Inversion-recovery Spin-echo Sequence Research Articles

Preoperative Discrimination of CDKN2A/B Homozygous Deletion Status in Isocitrate Dehydrogenase-Mutant Astrocytoma: A Deep Learning-Based Radiomics Model Using MRI.

Cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B) homozygous deletion has been verified as an independent and critical biomarker of negative prognosis and short survival in isocitrate dehydrogenase (IDH)-mutant astrocytoma. Therefore, noninvasive and accurate discrimination of CDKN2A/B homozygous deletion status is essential for the clinical management of IDH-mutant astrocytoma patients. To develop a noninvasive, robust preoperative model based on MR imagefeatures for discriminating CDKN2A/B homozygous deletion status of IDH-mutant astrocytoma. Retrospective. Two hundred fifty-one patients: 107 patients with CDKN2A/B homozygous deletion and 144 patients without CDKN2A/B homozygous deletion. 3.0 T/1.5 T: Contrast-enhanced T1-weighted spin-echo inversion recovery sequence (CE-T1WI) and T2-weighted fluid-attenuation spin-echo inversion recovery sequence (T2FLAIR). A total of 1106 radiomics and 1000 deep learning features extracted from CE-T1WI and T2FLAIR were used to develop models to discriminate the CDKN2A/B homozygous deletion status. Radiomics models, deep learning-based radiomics (DLR) models and the final integrated model combining radiomics features with deep learning features were developed and compared their preoperative discrimination performance. Pearson chi-square test and Mann Whitney U test were used for assessing the statistical differences in patients' clinical characteristics. The Delong test compared the statistical differences of receiver operating characteristic (ROC) curves and area under the curve (AUC) of different models. The significance threshold is P < 0.05. The final combined model (training AUC = 0.966; validation AUC = 0.935; test group: AUC = 0.943) outperformed the optimal models based on only radiomics or DLR features (training: AUC = 0.916 and 0.952; validation: AUC = 0.886 and 0.912; test group: AUC = 0.862 and 0.902). Whether based on a single sequence or a combination of two sequences, radiomics and DLR models have achieved promising performance in assessing CDKN2A/B homozygous deletion status. However, the final model combining both deep learning and radiomics features from CE-T1WI and T2FLAIR outperformed the optimal radiomics or DLR model. 4 TECHNICAL EFFICACY: Stage 2.

Temperature correction of post mortem quantitative magnetic resonance imaging using real-time forehead temperature acquisitions

Performing magnetic resonance imaging (MRI) of deceased is challenging due to altered body temperatures compared to in vivo temperatures and, hence, requires a temperature correction. This study investigates the possibility to correct brain MRI parameters real-time and non invasively based on the forehead temperature.17 post mortem cases were included and their forehead temperatures were measured continuously during the in situ brain MRI protocol consisting of a diffusion tensor imaging, multi-contrast spin echo, multi-echo gradient echo and inversion recovery spin echo sequence. Linear models were fitted to the quantitative MRI parameters in a forensically interesting temperature range for white matter, cerebral cortex and deep gray matter, separately, and the influence of the forehead temperature on the MRI parameters was determined.A statistically significant temperature sensitivity was found for T2 and mean diffusivity in white matter, for T1 in cerebral cortex, as well as for T1 and mean diffusivity in deep gray matter.Linear models were computed to temperature correct these MRI parameters in in situ post mortem scans to allow their comparison regardless of temperature.The here presented real-time and non invasive temperature correction method for the brain presents a crucial precondition for quantitative in situ post mortem MRI.

Deep Learning Radiomics for the Assessment of Telomerase Reverse Transcriptase Promoter Mutation Status in Patients With Glioblastoma Using Multiparametric MRI.

