Xuna Zhao

Philips, Eindhoven, North Brabant, Netherlands

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Publications (12)24.48 Total impact

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    ABSTRACT: PurposeTo develop a novel analysis method to evaluate quantitative amide proton transfer (qAPT) effects with reduced interference of conventional magnetization transfer effect.MethodsA modified Z-spectrum is generated by a fitting procedure that achieves an effectively reduced magnetization transfer asymmetry. A qAPT map is then produced by subtraction of the original Z-spectrum from the modified version. This approach has been tested on both healthy volunteers and patients with brain tumors. Comparisons are made between the maps of qAPT and the commonly-used MTRasym(3.5 ppm) at different saturation powers. The negative background (NB) in MTRasym(3.5 ppm) image is recovered from the difference between the MTRasym(3.5 ppm) and qAPT maps.ResultsBoth qAPT and MTRasym(3.5 ppm) are strongly dependent on saturation power. At a saturation power below 2 µT, the MTRasym(3.5 ppm) map is dominated by the NB rather than the APT effects for healthy brain tissue. Similar to the MTRasym(3.5 ppm) image, the qAPT image exhibits strong and robust tumor contrast.Conclusion The newly-developed analysis method of qAPT is able to obtain a quantitative APT effect with less inferences from magnetization transfer asymmetry as compared to the conventional MTRasym(3.5 ppm) and can be used to evaluate human brain tumors at 3T. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 08/2014; · 3.27 Impact Factor
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    ABSTRACT: To demonstrate the feasibility of using chemical exchange saturation transfer (CEST) imaging to detect Parkinson's disease (PD) in patients at 3 Tesla.
    European radiology. 07/2014;
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    ABSTRACT: Purpose To investigate the influence of dual source parallel radiofrequency (RF) excitation on clinical breast MR images. Methods A 3 T MR system with both dual source and conventional single source RF excitations was used to examine 22 patients. Axial TSE-T2WI with fat suppression, TSE-T1WI without fat suppression, THRIVE (3D field echo) and DWI (SE-EPI) were obtained by using both excitation techniques. Image homogeneity, image contrast and lesion conspicuity were measured or independently scored by two radiologists and were compared by paired sample t test or Wilcoxon test. Results Both excitations revealed 24 lesions. For SE sequences using dual source mode, image homogeneity was improved (P = 0.00), scan time was reduced, and ghost artifacts on DWI were significantly reduced (P = 0.00). However, image contrast was not increased and lesion conspicuity had no significant difference between two modes, except DWI on which lesion conspicuity was significantly improved (P = 0.00), due to less ghost artifacts. For field echo sequence, image homogeneity, acquisition time, image contrast and lesion conspicuity had no significant difference between the two modes. Conclusions Dual source parallel RF transmission has some added value for improving breast image quality. However, its value is limited in terms of improving lesion detection and characterization.
    Magnetic Resonance Imaging 06/2014; · 2.06 Impact Factor
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    ABSTRACT: To investigate the neuromechanisms of perceptual learning treatment in patients with anisometropic amblyopia using functional MRI (fMRI) and diffusion tensor imaging (DTI) techniques. 20 patients with monocular anisometropic amblyopia participated in the study. Both fMRI and DTI data were acquired for each patient twice: before and after 30 days' perceptual learning treatment for the amblyopic eye. During fMRI scanning, patients viewed the stimuli with either the sound or amblyopic eye. Changes of cortical activation after treatment were evaluated. In the DTI exams, the fractional anisotropy (FA) values, apparent diffusion coefficient (ADC) values, the voxel numbers of optic radiations (ORs), and the number of tracks were compared between the ipsilateral and the contralateral ORs and also between the previous and posterior scans. Remarkable increased activation via the amblyopic eyes was found in Brodmann Area (BA) 17-19, bilateral temporal lobes, and right cingulate gyrus after the perceptual learning treatment. No significant changes were found in the FA values, ADC values, voxel numbers, and the number of tracks after the treatment. These results indicate that perceptual learning treatment for amblyopia had a positive effect on the visual cortex and temporal lobe visual areas in patients with anisometropic amblyopia.
