Cost-effectiveness of MRE versus VCTE in staging fibrosis for nonalcoholic fatty liver disease (NAFLD) patients with advanced fibrosis.

INTRODUCTION: NAFLD is a common cause of liver disease. To determine the optimal testing strategy for NAFLD patients with advanced fibrosis, several factors such as diagnostic accuracy, failure rates, costs of examinations, and potential treatment options need to be considered. The purpose of this study was to determine the cost-effectiveness of combination testing involving vibration-controlled transient elastography (VCTE) versus magnetic resonance elastography (MRE) as a frontline imaging strategy for NAFLD patients with advanced fibrosis. METHODS: A Markov model was developed from the US perspective. The base-case scenario in this model included patients aged 50 years with a Fibrosis-4 score of ≥2.67 and suspected advanced fibrosis. The model included a decision tree and a Markov state-transition model including 5 health states: fibrosis stage 1-2, advanced fibrosis, compensated cirrhosis, decompensated cirrhosis, and death. Both deterministic and probabilistic sensitivity analyses were performed. RESULTS: Staging fibrosis with MRE cost $8388 more than VCTE but led to an additional 1.19 Quality-adjusted life years (QALYs) with the incremental cost-effectiveness ratio of $7048/QALY. The cost-effectiveness analysis of the 5 strategies revealed that MRE+biopsy and VCTE+MRE+biopsy were the most cost-effective with the incremental cost-effectiveness ratios of $8054/QALY and $8241/QALY, respectively. Furthermore, sensitivity analyses indicated that MRE remained cost-effective with a sensitivity of ≥0.77, whereas VCTE became cost-effective with a sensitivity of ≥0.82. CONCLUSIONS: MRE was not only cost-effective than VCTE as the frontline modality for staging NAFLD patients with Fibrosis-4 ≥2.67 with incremental cost-effectiveness ratio of $7048/QALY but also remained cost-effective when used as a follow-up in instances of VCTE failure to diagnose.

State-of-the-art magnetic resonance imaging sequences for pediatric body imaging.

Longer examination time, need for anesthesia in smaller children and the inability of most children to hold their breath are major limitations of MRI in pediatric body imaging. Fortunately, with technical advances, many new and upcoming MRI sequences are overcoming these limitations. Advances in data acquisition and k-space sampling methods have enabled sequences with improved temporal and spatial resolution, and minimal artifacts. Sequences to minimize movement artifacts mainly utilize radial k-space filling, and examples include the stack-of-stars method for T1-weighted imaging and the periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER)/BLADE method for T2-weighted imaging. Similarly, the sequences with improved temporal resolution and the ability to obtain multiple phases in a single breath-hold in dynamic imaging mainly use some form of partial k-space filling method. New sequences use a variable combination of data sampling methods like compressed sensing, golden-angle radial k-space filling, parallel imaging and partial k-space filling to achieve free-breathing, faster sequences that could be useful for pediatric abdominal and thoracic imaging. Simultaneous multi-slice method has improved diffusion-weighted imaging (DWI) with reduction in scan time and artifacts. In this review, we provide an overview of data sampling methods like parallel imaging, compressed sensing, radial k-space sampling, partial k-space sampling and simultaneous multi-slice. This is followed by newer available and upcoming sequences for T1-, T2- and DWI based on these other advances. We also discuss the Dixon method and newer approaches to reducing metal artifacts.

Reduction of motion artifacts in carotid MRI using free-induction decay navigators.