Studies have shown that magnetic resonance imaging (MRI)-based deep learning radiomics (DLR) has the potential to assess glioma grade; however, its role in predicting telomerase reverse transcriptase (TERT) promoter mutation status in patients with glioblastoma (GBM) remains unclear. To evaluate the value of deep learning (DL) in multiparametric MRI-based radiomics in identifying TERT promoter mutations in patients with GBM preoperatively. Retrospective. A total of 274 patients with isocitrate dehydrogenase-wildtype GBM were included in the study. The training and external validation cohorts included 156 (54.3± 12.7 years; 96 males) and 118 (54 .2± 13.4 years; 73 males) patients, respectively. Axial contrast-enhanced T1-weighted spin-echo inversion recovery sequence (T1CE), T1-weighted spin-echo inversion recovery sequence (T1WI), and T2-weighted spin-echo inversion recovery sequence (T2WI) on 1.5-T and 3.0-T scanners were used in this study. Overall tumor area regions (the tumor core and edema) were segmented, and the radiomics and DL features were extracted from preprocessed multiparameter preoperative brain MRI images-T1WI, T1CE, and T2WI. A model based on the DLR signature, clinical signature, and clinical DLR (CDLR) nomogram was developed and validated to identify TERT promoter mutation status. The Mann-Whitney U test, Pearson test, least absolute shrinkage and selection operator, and logistic regression analysis were applied for feature selection and construction of radiomics and DL signatures. Results were considered statistically significant at P-value <0.05. The DLR signature showed the best discriminative power for predicting TERT promoter mutations, yielding an AUC of 0.990 and 0.890 in the training and external validation cohorts, respectively. Furthermore, the DLR signature outperformed CDLR nomogram (P= 0.670) and significantly outperformed clinical models in the validation cohort. The multiparameter MRI-based DLR signature exhibited a promising performance for the assessment of TERT promoter mutations in patients with GBM, which could provide information for individualized treatment. 3 TECHNICAL EFFICACY: Stage 2.

Radiomic-Based MRI for Classification of Solitary Brain Metastases Subtypes From Primary Lymphoma of the Central Nervous System.

Differential diagnosis of brain metastases subtype and primary central nervous system lymphoma (PCNSL) is necessary for treatment decisions. The application of machine learning facilitates the classification of brain tumors, but prior investigations into primary lymphoma and brain metastases subtype classification have been limited. To develop a machine-learning model to classify PCNSL, brain metastases with primary lung and non-lung origin. Retrospective. A total of 211 subjects with pathologically confirmed PCNSL or brain metastases (training cohort 168 and testing cohort 43). A 3.0 T axial contrast-enhanced T1-weighted spin-echo inversion recovery sequence (T1WI-CE), axial T2-weighted fluid-attenuation inversion recovery sequence (T2FLAIR) ASSESSMENT: Several machine-learning models (support vector machine, random forest, and K-nearest neighbors) were built with least absolute shrinkage and selection operator (LASSO) using features from T1WI-CE, T2FLAIR, and clinical. The model with the highest performance in the training cohort was selected to differentiate lesions in the testing cohort. Then, three radiologists conducted a two-round classification (with and without model reference) using images and clinical information from testing cohorts. Five-fold cross-validation was used for model evaluation and calibration. Model performance was assessed based on sensitivity, specificity, accuracy, and area under the receiver operating characteristic curve (AUC). Twenty-five image features were selected by LASSO analysis. Random forest classifier was selected for its highest performance on the training set with an AUC of 0.73. After calibration, this model achieved an accuracy of 0.70 on the testing set. Accuracies of all three radiologists improved under model reference (0.49 vs. 0.70, 0.60 vs. 0.77, 0.58 vs. 0.72, respectively). The random forest model based on conventional MRI and clinical data can diagnose PCNSL and brain metastases subtypes (lung and non-lung origin). Model classification can help foster the diagnostic accuracy of specialists and streamline prognostication workflow. 4 TECHNICAL EFFICACY: Stage 2.

Deep Learning for Automatic Differential Diagnosis of Primary Central Nervous System Lymphoma and Glioblastoma: Multi-Parametric Magnetic Resonance Imaging Based Convolutional Neural Network Model.

Differential diagnosis of primary central nervous system lymphoma (PCNSL) and glioblastoma (GBM) is useful to guide treatment strategies. To investigate the use of a convolutional neural network (CNN) model for differentiation of PCNSL and GBM without tumor delineation. Retrospective. A total of 289 patients with PCNSL (136) or GBM (153) were included, the average age of the cohort was 54 years, and there were 173 men and 116 women. 3.0 T Axial contrast-enhanced T1 -weighted spin-echo inversion recovery sequence (CE-T1 WI), T2 -weighted fluid-attenuation inversion recovery sequence (FLAIR), and diffusion weighted imaging (DWI, b=0 second/mm2 , 1000 seconds/mm2 ). A single-parametric CNN model was built using CE-T1 WI, FLAIR, and the apparent diffusion coefficient (ADC) map derived from DWI, respectively. A decision-level fusion based multi-parametric CNN model (DF-CNN) was built by combining the predictions of single-parametric CNN models through logistic regression. An image-level fusion based multi-parametric CNN model (IF-CNN) was built using the integrated multi-parametric MR images. The radiomics models were developed. The diagnoses by three radiologists with 6 years (junior radiologist Y.Y.), 11 years (intermediate-level radiologist Y.T.), and 21 years (senior radiologist Y.L.) of experience were obtained. The 5-fold cross validation was used for model evaluation. The Pearson's chi-squared test was used to compare the accuracies. U-test and Fisher's exact test were used to compare clinical characteristics. The CE-T1 WI, FLAIR, and ADC based single-parametric CNN model had accuracy of 0.884, 0.782, and 0.700, respectively. The DF-CNN model had an accuracy of 0.899 which was higher than the IF-CNN model (0.830, P=0.021), but had no significant difference in accuracy compared to the radiomics model (0.865, P=0.255), and the senior radiologist (0.906, P=0.886). A CNN model can differentiate PCNSL from GBM without tumor delineation, and comparable to the radiomics models and radiologists. 4 TECHNICAL EFFICACY: Stage 2.

