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MR imaging has been optimized for the evaluation of a multitude of disease processes affecting the kidneys. A wide variety of noncontrast methods are available for the evaluation of both kidney structure and function, which are especially useful in clinical scenarios that obviate the use of intravenous contrast. Contrast-enhanced methods remain important, especially for tumor evaluation, and are used increasingly for functional analysis of quantitative biometrics, such as glomerular filtration rate and kidney blood flow., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Purpose To assess image quality and speed improvements for single-shot fast spin-echo (SSFSE) with variable refocusing flip angles and full-Fourier acquisition (vrfSSFSE) pelvic imaging via a prospective trial performed in the context of uterine leiomyoma evaluation. Materials and Methods Institutional review board approval and informed consent were obtained. vrfSSFSE and conventional SSFSE sagittal and coronal oblique acquisitions were performed in 54 consecutive female patients referred for 3-T magnetic resonance (MR) evaluation of known or suspected uterine leiomyomas. Two radiologists who were blinded to the image acquisition technique semiquantitatively scored images on a scale from -2 to 2 for noise, image contrast, sharpness, artifacts, and perceived ability to evaluate uterine, ovarian, and musculoskeletal structures. The null hypothesis of no significant difference between pulse sequences was assessed with a Wilcoxon signed rank test by using a Holm-Bonferroni correction for multiple comparisons. Results Because of reductions in specific absorption rate, vrfSSFSE imaging demonstrated significantly increased speed (more than twofold, P < .0001), with mean repetition times compared with conventional SSFSE imaging decreasing from 1358 to 613 msec for sagittal acquisitions and from 1494 to 621 msec for coronal oblique acquisitions. Almost all assessed image quality and perceived diagnostic capability parameters were significantly improved with vrfSSFSE imaging. These improvements included noise, sharpness, and ability to evaluate the junctional zone, myometrium, and musculoskeletal structures for both sagittal acquisitions (mean values of 0.56, 0.63, 0.42, 0.56, and 0.80, respectively; all P values < .0001) and coronal oblique acquisitions (mean values of 0.81, 1.09, 0.65, 0.93, and 1.12, respectively; all P values < .0001). For evaluation of artifacts, there was an insufficient number of cases with differences to allow statistical testing. Conclusion Compared with conventional SSFSE acquisition, vrfSSFSE acquisition increases 3-T imaging speed via reduced specific absorption rate and leads to significant improvements in perceived image quality and perceived diagnostic capability when evaluating pelvic structures. © RSNA, 2016 Online supplemental material is available for this article.

Purpose: To develop and validate clinically a single-shot fast spin echo (SSFSE) sequence utilizing variable flip angle refocusing pulses to shorten acquisition times via reductions in specific absorption rate (SAR) and improve image quality., Materials and Methods: A variable refocusing flip angle SSFSE sequence (vrfSSFSE) was designed and implemented, with simulations and volunteer scans performed to determine suitable flip angle modulation parameters. With Institutional Review Board (IRB) approval/informed consent, patients referred for 3T abdominal magnetic resonance imaging (MRI) were scanned with conventional SSFSE and either half-Fourier (n = 25) or full-Fourier vrfSSFSE (n = 50). Two blinded radiologists semiquantitatively scored images on a scale from -2 to 2 for contrast, noise, sharpness, artifacts, cardiac motion-related signal loss, and the ability to evaluate the pancreas and kidneys., Results: vrfSSFSE demonstrated significantly increased speed (∼2-fold, P < 0.0001). Significant improvements in image quality parameters with full-Fourier vrfSSFSE included increased contrast, sharpness, and visualization of pancreatic and renal structures with higher bandwidth technique (mean scores 0.37, 0.83, 0.62, and 0.31, respectively, P ≤ 0.001), and decreased image noise and improved visualization of renal structures when used with an equal bandwidth technique (mean scores 0.96 and 0.35, respectively, P < 0.001). Increased cardiac motion-related signal loss with full-Fourier vrfSSFSE was seen in the pancreas but not the kidney., Conclusion: vrfSSFSE increases speed at 3T over conventional SSFSE via reduced SAR, and when combined with full-Fourier acquisition can improve image quality, although with some increased sensitivity to cardiac motion-related signal loss., (© 2015 Wiley Periodicals, Inc.)

