Faculty Bibliography

PURPOSE/OBJECTIVE:To validate an optimal 12-fold accelerated real-time cine MRI pulse sequence with radial k-space sampling and compressed sensing (CS) in patients at 1.5T and 3T. METHODS:We used two strategies to reduce image artifacts arising from gradient delays and eddy currents in radial k-space sampling with balanced steady-state free precession readout. We validated this pulse sequence against a standard breath-hold cine sequence in two patient cohorts: a myocardial infarction (n = 16) group at 1.5T and chronic kidney disease group (n = 18) at 3T. Two readers independently performed visual analysis of 68 cine sets in four categories (myocardial definition, temporal fidelity, artifact, noise) on a 5-point Likert scale (1 = nondiagnostic, 2 = poor, 3 = adequate or moderate, 4 = good, 5 = excellent). Another reader calculated left ventricular (LV) functional parameters, including ejection fraction. RESULTS:Compared with standard cine, real-time cine produced nonsignificantly different visually assessed scores, except for the following categories: 1) temporal fidelity scores were significantly lower (P = 0.013) for real-time cine at both field strengths, 2) artifacts scores were significantly higher (P = 0.013) for real-time cine at both field strengths, and 3) noise scores were significantly (P = 0.013) higher for real-time cine at 1.5T. Standard and real-time cine pulse sequences produced LV functional parameters that were in good agreement (e.g., absolute mean difference in ejection fraction <4%). CONCLUSION/CONCLUSIONS:This study demonstrates that an optimal 12-fold, accelerated, real-time cine MRI pulse sequence using radial k-space sampling and CS produces good to excellent visual scores and relatively accurate LV functional parameters in patients at 1.5T and 3T. Magn Reson Med 79:2745-2751, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Purpose or Case Report: Free-breathing MRI scans are attractive in pediatric imaging as they reduce the need for sedation and breath-holds. In this work, we evaluate a 3D T1w radial "stack of stars" gradient echo (GRE) acquisition (RAVERAdial Volumetric Encoding) in post-contrast abdomen and spine protocols and compare results with conventional Cartesian MRI of similar spatial resolution and volume coverage. Methods & Materials: Studies were performed on a 3T Siemens Prisma. With radial MRI, data are acquired along kspace spokes during repetitions of the sequence. Consecutive spokes are rotated in-plane by the golden-angle (111.25 deg) to maximize k-space coverage. The center of k-space is oversampled and this feature affords RAVE's robustness to motion. When coupled with compressed sensing and parallel imaging, the radial data further yields dynamic images, (i.e., during contrast passage). We have evaluated free-breathing RAVE in 20 patients referred for non-sedated abdominal and spine MRI exams with contrast. In the abdomen, we have acquired RAVE in both axial and coronal orientations (i.e., liver, enterography). In the spine, we have acquired RAVE in the axial plane. Three radiologists compared RAVE to conventional breath-hold GRE in abdomen scans and free-breathing fast-spinecho (FSE) images in the spine. A 3-point scale was used to evaluate diagnostic image quality:-1=RAVE is superior, 0=equivalent, +1=RAVE is inferior. Results: In all cases, RAVE images were considered robust to respiratory, cardiac, and gastrointestinal motion, and no artifacts that impacted diagnostic image quality were noted. In the spine, RAVE was consistently superior to FSE (p<0.01) in delineating nerve tracts and roots against CSF. In the abdomen, RAVE was comparable to breath-hold GRE scans. Fig 1 shows a series of cervical, thoracic, and lumbar spine comparisons between FSE and RAVE in a 14y patient. Note the lack of motion-related artifacts in RAVE, without the use saturation bands. Fig 2 shows coronal RAVE dynamic frames ~15s apart, highlighting contrast uptake, in a 10y patient. A breath-hold post-contrast GRE image is shown for comparison. Figure 3 shows pre-and postcontrast axial RAVE images in a 14y patient. Conclusions: Our data demonstrates the potential utility of a free-breathing accelerated 3D T1w RAVE sequence in unsedated pediatric imaging. The technique is particularly useful in patients who are unable to follow breath-hold instructions and suspend respiration, and it is 30-50% faster in scan time than conventional methods