PURPOSE: To develop a framework for prospective free-induction decay (FID)-based navigator gating for suppression of motion artifacts in carotid magnetic resonance imaging (MRI) and to assess its capability in vivo. MATERIALS AND METHODS: An FID-navigator, comprising a spatially selective low flip-angle sinc-pulse followed by an analog-to-digital converter (ADC) readout, was added to a conventional turbo spin-echo (TSE) sequence. Real-time navigator processing delivered accept/reject-and-reacquire decisions to the sequence. In this Institutional Review Board (IRB)-approved study, seven volunteers were scanned with a 2D T2-weighted TSE sequence. A reference scan with volunteers instructed to minimize motion as well as nongated and gated scans with volunteers instructed to perform different motion tasks were performed in each subject. Multiple image quality measures were employed to quantify the effect of gating. RESULTS: There was no significant difference in lumen-to-wall sharpness (2.3 ± 0.3 vs. 2.3 ± 0.4), contrast-to-noise ratio (CNR) (9.0 ± 2.0 vs. 8.5 ± 2.0), or image quality score (3.1 ± 0.9 vs. 2.6 ± 1.2) between the reference and gated images. For images acquired during motion, all image quality measures were higher (P < 0.05) in the gated compared to nongated images (sharpness: 2.3 ± 0.4 vs. 1.8 ± 0.5, CNR: 8.5 ± 2.0 vs. 7.2 ± 2.0, score: 2.6 ± 1.2 vs. 1.8 ± 1.0). CONCLUSION: Artifacts caused by the employed motion tasks deteriorated image quality in the nongated scans. These artifacts were alleviated with the proposed FID-navigator.

High-resolution diffusion-weighted imaging for the separation of benign from malignant BI-RADS 4/5 lesions found on breast MRI at 3T.

PURPOSE: To determine whether readout-segmented echo-planar diffusion imaging (RESOLVE) improves separation of malignant versus benign lesions compared to standard single-shot echo-planar imaging (ss-EPI) on BI-RADS 4/5 lesions detected on breast magnetic resonance imaging (MRI). MATERIALS AND METHODS: Consecutive 3T breast MRI studies with BI-RADS 4/5 designation and subsequent biopsy or benign mastectomy were retrospectively identified. Freehand regions of interest (ROIs) were drawn on lesions and also on normal background fibroglandular tissue for comparison. Lesion-to-background contrast was evaluated by normalizing signal intensity of the lesion ROI by the normal background tissue ROI at b = 800. Statistical analysis used the Mann-Whitney/Wilcoxon rank-sum test for unpaired and Wilcoxon signed-rank for paired comparisons. RESULTS: Of 38 lesions in 32 patients, 10 were malignant. Lesion-to-background contrast was higher on RESOLVE than ss-EPI (1.80 ± 0.71 vs. 1.62 ± 0.63, P = 0.03). Mean apparent diffusion coefficient (ADC) was the same or lower on RESOLVE than ss-EPI, and this effect was largest in malignant lesions (RESOLVE 0.90 ± 0.13; ss-EPI 1.00 ± 0.13; median difference -0.10 (95% confidence interval [CI]: -0.17, -0.02) × 10(-3) mm(2) /sec; P = 0.014). By either diffusion method, there was a statistically significant difference between benign and malignant mean ADC (P < 0.001). CONCLUSION: Increased lesion-to-background contrast and improved separation of benign from malignant lesions by RESOLVE compared to standard diffusion suggests that RESOLVE may show promise as an adjunct to clinical breast MRI.

Isovolumic cardiac contraction on high-temporal-resolution cine MR images: study in heart failure patients and healthy volunteers.

PURPOSE: To prospectively implement high-temporal-resolution cine magnetic resonance (MR) imaging protocol to compare cardiac preejection contraction (PEC) and prefilling relaxation (PFR) times between heart failure (HF) patients and healthy control subjects and to assess accuracy of PEC times to stratify HF patients, with ejection fraction (EF) and New York Heart Association (NYHA) symptom class as reference standards. MATERIALS AND METHODS: Following institutional review board approval of this HIPAA-compliant study and written informed consent, 18 healthy volunteers (10 women, eight men; mean age, 43 years +/- 14 [standard deviation]) and 18 HF patients (five women, 13 men; mean age, 49.8 years +/- 3) were imaged (breath-hold true fast imaging with steady-state precession, with temporal resolution of 5.6 msec at 1.5 T). By using left ventricular (LV) outflow tract acquisition, PEC phase was defined as time at QRS trigger to immediately before aortic valve opening. PFR was defined as time from initial aortic valve closure to immediately before mitral valve opening. Group means were compared (unpaired Student t test). Accuracy of PEC parameters in stratifying participants with severe systolic HF on the basis of EF and NYHA symptom class was assessed (receiver operating characteristic curve analysis). RESULTS: Compared with control subjects, HF patients had prolonged mean PEC time (40.4 msec +/- 11.8 vs 91.3 msec +/- 26, P < .001) and mean PFR time (68.3 msec +/- 26.8 vs 103.7 msec +/- 41.8, P < .01). PEC time correlated with global EF (r = -0.73, P < .001) and LV mass (r = 0.69, P < .001). For identification of patients with severe LV systolic dysfunction (EF 2), PEC time had good accuracy (AUC, 0.875 [P < .001]). CONCLUSION: It is feasible to assess isovolumic PEC and PFR phases of the cardiac cycle with high-frame-rate cine MR images, and PEC time is a surrogate measure of moderate-to-severe systolic HF.