Background: Single-shot fast spin echo (SSFSE) is particularly appealing in pediatric patients because of its motion robustness. However radiofrequency energy deposition at 3 tesla forces long pauses between slices, leading to longer scans, longer breath-holds and more between-slice motion., Objective: We sought to learn whether modulation of the SSFSE refocusing flip-angle train could reduce radiofrequency energy deposition without degrading image quality, thereby reducing inter-slice pauses and overall scan times., Materials and Methods: We modulated the refocusing flip-angle train for SSFSE to minimize energy deposition while minimizing blurring and motion-related signal loss. In a cohort of 50 consecutive patients (25 boys, mean age 5.5 years, range 1 month to 17 years) referred for abdominal MRI we obtained standard SSFSE and variable refocusing flip-angle (vrfSSFSE) images and recorded sequence scan times. Two readers independently scored the images in blinded, randomized order for noise, tissue contrast, sharpness, artifacts and left lobe hepatic signal uniformity on a four-point scale. The null hypothesis of no difference between SSFSE and vrfSSFSE image-quality was assessed with a Mann-Whitney U test, and the null hypothesis of no scan time difference was assessed with the paired t-test., Results: SSFSE and vrfSSFSE mean acquisition times were 54.3 and 26.2 s, respectively (P-value <0.0001). For each reader, SSFSE and vrfSSFSE noise, tissue contrast, sharpness and artifacts were not significantly different (P-values 0.18-0.86). However, SSFSE had better left lobe hepatic signal uniformity (P < 0.01, both readers)., Conclusion: vrfSSFSE is twice as fast as SSFSE, with equivalent image quality with the exception of left hepatic lobe signal heterogeneity.

Purpose: To optimize the white-matter-nulled (WMn) Magnetization Prepared Rapid Gradient Echo (MP-RAGE) sequence at 7 Tesla (T), with comparisons to 3T., Methods: Optimal parameters for maximizing signal-to-noise ratio (SNR) efficiency were derived. The effect of flip angle and repetition time (TR) on image blurring was modeled using simulations and validated in vivo. A novel two-dimensional (2D) -centric radial fan beam (RFB) k-space segmentation scheme was used to shorten scan times and improve parallel imaging. Healthy subjects as well as patients with multiple sclerosis and tremor were scanned using the optimized protocols., Results: Inversion repetition times (TS) of 4.5 s and 6 s were found to yield the highest SNR efficiency for WMn MP-RAGE at 3T and 7T, respectively. Blurring was more sensitive to flip in WMn than in CSFn MP-RAGE and relatively insensitive to TR for both regimes. The 2D RFB scheme had 19% and 47% higher thalamic SNR and SNR efficiency than the 1D centric scheme for WMn MP-RAGE. Compared with 3T, SNR and SNR efficiency were higher for the 7T WMn regime by 56% and 41%, respectively. MS lesions in the cortex and thalamus as well as thalamic subnuclei in tremor patients were clearly delineated using WMn MP-RAGE., Conclusion: Optimization and new view ordering enabled MP-RAGE imaging with 0.8-1 mm(3) isotropic spatial resolution in scan times of 5 min with whole brain coverage., (© 2014 Wiley Periodicals, Inc.)

Purpose: The aim of this study was to optimize the 3-dimensional (3D) fluid attenuated inversion recovery (FLAIR) pulse sequence for isotropic high-spatial-resolution imaging of white matter (WM) and cortical lesions at 7 T., Materials and Methods: We added a magnetization-prepared (MP) FLAIR module to a Cube 3D fast spin echo sequence and optimized the refocusing flip angle train using extended phase graph simulations, taking into account image contrast, specific absorption rate (SAR), and signal-to-noise ratio (SNR) as well as T1/T2 values of the different species of interest (WM, grey matter, lesions) at 7 T. We also effected improved preparation homogeneity at 7 T by redesigning the refocusing pulse used in the MP segments. Two sets of refocusing flip angle trains-(a) an SNR-optimal and (b) a contrast-optimal set-were derived and used to scan 7 patients with Alzheimer disease/cognitive impairment and 7 patients with multiple sclerosis. Conventional constant refocusing flip MP-FLAIR images were also acquired for comparison. Lesion SNR, contrast, and lesion count were compared between the 2 optimized and the standard FLAIR sequences., Results: Whole brain coverage with 0.8 mm isotropic spatial resolution in ∼5-minute scan times was achieved using the optimized 3D FLAIR sequences at clinically acceptable SAR levels. The SNR efficiency of the SNR-optimal sequence was significantly better than that of conventional constant refocusing flip MP-FLAIR sequence, whereas the scan time was reduced more than 2-fold (∼5 vs >10 minutes). The contrast efficiency of the contrast-optimal sequence was comparable with that of the constant refocusing flip sequence. Lesion load ascertained by lesion counting was not significantly different among the sequences., Conclusion: Magnetization-prepared FLAIR-Cube with refocusing flip angle trains optimized for SNR and contrast can be used to characterize WM and cortical lesions at 7 T with 0.8 mm isotropic resolution in short scan times and without SAR penalty.

