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Background Cardiac magnetic resonance (CMR) flow quantification is typically performed using 2D phase-contrast (PC) imaging of a plane perpendicular to flow. 3D-PC imaging (4D-flow) allows offline quantification anywhere in a thick slab, but is often limited by suboptimal signal, potentially alleviated by contrast enhancement. We developed a non-contrast 4D-flow sequence, which acquires multiple overlapping thin slabs (MOTS) to minimize signal loss, and hypothesized that it could improve image quality, diagnostic accuracy, and aortic flow measurements compared to non-contrast single-slab approach. Methods We prospectively studied 20 patients referred for transesophageal echocardiography (TEE), who underwent CMR (GE, 3 T). 2D-PC images of the aortic valve and three 4D-flow datasets covering the heart were acquired, including single-slab, pre- and post-contrast, and non-contrast MOTS. Each 4D-flow dataset was interpreted blindly for ≥moderate valve disease and compared to TEE. Flow visualization through each valve was scored (0 to 4), and aortic-valve flow measured on each 4D-flow dataset and compared to 2D-PC reference. Results Diagnostic quality visualization was achieved with the pre- and post-contrast 4D-flow acquisitions in 25% and 100% valves, respectively (scores 0.9 ± 1.1 and 3.8 ± 0.5), and in 58% with the non-contrast MOTS (1.6 ± 1.1). Accuracy of detection of valve disease was 75%, 92% and 82%, respectively. Aortic flow measurements were possible in 53%, 95% and in 89% patients, respectively. The correlation between pre-contrast single-slab measurements and 2D-PC reference was weak (r = 0.21), but improved with both contrast enhancement (r = 0.71) and with MOTS (r = 0.67). Conclusions Although non-contrast MOTS 4D-flow improves valve function visualization and diagnostic accuracy, a significant proportion of valves cannot be accurately assessed. However, aortic flow measurements using non-contrast MOTS is feasible and reaches similar accuracy to that of contrast-enhanced 4D-flow.

Purpose To evaluate the impact of a novel postprocessing denoising technique on accuracy and precision in myocardial T1 mapping. Materials and Methods This study introduces a fast and robust denoising method developed for magnetic resonance T1 mapping. The technique imposes edge-preserving regularity and exploits the co-occurence of spatial gradients in the acquired T1-weighted images. The proposed approach was assessed in simulations, ex vivo data and in vivo imaging on a cohort of 16 healthy volunteers (12 males, average age 39 ± 8 years, 62 ± 9 bpm) both in pre- and postcontrast injection. The method was evaluated in myocardial T1 mapping at 3T with a saturation-recovery technique that is accurate but sensitive to noise. ROIs in the myocardium and left-ventricle blood pool were analyzed by an experienced reader. Mean T1 values and standard deviation were extracted and compared in all studies. Results Simulations on synthetic phantom showed signal-to-noise ratio and sharpness improvement with the proposed method in comparison with conventional denoising. In vivo results demonstrated that our method preserves accuracy, as no difference in mean T1 values was observed in the myocardium (precontrast: 1433/1426 msec, 95%CI: [−40.7, 55.9], p = 0.75, postcontrast: 766/759 msec, 95%CI: [−60.7, 77.2], p = 0.8). Meanwhile, precision was improved with standard deviations of T1 values being significantly decreased (precontrast: 223/151 msec, 95%CI: [27.3, 116.5], p = 0.003, postcontrast: 176/135 msec, 95%CI: [5.5, 77.1], p = 0.03). Conclusion The proposed denoising method preserves accuracy and improves precision in myocardial T1 mapping, with the potential to offer better map visualization and analysis. Level of Evidence: 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1377–1388.

4D-flow is a cardiac magnetic resonance technique which allows quantification of blood flow in 3-dimensional space; however, adequate image quality requires the use of contrast agents. We developed a new 4D-flow approach (multiple overlapping thin slabs (MOTS)) capable of generating sufficient

Background Inner volume (IV) excitation was explored with respect to scan time reduction of cardiac gated double inversion recovery multi-echo fast spin echo (MEFSE) to measure the transverse relaxation time (T2) in the myocardium. Methods The IV imaging was achieved by applying orthogonal slice selection for the excitation and refocusing pulses. The T2 map accuracy was investigated using different excitation and refocusing pulses. The performance of IV-MEFSE was compared with MEFSE on phantoms and eight healthy volunteers, acquiring eight echo times in a single breath-hold. Results Compared with MEFSE, IV-MEFSE allowed a scan time reduction from 26 s to 16 s, but caused a T2 overestimation of approximately 10% due to stimulated echoes. Conclusion IV successfully reduced the scan time to a single breath-hold feasible for many patients and remarkably facilitated the scan prescription, because there was no image aliasing concern. Care should be taken in using IV for T2 mapping because of T2 relaxation time overestimation. J. Magn. Reson. Imaging 2015;42:175–179. © 2014 Wiley Periodicals, Inc.

