Spin-echo Echo-planar Imaging Research Articles

A General Framework for Automated Accurate Calculation of b-Matrix (Auto-b) in Diffusion MRI Pulse Sequences

To derive accurate diffusion metrics, both imaging and diffusion-sensitizing gradient pulses should be accounted for when calculating the diffusion-weighted b-matrix. However, it is complex to derive analytical solutions due to complicated interactions between gradient pulses, including orthogonal directions. This study proposes a general framework to calculate the b-matrix automatically (dubbed as Auto-b). Based on the divide-and-conquer approach, the b-matrix calculation is appropriately segmented, and the symbolic mathematical library is applied to handle integration operations for each interval. If the specifications of all gradient pulses are provided to Auto-b, an accurate b-matrix can be obtained. Three examples are explored to validate the accuracy of Auto-b and to detect b-value errors when using approximate calculations. (1) In the conventional spin-echo example, Auto-b exhibits high accuracy, as indicated by the maximum relative deviation of 1.68‰ between its calculated b-matrices and those obtained from analytical expressions. (2) Auto-b is applied to investigate the contribution of imaging gradients to the b-matrix in an optimized spin-echo echo planar imaging sequence at submillimeter resolution. Specifically, ignoring the contribution of imaging gradients results in a b-value error of 12.16 s/mm2 at the 0.8 × 0.8 × 0.8 mm3 resolution and 22.47 s/mm2 at the 0.6 × 0.6 × 0.8 mm3 resolution, respectively, when nominal b = 0. (3) Auto-b is also utilized to analyze the influence of approximate calculations in the spatiotemporally encoded sequence. The results showed that neglecting the contribution of phase-encoding blips causes large b-value errors up to 11.02 s/mm2. In addition, the rectangularization of trapezoidal waveforms led to a high relative b-value error of 39.91%. This study validates the high accuracy of Auto-b and underscores the importance of accurate b-value calculations in both submillimeter imaging and spatiotemporally encoded sequences. Attributed to its automation, accuracy, and broad applicability, Auto-b is helpful for developers of diffusion sequences.

Evaluation of T2-prepared blood oxygenation level dependent functional magnetic resonance imaging with an event-related task: Hemodynamic response function and reproducibility.

T2-prepared (T2prep) blood oxygenation level dependent (BOLD) functional MRI (fMRI) is an alternative fMRI approach developed to mitigate the susceptibility artifacts that are typically observed in brain regions near air-filled cavities, bleeding and calcification, and metallic objects in echo-planar-imaging (EPI) based fMRI images. Here, T2prep BOLD fMRI was evaluated in an event-related paradigm for the first time. Functional experiments were performed using gradient-echo (GRE) EPI, spin-echo (SE) EPI, and T2prep BOLD fMRI during an event-related visual task in 10 healthy human subjects. Each fMRI method was performed with a low (3.4 × 3.4 × 4 mm3) and a high (1.5 mm isotropic) spatial resolution on 3T and a high resolution (1.5 mm isotropic) on 7T. Robust activation were detected in the visual cortex with all three fMRI methods. In each group of fMRI scans (3T low resolution, 3T high resolution, and 7T high resolution), GRE EPI showed the highest signal change (ΔS/S), largest full-width-at-half-maximum (FWHM) and longest time-to-peak (TTP) extracted from the hemodynamic response functions (HRF), indicating substantial signal contribution from large draining veins which have longer response times than microvessels. In contrast, T2prep BOLD showed the lowest ΔS/S, smallest FWHM, and shortest TTP, suggesting that T2prep BOLD may have a purer T2-weighted BOLD contrast that is more sensitive to microvessels compared to GRE/SE EPI BOLD. This trend was more obvious in fMRI scans performed with a lower spatial resolution on a lower field (3T with a 3.4 × 3.4 × 4 mm3 voxel). Scan-rescan reproducibility in the same subjects was comparable among the three fMRI methods. The results from the current study are expected to be useful to establish T2prep BOLD as a useful alternative fMRI approach for event-related fMRI in brain regions with large susceptibility artifacts.

Navigator-based slice tracking for kidney pCASL using spin-echo EPI acquisition.

To apply a navigator-based slice-tracking method to prospectively compensate respiratory motion for kidney pseudo-continuous arterial spin labeling (pCASL), using spin-echo (SE) EPI acquisition. A single gradient-echo slice selection and projection readout at the location of the diaphragm along the inferior-superior direction was applied as a navigator. Navigator acquisition and fat suppression were inserted before each transverse imaging slice of the readouts of a 2D-SE-EPI-based pCASL sequence. Motion information was calculated after exclusion of the signal saturation in the navigator signal caused by EPI excitations. The motion information was then used to directly adjust the slice positioning in real time. The respiratory motion from the navigator signal was calculated, and slice positioning was changed in real time based on the motion information. We could show that motion compensation reduces kidney movement, and that the coefficients of variation across renal perfusion values were significantly reduced when motion correction was applied. The average reduction of coefficients of variation was approximately 20%, resulting in a more accurate and detailed structure of the respective perfusion maps. This study demonstrates the feasibility of a navigator-based slice-tracking technique in kidney imaging with a SE-EPI readout pCASL sequence to reduce kidney motion.

