Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Kawakubo Masateru Last modified date:2022.05.25

Assistant Professor / Department of Health Sciences / Faculty of Medical Sciences


Papers
1. Kawakubo M*, **, Moriyama D**, Yamasaki Y, Abe K, Hosokawa K, Moriyama T, Triadyaksa P, Wibowo A, Nagao M, Arai H, Nishimura H, Kadokami T. *Corresponding author, **Equal contribution., Right ventricular strain and volume analyses through deep learning‐based fully automatic segmentation based on radial long‐axis reconstruction of short‐axis cine magnetic resonance images, Magnetic Resonance Materials in Physics, Biology and Medicine, doi.org/10.1007/s10334-022-01017-3, 2022.05,
Objective We propose a deep learning-based fully automatic right ventricle (RV) segmentation technique that targets radially reconstructed long-axis (RLA) images of the center of the RV region in routine short axis (SA) cardiovascular magnetic resonance (CMR) images. Accordingly, the purpose of this study is to compare the accuracy of deep learning-based fully automatic segmentation of RLA images with the accuracy of conventional deep learning-based segmentation in SA orientation in terms of the measurements of RV strain parameters.
Materials and methods We compared the accuracies of the above-mentioned methods in RV segmentations and in measuring RV strain parameters by Dice similarity coefficients (DSCs) and correlation coefficients.
Results DSC of RV segmentation of the RLA method exhibited a higher value than those of the conventional SA methods (0.84 vs. 0.61). Correlation coefficient with respect to manual RV strain measurements in the fully automatic RLA were superior to those in SA measurements (0.5–0.7 vs. 0.1–0.2).
Discussion Our proposed RLA realizes accurate fully automatic extraction of the entire RV region from an available CMR cine image without any additional imaging. Our findings overcome the complexity of image analysis in CMR without the limitations of the RV visualization in echocardiography..
2. Masateru Kawakubo, Michinobu Nagao, Risako Nakao, Eri Watanabe, Masami Yoneyama, Nobuhisa Hagiwara, and Shuji Sakai., Decelerated Dark Flow Measured Using Steady-State Free Precession Magnetic Resonance Imaging for Specific Detection of Left Ventricular Myocardial Strain and Dyssynchrony in Dilated Cardiomyopathy, Cardiovascular Imaging Asia, doi.org/10.22468/cvia.2021.00339, 6, 1, 4-12, 2022.01, [URL],
Objective
In steady-state free precession (SSFP) cine imaging, signal loss can be observed as accelerated dark flow in patients with valvular disease and decelerated dark flow (DDF) in patients with severe left ventricular (LV) dysfunction. In our study, we measured DDF with optical flow calculations and investigated the relationship between DDF and myocardial strain or intraventricular dyssynchrony.
Materials and Methods
Fifty-seven consecutive patients with heart failure were retrospectively enrolled. In the short-axis orientation, the optical flow magnitude vector of the DDF was calculated over a cardiac cycle. The maximum value of the mean magnitude vector in the LV blood region was defined as the DDF index. The systolic circumferential strain (CS) of the LV free-wall, as well as the absolute difference in systolic timing of the LV free-wall and interventricular septum (LV dyssynchrony, LVD), was measured using the feature-tracking method. Spearman’s correlation coefficients (ρ) were calculated between DDF and CS or LVD.
Results
Median and interquartile ranges (25th to 75th percentile) of measured DDF, CS, and LVD in 57 patients were 14.0 (10.3 to 20.4), -8.0% (-13.3 to -3.2), and 40 ms (21 to 99), respectively. There were statistically significant correlations between the values of DDF and CS as well as LVD (0.60 and 0.48; p<0.01 for both).
Conclusion
Measurement of DDF may provide a specific clinical picture of myocardial strain and intraventricular dyssynchrony. Furthermore, it is possible to cost-effectively measure DDF without additional image acquisition during routine MR examination.