T1 Relaxation Time of Achilles Tendon at 3 Tesla with Special Reference to Relevant Clinical Score: A Preliminary Study.

The purpose of this study was to investigate T1 relaxation time of the human Achilles tendon, to test its short-term repeatability as well as the minimal detectable change, and to assess the extent that correlate with clinical symptoms. Twenty asymptomatic volunteers and eighteen patients with clinically and sonographically confirmed tendinopathy were scanned for ankle using a 3 Tesla (T) MR scanner. T1 maps were calculated from a variable flip angle gradient echo Ultra-short echo time sequence (VFA-GE UTE) and inversion recovery spin echo sequence (IR-SE) using a self-developed matlab algorithm in three regions of interest of Achilles Tendon (AT). Signal to Noise Ratio (SNR) between the two sequences was evaluated. INTRA-class Correlation Coefficient (ICC), Coefficient of Variation (CV) and the Least Significant Change (LSC) were calculated, to test short-term repeatability of T1. Subjects were assessed by the VISA-A clinical score. P values less than 0.005 were considered statistically significant. Mean T1 values were 427.09 ± 53.37 ms and 528.70 ± 103.50 ms using IR-SE sequence and 575.43 ± 110.60 ms and 875.81 ± 425.77 ms with VFA-GE UTE sequence in the whole AT for volunteers and patients, respectively. T1 values showed a significant difference between volunteers and patients (P=0.001). Regional variation of T1 in healthy and tendinopathic AT were greater for VFA-GE UTE sequence than for IR-SE sequence. VFA-GE UTE sequence showed clearly higher SNR compared to IR-SE sequence. Short-term repeatability of T1 values for volunteers showed an LSC of 22% and 14% for IR-SE sequence and VFA-GE UTE sequence, respectively. For patients, LSC was 14% and 5% for IR-SE sequence and VFA-GE UTE sequence, respectively. There was no correlation between T1 and VISA-A clinical score (p>0.005). VFA-GE UTE sequence used for T1 mapping calculation demonstrated short acquisition time and clearly high SNR. Results revealed that T1 relaxation time can be used as a biomarker to differentiate between healthy and pathologic Achilles tendon. However, T1 showed no correlation with the VISA-A clinical score.

3D SASHA myocardial T1 mapping with high accuracy and improved precision

PurposeTo improve the precision of a free-breathing 3D saturation-recovery-based myocardial T1 mapping sequence using a post-processing 3D denoising technique.MethodsA T1 phantom and 15 healthy subjects were scanned on a 1.5 T MRI scanner using 3D saturation-recovery single-shot acquisition (SASHA) for myocardial T1 mapping. A 3D denoising technique was applied to the native T1-weighted images before pixel-wise T1 fitting. The denoising technique imposes edge-preserving regularity and exploits the co-occurrence of 3D spatial gradients in the native T1-weighted images by incorporating a multi-contrast Beltrami regularization. Additionally, 2D modified Look-Locker inversion recovery (MOLLI) acquisitions were performed for comparison purposes. Accuracy and precision were measured in the myocardial septum of 2D MOLLI and 3D SASHA T1 maps and then compared. Furthermore, the accuracy and precision of the proposed approach were evaluated in a standardized phantom in comparison to an inversion-recovery spin-echo sequence (IRSE).ResultsFor the phantom study, Bland–Altman plots showed good agreement in terms of accuracy between IRSE and 3D SASHA, both on non-denoised and denoised T1 maps (mean difference −1.4 ± 18.9 ms and −4.4 ± 21.2 ms, respectively), while 2D MOLLI generally underestimated the T1 values (69.4 ± 48.4 ms). For the in vivo study, there was a statistical difference between the precision measured on 2D MOLLI and on non-denoised 3D SASHA T1 maps (P = 0.005), while there was no statistical difference after denoising (P = 0.95).ConclusionThe precision of 3D SASHA myocardial T1 mapping was substantially improved using a 3D Beltrami regularization based denoising technique and was similar to that of 2D MOLLI T1 mapping, while preserving the higher accuracy and whole-heart coverage of 3D SASHA.