Quantitative muscle magnetic resonance imaging depicts microstructural abnormalities but no signs of inflammation or dystrophy in post-COVID-19 condition.

Post-COVID-19 condition (PCC) has high impact on quality of life, with myalgia and fatigue affecting at least 25% of PCC patients. This case-control study aims to noninvasively assess muscular alterations via quantitative muscle magnetic resonance imaging (MRI) as possible mechanisms for ongoing musculoskeletal complaints and premature exhaustion in PCC. Quantitative muscle MRI was performed on a 3 Tesla MRI scanner of the whole legs in PCC patients compared to age- and sex-matched healthy controls, including a Dixon sequence to determine muscle fat fraction (FF), a multi-echo spin-echo sequence for quantitative water mapping reflecting putative edema, and a diffusion-weighted spin-echo echo-planar imaging sequence to assess microstructural alterations. Clinical examination, nerve conduction studies, and serum creatine kinase were performed in all patients. Quantitative muscle MRI results were correlated to the results of the 6-min walk test and standardized questionnaires assessing quality of life, fatigue, and depression. Twenty PCC patients (female: n= 15, age=48.8±10.1 years, symptoms duration=13.4± 4.2months, body mass index [BMI] = 28.8±4.7kg/m2 ) were compared to 20 healthy controls (female: n= 15, age=48.1± 11.1 years, BMI=22.9± 2.2kg/m2 ). Neither FF nor T2 revealed signs of muscle degeneration or inflammation in either study groups. Diffusion tensor imaging (DTI) revealed reduced mean, axial, and radial diffusivity in the PCC group. Quantitative muscle MRI did not depict any signs of ongoing inflammation or dystrophic process in the skeletal muscles in PCC patients. However, differences observed in muscle DTI depict microstructural abnormalities, which may reflect potentially reversible fiber hypotrophy due to deconditioning. Further longitudinal and interventional studies should prove this hypothesis.

Effectiveness and Accuracy of MRI-Ultrasound Fusion Targeted Biopsy Based on PI-RADS v2.1 Category in Transition/Peripheral Zone of the Prostate.

MRI-ultrasound fusion targeted biopsy (MRI-TBx) improves the clinically significant prostate cancer (csPCa) detection with fewer cores. However, whether systematic biopsy-guided by transrectal ultrasound (TRUS-SBx) can be omitted when undergoing MRI-TBx in transition zone (TZ) and peripheral zone (PZ) remains unclear. To assess the performance and effectiveness of MRI-TBx based on PI-RADS v2.1 for csPCa diagnosis in TZ and PZ, respectively. Retrospective. A total of 309 selected cases (median age 70 years) with 356 lesions who underwent both MRI-TBx and TRUS-SBx were enrolled. A 3.0 T, multiparametric MRI (mp-MRI) including T2-weighted turbo-spin echo imaging (T2WI), diffusion-weighted spin-echo echo planar imaging (DWI), dynamic contrast-enhanced MRI with time-resolved T1-weighted imaging (DCE). Mp-MRI was assessed by two radiologists using PI-RADS v2.1. The csPCa detection rates provided by MRI-TBx, TRUS-SBx and combined biopsy in TZ and PZ were calculated, respectively. McNemar test was used to compare the csPCa detection rates in TZ and PZ, respectively. The frequencies and distribution of all detected prostate cancers by different biopsy methods were also compared. P < 0.05 was considered statistically significant. Among 356 lesions in 309 patients, 208 (68 in TZ, 140 in PZ) were pathologically confirmed as csPCa. In TZ, there were significant differences for csPCa detection with PI-RADS 3 between combined biopsy and TRUS-SBx (23.5% vs. 15.3%), MRI-TBx (23.5% vs. 16.3%), respectively. MRI-TBx detected 23% (19/83) cases missed by TRUS-SBx in which 68% (13/19) were csPCa. In PZ, there were no statistical differences between MRI-TBx and combined biopsy with PI-RADS 3-5 (P=0.21, 0.25, 0.07, respectively). In 9% (14/152) cases only detected by MRI-TBx, 86% (12/14) were clinically significant. Five percent (7/152) of cases only detected by TRUS-SBx were completely nonclinically significant. MRI-TBx played a positive role on csPCa diagnosis in TZ, but combined biopsy might be the best choice especially in the subgroup PI-RADS 3. In PZ, MRI-TBx had an advantage over TRUS-SBx for csPCa detection. 2. Stage 2.

