Hyeon-Man Baek

University of California, Irvine, Irvine, California, United States

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Publications (8)23.91 Total impact

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    ABSTRACT: In this work, we present the feasibility of using a parallel RF transmit with multiple RF sources imaging method (MultiTransmit imaging) in polymer gel dosimetry. Image quality and B1 field homogeneity was statistically better in the MultiTransmit imaging method than in conventional single source RF transmission imaging method. In particular, the standard uncertainty of R 2 was lower on the MultiTransmit images than on the conventional images. Furthermore, the MultiTransmit measurement showed improved dose resolution. Improved image quality and B1 homogeneity results in reduced dose uncertainty, thereby suggesting the feasibility of MultiTransmit MR imaging in gel dosimetry.
    Journal of Radioanalytical and Nuclear Chemistry 06/2014; 1(1):1. · 1.41 Impact Factor
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    ABSTRACT: The purpose of this study was to develop a special proton magnetic resonance spectroscopy (1H-MRS) phantom, to establish and verify a quality assurance (QA) protocol, and to perform QA for a MR system. For a complete QA protocol, seven principal quality factors (PQFs) were measured. For evaluation of localization and quantification accuracy, two PQFs which are difficult to measure in commercial phantoms, we developed the layered dumbbell-shaped phantom. The performance sensitivity of our phantom was determined as a function of the voxel size on three occasions over ∼1 year. All MRS QA factors were optimized on two different MRI/MRS systems. The correlation between the metabolite signal intensity and the metabolite concentration was verified. The seven principal MRS QA factors studied can be used to evaluate MR spectra as well as to measure the stability of MR systems. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 35B: 168–179, 2009
    Concepts in Magnetic Resonance Part B Magnetic Resonance Engineering 07/2009; 35B(3):168 - 179. · 0.71 Impact Factor
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    ABSTRACT: To compare changes in the concentration of choline-containing compounds (tCho) and in tumor size at follow-up after neoadjuvant chemotherapy (NAC) between patients who achieved pathologic complete response (pCR) and those who did not (non-pCR). This study was approved by the institutional review board and was compliant with HIPAA; each patient gave informed consent. Thirty-five patients (mean age, 48 years +/- 11 [standard deviation]; range, 29-75 years) with breast cancer were included. Treatment included doxorubicin and cyclophosphamide followed by a taxane-based regimen. Changes in tCho and tumor size in pCR versus non-pCR groups were compared by using the two-way Mann-Whitney nonparametric test. Receiver operating characteristic (ROC) analysis was performed to differentiate between them and the area under the ROC curve (AUC) was compared. In the pCR group, the tCho level change was greater compared with change in tumor size (P = .003 at first follow-up, P = .01 at second follow-up), but they were not significantly different in the non-pCR group. Changes in tumor size and tCho level at the first follow-up study were not significantly different between the pCR and non-pCR groups but reached significance at the second follow-up. In ROC analysis, the magnetic resonance (MR) imaging and MR spectroscopic parameters had AUCs of 0.65-0.68 at first follow-up; at second follow-up, AUC for change in tumor size was 0.9, AUC for change in tCho was 0.73. Patients who show greater reduction in tCho compared with changes in tumor size are more likely to achieve pCR. The change in tumor size halfway through therapy was the most accurate predictor of pCR.
    Radiology 04/2009; 251(3):653-62. · 6.34 Impact Factor
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    International Journal of Cancer 10/2008; 123(5):1219-21. · 6.20 Impact Factor
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    ABSTRACT: Proton magnetic resonance spectroscopy ((1)H MRS) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) provide functional information, including vascular volume, vascular permeability and choline (Cho) metabolism. In this study, we applied these two imaging modalities to quantitatively characterize 36 malignant breast lesions in 32 patients and analyzed the correlation between them. Cho concentration was quantified by single-voxel (1)H MRS using water as an internal reference. The measured Cho levels ranged from 0.32 to 10.47 mmol/kg, consistent with previously reported values. In 25 mass-type lesions, the Cho concentration was significantly correlated with tumor size (r=.69, P<.0002). In addition, the Cho level was found to be significantly higher in lesions presenting as mass-type lesions compared to non-mass-type diffuse enhancements (P=.035). The enhancement kinetics from tissues covered within each MRS voxel were measured and analyzed with a two-compartmental model to obtain pharmacokinetic parameters K(trans) and k(ep). A significant correlation was found between the Cho level and the pharmacokinetic parameter k(ep) (r=.62, P<.0001), indicating that tissues with a high Cho level have higher wash-out rates in DCE MRI. The results suggest a correlation between Cho metabolism and angiogenesis activity, which might be explained by the association of Cho with cell replication and angiogenesis required to support tumor growth.