Purpose To characterize and optimize the navigator-flip angle (FA), and the influence of imaging-FA on optimizing liver/lung contrast of the navigator profile, while avoiding visible navigator saturation artifacts, for hepatobiliary phase gadoxetic acid-enhanced MRI. Materials and Methods Ten volunteers; six men, four women; ages 37.1 ± 11.0 years underwent navigator-gated three-dimensional (3D) -spoiled-gradient-echo sequences in randomized combinations of imaging-FA (10°/30°) and navigator-FA (10-90°) before contrast and 20 min after injection of gadoxetic acid at 3 Tesla. The signal intensities of the liver and lung were measured from navigator profiles. Furthermore, the intensity of saturation artifacts for each navigator FA was quantified using measurements of relative contrast at the artifact location. Results For the postcontrast images, the optimal navigator FA was 90°. However, saturation artifacts were highly dependent on the imaging-FA and the presence of gadolinium contrast. A smaller imaging-FA of 10° led to greater saturation artifacts for both pre- and postcontrast, and saturation artifacts worsen with increasing navigator-FA. Using a higher imaging-FA of 30°, saturation artifacts are ignorable over the entire range of navigator-FA. Conclusion For navigator-gated gadoxetic acid-enhanced hepatobiliary imaging, navigator-FA of 90° and imaging-FA of 30° provide an optimal balance with maximum navigator liver/lung contrast while avoiding visible imaging saturation artifacts.J. Magn. Reson. Imaging 2014;40:1129–1136. © 2013 Wiley Periodicals, Inc.

Imaging using high channel-count coil arrays can benefit a broad range of clinical applications through improved signal-to-noise ratio (SNR), higher parallel imaging acceleration factors and increased anatomical coverage (1–3). However, maintaining clinically acceptable reconstruction times can be challenging when using high channel-count coil arrays. A variety of approaches have been explored to improve the efficiency of reconstruction algorithms for high channel-count imaging (4–14). Many of these techniques, including this work, have focused on combining or reducing the effective number of channels earlier in the reconstruction pipeline. In this way, the computational burden on subsequent steps in the reconstruction process is lessened. Channel combination methods can be categorized based on the domain in which channel combination is performed: image-space, time-domain or k-space. Image-space channel combination methods are widely used due to their ability to optimize final image SNR and their ease of use (15). However, image-space solutions can be computationally and memory intensive for high channel-count coil arrays, since channel combination must take place relatively late in the reconstruction pipeline. At the other end of the spectrum, time-domain channel combination (4) has received significant attention. Time-domain channel combination performs channel combination independently at each acquisition time point—at the beginning of the reconstruction pipeline. Time-domain channel combination is very effective in reducing the computation and memory requirements for the image reconstruction pipeline. The weaknesses of time-domain channel combination are (1) SNR can be degraded, sometimes significantly (16) and (2) phase cancellation artifacts are often unavoidable for some coil geometries (5). As a result, time-domain channel combination is not widely used to combine all receiver channels into a single channel data stream. Instead, the approach is typically used to reduce the channel-count significantly but without appreciably degrading image quality (6–12). Methods that take this approach are often referred to as either “array compression” or “coil selection” depending on whether or not they combine channel data streams during the channel reduction. Because these approaches do not output a single channel data set, they must be paired with another channel combination method later in the reconstruction pipeline. In this way, these approaches are complementary to other channel combination strategies, including image-space and k-space approaches (13,14). In comparison to image-space channel combination and time-domain channel combination, k-space channel combination has received relatively less attention. k-Space channel combination can be performed by convolving the k-space data for each channel with its own k-space convolution kernel and summing across channels to create a single or reduced number of k-space data sets. Unlike time-domain channel combination, it is challenging to implement k-space channel combination in hardware as the convolution coefficients are dependent on the k-space sampling strategy. Unlike image-space channel combination, k-space channel combination is unable to optimize SNR independently at every pixel location. However, k-space channel combination does have important advantages: it has more degrees of freedom compared to time-domain channel combination that allow it to achieve better SNR and it can be performed earlier in the reconstruction pipeline compared to image-space channel combination, potentially improving reconstruction efficiency. Early work in k-space channel combination was carried out as part of parallel imaging reconstruction methods. Methods such as SMASH, AUTO-SMASH and VD-AUTO-SMASH combine the parallel imaging unaliasing operation and the channel combination operation into a single step, both in the generation and application of reconstruction coefficients (17–19). Two challenges for these methods are that the SNR of the final combined images can be sub-optimal and they are prone to phase cancellation artifacts (20). Both of these issues can be attributed to sub-optimal channel combination. The GRAPPA method improved on prior k-space parallel imaging methods by separating the unaliasing operation from the channel combination operation and performing channel combination in image-space (20). While this approach has been very successful, it does lead to an increased computational burden, since the unaliasing operation in GRAPPA scales as the square of the number of channels. There is also a large memory requirement as separate data sets for each channel are formed in image-space. As the number of channels grows, a “channel-by-channel” approach becomes increasingly difficult to perform in clinically acceptable reconstruction times. The problem is exacerbated by the clinical motivations for moving to higher channel-counts: acquiring larger image matrices, and the use of more temporal phases for dynamic contrast enhanced imaging. For example, moving from a single phase eight-channel 256 × 256 × 64 acquisition to a 20 phase 32-channel 320 × 320 × 128 acquisition results in a 1000-fold increase in computation for the unaliasing operation of channel-by-channel parallel imaging with image-space channel combination. This increased computational load can be dealt with using both improvements in computing hardware and algorithmic improvements. Using more powerful reconstruction hardware without algorithmic changes has the advantage that this approach poses no risk to altering the image quality. In contrast, algorithmic changes can modify and potentially degrade image quality. However, hardware solutions can be more costly to roll out to a large installed base compared to software solutions. With such large potential increases in computation, it is likely that improvements in both computing hardware and algorithms will be needed. Because of this, it is important that improved algorithms work well with powerful hardware, which for the foreseeable future means that the algorithms must be amenable to parallel computing architectures. This work is motivated by a desire to reduce the computational demands for high channel-count image reconstruction while retaining image quality and supporting sampling schemes acquiring irregularly spaced k-space points on a Cartesian grid. Irregularly spaced sampling schemes used in the experiments in this work consist of the inclusion of internal calibration lines in the reconstruction and the use of variable sample spacing (e.g., acquire two, skip one or skip one, acquire one, skip two to create sampling reductions, R, of 1.5 and 2.5 respectively). The purpose of this work is to describe and evaluate a new method for designing local k-space channel combination kernels and integrating them with parallel imaging. We refer to the approach as the direct virtual coil (DVC) method (21). This work focuses on describing the technical methodology for DVC and relies on separate works to discuss specific clinical applications (22).