3. Hideo Arai, Masateru Kawakubo*, Kenichi Sanui, Ryoji Iwamoto, Hiroshi Nishimura, Toshiaki Kadokami. *Corresponding author, Assessment of Bi-Ventricular and Bi-Atrial Areas Using Four-Chamber Cine Cardiovascular Magnetic Resonance Imaging: Fully Automated Segmentation with a U-Net Convolutional Neural Network, International Journal of Environmental Research and Public Health, doi.org/10.3390/ijerph19031401, 19, 3, 1401, 2022.01, [URL], Four-chamber (4CH) cine cardiovascular magnetic resonance imaging (CMR) facilitates simultaneous evaluation of cardiac chambers; however, manual segmentation is time-consuming and subjective in practice. We evaluated deep learning based on a U-Net convolutional neural network (CNN) for fully automated segmentation of the four cardiac chambers using 4CH cine CMR. Cine CMR datasets from patients were randomly assigned for training (1400 images from 70 patients), validation (600 images from 30 patients), and testing (1000 images from 50 patients). We validated manual and automated segmentation based on the U-Net CNN using the dice similarity coefficient (DSC) and Spearman’s rank correlation coefficient (ρ); p < 0.05 was statistically significant. The overall median DSC showed high similarity (0.89). Automated segmentation correlated strongly with manual segmentation in all chambers—the left and right ventricles, and the left and right atria (end-diastolic area: ρ = 0.88, 0.76, 0.92, and 0.87; end-systolic area: ρ = 0.81, 0.81, 0.92, and 0.83, respectively; p < 0.01). The area under the curve for the left ventricle, left atrium, right ventricle, and right atrium showed high scores (0.96, 0.99, 0.88, and 0.96, respectively). Fully automated segmentation could facilitate simultaneous evaluation and detection of enlargement of the four cardiac chambers without any time-consuming analysis..
4. Kawakubo M, Nagao M, Yamamoto A, Nakao R, Matsuo Y, Kaneko K, Watanabe E, Sakai A, Sasaki M, Sakai S, 13 N-ammonia PET-derived right ventricular longitudinal strain and myocardial flow reserve in right coronary artery disease, Eur J Nucl Med Mol Imaging. Epub ahead of print., 10.1007/s00259-021-05647-y, 2021.12, Purpose: We developed a feature-tracking algorithm for use with electrocardiography-gated high-resolution 13N-ammonia positron emission tomography (PET) imaging, and we hypothesized it could be used to clarify the association between right ventricular (RV) longitudinal strain (LS) and right coronary artery (RCA) ischemia. The aim of this study was to investigate the association between the reduction of regional myocardial flow reserve (MFR) in RCA territories and PET-derived LS of the RV free wall.Methods: Ninety-three patients with coronary artery stenosis ≥50%, diagnosed by coronary computed tomography angiography, and 10 controls were retrospectively analyzed. RV-LS in the free wall was measured by a feature-tracking technique on the resting and stressed 13N-ammonia PET images of horizontal long-axis slices. The patients were sub-grouped according to regional MFR values at the territories of RCA, left anterior descending artery (LAD), and left circumflex coronary artery (LCx): RCA-MFR<2.0 [n=34], RCA-MFR≥2.0 but MFR<2.0 at LAD or LCx territories [n=11], and MFR≥2.0 for all territories [n=48]. Stress and resting RV-LS were compared in each of the four groups. Multiple comparisons of RV-LS among the four groups were performed in the stress and resting state.Results: Decreased stress RV-LS in patients with an RCA-MFR<2.0 was observed. In the patients with MFR≥2.0 for all territories, the stressed RV-LS was significantly increased compared to that in the resting state. Significantly decreased RV free-wall LS during adenosine stress in patients with RCA-MFR<2.0 was observed in the other three groups.Conclusions: We measured RV myocardial LS using feature tracking in cine imaging of 13N-ammonia PET. The results of this study suggest that PET-derived stressed RV-LS is useful for detecting reduced RV myocardial motion due to ischemia in the RCA territory..