Three-dimensional free breathing whole heart cardiovascular magnetic resonance T1 mapping at 3\xa0T

BackgroundThis study demonstrates a three-dimensional (3D) free-breathing native myocardial T1 mapping sequence at 3 T.MethodsThe proposed sequence acquires three differently T1-weighted volumes. The first two volumes receive a saturation pre-pulse with different recovery time. The third volume is acquired without magnetization preparation and after a significant recovery time. Respiratory navigator gating and volume-interleaved acquisition are adopted to mitigate misregistration. The proposed sequence was validated through simulation, phantom experiments and in vivo experiments in 12 healthy adult subjects.ResultsIn phantoms, good agreement on T1 measurement was achieved between the proposed sequence and the reference inversion recovery spin echo sequence (R2 = 0.99). Homogeneous 3D T1 maps were obtained from healthy adult subjects, with a T1 value of 1476 ± 53 ms and a coefficient of variation (CV) of 6.1 ± 1.4% over the whole left-ventricular myocardium. The averaged septal T1 was 1512 ± 60 ms with a CV of 2.1 ± 0.5%.ConclusionFree-breathing 3D native T1 mapping at 3 T is feasible and may be applicable in myocardial assessment. The proposed 3D T1 mapping sequence is suitable for applications in which larger coverage is desired beyond that available with single-shot parametric mapping, or breath-holding is unfeasible.

Carotid Intraplaque Hemorrhage Imaging with Quantitative Vessel Wall T1 Mapping: Technical Development and Initial Experience.

Purpose To develop a three-dimensional (3D) high-spatial-resolution time-efficient sequence for use in quantitative vessel wall T1 mapping. Materials and Methods A previously described sequence, simultaneous noncontrast angiography and intraplaque hemorrhage (SNAP) imaging, was extended by introducing 3D golden angle radial k-space sampling (GOAL-SNAP). Sliding window reconstruction was adopted to reconstruct images at different inversion delay times (different T1 contrasts) for voxelwise T1 fitting. Phantom studies were performed to test the accuracy of T1 mapping with GOAL-SNAP against a two-dimensional inversion recovery (IR) spin-echo (SE) sequence. In vivo studies were performed in six healthy volunteers (mean age, 27.8 years ± 3.0 [standard deviation]; age range, 24-32 years; five male) and five patients with atherosclerosis (mean age, 66.4 years ± 5.5; range, 60-73 years; five male) to compare T1 measurements between vessel wall sections (five per artery) with and without intraplaque hemorrhage (IPH). Statistical analyses included Pearson correlation coefficient, Bland-Altman analysis, and Wilcoxon rank-sum test with data permutation by subject. Results Phantom T1 measurements with GOAL-SNAP and IR SE sequences showed excellent correlation (R2 = 0.99), with a mean bias of -25.8 msec ± 43.6 and a mean percentage error of 4.3% ± 2.5. Minimum T1 was significantly different between sections with IPH and those without it (mean, 371 msec ± 93 vs 944 msec ± 120; P = .01). Estimated T1 of normal vessel wall and muscle were 1195 msec ± 136 and 1117 msec ± 153, respectively. Conclusion High-spatial-resolution (0.8 mm isotropic) time-efficient (5 minutes) vessel wall T1 mapping is achieved by using the GOAL-SNAP sequence. This sequence may yield more quantitative reproducible biomarkers with which to characterize IPH and monitor its progression. © RSNA, 2017.

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

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. 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. 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*. 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 . 2 J. Magn. Reson. Imaging 2017;45:1097-1104.

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

PurposeTo characterize the effect of fat on modified Look–Locker inversion recovery (MOLLI) T 1 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 T 1 measurement is influenced by the choice of TR.Materials and MethodsMOLLI T 1 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 T 1 at 3T and HLC were determined in patients (n = 8) before and after bariatric surgery.ResultsAt 3T, with HLC in the 0–35% range, higher fat fraction values lead to longer MOLLI T 1 values when TR = 2.3 msec. Patients were found to have higher MOLLI T 1 at elevated HLC (T 1 = 929 ± 97 msec) than at low HLC (T 1 = 870 ± 44 msec).ConclusionAt 3T, MOLLI T 1 values are affected by HLC, substantially changing MOLLI T 1 in a clinically relevant range of fat content. J. Magn. Reson. Imaging 2016;44:105–111.