Purpose To develop and demonstrate the feasibility of a new technique for respiratory-gated, fat-suppressed, three-dimensional spoiled gradient-recalled echo (3D-SPGR) with navigator gating for more accurate and robust motion detection. Methods A navigator-gated 3D-SPGR technique was modified to include a wait period immediately prior to the navigator sequence for magnetization recovery. Furthermore, a variable flip angle scheme was realized by a combination of ramp-up, ramp-down, and attenuation strategies for optimizing point spread functions. Phantom and human experiments were conducted with our technique on 1.5T scanners. Results Using the method, T1-weighted 3D images with improved signal homogeneity were acquired with a maximum flip angle of 30° in phantom and human tests. Also, compared with the conventional navigator-gated 3D-SPGR, accurate respiratory motion detection of free-breathing subjects was provided, leading to reduced motion artifacts. Conclusion The combination of wait insertion and the variable flip angle method improved both motion detection accuracy and image homogeneity in a navigator-gated 3D-SPGR study. Magn Reson Med 72:172–177, 2014. © 2013 Wiley Periodicals, Inc.

To develop an efficient motion-compensated reconstruction technique for free-breathing cardiac magnetic resonance imaging (MRI) that allows high-quality images to be reconstructed from multiple undersampled single-shot acquisitions. The proposed method is a joint image reconstruction and motion correction method consisting of several steps, including a non-rigid motion extraction and a motion-compensated reconstruction. The reconstruction includes a denoising with the Beltrami regularization, which offers an ideal compromise between feature preservation and staircasing reduction. Results were assessed in simulation, phantom and volunteer experiments. The proposed joint image reconstruction and motion correction method exhibits visible quality improvement over previous methods while reconstructing sharper edges. Moreover, when the acceleration factor increases, standard methods show blurry results while the proposed method preserves image quality. The method was applied to free-breathing single-shot cardiac MRI, successfully achieving high image quality and higher spatial resolution than conventional segmented methods, with the potential to offer high-quality delayed enhancement scans in challenging patients., Comment: 12 pages, 6 figures, accepted at MICCAI 2016

To evaluate the impact of a novel postprocessing denoising technique on accuracy and precision in myocardial TThis study introduces a fast and robust denoising method developed for magnetic resonance TSimulations on synthetic phantom showed signal-to-noise ratio and sharpness improvement with the proposed method in comparison with conventional denoising. In vivo results demonstrated that our method preserves accuracy, as no difference in mean TThe proposed denoising method preserves accuracy and improves precision in myocardial T3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1377-1388.

Purpose: To determine optimal delay times and flip angles for T1-weighted hepatobiliary imaging at 1.5 Tesla (T) with gadoxetic acid and to demonstrate the feasibility of using a high-resolution navigated optimized T1-weighted pulse sequence to evaluate biliary disease. Materials and Methods: Eight healthy volunteers were scanned at 1.5T using a T1-weighted three-dimensional (3D)-SPGR pulse sequence following the administration of 0.05 mmol/kg of gadoxetic acid. Navigator-gating enabled acquisition of high spatial resolution (1.2 × 1.4 × 1.8 mm3, interpolated to 0.7 × 0.7 × 0.9 mm3) images in approximately 5 min of free-breathing. Multiple breath-held acquisitions were performed at flip angles between 15° and 45° to optimize T1 weighting. To evaluate the performance of this optimized sequence in the setting of biliary disease, the image quality and biliary excretion of 51 consecutive clinical scans performed to assess primary sclerosing cholangitis (PSC) were evaluated. Results: Optimal hepatobiliary imaging occurs at 15–25 min, using a 40° flip angle. The image quality and visualization of biliary excretion in the PSC scans were excellent, despite the decreased liver function in some patients. Visualization of reduced excretion often provided diagnostic information that was unavailable by conventional magnetic resonance cholangiopancreatography (MRCP). Conclusion: High-resolution navigated 3D-SPGR hepatobiliary imaging using gadoxetic acid and optimized scan parameters is technically feasible and can be clinically useful, even in patients with decreased hepatobiliary function. J. Magn. Reson. Imaging 2012;36:890–899. © 2012 Wiley Periodicals, Inc.