Three-dimensional breathhold magnetization-prepared TrueFISP: a pilot study for magnetic resonance imaging of the coronary artery disease.

PURPOSE: X-ray angiography is currently the standard test for the assessment of coronary artery disease. A substantial minority of patients referred for coronary angiography have no significant coronary artery disease. The purpose of this work was the evaluation of the accuracy of a three-dimensional (3D) breathhold coronary magnetic resonance angiography (MRA) technique in detecting hemodynamically significant coronary artery stenoses in a patient population with x-ray angiographic correlation. MATERIALS AND METHODS: Sequential subjects (n = 33, M/F = 22/11, average age = 57) who were referred for conventional coronary angiography were enrolled in the study. The study protocol was approved by our institutional review board. Each subject gave written informed consent. Volume-targeted 3D breathhold coronary artery scans with ECG-triggered, segmented True Fast Imaging with Steady-state Precession (TrueFISP) were acquired for the left main (LM), left anterior descending (LAD), and right coronary arteries (RCAs). Coronary MRA was evaluated with conventional angiography as the gold standard. RESULTS: The overall sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) for diagnosing any hemodynamically significant coronary artery disease (> or =50% diameter reduction) with coronary MRA was 87%, 57%, 72%, 68%, and 80%, respectively. The sensitivity of the technique in the LM, LAD, and RCA was 100%, 83%, and 100%, respectively. The NPV of the technique in the LM, LAD, and RCA was 100%, 82%, and 100%, respectively. CONCLUSIONS: Three-dimensional breathhold True Fast Imaging with Steady-state Precession is a promising technique for coronary artery imaging. It has a relatively high sensitivity and NPV. Results of this study warrant further technical improvements and clinical evaluation of the technique.

Renal magnetic resonance angiography at 3.0 Tesla using a 32-element phased-array coil system and parallel imaging in 2 directions.

PURPOSE: The aim of the present study was to assess the feasibility of renal magnetic resonance angiography at 3.0 T using a phased-array coil system with 32-coil elements. Specifically, high parallel imaging factors were used for an increased spatial resolution and anatomic coverage of the whole abdomen. MATERIALS AND METHODS: Signal-to-noise values and the g-factor distribution of the 32 element coil were examined in phantom studies for the magnetic resonance angiography (MRA) sequence. Eleven volunteers (6 men, median age of 30.0 years) were examined on a 3.0-T MR scanner (Magnetom Trio, Siemens Medical Solutions, Malvern, PA) using a 32-element phased-array coil (prototype from In vivo Corp.). Contrast-enhanced 3D-MRA (TR 2.95 milliseconds, TE 1.12 milliseconds, flip angle 25-30 degrees , bandwidth 650 Hz/pixel) was acquired with integrated generalized autocalibrating partially parallel acquisition (GRAPPA), in both phase- and slice-encoding direction. Images were assessed by 2 independent observers with regard to image quality, noise and presence of artifacts. RESULTS: Signal-to-noise levels of 22.2 +/- 22.0 and 57.9 +/- 49.0 were measured with (GRAPPAx6) and without parallel-imaging, respectively. The mean g-factor of the 32-element coil for GRAPPA with an acceleration of 3 and 2 in the phase-encoding and slice-encoding direction, respectively, was 1.61. High image quality was found in 9 of 11 volunteers (2.6 +/- 0.8) with good overall interobserver agreement (k = 0.87). Relatively low image quality with higher noise levels were encountered in 2 volunteers. CONCLUSION: MRA at 3.0 T using a 32-element phased-array coil is feasible in healthy volunteers. High diagnostic image quality and extended anatomic coverage could be achieved with application of high parallel imaging factors.

