Multiparametric approach with synthetic MR imaging for diagnosing salivary gland lesions.

PURPOSE: To determine whether synthetic MR imaging can distinguish between benign and malignant salivary gland lesions. METHODS: The study population included 44 patients with 33 benign and 11 malignant salivary gland lesions. All MR imaging was obtained using a 3 Tesla system. The QRAPMASTER pulse sequence was used to acquire images with four TI values and two TE values, from which quantitative images of T1 and T2 relaxation times and proton density (PD) were generated. The Mann-Whitney U test was used to compare T1, T2, PD, and ADC values among the subtypes of salivary gland lesions. ROC analysis was used to evaluate diagnostic capability between malignant tumors (MTs) and either pleomorphic adenomas (PAs) or Warthin tumors (WTs). We further calculated diagnostic accuracy for distinguishing malignant from benign lesions when combining these parameters. RESULTS: PAs demonstrated significantly higher T1, T2, PD, and ADC values than WTs (all p < 0.001). Compared to MTs, PAs had significantly higher T1, T2, and ADC values (all p < 0.001), whereas WTs had significantly lower T1, T2, and PD values (p < 0.001, p = 0.008, and p = 0.003, respectively). T2 and ADC were most effective in differentiating between MTs and PAs (AUC = 0.928 and 0.939, respectively), and T1 and PD values for differentiating between MTs and WTs (AUC = 0.915 and 0.833, respectively). Combining T1 with T2 or ADC achieved accuracy of 86.4% in distinguishing between malignant and benign tumors. Similarly, combining PD with T2 or ADC reached accuracy of 86.4% for differentiating between malignant and benign tumors. CONCLUSIONS: Utilizing a combination of synthetic MRI parameters may assist in differentiating malignant from benign salivary gland lesions.

[Novel Application of Post-contrast T1map for Detection of Subendocardial Infarction].

In cardiac magnetic resonance (CMR) for myocardial infarction, there have been quite a few cases of obscure image contrast between subendocardial lesion and left ventricular (LV) blood pool on late gadolinium enhancement (LGE) images. This study was motivated by confirmation of usefulness of post-contrast T1map for detection of subendocardial infarction. From June 2017 to May 2018, forty-eight consecutive patients who underwent contrast-enhanced CMR to assess myocardial infarction were reviewed. We measured the contrast ratio (CR) between the infarcted myocardium and LV blood pool on LGE and on post-contrast T1map images, and compared them. The CR (mean±standard deviation) was -0.04±0.11 for LGE images and 0.02±0.04 for post-contrast T1map images (P<0.05). These results suggest that the post-contrast T1map, which uses the difference in T1 value as image contrast rather than magnitude image, can clearly depict the boundary between the infarcted myocardium and LV blood pool. The addition of post-contrast T1map to image interpretation might provide valuable information in the evaluation of subendocardial infarction.

Feasibility of Imaging-Based Quantitative Hepatic Function Assessment: Gd-EOB-DTPA-Enhanced Liver MR Imaging Combined with T1 Mapping.

OBJECTIVE: to investigate the feasibility of gadoxetic acid (Gd-EOB-DTPA) enhanced MRI combined with T1 mapping in quantitative hepatic function assessment. METHODS: this study retrospectively enrolled 94 patients with Gd-EOB-DTPA enhanced MRI combined with T1 mapping, divided into group A (grade A, n=73), group B (grade B, n=14) and group C (grade C, n=7) based on Child-Pugh classification. Liver T1 relaxation times on plain scan (T1P) and hepatocellular phase (T1E) were measured. Decrease in T1 (T1D) and the percentage of decrease in T1 (T1D%) were calculated as follows: T1D=T1P-T1E, T1D%= T1D/T1P×100%. The relationship between T1P, T1E, T1D, T1D% and liver function classification was analyzed. RESULTS: T1P, T1D, and T1D% in group A were significantly higher than those of group B and C. T1E in group A was lower than those of group B and C. T1D% was significantly different between group B and C. There was no significant difference in T1P, T1E, T1D between groups B and C. T1E was positively correlated with liver function levels, T1P and T1D had a negative correlation with liver function levels. T1P, T1E, T1D, T1D% were significantly different between cirrhotic and non-cirrhotic groups. T1D% of less than 70% suggests liver dysfunction. CONCLUSION: Gd-EOB-DTPA enhanced liver MRI combined with T1 mapping is feasible for quantitative assessment of hepatic function.

