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1. Real‐Time Magnetic Resonance Imaging

   https://doi.org/10.1002/jmri.27411  

   Nayak, Krishna S. ; Lim, Yongwan ; Campbell‐Washburn, Adrienne E. ; Steeden, Jennifer ( December 2020 , Journal of Magnetic Resonance Imaging)

   Real‐time magnetic resonance imaging (RT‐MRI) allows for imaging dynamic processes as they occur, without relying on any repetition or synchronization. This is made possible by modern MRI technology such as fast‐switching gradients and parallel imaging. It is compatible with many (but not all) MRI sequences, including spoiled gradient echo, balanced steady‐state free precession, and single‐shot rapid acquisition with relaxation enhancement. RT‐MRI has earned an important role in both diagnostic imaging and image guidance of invasive procedures. Its unique diagnostic value is prominent in areas of the body that undergo substantial and often irregular motion, such as the heart, gastrointestinal system, upper airway vocal tract, and joints. Its value in interventional procedure guidance is prominent for procedures that require multiple forms of soft‐tissue contrast, as well as flow information. In this review, we discuss the history of RT‐MRI, fundamental tradeoffs, enabling technology, established applications, and current trends.

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2. Temporally resolved parametric assessment of Z‐magnetization recovery (TOPAZ): Dynamic myocardial T 1 mapping using a cine steady‐state look‐locker approach

   https://doi.org/10.1002/mrm.26887  

   Weingärtner, Sebastian ; Shenoy, Chetan ; Rieger, Benedikt ; Schad, Lothar R. ; Schulz‐Menger, Jeanette ; Akçakaya, Mehmet ( August 2017 , Magnetic Resonance in Medicine)

   To develop and evaluate a cardiac phase‐resolved myocardial T₁mapping sequence.

   The proposed method for temporally resolved parametric assessment of Z‐magnetization recovery (TOPAZ) is based on contiguous fast low‐angle shot imaging readout after magnetization inversion from the pulsed steady state. Thereby, segmented k‐space data are acquired over multiple heartbeats, before reaching steady state. This results in sampling of the inversion‐recovery curve for each heart phase at multiple points separated by an R‐R interval. Joint T₁andestimation is performed for reconstruction of cardiac phase‐resolved T₁andmaps. Sequence parameters are optimized using numerical simulations. Phantom and in vivo imaging are performed to compare the proposed sequence to a spin‐echo reference and saturation pulse prepared heart rate–independent inversion‐recovery (SAPPHIRE) T₁mapping sequence in terms of accuracy and precision.

   In phantom, TOPAZ T₁values with integratedcorrection are in good agreement with spin‐echo T₁values (normalized root mean square error = 4.2%) and consistent across the cardiac cycle (coefficient of variation = 1.4 ± 0.78%) and different heart rates (coefficient of variation = 1.2 ± 1.9%). In vivo imaging shows no significant difference in TOPAZ T₁times between the cardiac phases (analysis of variance:P = 0.14, coefficient of variation = 3.2 ± 0.8%), but underestimation compared with SAPPHIRE (T₁time ± precision: 1431 ± 56 ms versus 1569 ± 65 ms). In vivo precision is comparable to SAPPHIRE T₁mapping until middiastole (P > 0.07), but deteriorates in the later phases.

   The proposed sequence allows cardiac phase‐resolved T₁mapping with integratedassessment at a temporal resolution of 40 ms. Magn Reson Med 79:2087–2100, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

    

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3. Simultaneous Mapping of T1 and T2 Using Cardiac Magnetic Resonance Fingerprinting in a Cohort of Healthy Subjects at 1. 5T

   https://doi.org/10.1002/jmri.27155  

   Hamilton, Jesse I. ; Pahwa, Shivani ; Adedigba, Joseph ; Frankel, Samuel ; O'Connor, Gregory ; Thomas, Rahul ; Walker, Jonathan R. ; Killinc, Ozden ; Lo, Wei‐Ching ; Batesole, Joshua ; et al ( March 2020 , Journal of Magnetic Resonance Imaging)

   Cardiac MR fingerprinting (cMRF) is a novel technique for simultaneous T₁and T₂mapping.

   To compare T₁/T₂measurements, repeatability, and map quality between cMRF and standard mapping techniques in healthy subjects.

   Prospective.

   In all, 58 subjects (ages 18–60).

   cMRF, modified Look–Locker inversion recovery (MOLLI), and T₂‐prepared balanced steady‐state free precession (bSSFP) at 1.5T.

   T₁/T₂values were measured in 16 myocardial segments at apical, medial, and basal slice positions. Test–retest and intrareader repeatability were assessed for the medial slice. cMRF and conventional mapping sequences were compared using ordinal and two alternative forced choice (2AFC) ratings.

   Pairedt‐tests, Bland–Altman analyses, intraclass correlation coefficient (ICC), linear regression, one‐way analysis of variance (ANOVA), and binomial tests.

