Search

Clinical MRI systems have continually improved over the years since their introduction in the 1980s. In MRI technical development, the developments in each MRI system component, including data acquisition, image reconstruction, and hardware systems, have impacted the others. Progress in each component has induced new technology development opportunities in other components. New technologies outside of the MRI field, for example, computer science, data processing, and semiconductors, have been immediately incorporated into MRI development, which resulted in innovative applications. With high performance computing and MR technology innovations, MRI can now provide large volumes of functional and anatomical image datasets, which are important tools in various research fields. MRI systems are now combined with other modalities, such as positron emission tomography (PET) or therapeutic devices. These hybrid systems provide additional capabilities.In this review, MRI advances in the last two decades will be considered. We will discuss the progress of MRI systems, the enabling technology, established applications, current trends, and the future outlook.

Purpose The purpose of this study was to evaluate whether deep learning reconstruction (DLR) improves the image quality of intracranial magnetic resonance angiography (MRA) at 1.5 T. Materials and methods In this retrospective study, MRA images of 40 patients (21 males and 19 females; mean age, 65.8 ± 13.2 years) were reconstructed with and without the DLR technique (DLR image and non-DLR image, respectively). Quantitative image analysis was performed by placing regions of interest on the basilar artery and cerebrospinal fluid in the prepontine cistern. We calculated the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) for analyses of the basilar artery. Two experienced radiologists evaluated the depiction of structures (the right internal carotid artery, right ophthalmic artery, basilar artery, and right superior cerebellar artery), artifacts, subjective noise and overall image quality in a qualitative image analysis. Scores were compared in the quantitative and qualitative image analyses between the DLR and non-DLR images using Wilcoxon signed-rank tests. Results The SNR and CNR for the basilar artery were significantly higher for the DLR images than for the non-DLR images (p p p p = 0.072–0.565), were also significantly higher for the DLR images than for the non-DLR images. Conclusion DLR enables the production of higher quality 1.5 T intracranial MRA images with improved visualization of arteries.

The silent navigator technique utilizes a non-selective excitation and an appropriate respiratory waveform generation method is necessary for an accurate motion detection. We compared three methods for silent navigator waveform generation. The profile generation method with coil selection (prof-selection) resulted in a high cross correlation with bellows signals and a large respiration amplitude. The prof-selection method should be used for silent navigator waveform generation.

Purpose : To determine the reproducibility of corrected quantitative cerebral blood flow (qCBF) through measurement of transit flow time using multi-delay three-dimensional pseudo-continuous arterial spin labeling (pCASL) in healthy men and women and to evaluate the differences in qCBF between not only men and women, but also the follicular and luteal phases of the women's menstrual cycle. Methods : The participants were 16 healthy volunteers (8 men and 8 women ; mean age, 25.3 years). Two MRI were conducted for all participants ; female participants were conducted in the follicular and luteal phases. The reproducibility of qCBF values was evaluated by the intraclass correlation coefficient (ICC) and differences between the two groups were estimated by voxel-based morphometry (VBM) analysis. Results : The qCBF values were lower in men than in women, and those in females were significantly different between the follicular and luteal phases (P 0.05). In VBM analysis, the qCBF values of the lower frontal lobes were significantly higher in women than in men (P 0.05). The qCBF values of the frontal pole were significantly higher in the follicular phase than in the luteal phase (P 0.01). Conclusion : Multi-delay pCASL can reveal physiological and sex differences in cerebral perfusion. J. Med. Invest. 67 : 321-327, August, 2020.

Purpose 2D cine phase contrast (PC)-MRI is a standard velocimetry for the superior mesenteric artery (SMA); however, the optimal localization of the measurement plane has never been fully discussed previously. The purpose of this Institutional Review Board approved prospective and single arm study is to test whether flow velocimetry of the SMA with combined use of 2D cine PC-MRI and meal challenge is dependent on the localizations of the measurement planes and to seek optimal section for velocimetry. Methods Seven healthy volunteers underwent cardiac phase resolved ECG gated 2D cine PC-MRI pre- and 30 min post-meal challenge at three measurement planes: proximal, curved mid section and distal straight section of the SMA at 3T. 4D Flow using 3D cine PC-MRI with vastly undersampled isotropic projection imaging (PC VIPR) was also performed right after 2D cine PC-MRI to delineate the flow dynamics within the SMA using streamline analysis. Two radiologists measured flow velocities, and rated the appearances of the abnormal flow in the SMA on streamlines derived from the 4D Flow and the computational fluid dynamics (CFD). Results 2D cine PC-MRI measured increased temporally averaged flow velocity (mm/s) after the meal challenge only in the proximal (129.3 vs. 97.8, P = 0.0313) and distal section (166.9 vs. 96.2, P = 0.0313), not in the curved mid section (113.1 vs. 85.5, P = 0.0625). The average velocities were highest and their standard errors (8.5-26.5) were smallest at the distal straight section both before and after the meal challenge as compared with other sections. The streamline analysis depicted more frequent appearances of vertical or helical flow in the curved mid section both on 4D Flow and CFD (κ: 0.27-0.68). Conclusion SMA velocimetry with 2D cine PC-MRI was dependent on the localization of the measurement planes. Distal straight section, not in the curved mid section is recommended for MR velocimetry.

BackgroundHepatic fibrosis is a dynamic, reversible process which can result in liver failure. Diagnosis and monitoring of hepatic fibrosis are clinically important.PurposeTo compare the diagnostic...

