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True real-time cardiac MRI in free breathing without ECG synchronization using a novel sequence with radial k-space sampling and balanced SSFP contrast mode

Bauer, Ralf W; Radtke, Isabel; Block, Kai T; Larson, Maya C; Kerl, J Matthias; Hammerstingl, Renate; Graf, Thomas G; Vogl, Thomas J; Zhang, Shuo
We investigated a novel sequence with radial k-space sampling, gridding and sliding window reconstruction with bSSFP contrast that allows for true real-time functional cardiac evaluation independent from respiration and ECG triggering. 12 healthy volunteers underwent 1.5 T cardiac MRI. Single-shot short axis views were acquired with a) standard retrospectively ECG-gated segmented breath-hold (bh) bSSFP and with the real-time radial bSSFP sequence with a nominal temporal resolution of b) 16 fps (frames per second) and c) 40 fps. Radial bSSFP were acquired during free breathing without ECG synchronization. Left ventricular functional parameters (EDV, ESV, SV and EF) were compared and quality of wall motion depiction was assessed. Contrast-to-noise-ratio (CNR) of myocardium/blood pool in the left ventricle was calculated. EF showed excellent correlation (Bland-Altman r = 0.99; Lin rho = 0.91) between bh-bSSFP (65 %) and 40 fps radial (64 %) and moderate correlation (r = 0.84, rho = 0.20) with 16 fps radial bSSFP (56 %). While EDV was in good agreement for all three sequences, ESV was significantly overestimated with 16 fps radial bSSFP. Despite lower CNR, image quality for wall motion assessment was rated significantly better for 40 fps compared to 16 fps radial bSSFP due to the faster temporal resolution. Left ventricular functional analysis with fast true real-time radial bSSFP is in good agreement with standard ECG-gated bh-bSSFP. The independency from ECG synchronization and breathing promises a robust method for patients with impaired cardiopulmonary status in whom breath-hold and good quality ECG cannot be achieved.
PMID: 23334191
ISSN: 1569-5794
CID: 489752

Free-breathing dynamic contrast-enhanced MRI of the abdomen and chest using a radial gradient echo sequence with K-space weighted image contrast (KWIC)

Kim, Kyung Won; Lee, Jeong Min; Jeon, Yong Sik; Kang, Sung Eun; Baek, Jee Hyun; Han, Joon Koo; Choi, Byung Ihn; Bang, Yung-Jue; Kiefer, Berthold; Block, Kai Tobias; Ji, Hyunjun; Bauer, Simon; Kim, Chin
OBJECTIVES: To evaluate the feasibility of free-breathing, dynamic contrast-enhanced (DCE) MRI of the abdomen and thorax using the radial-gradient-echo sequence with k-space weighted image contrast (KWIC) reconstruction. METHODS: Institutional review board approval was obtained. Fourteen patients underwent free-breathing radial DCE-MRI. Radial MRI yielded full-frame images by gridding all k-space data and time-resolved subframe images by using KWIC reconstruction technique. Using subframe KWIC images, voxel-wise perfusion maps were created. For comparison, the breath-hold conventional Cartesian 3D-gradient-echo sequence (VIBE) was also performed during the equilibrium phase. The image qualities of radial and conventional VIBE images were compared quantitatively and qualitatively. RESULTS: Radial DCE-MRI provided high spatial resolution (1.4 x 1.4 mm) and temporal resolution (4.1 s for subframe images) allowing voxel-wise perfusion mapping with negligible motion or streaking artefacts. There were no significant differences in SNR between full-frame radial images and conventional VIBE images (79.08 vs 74.80, P > 0.05). Overall image quality score of full-frame radial images was slightly lower than that of conventional VIBE images (3.88 +/- 0.59 vs. 4.31 +/- 0.97, P < 0.05), but provided clinically useful images. CONCLUSIONS: The free-breathing radial DCE-MRI can provide high spatial and temporal resolution while maintaining reasonably high image quality and thus is a feasible technique for DCE-MRI in the abdomen and thorax. KEY POINTS: * Dynamic contrast-enhanced magnetic resonance imaging (DCE) MRI is important in oncological imaging * Radial MRI with k-space weighted image contrast (KWIC) reconstruction offers potential improvements * Radial DCE-MRI provides good image quality, reduced artefacts and high spatial/temporal resolution.
PMID: 23187728
ISSN: 1432-1084
CID: 2544622