Pediatric body MRI exams often cover multiple body parts, making the development of broadly applicable protocols and obtaining uniform fat suppression a challenge. Volumetric T2 imaging with Dixon-type fat-water separation might address this challenge, but it is a lengthy process. We develop and evaluate a faster two-echo approach to volumetric T2 imaging with fat-water separation. A volumetric spin-echo sequence was modified to include a second shifted echo so two image sets are acquired. A region-growing reconstruction approach was developed to decompose separate water and fat images. Twenty-six children were recruited with IRB approval and informed consent. Fat-suppression quality was graded by two pediatric radiologists and compared against conventional fat-suppressed fast spin-echo T2-W images. Additionally, the value of in- and opposed-phase images was evaluated. Fat suppression on volumetric images had high quality in 96% of cases (95% confidence interval of 80–100%) and were preferred over or considered equivalent to conventional two-dimensional fat-suppressed FSE T2 imaging in 96% of cases (95% confidence interval of 78–100%). In- and opposed-phase images had definite value in 12% of cases. Volumetric fat-water separated T2-weighted MRI is feasible and is likely to yield improved fat suppression over conventional fat-suppressed T2-weighted imaging.

OBJECTIVE. The purpose of our study was to evaluate image quality in a 3D spoiled gradient-recalled echo (SPGR) sequence that was modified to incorporate respiratory navigation to limit the deleterious effects of respiratory motion and to compare it with conventional scanning during breath-holding and free breathing.CONCLUSION. Respiratory navigation of 3D SPGR sequences is technically feasible, and image quality is modestly improved over free breathing acquisitions using conventional 3D SPGR sequences. This may represent a promising imaging alternative for patients who cannot hold their breath.

Purpose: To assess the feasibility and the quality of abdominal three-dimensional (3D) contrast enhanced MR angiograms acquired at 3.0 Tesla (T) using a new 2D-accelerated autocalibrating parallel reconstruction method for Cartesian sampling (2D-ARC). Materials and Methods: With institutional review board approval and written informed consent, a prospective trial in 6 normal healthy volunteers and 23 patients referred for evaluation of suspected renovascular disease was performed. The volunteers underwent abdominal MRA with and without 2D-ARC acceleration. Images were evaluated independently by two blinded vascular radiologists in randomized order. Vessel conspicuity was rated on a five-point scale. Evaluation for significant differences between the scores for each technique was performed using a Wilcoxon signed-rank test. Results: In the series of six volunteers, no statistical significance was found between the image quality scores for 2D-ARC accelerated and nonaccelerated exams. A high proportion of the 23 clinical 2D-ARC exams were graded as diagnostic (vessel conspicuity score ≥2; Reader 1, 96%; Reader 2, 100%) for overall image quality. Conclusion: Subjective image quality of 2D-ARC accelerated MRA was equivalent to the conventional MRA method. However, the 2D-ARC accelerated sequence provided a 3.5-fold increase in imaging volume, complete abdominal coverage, and a 30% reduction in voxel volume, all within the same acquisition time. J. Magn. Reson. Imaging 2009;30:1093–1100. © 2009 Wiley-Liss, Inc.

To retrospectively evaluate the detection of small (2-cm) urothelial tumors by using gadolinium-enhanced three-dimensional (3D) spoiled gradient-recalled echo (GRE) magnetic resonance (MR) urography.This HIPAA-compliant study received institutional review board approval. All patients included had previously consented to the use of their medical records for research purposes. Eleven of 110 patients (10 men, one woman; mean age, 73.5 years) who underwent MR urography were ultimately identified to have 23 upper-tract urothelial carcinomas smaller than 2 cm or carcinoma in situ. Breath-hold coronal T2-weighted single-shot fast spin-echo and breath-hold coronal 3D T1-weighted spoiled GRE images with fat suppression during nephrographic and excretory phases after intravenous injection of gadolinium-based contrast material were obtained in all patients with a 1.5-T imager. Two radiologists reviewed the MR images in consensus for the presence of tumors. Lesion detectability was compared between each sequence by using the McNemar test.Of 23 tumors, 17 (74%) were detected by using at least one sequence, eight (35%) were detected with T2-weighted imaging, 15 (65%) were detected on nephrographic phase images, and 15 (65%) were detected on excretory phase images. Two lesions each were detected only on either nephrographic or excretory phase images. Detectability was significantly higher on nephrographic and excretory phase images compared with T2-weighted images (P.05).Gadolinium-enhanced 3D spoiled GRE MR urography helped detect 74% of small urothelial carcinomas. Nephrographic and excretory phase images are essential for helping detect small urothelial carcinomas.