Novel MR image acquisition strategies have been investigated to elicit contrast within the thalamus, but direct visualization of individual thalamic nuclei remains a challenge because of their small size and the low intrinsic contrast between adjacent nuclei. We present a step-by-step specific optimization of the 3D MPRAGE pulse sequence at 7T to visualize the intra-thalamic nuclei. We first measured T1 values within different sub-regions of the thalamus at 7T in 5 individuals. We used these to perform simulations and sequential experimental measurements (n=17) to tune the parameters of the MPRAGE sequence. The optimal set of parameters was used to collect high-quality data in 6 additional volunteers. Delineation of thalamic nuclei was performed twice by one rater and MR-defined nuclei were compared to the classic Morel histological atlas. T1 values within the thalamus ranged from 1400ms to 1800ms for adjacent nuclei. Using these values for theoretical evaluations combined with in vivo measurements, we showed that a short inversion time (TI) close to the white matter null regime (TI=670ms) enhanced the contrast between the thalamus and the surrounding tissues, and best revealed intra-thalamic contrast. At this particular nulling regime, lengthening the time between successive inversion pulses (TS=6000ms) increased the thalamic signal and contrast and lengthening the α pulse train time (N*TR) further increased the thalamic signal. Finally, a low flip angle during the gradient echo acquisition (α=4°) was observed to mitigate the blur induced by the evolution of the magnetization along the α pulse train. This optimized set of parameters enabled the 3D delineation of 15 substructures in all 6 individuals; these substructures corresponded well with the known anatomical structures of the thalamus based on the classic Morel atlas. The mean Euclidean distance between the centers of mass of MR- and Morel atlas-defined nuclei was 2.67mm (±1.02mm). The reproducibility of the MR-defined nuclei was excellent with intraclass correlation coefficient measured at 0.997 and a mean Euclidean distance between corresponding centers of mass found at first versus second readings of 0.69mm (±0.38mm). This 7T strategy paves the way to better identification of thalamic nuclei for neurosurgical planning and investigation of regional changes in neurological disorders., (© 2013.)

The Bloch-Siegert (B-S) B1 (+) mapping technique is a fast, phase-based method that is highly SAR limited especially at 7T, necessitating the use of long repetition times. Spiral and echo-planar readouts were incorporated in a gradient-echo based B-S sequence to reduce specific absoprtion rate (SAR) and improve its scan efficiency. A novel, numerically optimized 4 ms B-S off-resonant pulse at + 1960 Hz was used to increase sensitivity and further reduce SAR compared with the conventional 6 ms Fermi B-S pulse. Using echo-planar and spiral readouts, scan time reductions of 8-16 were achieved. By reducing the B-S pulse width by a factor of 1.5, SAR was reduced by a factor of 1.5 and overall sensitivity was increased by a factor of 1.33 due to the nearly halved resonance offset of the new B-S pulse. This was validated on phantoms and volunteers at 7 T., (Copyright © 2013 Wiley Periodicals, Inc.)

Purpose: To develop a breathhold three-dimensional (3D) Dixon technique for fat suppressed imaging of myocardial infarction., Materials and Methods: A pulse sequence was developed that uses a radial fan-beam k-space segmentation scheme for efficient coverage of k-space, enabling 3D scans in a single breathhold. The sequence uses a dual-echo bipolar readout to enable Dixon fat-water separation for improved visualization of epicardial and pericardial delayed enhancement. The 3D Dixon method was compared with a conventional 2D fast gradient recalled echo (FGRE) -based technique in 25 patients., Results: Pericardial visualization scores and confidence were higher while overall image quality and artifacts were slightly worse for 3D Dixon compared with 2D FGRE. Robust fat suppression was achieved in 21 of 25 cases using the 3D Dixon method., Conclusion: A 3D breathhold method for fat-water separated imaging of myocardial delayed enhancement was developed and validated., (Copyright © 2013 Wiley Periodicals, Inc.)