    Magnetic Resonance Imaging 05/2008; 26(4):523-31. · 2.06 Impact Factor
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    ABSTRACT: Studies specifically reporting MRI of fibrocystic change (FCC) of the breast are very few and its MRI features are not clearly known. The purpose of this study was to analyze the MRI features of FCC of the breast. Thirty-one patients with pathologically proven FCC of the breast were retrospectively reviewed. The MRI study was performed using a 1.5-T MR scanner with standard bilateral breast coil. The imaging protocol consisted of pre-contrast T1-weighed imaging and dynamic contrast-enhanced axial T1-weighed imaging. The MRI features were interpreted based on the morphologic and enhancement kinetic descriptors defined on ACR BIRADS-MRI lexicon. FCC of the breast had a wide spectrum of morphologic and kinetic features on MRI. Two types of FCC were found, including a more diffuse type of nonmass lesion (12/31, 39%) showing benign enhancement kinetic pattern with medium wash-in in early phase (9/10, 90%) and a focal mass-type lesion (11/31, 35%) with enhancement kinetic usually showing rapid up-slope mimicking a breast cancer (8/11, 73%). MRI is able to elaborate the diverse imaging features of FCC of the breast. Our result showed that FCC presenting as a focal mass-type lesion was usually overdiagnosed as malignancy. Understanding MRI of FCC is important to determine which cohort of patients should be followed up alone or receive aggressive management.
    Magnetic Resonance Imaging 05/2008; 26(9):1207-14. · 2.06 Impact Factor
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    ABSTRACT: To compare the MRI features between estrogen receptor (ER) positive and negative breast cancers. Breast MRI of 90 consecutive patients confirmed with invasive ductal carcinoma (IDC), 51 ER positive and 39 ER negative, were analyzed. The tumor morphology and dynamic contrast-enhanced (DCE) kinetics were evaluated based on the American College of Radiology (ACR) Breast Imaging Reporting and Data System (BI-RADS) MRI lexicon and compared. Enlarged axillary lymph nodes on MRI and choline (Cho) detection using MR spectroscopy (MRS) were also analyzed and compared. For patients receiving axillary node dissection the pathological nodal status was also compared. ER negative breast cancer had bigger tumors compared to ER positive cancer (3.6 +/- 2.0 cm vs. 1.8 +/- 1.3 cm, P < 0.00005). ER negative cancer was more likely to exhibit nonmass type enhancements compared to ER positive cancer (P < 0.005). Enlarged axillary lymph nodes were more frequently identified on MRI in ER negative compared to ER positive patients (P < 0.05). After excluding patients undergoing neoadjuvant chemotherapy, auxiliary lymph node status did not show significant difference between ER positive and ER negative cancer on MRI and pathology. ER negative cancer was more likely to show the malignant type enhancement kinetics (P = 0.15), rim enhancement (P = 0.15), and Cho detection on MRS (P = 0.23) compared to ER positive cancer, but it did not reach a level of statistical significance. ER negative breast cancer was more aggressive, with larger tumor size, more non-mass-type enhancement lesions, and a higher percentage showing enlarged axillary nodes on MRI. These features might be related to its poorer cellular differentiation and/or a higher angiogenesis.
    Journal of Magnetic Resonance Imaging 05/2008; 27(4):825-33. · 2.57 Impact Factor
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    ABSTRACT: PurposeTo investigate the application of MR spectroscopy using chemical-shift imaging (CSI) for characterizing human breast lesions at 1.5T, and to evaluate the diagnostic performance using ROC (receiver operating characteristics) analysis.Materials and Methods Thirty-six patients (35–73 years old, mean 52), with 27 malignant and 9 benign lesions, underwent anatomical imaging, dynamic contrast-enhanced MR imaging, and CSI. The ROC analysis was performed and the cutoff point yielding the highest accuracy was found to be a choline (Cho) signal-to-noise ratio (SNR) >3.2.ResultsThe mean Cho SNR was 2.8 ± 0.8 (range, 1.8–4.3) for the benign group and 5.9 ± 3.4 (2.1–17.5) for the malignant group (P = 0.01). Based on the criterion of Cho SNR >3.2 as malignant, CSI correctly diagnosed 22 of 27 malignant lesions and 7 of 9 benign lesions, resulting in a sensitivity of 81%, specificity of 78%, and overall accuracy of 81%. If the criterion was set higher at Cho SNR >4.0 the specificity improved to 89% but sensitivity was lowered to 67%.Conclusion The ROC analysis presented in this work could be used to set an objective diagnostic criterion depending on preferred emphasis on sensitivity or specificity. J. Magn. Reson. Imaging 2008;27:1114–1121. © 2008 Wiley-Liss, Inc.
    Journal of Magnetic Resonance Imaging 04/2008; 27(5):1114 - 1121. · 2.57 Impact Factor

Publication Stats

111 Citations
23.91 Total Impact Points

Institutions

  • 2008–2009
    • University of California, Irvine
      Irvine, California, United States
    • China Medical University Hospital
      • Department of Radiology
      Taichung, Taiwan, Taiwan