Free-breathing contrast-enhanced multiphase MRI of the liver using a combination of compressed sensing, parallel imaging, and golden-angle radial sampling

Chandarana, Hersh; Feng, Li; Block, Tobias K; Rosenkrantz, Andrew B; Lim, Ruth P; Babb, James S; Sodickson, Daniel K; Otazo, Ricardo
OBJECTIVE: The objectives of this study were to develop a new method for free-breathing contrast-enhanced multiphase liver magnetic resonance imaging (MRI) using a combination of compressed sensing, parallel imaging, and radial k-space sampling and to demonstrate the feasibility of this method by performing image quality comparison with breath-hold cartesian T1-weighted (conventional) postcontrast acquisitions in healthy participants. MATERIALS AND METHODS: This Health Insurance Portability and Accountability Act-compliant prospective study received approval from the institutional review board. Eight participants underwent 3 separate contrast-enhanced fat-saturated T1-weighted gradient-echo MRI examinations with matching imaging parameters: conventional breath-hold examination with cartesian k-space sampling volumetric interpolate breath hold examination (BH-VIBE) and free-breathing acquisitions with interleaved angle-bisection and continuous golden-angle radial sampling schemes. Interleaved angle-bisection and golden-angle data from each 100 consecutive spokes were reconstructed using a combination of compressed sensing and parallel imaging (interleaved-angle radial sparse parallel [IARASP] and golden-angle radial sparse parallel [GRASP]) to generate multiple postcontrast phases.Arterial- and venous-phase BH-VIBE, IARASP, and GRASP reconstructions were evaluated by 2 radiologists in a blinded fashion. The readers independently assessed quality of enhancement (QE), overall image quality (IQ), and other parameters of image quality on a 5-point scale, with the highest score indicating the most desirable examination. Mixed model analysis of variance was used to compare each measure of image quality. RESULTS: Images of BH-VIBE and GRASP had significantly higher QE and IQ values compared with IARASP for both phases (P < 0.05). The differences in QE between BH-VIBE and GRASP for the arterial and venous phases were not significant (P > 0.05). Although GRASP had lower IQ score compared with BH-VIBE for the arterial (3.9 vs 4.8; P < 0.0001) and venous (4.2 vs 4.8; P = 0.005) phases, GRASP received IQ scores of 3 or more in all participants, which was consistent with acceptable or better diagnostic image quality. CONCLUSION: Contrast-enhanced multiphase liver MRI of diagnostic quality can be performed during free breathing using a combination of compressed sensing, parallel imaging, and golden-angle radial sampling.
PMCID:3833720
PMID: 23192165
ISSN: 0020-9996
CID: 202342

Self-gated radial MRI for respiratory motion compensation on hybrid PET/MR systems

Grimm, Robert; Furst, Sebastian; Dregely, Isabel; Forman, Christoph; Hutter, Jana Maria; Ziegler, Sibylle I; Nekolla, Stephan; Kiefer, Berthold; Schwaiger, Markus; Hornegger, Joachim; Block, Tobias
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 mu-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.
PMID: 24505739
ISSN: 0302-9743
CID: 806942

Accelerated 3D radial imaging with 3D variational regularization [Meeting Abstract]

Knoll, Florian; Block, Kai Tobias; Bredies, Kristian; Diwoky, Clemens; Axel, Leon; Sodickson, Daniel K; Stollberger, Rudolf
ORIGINAL:0014699
ISSN: 1524-6965
CID: 4534492

COMBINATION OF COMPRESSED SENSING AND PARALLEL IMAGING FOR HIGHLY-ACCELERATED DYNAMIC MRI

Chapter by: Otazo, Ricardo; Feng, Li; Chandarana, Hersh; Block, Tobias; Axel, Leon; Sodickson, Daniel K
in: 2012 9TH IEEE INTERNATIONAL SYMPOSIUM ON BIOMEDICAL IMAGING (ISBI) by
NEW YORK : IEEE, 2012
pp. 980-983
ISBN:
CID: 2061812

