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StarVIBE is a 3D gradient-echo sequence with a radial, stack-of-stars acquisition having spatial resolution and tissue contrast. With newer sequences, it is important to be familiar with sequence tissue contrasts and appearance of anatomical variants. We evaluated 450 patients utilizing this sequence; 35 patients demonstrated fluffy “cotton wool” enhancement at the internal auditory canal fundus without clear pathology. We favor this represents anatomic neurovascular enhancement that StarVIBE is sensitive to and is a touch-me-not finding.

Objectives The goal of this study was to investigate the precise timeline of respiratory events occurring after the administration of two gadolinium-based contrast agents, gadoxetate disodium and gadoterate meglumine. Materials and methods This retrospective study examined 497 patients subject to hepatobiliary imaging using the GRASP MRI technique (TR/TE = 4/2 ms; ST = 2.5 mm; 384 × 384 mm). Imaging was performed after administration of gadoxetate (N = 338) and gadoterate (N = 159). All GRASP datasets were reconstructed using a temporal resolution of 1 s. Four regions-of-interest (ROIs) were placed in the liver dome, the right and left cardiac ventricle, and abdominal aorta detecting liver displacement and increasing vascular signal intensities over time. Changes in hepatic intensity reflected respiratory dynamics in temporal correlation to the vascular contrast bolus. Results In total, 216 (67%) and 41 (28%) patients presented with transient respiratory motion after administration of gadoxetate and gadoterate, respectively. The mean duration from start to acme of the respiratory episode was similar (p = 0.4) between gadoxetate (6.0 s) and gadoterate (5.6 s). Its mean onset in reference to contrast arrival in the right ventricle differed significantly (p < 0.001) between gadoxetate (15.3s) and gadoterate (1.8 s), analogously to peak inspiration timepoint in reference to the aortic enhancement arrival (gadoxetate: 0.9s after, gadoterate: 11.2 s before aortic enhancement, p < 0.001). Conclusions The timepoint of occurrence of transient respiratory anomalies associated with gadoxetate disodium and gadoterate meglumine differs significantly between both contrast agents while the duration of the event remains similar. Key Points • Transient respiratory anomalies following the administration of gadoterate meglumine occurred during a time period usually not acquired in MR imaging. • Transient respiratory anomalies following the administration of gadoxetate disodium occurred around the initiation of arterial phase imaging. • The estimated duration of respiratory events was similar between both contrast agents.

To assess if adding perfusion information from dynamic contrast-enhanced (DCE MRI) acquisition schemes with high spatiotemporal resolution to T2w/DWI sequences as input features for a gradient boosting machine (GBM) machine learning (ML) classifier could better classify prostate cancer (PCa) risk groups than T2w/DWI sequences alone. One hundred ninety patients (68 ± 9 years) were retrospectively evaluated at 3T MRI for clinical suspicion of PCa. Included were 201 peripheral zone (PZ) PCa lesions. Histopathological confirmation on fusion biopsy was matched with normal prostate parenchyma contralaterally. Biopsy results were grouped into benign tissue and low-, intermediate-, and high-risk groups (Gleason sum score 6, 7, and > 7, respectively). DCE MRI was performed using golden-angle radial sparse MRI. Perfusion maps (Ktrans, Kep, Ve), apparent diffusion coefficient (ADC), and absolute T2w signal intensity were determined and used as input features for building two ML models: GBM with/without perfusion maps. Areas under the receiver operating characteristic curve (AUC) values for correlated models were compared. For the classification of benign vs. malignant and intermediate- vs. high-grade PCa, perfusion information added relevant information (AUC values 1 vs. 0.953 and 0.909 vs. 0.700, p

PURPOSE To develop a 3D sequence for T1ρ relaxation mapping using radial volumetric encoding (3D-T1ρ -RAVE) and to evaluate the multi relaxation components in the liver of healthy controls and chronic liver disease (CLD) patients. METHODS Fat saturation and T1ρ preparation modules were followed by a train of gradient-echo acquisitions and T1 restoration delay. The series of T1ρ -weighted images were fitted using mono-exponential, bi-exponential, and stretched-exponential models. The repeatability and reproducibility of the proposed technique were evaluated on National Institute of Standards and Technology phantom by calculating the coefficient of variation between test-retest scans on the same scanner and between two different 3T scanners, respectively. Mann-Whitney U-test was performed to assess differences in T1ρ components among patients (n = 3) and a control group (n = 10). RESULTS The phantom study showed an error of 8.9% and 11.5% in mono T2 relaxation time measurement relative to the reference on 2 different scanners. The coefficient of variation for test-retest scans performed on the same scanner was 5.7% and 2.4% for scans performed on 2 scanners. The comparison between healthy controls and CLD patients showed a significant difference (P < .05) in mono relaxation time (P = .002), stretched-exponential relaxation parameter (P = .04). The Akaike information criteria C criterion showed 2.53 ± 0.9% (2.3 ± 0.3% for CLD) of the voxels are bi-exponential while in 65.3 ± 5.8% (81.2 ± 0.06% for CLD) of the liver voxels, the stretched-exponential model was preferred. CONCLUSION The 3D-T1ρ -RAVE sequence allows volumetric, multicomponent T1ρ assessment of the liver during free breathing and can distinguish between healthy volunteers and CLD patients.

