Kyunghyun Sung

Transmit B1+ field inhomogeneity and T1 estimation errors in breast DCE-MRI at 3 tesla

To quantify B1+ variation across the breasts and to evaluate the accuracy of precontrast T1 estimation with and without B1+ variation in breast MRI patients at 3 Tesla (T).

Compressed-sensing multispectral imaging of the postoperative spine.

To apply compressed sensing (CS) to in vivo multispectral imaging (MSI), which uses additional encoding to avoid magnetic resonance imaging (MRI) artifacts near metal, and demonstrate the feasibility of CS‐MSI in postoperative spinal imaging.

Simultaneous T1 and B1+ Mapping Using Reference Region Variable Flip Angle Imaging

To present a new method that can simultaneously and efficiently measure T1 and B1+ maps using reference region variable flip angle (RR‐VFA) imaging.

Deep learning with domain adaptation for accelerated projection-reconstruction MR

The radial k‐space trajectory is a well‐established sampling trajectory used in conjunction with magnetic resonance imaging. However, the radial k‐space trajectory requires a large number of radial lines for high‐resolution reconstruction. Increasing the number of radial lines causes longer acquisition time, making it more difficult for routine clinical use. On the other hand, if we reduce the number of radial lines, streaking artifact patterns are unavoidable. To solve this problem, we propose a novel deep learning approach with domain adaptation to restore high‐resolution MR images from under‐sampled k‐space data.

Reducing Artifacts during Arterial Phase of Gadoxetate Disodium–enhanced MR Imaging: Dilution Method versus Reduced Injection Rate

Purpose To compare two contrast material-administration protocols (dilution vs slow injection) in terms of their effectiveness in arterial phase artifact reduction at gadoxetic acid-enhanced magnetic resonance (MR) imaging. Materials and Methods This HIPAA-compliant retrospective case-controlled cohort study was approved by the institutional review board, with a waiver of informed patient consent. A total of 318 consecutive patients undergoing gadoxetic acid-enhanced MR imaging were placed into one of two subcohorts of 159 consecutive patients each: the dilution subcohort (gadoxetic acid was diluted 1:1 with saline and injected at a rate of 2.0 mL/sec) and the slow injection subcohort (gadoxetic acid was not diluted and was injected at a rate of 1.0 mL/sec). Eighty-nine patients in the dilution subcohort also underwent follow-up MR imaging with the slow injection method, and 34 patients in the slow injection subcohort underwent follow-up MR imaging with the dilution method. Both patient- and image-based analyses, as well as intraindividual analysis, were used to compare two parameters-mean artifact score rated by two observers using a five-point scale and frequency of severe artifact-between the dilution and slow injection subcohorts with the Wilcoxon Mann-Whitney test, χ2 test, and generalized estimating equation. Results In both patient- and image-based analyses, the mean artifact score and frequency of severe artifact were lower in the dilution subcohort (mean, 1.46% and 3.8% [six of 159]) than in the slow injection subcohort (mean, 1.95% and 15.1% [24 of 159]) (P ≤ .001 and P < .001, respectively). In intraindividual analysis, both variables were also decreased in the dilution subcohort (P = .007 and P = .001, respectively). We found the two variables to be significantly increased in the slow injection subcohort when compared with that in the dilution subcohort for three different MR platforms (P < .05). Conclusion In comparison with slow injection of undiluted contrast material at a rate of 1.0 mL/sec, gadoxetic acid diluted to 50% and injected at a rate of 2 mL/sec had a significantly less severe ghosting artifact in the arterial phase of gadoxetic acid-enhanced MR imaging.

Rapid quantitative T2 mapping of the prostate using three-dimensional dual echo steady state MRI at 3T.

To develop and evaluate a rapid three‐dimensional (3D) quantitative T2 mapping method for prostate cancer imaging using dual echo steady state (DESS) MRI at 3T.

Contrast Enhancement Patterns after Irreversible Electroporation: Experimental Study of CT Perfusion Correlated to Histopathology in Normal Porcine Liver

PURPOSE To analyze ablated tissue zones after irreversible electroporation (IRE) of porcine liver using computed tomography (CT) perfusion imaging with histopathologic correlation. MATERIALS AND METHODS Under ultrasound and CT guidance, 10 IRE ablations were performed percutaneously in three Yorkshire pigs using a single bipolar electrode. CT perfusion imaging was performed in all pigs immediately after ablation and on day 2. Pathologic sections were prepared for correlation with histopathology (hematoxylin-eosin and terminal deoxynucleotidyl transferase dUTP nick end labeling stains, 5-mm-thick slices). The short diameter of different enhancing zones on CT was correlated with the gross specimen. RESULTS CT perfusion images showed three differently enhancing zones: zone 1, inner nonenhancing zone; zone 2, middle well-defined progressive internal enhancement zone; and zone 3, outer ill-defined arterial enhancement zone with rapid washout. On histopathology, zone 1 showed a strong correlation with a pale zone, and zone 2 correlated with a red zone, together accounting for the extent of cell death. Zone 3 was outside of the ablation zone and contained inflammatory cells. Each enhancing zone had different perfusion parameters. CONCLUSIONS CT perfusion imaging in the acute setting effectively demonstrates histopathologic tissue zones after IRE ablation. Zone 2 is unique to IRE not seen in thermal ablation, characterized by progressive intra-zonal enhancement, and its outer boundary defines the extent of cell death.

High‐frequency subband compressed sensing MRI using quadruplet sampling

To present and validate a new method that formalizes a direct link between k‐space and wavelet domains to apply separate undersampling and reconstruction for high‐ and low‐spatial‐frequency k‐space data.

Location constrained approximate message passing for compressed sensing MRI

Iterative thresholding methods have been extensively studied as faster alternatives to convex optimization methods for solving large‐sized problems in compressed sensing. A novel iterative thresholding method called LCAMP (Location Constrained Approximate Message Passing) is presented for reducing computational complexity and improving reconstruction accuracy when a nonzero location (or sparse support) constraint can be obtained from view shared images. LCAMP modifies the existing approximate message passing algorithm by replacing the thresholding stage with a location constraint, which avoids adjusting regularization parameters or thresholding levels. This work is first compared with other conventional reconstruction methods using random one‐dimention signals and then applied to dynamic contrast‐enhanced breast magnetic resonance imaging to demonstrate the excellent reconstruction accuracy (less than 2% absolute difference) and low computation time (5–10 s using Matlab) with highly undersampled three‐dimentional data (244 × 128 × 48; overall reduction factor = 10). Magn Reson Med 70:370–381, 2013.

Free-breathing liver fat quantification using a multiecho 3D stack-of-radial technique: Free-Breathing Radial Liver Fat Quantification

The diagnostic gold standard for nonalcoholic fatty liver disease is an invasive biopsy. Noninvasive Cartesian MRI fat quantification remains limited to a breath‐hold (BH). In this work, a novel free‐breathing 3D stack‐of‐radial (FB radial) liver fat quantification technique is developed and evaluated in a preliminary study.