How accurate is MOLLI T1 mapping in vivo? Validation by spin echo methods.

T1 mapping is a promising quantitative tool for assessing diffuse cardiomyopathies. The purpose of this study is to quantify in vivo accuracy of the Modified Look-Locker Inversion Recovery (MOLLI) cardiac T1 mapping sequence against the spin echo gold standard, which has not been done previously. T1 accuracy of MOLLI was determined by comparing with the gold standard inversion recovery spin echo sequence in the calf muscle, and with a rapid inversion recovery fast spin echo sequence in the heart. T1 values were obtained with both conventional MOLLI fitting and MOLLI fitting with inversion efficiency correction. In the calf (n = 6), conventional MOLLI fitting produced inconsistent T1 values with error ranging from 8.0% at 90° to 17.3% at 30°. Modified MOLLI fitting with inversion efficiency correction improved error to under 7.4% at all flip angles. In the heart (n = 5), modified MOLLI fitting with inversion correction reduced T1 error to 5.5% from 14.0% by conventional MOLLI fitting. This study shows that conventional MOLLI fitting can lead to significant in vivo T1 errors when not accounting for the lower adiabatic inversion efficiency often experienced in vivo.

Cardiac T 1 Imaging

T(1) mapping of the heart has evolved into a valuable tool to evaluate myocardial tissue properties, with or without contrast injection, including assessment of myocardial edema and free water content, extracellular volume (expansion), and most recently cardiomyocyte hypertrophy. The magnetic resonance imaging pulse sequence techniques developed for these applications have had to address at least 2 important considerations for cardiac applications: measure magnetization-inversion recoveries during cardiac motion with sufficient temporal resolution for the shortest expected T(1) values, and, second, obtain these measurements within a time during which a patient can comfortably suspend breathing. So-called Look-Locker techniques, and variants thereof, which all sample multiple points of a magnetization recovery after each magnetization preparation, have therefore become a mainstay in this field. The rapid pace of advances and new findings based on cardiac T(1) mapping for assessment of diffuse fibrosis or myocardial edema show that these techniques enrich the capabilities of magnetic resonance imaging for myocardial tissue profiling, which is arguably unmatched by other cardiac imaging modalities.

Abstract 3930: Analysis of longitudinal relaxation time mapping for monitoring vascular permeability in brain tumors.

Abstract Introduction: Vessel permeability measurement in tumors, as assessed by Ktrans exchange coefficient, may have diagnostic value for determining treatment effectiveness and are an emerging parameter for drug transport modeling. Transvascular exchange models have been the standard for deriving Ktrans in an imaging voxel based on the pharmacokinetic analysis of the longitudinal relaxation time (T1) measurements following systemic delivery of T1-shortening contrast reagent (CR) in tissue using dynamic contrast-enhanced (DCE)-MRI. Analysis requires a pre-contrast longitudinal relaxation time (T10) as a model input. This study investigates the effect of using T10 maps versus an average value for analyzing changes in Ktrans measurements in intracerebral lung carcinoma, glioma, and melanoma xenograft models before and after treatment with agents targeting tumor edema. Materials and Methods: Rats were inoculated in the right basal ganglia with LX-1 human lung carcinoma (n = 10), UW28 human glioma (n = 11), or A2058 human melanoma cells (n = 15). After baseline MRI scans, animals received glyburide (∼24 μg/kg oral), dexamethasone (∼1.8 mg/kg IV) or vehicle control. MRI study was performed using a horizontal bore 11.75 T magnet system. T10 in tumor tissue was measured using a spin-echo inversion recovery sequence. DCE-MRI was done with a fast-gradient-echo sequence. Ktrans was calculated by non-linear squared fitting to the T1 measurements; animal-specific arterial input functions were used. A Student's two-tailed, paired t-test was used to test statistical significance of change in Ktrans between using T10 maps versus ROI-based T10 value. Results and Discussion: On pre-treatment MRI, 50% of lung and melanoma metastases showed standard deviation ≥10% the average T10 value. For UW28 tumors, standard deviation was &amp;lt;10% of the average T10 for all animals. LX-1 metastases became more heterogeneous based on σ increase. Ktrans was assessed using an ROI-based average T10 value and T10 maps before and after treatment. T10 mapping reduced average Ktrans in over 88% of cases (including pre- and post- treatment). Change in Ktrans from T10 mapping did not change with treatment (p ≥ 0.07) and change in Ktrans resulting from treatment was not significantly affected by T10 mapping (p ≥ 0.09) the treatment groups. There was a trend towards significance observed with larger animal numbers. Conclusions: LX-1 and A2058 metastases were more heterogeneous than the UW28 model based on standard deviation of T10 values within tumor. Using an ROI-based average T10 value was likely to overpredict average Ktrans values, but not likely to significantly affect treatment outcomes of study for these tumors and therapies despite tumor heterogeneity. Overpredicted Ktrans hot spots could have more consequences on hot spot analysis to monitor treatment outcome rather than average Ktrans. Citation Format: Gregory L. Pishko, Eric M. Thompson, Edward A. Neuwelt. Analysis of longitudinal relaxation time mapping for monitoring vascular permeability in brain tumors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3930. doi:10.1158/1538-7445.AM2013-3930