Background Gadoxetate disodium has been associated with various respiratory irregularities at arterial imaging MRI. Purpose To measure the relationship between gadolinium-based contrast agent administration and irregularities by comparing gadoxetate disodium and gadoterate meglumine at free breathing. Materials and Methods This prospective observational cohort study (January 2015 to May 2017) included consecutive abdominal MRI performed with either gadoxetate disodium or gadoterate meglumine enhancement. Participants underwent dynamic imaging by using the golden-angle radial sparse parallel sequence at free breathing. The quantitative assessment evaluated the aortic contrast enhancement, the respiratory hepatic translation, and the k-space-derived respiratory pattern. Analyses of variance compared hemodynamic metrics, respiratory-induced hepatic motion, and respiratory parameters before and after respiratory gating. Results A total of 497 abdominal MRI examinations were included. Of these, 338 participants were administered gadoxetate disodium (mean age, 59 years ± 15; 153 women) and 159 participants were administered gadoterate meglumine (mean age, 59 years ± 17; 85 women). The arterial bolus of gadoxetate disodium arrived later than gadoterate meglumine (19.7 vs 16.3 seconds, respectively; P < .001). Evaluation of the hepatic respiratory translation showed respiratory motion occurring in 70.7% (239 of 338) of participants who underwent gadoxetate-enhanced examinations and in 28.9% (46 of 159) of participants who underwent gadoterate-enhanced examinations (P < .001). The duration of motion irregularities was longer for gadoxetate than for gadoterate (19.2 seconds vs 17.2 seconds, respectively) and the motion irregularities were more severe (P < .001). Both the respiratory frequency and amplitude were shorter for participants administered gadoxetate from the prebolus phase to the late arterial phase compared with gadoterate (P < .001). Conclusion The administration of two different gadolinium-based contrast agents, gadoxetate and gadoterate, at free-breathing conditions potentially leads to respiratory irregularities with differing intensity and onset. © RSNA, 2019 Online supplemental material is available for this article.

PURPOSE: The aim of this study was to investigate the diagnostic value of descriptive prostate perfusion parameters derived from signal enhancement curves acquired using golden-angle radial sparse parallel dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) with high spatiotemporal resolution in advanced, quantitative evaluation of prostate cancer compared with the usage of apparent diffusion coefficient (ADC) values. METHODS: A retrospective study (from January 2016 to July 2019) including 75 subjects (mean, 65 years; 46–80 years) with 2.5-second temporal resolution DCE-MRI and PIRADS 4 or 5 lesions was performed. Fifty-four subjects had biopsy-proven prostate cancer (Gleason 6, 15; Gleason 7, 20; Gleason 8, 13; Gleason 9, 6), whereas 21 subjects had negative MRI/ultrasound fusion-guided biopsies. Voxel-wise analysis of contrast signal enhancement was performed for all time points using custom-developed software, including automatic arterial input function detection. Seven descriptive parameter maps were calculated: normalized maximum signal intensity, time to start, time to maximum, time-to-maximum slope, and maximum slope with normalization on maximum signal and the arterial input function (SMN1, SMN2). The parameters were compared with ADC using multiparametric machine-learning models to determine classification accuracy. A Wilcoxon test was used for the hypothesis test and the Spearman coefficient for correlation. RESULTS: There were significant differences (P < 0.05) for all 7 DCE-derived parameters between the normal peripheral zone versus PIRADS 4 or 5 lesions and the biopsy-positive versus biopsy-negative lesions. Multiparametric analysis showed better performance when combining ADC + DCE as input (accuracy/sensitivity/specificity, 97%/93%/100%) relative to ADC alone (accuracy/sensitivity/specificity, 94%/95%/95%) and to DCE alone (accuracy/sensitivity/specificity, 78%/79%/77%) in differentiating the normal peripheral zone from PIRADS lesions, biopsy-positive versus biopsy-negative lesions (accuracy/sensitivity/specificity, 68%/33%/81%), and Gleason 6 versus ≥7 prostate cancer (accuracy/sensitivity/specificity, 69%/60%/72%). CONCLUSIONS: Descriptive perfusion characteristics derived from high-resolution DCE-MRI using model-free computations show significant differences between normal and cancerous tissue but do not reach the accuracy achieved with solely ADC-based classification. Combining ADC with DCE-based input features improved classification accuracy for PIRADS lesions, discrimination of biopsy-positive versus biopsy-negative lesions, and differentiation between Gleason 6 versus Gleason ≥7 lesions.