A novel 3D breath-held Dixon fat-water separated balanced steady state free precession (b-SSFP) sequence for MR cholangiopancreatography (MRCP) is described and its potential clinical utility assessed in a series of patients. The main motivation is to develop a robust breath-held alternative to the respiratory gated 3D Fast Spin Echo (FSE) sequence, the current clinical sequence of choice for MRCP. Respiratory gated acquisitions are susceptible to motion artifacts and blurring in patients with significant diaphragmatic drift, erratic respiratory rhythms or sleep apnea. A two point Dixon fat-water separation scheme was developed which eliminates signal loss arising from B0 inhomogeneity effects and minimizes artifacts from perturbation of the b-SSFP steady state. Preliminary results from qualitative analysis of 49 patients demonstrate robust performance of the 3D Dixon b-SSFP sequence with diagnostic image quality acquired in a 20-24s breath-hold., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Purpose: To present a new method that can simultaneously and efficiently measure T1 and B1 (+) maps using reference region variable flip angle (RR-VFA) imaging., Methods: Assuming T1 relaxation time in a reference region such as fat is well characterized, and the reference region sufficiently covers smoothly varying B1 (+) field inhomogeneity, B1 (+) maps can be measured from VFA images, conventionally used for T1 measurements. Fat-only images from two-point Dixon acquisitions were used to compute B1 (+) maps, and the B1 (+) maps were compared with ones using the double-angle method (DAM) in 22 breast MRI patients at 3T. Additionally, high spatial resolution VFA images were acquired to show T1 measurements with and without the RR-VFA B1 (+) correction in six patients., Results: RR-VFA is able to generate reliable B1 (+) maps, similar to those using the conventional DAM. This simultaneous T1 and B1 (+) mapping can also be used to reduce T1 estimation errors, where T1 maps have more uniform fibroglandular tissue T1 and better depiction of heterogeneous T1 of breast masses., Conclusion: A new method that can measure both T1 and B1 (+) maps based on Dixon VFA images is described, offering improved T1 quantification with no scan time penalty., (Copyright © 2013 Wiley Periodicals, Inc.)

Objective: The purpose of this study was to measure and compare the relaxation times of musculoskeletal tissues at 3.0 T and 7.0 T, and to use these measurements to select appropriate parameters for musculoskeletal protocols at 7.0 T., Materials and Methods: We measured the T₁ and T₂ relaxation times of cartilage, muscle, synovial fluid, bone marrow and subcutaneous fat at both 3.0 T and 7.0 T in the knees of five healthy volunteers. The T₁ relaxation times were measured using a spin-echo inversion recovery sequence with six inversion times. The T₂ relaxation times were measured using a spin-echo sequence with seven echo times. The accuracy of both the T₁ and T₂ measurement techniques was verified in phantoms at both magnetic field strengths. We used the measured relaxation times to help design 7.0 T musculoskeletal protocols that preserve the favorable contrast characteristics of our 3.0 T protocols, while achieving significantly higher resolution at higher SNR efficiency., Results: The T₁ relaxation times in all tissues at 7.0 T were consistently higher than those measured at 3.0 T, while the T₂ relaxation times at 7.0 T were consistently lower than those measured at 3.0 T. The measured relaxation times were used to help develop high resolution 7.0 T protocols that had similar fluid-to-cartilage contrast to that of the standard clinical 3.0 T protocols for the following sequences: proton-density-weighted fast spin-echo (FSE), T₂-weighted FSE, and 3D-FSE-Cube., Conclusion: The T₁ and T₂ changes were within the expected ranges. Parameters for musculoskeletal protocols at 7.0 T can be optimized based on these values, yielding improved resolution in musculoskeletal imaging with similar contrast to that of standard 3.0 T clinical protocols., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Purpose: To develop and evaluate a multiphasic contrast-enhanced MRI method called DIfferential Sub-sampling with Cartesian Ordering (DISCO) for abdominal imaging., Materials and Methods: A three-dimensional, variable density pseudo-random k-space segmentation scheme was developed and combined with a Dixon-based fat-water separation algorithm to generate high temporal resolution images with robust fat suppression and without compromise in spatial resolution or coverage. With institutional review board approval and informed consent, 11 consecutive patients referred for abdominal MRI at 3 Tesla (T) were imaged with both DISCO and a routine clinical three-dimensional SPGR-Dixon (LAVA FLEX) sequence. All images were graded by two radiologists using quality of fat suppression, severity of artifacts, and overall image quality as scoring criteria. For assessment of arterial phase capture efficiency, the number of temporal phases with angiographic phase and hepatic arterial phase was recorded., Results: There were no significant differences in quality of fat suppression, artifact severity or overall image quality between DISCO and LAVA FLEX images (P > 0.05, Wilcoxon signed rank test). The angiographic and arterial phases were captured in all 11 patients scanned using the DISCO acquisition (mean number of phases were two and three, respectively)., Conclusion: DISCO effectively captures the fast dynamics of abdominal pathology such as hyperenhancing hepatic lesions with a high spatio-temporal resolution. Typically, 1.1 × 1.5 × 3 mm spatial resolution over 60 slices was achieved with a temporal resolution of 4-5 s., (Copyright © 2012 Wiley Periodicals, Inc.)

