Rapid volumetric T1 mapping of the abdomen using three-dimensional through-time spiral GRAPPA.

PURPOSE: To develop an ultrafast T1 mapping method for high-resolution, volumetric T1 measurements in the abdomen. METHODS: The Look-Locker method was combined with a stack-of-spirals acquisition accelerated using three-dimensional (3D) through-time spiral GRAPPA reconstruction for fast data acquisition. A segmented k-space acquisition scheme was proposed and the time delay between segments for the recovery of longitudinal magnetization was optimized using Bloch equation simulations. The accuracy of this method was validated in a phantom experiment and in vivo T1 measurements were performed with 35 asymptomatic subjects on both 1.5 Tesla (T) and 3T MRI systems. RESULTS: Phantom experiments yielded close agreement between the proposed method and gold standard measurements for a large range of T1 values (200 to 1600 ms). The in vivo results further demonstrate that high-resolution T1 maps (2 × 2 × 4 mm(3)) for 32 slices can be achieved in a single clinically feasible breath-hold of approximately 20 s. The T1 values for multiple organs and tissues in the abdomen are in agreement with the published literature. CONCLUSION: A high-resolution 3D abdominal T1 mapping technique was developed, which allows fast and accurate T1 mapping of multiple abdominal organs and tissues in a single breath-hold.

Evaluation of left ventricular ejection fraction using through-time radial GRAPPA.

BACKGROUND: The determination of left ventricular ejection fraction using cardiovascular magnetic resonance (CMR) requires a steady cardiac rhythm for electrocardiogram (ECG) gating and multiple breathholds to minimize respiratory motion artifacts, which often leads to scan times of several minutes. The need for gating and breathholding can be eliminated by employing real-time CMR methods such as through-time radial GRAPPA. The aim of this study is to compare left ventricular cardiac functional parameters obtained using current gold-standard breathhold ECG-gated functional scans with non-gated free-breathing real-time imaging using radial GRAPPA, and to determine whether scan time or the occurrence of artifacts are reduced when using this real-time approach. METHODS: 63 patients were scanned on a 1.5T CMR scanner using both the standard cardiac functional examination with gating and breathholding and the real-time method. Total scan durations were noted. Through-time radial GRAPPA was employed to reconstruct images from the highly accelerated real-time data. The blood volume in the left ventricle was assessed to determine the end systolic volume (ESV), end diastolic volume (EDV), and ejection fraction (EF) for both methods, and images were rated for the presence of artifacts and quality of specific image features by two cardiac readers. Linear regression analysis, Bland-Altman plots and two-sided t-tests were performed to compare the quantitative parameters. A two-sample t-test was performed to compare the scan durations, and a two-sample test of proportion was used to analyze the presence of artifacts. For the reviewers´ ratings the Wilcoxon test for the equality of the scores' distributions was employed. RESULTS: The differences in EF, EDV, and ESV between the gold-standard and real-time methods were not statistically significant (p-values of 0.77, 0.82, and 0.97, respectively). Additionally, the scan time was significantly shorter for the real-time data collection (p<0.001) and fewer artifacts were reported in the real-time images (p<0.01). In the qualitative image analysis, reviewers marginally preferred the standard images although some features including cardiac motion were equivalently rated. CONCLUSION: Real-time functional CMR with through-time radial GRAPPA performed without ECG-gating under free-breathing can be considered as an alternative to gold-standard breathhold cine imaging for the evaluation of ejection fraction in patients.

Parallel imaging-based reduction of acoustic noise for clinical magnetic resonance imaging.

OBJECTIVES: The objective of this study was to demonstrate the feasibility of improving perceived acoustic comfort for a standard clinical magnetic resonance imaging protocol via gradient wave form optimization and validate parallel imaging as a means to achieve a further reduction of acoustic noise. MATERIALS AND METHODS: The gradient wave forms of a standard T2 axial turbo spin-echo (TSE) sequence in head examinations were modified for acoustic performance while attempting to keep the total acquisition and inter-echo spacing the same. Parallel imaging was then used to double the inter-echo spacing and allow further wave form optimization. Along with comparative acoustic noise measurements, a statistical analysis of radiologist scoring was conducted on volumes from standard and modified sequences acquired from 10 patients after informed consent was obtained. RESULTS: Compared with TSE, significant improvement of acoustic comfort was measured for modified-sequences quiet TSE and quiet TSE with generalized autocalibrating partially parallel acquisitions (P = 0.0034 and P = 0.0003, respectively), and no statistically significant difference in diagnostic quality was observed without the use of parallel imaging. CONCLUSIONS: Standard clinical magnetic resonance imaging protocols can be made quieter through adequate gradient wave form optimization. In scans with high signal-to-noise ratio, parallel imaging can be used to further reduce acoustic noise.

A comparison of computer-aided detection (CAD) effectiveness in pulmonary nodule identification using different methods of bone suppression in chest radiographs.

This study aimed to compare the diagnostic effectiveness of computer-aided detection (CAD) software (OnGuard™ 5.2) in combination with hardware-based bone suppression (dual-energy subtraction radiography (DESR)), software-based bone suppression (SoftView™, version 2.4), and standard posteroanterior images with no bone suppression. A retrospective pilot study compared the diagnostic performance of two commercially available methods of bone suppression when used with commercially available CAD software. Chest images from 27 patients with computed tomography (CT) and pathology-proven malignant pulmonary nodules (8-34 mm) and 25 CT-negative patient controls were used for analysis. The Friedman, McNemar, and chi-square tests were used to compare diagnostic performance and the kappa statistic was used to evaluate method agreement. The average number of regions of interest and false-positives per image identified by CAD were not found to be significantly different regardless of the bone suppression methods evaluated. Similarly, the sensitivity, specificity, and test efficiency were not found to be significantly different. Agreement between the methods was between poor and excellent. The accuracy of CAD (OnGuard™, version 5.2) is not statistically different with either DESR or SoftView™ (version 2.4) bone suppression technology in digital chest images for pulmonary nodule identification. Low values for sensitivity (<80 %) and specificity (<50 %) may limit their utility for clinical radiology.

Low-rank and sparse matrix decomposition for compressed sensing reconstruction of magnetic resonance 4D phase contrast blood flow imaging (loSDeCoS 4D-PCI).

Blood flow measurements using 4D Phase Contrast blood flow imaging (PCI) provide an excellent fully non-invasive technique to assess the hemodynamics clinically in-vivo. Iterative reconstruction techniques combined with parallel MRI have been proposed to reduce the data acquisition time, which is the biggest drawback of 4D PCI. The novel LoSDeCoS technique combines these ideas with the separation into a low-rank and a sparse component. The high-dimensionality of the PC data renders it ideally suited for this approach. The proposed method is not limited to a single body region, but can be applied to any 4D flow measurement. The benefits of the new method are twofold: It allows to significantly accelerate the acquisition; and generates additional images highlighting temporal and directional flow changes. Reduction in acquisition time improves patient comfort and can be used to achieve better temporal or spatial resolution, which in turn allows more precise calculations of clinically important quantitative numbers such as flow rates or the wall shear stress. With LoSDeCoS, acceleration factors of 6-8 were achieved for 16 in-vivo datasets of both the carotid artery (6 datasets) and the aorta (10 datasets), while decreasing the Normalized Root Mean Square Error by over 10 % compared to a standard iterative reconstruction and by achieving similarity values of over 0.93. Inflow-Outflow phantom experiments showed good parabolic profiles and an excellent mass conservation.