Cardiac cine imaging at 3 Tesla: initial experience with a 32-element body-array coil.

PURPOSE: We sought to assess the feasibility of cardiac cine imaging and evaluate image quality at 3 T using a body-array coil with 32 coil elements. MATERIALS AND METHODS: Eight healthy volunteers (3 men; median age 29 years) were examined on a 3-T magnetic resonance scanner (Magnetom Trio, Siemens Medical Solutions) using a 32-element phased-array coil (prototype from In vivo Corp.). Gradient-recalled-echo (GRE) cine (GRAPPAx3), GRE cine with tagging lines, steady-state-free-precession (SSFP) cine (GRAPPAx3 and x4), and SSFP cine(TSENSEx4 andx6) images were acquired in short-axis and 4-chamber view. Reference images with identical scan parameters were acquired using the total-imaging-matrix (Tim) coil system with a total of 12 coil elements. Images were assessed by 2 observers in a consensus reading with regard to image quality, noise and presence of artifacts. Furthermore, signal-to-noise values were determined in phantom measurements. RESULTS: In phantom measurements signal-to-noise values were increased by 115-155% for the various cine sequences using the 32-element coil. Scoring of image quality yielded statistically significant increased image quality with the SSFP-GRAPPAx4, SSFP-TSENSEx4, and SSFP-TSENSEx6 sequence using the 32-element coil (P < 0.05). Similarly, scoring of image noise yielded a statistically significant lower noise rating with the SSFP-GRAPPAx4, GRE-GRAPPAx3, SSFP-TSENSEx4, and SSFP-TSENSEx6 sequence using the 32-element coil (P < 0.05). CONCLUSION: This study shows that cardiac cine imaging at 3 T using a 32-element body-array coil is feasible in healthy volunteers. Using a large number of coil elements with a favorable sensitivity profile supports faster image acquisition, with high diagnostic image quality even for high parallel imaging factors.

Coronary magnetic resonance angiography using magnetization-prepared contrast-enhanced breath-hold volume-targeted imaging (MPCE-VCATS).

OBJECTIVES: Coronary artery x-ray angiography (XRA) is currently the gold standard for the assessment of coronary artery disease. A substantial minority of patients referred for coronary angiography have no significant coronary artery disease. The purpose of this study is to evaluate magnetization-prepared contrast-enhanced breath-hold volume-targeted imaging (MPCE-VCATS), a new 3-dimensional breath-hold coronary magnetic resonance angiography (MRA) technique, in detecting hemodynamically significant coronary artery stenoses in a patient population, with XRA correlation. MATERIALS AND METHODS: A total of 19 subjects who were referred for conventional coronary angiography were enrolled in the study. ECG-triggered MPCE-VCATS coronary artery scans were acquired for the left main coronary artery (LCA), left anterior descending (LAD), and right coronary artery (RCA). Coronary MRA and XRA results were compared. RESULTS: The overall sensitivity, accuracy, and negative predictive value for diagnosing any hemodynamically significant coronary artery disease (> or =50% diameter reduction) was 91%, 80%, and 90%, respectively. The sensitivity of the technique in the LCA, LAD, and RCA was 100%, 100% and 78%, respectively. The negative predictive value of the technique was 100%, 100%, and 71%, respectively. DISCUSSION: MPCE-VCATS is a promising technique for coronary artery imaging. It has a relatively high sensitivity as well as a high NPV. The results of the study may indicate a future role for the technique in obviating the need for some patients to undergo XRA.

Comparison of gradient-echo and steady-state free precession for coronary artery magnetic resonance angiography using a gadolinium-based intravascular contrast agent.