Multidelay pseudocontinuous arterial spin labeling to measure blood flow in the head and neck.

Perfusion MRI is promising for the assessment, prediction, and monitoring of radiation toxicity in organs at risk in head and neck cancer. Arterial spin labeling (ASL) may be an attractive alternative for conventional perfusion MRI, that does not require the administration of contrast agents. However, currently, little is known about the characteristics and performance of ASL in healthy tissues in the head and neck region. Therefore, the purpose of this study was to optimize and evaluate multidelay pseudocontinuous ASL (pCASL) for the head and neck region and to explore nominal values and measurement repeatability for the blood flow (BF), and the transit time and T1 values needed for BF quantification in healthy tissues. Twenty healthy volunteers underwent a scan session consisting of four repeats of multidelay pCASL (postlabel delays: 1000, 1632, 2479 ms). Regions of interest were defined in the parotid glands, submandibular glands, tonsils, and the cerebellum (as a reference). Nominal values of BF were calculated as the average over four repeats per volunteer. The repeatability coefficient and within-subject coefficient of repeatability (wCV) of BF were calculated. The effect of T1 (map vs. cohort average) and transit time correction on BF was investigated. The mean BF (± SE) was 55.7 ± 3.1 ml/100 g/min for the parotid glands, 41.2 ± 2.8 ml/100 g/min for the submandibular glands, and 32.3 ± 2.2 ml/100 g/min for the tonsils. The best repeatability was found in the parotid glands (wCV = 13.3%-16.1%), followed by the submandibular glands and tonsils (wCV = 20.0%-24.6%). On average, the effect of T1 and transit time correction on BF was limited, although substantial bias occurred in individual acquisitions. In conclusion, we demonstrated the feasibility of BF measurements in the head and neck region using multidelay pCASL and reported on nominal BF values, BF repeatability, the effect of T1, and transit time in various tissues in the head and neck region.

Multiparametric study for glioma grading with FLAIR, ADC map, eADC map, T1 map, and SWI images.

PURPOSE: This paper is a preliminary attempt to compare the diagnostic efficiency and performance of Fluid-attenuated inversion recovery (FLAIR), apparent diffusion coefficient (ADC) map, exponential ADC (eADC) map, T1 map, and Susceptibility-weighted image (SWI) for glioma grading and combine these image data pairs to compare the diagnostic performance of different image data pairs for glioma grading. MATERIAL AND METHODS: Fifty-nine patients underwent FLAIR, ADC map, eADC map, Variable flip-angle (VFA) spoiled gradient recalled echo (SPGR) method, and SWI MRI imaging. The T1 map was reconstructed by the VFA-SPGR method. The average Relative Signal Contrast (RSC) and receiver operating characteristic curve (ROC) was calculated in a different image. The multivariate binary logistic regression model combined different image data pairs. RESULTS: The average RSC of SWI and ADC maps in high-grade glioma is significantly lower than RSCs in low-grade. The average RSC of the eADC map and T1 maps increased with glioma grade. No significant difference was detected between low and high-grade glioma on FLAIR images. The AUC for low and high-grade glioma differentiation on ADC maps, eADC maps, T1 map, and SWI were calculated 0.781, 0.864, 0.942, and 0.904, respectively. Also, by adding different image data, diagnostic performance was increased. CONCLUSION: Interestingly, the T1 map and SWI image have the potential to use in the clinic for glioma grading purposes due to their high performance. Also, the eADC map+T1 map and T1 map+SWI image weights have the highest diagnostic performance for glioma grading.