    The British journal of ophthalmology 09/2013; · 2.92 Impact Factor
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    ABSTRACT: Previous studies have shown that the diagnostic accuracy for prostate cancer improved with diffusion tensor imaging (DTI) or quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) only. However, the efficacy of combined DTI and quantitative DCE-MRI in detecting prostate cancer at 3.0 T is still indeterminate. To investigate the utility of diffusion tensor imaging (DTI), quantitative DCE-MRI, and the two techniques combined at 3.0 T in detecting prostate cancer of the peripheral zone (PZ).Material and Methods: DTI and DCE-MRI of 33 patients was acquired prior to prostate biopsy. Regions of interest (ROIs) were drawn according to biopsy zones which were apex, mid-gland, and base on each side of the PZ. Apparent diffusion coefficient (ADC), fractional anisotropy (FA), volume transfer constant (K(trans)), and rate constant (kep) values of cancerous sextants and non-cancerous sextants in PZ were calculated. Logistic regression models were generated for DTI, DCE-MRI, and DTI + DCE-MRI. Receiver-operating characteristic (ROC) curves were used to compare the ability of these models to differentiate cancerous sextants from non-cancerous sextants of PZ. There were significant differences in the ADC, FA, K(trans), and kep values between cancerous sextants and non-cancerous sextants in PZ (P < 0.0001, P < 0.0001, P < 0.0001, and P < 0.0001, respectively). The area under curve (AUC) for DTI + DCE-MRI was significantly greater than that for either DTI (0.93 vs. 0.86, P = 0.0017) or DCE-MRI (0.93 vs. 0.84, P = 0.0034) alone. The combination of DTI and quantitative DCE-MRI has better diagnostic performance in detecting prostate cancer of the PZ than either technique alone.
    Acta Radiologica 07/2013; · 1.33 Impact Factor
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    ABSTRACT: PURPOSE: To investigate the saturation-power dependence of amide proton transfer (APT)-weighted and nuclear Overhauser enhancement-weighted image contrasts in a rat glioma model at 4.7 T. METHODS: The 9L tumor-bearing rats (n = 8) and fresh chicken eggs (n = 4) were scanned on a 4.7-T animal magnetic resonance imaging scanner. Z-spectra over an offset range of ±6 ppm were acquired with different saturation powers, followed by the magnetization transfer-ratio asymmetry analyses around the water resonance. RESULTS: The nuclear Overhauser enhancement signal upfield from the water resonance (-2.5 to -5 ppm) was clearly visible at lower saturation powers (e.g., 0.6 µT) and was larger in the contralateral normal brain tissue than in the tumor. Conversely, the APT effect downfield from the water resonance was maximized at relatively higher saturation powers (e.g., 2.1 µT) and was larger in the tumor than in the contralateral normal brain tissue. The nuclear Overhauser enhancement decreased the APT-weighted image signal, based on the magnetization transfer-ratio asymmetry analysis, but increased the APT-weighted image contrast between the tumor and contralateral normal brain tissue. CONCLUSION: The APT and nuclear Overhauser enhancement image signals in tumor are maximized at different saturation powers. The saturation power of roughly 2 μT is ideal for APT-weighted imaging at clinical B0 field strengths. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 05/2013; · 3.27 Impact Factor
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    ABSTRACT: PURPOSE: Amide proton transfer (APT) imaging is able to extend the achievable magnetic resonance imaging (MRI) contrast to the protein level. In this study, we demonstrate the feasibility of applying a turbo-spin-echo (TSE)-based, three-dimensional (3D) APT sequence into routine clinical practice for patients with brain tumors. PROCEDURES: Experiments were performed on a Philips 3-Tesla (3-T) MRI scanner using an eight-channel phased-array coil for reception. A fast 3D APT sequence with a TSE acquisition was proposed (saturation power, 2 μT; saturation time, 500 ms; 8 slices). The gradient echo (GRE)-based field-mapping technique or water-saturation-shift-referencing (WASSR) technique was used to acquire B(0) maps to correct for B(0)-induced