Purpose: To evaluate the capability of a new breathhold non-contrast-enhanced MRA method (Non-contrast Outer Radial Inner Square k-space Scheme, NORISKS) to visualize renal arteries by comparing the method with a routine clinical but significantly longer non-contrast-enhanced (non-CE) MRA technique., Materials and Methods: Eighteen subjects referred for abdominal MRI were examined with NORISKS and a routine non-contrast-enhanced MRA technique. Two versions of NORISKS were evaluated: with and without ECG gating. The images were then scored independently and in blinded manner by two radiologists on 5-point scales for visualization of the proximal and distal renal arteries and quality of fat suppression., Results: No statistically significant difference was detected between NORISKS and routine clinical non-CE MRA in all categories except for visualization of the distal renal arteries where ungated NORISKS performed poorer than the routine non-CE MRA (P < 10(-4) )., Conclusion: We have demonstrated a promising non-CE MRA method for acquiring renal angiograms within a breathhold without any compromise in spatial resolution or coverage. ECG-gated NORISKS is able to acquire renal angiograms that are comparable to a routine clinical non-CE MRA method (Inhance IFIR, GE Healthcare), which requires approximately seven times the scan time of NORISKS., (Copyright © 2011 Wiley Periodicals, Inc.)

A three-dimensional balanced steady-state free precession (b-SSFP)-Dixon technique with a novel group-encoded k-space segmentation scheme called GUINNESS (Group-encoded Ungated Inversion Nulling for Non-contrast Enhancement in the Steady State) was developed. GUINNESS was evaluated for breath-held non-contrast-enhanced MR angiography of the renal arteries on 18 subjects (6 healthy volunteers, 12 patients) at 3.0 T. The method provided high signal-to-noise and contrast renal angiograms with homogeneous fat and background suppression in short breath-holds on the order of 20 s with high spatial resolution and coverage. GUINNESS has potential as a short breath-hold alternative to conventional respiratory-gated methods, which are often suboptimal in pediatric subjects and patients with significant diaphragmatic drift/sleep apnea., (Copyright © 2012 Elsevier Inc. All rights reserved.)

In rapid parallel magnetic resonance imaging, the problem of image reconstruction is challenging. Here, a novel image reconstruction technique for data acquired along any general trajectory in neural network framework, called "Composite Reconstruction And Unaliasing using Neural Networks" (CRAUNN), is proposed. CRAUNN is based on the observation that the nature of aliasing remains unchanged whether the undersampled acquisition contains only low frequencies or includes high frequencies too. Here, the transformation needed to reconstruct the alias-free image from the aliased coil images is learnt, using acquisitions consisting of densely sampled low frequencies. Neural networks are made use of as machine learning tools to learn the transformation, in order to obtain the desired alias-free image for actual acquisitions containing sparsely sampled low as well as high frequencies. CRAUNN operates in the image domain and does not require explicit coil sensitivity estimation. It is also independent of the sampling trajectory used, and could be applied to arbitrary trajectories as well. As a pilot trial, the technique is first applied to Cartesian trajectory-sampled data. Experiments performed using radial and spiral trajectories on real and synthetic data, illustrate the performance of the method. The reconstruction errors depend on the acceleration factor as well as the sampling trajectory. It is found that higher acceleration factors can be obtained when radial trajectories are used. Comparisons against existing techniques are presented. CRAUNN has been found to perform on par with the state-of-the-art techniques. Acceleration factors of up to 4, 6 and 4 are achieved in Cartesian, radial and spiral cases, respectively., (Copyright © 2010 Elsevier Inc. All rights reserved.)