PURPOSE To assess the performance of four-dimensional phase-contrast vastly undersampled isotropic projection reconstruction (4D PC-VIPR) at 3.0T in depicting intrarenal arteries compared with computed tomography angiography (CTA), and its correlation with arterial flowmetry in comparison with Doppler ultrasonography (DUS). MATERIALS AND METHODS In our prospective single-arm study, subjects were 25 patients who underwent renal transplant-related surgery at our hospital between July 2011 and June 2015. In the morphological study, depictions of renal artery branches delineated by magnetic resonance angiography (MRA)/4D PC-VIPR without gadolinium contrast agent were compared in seven living transplant recipients with the same kidney delineated by CTA in seven living transplant donors. In the flowmetric study, flow velocities in the renal (main stem), segmental, and interlobar arteries during systole and diastole were measured in 12 recipients using noncontrast MRA/4D PC-VIPR, and were compared with those obtained from DUS. RESULTS Concerning MRA, average confidence levels of delineation rated by six observers for secondary to third level renal artery branches were 82.9-100% and for the fourth to fifth branches were 60.8-89.7% (average kappa value of 0.588 [95% confidence interval: 0.522-0.653]). Total flow velocities measured using 4D PC-VIPR and DUS demonstrated significant correlations during both systole and diastole with acceptable bias (r = 0.902; P < 0.001 in systole and r = 0.734; P < 0.001 in diastole). CONCLUSION 4D PC-VIPR was useful in generating both morphological and hemodynamic information for evaluation of transplant intrarenal arteries without the need for contrast media. LEVEL OF EVIDENCE 2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:595-603.

Background Magnetic resonance vessel wall imaging (VWI) techniques have been developed to assess atherosclerotic plaques in intracranial arteries, which are a cardinal cause of ischemic stroke. However, the clinical roles of plaque-related vulnerability and inflammation remain unclear. Hence, we evaluated plaque characteristics using VWI of the proximal middle cerebral artery (M1) in patients with acute ischemic stroke. Methods We prospectively examined 30 consecutive patients with acute noncardioembolic stroke in the M1 territory using pre-/postcontrast T1-weighted (T1W) three-dimensional (3D) VWI with a 3-Tesla scanner. The contrast ratio (CR) and contrast enhancement of the plaques were measured bilaterally at M1. Results Plaques were identified in the bilateral M1s of all patients, and no substantial stenosis existed. The M1 plaque CRs ipsilateral to the infarct (46.7%-67.9%) were significantly higher than the plaque CRs on the contralateral side (34.3%-69.4%), particularly in patients with lacunar infarcts ( P .01). In contrast, the occurrence of plaque enhancement was not different between the ipsilateral (20.0%) and contralateral (16.7%) sides. Further, the CRs in the nonlacunar group were significantly higher than the CRs in the lacunar group ( P .05), whereas enhanced plaques tended to be more frequent in the nonlacunar group, but this difference was not significant ( P = .09). Conclusions T1W 3D-VWI revealed that the signal intensity of M1 plaques was significantly higher in the affected side and in nonlacunar-type infarcts of patients with acute stroke, suggesting that unstable plaques in the M1 can cause stroke events presumably due to atherothrombotic mechanisms.

Purpose To develop and demonstrate the feasibility of a pencil-beam navigator using a gradient reversal technique for reducing signal contamination from undesired excitation for precise motion detection and correction. Materials and methods The navigator echo was obtained using normal and reversed gradient waveforms sequentially in three-dimensional spoiled gradient-recalled echo imaging. These two signals were combined in the complex domain for generating the final navigator data, which were used for detecting the diaphragm motion to nullify the side lobe effects with the smallest radius from the beam center. The navigator signals were compared with and without the proposed technique in phantom and human scans. In addition, navigator-gated imaging was performed in the human scans. Results In a phantom experiment, the proposed technique diminished signals from a phantom placed outside the beam’s area. In human scans, the proposed technique reduced undesired signals in the navigator data for all subjects. The resultant images had fewer motion-induced ghosts than the images from the conventional technique for 8 subjects out of 10. Conclusions We have demonstrated that the gradient reversal technique reduced undesired signals in a pencil-beam navigator. This technique can be an alternative for free-breathing abdominal scan when the conventional navigator technique cannot detect the patient’s respiratory motion precisely.

On arterial spin-labeled (ASL) images, areas of bright intravascular signal will appear when the post labeling delay time is shorter than arterial transit time. Vascular suppression (VS) schemes reduce artefactual bright signal by dephasing intravascular labeled spins. However, existing VS methods, such as Motion-Sensitized Driven-Equilibrium (MSDE), decrease the uniformity of the signal intensity distribution and extend the echo time. The purpose of this study is to compare VS using a Delays Alternating with Nutation for Tailored Excitation (DANTE) preparation pulse, with MSDE for ASL imaging on a flow phantom and volunteer data. In the phantom study, the signal decay pattern of moving water was similar for both methods. In the volunteer study, the bright intravascular signal artifact was decreased by both methods. However right-left differences in signal intensity were smaller using DANTE-prepared ASL. The proposed DANTE-prepared ASL sequence has a vessel suppression effect while maintaining a uniform signal intensity distribution. This study indicates that DANTE is a potentially useful method for vessel suppression in ASL imaging.

Purpose To develop and demonstrate the feasibility of a new technique for respiratory-gated, fat-suppressed, three-dimensional spoiled gradient-recalled echo (3D-SPGR) with navigator gating for more accurate and robust motion detection. Methods A navigator-gated 3D-SPGR technique was modified to include a wait period immediately prior to the navigator sequence for magnetization recovery. Furthermore, a variable flip angle scheme was realized by a combination of ramp-up, ramp-down, and attenuation strategies for optimizing point spread functions. Phantom and human experiments were conducted with our technique on 1.5T scanners. Results Using the method, T1-weighted 3D images with improved signal homogeneity were acquired with a maximum flip angle of 30° in phantom and human tests. Also, compared with the conventional navigator-gated 3D-SPGR, accurate respiratory motion detection of free-breathing subjects was provided, leading to reduced motion artifacts. Conclusion The combination of wait insertion and the variable flip angle method improved both motion detection accuracy and image homogeneity in a navigator-gated 3D-SPGR study. Magn Reson Med 72:172–177, 2014. © 2013 Wiley Periodicals, Inc.