artifacts in APT images. The test was performed on a box of homogenous protein solution, four healthy volunteers, and eight patients with high-grade gliomas. RESULTS: The experimental data from a homogenous, protein-containing phantom and healthy volunteers show that the sequence produced a uniform contrast across all slices. The average MTR(asym)(3.5 ppm) values with GRE B(0)-corrected 3D APT imaging and WASSR-corrected 3D APT imaging were both comparable to the values obtained using the undemanding single-slice acquisition. The average APT image intensity was consistently higher in the tumor core than in the peripheral edema and in the contralateral normal-appearing white matter (both P < 0.001). CONCLUSION: 3D APT imaging of brain tumors can be performed in about 5 min at 3-T using a routine, commercial eight-channel SENSE coil.
    Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 05/2012; · 2.47 Impact Factor
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    ABSTRACT: The feasibility of diffusion tensor imaging (DTI) of prostate has been confirmed by several studies. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values of prostate with healthy or pathological changes remain controversial. To investigate the efficacy of DTI at 3.0 T in diagnosing prostate cancer in the peripheral zone and to determine the normative ADC and FA values of the normal prostate. T2-weighted imaging (T2WI) and DTI of the prostate was performed in 33 cases with diagnosis confirmed by biopsy at 3.0 T MR. ADC and FA values of cancerous and non-cancerous sextants were compared. Receiver-operating characteristic (ROC) curves were used to compare the ability of ADC, FA and the two values combined in diagnosing prostate cancer in the peripheral zone. DTI data of 20 healthy young volunteers were also acquired. ADC and FA values of the normal central gland and the peripheral zone were compared. ADC value (1.10 ± 0.09 × 10(-3) mm(2)/s) was lower while FA value (0.37 ± 0.05) was higher in normal central gland, compared with that in normal peripheral zone (1.63 ± 0.15 × 10(-3) mm(2)/s, 0.21 ± 0.07, respectively) (P < 0.0001, P < 0.0001, respectively). Sixteen of 33 cases were confirmed to be malignant while 17 of 33 cases were benign. All the 198 sextants were confirmed by biopsy, including 136 non-cancerous sextants and 62 cancerous sextants. There were significant differences between cancerous sextants (1.02 ± 0.16 × 10(-3) mm(2)/s, 0.38 ± 0.09) and non-cancerous sextants (1.22 ± 0.14 × 10(-3) mm(2)/s, 0.31 ± 0.06) for both ADC and FA values (P <0.0001, P <0.0001, respectively). Significant differences were noted between the AUC of DTI and FA alone (0.86 vs. 0.76, P = 0.0009), but no differences between the AUC of DTI and ADC alone (0.86 vs. 0.84, P = 0.1595). ADC and FA values of normal prostate may be compatible with the microstructural organization of prostate. Furthermore, DTI may be a potential tool in diagnosing prostate cancer in the peripheral zone.
    Acta Radiologica 05/2011; 52(7):813-7. · 1.33 Impact Factor
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    ABSTRACT: MR elastography is a new imaging tool capable of non-invasively assessing the viscoelastic properties of tissues. The clinical application of MR elastography in the diagnosis of prostate cancer remains to be elucidated. To investigate the feasibility of MR elastography in the diagnosis of prostate cancer at 3.0T, and to assess the elasticity and viscosity of prostate cancer and benign prostatic disease. Eight patients (63 ± 7.25 years old) with 12 foci of prostate cancer and 10 patients (59 ± 3.25 years old) with 14 foci of prostatitis in the peripheral zone were evaluated by MRE. Ten healthy volunteers (41 ± 4.32 years old) with 18 ROIs in the peripheral zone of the prostate were also assessed with MR elastography as a control group. The results were confirmed by histopathological findings. All examinations were performed on a 3.0T Philips Achieva scanner. MRE was implemented by transmitting low-frequency longitudinal mechanical waves of 100Hz into the prostate with a transducer placed above the pubic bones. The phase images were reconstructed to acquire viscoelastic mapping. T-test was used to compare the mean elasticity and viscosity of prostate cancer and prostatitis. A comparison of prostate cancer and healthy prostate tissue in elasticity was also evaluated. The correlation of elasticity and Gleason scores between prostate cancer and prostatitis were retrospectively