5. Kawakubo M, Nagao M, Kikuchi N, Yamamoto A, Nakao R, Matsuo Y, Kaneko K, Watanabe E, Sasaki M, Nunoda S, Sakai S, 13N-ammonia positron emission tomography-derived left-ventricular strain in patients after heart transplantation validated using cardiovascular magnetic resonance feature tracking as reference, Ann Nucl Med. Epub ahead of print., 10.1007/s12149-021-01686-5, 36, 1, 70-81, 2022.01, Objective: Heart transplant rejection leads to cardiac allograft vasculopathy (CAV). 13N-ammonia positron emission tomography (PET) can be useful in detecting CAV, as it can evaluate both epicardial vessels and microvasculature. In this study, we evaluated the regional wall motion in heart transplant patients using our PET-specific feature-tracking (FT) algorithm for myocardial strain calculation and validated it using a cardiovascular magnetic resonance (CMR) FT strain as a reference.
Methods: A total of 15 heart transplant patients who underwent both 13N-ammonia PET and CMR within 3 months were retrospectively enrolled. The same slice position of short-axis cine images of the middle slice of left ventricle (LV) and the same slice position of horizontal long-axis cine images were selected for the two modalities to measure the circumferential strain (CS) and longitudinal strain (LS), respectively. Based on the FT technique, time-strain curves were calculated by semi-automatic tracking of the endocardial contour on cine images throughout a cardiac cycle. The peak value in the time-strain curve was defined as the representative value. Correlations of CS and LS between PET and CMR were analyzed using Pearson correlation coefficients. The inter-modality error of strain measurements was evaluated using intraclass correlation coefficients (ICCs) with two-way random single measures.
Results: Excellent correlations of CS and LS between PET and CMR were observed (CS: r = 0.80; p < 0.01; LS: r = 0.87; p < 0.01). Excellent ICCs were observed (0.89 and 0.85) in CS and LS derived from PET.
Conclusions: We propose the first PET strain showing an excellent agreement with the CMR strain and high reproducibility in measurement..
6. Kawakubo M*, Yamasaki Y, Toyomura D, Yamamura K, Sakamoto I, Moriyama T, Yabuuchi H, Ishigami K, *Corresponding author, Unchanged right ventricular strain in repaired tetralogy of Fallot after pulmonary valve replacement with radial long-axis cine magnetic resonance images, Scientific Reports, 10.1038/s41598-021-98464-0, 11, 1, 2021.09, We measured right ventricular (RV) strain by applying a novel postprocessing technique to conventional short-axis cine magnetic resonance imaging in the repaired tetralogy of Fallot (TOF) and investigated whether pulmonary valve replacement (PVR) changes the RV strain. Twenty-four patients with repaired TOF who underwent PVR and 16 healthy controls were enrolled. Global maximum and minimum principal strains (GPSmax, GPSmin) and global circumferential and longitudinal strains (GCS, GLS) were measured from short-axis cine images reconstructed radially along the long axis. Strain parameters before and after PVR were compared using paired t-tests. One-way ANOVA with Tukey post-hoc analysis was used for comparisons between the before and after PVR groups and the control group. There were no differences in strain parameters before and after PVR. The GPSmax before PVR was lower than that in the control group (P = 0.002). Before and after PVR, GCSs were higher and GLSs were lower than those in the control group (before and after GCSs: P = 0.002 for both, before and after GLSs: P < 0.0001 and P = 0.0003). RV strains from radially reconstructed short-axis cine images revealed unchanged myocardial motion after PVR. When compared to the control group, changes in GCS and GLS in TOF patients before and after PVR might be due to RV remodeling..