Purpose To develop and demonstrate the feasibility of a silent respiratory navigator technique for prospective triggering, which was incorporated into a three-dimensional radial zero-echo-time sequence for respiratory navigated silent abdominal imaging. Methods A nonselective hard excitation radiofrequency pulse was used for the navigator sequence with a derated readout gradient, to avoid generation of high levels of acoustic noise. The acquired navigator signals were processed in real time and used for prospective triggering of the zero-echo-time sequence. Ten healthy volunteers were scanned using the proposed and conventional techniques at 1.5 T. An acoustic noise measurement with A-weighted continuous equivalent sound pressure level was also performed. Results The sound pressure–level values of the background noise, zero-echo-time imaging, conventional, and silent navigators were 68.3, 68.4, 102.5, and 69.4 dBA, respectively. Excellent correlation with correlation coefficients greater than 0.9 was observed between the bellows signals and displacement values calculated from the navigators. Sharpness of the portal vein of both conventional and silent navigator–triggered images was significantly higher than those of nontriggered images. Conclusions The silent navigator–triggered zero-echo-time technique is feasible and might improve image quality and workflow of abdominal MRI of patients who are prone to acoustic noise. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

To assess the performance of four-dimensional phase-contrast vastly undersampled isotropic projection reconstruction (4D PC-VIPR) at 3.0T in depicting intrarenal arteries compared with computed tomography angiography (CTA), and its correlation with arterial flowmetry in comparison with Doppler ultrasonography (DUS).In our prospective single-arm study, subjects were 25 patients who underwent renal transplant-related surgery at our hospital between July 2011 and June 2015. In the morphological study, depictions of renal artery branches delineated by magnetic resonance angiography (MRA)/4D PC-VIPR without gadolinium contrast agent were compared in seven living transplant recipients with the same kidney delineated by CTA in seven living transplant donors. In the flowmetric study, flow velocities in the renal (main stem), segmental, and interlobar arteries during systole and diastole were measured in 12 recipients using noncontrast MRA/4D PC-VIPR, and were compared with those obtained from DUS.Concerning MRA, average confidence levels of delineation rated by six observers for secondary to third level renal artery branches were 82.9-100% and for the fourth to fifth branches were 60.8-89.7% (average kappa value of 0.588 [95% confidence interval: 0.522-0.653]). Total flow velocities measured using 4D PC-VIPR and DUS demonstrated significant correlations during both systole and diastole with acceptable bias (r = 0.902; P0.001 in systole and r = 0.734; P0.001 in diastole).4D PC-VIPR was useful in generating both morphological and hemodynamic information for evaluation of transplant intrarenal arteries without the need for contrast media.2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:595-603.

OBJECTIVE: Many studies have reported pre-processing effects for brain volumetry; however, no study has investigated whether non-parametric non-uniform intensity normalization (N3) correction processing results in reduced system dependency when using an atlas-based method. To address this shortcoming, the present study assessed whether N3 correction processing provides reduced system dependency in atlas-based volumetry. MATERIALS AND METHODS: Contiguous sagittal T1-weighted images of the brain were obtained from 21 healthy participants, by using five magnetic resonance protocols. After image preprocessing using the Statistical Parametric Mapping 5 software, we measured the structural volume of the segmented images with the WFU-PickAtlas software. We applied six different bias-correction levels (Regularization 10, Regularization 0.0001, Regularization 0, Regularization 10 with N3, Regularization 0.0001 with N3, and Regularization 0 with N3) to each set of images. The structural volume change ratio (%) was defined as the change ratio (%) = (100 × [measured volume - mean volume of five magnetic resonance protocols] / mean volume of five magnetic resonance protocols) for each bias-correction level. RESULTS: A low change ratio was synonymous with lower system dependency. The results showed that the images with the N3 correction had a lower change ratio compared with those without the N3 correction. CONCLUSION: The present study is the first atlas-based volumetry study to show that the precision of atlas-based volumetry improves when using N3-corrected images. Therefore, correction for signal intensity non-uniformity is strongly advised for multi-scanner or multi-site imaging trials.

Previous studies revealed a correlation between local brain volume and cognitive function. The aim of the present study was to investigate the correlation between local gray matter volume and the Wechsler Memory Scale-Revised (WMS-R) logical/verbal memory (WMS-R-verbal) score in healthy adults using a 3 Tesla magnetic resonance scanner and voxel-based morphometry (VBM). T1-weighted magnetic resonance images were obtained in 1,169 healthy adults. The T1-weighted images in native space were bias-corrected, spatially normalized, and segmented into gray matter, white matter, and cerebrospinal fluid images with Statistical Parametric Mapping 5. To investigate regionally the specific effects of the WMS-R-verbal score on the gray matter images, simple regression analysis was performed by VBM treating age, total intracranial volume, and gender as confounding covariates. A P value of less than 0.05 corrected with false discovery rate in voxel difference was considered to be statistically significant. Our study showed a significant positive correlation between the WMS-R-verbal score and the bilateral entorhinal cortex volume. In the right entorhinal, T value is 4.75, and the size of the clusters is 155 voxels. In the left entorhinal, T value is 4.08, and the size of the clusters is 23 voxels. A significant negative correlation was not found. To our knowledge, this is the first VBM study showing that entorhinal cortex volume is positively correlated with the WMS-R-verbal score for healthy subjects. Therefore, in our structural neuroimaging study, we add evidence to the hypothesis that the entorhinal cortex is involved in verbal memory processing.