PURPOSE: To investigate the diagnostic performance of a dual-parameter approach by combining either volumetric interpolated breath-hold examination (VIBE)- or golden-angle radial sparse parallel (GRASP)–derived dynamic contrast agent–enhanced (DCE) MRI with established diffusion-weighted imaging (DWI) compared with traditional single-parameter evaluations on the basis of DWI alone. MATERIALS AND METHODS: Ninety-four male participants (66 years ± 7 [standard deviation]) were prospectively evaluated at 3.0-T MRI for clinical suspicion of prostate cancer. Included were 101 peripheral zone prostate cancer lesions. Histopathologic confirmation at MRI transrectal US fusion biopsy was matched with normal contralateral prostate parenchyma. MRI was performed with diffusion weighting and DCE by using GRASP (temporal resolution, 2.5 seconds) or VIBE (temporal resolution, 10 seconds). Perfusion (influx forward volume transfer constant [K(trans)] and rate constant [K(ep)]) and apparent diffusion coefficient (ADC) parameters were determined by tumor volume analysis. Areas under the receiver operating characteristic curve were compared for both sequences. RESULTS: Evaluated were 101 prostate cancer lesions (GRASP, 61 lesions; VIBE, 40 lesions). In a combined analysis, diffusion and perfusion parameters ADC with K(trans) or K(ep) acquired with GRASP had higher diagnostic performance compared with diffusion characteristics alone (area under the curve, 0.97 ± 0.02 [standard error] vs 0.93 ± 0.03; P < .006 and .021, respectively), whereas ADC with perfusion parameters acquired with VIBE had no additional benefit (area under the curve, 0.94 ± 0.03 vs 0.93 ± 0.04; P = .18and .50, respectively, for combination of ADC with K(trans) and K(ep)). CONCLUSION: If used in a dual-parameter model, incorporating diffusion and perfusion characteristics, the golden-angle radial sparse parallel acquisition technique improves the diagnostic performance of multiparametric MRI examinations of the prostate. This effect could not be observed combining diffusing with perfusion parameters acquired with volumetric interpolated breath-hold examination.

Purpose To compare a novel multicoil compressed sensing technique with flexible temporal resolution, golden-angle radial sparse parallel (GRASP), to conventional fat-suppressed spoiled three-dimensional (3D) gradient-echo (volumetric interpolated breath-hold examination, VIBE) MRI in evaluating the conspicuity of benign and malignant breast lesions. Materials and Methods Between March and August 2015, 121 women (24–84 years; mean, 49.7 years) with 180 biopsy-proven benign and malignant lesions were imaged consecutively at 3.0 Tesla in a dynamic contrast-enhanced (DCE) MRI exam using sagittal T1-weighted fat-suppressed 3D VIBE in this Health Insurance Portability and Accountability Act-compliant, retrospective study. Subjects underwent MRI-guided breast biopsy (mean, 13 days [1–95 days]) using GRASP DCE-MRI, a fat-suppressed radial “stack-of-stars” 3D FLASH sequence with golden-angle ordering. Three readers independently evaluated breast lesions on both sequences. Statistical analysis included mixed models with generalized estimating equations, kappa-weighted coefficients and Fisher's exact test. Results All lesions demonstrated good conspicuity on VIBE and GRASP sequences (4.28 ± 0.81 versus 3.65 ± 1.22), with no significant difference in lesion detection (P = 0.248). VIBE had slightly higher lesion conspicuity than GRASP for all lesions, with VIBE 12.6% (0.63/5.0) more conspicuous (P

ObjectiveThe purpose of this study was to estimate perfusion metrics in healthy and cirrhotic liver with pharmacokinetic modeling of high–temporal resolution reconstruction of continuously acquired free-breathing gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid–enhanced acquisition in pat

Radial spin-echo diffusion imaging allows motion-robust imaging of tissues with very low T2 values like articular cartilage with high spatial resolution and signal-to-noise ratio (SNR). However, in vivo measurements are challenging, due to the significantly slower data acquisition speed of spin-echo sequences and the less efficient k-space coverage of radial sampling, which raises the demand for accelerated protocols by means of undersampling. This work introduces a new reconstruction approach for undersampled diffusion-tensor imaging (DTI). A model-based reconstruction implicitly exploits redundancies in the diffusion-weighted images by reducing the number of unknowns in the optimization problem and compressed sensing is performed directly in the target quantitative domain by imposing a total variation (TV) constraint on the elements of the diffusion tensor. Experiments were performed for an anisotropic phantom and the knee and brain of healthy volunteers (three and two volunteers, respectively). Evaluation of the new approach was conducted by comparing the results with reconstructions performed with gridding, combined parallel imaging and compressed sensing and a recently proposed model-based approach. The experiments demonstrated improvements in terms of reduction of noise and streaking artifacts in the quantitative parameter maps, as well as a reduction of angular dispersion of the primary eigenvector when using the proposed method, without introducing systematic errors into the maps. This may enable an essential reduction of the acquisition time in radial spin-echo diffusion-tensor imaging without degrading parameter quantification and/or SNR.