Purpose or Case Report: With increasing interest in rapid MRIs aimed to reduce sedation in pediatric imaging, the purpose of this study was to evaluate a 3D golden-angle radial "stack of stars" gradient echo scan (i.e., RAVE-RAdial Volumetric Encoding) and to compare results with a conventional 3D inversion recovery sequence in post contrast brain imaging. Methods & Materials: Studies were performed on a 3T Siemens Prisma system using either a 20 or 64-channel head array. Unlike traditional Cartesian acquisitions, MRI data in RAVE is acquired with consecutive k-space spokes that are rotated by the golden-angle (111.25 deg) to maximize k-space coverage efficiency. As a result of the radial trajectory, the center of k-space is oversampled and this feature affords RAVE's robustness to motion. When coupled with compressed sensing and parallel imaging, RAVE data can further yield time-resolved images during contrast passage. We evaluated RAVE in 20 patients (average age: 12.5y, range 2.2-21y) referred for brain MRI exams with contrast. Upon injection of standard dose contrast media (Gadavist), data from a RAVE acquisition and a conventional 3D IR-GRE (i.e., MPRAGE) were implemented (MPRAGE first). The two scans were matched in 1 mm native isotropic spatial resolution and volume coverage. On average, the MPRAGE acquisition took 5-6 minutes to complete, whereas the RAVE scan is ~25-30% faster. Three radiologists independently compared the data in terms of conspicuity of contrast-enhancing lesions and diagnostic image quality with respect to motion-related artifacts. A 3-point scale was used:-1=RAVE is superior, 0=RAVE and MPRAGE are equivalent, +1=MPRAGE is superior. Results: All evaluators found the RAVE with MPRAGE reformats to be similar when presenting contrast-enhanced details in 15 cases (score= 0). In the remaining 5, RAVE was preferred (score=-1). RAVE was notably more resistant to subject motion and pulsation artifacts. No significant artifacts were noted in RAVE. Figures 1 and 2 show data in non-sedated 13y and 11y old patients, respectively, with significant head movements. Figure 3 illustrates time-resolved images from RAVE in a 7y old, 20s apart, showing an enhancing lesion (arrow). Conclusions: Our study demonstrates the potential clinical utility of an accelerated 3D T1-weighted RAVE MRI sequence in unsedated pediatric brain imaging. The complementary technique is particularly useful in patients prone to head (and body) motion. Further evaluation in neonatal imaging and body and spine applications are warranted

PURPOSE/OBJECTIVE:To compare patellar instability with magnetic resonance imaging analysis using continuous real-time radial gradient-echo (GRE) imaging in the assessment of symptomatic patients and asymptomatic subjects. METHODS:Symptomatic patients with suspected patellofemoral maltracking and asymptomatic volunteers were scanned in real time by a radial 2-dimensional GRE sequence at 3 T in axial orientation at the patella level through a range of flexion-extension. The degree of lateral maltracking, as well as the associated tibial tubercle-trochlear groove distance and trochlea depth, was measured. Patellar lateralization was categorized as normal (≤2 mm), mild (>2 to ≤5 mm), moderate (>5 to ≤10 mm), or severe (>10 mm). The patellofemoral cartilage was also assessed according to the modified Outerbridge grading system. RESULTS:The study included 20 symptomatic patients (13 women and 7 men; mean age, 36 ± 12.8 years) and 10 asymptomatic subjects (3 women and 7 men; mean age, 33.1 years). The mean time to perform the dynamic component ranged from 3 to 7 minutes. Lateralization in the symptomatic group was normal in 10 patients, mild in 1, moderate in 8, and severe in 1. There was no lateral tracking greater than 3 mm in the volunteer group. Lateral maltracking was significantly higher in symptomatic patients than in asymptomatic subjects (4.4 ± 3.7 mm vs 1.5 ± 0.71 mm, P = .007). Lateral tracking significantly correlated with tibial tubercle-trochlear groove distance (r = 0.48, P = .006). There was excellent agreement on lateral tracking between the 2 reviewers (intraclass correlation coefficient, 0.979; 95% confidence interval, 0.956-0.990). CONCLUSIONS:The inclusion of a dynamic radial 2-dimensional GRE sequence is a rapid and easily performed addition to the standard magnetic resonance imaging protocol and allows dynamic quantitative assessment of patellar instability and lateral maltracking in symptomatic patients. With a paucity of reported data using this technique confirming that these results reach clinical significance, future work is required to determine how much lateral tracking is clinically significant. LEVEL OF EVIDENCE/METHODS:Level III, case control.