Comparison of two ultrashort echo time sequences for the quantification of T1 within phantom and human Achilles tendon at 3 T

Ultrashort echo time (UTE) techniques enable direct imaging of musculoskeletal tissues with short T2 allowing measurement of T1 relaxation times. This article presents comparison of optimized 3D variable flip angle UTE (VFA-UTE) and 2D saturation recovery UTE (SR-UTE) sequences to quantify T1 in agar phantoms and human Achilles tendon. Achilles tendon T1 values for asymptomatic volunteers were compared to Achilles tendon T1 values calculated from patients with clinical diagnoses of spondyloarthritis (SpA) and Achilles tendinopathy using an optimized VFA-UTE sequence. T1 values from phantom data for VFA- and SR-UTE compare well against calculated T1 values from an assumed gold standard inversion recovery spin echo sequence. Mean T1 values in asymptomatic Achilles tendon were found to be 725±42 ms and 698±54 ms for SR- and VFA-UTE, respectively. The patient group mean T1 value for Achilles tendon was found to be 957±173 ms (P<0.05) using an optimized VFA-UTE sequence with pulse repetition time of 6 ms and flip angles 4, 19, and 24°, taking a total 9 min acquisition time. The VFA-UTE technique appears clinically feasible for quantifying T1 in Achilles tendon. T1 measurements offer potential for detecting changes in Achilles tendon due to SpA without need for intravenous contrast agents.

Musculoskeletal MRI at 3.0 T and 7.0 T: A comparison of relaxation times and image contrast

ObjectiveThe purpose of this study was to measure and compare the relaxation times of musculoskeletal tissues at 3.0T and 7.0T, and to use these measurements to select appropriate parameters for musculoskeletal protocols at 7.0T. Materials and methodsWe measured the T1 and T2 relaxation times of cartilage, muscle, synovial fluid, bone marrow and subcutaneous fat at both 3.0T and 7.0T in the knees of five healthy volunteers. The T1 relaxation times were measured using a spin-echo inversion recovery sequence with six inversion times. The T2 relaxation times were measured using a spin-echo sequence with seven echo times. The accuracy of both the T1 and T2 measurement techniques was verified in phantoms at both magnetic field strengths. We used the measured relaxation times to help design 7.0T musculoskeletal protocols that preserve the favorable contrast characteristics of our 3.0T protocols, while achieving significantly higher resolution at higher SNR efficiency. ResultsThe T1 relaxation times in all tissues at 7.0T were consistently higher than those measured at 3.0T, while the T2 relaxation times at 7.0T were consistently lower than those measured at 3.0T. The measured relaxation times were used to help develop high resolution 7.0T protocols that had similar fluid-to-cartilage contrast to that of the standard clinical 3.0T protocols for the following sequences: proton-density-weighted fast spin-echo (FSE), T2-weighted FSE, and 3D-FSE-Cube. ConclusionThe T1 and T2 changes were within the expected ranges. Parameters for musculoskeletal protocols at 7.0T can be optimized based on these values, yielding improved resolution in musculoskeletal imaging with similar contrast to that of standard 3.0T clinical protocols.

Determining the Extent of Disease with Magnetic Resonance Imaging of the Bone Marrow (BM-MRI) in Patients with Multiple Myeloma (MM).