Purpose 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

Dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) of the prostate comprises sequential T1-weighted imaging (T1WI) acquisitions following injection of gadolinium-based contrast agent and aims to depict abnormal pharmacokinetics within tumorous regions (1). DCE has become a routine component of multiparametric prostate MRI protocols and improves the detection, localization, and staging of prostate cancer (2,3). Findings on DCE have been incorporated into standardized reporting schemes for prostate MRI (2) and are useful for guiding prostate biopsy (4), planning treatment (5), and monitoring posttherapy recurrences (6). One challenge in the implementation of DCE in the prostate is the inherent trade-off between spatial and temporal resolution in MRI (Table 1) (7–9). As the prostate is often highly vascular, differences in enhancement kinetics between benign and malignant regions can be subtle, such that high temporal resolution can assist in their differentiation (1). Indeed, recent expert guidelines advise a temporal resolution of at least 15 seconds (2). Nonetheless, many investigations report a considerably higher temporal resolution, in some instances under 3 seconds per acquisition (10). A higher temporal resolution is also essential for advanced pharmacokinetic modeling requiring an arterial input function (11). However, as prostate tumors are frequently small in size, potentially measuring less than 1 cm (12), their precise depiction can be critical for guiding a targeted biopsy or treatment, and a higher spatial resolution may be preferred. To this end, other studies have achieved higher spatial resolution by using a temporal resolution as low as 30 seconds (13,14). Also influencing this balance between spatial and temporal resolution is the impact of acquisition parameters on anatomic coverage, tissue contrast, motion robustness, and other artifacts (7). Given these confounding factors, there is currently a lack of technical standardization for prostate DCE in clinical practice (7). Table 1 Representative Combinations of Spatial and Temporal Resolutions Reported for DCE-MRI of the Prostate Within the Recent Peer-Reviewed Literaturea A number of recent advances in 3D gradient-echo T1WI may be useful for addressing these challenges. Compressed sensing (CS) exploits spatial correlations within images or spatiotemporal correlations among sequentially acquired images to substantially accelerate acquisitions (15). CS requires randomly under-sampled k-space data, which are preferably acquired using non-Cartesian k-space sampling schemes such as radial trajectories (16). Furthermore, advanced reconstruction techniques allow for the synergistic combination of CS and parallel imaging for processing of DCE data (17), which collectively offers simultaneous high spatial and high temporal resolution. The use of an underlying radial k-space sampling technique for this approach additionally increases robustness with respect to motion artifacts (18,19). A robust combination of CS and parallel imaging for rapid continuous acquisition with flexible spatiotemporal resolution using the golden-angle radial sampling scheme (20,21) (termed Golden-angle RAdial Sparse Parallel, or GRASP, imaging) has recently been applied to perform high-quality multiphase DCE of the liver during free-breathing (22). The prostate may provide an ideal additional application of the GRASP technique. The high degree of spatiotemporal correlation of data over the course of a DCE acquisition facilitates the sparse data representations that form the basis of CS reconstruction. In addition, given the small size of prostate tumors, overlap in tumors’ enhancement characteristics with benign prostate, and presence of prostatic motion during an extended DCE acquisition, prostate DCE would stand to benefit greatly from the advantages offered by GRASP. Therefore, our aim in this study was to demonstrate the feasibility of performing high-spatiotemporal resolution DCE of the prostate by using GRASP and to compare image quality and lesion depiction between GRASP and conventional DCE in patients with biopsy-proven prostate cancer.

Gadoxetic acid-enhanced magnetic resonance cholangiopancreatography (MRCP) was performed for evaluation of living donor liver transplantation. T2-weighted MRCP and hepatobiliary-phase postcontrast MRCP showed an aberrant right posterior bile duct, although the precise variant was uncertain. Optimized hepatobiliary-phase MRCP was obtained using 3 sequence modifications: increased flip angle to improve contrast between the biliary tree and surrounding tissues; radial k-space sampling to minimize motion artifact; and free-breathing acquisition to improve signal-to-noise ratio and, in turn, spatial resolution (resolution of 1.28 × 1.28 × 1.5 mm). The optimized sequence demonstrated that the right posterior bile duct drained into the cystic duct, consistent with type 3C biliary variant, thus modifying surgical planning.