Evaluation of apparent diffusion coefficient of two-dimensional BLADE turbo gradient- and spin-echo diffusion-weighted imaging with a breast phantom.

This study aimed to evaluate the reliability of apparent diffusion coefficient (ADC) values generated with two-dimensional turbo gradient- and spin-echo with BLADE trajectory diffusion-weighted imaging (TGSE-BLADE-DWI) sequence using a breast diffusion phantom. TGSE-BLADE-DWI and single-shot spin-echo echo-planar imaging (SS-EPI-DWI) were performed using a 3.0T magnetic resonance imaging scanner. Concordance rates of ADC values and the signal-to-noise ratio (SNR) were compared between TGSE-BLADE-DWI and SS-EPI-DWI. TGSE-BLADE-DWI provided a higher concordance rate for ADC values than SS-EPI-DWI when b-values > 2000s/mm2 and a slice thickness of 1mm were used. TGSE-BLADE-DWI showed less image distortion than SS-EPI-DWI. The SNR of TGSE-BLADE-DWI was higher than that of SS-EPI-DWI, except at a number of excitations of 7 and a slice thickness of 1mm. In conclusion, TGSE-BLADE-DWI can offer a better SNR, less distortion, and more reliable ADC measurements than SS-EPI-DWI in a breast phantom.

Arterial spin labeling using spatio-temporal encoding readout for robust perfusion imaging ininhomogenous magnetic fields.

To evaluate the feasibility of spatio-temporal encoding (SPEN) readout for pseudo-continuous ASL (pCASL) in brain, and its robustness to susceptibility artifacts as introduced by aneurysm clips. A 2D self-refocused T2 *-compensated hybrid SPEN scheme, with super-resolution reconstruction was implemented on a 1.5T Philips system. Q (=BWchirp *Tchirp ) was varied and, the aneurysm clip-induced artifact was evaluated in phantom (label-images) as well as in vivo (perfusion-weighted signal (PWS)-maps and temporal SNR (tSNR)). In vivo results were compared to gradient-echo EPI (GE-EPI) and spin-echo EPI (SE-EPI). The dependence of tSNR on TR was evaluated separately for SPEN and SE-EPI. SPEN with Q˜ 75 encodes with the same off-resonance robustness as EPI. The clip-induced artifact with SPEN decreased with increase in Q, and was smaller compared to SE-EPI and GE-EPI in vivo. tSNR decreased with Q and the tSNR of GE-EPI and SE-EPI corresponded to SPEN with a Q-value of approximately ˜85 and ˜108, respectively. In addition, SPEN perfusion images showed a higher tSNR (p< 0.05) for TR=4000 ms compared to TR=2100 ms, while SE-EPI did not. tSNR remained relatively stable when the time between SPEN-excitation and start of the next labeling-module was more than ˜1000 ms. Feasibility of combining SPEN with pCASL imaging was demonstrated, enabling cerebral perfusion measurements with a higher robustness to field inhomogeneity (Q> 75) compared to SE-EPI and GE-EPI. However, the SPEN chirp-pulse saturates incoming blood, thereby reducing pCASL labeling efficiency of the next acquisition for short TRs. Future developments are needed to enable 3D scanning.

Exploration of Interstitial Fibrosis in Chronic Kidney Disease by Diffusion-Relaxation Correlation Spectrum MR Imaging: A Preliminary Study.

Renal interstitial fibrosis is one of the most common pathways in the progression of chronic kidney disease (CKD). Noninvasive evaluation of interstitial fibrosis would help monitoring CKD progression and prognosis prediction. To evaluate the severity of renal interstitial fibrosis by diffusion-relaxation correlation spectrum imaging (DR-CSI). Prospective. Forty patients with CKD and 10 healthy controls (average age 49.2 ± 14.8 years, 18 females). 3-T, DR-CSI with 36 axial spin-echo echo-planar diffusion-weighted images (6 b-values, 6 echo times). Interstitial fibrosis level (IFL) was assessed from biopsy results (IFL=1, fibrosis percentage <25%, defined as mild; IFL=2, 25%-50%, moderate; IFL=3, >50%, severe). Estimated glomerular filtration rate (eGFR) was calculated using serum creatinine. The regions of interest included cortex for both kidneys. The diffusivity-T2 spectrum was assessed considering three compartments (threshold: T2 30-40 msec, diffusivity 5-9μm2 /msec, according to visible peaks): A (low diffusivity, short T2), B (low diffusivity, long T2), and C (high diffusivity). Volume fractions Vi (i=A, B, C) were calculated. Intra-class coefficient (ICC, >0.6 as good) to assess inter-reader agreement of DR-CSI Vi . Spearman's correlation to assess relationship of Vi to IFL and eGFR. Receiver operating characteristic analyses with the area under the curve (AUC) to discriminate patients with moderate-severe fibrosis from mild ones. Statistical significance criteria: P-value <0.05. ICCs were good for all Vi . Correlations were found between IFL and VB (r=0.424, significant) and VC (r=-0.400, significant), and between eGFR and VB (r=-0.303, P=0.058) and VC (r=0.487, significant). Regarding VB and VC , the AUCs were 0.903 and 0.824. DR-CSI help distinguish patients with moderate or severe renal interstitial fibrosis from mild ones. 2 Technical Efficacy: Stage 2.