Background: MM remains an incurable cancer. Treatment is often initiated with progressive increase in tumor burden and clinical symptoms. Tumor burden assessment is commonly done by disease stage, presence of lytic bone disease and beta-2 microglobulin (B2M). We investigated bone marrow imaging as a novel approach to quantify disease burden. In a separate report, we observed that MRI is more sensitive than BM aspirate/biopsy (BM-Bx) for assessing extent of marrow involvement in MM patients. In this study we validate that extent of marrow disease detected by BM-MRI correlates with the clinical stage, presence of lytic bone lesions, B2M and secretor vs. non-secretor status of MM patients.Methods: Extent of marrow involvement as evaluated by BM-MRI included sagittal T1 and fast spin echo inversion recovery sequences of the cervical, thoracic and lumbosacral spine and coronal T1 and fast spin echo inversion recovery sequences of the sacrum and pelvic bones. Clinical staging was done as per Durie-Salmon (DS) and the International Staging System (ISS) while lytic bone lesions were assessed by skeletal radiographs. Secretory MM was identified by presence of M-protein in serum or urine by electrophoresis. To study the statistical relationship between pairs of ordinal variables the test corresponding to the Spearman correlation was used and statistical relationship between nominal and ordinal variables was determined by the Wilcoxon or Kruskal-Wallis test. A 0.05 nominal significance level was used in all testing. Following staging system was defined for evaluation of the marrow involvement by BM-MRI: A (0%), B (< 10%), C (10%–25%), D (26%–50%), E (> 50%).Results: We evaluated 170 consecutive patients (77 females and 93 males). Median age was 61 years (range 35–83). Advance stage disease (> stage 1) based on DS or the ISS criteria was observed in 47.6% (n=81) and 53.3% (n=77) patients, respectively. Lytic lesions were noted in 70.6% (n=120) patients and secretory disease in 85.9% (n=146) patients. Estimated Spearman correlation coefficient between BM-MRI involvement and DS stage was 0.2795 (p = 0.0006; 95% CI 0.1222, 0.4368) demonstrating a significant association between BM-MRI involvement and DS stage. This correlation with clinical stage remained significant using the ISS system (p = 0.0001). The correlation of marrow infiltration on BM-MRI was also significantly associated with the presence of lytic bone disease (p<0.0001) as well as the B2M levels (p<0.0001). There was no significant association between MRI involvement and patient age (p = 0.7921) or the Ig type (p=0.8123). Interestingly, marrow involvement on BM-MRI had a significant association with secretor-status of the patients (p=0.0081).Conclusions: BM-MRI is novel approach to quantify disease burden in patients with MM. Our investigation in a large cohort of patients demonstrates that the extent of marrow involvement determined by this method correlates accurately with other conventional methods used to assess myeloma disease burden such as clinical stage, lytic bone disease or B2M. We therefore conclude that BM-MRI can be routinely used to determine disease burden in patients with multiple and can be effectively employed in monitoring response to therapy.

Improved Sensitivity of Bone Marrow Magnetic Resonance Imaging (BM-MRI) in Quantifying the Extent of Bone Marrow Involvement in Patients with Multiple Myeloma (MM).

Background: Traditionally, bone marrow aspirate/biopsy (BM-Bx) has been used for diagnosis and quantification of the extent of disease as well as response to therapy in MM patients. This information is used to make decision for treatment initiation. Since MM is not a contiguous disease, marrow involvement can be patchy and BM-Bx may be misleading in assessing the true extent of the disease. BM-MRI is a non-invasive technique that can evaluate a large amount of marrow for tumor infiltration. We prospectively investigated the sensitivity of BM-MRI and compared its results with those obtained by BM-Bx as well as with the clinical stage of disease.Methods: All patients with the diagnosis of MM who had BM-MRI at our center were evaluable. Patients must have received a BM-Bx within 4 weeks of the BM-MRI. In these patients sagittal T1 and fast spin echo inversion recovery sequences of the cervical, thoracic and lumbosacral spine and coronal T1 and fast spin echo inversion recovery sequences of the sacrum and pelvic bones were reviewed on the MRI. Durie-Salmon (DS) staging criteria were used for correlation. To study the statistical relationship between pairs of ordinal variables the test corresponding to the Spearman correlation was used. To study the statistical relationship between nominal and ordinal variables, the Wilcoxon or Kruskal-Wallis test was used. A 0.05 nominal significance level was used in all testing. Following staging system was defined for evaluation of the involvement of the marrow by BM-MRI: A (0%), B (< 10%), C (10%–25%), D (26%–50%), E (> 50%). Results of this were then compared with the extent of involvement reported on histological evaluation of the BM-Bx.Results: A total of 50 patients (23 females and 27 males) were identified. Median age was 61.5 years (range 35–82 years) with 23 (46%) having stage IIIA disease. As per the staging system defined above, 6%, 10%, 10%, 22% and 52% of the patients had categories A, B, C, D and E involvement as per BM-MRI, respectively. Similarly, involvement observed on the BM-Bx was 8%, 24%, 22%, 16% and 30%, respectively. Categories of marrow involvement on BM-Bx and BM-MRI were concordant in 23 (46%) and discordant in 27 (54%) patients. Of the patients that showed discordance, 89% had a more extensive BM involvement detected by the BM-MRI and 11% had a higher reading on BM-Bx. The estimated Spearman correlation coefficient between MRI involvement and MM stage was 0.4849 (95% CI; 0.2494, 0.7205), showing a significant association between BM-MRI involvement and MM stage (p =0.0002). The estimated Spearman correlation coefficient between BM-Bx involvement and MM stage was 0.1775 (95% CI; −0.1406, 0.4956), showing no significant association between BM-Bx involvement and MM stage (p = 0.2764).Conclusions: We demonstrate for the first time that BM-MRI is a more sensitive technique to assess the true disease burden in MM and is significantly better than BM-Bx. We also observe that the extent of marrow infiltration noted on the BM-MRI correlates significantly with other prognostic characteristics like DS stage. Based on this observation we recommend that BM-MRI should be considered as part of the pre-treatment evaluation of patients with multiple myeloma.