7. Masateru Kawakubo, Michinobu Nagao, Atsushi Yamamoto, Risako Nakao, Yuka Matsuo, Kenji Fukushima, Eri Watanabe, Akiko Sakai, Masayuki Sasaki, and Shuji Sakai, 13N-ammonia positron emission tomography-derived endocardial strain for the assessment of ischemia using feature-tracking in high-resolution cine imaging, Journal of Nuclear Cardiology. Epub ahead of print. Picked up in Editorial (https://link.springer.com/content/pdf/10.1007/s12350-021-02747-y.pdf)., 10.1007/s12350-021-02677-9, 2021.06, Background: Assessing endocardial strain using a single 13N-ammonia positron emission tomography (PET) scan would be clinically useful, given the association between ischemia and myocardial deformation. However, no software has been developed for strain analysis using PET. We evaluated the clinical potential of feature tracking-derived strain values measured using PET, based on associations
with the myocardial flow reserve (MFR).
Methods and Results: This retrospective study included 95 coronary artery disease patients who underwent myocardial 13N-ammonia PET. Semi-automatic measurements were made using a feature-tracking technique during myocardial cine imaging, and values were calculated using a 16-segment model. Adenosine-stressed global circumferential strain (CS) and global longitudinal strain (LS) values were compared with global MFR values. Stressed and resting global strain values were also compared. Global strain values were significantly lower in 39 patients with abnormal MFRs [<2.0] than in 56 patients with normal MFRs [≥2.0]. The global CS values in the stressed state were significantly decreased than the resting state values in patients with abnormal MFRs.
Conclusions: This study applied endocardial feature-tracking to 13N-ammonia PET, and the results suggested that blood flow and myocardial motility could be clinically assessed in ischemic patients using a single PET scan..
8. Kanatani R, Shirasaka T, Kojima T, Kato T, Kawakubo M*. *Corresponding author, Influence of beam hardening in dual- energy CT imaging: phantom study for iodine mapping, virtual monoenergetic imaging, and virtual non-contrast imaging, European Radiology Experimental, https://doi.org/10.1186/s41747-021-00217-1, 5, 18, 2021.04,
In this study, we investigated the influence of beam hardening on the dual-energy computed tomography (DECT) values of iodine maps, virtual monoenergetic (VME) images, and virtual non-contrast (VNC) images. 320-row DECT imaging was performed by changing the x-ray tube energy for the first and second rotations. DECT values of 5 mg/ mL iodine of the multi-energy CT phantom were compared with and without a 2-mm-thick attenuation rubber layer (~700 HU) wound around the phantom. It was found that the CT density values UH, with/without the rubber layer had statistical differences in the iodine map (184 ± 0.7 versus 186 ± 1.8), VME images (125 ± 0.3 versus 110 ± 0.4), and VNC images (−58 ± 0.7 versus −76 ± 1.7) (p < 0.010 for all). This suggests that iodine mapping may be underestimated by DECT and overestimated by VME imaging because of x-ray beam hardening. The use of VNC images instead of plain CT images requires further investigation because of underestimation..
9. Shiina Y, Kawakubo M, Inai K, Asagai S, Nagao M., Dual VENC 4D flow magnetic resonance imaging demonstrates arterial-pulmonary collaterals in an adult with tetralogy of Fallot, Eur Heart J Cardiovasc Imaging., 10.1093/ehjci/jeaa343., Online ahead of print., 2020.12.
10. T Kojima, M Nagao, H Yabuuchi, Y Yamasaki, T Shirasaka, M Kawakubo, K Fukushima, T Koto, A Yamamoto, R Nakao, A Sakai, E Watanabe, and S Sakai, New transluminal attenuation gradient derived from dynamic coronary CT angiography: diagnostic ability of ischemia detected by 13N-ammonia PET, Heart and Vessels, In Press, 2020.10.