The Relationship Between Quadriceps Femoris Muscle Function and MRI-Derived Water Diffusion and Adipose Tissue Measurements in Young Healthy Males.

Water diffusion and adipose tissue in a muscle can be evaluated by MRI. However, determining which quadriceps femoris muscle (QM) characteristics independently predict peak knee extension torque during maximum voluntary isometric contractions (MVICs), individual muscle activity during MVICs and sit-to-stand transitions is unknown. To determine which QM characteristics predict knee extension muscle strength and individual muscle activity. Prospective, cross-sectional. A total of 20 healthy males (aged 22-40 years) with a physical activity level <1 hour/week. 1.5-T, diffusion-weighted fast spin-echo echo-planar imaging and T1-weighted fast spin-echo sequences. The vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), and vastus intermedius were segmented in a single axial diffusion-weighted image and T1-weighted image at the right mid-thigh region. λ1-3 and fractional anisotropy (FA), and the percentage of intramuscular adipose tissue (IMAT) were measured. The knee extension peak force during MVICs was measured by a dynamometer, and the torque was calculated at the peak force × length. The ratios of the individual muscle activity to the total muscle (VM, VL, and RF) during MVICs and sit-to-stand transitions were assessed using surface electromyography. Regression analysis was conducted to identify the predictors of peak knee extension torque and of individual muscle activity ratios. A P value < 0.05 was considered statistically significant. The RF λ1 significantly predicted the peak knee extension torque (β=-0.51). The IMAT percentage of the VM significantly predicted the VM muscle activity ratio during the MVIC and sit-to-stand transition (β=-0.82 and β=-0.61, respectively), whereas the ratio of the VM λ1 to the whole QM λ1 significantly predicted the VM muscle activity ratio during the sit-to-stand transitions (β=0.35 and β=0.46, respectively). The RF λ1 may allow to estimate peak knee extension muscle torque, and the VM IMAT and λ1 may predict muscle activity in youth. 3. Stage 3.

Amide proton transfer-weighted magnetic resonance imaging for the diagnosis of symptomatic chronic intracranial artery stenosis: a feasibility study.

Hemodynamic changes after intracranial artery stenosis (ICAS) or occlusion are important causes of metabolic alterations in tissue. This study aimed to explore the feasibility of using amide proton transfer-weighted (APTw) magnetic resonance imaging (MRI) to diagnose patients with symptomatic chronic ICAS based on pH variations caused by metabolite damage. Sixty-seven patients with clinically confirmed unilateral anterior circulation ICAS (≥70% arterial narrowing) and 20 healthy volunteers were recruited for the study. Each patient underwent an MRI examination including a T2 fluid-attenuated inversion recovery (T2-FLAIR) sequence, spin-echo echo-planar diffusion-weighted imaging (DWI), three-dimensional pseudo-continuous arterial spin labeling (pcASL), and an APTw sequence. Areas with abnormal perfusion and APTw effects were defined as perfusion/pH matched areas; areas with abnormal perfusion but normal APTw effects were defined as perfusion/pH unmatched areas; the contralateral mirror areas were defined as the normal areas. Regions of interest (ROIs) were selected within these three areas, and the corresponding apparent diffusion coefficient (ADC), cerebral blood flow (CBF), and magnetization transfer ratio asymmetry (MTRasym) were measured. High intraclass correlation coefficient (ICC) values (0.78≤ ICCs ≤0.97; P<0.05) were observed between the two radiologists who independently performed the data analysis. Significant differences were found in CBF and MTRasym between the perfusion/pH matched, perfusion/pH unmatched, and normal areas [F(2,64)=288.5, 163.5; both P<0.05], but the ADC values were comparable between the three [F(2,64)=2.11; P>0.05]. Spearman correlation analysis revealed no significant correlation between changes in MTRasym and CBF (P>0.05). Finally, APTw showed a robust performance in diagnosing symptomatic chronic ICAS, with an area under the receiver operating characteristic curve (ROC) of 0.953 (sensitivity 97.01%; specificity 85.07%; cut-off value 1.005%). The present study has demonstrated that metabolic alterations are present in patients with symptomatic chronic ICAS. Our findings illustrate that APTw imaging could potentially serve as an effective method to provide a robust clinical diagnosis for patients with symptomatic chronic ICAS.