OBJECTIVES: Intravascular contrast agents may offer longer imaging times and better vessel visualization over conventional extravascular agents for magnetic resonance coronary angiography. The purpose of this study was to evaluate the effect of intravascular contrast (B-22956/1) on coronary visualization. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were compared in inversion-recovery (IR)-prepared FLASH (fast low-angle shot) and IR-trueFISP (true fast imaging with steady-state precession) sequences before and after contrast. MATERIALS AND METHODS: Numeric simulations were performed to compare blood signals in IR-trueFISP and IR-FLASH sequences. Coronary imaging was performed in 15 swine. RESULTS: Postcontrast CNR was improved 23% with breathhold IR-FLASH and 55% with breathhold IR-trueFISP as compared with precontrast trueFISP. With free-breathing, long TR IR-FLASH provided 131% and 55.8% higher SNR and 132% and 58.7% increased CNR compared with IR-FLASH with shorter TR and IR-trueFISP, respectively. CONCLUSION: Intravascular contrast agents improve CNR and vessel visualization in coronary magnetic resonance angiography with IR-FLASH and IR-trueFISP.

Coronary artery imaging using three-dimensional breath-hold steady-state free precession with two-dimensional iterative partial fourier reconstruction.

PURPOSE: To assess the feasibility of using a two-dimensional partial Fourier (PF) reconstruction scheme to reduce the acquisition time of magnetic resonance imaging (MRI) of coronary arteries. MATERIALS AND METHODS: Symmetric k-space data sets of coronary arteries were collected in seven volunteers using a three-dimensional breath-hold steady-state free precession (SSFP) sequence. Partial, asymmetric k-space data sets were generated by removing 25% of the data in the readout direction and 25% of the data in the phase encoding direction. The missing data were then estimated using a two-dimensional projection-onto-convex-sets (POCS) algorithm or filled with zeroes. Images were reconstructed from the full data set, the PF data set, and the zero-filled (ZF) data set, respectively. Coronary artery sharpness was evaluated quantitatively and qualitatively. RESULTS: Coronary artery sharpness in PF images was comparable to that in full k-space images and significantly better than that in ZF images. CONCLUSION: Two-dimensional POCS PF reconstruction is a potentially useful technique for reducing acquisition time or improving spatial resolution for breath-hold coronary MR angiography.

Contrast-enhanced coronary artery imaging using 3D trueFISP.

An ECG-triggered, segmented, magnetization-prepared, 3D, trueFISP sequence was recently developed for coronary artery imaging. Fat saturation was achieved by a chemically selective fat saturation pulse, which is susceptible to field inhomogeneities. In addition, the blood-myocardial contrast was compromised because data were acquired during signal transience to steady state. The goals of this work were to investigate the potential benefits of T(1)-shortening agents in improving blood-myocardial contrast, and to develop a technique to make fat suppression robust to resonance offsets for coronary artery imaging using trueFISP. A magnetization-preparation scheme using saturation and inversion pulses was developed for simultaneous suppression of tissues over a wide range of T(1)'s, including myocardium and fat. An additional advantage of this method is that it is insensitive to heart rate variations. Computer simulations were used to design the magnetization preparation, and volunteer studies were performed to compare precontrast imaging to contrast-enhanced (CE) imaging. Results showed consistent fat suppression and a 78% increase in the blood-myocardial contrast-to-noise ratio (CNR) for postcontrast imaging over precontrast imaging. In conclusion, contrast agents are useful for trueFISP coronary artery imaging.

Artifact reduction in true-FISP imaging of the coronary arteries by adjusting imaging frequency.

The presence of resonance frequency offsets often causes artifacts in images acquired with true fast imaging with steady-state precession (true-FISP). One source of resonance offsets is a suboptimal setting of the synthesizer frequency. The goal of this work was to demonstrate that shifting the synthesizer frequency could minimize the off-resonance related image artifacts in true-FISP. A simple scouting method was developed to estimate the optimal synthesizer frequency for the volume of interest (VOI). To improve fat suppression, a similar scouting method was also developed to determine the optimal frequency offset for the fat saturation pulse. Coronary artery imaging was performed in healthy subjects using a 3D true-FISP sequence to validate the effectiveness of the frequency corrections. Substantial reduction in image artifacts and improvement in fat suppression were observed by using the water and fat frequencies estimated by the scouting scans. Frequency shifting is a useful and practical method for improving coronary artery imaging using true-FISP.