11. Hideo Arai, Masateru Kawakubo*, Kenichi Sanui, Hiroshi Nishimura, Toshiaki Kadokami. *Corresponding author, Assessing myocardial circumferential strain using cardiovascular magnetic resonance after magnetic resonance-conditional cardiac resynchronization therapy, Radiology Case Reports, doi.org/10.1016/j.radcr.2020.07.063, 15, 10, 1954-1959, 2020.08, Nondrug therapy for arrhythmia patients had been developed dramatically until recent years. Cardiac resynchronization therapy (CRT), a nondrug therapy for arrhythmia, is especially utilized for the treatment of left ventricular (LV) severe heart failure caused by cardiac dyssynchrony. Prolonged QRS duration (≥130 ms) is strongly used as a CRT indication criterion, but QRS is not the direct clinical index of mechanical contraction delay of the LV myocardium. Therefore, identifying the presence of dyssynchrony by diagnostic imaging is necessary. Echocardiography is widely used for the assessment of dyssynchrony as a standard diagnostic imaging. Several studies have addressed the efficacy of cardiovascular magnetic resonance feature tracking (CMR-FT) in the diagnosis of dyssynchrony for arry- thmia patients. In addition, cardiac implantable electronic devices (CIEDs) were not avail- able to examine CMR until recent years; however, new MR-conditional CIEDs have become available for use before and after CRT. Recently, diagnostic imaging using CMR-FT has been attracting attention for the assessment of dyssynchrony. However, a strong metal artifact caused by CIEDs may make the analysis difficult after CRT implantation. Strain analysis us- ing short-axis (SA) cine CMR overcame this issue of artifact by enabling slice selection by avoiding artifact. Moreover, circumferential strain has superiority over other strain methods with respect to sensitivity, and we focused on these advantages. This case illustrates that circumferential strain with CMR-FT using SA cine CMR is useful in the assessment of improvement of myocardial motion after CRT and can provide useful additional information with imaging to determine the responders of CRT..
12. Yamasaki Y, Abe K, Kamitani T, Hosokawa K, Kawakubo M, Sagiyama K, Hida T, Matsuura Y, Murayama Y, Funatsu R, Tsutsui H, Yabuuchi H., Balloon pulmonary angioplasty improves right atrial reservoir and conduit functions in chronic thromboembolic pulmonary hypertension., European Heart Journal Cardiovascular Imaging, 10.1093/ehjci/jeaa064, 2020.05,
AIMS:
Right atrial (RA) function largely contributes to the maintenance of right ventricular (RV) function. This study investigated the effect of balloon pulmonary angioplasty (BPA) on RA functions in patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH) using cardiac magnetic resonance imaging (CMRI).
METHODS AND RESULTS:
CMRI and RV catheterization were performed before BPA sessions and at the follow-up periods in 29 CTEPH patients. Reservoir [RA longitudinal strain (RA-LS)], passive conduit [RA early LS rate (LSR)], and active (RA late LSR) phases were assessed by using cine CMRI and a feature-tracking algorithm. The relationships between the changes in RA functions and in brain natriuretic peptide (BNP) were evaluated in both the dilated and non-dilated RA groups. RA-LS (32.4% vs. 42.7%), RA LSR (6.3% vs. 8.3%), and RA early LSR (-2.3% vs. -4.3%) were improved after BPA, whereas no significant change was seen in RA late LSR. The changes in RA peak LS and in RA early LSR were significantly correlated with the changes in BNP (ΔRA-LS: r = -0.63, ΔRA-early LSR: r = 0.65) and pulmonary vascular resistance (PVR) (ΔRA-LS: r = -0.69, ΔRA-early LSR: r = 0.66) in the nondilated RA group.
CONCLUSION:
The RA reservoir and passive conduit functions were impaired in inoperable CTEPH, whereas RA active function was preserved. BPA markedly reversed these impaired functions. The improvements in RA reservoir and conduit functions were significantly correlated with the changes in BNP levels and PVR in CTEPH patients with normal RA sizes..
13. Shiina Y, Taniguchi K, Nagao M, Takahashi T, Niwa K, Kawakubo M, and Inai K., The relationship between extracellular volume fraction in symptomatic adults with tetralogy of Fallot and adverse cardiac events., Journal of Cardiology, DOI: 10.1016/j.jjcc.2019.09.009., 75, 4, 424-431, 2020.04.