Quantification of the Intrinsic T1 and T2 of Heschl's Gyri with MR Fingerprinting.

PURPOSE: The human primary auditory cortex is located in the Heschl's gyrus (HG). To assess the intrinsic MR property in the gray matter of the HG (GM-HG) with T1 and T2 values using a commercially available MR fingerprinting (MRF) technique. METHODS: The subjects were 10 healthy volunteers (with 20 HGs; mean age, 31.5 years old; range, 25-53 years old). Coronal T1 and T2 maps were obtained with commercially available MRF using a 3-Tesla MR system. Two radiologists measured the T1 and T2 values of the GM-HG, the GM in the superior temporal gyrus (GM-STG), and the GM in the middle temporal gyrus (GM-MTG) by drawing a ROI on coronal maps. RESULTS: For both radiologists, the mean T1 and T2 values of the GM-HG were significantly lower than those in the GM-STG or GM-MTG (P < 0.01). The interobserver reliability using the intraclass correlation coefficients (ICC) (2,1) showed strong agreement for the measurement of the T1 and T2 values (ICCs =⃥ 0.80 and 0.78 for T1 and T2 values, respectively). CONCLUSION: The T1 and T2 values on MRF for the GM-HG were lower than those for the GM-STG and GM-MTG, likely reflecting a higher myelin content and iron deposition in the GM-HG. Quantitative measurements using the MRF can clarify cortical properties with high reliability, which may indicate that MRF mapping provides new insights into the structure of the human cortical GM.

T1 Mapping From MPRAGE Acquisitions: Application to the Measurement of the Concentration of Nanoparticles in Tumors for Theranostic Use.

BACKGROUND: The measurement of the concentration of theranostic agents in vivo is essential for the assessment of their therapeutic efficacy and their safety regarding healthy tissue. To this end, there is a need for quantitative T1 measurements that can be obtained as part of a standard clinical imaging protocol applied to tumor patients. PURPOSE: To generate T1 maps from MR images obtained with the magnetization-prepared rapid gradient echo (MPRAGE) sequence. To evaluate the feasibility of the proposed approach on phantoms, animal and patients with brain metastases. STUDY TYPE: Pilot. PHANTOM/ANIMAL MODEL/POPULATION: Solutions containing contrast agents (chelated Gd3+ and iron nanoparticles), male rat of Wistar strain, three patients with brain metastases. FIELD STRENGTH/SEQUENCE: A 3-T and 7-T, saturation recovery (SR), and MPRAGE sequences. ASSESSMENT: The MPRAGE T1 measurement was compared to the reference SR method on phantoms and rat brain at 7-T. The robustness of the in vivo method was evaluated by studying the impact of misestimates of tissue proton density. Concentrations of Gd-based theranostic agents were measured at 3-T in gray matter and metastases in patients recruited in NanoRad clinical trial. STATISTICAL TESTS: A linear model was used to characterize the relation between T1 measurements from the MPRAGE and the SR acquisitions obtained in vitro at 7-T. RESULTS: The slope of the linear model was 0.966 (R2  = 0.9934). MPRAGE-based T1 values measured in the rat brain were 1723 msec in the thalamus. MPRAGE-based T1 values measured in patients in white matter and gray matter amounted to 747 msec and 1690 msec. Mean concentration values of Gd3+ in metastases were 61.47 µmol. DATA CONCLUSION: The T1 values obtained in vitro and in vivo support the validity of the proposed approach. The concentrations of Gd-based theranostic agents may be assessed in patients with metastases within a standard clinical imaging protocol using the MPRAGE sequence. EVIDENCE LEVEL: 2. TECHNICAL EFFICACY: Stage 1.