Assessment of arterial and venous phases of enhancement is essential for liver lesion detection and characterization.1,2 Contrast-enhanced multiphase liver magnetic resonance (MR) examination is usually performed using a T1-weighted fat-saturated 3-dimensional (3D) volumetric interpolated sequence with cartesian k-space sampling in a breath hold (BH). However, this method is sensitive to respiratory motion and can result in suboptimal images in patients who cannot adequately hold their breath. Although parallel-imaging and partial-Fourier techniques are usually used for accelerating the examination, this may be insufficient in elderly patients, patients with debilitations, or pediatric patients who have severely limited breath-holding capacity.3,4 Furthermore, achievable in-plane spatial resolution and anatomic coverage remain limited because of the need to acquire data within a BH. Recently, a more motion-robust 3D gradient-echo sequence has been developed (radial VIBE) that uses the “stack-of-stars”scheme to acquire volumetric k-space data, where radial sampling is performed in-plane (along ky and kx) and cartesian sampling is used along the slice dimension (kz).5,6 Studies have shown that free-breathing acquisitions with the stack-of-stars radial VIBE sequence can yield images of comparable image quality with conventional BH examination at the expense of a longer acquisition time.7,8 This relatively long acquisition time limits its utility for dynamic liver imaging, which requires multiphase acquisitions with temporal resolution of 15 to 20 seconds. One potential solution to improve the temporal resolution is the application of the compressed sensing (CS) concept, which has recently emerged as a powerful tool for fast imaging by exploiting redundancies in the images.9 Successful application of CS requires sparsity, incoherence, and nonlinear reconstruction. Magnetic resonance images often can be represented using only few coefficients in an appropriate transform basis. Multiphase liver MRI is a perfect candidate for CS because of extensive spatiotemporal data correlations that result in sparse representations. Compressed sensing can be synergistically combined with parallel imaging to further increase imaging speed.10–12 High level of incoherence can be achieved by using irregular k-space sampling patterns. Radial sampling of k-space compares favorably with conventional cartesian schemes for CS because of the inherent presence of incoherent aliasing artifacts from undersampled radial trajectories,10 which are essential for application of the CS reconstruction. We have recently developed a reconstruction technique that combines CS with parallel imaging for radially acquired dynamic MRI.13 Two different types of radial acquisition schemes are investigated in this study: the interleaved angle-bisection scheme and the golden-angle scheme, which mainly differ in the temporal order of the k-space sampling. With the interleaved angle-bisection scheme, radial spokes are acquired at a regular angular distance (Fig. 1) in multiple interleaves, such that all spokes from 1 interleave intersect the spokes from the previously acquired interleave.14 With the recently proposed golden-angle acquisition scheme, on the other hand, the angle of the acquired spokes is continuously increased by 111.25 degrees during the acquisition, resulting in a series of complementary radial spokes with large angular distance that, for an arbitrary number of spokes, always add up to an approximately uniform angular coverage of the k-space15 (Fig. 1). FIGURE 1 Schematic of sampling scheme for interleaved angle-bisection and continuous golden-angle acquisitions. Temporal frames in the bisection scheme need to be predefined, whereas the golden-angle scheme provides freedom in defining temporal frames retrospectively ... The purposes of this study were to demonstrate the feasibility of performing free-breathing multiphase liver MRI using a combination of CS and parallel imaging with golden-angle (golden-angle radial sparse parallel [GRASP]) and interleaved-angle (interleaved-angle radial sparse parallel [IARASP]) radial sampling scheme and to compare image quality of GRASP and IARASP with conventional BH T1-weighted gradient-echo imaging with cartesian sampling (volumetric interpolate breath hold examination [BH-VIBE]) in healthy participants with normal breath-holding capacity.

Aims and objectives The purpose of the present study was to evaluate a recently introduced technique for free-breathing dynamic contrast-enhanced renal magnetic resonance imaging (MRI) applying a combination of radial k-space sampling, parallel imaging, and compressed sensing. The technique allows retrospective reconstruction of 2 motion-suppressed sets of images from the same acquisition: one with lower temporal resolution but improved image quality for subjective image analysis, and one with high temporal resolution for quantitative perfusion analysis. Materials and methods In this study, 25 patients underwent a kidney examination, including a prototypical fat-suppressed, golden-angle radial stack-of-stars T1-weighted 3-dimensional spoiled gradient-echo examination (GRASP) performed after contrast agent administration during free breathing. Images were reconstructed at temporal resolutions of 55 spokes per frame (6.2 seconds) and 13 spokes per frame (1.5 seconds). The GRASP images were evaluated by 2 blinded radiologists. First, the reconstructions with low temporal resolution underwent subjective image analysis: the radiologists assessed the best arterial phase and the best renal phase and rated image quality score for each patient on a 5-point Likert-type scale.In addition, the diagnostic confidence was rated according to a 3-point Likert-type scale. Similarly, respiratory motion artifacts and streak artifacts were rated according to a 3-point Likert-type scale.Then, the reconstructions with high temporal resolution were analyzed with a voxel-by-voxel deconvolution approach to determine the renal plasma flow, and the results were compared with values reported in previous literature. Results Reader 1 and reader 2 rated the overall image quality score for the best arterial phase and the best renal phase with a median image quality score of 4 (good image quality) for both phases, respectively. A high diagnostic confidence (median score of 3) was observed. There were no respiratory motion artifacts in any of the patients. Streak artifacts were present in all of the patients, but did not compromise diagnostic image quality.The estimated renal plasma flow was slightly higher (295 ± 78 mL/100 mL per minute) than reported in previous MRI-based studies, but also closer to the physiologically expected value. Conclusions Dynamic, motion-suppressed contrast-enhanced renal MRI can be performed in high diagnostic quality during free breathing using a combination of golden-angle radial sampling, parallel imaging, and compressed sensing. Both morphologic and quantitative functional information can be acquired within a single acquisition.

