnetic resonance (MR) T1 mapping for quantification of diffuse myocardial fibrosis compared with the standard of endomyocardial biopsy. MATERIALS AND METHODS: This HIPAA-compliant study was approved by the institutional review board. Cardiomyopathy patients were retrospectively identified who had undergone endomyocardial biopsy and cardiac MR at one institution during a 5-year period. Forty-seven patients (53% male; mean age, 46.8 years) had undergone diagnostic cardiac MR and endomyocardial biopsy. Thirteen healthy volunteers (54% male; mean age, 38.1 years) underwent cardiac MR as a reference. Myocardial T1 mapping was performed 10.7 minutes ± 2.7 (standard deviation) after bolus injection of 0.2 mmol/kg gadolinium chelate by using an inversion-recovery Look-Locker sequence on a 1.5-T MR imager. Late gadolinium enhancement was assessed by using gradient-echo inversion-recovery sequences. Cardiac MR results were the consensus of two radiologists who were blinded to histopathologic findings. Endomyocardial biopsy fibrosis was quantitatively measured by using automated image analysis software with digital images of specimens stained with Masson trichrome. Histopathologic findings were reported by two pathologists blinded to cardiac MR findings. Statistical analyses included Mann-Whitney U test, analysis of variance, and linear regression. RESULTS: Median myocardial fibrosis was 8.5% (interquartile range, 5.7-14.4). T1 times were greater in control subjects than in patients without and in patients with evident late gadolinium enhancement (466 msec ± 14, 406 msec ± 59, and 303 msec ± 53, respectively; P < .001). T1 time and histologic fibrosis were inversely correlated (r = -0.57; 95% confidence interval: -0.74, -0.34; P < .0001). The area under the curve for myocardial T1 time to detect fibrosis of greater than 5% was 0.84 at a cutoff of 383 msec. CONCLUSION: Cardiac MR with T1 mapping can provide noninvasive evidence of diffuse myocardial fibrosis in patients referred for evaluation of cardiomyopathy.

Fast T1 mapping determined using incomplete inversion recovery look-locker 3D balanced SSFP acquisition and a simple two-parameter model fit.

PURPOSE: To evaluate a fast T1 mapping technique using incomplete inversion recovery 3D balanced steady-state free precession acquisition along with a two-parameter model fit. MATERIALS AND METHODS: Using Bloch simulations, we explored the two-parameter model fit for data acquired using such an acquisition scheme. The parameter space over which the fit holds good was determined through simulations. A linear correction was derived for the R1* (1/T1*) values so determined. Two phantoms and six volunteers were scanned using the described technique. Comparison scans using full recovery as well as gold standard inversion recovery spin echo were also performed. RESULTS: The two-parameter fit works exceedingly well over a large parameter space. T1 values in the phantoms showed an error of 4.9% and 39% before correction and 0.9% and 1.6% after correction. For the six volunteers, error in T1 value was 5.3% for white matter (WM) and 2.4% for gray matter (GM) after correction, while it was 11.2% and 18.2% before correction. CONCLUSION: The work presented here allows for T1 map determination with higher resolution and shorter acquisition time than previously possible. The technique is especially well suited for GM/WM T1 mapping.

Fat-corrected T2 measurement as a marker of active muscle disease in inflammatory myopathy.

OBJECTIVE: We sought to improve the utility of T2 measurement as a marker of active muscle disease in patients with idiopathic inflammatory myopathy by correcting for T2 prolongations caused by fatty replacement of muscle that accompnaies chronic muscle damage. SUBJECTS AND METHODS: Twenty-one patients with idiopathic inflammatory myopathy underwent a standardized MRI evaluation of the thighs. Fat fraction maps were calculated from dual-echo gradient-echo images. Fat-corrected T2 maps were generated from multiecho spin-echo images on the basis of a biexponential model that incorporated voxelwise fat fraction estimates. Semiautomated summaries of conventional and fat-corrected muscle T2 values were compared with one another and with standardized visual scores of muscle disease based on T1-weighted spin-echo and STIR images. RESULTS: Fat-corrected muscle T2 maps showed lower mean values and greater histogram entropy than conventional T2 maps, as analyzed over a standardized portion of the thigh muscles. Conventional and fat-corrected T2 values correlated with visual scores of active muscle disease on STIR images and with the varying intensity of disease depicted with STIR in focal muscle regions. CONCLUSION: MRI T2 maps of muscle can be corrected for varying fat content by combining the information from chemical shift-sensitive gradient-echo and multiecho spin-echo images. Use of this strategy may prove useful in the study of idiopathic inflammatory myopathy and other diseases characterized by both muscle inflammation and atrophy.