MRI to detect atherosclerosis with gadolinium‐containing immunomicelles targeting the macrophage scavenger receptor

The ability to specifically image macrophages may enable improved detection and characterization of atherosclerosis. In this study we evaluated the in vitro uptake of gadolinium (Gd)-containing immunomicelles (micelles linked to macrophage-specific antibody), micelles, and standard contrast agents by murine macrophages, and sought to determine whether immunomicelles and micelles improve ex vivo imaging of apolipoprotein E knockout (ApoE KO) murine atherosclerosis. Murine RAW 264.7 macrophages were incubated with Gd-DTPA, micelles, and immunomicelles. Cell pellets were prepared and imaged using a 1.5 T MR system with an inversion recovery spin-echo sequence to determine the in vitro T1 values. Ex vivo analysis of mouse aortas was performed using a 9.4T MR system with a high-spatial-resolution sequence (78x39x78 microm3). The T1 value was significantly decreased in cells treated with micelles compared to Gd-DTPA (P<0.0001), and in cells incubated at 4 degrees C with immunomicelles compared to micelles (P<0.05). Ex vivo MRI signal intensity (SI) was significantly increased by 81% and 20% in aortas incubated with immunomicelles and micelles, respectively. Confocal microscopy demonstrated in vitro and ex vivo uptake of fluorescent immunomicelles by macrophages. Immunomicelles and micelles improve in vitro and ex vivo MR detection of macrophages, and may prove useful in the detection of macrophage-rich plaques.

SU‐FF‐I‐61: A New Gel Phantom for MRI

Purpose: To develop a gel‐based quality control phantom for MRI that does not suffer from flow artifacts seen in liquid‐based phantoms. Method and Materials: We have developed a gel based phantom incorporating NiCl and NaCl that does not suffer from flow artifacts. The phantom was evaluated for accuracy of the stated T1 and T2 values, uniformity and dehydration properties. The T1 relaxation time was measured using a spin echo sequence with TR = 1000 mS and TE varied between 10 mS and 350 mS. The T2 relaxation time was measured through a fast spin echo inversion recovery sequence with TR = 1000 mS, TE = 50 mS and TI varied between 50 and 983 mS. All measurements and images were made on a GE Signa 1.5T MRI scanner. Results: Measured T1 and T2 values were within 1.3% of the nominal values of 260.3 mS for T1 and 234.1 mS for T2. Uniformity was measured using the ACR T1 sequence of TR = 500 mS, TE = 20 mS. The gel phantom demonstrated a uniformity of 86.5% over its volume in a dedicated head coil, compared to 87.2% for a still liquid phantom in an identical container. The measured mass of 4691 grams did not change over a 6 month period. Conclusion: This new gel phantom shows promise as a replacement for liquid MRI phantoms. Future efforts will focus on adapting the gel to other container geometries and modifying the formulation for more tissue equivalent relaxation times and to match the ACR MRI accreditation program phantom. Conflict of Interest: Research sponsored by Computerized Imaging Reference Systems, Inc.