The task of imaging is to gather spatiotemporal information which can be organized into a coherent map. Tomographic imaging in particular involves the use of multiple projections, or other interactions of a probe (light, sound, etc.) with a body, in order to determine cross-sectional information. Though the probes and the corresponding imaging modalities may vary, and though the methodology of particular imaging approaches is in constant ferment, the conceptual underpinnings of tomographic imaging have in many ways remained fixed for many decades. Recent advances in applied mathematics, however, have begun to roil this intellectual landscape. The advent of compressed sensing, anticipated in various algorithms dating back many years but unleashed in full theoretical force in the last decade, has changed the way imagers have begun to think about data acquisition and image reconstruction. The power of incoherent sampling and sparsity-enforcing reconstruction has been demonstrated in various contexts and, when combined with other modern fast imaging techniques, has enabled unprecedented increases in imaging efficiency. Perhaps more importantly, however, such approaches have spurred a shift in perspective, prompting us to focus less on nominal data sufficiency than on information content. Beginning with examples from MRI, then proceeding through selected other modalities such as CT and PET, as well as multimodality combinations, this paper explores the potential of newly evolving acquisition and reconstruction paradigms to change the way we do imaging in the lab and in the clinic.

Traditional fat-suppressed T1-weighted spin-echo or turbo spin-echo (TSE) sequences (T1-weighted images) may be degraded by motion and pulsation artifacts in head-and-neck studies. Our purpose is to evaluate the role of a fat-suppressed T1-weighted 3D radial gradient-recalled echo sequence (radial-volumetric interpolated breath-hold examination [VIBE]) in the head and neck as compared with standard contrast-enhanced fat-suppressed T1-weighted images.We retrospectively evaluated 21 patients (age range, 9-67 years) who underwent head-and-neck MRI at 1.5 T. Both contrast-enhanced radial-VIBE and conventional fat-suppressed TSE contrast-enhanced T1-weighted imaging were performed. Two radiologists evaluated multiple parameters of image quality, graded on a 5-point scale. Mixed-model analysis of variance and interobserver variability assessment were performed.The following parameters were scored as significantly better for the contrast-enhanced radial-VIBE sequence than for conventional contrast-enhanced T1-weighted imaging: overall image quality (p0.0001), degree of fat suppression (p = 0.006), mucosal enhancement (p = 0.004), muscle edge clarity (p = 0.049), vessel clarity (p0.0001), respiratory motion artifact (p = 0.002), pulsation artifact (p0.0001), and lesion edge sharpness (p = 0.004). Interobserver agreement in qualitative evaluation of the two sequences showed fair-to-good agreement for the following variables: overall image quality (intraclass correlation coefficient [ICC], 0.779), degree of fat suppression (ICC, 0.716), mucosal enhancement (ICC, 0.693), muscle edge clarity (ICC, 0.675), respiratory motion artifact (ICC, 0.516), lesion enhancement (ICC, 0.410), and lesion edge sharpness (ICC, 0.538). Excellent agreement was shown for vessel clarity (ICC, 0.846) and pulsation artifact (ICC, 0.808).The radial-VIBE sequence is a viable motion-robust improvement on the conventional fat-suppressed T1-weighted sequence.

To demonstrate dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) of the prostate with both high spatial and temporal resolution via a combination of golden-angle radial k-space sampling, compressed sensing, and parallel-imaging reconstruction (GRASP), and to compare image quality and lesion depiction between GRASP and conventional DCE in prostate cancer patients.Twenty prostate cancer patients underwent two 3T prostate MRI examinations on separate dates, one using standard DCE (spatial resolution 3.0 × 1.9 × 1.9 mm, temporal resolution 5.5 sec) and the other using GRASP (spatial resolution 3.0 × 1.1 × 1.1 mm, temporal resolution 2.3 sec). Two radiologists assessed measures of image quality and dominant lesion size. The experienced reader recorded differences in contrast arrival times between the dominant lesion and benign prostate.Compared with standard DCE, GRASP demonstrated significantly better clarity of the capsule, peripheral/transition zone boundary, urethra, and periprostatic vessels; image sharpness; and lesion conspicuity for both readers (P 0.001-0.020). GRASP showed improved interreader correlation for lesion size (GRASP: r = 0.691-0.824, standard: r = 0.495-0.542). In 8/20 cases, only GRASP showed earlier contrast arrival in tumor than benign; in no case did only standard DCE show earlier contrast arrival in tumor.High spatiotemporal resolution prostate DCE is possible with GRASP, which has the potential to improve image quality and lesion depiction as compared with standard DCE.