The purpose of this study was to evaluate the effects of longitudinal drift in scanner hardware, inter‐scanner variability (bias), and scanner upgrade on longitudinal changes in global and regional diffusion properties using longitudinal data obtained on two scanners of the exact same model at one institution. A total of 224 normal subjects were scanned twice, at an interval of about 1 year, using two 3.0‐T scanners of the exact same model. Both scanners were simultaneously upgraded during the study period. The subjects were divided into four groups according to the combination of scanners used. With use of tract‐based spatial statistics, we evaluated the effects of scanner drift and inter‐scanner variability (bias) on global and regional fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) changes of the white matter. Even with scanners of the exact same model, inter‐scanner variability (bias) significantly affected longitudinal results. FA, AD, and RD of the white matter were relatively stable within the same scanner. We also investigated the effect of scanner upgrade on longitudinal FA, AD, and RD changes. The scanner upgrade included only software upgrade, not hardware upgrade; however, there was a significant effect of scanner upgrade on longitudinal results. These results indicate that inter‐scanner variability and scanner upgrade can significantly affect the results of longitudinal diffusion tensor imaging studies. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc.

OBJECTIVE Magnetic resonance imaging (MRI) is the most popular follow-up study for patients who have undergone spinal surgery. However, the image quality often becomes poor because of artifacts from metal implants and/or from failed fat suppression, which obscure diagnosis. Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) is a new fat suppression method that is less affected by inhomogeneity of the magnetic field. Here, we compared postsurgical spinal MRI with IDEAL versus chemical shift selective saturation (CHESS). METHODS For 35 patients who had spinal surgery, we examined T2-weighted fast spin-echo sagittal images of the spine with both IDEAL and CHESS. Two radiologists evaluated the degrees of fat suppression and spinal canal projection from 0 (least/worst) to 2 (most/best). RESULTS Fat suppression and spinal canal scores for IDEAL were statistically higher than those for CHESS (P < 0.05). CONCLUSIONS Iterative decomposition of water and fat with echo asymmetry and least-squares estimation is clinically useful for postoperative spinal MRI.

Purpose: To evaluate the effects of gradient nonlinearity correction and intensity nonuniformity correction on longitudinal (two-year) changes in global and regional brain volumes. Materials and Methods: A total of 208 subjects (70 females and 138 males, age range = 38.1–83.0 years) were included in this study. Each subject was scanned twice, at an interval of approximately two years (range = 1.5–2.3 years). Three-dimensional fast spoiled-gradient recalled acquisition in the steady state (3D-FSPGR) images corrected for gradient nonlinearity and/or intensity nonuniformity were compared with uncorrected 3D-FSPGR images with use of structural image evaluation using normalization of atrophy 2.6 (SIENA). Results: The mean absolute deviations of percentage brain volume change (PBVC) values in the gradient nonlinearity ± intensity nonuniformity corrected images were significantly less than that in the uncorrected images, and the difference in the mean absolute deviation of PBVC was the most significant between the uncorrected images and the images corrected for both gradient nonlinearity and intensity nonuniformity. Voxel-wise comparisons showed large significant differences between the uncorrected images and the corrected images. Conclusion: Correction for gradient nonlinearity and intensity nonuniformity reduces the variance of measured longitudinal changes in brain volumes and will improve accuracy for detecting subtle brain changes. J. Magn. Reson. Imaging 2010;32:489–492. © 2010 Wiley-Liss, Inc.

Introduction Diffusion tensor imaging (DTI) has provided important insights into the neurobiological basis for normal development and aging and various disease processes in the central nervous system. The aim of this article is to review the current protocols for DTI acquisition and preprocessing and statistical testing for a voxelwise analysis of DTI, focused on statistical parametric mapping (SPM) and tract-based spatial statistics (TBSS). Methods We tested the effects of distortion correction induced by gradient nonlinearity on fractional anisotropy (FA) maps or FA skeletons processed via two SPM-based methods (coregistration and FA template methods), or TBSS-based method, respectively. Results With two SPM-based methods, we found similar results in some points (e.g., significant FA elevation for uncorrected images in anterior-dominant white matter and for corrected images in bilateral middle cerebellar peduncles) and different results in other points (e.g., significantly larger FA for corrected images with coregistration method, but significantly smaller with FA template method in bilateral internal capsules, extending to corona radiata, and semioval centers). In contrast, there was no area with significant difference between uncorrected and corrected FA skeletons with TBSS-based method. Conclusion The discrepancy among these results was not explained in full, but possible explanations were misregistration and smoothing for the SPM-based methods and insensitivity to FA changes outside the local centers of white matter bundles for TBSS-based method.

The purpose of this study is to elucidate sex differences in global and regional gray/white matter volume, mean diffusivity (MD), and fractional anisotropy (FA) during normal aging using voxel-based analysis. We studied 245 healthy right-handed subjects with a wide range of ages (115 women, 22-70 years; 130 men, 21-71 years). Regarding global effects, inclusion of a quadratic age term improved the fit to data for white matter fraction and MD, but not for global gray matter volume/fraction or FA. Regarding regional effects, we found anterior-dominant volume loss, FA decrease predominantly in the anterior white matter, and MD increase predominantly in perisylvian regions and periventricular white matter against age for both sexes. Compared with women, we found a steeper FA decline for men in the right inferior fronto-temporal areas, extending to the anterior cingulate cortex, and an accelerated MD increase for men in the bilateral frontal, temporal, and parietal areas. There was no area in which interaction of sex with age was significant for regional volume, or in which a steeper FA decline or accelerated MD increase for women was significant. Our results provide strong evidence of sex dimorphism in global and focal diffusion characteristics during normal aging.