analyzed with Pearson Correlation. The mean elasticity and viscosity were significantly higher in the lesions with prostate cancer (6.55 ± 0.47 kPa, 6.56 ± 0.99 Pa.s, respectively) than in regions with prostatitis (1.99 ± 0.66 kPa, 2.13 ± 0.21 Pa.s). The difference between prostate cancer and prostatitis was statistically significant (t = 19.392, p < 0.01; t = 16.372, p < 0.01). The elasticity and viscosity of the healthy peripheral zone of prostate were 2.26 ± 0.45 kPa, 2.38 ± 0.54 Pa.s, respectively. There also was significant difference in elasticity between prostate cancer and normal peripheral zone (t = 25.136, p < 0.01). In addition, we observed a positive correlation between Gleason scores and elasticity of the prostate cancer (r = 0.913, P < 0.01) in this study. MR elastography can be used to visualize the difference in stiffness between prostate cancer and benign prostatic disease. It is a new imaging method with potential in the diagnosis of prostate cancer.
    Acta Radiologica 04/2011; 52(3):354-8. · 1.33 Impact Factor
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    ABSTRACT: Amide proton transfer (APT) imaging is capable of detecting mobile cellular proteins and peptides in tumor and monitoring pH effects in stroke, through the saturation transfer between irradiated amide protons and water protons. In this work, four healthy subjects, eight brain tumor patients (four with high-grade glioma, one with lung cancer metastasis, and three with meningioma), and four stroke patients (average 4.3 ± 2.5 days after the onset of the stroke) were scanned at 3 T, using different radiofrequency saturation powers. The APT effect was quantified using the magnetization transfer ratio (MTR) asymmetry at 3.5 ppm with respect to the water resonance. At a saturation power of 2 μT, the measured APT-MRI signal of the normal brain tissue was almost zero, due to the contamination of the negative conventional magnetization transfer ratio asymmetry. This irradiation power caused an optimal hyperintense APT-MRI signal in the tumor and an optimal hypointense signal in the stroke, compared to the normal brain tissue. The results suggest that the saturation power of 2 μT is ideal for APT imaging of these two pathologies at 3 T with the existing clinical hardware.
    Magnetic Resonance in Medicine 03/2011; 66(4):1033-41. · 3.27 Impact Factor
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    ABSTRACT: In this paper, a low-noise preamplifier for MRI is designed and studied. A noise matching network consisting of three elements is presented. To the single-stage AsGa-FET preamplifier working at 128 MHz, the measured gain through network analyzer (HP8712C) and noise figure through noise figure analyzer (8970B) are 25 and 0.43 dB, respectively.
    Science China Technological Sciences 01/2011; 54(7):1766-1770. · 1.19 Impact Factor
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    ABSTRACT: To shorten scanning time and increase the feasibility of experimental results, we performed right coronary artery magnetic resonance angiography (CMRA) at 3.0 T using dual acceptance window weighting function in 25 normal subjects. We examined these subjects using conventional navigator with fixed gating window and 6 dual acceptance window weighted gating (DAWG) sequences with different central weighted ratio (CWR). Compared with the conventional navigator sequence, DAWG sequences with CWRs of 20% and 25% increased the scanning efficiency by 30% and 26% respectively (P<.05), while maintaining good image quality; further the corresponding scanning time decreased from 2.12-1.64 and 1.69 min, respectively (P<.05). However, CWRs less than 15% caused image degradation to some extent. The coronary artery lengths and diameters did not show statistically significant differences between the two techniques (P>.05). Briefly, to avoid the problems caused by low navigator efficiency and to maintain comparable image quality, the weighted gating parameters of 3 mm width central acceptance window and 15 mm width outer acceptance window with CWR between 20% and 25% are recommended for right CMRA at 3 T.
    Magnetic Resonance Imaging 07/2010; 28(6):797-801. · 2.06 Impact Factor

Publication Stats

54 Citations
24.48 Total Impact Points

Institutions

  • 2014
    • Philips
      Eindhoven, North Brabant, Netherlands
  • 2010–2014
    • Peking University
      • • Institute of Heavy Ion Physics
      • • Department of Physics
      • • School of Physics
      Peping, Beijing, China