Intravoxel Incoherent Motion MRI and PET in Locally Advanced Cervical Carcinoma Undergoing Concurrent Chemoradiation Therapy

<h3>Purpose/Objective(s)</h3> Dynamic contrast enhanced (DCE) CT or MRI and FDG PET have been used to evaluate the impact of tumor perfusion and metabolism on the course and effectiveness of concurrent chemoradiation therapy (CCRT) for cervical cancer. Combining perfusion and metabolic measures allows better identification of radioresistant sub-volumes: however, use of contrast and additional dose are barriers to frequent dual perfusion-metabolic imaging. Here, we investigated a contrast-free, non-ionizing alternative to DCE: intravoxel incoherent motion (IVIM) MRI which provides both perfusion and diffusion measurements. Our objective was to evaluate changes of PET and IVIM parameters in cervical cancer patients before and during CCRT and to correlate these parameters and their changes with tumor volume response during CCRT. <h3>Materials/Methods</h3> Pre- and on-treatment IVIM scans were performed on 15 cervical cancer patients undergoing definitive chemoradiation (median [range] age: 66 [29 to 85]; FIGO: 1 IB1, 1 IIA, 3 IIB, 1 IIIB, 1 IIIC, 5 IIIC1, 2 IIIC2, 1 IVA; hist: 11 squamous cell carcinoma, 3 endocervical adenocarcinoma, 1 large cell neuroendocrine carcinoma), of whom 14 also underwent pre-treatment PET scans. The on-treatment MRI occurred generally during the last week or shortly after completing EBRT. Diffusion weighted images (DWIs) were acquired at 3T scanners using a free-breathing single shot spin echo planar imaging (EPI) sequence. IVIM MRI maps were generated by Bayesian fitting of a two-compartment IVIM model to the DWIs. Three-dimensional co-registered maps of PET standardized uptake value (SUV) and IVIM diffusion coefficient (D), perfusion fraction (f), and pseudo-diffusion coefficient (D*) were generated. Summary statistics (mean +/- standard deviation) for these and other imaging parameters were calculated pre- and on-treatment. Univariate analysis was performed to determine relationships between relative change in gross tumor volume (ΔGTV) and pre-treatment imaging measurements. <h3>Results</h3> In tumors, pre- versus on-treatment values significantly changed for the following parameters: ΔGTV (66.8 +/- 43.2 vs. 32.0+/-23.0 ml, p<.001) and D (0.00109 +/- 0.00023 vs. 0.00120 +/- 0.00026 mm²/s, p=.02). The perfusion fraction f increased and D* decreased, but not significantly (f: 0.127 +/- 0.022 vs. 0.154 +/- 0.057 %, p=.07, D*: 0.0137 +/- 0.0035 vs. 0.0133 +/- 0.0039 mm²/s, p=.6). Pre-treatment SUV_max (r=.76, p=.002) and SUV_mean (r=.70, p=.007) were positively related with ΔGTV, while pre-treatment f, D*, and D were negatively but not significantly related with ΔGTV (r=-.44, p=.1; D*: r=-.14, p=.6; D: r=-.12, p=.7). <h3>Conclusion</h3> Both perfusion fraction and diffusion coefficient IVIM increased in locally advanced cervical carcinoma patients undergoing CCRT – reflecting changes in the tumor microenvironment during treatment. These weak relationships observed here suggest a potential complementary role and motivating the combined use of these modalities for tumor characterization.

The ultrastructural and morphological characteristics of the anterior cruciate ligament of the pig: a study using 7.0-Tesla diffusion tensor imaging.

Diffusion tensor imaging research on the anterior cruciate ligament (ACL) is limited, and no study has revealed the ACL fibrous microstructure by 7.0-Tesla magnetic resonance imaging. Therefore, we used magnetic resonance imaging to assess the ACL. Eight porcine ACLs were investigated by diffusion tensor imaging. Imaging was performed with a 7.0-Tesla scanner using a diffusion-weighted two-dimensional spin-echo echo-planar imaging pulse sequence optimised for muscle. The diffusion tensor eigenparameters, fractional anisotropy (FA), and apparent diffusion coefficient (ADC) were used for bones and muscles. Three-dimensional projection maps of the principal eigenvectors were plotted to visualise the microstructure. The mean FA and ADC for the ACL were 0.27 ± 0.079 and 0.0012 ± 0.0005, respectively. There were no significant differences between the values in the proximal and distal portions . However, the ADC was smaller in the centre than on the sides (0.0015 ± 0.0007), and the mean FA was larger in the centre than on the sides (0.42 ± 0.23). The ACL fibres were parallel on the proximal and distal sides but interweaved in the centre. These findings may be beneficial for artificial ligaments.