Left ventricular thrombus after acute ST-segment elevation myocardial infarction: multi-parametric cardiac magnetic resonance imaging with long-term outcomes.

Left ventricular thrombus (LVT) after acute ST-segment elevation myocardial infarction (STEMI) are generally associated with poorer outcomes for patients at long-term follow-up. We hypothesis that tissue characteristics and strain parameters by cardiac magnetic resonance (CMR) imaging may indicate the interactions of LVT with ventricular myocardium remodeling at both acute stage and chronic stages in STEMI patients. This retrospective study included 111 consecutive STEMI patients (38 with LVT and 73 without LVT). All patients underwent CMR during acute stage (within 7 days) and chronic stage (after at least 2 months) periods after percutaneous coronary intervention (PCI). Left ventricular native T1, extracellular volume (ECV), radial, circumferential, and longitudinal strain were analyzed in both phases. Major adverse cardiac events (MACE, including cardiovascular death, myocardial reinfarction, and hospitalization for heart failure), thromboembolic and bleeding events, were the clinical endpoints of the study. During the acute stage, left ventricular ejection fraction (LVEF) (OR 0.77, P value = 0.01) and longitudinal strain (OR 1.90, P value < 0.001) were correlated with LVT formation. Strain parameters were reduced, while the native T1 and ECV values of both the infarcted area and remote myocardium were elevated in LVT patients. During the chronic stage, LVT resolved in 29 of 38 patients (76%). LVT remaining patients had lower LVEF, a larger LV, and higher ECV in the acute stage than those of the LVT-resolved patients. In the long-term follow up of 678 days, LVT (HR 2.45, P value = 0.02), aneurysm (HR 1.81, P value = 0.04), and native T1 (HR 2.44, P value = 0.01) were identified as three independent predictors of MACE, the incidence of thromboembolic events and bleeding events by a multivariable stepwise Cox proportional hazards regression. STEMI patients developing LVT had worse LV function, myocardial infarction extent, strain, and higher T1 and ECV values than STEMI patients without LVT. The LVT-remaining patients in the chronic stage had poorer functional and mapping parameters beginning in the first week. During the acute stage, LVEF and global longitudinal strain were independent correlated with LVT formation. During the long-term follow up, LVT, aneurysm and elevated myocardial T1 were associated with adverse outcomes in acute STEMI patients.

Bright-blood and dark-blood phase sensitive inversion recovery late gadolinium enhancement and T1 and T2 maps in a single free-breathing scan: an all-in-one approach.

BACKGROUND: Quantitative cardiovascular magnetic resonance (CMR) T1 and T2 mapping are used to detect diffuse disease such as myocardial fibrosis or edema. However, post gadolinium contrast mapping often lacks visual contrast needed for assessment of focal scar. On the other hand, late gadolinium enhancement (LGE) CMR which nulls the normal myocardium has excellent contrast between focal scar and normal myocardium but has poor ability to detect global disease. The objective of this work is to provide a calculated bright-blood (BB) and dark-blood (DB) LGE based on simultaneous acquisition of T1 and T2 maps, so that both diffuse and focal disease may be assessed within a single multi-parametric acquisition. METHODS: The prototype saturation recovery-based SASHA T1 mapping may be modified to jointly calculate T1 and T2 maps (known as multi-parametric SASHA) by acquiring additional saturation recovery (SR) images with both SR and T2 preparations. The synthetic BB phase sensitive inversion recovery (PSIR) LGE may be calculated from the post-contrast T1, and the DB PSIR LGE may be calculated from the post-contrast joint T1 and T2 maps. Multi-parametric SASHA maps were acquired free-breathing (45 heartbeats). Protocols were designed to use the same spatial resolution and achieve similar signal-to-noise ratio (SNR) as conventional motion corrected (MOCO) PSIR. The calculated BB and DB LGE were compared with separate free breathing (FB) BB and DB MOCO PSIR acquisitions requiring 16 and 32 heart beats, respectively. One slice with myocardial infarction (MI) was acquired with all protocols within 4 min. RESULTS: Multiparametric T1 and T2 maps and calculated BB and DB PSIR LGE images were acquired for patients with subendocardial chronic MI (n = 10), acute MI (n = 3), and myocarditis (n = 1). The contrast-to-noise (CNR) between scar (MI and myocarditis) and remote was 26.6 ± 7.7 and 20.2 ± 7.4 for BB and DB PSIR LGE, and 31.3 ± 10.6 and 21.8 ± 7.6 for calculated BB and DB PSIR LGE, respectively. The CNR between scar and the left ventricualr blood pool was 5.2 ± 6.5 and 29.7 ± 9.4 for conventional BB and DB PSIR LGE, and 6.5 ± 6.0 and 38.6 ± 11.6 for calculated BB and DB PSIR LGE, respectively. CONCLUSIONS: A single free-breathing acquisition using multi-parametric SASHA provides T1 and T2 maps and calculated BB and DB PSIR LGE images for comprehensive tissue characterization.