Water-fat separation can be challenging in the presence of field inhomogeneities. Three-point (3-pt) water-fat separation methods achieve robust performance by measuring and compensating for field inhomogeneities; however, they triple the scan time. The "1+-pt" water-fat separation method proposed in this article for dynamic or repetitive imaging situations combines 3-pt methods' ability to correct for field inhomogeneities with the scan efficiency of a single acquisition method to achieve high temporal and spatial resolutions and robust water-fat separation. Single-echo data are collected with water and fat at a relative phase shift of an odd multiple of pi/2. To correct for undesired phase modulation, phase maps are estimated from a 3-pt calibration scan acquired prior to dynamic imaging. The phase maps are assumed to be slowly varying in time, so they may be used for correcting the phase of the subsequent single-echo signals at the same imaging location. Noise performance was investigated and shown to be equivalent to a single excitation acquisition. The 1+-pt method can also be used in conjunction with parallel imaging. In this situation, the calibration scans required by both methods can be integrated into a shared calibration scan. Promising results were obtained in breast, abdominal, and cardiac imaging applications.

Patient motion remains a primary obstacle to diagnostic image quality, especially in the abdomen, despite the existence of various motion artifact reduction techniques. This work presents a self-navigated motion detection method that can be generalized for most pulse sequences and k-space trajectories. Motion information is extracted directly from raw MR data, requiring no additional gradient or RF pulses, no physiologic monitoring equipment, and minimal—if any—impact on scan time. Initial feasibility results with a two-dimensional gradient echo sequence are shown in phantom studies and in vivo volunteer abdominal studies, demonstrating the sensitivity of the method to both respiratory motion and cardiovascular pulsatility. Prospectively gated images were acquired using the self-navigated data to synchronize image acquisition with motion. These preliminary results suggest that the self-navigated method is a promising technique for reducing motion artifacts in clinical abdominal and cardiac applications. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc.

Background Myocardial late gadolinium enhancement (LGE) MRI has become a standard clinical exam for characterizing myocardial viability after infarction and for assessing many nonischemic myocardial diseaseses. Typically, a 3D slab covering the myocardium is scanned within a single breath-hold. However, 3D LGE with sufficient resolution and slice coverage requires a long scan time and is challenging in cardiac patients with limited breath-hold capability. Recently, compressed sensing (CS) [1] has demonstrated the ability to further accelerate MRI on top of parallel imaging (PI) and has demonstrated promising results for 3D LGE [2]. This work intended to evaluate the feasibility of a CS-PI method based on ESPIRiT [3-5] and optimize its data acquisition for improving the robustness of 3D LGE with high acceleration.

Three-dimensional (3D) multispectral magnetic resonance imaging (MRI) techniques can significantly reduce image artifacts commonly encountered near embedded metal hardware. These artifact reductions are enabled by applying alternative spectral and spatial encoding schemes to conventional spin-echo imaging techniques. Here, the multi-acquisition with variable resonance image combination (MAVRIC) and slice-encoding for metal artifact correction (SEMAC) multispectral imaging techniques are connected and discussed. The development of a hybrid technique that utilizes the strengths of both methods is then described. This optimized 3D multispectral imaging approach is shown to be capable of producing minimal-artifact, high-resolution images near total joint replacements in a clinical setting.

To characterize and optimize the navigator-flip angle (FA), and the influence of imaging-FA on optimizing liver/lung contrast of the navigator profile, while avoiding visible navigator saturation artifacts, for hepatobiliary phase gadoxetic acid-enhanced MRI.Ten volunteers; six men, four women; ages 37.1 ± 11.0 years underwent navigator-gated three-dimensional (3D) -spoiled-gradient-echo sequences in randomized combinations of imaging-FA (10°/30°) and navigator-FA (10-90°) before contrast and 20 min after injection of gadoxetic acid at 3 Tesla. The signal intensities of the liver and lung were measured from navigator profiles. Furthermore, the intensity of saturation artifacts for each navigator FA was quantified using measurements of relative contrast at the artifact location.For the postcontrast images, the optimal navigator FA was 90°. However, saturation artifacts were highly dependent on the imaging-FA and the presence of gadolinium contrast. A smaller imaging-FA of 10° led to greater saturation artifacts for both pre- and postcontrast, and saturation artifacts worsen with increasing navigator-FA. Using a higher imaging-FA of 30°, saturation artifacts are ignorable over the entire range of navigator-FA.For navigator-gated gadoxetic acid-enhanced hepatobiliary imaging, navigator-FA of 90° and imaging-FA of 30° provide an optimal balance with maximum navigator liver/lung contrast while avoiding visible imaging saturation artifacts.J. Magn. Reson. Imaging 2014;40:1129-1136. © 2013 Wiley Periodicals, Inc.