14. Arai H, Kawakubo M*, Abe K, Hatashima H, Sanui K, Nishimura H, and Kadokami T. *Corresponding author, Quantification of intramyocardial hemorrhage volume using magnetic resonance imaging with three-dimensional T1-weighted sequence in patients with ischemia-reperfusion injury—a semi-automated image processing technique, The International Journal of Cardiovascular Imaging, 10.1007/s10554-019-01697-4, 36, 1, 111-119, 2020.01.
15. M Kawakubo, M Nagao, U Ishizaki, Y Shina, K Inai, Y Yamasaki, M Yoneyama, S Sakai., Feature-Tracking MRI Fractal Analysis of Right Ventricular Remodeling in Adults with Congenitally Corrected Transposition of the Great Arteries, Radiology: Cardiothoracic Imaging, 10.1148/ryct.2019190026, 1, 4, 2019.10, PurposeTo assess a recently available technique for quantification of right ventricular (RV) trabeculae that is based on fractal analysis performed by using cardiac MRI feature tracking, in patients with congenitally corrected transposition of the great arteries (cc-TGA).Materials and MethodsA total of 19 patients (eight men, 11 women; mean age, 35 years ± 10 [standard deviation]) with consecutive cc-TGA who underwent cardiac MRI were enrolled in the study. For analysis, patients were divided into two groups: six patients (four men, two women; mean age, 34 years ± 14) with an end-systolic RV volume index higher than 72 mL/m2 (indicative of adverse RV remodeling) and 13 patients (four men, nine women; mean age, 36 years ± 9) in whom this index was lower than or equal to 72 mL/m2 (indicative of adapted RV). The following outcomes were quantified in the midsection of the RV: fractional fractal dimension (FD) and diastolic FD, circumferential strain, and radial strain. Receiver operating characteristic (ROC) analysis was performed to determine the cutoff FD values for the detection of adverse RV remodeling. Correlations among fractional FD, diastolic FD, circumferential strain, and radial strain were calculated by using Pearson correlation coefficient (r) analysis.ResultsThe following ROC values were identified for fractional and diastolic FD: cutoff, 0.09 and 1.39, respectively; area under the ROC curve, 0.95 and 0.68, respectively; sensitivity, 1.00 and 0.33, respectively; and specificity, 0.92 and 1.00, respectively. Fractional FD correlated with circumferential strain and radial strain (r = −0.70 and 0.69, respectively; P < .01), as did diastolic FD (r = 0.37 and −0.38, respectively; P < .05).ConclusionThe fractional FD derived from cardiac MRI feature-tracking analysis correlates with adverse RV remodeling, including a changed strain pattern and trabeculae, in patients with cc-TGA..
16. R Nakao, M Nagao, K Fukushima, A Sakai, E Watanabe, M Kawakubo, S Sakai, N Hagiwara., Prediction of Cardiac Resynchronization Therapy Response in Dilated Cardiomyopathy Using Vortex Flow Mapping on Cine Magnetic Resonance Imaging, Circulation Reports, 10.1253/circrep.CR-18-0024, 1, 8, 333-341, 2019.08.
17. Kawakubo M*, Yamasaki Y, Kamitani T, Sagiyama K, Matsuura Y, Hino T, Abe K, Hosokawa K, Yabuuchi H, and Honda H. *Corresponding author, Clinical usefulness of right ventricular 3D area strain in the assessment of treatment effects of balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension: comparison with 2D feature-tracking MRI, European Radiology, https://doi.org/10.1007/s00330-019-6008-3, 29, 9, 4583-4592, 2019.09, OBJECTIVES:
To evaluate the usefulness of right ventricular (RV) area strain analysis via cardiac MRI (CMRI) as a tool for assessing the treatment effects of balloon pulmonary angioplasty (BPA) in inoperable chronic thromboembolic pulmonary hypertension (CTEPH), RV area strain was compared to two-dimensional (2D) strain with feature-tracking MRI (FTMRI) before and after BPA.