Dynamic Contrast Enhanced (DCE) MRI-Derived Renal Perfusion and Filtration: Experimental Protocol.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can provide a noninvasive way for assessing renal functional information following the administration of a small molecular weight gadolinium-based contrast agent. This method may be useful for investigating renal perfusion and glomerular filtration rates of rodents in vivo under various experimental (patho)physiological conditions. Here we describe a step-by-step protocol for DCE-MRI studies in small animals providing practical notes on acquisition parameters, sequences, T1 mapping approaches and procedures.This chapters is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This experimental protocol chapter is complemented by two separate chapters describing the basic concept and data analysis.

3D free-breathing cardiac magnetic resonance fingerprinting.

PURPOSE: To develop a novel respiratory motion compensated three-dimensional (3D) cardiac magnetic resonance fingerprinting (cMRF) approach for whole-heart myocardial T1 and T2 mapping from a free-breathing scan. METHODS: Two-dimensional (2D) cMRF has been recently proposed for simultaneous, co-registered T1 and T2 mapping from a breath-hold scan; however, coverage is limited. Here we propose a novel respiratory motion compensated 3D cMRF approach for whole-heart myocardial T1 and T2 tissue characterization from a free-breathing scan. Variable inversion recovery and T2 preparation modules are used for parametric encoding, respiratory bellows driven localized autofocus is proposed for beat-to-beat translation motion correction and a subspace regularized reconstruction is employed to accelerate the scan. The proposed 3D cMRF approach was evaluated in a standardized T1 /T2 phantom in comparison with reference spin echo values and in 10 healthy subjects in comparison with standard 2D MOLLI, SASHA and T2 -GraSE mapping techniques at 1.5 T. RESULTS: 3D cMRF T1 and T2 measurements were generally in good agreement with reference spin echo values in the phantom experiments, with relative errors of 2.9% and 3.8% for T1 and T2 (T2 < 100 ms), respectively. in vivo left ventricle (LV) myocardial T1 values were 1054 ± 19 ms for MOLLI, 1146 ± 20 ms for SASHA and 1093 ± 24 ms for the proposed 3D cMRF; corresponding T2 values were 51.8 ± 1.6 ms for T2-GraSE and 44.6 ± 2.0 ms for 3D cMRF. LV coefficients of variation were 7.6 ± 1.6% for MOLLI, 12.1 ± 2.7% for SASHA and 5.8 ± 0.8% for 3D cMRF T1 , and 10.5 ± 1.4% for T2-GraSE and 11.7 ± 1.6% for 3D cMRF T2 . CONCLUSION: The proposed 3D cMRF can provide whole-heart, simultaneous and co-registered T1 and T2 maps with accuracy and precision comparable to those of clinical standards in a single free-breathing scan of about 7 min.

Free breathing lung T1 mapping using image registration in patients with idiopathic pulmonary fibrosis.

