Diffusion tensor field estimation based on 3D U-Net and diffusion tensor imaging model constraint / 南方医科大学学报

OBJECTIVE@#To propose a diffusion tensor field estimation network based on 3D U-Net and diffusion tensor imaging (DTI) model constraint (3D DTI-Unet) to accurately estimate DTI quantification parameters from a small number of diffusion-weighted (DW) images with a low signal-to-noise ratio.@*METHODS@#The input of 3D DTI-Unet was noisy diffusion magnetic resonance imaging (dMRI) data containing one non-DW image and 6 DW images with different diffusion coding directions. The noise-reduced non-DW image and accurate diffusion tensor field were predicted through 3D U-Net. The dMRI data were reconstructed using the DTI model and compared with the true value of dMRI data to optimize the network and ensure the consistency of the dMRI data with the physical model of the diffusion tensor field. We compared 3D DTI-Unet with two DW image denoising algorithms (MP-PCA and GL-HOSVD) to verify the effect of the proposed method.@*RESULTS@#The proposed method was better than MP-PCA and GL-HOSVD in terms of quantitative results and visual evaluation of DW images, diffusion tensor field and DTI quantification parameters.@*CONCLUSION@#The proposed method can obtain accurate DTI quantification parameters from one non-DW image and 6 DW images to reduce image acquisition time and improve the reliability of quantitative diagnosis.

Evaluation of renal oxygenation in rats with acute aristolochic acid nephropathy using blood oxygenation level-dependent magnetic resonance imaging / 南方医科大学学报

OBJECTIVE@#To evaluate the changes in renal oxygenation in rats with acute aristolochic acid nephropathy using blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) at 7.0T.@*METHODS@#Wistar rats were randomly divided into AAN group (=18) and control group (=6) for intraperitoneal injections of AAI at 40 mg/kg and PEG400, respectively, on a daily basis for 6 consecutive days. All the control rats and 6 rats from AAN group underwent BOLD MRI scan before and at 2, 4, and 6 days after the initial injection for measuring renal cortical and medullary R2 values. At each of the 4 time points, 3 rats in AAN group were sacrificed for histological evaluation; the control rats were examined at 6 days after the initial injection.@*RESULTS@#The cortical and medullary R2 values of the rats in AAN group on days 4 and 6 were significantly higher than those in the control group ( < 0.05). In AAN group, the cortical R2 values showed no obvious changes on day 2 as compared with the baseline values, but increased significantly on day 4 ( < 0.05) and day 6 ( < 0.01); the medullary R2 values increased progressively and were significantly higher than the baseline values on day 4 ( < 0.01) and day 6 ( < 0.01). In the control group, no significant changes were detected in either cortical or medullary R2 values throughout the experiment.@*CONCLUSIONS@#BOLD MRI allows non-invasive measurement of renal oxygenation levels in rats with AAN. The increase of renal cortical and medullary R2 values, and particularly the latter, indicates a lowered renal oxygenation level, which provides potentially useful information for clinical decisions.

Elimination of Gibbs artifact based on local subpixel shift and interlaced local variation / 南方医科大学学报

OBJECTIVE@#To extend the application of Gibbs artifact reduction method that exploits local subvoxel- shifts (LSS) to zero- padded k-space magnetic resonance imaging (MRI) data.@*METHODS@#We investigated two approaches to extending the application of LSS-based method to under-sampled data. The first approach, namely LSS+ interpolation, utilized the original LSS-based method to minimize the local variation on nonzero-padding reconstructed images, followed by image interpolation to obtain the final images. The second approach, interlaced local variation, used zero-padded Fourier transformation followed by elimination of Gibbs artifacts by minimizing a novel interlaced local variations (iLV) term. We compared the two methods with the original LSS and Hamming window filter algorithms, and verified their feasibility and robustness in phantom and data.@*RESULTS@#The two methods proposed showed better performance than the original LSS and Hamming window filters and effectively eliminated Gibbs artifacts while preserving the image details. Compared to LSS + interpolation method, iLV method better preserved the details of the images.@*CONCLUSIONS@#The iLV and LSS+interpolation methods proposed herein both extend the application of the original LSS method and can eliminate Gibbs artifacts in zero-filled k-space data reconstruction images, and iLV method shows a more prominent advantage in retaining the image details.

Preliminary application study of quantitative susceptibility mapping in evaluating the osteoporosis / 中华放射学杂志