To develop and demonstrate the feasibility of a new technique for respiratory-gated, fat-suppressed, three-dimensional spoiled gradient-recalled echo (3D-SPGR) with navigator gating for more accurate and robust motion detection.A navigator-gated 3D-SPGR technique was modified to include a wait period immediately prior to the navigator sequence for magnetization recovery. Furthermore, a variable flip angle scheme was realized by a combination of ramp-up, ramp-down, and attenuation strategies for optimizing point spread functions. Phantom and human experiments were conducted with our technique on 1.5T scanners.Using the method, T1-weighted 3D images with improved signal homogeneity were acquired with a maximum flip angle of 30° in phantom and human tests. Also, compared with the conventional navigator-gated 3D-SPGR, accurate respiratory motion detection of free-breathing subjects was provided, leading to reduced motion artifacts.The combination of wait insertion and the variable flip angle method improved both motion detection accuracy and image homogeneity in a navigator-gated 3D-SPGR study.

In this work, a new method is described for producing local k-space channel combination kernels using a small amount of low-resolution multichannel calibration data. Additionally, this work describes how these channel combination kernels can be combined with local k-space unaliasing kernels produced by the calibration phase of parallel imaging methods such as GRAPPA, PARS and ARC.Experiments were conducted to evaluate both the image quality and computational efficiency of the proposed method compared to a channel-by-channel parallel imaging approach with image-space sum-of-squares channel combination.Results indicate comparable image quality overall, with some very minor differences seen in reduced field-of-view imaging. It was demonstrated that this method enables a speed up in computation time on the order of 3-16X for 32-channel data sets.The proposed method enables high quality channel combination to occur earlier in the reconstruction pipeline, reducing computational and memory requirements for image reconstruction.

Purpose: To evaluate two magnetic resonance imaging (MRI) techniques, slice encoding for metal artifact correction (SEMAC) and multiacquisition variable-resonance image combination (MAVRIC), for their ability to correct for artifacts in postoperative knees with metal. Materials and Methods: A total of 25 knees were imaged in this study. Fourteen total knee replacements (TKRs) in volunteers were scanned with SEMAC, MAVRIC, and 2D fast spin-echo (FSE) to measure artifact extent and implant rotation. The ability of the sequences to measure implant rotation and dimensions was compared in a TKR knee model. Eleven patients with a variety of metallic hardware were imaged with SEMAC and FSE to compare artifact extent and subsequent patient management was recorded. Results: SEMAC and MAVRIC significantly reduced artifact extent compared to FSE (P < 0.0001) and were similar to each other (P = 0.58), allowing accurate measurement of implant dimensions and rotation. The TKRs were properly aligned in the volunteers. Clinical imaging with SEMAC in symptomatic knees significantly reduced artifact (P < 0.05) and showed findings that were on the majority confirmed by subsequent noninvasive or invasive patient studies. Conclusion: SEMAC and MAVRIC correct for metal artifact, noninvasively providing high-resolution images with superb bone and soft tissue contrast. J. Magn. Reson. Imaging 2011;33:1121–1127. © 2011 Wiley-Liss, Inc.

Purpose: To demonstrate accelerated imaging with both artifact reduction and different contrast mechanisms near metallic implants. Materials and Methods: Slice-encoding for metal artifact correction (SEMAC) is a modified spin echo sequence that uses view-angle tilting and slice-direction phase encoding to correct both in-plane and through-plane artifacts. Standard spin echo trains and short-TI inversion recovery (STIR) allow efficient PD-weighted imaging with optional fat suppression. A completely linear reconstruction allows incorporation of parallel imaging and partial Fourier imaging. The signal-to-noise ratio (SNR) effects of all reconstructions were quantified in one subject. Ten subjects with different metallic implants were scanned using SEMAC protocols, all with scan times below 11 minutes, as well as with standard spin echo methods. Results: The SNR using standard acceleration techniques is unaffected by the linear SEMAC reconstruction. In all cases with implants, accelerated SEMAC significantly reduced artifacts compared with standard imaging techniques, with no additional artifacts from acceleration techniques. The use of different contrast mechanisms allowed differentiation of fluid from other structures in several subjects. Conclusion: SEMAC imaging can be combined with standard echo-train imaging, parallel imaging, partial-Fourier imaging, and inversion recovery techniques to offer flexible image contrast with a dramatic reduction of metal-induced artifacts in scan times under 11 minutes. J. Magn. Reson. Imaging 2010;31:987–996. ©2010 Wiley-Liss, Inc.

T1-weighted imaging in the pediatric abdomen suffers from respiratory motion artifacts. Though navigation has been employed commonly for coronary MRA and T2 imaging, navigation for T1-weighted imaging is less developed. Thus, a navigator pulse was incorporated into a fat-suppressed T1-weighted SPGR sequence such that steady-state contrast was not disrupted. 10 pediatric patients were recruited and scanned after gadolinium administration three times in immediate succession: breath-hold with no navigation, free-breathing with navigation, and free-breathing without navigation. Motion artifacts were scored for each sequence by two radiologists, showing less motion artifacts with navigation compared to free-breathing and greater motion artifacts than with breath-holding. This work demonstrates the feasibility and potential utility of navigation for pediatric abdominal T1-weighted imaging.