PURPOSE: To assess the use of image registration for correcting respiratory motion in free breathing lung T1 mapping acquisition in patients with idiopathic pulmonary fibrosis (IPF). THEORY AND METHODS: The method presented used image registration to synthetic images during postprocessing to remove respiratory motion. Synthetic images were generated from a model of the inversion recovery signal of the acquired images that incorporated a periodic lung motion model. Ten healthy volunteers and 19 patients with IPF underwent 2D Look-Locker T1 mapping acquisition at 1.5T during inspiratory breath-hold and free breathing. Eight healthy volunteers and seven patients with IPF underwent T1 mapping acquisition during expiratory breath-hold. Fourteen patients had follow-up scanning at 6 months. Dice similarity coefficient (DSC) was used to evaluate registration efficacy. RESULTS: Image registration increased image DSC (P < .001) in the free breathing inversion recovery images. Lung T1 measured during a free breathing acquisition was lower in patients with IPF when compared with healthy controls (inspiration: P = .238; expiration: P = .261; free breathing: P = .021). Measured lung T1 was higher in expiration breath-hold than inspiration breath-hold in healthy volunteers (P < .001) but not in patients with IPF (P = .645). There were no other significant differences between lung T1 values within subject groups. CONCLUSIONS: The registration technique significantly reduced motion in the Look-Locker images acquired during free breathing and may improve the robustness of lung T1 mapping in patients who struggle to hold their breath. Lung T1 measured during a free breathing acquisition was significantly lower in patients with IPF when compared with healthy controls.

Accelerated MP2RAGE imaging using Cartesian phyllotaxis readout and compressed sensing reconstruction.

PURPOSE: MP2RAGE T1 -weighted imaging has been shown to be beneficial for various applications, mainly because of its good grey-white matter contrast, its B1 -robustness and ability to derive T1 maps. Even using parallel imaging, the method requires long acquisition times, especially at high resolution. This work aims at accelerating MP2RAGE imaging using compressed sensing. METHODS: A pseudo-phyllotactic Cartesian MP2RAGE readout was implemented allowing for flexible reordering and undersampling factors. The sampling pattern was first optimized based on fully sampled data and a compressed sensing reconstruction. Changes in contrast ratios, automated brain segmentation results, and quantitative T1 values were used for benchmarking. In vivo undersampled data from eleven healthy subjects were then acquired using a 4-fold acceleration with the optimized sampling pattern. The resulting images were compared to the standard parallel imaging MP2RAGE protocol by visual inspection and using the above quality metrics. RESULTS: The application of incoherent undersampling and iterative compressed sensing reconstruction on MP2RAGE acquisitions allows for a 57% time reduction (corresponding to 4-fold undersampling with maintained reference lines, TA = 3:35 minutes) compared to the reference protocol using parallel imaging (GRAPPAx3 acceleration, TA = 8:22 minutes) while obtaining images with similar image quality, morphometric (volume differences = [0.07 ± 1.2-3.8 ± 1.9]%) and T1 -mapping outcomes (T1 error = [6 ± 5.1-37 ± 12.3] ms depending on the different structures). CONCLUSION: A whole-brain MP2RAGE acquisition is feasible with compressed sensing in less than 4 minutes without appreciably compromising image quality.

The effect of motion correction interpolation on quantitative T1 mapping with MRI.

Quantitative magnetic resonance imaging (qMRI) is a technique for mapping the physical properties of the underlying tissue using several MR images with different contrasts. To overcome subject motion between the acquired images, it is necessary to register the images to a common reference frame. A drawback of registration is the use of interpolation and resampling techniques, which can introduce artifacts into the interpolated data. These artifacts could have unfavorable effects on the accuracy of the estimated tissue's physical properties. Here, we quantified the error of interpolation and resampling on T1-weighted images and studied its effects on the mapping of the longitudinal relaxation time (T1) using variable flip angles. We simulated T1-weighted images and calculated the transformation error resulting from interpolation and resampling. We found that the error is a function of the image contrast (i.e., flip angle) and of the translation and rotation of the image. Furthermore, we found that the error in the T1-weighted images has a substantial effect on the T1 estimation, of the order of 10% of the signal in the brain's gray and white matter. Hence, minimizing the registration error can enable more accurate in vivo modeling of brain microstructure.