Object Although conventional catheter angiography is commonly used in the evaluation of intracranial arteriovenous malformations (AVMs), less invasive tools are more suitable for screening or follow-up. Older MR angiography techniques cannot provide high enough temporal and spatial resolution for assessing AVMs. Threetesla time-resolved imaging of contrast kinetics (TRICKS)—a time-resolved, contrast-enhanced 3D MR angiography technique—achieves subsecond time resolution without sacrificing spatial resolution. The purpose of this study was to assess the accuracy of TRICKS at 3 T in the evaluation of AVMs. Methods Between November 2006 and November 2007, 31 patients who were known to have AVMs underwent evaluation in a 3-T unit with the TRICKS technique. The TRICKS images were then evaluated independently by 2 radiologists for nidus detection, early venous filling detection, and Spetzler-Martin classification, and these results were compared with the results of catheter angiography. Results Time-resolved imaging of contrast kinetics achieved 96% sensitivity and 100% specificity both in nidus detection and early venous filling detection. The Spetzler-Martin grades also showed excellent correlation with catheter angiography findings (κ= 0.89). Conclusions Although this is a preliminary study, the authors' results indicate that time-resolved contrast-enhanced 3D MR angiography at 3 T is a good tool to assess AVMs, and has the potential to replace catheter angiography in screening or follow-up examinations of patients with AVMs.

The aim of this study was to evaluate the usefulness of periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER)-based diffusion tensor fiber tractography (DTT) at 3T to visualize infratentorial small fiber structures that cannot be visualized adequately using a conventional single shot echo planar imaging (ssEPI)-based pulse sequence.Four healthy male volunteers were examined in this study. Diffusion tensor images were acquired on a 3T clinical magnetic resonance scanner using PROPELLER and echo planar imaging sequences in six motion-probing gradient orientations. Fiber tracking results for the trigeminal and auditory nerves were compared quantitatively.The trigeminal nerve tract was successfully reconstructed using both acquisition methods (100%). Among these reconstructed tracts, 62.5% of the tracts on PROPELLER-DTT and 25% on ssEPI-DTT were followed to branches beyond the trigeminal ganglion. The reconstructed auditory nerve tract could be identified on PROPELER-DTT (62.5%), whereas no tract or only a short tract was obtained on ssEPI-DTT (37.5%).3T PROPELLER-DTT is useful for visualizing infratentorial small neurofiber structures.

The relationship between water diffusion parameters measured using diffusion tensor imaging (DTI) and histological malignancy of gliomas was investigated. DTI was performed using a 3.0T MR scanner in 41 consecutive patients with histologically proven gliomas. Fractional anisotropy (FA) and mean diffusivity (MD) were calculated and compared with the WHO classification of the gliomas. The FA values of grade 1 gliomas (0.150 +/- 0.017) were significantly lower than those of grade 3 (0.23 +/- 0.033) or grade 4 gliomas (0.229 +/- 0.033) (P < 0.0001, respectively). The FA values of grade 2 gliomas (0.159 +/- 0.018) were significantly lower than those of grade 3 or grade 4 gliomas (P = 0.0002, P < 0.0001, respectively). The FA threshold between low grade and high grade gliomas was 0.188. The MD values of grade 1 gliomas (1619.1 +/- 157.4 x 10(-6) mm2/s) were significantly higher than those of grade 3 (1084.5 +/- 218.9 x 10(-6) mm2/s) (P = 0.0036) or grade 4 gliomas (1098.0 +/- 291.6 x 10(-6) mm2/s) (P = 0.0002). The MD values were not correlated with the other grades of glioma. FA values can distinguish between high grade and low grade gliomas. This is useful in deciding the surgical strategy or selecting the site of stereotactic biopsy.

Background In vivo, water diffusion displays directionality due to presence of complex microstructural barriers in tissue. The extent of directionality of water diffusion can be expressed as a fractional anisotropy (FA) value using diffusion tensor magnetic resonance imaging (DTI). The FA value has been suggested as an indicator of the cell density of astrocytic tumors. The aim of the present study was to confirm beyond doubt that FA values indicate cell density even when limited in glioblastomas and to determine whether the FA value of a given patient predicts proliferation activity in the individual glioblastoma. Methods We performed DTI in 19 patients with glioblastoma and measured the FA values of tumor and normal brain regions prior to computed tomography–guided stereotactic biopsy. Differences in mean FA value between normal brain regions and glioblastoma lesion were compared. Cell density and MIB-1 indices were examined using tumor specimens obtained from biopsies. Correlation among FA values, cell density, and MIB-1 indices was also evaluated. Results The mean FA value significantly differed between normal brain regions and glioblastoma lesions. Positive correlation was observed between FA value and cell density (r = 0.73, P Conclusions Our results suggest that the FA value of glioblastoma as determined by DTI prior to surgery is a good predictor of cell density and, consequently, proliferation activity.

The fractional anisotropy (FA) value calculated by diffusion tensor MRI can indicate the degree of directionality of water diffusion in astrocytic tumors. Here, we report a case of anaplastic astrocytoma in which FA proved invaluable for the preoperative differential diagnosis. A 60-year-old man complained of headache, and underwent routine neuroimaging and DTI. The routine images suggested a low-grade glioma in the left temporal lobe, based on lack of enhancement on MRI with contrast medium and lack of tumor staining on angiograms, whereas FA value was very high. Based on these findings, a preoperative diagnosis of high-grade glioma was suspected. The surgical specimen exhibited the histological features of anaplastic astrocytoma with a high density of spindle shaped cells and low vascularity. In this report, we discuss the relationship between FA and other characteristics of the present tumor, and discuss the utility of FA measurement in astrocytic tumors.