Objective To explore the efficacy of quantitative susceptibility mapping (QSM) in the assessment of osteoporosis and the impact factors on the QSM values.Methods A total of 105 volunteers (35 males and 70 females) were recruited in this study.The height,weight,waistline and hipline were measured,and the body mass index was calculated.All the subjects underwent MRI-based QSM and quantitative computed tomography (QCT).The measurement of QSM and QCT values was performed on L3 vertebrae body.According to QCT value,the subjects were divided into three groups (normal,osteopenia and osteoporosis).According to age,the subjects were divided into group I (21-30 years old),group 2 (31-40 years old),group 3 (41-50 years old),group 4 (51-60 years old),and group 5 (＞60 years old).Differences among all groups were compared using one-way ANOVA or Kruskal-Wallis.Results According to QCT value,54 subjects were normal,22 osteopenic and 29 osteoporotic.The QSM value for the subjects with osteoporosis [148.60(109.42,188.81)ppb] was significantly higher than that of normal (P＜0.001)and the osteopenia (P＜0.001).The QSM value for the subjects with osteopenia was significantly higher than the normal (P＜0.001).The coefficient of QSM and BMD was-0.749 (P＜0.001).Multiple linear regression showed age was the independent influence factor for QSM value (r=0.72,P＜0.001),whereas the gender,BMI,waistline and hipline showed no significant difference (P＞0.05).With the increasing of age,the QSM value showed a gradual increasing trend.And there were significant differences of QSM values among the different age groups (P＜0.001).The QSM value of 138.98 (100.37,183.84)ppb for group 5 (＞60 years old) was significantly higher than that of group 1,group 2,and group 3 (P＜0.001).There is no difference between group 5 and group 4 (P＞0.05).The QSM value of 96.62(28.62,143.99)ppb for group 4 (51-60 years old) was significantly higher than that of group 1 and group 2 (P＜0.001).And there was no difference between group 4 and group 3 (P＞0.05).The QSM value of group 1,group 2,and group 3 showed no significant difference (P＞0.05).Conclusions The QSM of bone is feasible in the assessment of osteoporosis and has the potential to be a biomarker providing new insights into osteoporosis.And age is the critical factor affecting QSM value.

An automatic subregion delineation method for T2 measurement of articular cartilage in the knee / 南方医科大学学报

<p><b>OBJECTIVE</b>To propose a new method for automatic segmentation of manually determined knee articular cartilage into 9 subregions for T2 measurement.</p><p><b>METHODS</b>The middle line and normal line were automatically obtained based on the outline of articular cartilage manually drawn by experienced radiologists. The region of articular cartilage was then equidistantly divided into 3 layers along the direction of the normal line, and each layer was further equidistantly divided into 3 segments along the direction of the middle line. Finally the mean T2 value of each subregion was calculated. Bland-Altman analysis was used to evaluate the agreement between the proposed and manual subregion segmentation methods.</p><p><b>RESULTS</b>The 95% limits of agreement of manual and automatic methods ranged from -3.04 to 3.20 ms, demonstrating a narrow 95% limits of agreement (less than half of the minimum average). The coefficient of variation between the manual and proposed subregion methods was 4.04%.</p><p><b>CONCLUSION</b>The proposed subregion segmentation method shows a good agreement with the manual segmentation method and minimizes potential subjectivity of the manual method.</p>

Low-dose CT perfusion imaging based on pre-scan regulation and on reconstruction with sparsity constraints / 生物医学工程学杂志

The long-period CT perfusion imaging leads to an excess amount of radiation dose to the patient. However, the radiation dose could be significantly reduced if a previous normal-dose image is acquired before a set of low-dose scans of perfusion, and a filtering processing is performed on the differences between the current low-dose images and the previous normal-dose image, then the results are added to the previous image. But the selection of plenty of parameters makes the algorithm complicated. This paper proposes an innovative approach performed in sinogram domain instead of in image domain. First a normal-dose image and a set of low-dose projection data are acquired before the perfusion. Second the perfusion information is commendably reconstructed with sparsity constraints of the differences between current low-dose perfusion sinograms and previous low-dose sinogram. Finally, the reconstructed perfusion information is added to the previous normal-dose image. The proposed method was validated by simulated experiments with a set of brain CT perfusion images, which showed that the new method provided more accurate perfusion information; the time-attenuation curve was more close to that for normal-dose scan and the mean transit time more repeatable.

A new algorithm for affine motion compensation in PROPELLER MRI based on image domain / 生物医学工程学杂志

Affine motion is common during PROPELLER magnetic resonance imaging (MRI) in abdomen or other soft tissues. The current algorithm, up till now, for affine motion compensation is based on frequency domain, which compensates the motion in k space and then reconstruct the final image based on gridding method. But aliasing and some tiny artifacts may exist. This paper proposed a new algorithm for affine motion compensation based on image domain. Firstly, exact affine motion information was obtained through the image registration, secondly k space coordinate was corrected for compensating the k space strips sampling density, then the images obtained from inverse FFT was compensated using motion information, finally the final results were composited after rotation. The experimental results showed that the proposed method could more effectively suppress the motion artifacts compared to the current algorithm.

Decoupling of multi-channel RF coil and its application in the intraoperative MRI / 生物医学工程学杂志

The coupling from different elements of the multi-channel coil leads to the splitting of the resonance frequency and deviation from the Lamor frequency. Decoupling between different elements is the key technology in the design of the radiofrequency (RF) coil. The electrical decoupling circuits should vary with different arrangements of the elements. A novel method of decoupling for the RF coil used in the intraoperative MR-guided focused ultrasound system is reported in the paper. The prototype RF coil was made according to the proposed decoupling method. The bench test of the prototype showed that the performance of the decoupling of the coil was excellent. The images in vivo were acquired with the designed prototype RF coil.