   Average T₁measurements were: basal 1007.4±96.5 msec (cMRF), 990.0±45.3 msec (MOLLI); medial 995.0±101.7 msec (cMRF), 995.6±59.7 msec (MOLLI); apical 1006.6±111.2 msec (cMRF); and 981.6±87.6 msec (MOLLI). Average T₂measurements were: basal 40.9±7.0 msec (cMRF), 46.1±3.5 msec (bSSFP); medial 41.0±6.4 msec (cMRF), 47.4±4.1 msec (bSSFP); apical 43.5±6.7 msec (cMRF), 48.0±4.0 msec (bSSFP). A statistically significant bias (cMRF T₁larger than MOLLI T₁) was observed in basal (17.4 msec) and apical (25.0 msec) slices. For T₂, a statistically significant bias (cMRF lower than bSSFP) was observed for basal (–5.2 msec), medial (–6.3 msec), and apical (–4.5 msec) slices. Precision was lower for cMRF—the average of the standard deviation measured within each slice was 102 msec for cMRF vs. 61 msec for MOLLI T₁, and 6.4 msec for cMRF vs. 4.0 msec for bSSFP T₂. cMRF and conventional techniques had similar test–retest repeatability as quantified by ICC (0.87 cMRF vs. 0.84 MOLLI for T₁; 0.85 cMRF vs. 0.85 bSSFP for T₂). In the ordinal image quality comparison, cMRF maps scored higher than conventional sequences for both T₁(all five features) and T₂(four features).

   This work reports on myocardial T₁/T₂measurements in healthy subjects using cMRF and standard mapping sequences. cMRF had slightly lower precision, similar test–retest and intrareader repeatability, and higher scores for map quality.

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   Stage 1 J. Magn. Reson. Imaging 2020;52:1044–1052.

    

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4. A black‐blood ultra‐short echo time (UTE) sequence for 3D isotropic resolution imaging of the lungs

   https://doi.org/10.1002/mrm.27679  

   Delacoste, Jean ; Feliciano, Helene ; Yerly, Jérôme ; Dunet, Vincent ; Beigelman‐Aubry, Catherine ; Ginami, Giulia ; van Heeswijk, Ruud B. ; Piccini, Davide ; Stuber, Matthias ; Sauty, Alain ( February 2019 , Magnetic Resonance in Medicine)

   Ultra‐short echo time MRI is a promising alternative to chest CT for cystic fibrosis patients. Black‐blood imaging in particular could help discern small‐sized anomalies, such as mucoid plugging, which may otherwise be confused with neighboring blood vessels, particularly when contrast agent is not used. We, therefore, implemented and tested an ultra‐short echo time sequence with black‐blood preparation. Additionally, this sequence may also be used to generate bright‐blood angiograms.

   Using this sequence, data was acquired during free breathing in 10 healthy volunteers to obtain respiratory‐motion‐resolved 3D volumes covering the entire thorax with an isotropic resolution of (1 mm)³. The magnitude of signal suppression relative to a bright‐blood reference acquisition was quantified and compared with that obtained with a turbo‐spin echo (TSE) acquisition. Bright‐blood angiograms were also generated by subtraction. Finally, an initial feasibility assessment was performed in 2 cystic fibrosis patients, and images were visually compared with contrast‐enhanced images and with CT data.

   Black‐blood preparation significantly decreased the average normalized signal intensity in the vessel lumen (−66%;P< 0.001). Similarly, blood signal was significantly lowered (−60%;P= 0.001) compared with the TSE acquisition. In patients, mucoid plugging could be emphasized in the black‐blood datasets. An intercostal artery could also be visualized in the subtraction angiograms.

   Black‐blood free‐breathing ultra‐short echo time imaging was successfully implemented and motion‐resolved full volumetric coverage of the lungs with high spatial resolution was achieved, while obtaining an angiogram without contrast agent injection. Encouraging initial results in patients prompt further investigations in a larger cohort.

    

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5. Automatic recognition of subject‐specific cerebrovascular trees

   https://doi.org/10.1002/mrm.26087  

   Hsu, Chih‐Yang ; Schneller, Ben ; Alaraj, Ali ; Flannery, Michael ; Zhou, Xiaohong Joe ; Linninger, Andreas ( January 2016 , Magnetic Resonance in Medicine)

   An image filter designed for reconstructing cerebrovascular trees from MR images is described. Current imaging techniques capture major cerebral vessels reliably, but often fail to detect small vessels, whose contrast is suppressed due to limited resolution, slow blood flow rate, and distortions around bifurcations or nonvascular structures. An incomplete view of angioarchitecture limits the information available to physicians.

   A novel Hessian‐based filter for contrast‐enhancement in MR angiography and venography for blood vessel reconstruction without introducing dangling segments is presented. We quantify filter performance with receiver‐operating‐characteristic and dice‐similarity‐coefficient analysis. Total extracted vascular length, number‐of‐segments, volume, surface‐to‐distance, and positional error are calculated for validation.

   Reconstruction of cerebrovascular trees from MR images of six volunteers show that the new filter renders more complete representations of subject‐specific cerebrovascular networks. Validation with phantom models shows the filter correctly detects blood vessels across all length scales without failing at bifurcations or distorting diameters.

   The novel filter can potentially improve the diagnosis of cerebrovascular diseases by delivering metrics and anatomy of the vasculature. It also facilitates the automated analysis of large datasets by computing biometrics free of operator subjectivity. The high quality reconstruction enables computational mesh generation for subject‐specific hemodynamic simulations. Magn Reson Med 77:398–410, 2017. © 2016 Wiley Periodicals, Inc.

    

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