Free-Breathing Radial 3D Fat-Suppressed T1-Weighted Gradient Echo Sequence: A Viable Alternative for Contrast-Enhanced Liver Imaging in Patients Unable to Suspend Respiration

Chandarana H; Block TK; Rosenkrantz AB; Lim RP; Kim D; Mossa DJ; Babb JS; Kiefer B; Lee VS
OBJECTIVE:: 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. MATERIALS AND METHODS:: 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. RESULTS:: 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 (P < 0.0001), 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 (P < 0.0001). 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. CONCLUSION:: 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
PMID: 21577119
ISSN: 1536-0210
CID: 135367

Magnetic resonance imaging in real time: advances using radial FLASH

Zhang, Shuo; Block, Kai Tobias; Frahm, Jens
PURPOSE: To develop technical advances for real-time magnetic resonance imaging (MRI) that allow for improved image quality and high frame rates. MATERIALS AND METHODS: The approach is based on a combination of fast low-angle shot (FLASH) MRI sequences with radial data sampling and view sharing of successive acquisitions. Gridding reconstructions provide images free from streaking or motion artifacts and with a flexible trade-off between spatial and temporal resolution. Immediate image reconstruction and online display is accomplished with the use of an unmodified 3 T MRI system. For receive coils with a large number of elements this process is supported by a user-selectable channel compression that is based on a principal component analysis and performed during initial preparation scans. RESULTS: In preliminary applications to healthy volunteers, real-time radial FLASH MRI visualized continuous movements of the temporomandibular joint during voluntary opening and closing of the mouth at high spatial resolution (0.75 mm in-plane) and monitored cardiac functions at high temporal resolution (20 images per second) during free breathing and without synchronization to the electrocardiogram. CONCLUSION: Real-time radial FLASH MRI emerges as a simple and versatile tool for a large range of clinical applications
PMID: 19938046
ISSN: 1522-2586
CID: 146291

Model-based iterative reconstruction for radial fast spin-echo MRI

Block, Kai Tobias; Uecker, Martin; Frahm, Jens
In radial fast spin-echo magnetic resonance imaging (MRI), a set of overlapping spokes with an inconsistent T2 weighting is acquired, which results in an averaged image contrast when employing conventional image reconstruction techniques. This work demonstrates that the problem may be overcome with the use of a dedicated reconstruction method that further allows for T2 quantification by extracting the embedded relaxation information. Thus, the proposed reconstruction method directly yields a spin-density and relaxivity map from only a single radial data set. The method is based on an inverse formulation of the problem and involves a modeling of the received MRI signal. Because the solution is found by numerical optimization, the approach exploits all data acquired. Further, it handles multicoil data and optionally allows for the incorporation of additional prior knowledge. Simulations and experimental results for a phantom and human brain in vivo demonstrate that the method yields spin-density and relaxivity maps that are neither affected by the typical artifacts from TE mixing, nor by streaking artifacts from the incomplete k-space coverage at individual echo times
PMID: 19502124
ISSN: 0278-0062
CID: 146292

Image reconstruction by regularized nonlinear inversion--joint estimation of coil sensitivities and image content

Uecker, Martin; Hohage, Thorsten; Block, Kai Tobias; Frahm, Jens
The use of parallel imaging for scan time reduction in MRI faces problems with image degradation when using GRAPPA or SENSE for high acceleration factors. Although an inherent loss of SNR in parallel MRI is inevitable due to the reduced measurement time, the sensitivity to image artifacts that result from severe undersampling can be ameliorated by alternative reconstruction methods. While the introduction of GRAPPA and SENSE extended MRI reconstructions from a simple unitary transformation (Fourier transform) to the inversion of an ill-conditioned linear system, the next logical step is the use of a nonlinear inversion. Here, a respective algorithm based on a Newton-type method with appropriate regularization terms is demonstrated to improve the performance of autocalibrating parallel MRI--mainly due to a better estimation of the coil sensitivity profiles. The approach yields images with considerably reduced artifacts for high acceleration factors and/or a low number of reference lines
PMID: 18683237
ISSN: 1522-2594
CID: 146294