Intersession Repeatability of Diffusion-Tensor Imaging in the Supraspinatus and the Infraspinatus Muscles of Volunteers.

Quantifying the rotator cuff (RC) muscles' viscoelasticity could provide outcome relevant information in patients with RC tears. MR-elastography requires robust diffusion-tensor imaging (DTI) to account for tissue anisotropy in muscles stiffness computation. To assess the repeatability of DTI parameters in the supraspinatus and infraspinatus muscles and to explore DTI tractography conformity with the muscles' anatomy. Prospective. Six healthy volunteers underwent three consecutive shoulder MRI sessions about 10 minutes apart. 3T/T1-vibe Dixon and Spin echo EPI DTI (12 gradient encoding directions, b-values 500 and 800 sec/mm2 ). Supraspinatus and infraspinatus muscles were segmented on the T1-vibe Dixon sequence. DTI image quality was assessed using a quantitative threshold based on the signal-to-noise ratio (SNR). The eigenvalues ( ), fractional anisotropy (FA) and mean diffusivity were calculated. DTI tractography was visually assessed. DTI parameters within-subject intersession repeatability was assessed with Bland-Altman analysis and the coefficient of variation (CV). Repeatability was considered good for CV < 10%. The SNR between diffusion-weighted and non-diffusion-weighted images was greater than 3, which aligns with standards for estimating DTI parameters. The FA showed the lowest mean bias (-0.007; 95% confidence interval [CI] -0.031 to 0.018) whereas the λ1 had the highest mean bias (0.146 × 10-3 mm2 /sec; CI -0.034 to 0.326 × 10-3 mm2 /sec). CVs of the DTI parameters varied between 3.5% (FA) and 8.4% (λ3 ) for the supraspinatus and between 3.2% (λ1 ) and 6.8% (λ3 ) for the infraspinatus. Tractography provided muscle fiber representations in three-dimensional space concordant with RC anatomy. DTI of the supraspinatus and infraspinatus muscles achieved an adequate SNR, allowing the measurement of the DTI metrics with good repeatability, and thus can be used for optimizing stiffness estimation in these anisotropic tissues. 2 TECHNICAL EFFICACY: Stage 2.

Magnetic Resonance Elastography (MRE) of Bleomycin-Induced Pulmonary Fibrosis in an Animal Model.

Idiopathic pulmonary fibrosis is responsible for 40,000 deaths annually in the United States. A hallmark of idiopathic pulmonary fibrosis is elevated collagen deposition, which alters lung stiffness. Clinically relevant ways to measure changes in lung stiffness during pulmonary fibrosis are not available, and new noninvasive imaging methods are needed to measure changes in lung mechanical properties. Magnetic resonance elastography (MRE) is an in vivo magnetic resonance imaging technique proven to detect changes in shear stiffness in different organs. This study used MRE, histology, and bronchoalveolar lavage (BAL) to study changes in the mechanical and structural properties of the lungs after bleomycin-induced pulmonary fibrosis in pigs. Pulmonary fibrosis was induced in 9 Yorkshire pigs by intratracheal instillation of 2 doses of bleomycin into the right lung only. Magnetic resonance elastography scans were performed at baseline and week 4 and week 8 postsurgery in a 1.5 T magnetic resonance imaging scanner using a spin-echo echo planar imaging sequence to measure changes in lung shear stiffness. At the time of each scan, a BAL was performed. After the final scan, whole lung tissue was removed and analyzed for histological changes. Mean MRE-derived stiffness measurements at baseline, week 4, and week 8 for the control (left) lungs were 1.02 ± 0.27 kPa, 0.86 ± 0.29 kPa, and 0.68 ± 0.20 kPa, respectively. The ratio of the shear stiffness in the injured (right) lung to the uninjured control (left) lung at baseline, week 4, and week 8 was 0.98 ± 0.23, 1.52 ± 0.41, and 1.64 ± 0.40, respectively. High-dose animals showed increased protein in BAL fluid, elevated inflammation observed by the presence of patchy filtrates, and enhanced collagen and α-smooth muscle actin staining on histological sections. Low-dose animals and the control (left) lungs of high-dose animals did not show significant histopathological changes. This study demonstrated that MRE can be used to detect changes in lung stiffness in pigs after bleomycin challenge.

Multi-modal MRI reveals changes in placental function following preterm premature rupture of membranes.