METHODS:
We retrospectively analyzed 21 CTEPH patients who underwent BPA. End-systolic global area strain (GAS), longitudinal strain (LS), circumferential strain (CS), and radial strain (RS) were measured before and after BPA. Changes in GAS and RV ejection fraction (RVEF) values after BPA were defined as ΔGAS and ΔRVEF. Receiver operating characteristic (ROC) analyses were performed to determine the optimal cutoff of the strain at after BPA for detection of improved patients with decreased mean pulmonary artery pressure (mPAP) less than 30 mmHg and increased RVEF more than 50%.
RESULTS:
ROC analysis revealed the optimal cutoffs of strains (GAS, LS, CS, and RS) for identifying improved patients with mPAP < 30 mmHg (cutoff (%) = - 41.2, - 13.8, - 16.7, and 14.4: area under the curve, 0.75, 0.56, 0.65, and 0.75) and patients with RVEF > 50% (cutoff (%) = - 37.2, - 29.5, - 2.9, and 14.4: area under the curve, 0.81, 0.60, 0.56, and 0.56).
CONCLUSIONS:
Area strain analysis via CMRI may be a more useful tool for assessing the treatment effects of BPA in patients with CTEPH than 2D strains with FTMRI..
18. Arai H, Kawakubo M, Sanui K, Nishimura H, Kadokami T., Accurate and robust systolic myocardial T1 mapping using saturation recovery with individualized delay time: Comparison with diastolic T1 mapping, Radiol Phys Technol., https://doi.org/10.1007/s12194-018-0478-x, 11, 4, 415-422, 2018.09.
19. Kawakubo M*, Arai H, Nagao M, Yamasaki Y, Sanui K, Nishimura H, Kadokami T. *Corresponding author, Global left ventricular area strain using standard two-dimensional cine MR imaging with inter-slice interpolation, Cardiovascular Imaging: Asia, https://doi.org/10.22468/cvia.2018.00108, 2, 4, 187-193, 2018.10.
20. Kojima T, Kawakubo M, Nishizaka MK, Rahmawati A, Ando S, Chishaki SA, Nakamura Y, Nagao M, Assessment by airway ellipticity on cine-MRI to differentiate severe obstructive sleep apnea., Clinical Respiratory Journal, 10.1111/crj.12598., 12, 3, 878-884, 2018.03.
21. Kawakubo M*, Akamine H, Yamasaki Y, Takemura A, Abe K, Hosokawa K, Morishita J, Nagao M. *Corresponding author, Three-dimensional phase contrast magnetic resonance imaging validated to assess pulmonary artery flow in patients with chronic thromboembolic pulmonary hypertension., Radiological Physics and Technologies, 2016.10.
22. Kawakubo M*, Nagao M, Kumazawa S, Yamasaki Y, Chishaki AS, Nakamura Y, Honda H, Morishita J. *Corresponding author, Evaluation of ventricular dysfunction using semi-automatic longitudinal strain analysis of four-chamber cine MR imaging., The International Journal of Cardiovascular Imaging., 32, 2, 283-9, 2016.02.
23. Kawakubo M*, Yamasaki Y, Sakamoto I, Yamamura K, Nagao M. *Corresponding author, Clinical Impact of Interventricular Dyssynchrony in Repaired Tetralogy of Fallot: Myocardial Strain Analysis Using Semi-automatic Tracking of Cine Magnetic Resonance Imaging., Journal of Adult Congenital Heart Disease, Vol. 4, No. 2, 69-73, 2015.12.
24. Kawakubo M*, Nagao M, Kumazawa S, Chishaki AS, Mukai Y, Nakamura Y, Honda H, Morishita J. *Corresponding author, Evaluation of cardiac dyssynchrony with longitudinal strain analysis in 4-chamber cine MR imaging., European Journal of Radiology, 82, 12, 2212-2216, 2013.12.
25. Kudomi S, Ueda K, Ueda Y, Kawakubo M, Sanada T, Evaluation of the spatial resolution of multiplanar reconstruction images., Radiological Physics and Technologies, 1, 2, 229-233, 2008.07.