Coronary MR angiography: true FISP imaging improved by prolonging breath holds with preoxygenation in healthy volunteers.

In 15 healthy volunteers undergoing coronary magnetic resonance (MR) angiography, the breath-hold duration with and without preoxygenation was measured. The effect of preoxygenation on coronary artery imaging was also evaluated. A three-dimensional magnetization-prepared true fast imaging with steady-state precession sequence was employed for coronary MR angiography. All subjects showed an increase in comfortable breath-hold duration with preoxygenation. This extra imaging time allowed coronary artery imaging with increased spatial resolution.

Reduction of transient signal oscillations in true-FISP using a linear flip angle series magnetization preparation.

An electrocardiogram (ECG)-triggered, magnetization-prepared, segmented, 3D true fast imaging with steady-state precession (true-FISP) sequence with fat saturation was recently proposed for coronary artery imaging. A magnetization preparation scheme consisting of an alpha/2 radiofrequency (RF) pulse followed by 20 constant flip angle dummy RF cycles was used to reduce signal oscillations in the approach to steady state. However, if large resonance offsets on the order of 70-100 Hz are present, significant magnetization oscillations will still occur during data acquisition, which will result in image ghosting and blurring. The goal of this work was to validate that a linear flip angle (LFA) series can be used during magnetization preparation to reduce these image artifacts. Computer simulations, phantom studies, and coronary artery imaging in healthy volunteers were performed to compare this magnetization preparation scheme with that of an alpha/2 pulse followed by constant flip angle dummy RF cycles. The results demonstrated substantial reduction in the apparent image artifacts when using linearly increasing flip angles during magnetization preparation.

Three-dimensional true-FISP imaging of the coronary arteries: improved contrast with T2-preparation.

PURPOSE: To evaluate the effectiveness of a T2-magnetization preparation scheme for improving coronary artery imaging with true fast imaging with steady-state precession (True-FISP). MATERIALS AND METHODS: Simulations were performed to compare the blood-myocardium signal difference with no T2-preparation to that with various T2-preparation times (24, 40, and 60 msec) using an electrocardiogram (ECG)-triggered, segmented True-FISP acquisition. Seven volunteers were imaged to evaluate the effectiveness of T2-preparation for coronary artery delineation using True- FISP and to optimize the T2-preparation time. RESULTS: Simulations showed that T2-preparation improved the signal difference between blood and myocardium over that without T2-preparation. The optimal T2- preparation time was determined to be 40 msec. In volunteer studies, a T2- preparation time of 40 msec provided a significant improvement in contrast- to-noise ratio (CNR) between the coronary arteries and myocardium over that without T2-preparation. It also showed a significant improvement in visualizing the distal portions of the coronary arteries. CONCLUSION: T2-preparation improves coronary artery delineation with True-FISP.

Breath-hold three-dimensional true-FISP imaging of coronary arteries using asymmetric sampling.

PURPOSE: To evaluate the feasibility of using asymmetric sampling in a three-dimensional, magnetization-prepared, segmented true-FISP (fast imaging with steady-state precession) sequence in order to reduce the sensitivity to resonance offsets, while simultaneously improving imaging speed. MATERIALS AND METHODS: Asymmetric sampling reduces the repetition time, leading to reduced resonance offset effects and improved resolution in a fixed imaging time. However, it introduces additional phase terms due to blood flow, which can cause image artifacts. Computer simulations were performed to study the off-resonance and flow effects of asymmetric sampling in true-FISP. Coronary artery imaging was performed in healthy volunteers. RESULTS: Simulations and volunteer studies show that image artifacts due to flow-induced phase variations may be acceptable at low velocities. Volunteer studies demonstrate that relatively high-resolution coronary artery images can then be acquired within a single breath-hold with segmented three-dimensional true-FISP imaging using data asymmetry in the readout direction. CONCLUSION: Asymmetric sampling is a useful modification to true-FISP for reducing the off-resonance artifacts and improving imaging speed when the flow velocities are small.