Preterm premature rupture of membranes complicates up to 40% of premature deliveries. Fetal infection may occur in the absence of maternal symptoms, delaying diagnosis and increasing morbidity and mortality. A noninvasive antenatal assessment of early signs of placental inflammation is therefore urgently required. Sixteen women with preterm premature rupture of membranes < 34 weeks gestation and 60 women with uncomplicated pregnancies were prospectively recruited. A modified diffusion-weighted spin-echo single shot EPI sequence with a diffusion preparation acquiring 264 unique parameter combinations in < 9min was obtained on a clinical 3 Tesla MRI scanner. The data was fitted to a 2-compartment -intravoxel incoherent motion model comprising fast and slowly circulating fluid pools to obtain quantitative information on perfusion, density, and tissue composition. Z values were calculated, and correlation with time from between the rupture of membranes and the scan, gestational age at delivery, and time between scan and delivery assessed. Placental was significantly reduced in preterm premature rupture of membranes, and the 2-compartmental model demonstrated that this decline is mainly linked to the perfusion component observed in the placental parenchyma. Multi-modal MRI measurement of placental function is linked to gestational age at delivery and time from membrane rupture. More complex models and data acquisition can potentially improve fitting of the underlying etiology of preterm birth compared with individual single-contrast models and contribute to additional insights in the future. This will need validation in larger cohorts. A multi-modal MRI acquisition between rupture of the membranes and delivery can be used to measure placental function and is linked to gestational age at delivery.

Proton exchange rate of chemical exchange saturation transfer MRI constructed from direct saturation-removed omega plots to improve the assessment of patients with ischemic stroke.

BackgroundProton exchange rate (kex) magnetic resonance imaging (MRI) has recently been developed, with preliminary results demonstrating its potential for evaluating reactive oxygen species. This prospective cohort study investigated the kex in different stroke stages and its correlation with stroke severity and prognosis.MethodsIn all, 96 ischemic stroke patients were included in the study. Patients were divided into 3 groups based on stroke phase (acute, subacute, and chronic). A spin echo-echo planar imaging sequence with presaturation powers of 1.5, 2.5, and 3.5 µT was implemented to obtain Z-spectra, and kex maps were constructed from direct saturation-removed omega plots. Relative kex (rkex) and the relative apparent diffusion coefficient (rADC) were calculated as the ratio of kex or ADC in the infarcts to values in contralateral tissue, respectively. Correlations between both kex and rkex and National Institute of Health Stroke Scale (NIHSS) scores were evaluated. Receiver operating characteristic (ROC) analysis was used to evaluate the performance of kex, rkex, rADC, and lesion volume for predicting acute stroke outcome.ResultsThe kex was significantly higher in ischemic lesions than in contralateral tissue at all stages. In addition, the kex of acute lesions was higher than that of subacute and chronic lesions [mean (± SD) 935.1±81.5 vs. 881.4±55.7 and 866.9±76.7 s–1, respectively; P<0.05 and P<0.01, respectively]. The difference in kex between subacute and chronic lesions was not significant. In acute stroke, there was a limited correlation between a lesion’s kex and NIHSS score (R2=0.16; P=0.01) and between rkex and NIHSS score (R2=0.28; P=0.001). Acute stroke patients with poor prognosis had significantly higher lesion kex and rkex than did those with good prognosis (kex: 991.1±78.2 vs. 893.1±55.1 s–1, P<0.001; rkex: 1.28±0.09 vs. 1.15±0.06, P<0.001). In ROC analyses, kex and rkex showed favorable predictive performance for acute stroke outcome, with areas under the curve (AUC) of 0.837 and 0.880, respectively, which were slightly but not significantly higher than the AUCs for lesion volume (0.730) and rADC (0.673).ConclusionsThis study indicates that kex MRI is promising for the diagnosis and management of ischemic stroke because it can reflect the oxidative stress of lesions and predict prognosis.

Characterization of the echo-time dependence of spin-echo BOLD fMRI at 3 Tesla in grey and white matter

• We characterize the regional-specific behavior of the spin-echo (SE) EPI BOLD fMRI sensitivity in grey and white matter. • We inducing global BOLD responses in 7 healthy adults using hypercapnia. • SE-BOLD sensitivity is not maximized at tissue T 2 , as is widely assumed. • Our findings suggest the use of significantly shorter TEs than tissue T 2 for grey and white matter.

Predictive Value of 18 F-FDG PET/MRI for Pleural Invasion in Solid and Subsolid Lung Adenocarcinomas Smaller Than 3cm.