Optimization method of MRI scan parameters of a double inversion recovery sequence using a T1 map and a developed analysis algorithm.

BACKGROUND: Optimizing scan parameters for double inversion recovery (DIR) sequences remains difficult. OBJECTIVE: To evaluate a new method for optimizing DIR sequence scan parameters using T1 mapping and a newly developed analysis algorithm. METHODS: Twelve healthy volunteers underwent T1 mapping and DIR magnetic resonance imaging. The following steps were used for image optimization including: 1) measurement of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) T1 values to create a T1 map; 2) calculation of optimized scan parameters by using a developed analysis algorithm; 3) performance assessment of DIR magnetic resonance imaging by using the calculated optimized imaging parameters. Additionally, we used scan parameters from previous studies to obtain DIR images in order to evaluate our new method. The contrast between GM and suppressed tissues was compared between these images and those obtained using the optimized parameters. RESULTS: Using our optimization method, WM and CSF regions were suppressed uniformly for all scan conditions. The contrast was significantly higher in images obtained using this optimization method compared to those obtained using previously published parameters (p < 0.01). CONCLUSIONS: It is possible to obtain superior DIR images by using an optimization method that involves T1 mapping and a newly developed analysis algorithm.

Analysis of the Precision of Variable Flip Angle T1 Mapping with Emphasis on the Noise Propagated from RF Transmit Field Maps.

In magnetic resonance imaging, precise measurements of longitudinal relaxation time (T1) is crucial to acquire useful information that is applicable to numerous clinical and neuroscience applications. In this work, we investigated the precision of T1 relaxation time as measured using the variable flip angle method with emphasis on the noise propagated from radiofrequency transmit field ([Formula: see text]) measurements. The analytical solution for T1 precision was derived by standard error propagation methods incorporating the noise from the three input sources: two spoiled gradient echo (SPGR) images and a [Formula: see text] map. Repeated in vivo experiments were performed to estimate the total variance in T1 maps and we compared these experimentally obtained values with the theoretical predictions to validate the established theoretical framework. Both the analytical and experimental results showed that variance in the [Formula: see text] map propagated comparable noise levels into the T1 maps as either of the two SPGR images. Improving precision of the [Formula: see text] measurements significantly reduced the variance in the estimated T1 map. The variance estimated from the repeatedly measured in vivoT1 maps agreed well with the theoretically-calculated variance in T1 estimates, thus validating the analytical framework for realistic in vivo experiments. We concluded that for T1 mapping experiments, the error propagated from the [Formula: see text] map must be considered. Optimizing the SPGR signals while neglecting to improve the precision of the [Formula: see text] map may result in grossly overestimating the precision of the estimated T1 values.

Native T1 value in the remote myocardium is independently associated with left ventricular dysfunction in patients with prior myocardial infarction.