Nonalcoholic Fatty Liver Disease in Patients with Inherited and Sporadic Motor Neuron Degeneration.

We describe evidence of fatty liver disease in patients with forms of motor neuron degeneration with both genetic and sporadic etiology compared to controls. A group of 13 patients with motor neuron disease underwent liver imaging and laboratory analysis. The cohort included five patients with hereditary spastic paraplegia, four with sporadic amyotrophic lateral sclerosis (ALS), three with familial ALS, and one with primary lateral sclerosis. A genetic mutation was reported in nine of the thirteen motor neuron disease (MND) patients. Fatty liver disease was detected in 10 of 13 (77%) MND patients via magnetic resonance spectroscopy, with an average dome intrahepatic triacylglycerol content of 17% (range 2-63%, reference ≤5.5%). Liver ultrasound demonstrated evidence of fatty liver disease in 6 of the 13 (46%) patients, and serum liver function testing revealed significantly elevated alanine aminotransferase levels in MND patients compared to age-matched controls. Fatty liver disease may represent a non-neuronal clinical component of various forms of MND.

Left Ventricular Structure, Tissue Composition, and Aortic Distensibility in the Diabetes Control and Complications Trial/Epidemiology of Diabetes Intervention and Complications.

Alterations in myocardial structure, function, tissue composition (e.g., fibrosis) may be associated with metabolic syndrome (MetS). This study aimed to determine the relation of MetS and its individual components to markers of cardiovascular disease in patients with type 1 Diabetes Mellitus (T1DM). A total of 978 subjects of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications T1DM cohort (age: 49 ± 7 years, 47% female, DM duration 28 ± 5 years) underwent cardiovascular magnetic resonance. In a subset of 200 patients, myocardial tissue composition was measured with cardiovascular magnetic resonance T1 mapping after contrast administration. MetS was defined as T1DM plus 2 other abnormalities based on the American Heart Association/National Cholesterol Education Program criteria. MetS was present in 34.1% of subjects. After adjustment for age, height, scanner, study cohort, gender, smoking, mean glycated hemoglobin levels, history of macroalbuminuria and end-stage renal disease, left ventricle mass was greater by 12.3 g, end-diastolic volume was higher by 5.4 ml, and mass to end-diastolic volume ratio was higher by 5% in patients with MetS versus those without MetS (p <0.001 for all). Myocardial T1 times were lower by 29 ms in patients with MetS than those without (p <0.001). Elevated waist circumference showed the strongest associations with left ventricle mass (+10.1 g), end-diastolic volume (+6.7 ml), and lower myocardial T1 times (+31 ms) in patients with MetS compared with those without (p <0.01). In conclusion, in a large cohort of patients with T1DM, 34.1% of subjects met MetS criteria. MetS was associated with adverse myocardial structural remodeling and change in myocardial tissue composition.

T1 mapping of the gadolinium-enhanced myocardium: adjustment for factors affecting interpatient comparison.

Quantitative T(1) mapping of delayed gadolinium-enhanced cardiac magnetic resonance imaging has shown promise in identifying diffuse myocardial fibrosis. Despite careful control of magnetic resonance imaging parameters, comparison of T(1) times between different patients may be problematic because of patient specific factors such as gadolinium dose, differing glomerular filtration rates, and patient specific delay times. In this work, a model driven approach to account for variations between patients to allow for comparison of T(1) data is provided. Kinetic model parameter values were derived from healthy volunteer time-contrast curves. Correction values for the factors described above were used to normalize T(1) values to a matched state. Examples of pre- and postcorrected values for a pool of normal subjects and in a patient cohort of type 1 diabetic patients shows tighter clustering and improved discrimination of disease state.