OBJECTIVES: The aims of this study were to observe the pattern of transient motion after gadoxetic acid administration including incidence, onset, and duration, and to evaluate the clinical feasibility of free-breathing gadoxetic acid-enhanced liver magnetic resonance imaging using golden-angle radial sparse parallel (GRASP) imaging with respiratory gating. MATERIALS AND METHODS: In this institutional review board-approved prospective study, 59 patients who provided informed consents were analyzed. Free-breathing dynamic T1-weighted images (T1WIs) were obtained using GRASP at 3 T after a standard dose of gadoxetic acid (0.025 mmol/kg) administration at a rate of 1 mL/s, and development of transient motion was monitored, which is defined as a distinctive respiratory frequency alteration of the self-gating MR signals. Early arterial, late arterial, and portal venous phases retrospectively reconstructed with and without respiratory gating and with different temporal resolutions (nongated 13.3-second, gated 13.3-second, gated 6-second T1WI) were evaluated for image quality and motion artifacts. Diagnostic performance in detecting focal liver lesions was compared among the 3 data sets. RESULTS: Transient motion (mean duration, 21.5 +/- 13.0 seconds) was observed in 40.0% (23/59) of patients, 73.9% (17/23) of which developed within 15 seconds after gadoxetic acid administration. On late arterial phase, motion artifacts were significantly reduced on gated 13.3-second and 6-second T1WI (3.64 +/- 0.34, 3.61 +/- 0.36, respectively), compared with nongated 13.3-second T1WI (3.12 +/- 0.51, P < 0.0001). Overall, image quality was the highest on gated 13.3-second T1WI (3.76 +/- 0.39) followed by gated 6-second and nongated 13.3-second T1WI (3.39 +/- 0.55, 2.57 +/- 0.57, P < 0.0001). Only gated 6-second T1WI showed significantly higher detection performance than nongated 13.3-second T1WI (figure of merit, 0.69 [0.63-0.76]) vs 0.60 [0.56-0.65], P = 0.004). CONCLUSIONS: Transient motion developed in 40% (23/59) of patients shortly after gadoxetic acid administration, and gated free-breathing T1WI using GRASP was able to consistently provide acceptable arterial phase imaging in patients who exhibited transient motion.

Magnetic resonance (MR)/PET scanners provide an imaging platform that enables simultaneous acquisition of MR and PET data in perfect spatial and temporal registration. This feature allows improving image quality for the MR and PET images obtained during the course of an examination. In this work the authors demonstrate the use of prospective MR-based motion tracking information for removing motion blur in MR/PET images of small pulmonary nodules. The theoretical basis for the algorithms is presented alongside clinical examples of its use.

Non-Cartesian magnetic resonance imaging (MRI) sequences have shown great promise for abdominal examination during free breathing, but break down in the presence of bulk patient motion (i.e. voluntary or involuntary patient movement resulting in translation, rotation or elastic deformations of the body). This work describes a data-consistency-driven image stabilization technique that detects and excludes bulk movements during data acquisition. Bulk motion is identified from changes in the signal intensity distribution across different elements of a multi-channel receive coil array. A short free induction decay signal is acquired after excitation and used as a measure to determine alterations in the load distribution. The technique has been implemented on a clinical MR scanner and evaluated in the abdomen. Six volunteers were scanned and two radiologists scored the reconstructions. To show the applicability to other body areas, additional neck and knee images were acquired. Data corrupted by bulk motion were successfully detected and excluded from image reconstruction. An overall increase in image sharpness and reduction of streaking and shine-through artifacts were seen in the volunteer study, as well as in the neck and knee scans. The proposed technique enables automatic real-time detection and exclusion of bulk motion during MR examinations without user interaction. It may help to improve the reliability of pediatric MRI examinations without the use of sedation.