PURPOSE: To compare remote myocardium native T1 in patients with chronic myocardial infarction (MI) and controls without MI and to elucidate the relationship of infarct size and native T1 in the remote myocardium for the prediction of left ventricular (LV) systolic dysfunction after MI. MATERIALS AND METHODS: A total of 41 chronic MI (18 anterior MI) patients and 15 age-matched volunteers with normal LV systolic function and no history of MI underwent cardiac magnetic resonance imaging (MRI) at 1.5T. Native T1 map was performed using a slice interleaved T1 mapping and late gadolinium enhancement (LGE) imaging. Cine MR was acquired to assess LV function and mass. RESULTS: The remote myocardium native T1 time was significantly elevated in patients with prior MI, compared to controls, for both anterior MI and nonanterior MI (anterior MI: 1099 ± 30, nonanterior MI: 1097 ± 39, controls: 1068 ± 25 msec, P < 0.05). Remote myocardium native T1 moderately correlated with LV volume, mass index, and ejection fraction (r = 0.38, 0.50, -0.49, respectively, all P < 0.05). LGE infarct size had a moderate correlation with reduced LV ejection fraction (r = -0.33, P < 0.05), but there was no significant association between native T1 and infarct size. Native T1 time in the remote myocardium was independently associated with reduced LV ejection fraction, after adjusting for age, gender, infarct size, and comorbidity (ß = -0.34, P = 0.03). CONCLUSION: In chronic MI, the severity of LV systolic dysfunction after MI is independently associated with native T1 in the remote myocardium. Diffuse myocardial fibrosis in the remote myocardium may play an important pathophysiological role of post-MI LV dysfunction. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017;46:1073-1081.

Characterization of T1 bias in skeletal muscle from fat in MOLLI and SASHA pulse sequences: Quantitative fat-fraction imaging with T1 mapping.

PURPOSE: To characterize the effects of fat on commonly used T1 mapping sequences and evaluate a new method of quantitative fat fraction (FF) imaging for low fractions based on the modulation of T1 values by the fat pool. METHODS: Bloch equation simulations and phantom and in vivo (skeletal muscle) experiments were used to characterize the response of the modified Look-Locker inversion recovery (MOLLI) and saturation recovery single-shot acquisition (SASHA) T1 mapping sequences to fat-water systems with known FFs (0%-10%) at 1.5T. FFs were measured with single voxel spectroscopy and Dixon imaging methods. A new T1 -based FF imaging method was evaluated using Monte Carlo simulations and phantom and in vivo experiments. RESULTS: SASHA and MOLLI had similar T1 dependence on FF, with characteristic under- or overestimation of T1 values as a function of off-resonance frequency (30-70 ms variation in native T1 per 1% FF). FF maps generated from the SASHA method yielded a low variability of ±0.25% for a signal-to-noise ratio of 150:1 in the nonsaturation image, with good agreement with spectroscopy and a performance that is superior to that of Dixon methods at low FFs. CONCLUSION: Fat results in negative or positive shifts in native tissue T1 measured with MOLLI and SASHA over a narrow range of off-resonance frequencies; T1 shifts from fat can be used to accurately quantify FF. Magn Reson Med 77:237-249, 2017. © 2016 Wiley Periodicals, Inc.

Influence of fat on liver T1 measurements using modified Look-Locker inversion recovery (MOLLI) methods at 3T.

PURPOSE: To characterize the effect of fat on modified Look-Locker inversion recovery (MOLLI) T1 maps of the liver. The balanced steady-state free precession (bSSFP) sequence causes water and fat signals to have opposite phase when repetition time (TR) = 2.3 msec at 3T. In voxels that contain both fat and water, the MOLLI T1 measurement is influenced by the choice of TR. MATERIALS AND METHODS: MOLLI T1 measurements of the liver were simulated using the Bloch equations while varying the hepatic lipid content (HLC). Phantom scans were performed on margarine phantoms, using both MOLLI and spin echo inversion recovery sequences. MOLLI T1 at 3T and HLC were determined in patients (n = 8) before and after bariatric surgery. RESULTS: At 3T, with HLC in the 0-35% range, higher fat fraction values lead to longer MOLLI T1 values when TR = 2.3 msec. Patients were found to have higher MOLLI T1 at elevated HLC (T1 = 929 ± 97 msec) than at low HLC (T1 = 870 ± 44 msec). CONCLUSION: At 3T, MOLLI T1 values are affected by HLC, substantially changing MOLLI T1 in a clinically relevant range of fat content. J. Magn. Reson. Imaging 2016;44:105-111.