The development of arterial spin labeling (ASL) techniques has provided a useful strategy for quantitative measurement of cerebral blood flow (CBF). However, quantification of transit time has historically been difficult to achieve without prolonged scan times, since ASL has suffered from low signal-to-noise ratio (SNR). Continuous ASL (CASL) has recently been implemented on the 3T magnetic resonance (MR) system, which can provide a more favorable perfusion signal SNR because of the higher Lamor frequency and prolonged T1 times. Therefore, the goal of the present study was to determine whether CASL perfusion imaging on the 3T MR system could evaluate transit time within a reasonable scan time. This study describes a theoretical framework for measuring arterial transit time using a two-compartment model, followed by application of the model to CASL perfusion data obtained from six normal subjects. CBF and arterial arrival time maps were successfully created using a two-parameter fitting procedure, and the transit time obtained with this model was consistent with those obtained from previous reports. However, the CBF values calculated with the present model were lower than those reported when using 1.5T. Possible reasons for this discrepancy, including transit time, CBV, label efficiency and MT effect, are discussed.

In vivo, water diffusion displays directionality due to presence of complex microstructural barriers in tissue. The extent of directionality of water diffusion can be expressed as a fractional anisotropy (FA) value, using diffusion tensor MR imaging (DTI). The aim of this study was to determine whether FA values indicate microstructures in astrocytic tumors. We performed DTI in 31 patients with astrocytic tumor, and measured the FA values of tumor and normal brain regions prior to CT-guided stereotactic biopsy. After biopsy, FA values were compared to assess the cellularity and vascularity of tumor tissue. Although mean FA values trended to differ among histological types, all mean tumor FA values were lower than those of normal brain regions. Positive correlation was observed between FA values and both cellularity (r = 0.65, p < 0.05) and vascularity (r = 0.45, p < 0.05). We had hypothesized that the FA value of an astrocytic tumor would be determined by a balance between factors increasing the directionality of water diffusion, such as high cellularity and/or vascularity, and factors decreasing the directionality of water diffusion, such as fiber destruction. However, our results suggest that the FA values of glioblastoma, anaplastic astrocytoma, diffuse astrocytoma and pilocytic astrocytoma are largely affected by cellularity and/or vascularity, whereas that of gliomatosis cerebri are largely affected by the preservation of nerve fibers. Measurement of FA value using DTI will allow prediction of histological characteristics such as cellularity, vascularity and/or fiber structure in astrocytic tumors.

We determined the apparent diffusion coefficients of normal and dysfunctional salivary glands.A diffusion-weighted single-shot spin-echo type of echoplanar MR imaging was performed on the parotid or submandibular glands, or both, in 36 healthy subjects, 20 patients with Sjögren's syndrome, and six patients with sialoadenitis. The apparent diffusion coefficient of the salivary gland was calculated using two b factors (b = 500 and 1,000 sec/mm(2)).The apparent diffusion coefficient was lower in the parotid glands (0.28 x 10(-3) mm(2)/sec) than that of the submandibular glands (0.37 x 10(-3) mm(2)/sec). The apparent diffusion coefficient was increased in sialoadenitis, whereas it decreased with abscess formation. The apparent diffusion coefficients of the parotid glands in patients with Sjögren's syndrome correlated with the salivary flow rates but not with the sialographic gradings of the glands. We also found a correlation of the decreases in apparent diffusion coefficients with the severity of gland damage as assessed on T1-weighted MR images.Diffusion-weighted echoplanar MR imaging may reveal diseased states of the salivary glands.

Purpose: Our goal was to test the hypothesis, as previously reported in other studies, that apparent diffusion coefficients (ADCs) provide specific information to diagnose ovarian tumors, especially to discriminate between benign and malignant lesions. Method: Tl- and T2-weighted spin echo imaging and diffusion-weighted echo planar imaging were performed in 31 women with 61 cystic components of ovarian tumors. Results: The lesions that showed typical watery intensity, hypointensity in Ti-weighted imaging, and hyperintensity in T2-weighted imaging had similar ADCs, ranging from 1.54 to 1.84 x 10 -3 mm 2 /s. The lesions that showed signal intensity different from typical watery intensity in conventional MRI tended to have low ADCs. In endometrial cysts, the mean ADC of the subgroup that showed typical watery intensity was higher than that of other subgroups. Conclusion: With conventional MRI, a tendency of ADCs could be predicted. ADCs may not provide additional information, especially to discriminate benign from malignant lesions.