OBJECTIVES: The aim of this study was to assess the applicability of Dixon radial volumetric encoding (Dixon-RAVE) for comprehensive dynamic contrast-enhanced 3D magnetic resonance imaging (MRI) of the breast using a combination of radial sampling, model-based fat/water separation, compressed sensing, and parallel imaging. MATERIALS AND METHODS: In this Health Insurance Portability and Accountability Act-compliant prospective study, 24 consecutive patients underwent bilateral breast MRI, including both conventional fat-suppressed and non-fat-suppressed precontrast T1-weighted volumetric interpolated breath-hold examination (VIBE). Afterward, 1 continuous Dixon-RAVE scan was performed with the proposed approach while the contrast agent was injected. This scan was immediately followed by the acquisition of 4 conventional fat-saturated VIBE scans. From the comprehensive Dixon-RAVE data set, different image contrasts were reconstructed that are comparable to the separate conventional VIBE scans.Two radiologists independently rated image quality, conspicuity of fibroglandular tissue from fat (FG), and degree of fat suppression (FS) on a 5-point Likert-type scale for the following 3 comparisons: precontrast fat-suppressed (pre-FS), precontrast non-fat-suppressed (pre-NFS), and dynamic fat-suppressed (dyn-FS) images. RESULTS: When scores were averaged over readers, Dixon-RAVE achieved significantly higher (P < 0.001) degree of fat suppression compared with VIBE, for both pre-FS (4.25 vs 3.67) and dyn-FS (4.10 vs 3.46) images. Although Dixon-RAVE had lower image quality score compared with VIBE for the pre-FS (3.56 vs 3.67, P = 0.490), the pre-NFS (3.54 vs 3.88, P = 0.009), and the dyn-FS images (3.06 vs 3.67, P < 0.001), acceptable or better diagnostic quality was achieved (score >/= 3). The FG score for Dixon-RAVE in comparison to VIBE was significantly higher for the pre-FS image (4.23 vs 3.85, P = 0.044), lower for the pre-NFS image (3.98 vs 4.25, P = 0.054), and higher for the dynamic fat-suppressed image (3.90 vs 3.85, P = 0.845). CONCLUSIONS: Dixon-RAVE can serve as a one-stop-shop approach for comprehensive T1-weighted breast MRI with diagnostic image quality, high spatiotemporal resolution, reduced overall scan time, and improved fat suppression compared with conventional imaging.

PURPOSE: Conventional fat/water separation techniques require that patients hold breath during abdominal acquisitions, which often fails and limits the achievable spatial resolution and anatomic coverage. This work presents a novel approach for free-breathing volumetric fat/water separation. METHODS: Multiecho data are acquired using a motion-robust radial stack-of-stars three-dimensional GRE sequence with bipolar readout. To obtain fat/water maps, a model-based reconstruction is used that accounts for the off-resonant blurring of fat and integrates both compressed sensing and parallel imaging. The approach additionally enables generation of respiration-resolved fat/water maps by detecting motion from k-space data and reconstructing different respiration states. Furthermore, an extension is described for dynamic contrast-enhanced fat-water-separated measurements. RESULTS: Uniform and robust fat/water separation is demonstrated in several clinical applications, including free-breathing noncontrast abdominal examination of adults and a pediatric subject with both motion-averaged and motion-resolved reconstructions, as well as in a noncontrast breast exam. Furthermore, dynamic contrast-enhanced fat/water imaging with high temporal resolution is demonstrated in the abdomen and breast. CONCLUSION: The described framework provides a viable approach for motion-robust fat/water separation and promises particular value for clinical applications that are currently limited by the breath-holding capacity or cooperation of patients. Magn Reson Med, 2016. (c) 2016 International Society for Magnetic Resonance in Medicine.

BACKGROUND: Interest in MR-only treatment planning for radiation therapy is growing rapidly with the emergence of integrated MRI/linear accelerator technology. The purpose of this study was to evaluate the feasibility of using synthetic CT images generated from conventional Dixon-based MRI scans for radiation treatment planning of lung cancer. METHODS: Eleven patients who underwent whole-body PET/MR imaging following a PET/CT exam were randomly selected from an ongoing prospective IRB-approved study. Attenuation maps derived from the Dixon MR Images and atlas-based method was used to create CT data (synCT). Treatment planning for radiation treatment of lung cancer was optimized on the synCT and subsequently copied to the registered CT (planCT) for dose calculation. Planning target volumes (PTVs) with three sizes and four different locations in the lung were planned for irradiation. The dose-volume metrics comparison and 3D gamma analysis were performed to assess agreement between the synCT and CT calculated dose distributions. RESULTS: Mean differences between PTV doses on synCT and CT across all the plans were -0.1% +/- 0.4%, 0.1% +/- 0.5%, and 0.4% +/- 0.5% for D95, D98 and D100, respectively. Difference in dose between the two datasets for organs at risk (OARs) had average differences of -0.14 +/- 0.07 Gy, 0.0% +/- 0.1%, and -0.1% +/- 0.2% for maximum spinal cord, lung V20, and heart V40 respectively. In patient groups based on tumor size and location, no significant differences were observed in the PTV and OARs dose-volume metrics (p > 0.05), except for the maximum spinal-cord dose when the target volumes were located at the lung apex (p = 0.001). Gamma analysis revealed a pass rate of 99.3% +/- 1.1% for 2%/2 mm (dose difference/distance to agreement) acceptance criteria in every plan. CONCLUSIONS: The synCT generated from Dixon-based MRI allows for dose calculation of comparable accuracy to the standard CT for lung cancer treatment planning. The dosimetric agreement between synCT and CT calculated doses warrants further development of a MR-only workflow for radiotherapy of lung cancer.