To assess diagnostic sensitivity of radial T1-weighted gradient-echo (radial volumetric interpolated breath-hold examination [VIBE]) magnetic resonance (MR) imaging, positron emission tomography (PET), and combined simultaneous PET and MR imaging with an integrated PET/MR system in the detection of lung nodules, with combined PET and computed tomography (CT) as a reference.In this institutional review board-approved HIPAA-compliant prospective study, 32 patients with tumors who underwent clinically warranted fluorine 18 ((18)F) fluorodeoxyglucose (FDG) PET/CT followed by PET/MR imaging were included. In all patients, the thorax station was examined with free-breathing radial VIBE MR imaging and simultaneously acquired PET data. Presence and size of nodules and FDG avidity were assessed on PET/CT, radial VIBE, PET, and PET/MR images. Percentage of nodules detected on radial VIBE and PET images was compared with that on PET/MR images by using generalized estimating equations. Maximum standardized uptake value (SUVmax) in pulmonary nodules with a diameter of at least 1 cm was compared between PET/CT and PET/MR imaging with Pearson rank correlation.A total of 69 nodules, including 45 FDG-avid nodules, were detected with PET/CT. The sensitivity of PET/MR imaging was 70.3% for all nodules, 95.6% for FDG-avid nodules, and 88.6% for nodules 0.5 cm in diameter or larger. PET/MR imaging had higher sensitivity than PET for all nodules (70.3% vs 61.6%, P = .002) and higher sensitivity than MR imaging for FDG-avid nodules (95.6% vs 80.0%, P = .008). There was a significantly strong correlation between SUVmax of pulmonary nodules obtained with PET/CT and that obtained with PET/MR imaging (r = 0.96, P.001).Radial VIBE and PET data acquired simultaneously with PET/MR imaging have high sensitivity in the detection of FDG-avid nodules and nodules 0.5 cm in diameter or larger, with low sensitivity for small non-FDG-avid nodules.

Accurate localization and uptake quantification of lesions in the chest and abdomen using PET imaging is challenging due to the respiratory motion during the exam. The advent of hybrid PET/MR systems offers new ways to compensate for respiratory motion without exposing the patient to additional radiation. The use of self-gated reconstructions of a 3D radial stack-of-stars GRE acquisition is proposed to derive a high-resolution MRI motion model. The self-gating signal is used to perform respiratory binning of the simultaneously acquired PET raw data. Matching μ-maps are generated for every bin, and post-reconstruction registration is performed in order to obtain a motion-compensated PET volume from the individual gates. The proposed method is demonstrated in-vivo for three clinical patients. Motion-corrected reconstructions are compared against ungated and gated PET reconstructions. In all cases, motion-induced blurring of lesions in the liver and lung was substantially reduced, without compromising SNR as it is the case for gated reconstructions.

The introduction of compressed sensing methods to speed up image acquisition has received great attention in the Magnetic Resonance Imaging (MRI) community. Compressed sensing exploits the compressibility of medical images to reconstruct unaliased images from undersampled data. Moreover, compressed sensing can be synergistically combined with previously introduced acceleration methods such as parallel imaging, which employs arrays of receiver coils to further increase imaging speed. Over the past three years, we have been working on the combination of compressed sensing and parallel imaging, exploiting the idea of joint multicoil sparsity. In this work, we present a summary of our image acquisition and reconstruction methods for the combination of compressed sensing and parallel imaging, and describe applications to cardiac and body dynamic MRI.