The purpose of this prospective study was to compare a new isotropic three-dimensional (3D) fast spin-echo (FSE) pulse sequence with parallel imaging and extended echo train acquisition (3D-FSE-Cube) with a conventional two-dimensional (2D) FSE sequence for magnetic resonance (MR) imaging of the ankle. After institutional review board approval and informed consent were obtained and in accordance with HIPAA privacy guidelines, MR imaging was performed in the ankles of 10 healthy volunteers (four men, six women; age range, 25–41 years). Imaging with the 3D-FSE-Cube sequence was performed at 3.0 T by using both one-dimensional– and 2D-accelerated autocalibrated parallel imaging to decrease imaging time. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) with 3D-FSE-Cube were compared with those of the standard 2D FSE sequence. Cartilage, muscle, and fluid SNRs were significantly higher with the 3D-FSE-Cube sequence (P < .01 for all). Fluid-cartilage CNR was similar for both techniques. The two sequences were also compared for overall image quality, blurring, and artifacts. No significant difference for overall image quality and artifacts was demonstrated between the 2D FSE and 3D-FSE-Cube sequences, although the section thickness in 3D-FSE-Cube imaging was much thinner (0.6 mm). However, blurring was significantly greater on the 3D-FSE-Cube images (P < .04). The 3D-FSE-Cube sequence with isotropic resolution is a promising new MR imaging sequence for viewing complex joint anatomy.

Recent advances have reduced scan time in three-dimensional fast spin echo (3D-FSE) imaging, including very long echo trains through refocusing flip angle (FA) modulation and 2D-accelerated parallel imaging. This work describes a method to modulate refocusing FAs that produces sharp point spread functions (PSFs) from very long echo trains while exercising direct control over minimum, center-k-space, and maximum FAs in order to accommodate the presence of flow and motion, SNR requirements, and RF power limits. Additionally, a new method for ordering views to map signal modulation from the echo train into k(y)-k(z) space that enables nonrectangular k-space grids and autocalibrating 2D-accelerated parallel imaging is presented. With long echo trains and fewer echoes required to encode large matrices, large volumes with high in- and through-plane resolution matrices may be acquired with scan times of 3-6 min, as demonstrated for volumetric brain, knee, and kidney imaging.

The class of autocalibrating "data-driven" parallel imaging (PI) methods has gained attention in recent years due to its ability to achieve high quality reconstructions even under challenging imaging conditions. The aim of this work was to perform a formal comparative study of various data-driven reconstruction techniques to evaluate their relative merits for certain imaging applications. A total of five different reconstruction methods are presented within a consistent theoretical framework and experimentally compared in terms of the specific measures of reconstruction accuracy and efficiency using one-dimensional (1D)-accelerated Cartesian datasets. It is shown that by treating the reconstruction process as two discrete phases, a calibration phase and a synthesis phase, the reconstruction pathway can be tailored to exploit the computational advantages available in certain data domains. A new "split-domain" reconstruction method is presented that performs the calibration phase in k-space (k(x), k(y)) and the synthesis phase in a hybrid (x, k(y)) space, enabling highly accurate 2D neighborhood reconstructions to be performed more efficiently than previously possible with conventional techniques. This analysis may help guide the selection of PI methods for a given imaging task to achieve high reconstruction accuracy at minimal computational expense.

Purpose To describe and demonstrate the feasibility of a novel multiecho reconstruction technique that achieves simultaneous water-fat decomposition and T2* estimation. The method removes interference of water-fat separation with iron-induced T2* effects and therefore has potential for the simultaneous characterization of hepatic steatosis (fatty infiltration) and iron overload. Materials and Methods The algorithm called “T2*-IDEAL” is based on the IDEAL water-fat decomposition method. A novel “complex field map” construct is used to estimate both R2* (1/T2*) and local B0 field inhomogeneities using an iterative least-squares estimation method. Water and fat are then decomposed from source images that are corrected for both T2* and B0 field inhomogeneity. Results It was found that a six-echo multiecho acquisition using the shortest possible echo times achieves an excellent balance of short scan and reliable R2* measurement. Phantom experiments demonstrate the feasibility with high accuracy in R2* measurement. Promising preliminary in vivo results are also shown. Conclusion The T2*-IDEAL technique has potential applications in imaging of diffuse liver disease for evaluation of both hepatic steatosis and iron overload in a single breath-hold. J. Magn. Reson. Imaging 2007;26:1153–1161. © 2007 Wiley-Liss, Inc.

The purpose of our study was to prospectively compare a recently developed method of isotropic 3D fast spin-echo (FSE) with extended echo-train acquisition (XETA) with 2D FSE and 2D fast recovery FSE (FRFSE) for MRI of the knee.Institutional review board approval, Health Insurance Portability and Accounting Act (HIPAA) compliance, and informed consent were obtained. We studied 10 healthy volunteers and one volunteer with knee pain using 3D FSE XETA, 2D FSE, and 2D FRFSE. Images were obtained both with and without fat suppression. Cartilage and muscle signal-to-noise ratio (SNR) and cartilage-fluid contrast-to-noise ratio (CNR) were compared using a Student's t test. We also compared reformations of 3D FSE XETA with 2D FSE images directly acquired in the axial plane.Cartilage SNR was higher with 3D FSE XETA (56.8 +/- 9 [SD]) compared with the 2D FSE (45.8 +/- 8, p0.01) and 2D FRFSE (32.5 +/- 5.3, p0.01). Muscle SNR was significantly higher with 3D FSE XETA (52.1 +/- 4.3) than 2D FSE (45.2 +/- 9, p0.01) and 2D FRFSE (23.6 +/- 6.2, p0.01). Fluid SNR was significantly higher for 2D FSE (144.9 +/- 33) than 3D FSE XETA (104.7 +/- 18, p0.01). Compared with 2D FSE and 2D FRFSE, 3D FSE XETA had lower cartilage-fluid CNR due to higher cartilage SNR (p0.01). Three-dimensional FSE XETA acquired volumetric data sets with isotropic resolution. Reformatted images in the axial plane were similar to axial 2D FSE acquisitions but with thinner slices.Three-dimensional FSE XETA acquires high-resolution (approximately 0.7 mm) isotropic data with intermediate and T2-weighting that may be reformatted in arbitrary planes. Three-dimensional FSE XETA is a promising technique for MRI of the knee.