Positron emission tomography (PET)/MRI combines the characteristics of metabolism imaging and high soft tissue resolution, and could provide high diagnostic efficacy for assessment of pleural invasion (PI) of lung cancer. To investigate the application of 18 F-fluorodeoxyglucose (FDG) PET/MRI for predicting PI of lung cancer with the maximum diameter ≤3cm. Prospective. A total of 44 patients with non-small cell lung cancer (NSCLC), age from 39 to 79 years old, including 19 (56.82%) females. A 3-T, hybrid PET/MRI including axial fast spin echo respiratory-triggered T2 fat-suppressed imaging (T2FS) and echo planar imaging diffusion-weighted imaging (DWI). The maximum standardized uptake value (SUVmax) of all lesions was measured on PET images. Localized effusion outside the contact between the nodules and the pleura on T2FS and signal at the contact between the nodules and the pleura on DWI were evaluated by experienced physicians through visual assessment of the MRI sequences. Three models (models 1-3) were developed, incorporating CT, CT and PET, PET and MRI features, and Lasso regression was used in feature selection. The receiver operating characteristic (ROC) curve for PI diagnosis was visualized for each model, and the area under the curve (AUC) was calculated. The DeLong test was used to compare the different AUCs. A P value < 0.05 was considered statistically significant. The AUC of models 1-3 was 0.762, 0.829, and 0.915, respectively. The DeLong test showed a statistically significant difference between the AUCs of model 1 vs. model 3, while the differences between the AUCs of model 1 vs. model 2 (P=0.253) and model 2 vs. model 3 (P=0.075) were not statistically significant. 18 F-FDG PET/MRI might show high predictive value for lung adenocarcinoma smaller than 3cm with PI. 1 TECHNICAL EFFICACY: Stage 2.

Comparison of spin-echo echo-planar imaging magnetic resonance elastography with gradient-recalled echo magnetic resonance elastography and their correlation with transient elastography

PURPOSE This study aimed to assess the agreement between liver stiffness (LS) values obtained by the gradient-recalled echo (GRE) magnetic resonance elastography (MRE) and spin-echo echo-planar imaging (SE-EPI) MRE with those of transient elastography (TE), respectively. METHODS We retrospectively included 48 participants who underwent liver MRE with both GRE and SE-EPI sequences in the same session and also TE within 1 year. We obtained LS values for MRE by drawing free-hand region of interest, and TE was performed using a FibroScan device. We assessed the relationship between the mean LS values obtained by each MRE sequence and TE using the correlation coefficients and Bland-Altman plots, respectively. We also compared LS values and technical failure rates of measured values from MRE between SE-EPI and GRE sequences using the paired t-test and McNemar's test. The MRE failure was defined as the absence of pixel value with a confidence index above 95%. RESULTS The LS values from SE-EPI and GRE sequences strongly correlated with those from TE (GRE; r = 0.73, P < .001 vs. SE-EPI; r = 0.79, P < .001). In addition, the LS values from the 2 MRE sequences showed excellent relationship (intraclass correlation coefficient, 0.94 [0.89-0.97], P < .001). The LS values from SE-EPI and GRE MRE were not significantly different (4.14 kPa vs. 3.88 kPa, P = .19). Furthermore, the technical success rate of SE-EPI MRE was superior to that of GRE (100% vs. 83.8%, P = .031). CONCLUSION The measured LS values obtained using TE correlated strongly with those obtained using GRE and SE-EPI MRE techniques, even though SE-EPI-MRE resulted a higher technical success rate than GRE-MRE. Therefore, we believe that TE, GRE, and SE-EPI MR elastography techniques may complement each other according to the appropriate individual situation.

A relaxometry method that emphasizes practicality and availability.

Although many methods have been proposed to quantitatively map the main MRI parameters (e.g., T1 , T2 , C × M0 ), these methods often involve special sequences not readily available on clinical scanners and/or may require long scan times. In contrast, the proposed method can readily run on most scanners, offer flexible tradeoffs between scan time and image quality, and map MRI parameters jointly to ensure spatial alignment. The approach is based on the multi-shot spin-echo (SE) EPI sequence. The corresponding signal equation was derived and strategies for solving it were developed. As usual with multi-shot EPI, scan time can readily be traded-off against image quality by adjusting the echo train length. Validation was performed against reference relaxometry methods, in gel phantoms with varying concentrations of gadobutrol and gadoterate meglumine contrast agents. In vivo examples are further presented, from 3 neuroradiology patients. Bland-Altman analysis was performed: for T2 , as compared to 2D SE, bias was 0.29 ms and the 95% limits of agreement ranged from -1.15 to +1.73 ms. For T1 , compared to inversion-recovery SE (and MOLLI), bias was -20.2ms (and -14.5ms) and the limits of agreement ranged from -62.4 to +22.0ms (and -53.8 to +24.9ms). The mean relative T1 error between the proposed method and each of the 2 reference methods was similar to that of the reference methods among themselves. In the constellation of existing relaxometry methods, the proposed method is meant to stand out in terms of its practicality and availability.