A popular dynamic imaging technique, k-t BLAST (ktB) is studied here for fMR imaging. ktB utilizes correlations in k-space and time, to reconstruct the image time series with only a fraction of the data. The algorithm works by unwrapping the aliased Fourier conjugate space of k-t (y-f-space). The unwrapping process utilizes the estimate of the true y-f-space, by acquiring densely sampled low k-space data. The drawbacks of this method include separate training scan, blurred training estimates and aliased phase maps. The proposed changes are incorporation of phase information from the training map and using generalized-series-extrapolated training map. The proposed technique is compared with ktB on real fMRI data. The proposed changes allow for ktB to operate at an acceleration factor of 6. Performance is evaluated by comparing activation maps obtained using reconstructed images. An improvement of up to 10 dB is observed in the PSNR of activation maps. Besides, a 10% reduction in RMSE is obtained over the entire time series of fMRI images. Peak improvement of the proposed method over ktB is 35%, averaged over five data sets., ((c) 2010 Elsevier Inc. All rights reserved.)

Purpose: To evaluate a new dynamic contrast-enhanced (DCE) imaging technique called multiecho time-resolved acquisition (META) for abdominal/pelvic imaging. META combines an elliptical centric time-resolved three-dimensional (3D) spoiled gradient-recalled echo (SPGR) imaging scheme with a Dixon-based fat-water separation algorithm to generate high spatiotemporal resolution volumes., Materials and Methods: Twenty-three patients referred for hepatic metastases or renal masses were imaged using the new META sequence and a conventional fat-suppressed 3D SPGR sequence on a 3T scanner. In 12 patients, equilibrium-phase 3D SPGR images acquired immediately after META were used for comparing the degree and homogeneity of fat suppression, artifacts, and overall image quality. In the remaining 11 of 23 patients, DCE 3D SPGR images acquired in a previous or subsequent examination were used for comparing the efficiency of arterial phase capture in addition to the qualitative analysis for the degree and homogeneity of fat suppression, artifacts, and overall image quality., Results: META images were determined to be significantly better than conventional 3D SPGR images for degree and uniformity of fat suppression and ability to visualize the arterial phase. There were no significant differences in artifact levels or overall image quality., Conclusion: META is a promising high spatiotemporal resolution imaging sequence for capturing the fast dynamics of hyperenhancing hepatic lesions and provides robust fat suppression even at 3T.

This work describes a technique that combines multishot echo-planar imaging (EPI) with steady-state free precession (SSFP, also known as TrueFISP, FIESTA, and balanced FFE) for multislice, cine MR imaging of the heart. Unlike recently reported methods, the technique presented here (FIESTA-ET) is high-resolution and does not require offline reconstruction or postprocessing. It is therefore suitable for use on standard clinical scanners. FIESTA-ET was compared with conventional FIESTA imaging in 10 volunteers and quantitative analyses of myocardial signal-to-noise ratios (SNR) and ventricular volumes were performed. While providing comparable image quality, FIESTA-ET required half the acquisition time per slice of conventional FIESTA. Because multiple slices could be imaged in a single breathhold, the entire heart could be scanned in less than 2 min. Although the FIESTA-ET images exhibited an unexpected increase (P < 0.0005) in myocardial SNR of 16% over FIESTA, the volumetric measurements showed excellent correlation., (Copyright 2002 Wiley-Liss, Inc.)

PurposeTo present a new method that can simultaneously and efficiently measure T1 and B1 (+) maps using reference region variable flip angle (RR-VFA) imaging.MethodsAssuming T1 relaxation time in a reference region such as fat is well characterized, and the reference region sufficiently covers smoothly varying B1 (+) field inhomogeneity, B1 (+) maps can be measured from VFA images, conventionally used for T1 measurements. Fat-only images from two-point Dixon acquisitions were used to compute B1 (+) maps, and the B1 (+) maps were compared with ones using the double-angle method (DAM) in 22 breast MRI patients at 3T. Additionally, high spatial resolution VFA images were acquired to show T1 measurements with and without the RR-VFA B1 (+) correction in six patients.ResultsRR-VFA is able to generate reliable B1 (+) maps, similar to those using the conventional DAM. This simultaneous T1 and B1 (+) mapping can also be used to reduce T1 estimation errors, where T1 maps have more uniform fibroglandular tissue T1 and better depiction of heterogeneous T1 of breast masses.ConclusionA new method that can measure both T1 and B1 (+) maps based on Dixon VFA images is described, offering improved T1 quantification with no scan time penalty.