To compare free-breathing radially sampled 3D fat suppressed T1-weighted gradient-echo acquisitions (radial volumetric interpolated breath-hold examination [VIBE]) with breath-hold (BH) and free-breathing conventional (rectilinearly sampled k-space) VIBE acquisitions for postcontrast imaging of the liver.: Eighteen consecutive patients referred for clinically indicated liver magnetic resonance imaging were imaged at 3 T. Three minutes after a single dose of gadolinium contrast injection, free-breathing radial VIBE, BH VIBE, and free-breathing VIBE with 4 averages were acquired in random order with matching sequence parameters. Radial VIBE was acquired with the "stack-of-stars" scheme, which uses conventional sampling in the slice direction and radial sampling in-plane.All image data sets were evaluated independently by 3 radiologists blinded to patient and sequence information. Each reader scored the following parameters: overall image quality, respiratory motion artifact, pulsation artifact, liver edge sharpness, and hepatic vessel clarity using a 5-point scale, with the highest score indicating the most optimum examination. Mixed model analysis of variance was used to compare sequences in terms of each measure of image quality.: When scores were averaged over readers, there was no statistically significant difference between radial VIBE and BH VIBE regarding overall image quality (P = 0.1015), respiratory motion artifact (P = 1.0), and liver edge sharpness (P = 0.2955). Radial VIBE demonstrated significantly lower pulsation artifact (P0.0001), but had lower hepatic vessel clarity (P = 0.0176), when compared with BH VIBE. Radial VIBE had significantly higher image quality scores for all parameters when compared with free-breathing VIBE (P0.0001). Acquisition time for BH VIBE was 14 seconds and that of free-breathing radial VIBE and conventional VIBE with multiple averages was 56 seconds each.: Radial VIBE can be performed during free breathing for contrast-enhanced imaging of the liver with comparable image quality to BH VIBE. However, further work is necessary to shorten the acquisition time to perform dynamic imaging.

Contrast-enhanced fat-suppressed T1 weighted (T1W) two-dimensional (2D) turbo spin echo (TSE) and magnetization-prepared gradient echo (MPRAGE) sequences with water excitation are routinely obtained to evaluate orbit pathology. However, these sequences can be marred by artefacts. The radial-volume-interpolated breath-hold examination (VIBE) sequence is a motion-robust fat-suppressed T1W sequence which has demonstrated value in paediatric and body imaging. The purpose of our study was to evaluate its role in assessing the orbit and to compare it with routinely acquired sequences.A Health Insurance Portability and Accountability Act-compliant and institutional review board-approved retrospective study was performed in 46 patients (age range: 1-81 years) who underwent orbit studies on a 1.5-T MRI system using contrast-enhanced Radial-VIBE, MPRAGE and 2D TSE sequences. Two radiologists blinded to the sequence analysed evaluated multiple parameters of image quality including motion artefact, degree of fat suppression, clarity of choroidal enhancement, intraorbital vessels, extraocular muscles, optic nerves, brain parenchyma and evaluation of pathology. Each parameter was assessed on a 5-point scale, with a higher score indicating the more optimal examination. Mix model analysis of variance and interobserver variability were assessed.Radial-VIBE demonstrated superior quality (p 0.001) for all orbit parameters when compared with MPRAGE and 2D TSE. Interobserver agreement demonstrated average fair-to-good agreement for degree of motion artefact (0.745), fat suppression (0.678), clarity of choroidal enhancement (0.688), vessels (0.655), extraocular muscles (0.675), optic nerves (0.518), brain parenchyma (0.710) and evaluation of pathology (0.590).Radial-VIBE sequence demonstrates superior image quality when evaluating the orbits as compared with conventional MPRAGE and 2D TSE sequences.Radial-VIBE employs unique non-Cartesian k-space sampling in a radial or spoke-wheel fashion which provides superior image quality improving diagnostic capability in the evaluation of the orbits.

State-of-the-art MR-PET scanners allow simultaneous data acquisition. However, image reconstruction is performed separately and results are only combined at the visualization stage. PET images are reconstructed using a variant of EM and MR data are reconstructed using an inverse Fourier transform or iterative algorithms for parallel imaging or compressed sensing. We propose a new iterative joint reconstruction framework based on multi-sensor compressed sensing that exploits anatomical correlations between MR and PET. Joint reconstruction is motivated by the fact that MR and PET are based on the same anatomy. High resolution MR information can be used to enhance the PET reconstruction and MR artifacts are not present in the PET image. Therefore a dedicated reconstruction can exploit the incoherence of artifacts in the joint space. Our approach uses a nonlinear constrained optimization problem. In each iteration OSEM enforces data consistency of the current solution with measured PET rawdata. An l1-norm based joint sparsity term exploits anatomical correlations. MR data consistency is enforced with the MR forward operator, consisting of coil sensitivity modulation and a (non-uniform) Fourier transform. Data were acquired on a clinical 3T MR-PET unit (Siemens Biograph mMR). 10 mCi 18F-FDG were injected followed by a 60min list mode scan. 3D MP-RAGE was used for MR data acquisition: TR=2300ms, TE=2.98ms, TI=900ms, FA=9°, acceleration factor 2, 24 ACS lines, 256 matrix, voxel size=1×1×1mm3, 192 slices. Joint MR-PET reconstruction improves resolution in PET images when structures are aligned with MR. PET signal information cannot be improved in regions showing no distinctive MR contrast, but it is also not influenced falsely. The availability of simultaneously-acquired MR and PET data will also enable incorporation of dynamic correlations and motion correction into the joint reconstruction framework. We expect that this provides additional enhancements to the information content of multimodality studies.