In this work the generalized autocalibrating partially parallel acquisition (GRAPPA) technique was implemented with modified reconstruction and applied to in vivo high-resolution (HR) magnetic resonance imaging (MRI) of the trabecular bone microarchitecture at 3 Tesla (T) with a multiple-acquisition balanced steady-state free precession (b-SSFP) sequence. Trabecular bone is made up of a network of microstructures (80-140 microm), and its structural deterioration is associated with the skeletal metabolic disorder osteoporosis. HR-MRI is a promising noninvasive tool for assessing the trabecular microarchitecture in vivo, but it involves long acquisition times. Using partially parallel imaging (PPI) to accelerate the acquisition may help mitigate this shortcoming and allow more flexibility in protocol design. In this study the effects of GRAPPA-based reconstruction on image characteristics and the measurement of trabecular bone structural parameters were evaluated. Initial studies showed that image quality and depiction of microstructure were preserved in the GRAPPA-based reconstruction, indicating the feasibility of PPI in HR-MRI of trabecular bone. The results also demonstrated the potential of PPI for increasing the signal-to-noise ratio (SNR) efficiency of multiple-acquisition b-SSFP imaging protocols.

Background Single-shot (SSH) pulse sequences in CMR are beneficial for rapid image acquisition that is robust to motion, especially in arrhythmic patients or poor breath-holders. However, this fast scanning technique trades scan time for a lower signal-to-noise ratio compared to conventional multi-shot acquisitions. Here we propose a motion-compensated denoising technique that improves the image quality from multiple free-breathing singleshot acquisitions.

Background Recently, 3D cine has gained attention due to its capability for single breath-hold volumetric measurement [1]. Nonetheless, conventional 2D cine maintains two intrinsic advantages, namely, its superior blood-myocardium contrast owing to blood in-flow effects and reduced SSFP banding artifacts with more localized slice-by-slice shimming. These advantages are more prominent at high field. This work intends to optimize a k-t acceleration method, kat ARC [2], for 2D cine and preliminarily investigate its performance vs. 3D cine at 3T.

Background Late Gadolinium Enhancement (LGE) allows imaging of infarction and cardiomyopathies by measuring the accumulation of contrast agent within the myocardium. The shortened T1 relaxation time compared to healthy myocardium is imaged by an inversion recovery (IR) prepared segmented fast gradient echo sequence in which pathology and fat show as bright signal. The fat signal can lead to misinterpretation and poor visualization of epicardial enhancement. In previous work fat was suppressed by using two appropriately timed fat-selective RF pulses which re-invert and invert fat signal [Foo et al., JMRI, 2007] but this technique was sensitive to off-resonance and heart rate variations. The goal of the present work is to make two improvements to fat-saturated LGE: (1) increase robustness against B0 and B1 variations by using asymmetric adiabatic RF pulses, and (2) increase robustness against heart rate variations through dynamic timing of fat-selective RF pulses.

Background Recently, 3D CINE phase-contrast MRI (4D Flow) has demonstrated potential for quantitative measurement of blood flow of the cardiovascular systems in the entire thoracic trunk [1]. However, the needs of 4D flow for high resolution, large volume coverage & respiratory gating render very long scan time. This work intended to improve the data acquisition efficiency of free-breathing cardiac 4D flow.

Background Residual background phase in cardiac phase-contrast (PC) imaging introduces velocity errors that bias quantitative flow measurements [1]. While the bias can be offset using static phantoms [2], improved workflow is realized if self-calibrated correction is performed by fitting the phase of static tissue from the in vivo images. However, the residual phase can be nonlinear in space and the vessels of interest, e.g. great vessels, are often far from any static tissue in the image. This means that a linear fit [3] can sometimes result in under-fitting, while fitting with higher spatial-orders can result in over-fitting. Methods We propose a nonlinear self-calibrated approach, which assumes a nonlinear shape. This follows observations that the residual phase is similar in shape to that of the concomitant field. Therefore as compared to linear fitting that uses 4 terms (constant + XYZ), the nonlinear-fit has 5 terms that also include the concomitant field. Further steps are taken to improve the fit, which include iterative removal of outliers that frequently occur at tissue boundaries, and weighting velocities from the quiescent cardiac phase more heavily to reduce effects from flow artifacts at systole. To prevent over