Joji Nishimura,1 Shingo Kakeda,1 Osamu Abe,2 Reiji Yoshimura,3 Keita Watanabe,1 Naoki Goto,3 Hikaru Hori,3 Toru Sato,1 Hidemasa Takao,4 Hiroyuki Kabasawa,5 Jun Nakamura,3 Yukunori Korogi1 1Department of Radiology, University of Occupational and Environmental Health School of Medicine, Fukuoka, Japan; 2Department of Radiology, Graduate School of Medicine, Nihon University, Tokyo, Japan; 3Department of Psychiatry, University of Occupational and Environmental Health School of Medicine, Fukuoka, Japan; 4Department of Radiology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan; 5MR Applied Science Laboratory Japan, GE Yokogawa Medical Systems, Hino-shi, Tokyo, Japan Abstract: The aims of this study are to determine how the interval changes of the brain structures in the early stage of first-episode schizophrenia relate to the interval changes in the clinical data, including the clinical symptoms of schizophrenia and catecholaminergic measures (plasma homovanillic acid [HVA] and 3-methoxy-4-hydroxyphenylglycol [MHPG]). Regional brain volumes and fractional anisotropy (FA)/mean diffusivity (MD) with diffusion tensor imaging (DTI) were measured at baseline and 6-month follow-up in a 3T magnetic resonance imaging (MRI) system in a cohort of 16 schizophrenic patients, who were in their first episode at the time of baseline MRI. At the time of baseline and follow-up MRI, all 16 patients underwent evaluations that included a psychopathological assessment (Positive and Negative Syndrome Scale [PANSS]) and peripheral catecholaminergic measures (plasma MHPG or HVA). For interval changes between baseline and follow-up MRI data (morphological change, MD, and FA), the correlation/regression analysis was performed as a series of single regression correlations in Statistical Parametric Mapping 5, with the interval changes in PANSS or plasma HVA and MHPG as the covariates of interest. Positive and inverse correlations contrasts were created, and in this preliminary analysis, a family-wise error-corrected threshold of P

Background Spontaneous intracranial vertebrobasilar artery dissection (iVBD) is a cause of ischemic stroke and subarachnoid hemorrhage in young adults that can be detected noninvasively by using multisequence magnetic resonance imaging (MRI). However, MRI findings are sometimes difficult to interpret, and its accuracy tends to be suboptimal, especially during the acute period. Therefore, we investigated whether 3-dimensional (3D) vessel wall imaging (VWI) technique could readily detect iVBD lesions in acute phase patients. Methods Sixteen consecutive patients with acute ischemic stroke caused by iVBD were prospectively examined with a 1.5-T magnetic resonance scanner. T1-weighted (T1W) 3D-VWI was obtained using a flow-sensitized 3D fast spin-echo technique. In addition, multisequence MRI comprising magnetic resonance angiography (MRA), basiparallel anatomical scanning (BPAS), and axial T1W imaging (T1WI) were also examined. Presence of luminal stenosis, aneurysmal dilatation, intramural high signal, and intimal flap/double lumen of the vertebral and basilar arteries were visually assessed using each technique. Results On 3D-VWI, luminal stenosis, aneurysmal dilatation, intramural high signal, and intimal flap were observed in 16 (100%), 11 (68.8%), 16 (100%), and 1 (6.3%) patients, respectively. In contrast, on conventional techniques, these findings were observed in 15 (93.8%, MRA with BPAS), 12 (75.0%, MRA with BPAS), 12 (75.0%, T1WI), and 12 (75.0%, MRA) patients, respectively. Conclusions The T1W 3D-VWI can directly visualize vessel wall iVBD lesions during the acute period of stroke compared with multisequence MRI.

The spatial functional distribution of the nerve fibers was investigated in the corticospinal tract at the level of the corona radiata. Thirteen patients with corona radiata infarction underwent axial single-shot echo planar diffusion-weighted magnetic resonance imaging using a 1.5 Tesla scanner. Image analysis used the three-dimensional anisotropy contrast (3DAC) method to demarcate the nerve fibers in the corticospinal tract. Axial 3DAC images demonstrated the corticospinal tract as a distinct area indicating nerve fiber integrity in all normal hemispheres and infarction as a dark or black area in affected hemispheres. Seven patients with upper extremity-dominant motor dysfunction had infarction located in the middle one third of the corticospinal tract. A patient with lower extremity-dominant motor dysfunction had infarction in the posterior one third. Five patients with equal motor dysfunction in the upper and lower extremities had infarction in both the middle and posterior one thirds of the corticospinal tract. The recovery of motor dysfunction at one month follow up correlated with the location of the corticospinal tract injury on the initial 3DAC images. The findings of the 3DAC images provide an indicator of the pattern and the recovery from acute and chronic motor dysfunction in patients with corona radiata infarction.

The purpose of our study was to compare the value of respiratory-triggered fast spin-echo, breath-hold single-shot fast spin-echo, and breath-hold fast-recovery fast spin-echo sequences in detecting hepatic lesions. Fat-suppressed T2-weighted magnetic resonance (MR) images obtained with the three sequences in 36 patients with 138 lesions and nine patients without lesions were prospectively analyzed. Quantitative and qualitative analyses, including receiver operating characteristic (ROC) analyses, were performed. The mean lesion-to-liver contrast-to-noise ratio (CNR) for hepatic lesions was highest with the respiratory-triggered fast spin-echo sequence. On the basis of receiver-operating characteristic analyses, tumor detection rates were higher with the breath-hold fast-recovery fast spin-echo sequence (Az = 0.94) than with the respiratory-triggered fast spin-echo sequence (AZ = 0.80, P < 0.0001) or the single-shot fast spin-echo sequence (Az = 0.77, P < 0.0001). The image quality with the breath-hold fast-recovery fast spin-echo sequence was acceptable in all patients. The breath-hold fast-recovery fast spin-echo sequence provided the highest tumor detection in a short imaging time, although the mean lesion-to-liver CNRs were inferior to those of the respiratory-triggered fast spin-echo and the breath-hold single-shot fast spin-echo sequences. J. Magn. Reson. Imaging 2001;14:439–449. © 2001 Wiley-Liss, Inc.

Purpose To improve the workflow of MRI abdominal scans by reducing the examination time and operator skill dependence related to bolus tracker positioning. Methods Ten or more axial images of two-dimensional scout scan were analyzed to identify the aorta and detect its center position using the mean shift to allow automated bolus tracker placement. Adaptive boosting (AdaBoost) classifier was used to identify the aorta rotating a sub-window around the cerebrospinal fluid (CSF), the location of which was detected in each axial image in advance. The search region of the aorta in the next inferior axial image was restricted to half to reduce computation time. Tests were conducted using the proposed method with a 1.5 T scanner in 31 volunteers. Results The success rate of aorta detection was 98.4%, and the accuracy of center location was around 0 – 5 mm shift from the true center. The computation time was 30 s on MATLAB, which was half that required for non-restrictive search. Conclusion The proposed algorithm was able to accurately detect the aorta in all volunteers with practical computation time so that the automated bolus tracker placement improved the workflow of MRI abdominal scans.

Serial magnetic resonance imaging (MRI) images acquired from multisite and multivendor MRI scanners are widely used in measuring longitudinal structural changes in the brain. Precise and accurate measurements are important in understanding the natural progression of neurodegenerative disorders such as Alzheimer's disease. However, geometric distortions in MRI images decrease the accuracy and precision of volumetric or morphometric measurements. To solve this problem, the authors suggest a commercially available phantom-based distortion correction method that accommodates the variation in geometric distortion within MRI images obtained with multivendor MRI scanners.The authors' method is based on image warping using a polynomial function. The method detects fiducial points within a phantom image using phantom analysis software developed by the Mayo Clinic and calculates warping functions for distortion correction. To quantify the effectiveness of the authors' method, the authors corrected phantom images obtained from multivendor MRI scanners and calculated the root-mean-square (RMS) of fiducial errors and the circularity ratio as evaluation values. The authors also compared the performance of the authors' method with that of a distortion correction method based on a spherical harmonics description of the generic gradient design parameters. Moreover, the authors evaluated whether this correction improves the test-retest reproducibility of voxel-based morphometry in human studies.A Wilcoxon signed-rank test with uncorrected and corrected images was performed. The root-mean-square errors and circularity ratios for all slices significantly improved (p0.0001) after the authors' distortion correction. Additionally, the authors' method was significantly better than a distortion correction method based on a description of spherical harmonics in improving the distortion of root-mean-square errors (p0.001 and 0.0337, respectively). Moreover, the authors' method reduced the RMS error arising from gradient nonlinearity more than gradwarp methods. In human studies, the coefficient of variation of voxel-based morphometry analysis of the whole brain improved significantly from 3.46% to 2.70% after distortion correction of the whole gray matter using the authors' method (Wilcoxon signed-rank test, p0.05).The authors proposed a phantom-based distortion correction method to improve reproducibility in longitudinal structural brain analysis using multivendor MRI. The authors evaluated the authors' method for phantom images in terms of two geometrical values and for human images in terms of test-retest reproducibility. The results showed that distortion was corrected significantly using the authors' method. In human studies, the reproducibility of voxel-based morphometry analysis for the whole gray matter significantly improved after distortion correction using the authors' method.

To develop and demonstrate the feasibility of a new technique for respiratory-gated, fat-suppressed, three-dimensional spoiled gradient-recalled echo (3D-SPGR) with navigator gating for more accurate and robust motion detection.A navigator-gated 3D-SPGR technique was modified to include a wait period immediately prior to the navigator sequence for magnetization recovery. Furthermore, a variable flip angle scheme was realized by a combination of ramp-up, ramp-down, and attenuation strategies for optimizing point spread functions. Phantom and human experiments were conducted with our technique on 1.5T scanners.Using the method, T1-weighted 3D images with improved signal homogeneity were acquired with a maximum flip angle of 30° in phantom and human tests. Also, compared with the conventional navigator-gated 3D-SPGR, accurate respiratory motion detection of free-breathing subjects was provided, leading to reduced motion artifacts.The combination of wait insertion and the variable flip angle method improved both motion detection accuracy and image homogeneity in a navigator-gated 3D-SPGR study.

Purpose We propose an automated scan prescription to assess normal and deformed livers and demonstrate its efficacy in normal volunteers and in simulated deformed livers. Methods Our automated scan prescription can be used to identify the upper and lower edges of the liver enables in commonly used axial slice positioning. The liver's upper edge is detected by template matching and finally identified by applying an active shape model to a sagittal projection image. The lower edge is detected using a maximum a posteriori (MAP) probability estimate that utilizes statistical information from a region of interest (ROI) placed in the liver. This places no restraints on liver shape and is therefore effective in assessing a deformed liver. Following institutional review and approval, we tested our method in 45 healthy volunteers. We also used clinical information to simulate deformed livers and tested our method with those datasets offline. Results We could detect the upper edges within an error range of -3 to 6 mm, even without intensity correction for normal volunteers. Similar detection of the lower edges with maximum 21-mm and 7.84-mm standard deviation for normal volunteers confirmed the superior efficacy of our modified approach for deformed livers to that using our previous method. Clinical use required approximately 10 s' computational time on a Core i5 laptop with 2-GB memory. Conclusion We propose a method for automated scan prescription in magnetic resonance (MR) imaging of the liver and demonstrate the efficacy of our algorithm for evaluating deformed livers within a practical computation time. Detection of liver edges of various shapes by applying the MAP estimate combined with statistical information from the ROI demonstrated the potential clinical utility of this technique.

The introduction of ultrahigh-field MRI at 7 tesla (7T) has increased the interest in the use of neuroimaging techniques in clinical research. The high signal-to-noise ratio and profound susceptibility effect at 7T can remarkably improve the spatial resolution and image contrast of structural imaging, susceptibility imaging, and functional imaging techniques, whereas the heating effects of the radio frequency and the inhomogeneities of the local magnetic field can have substantial negative effects on parameter setting, acquisition time, and image quality. T1 prolongation at 7T can improve the enhancement effects of gadolinium agents and the inflow effects on MR angiography and arterial spin labeling. Ultrahigh-field MRI is expected to have a high clinical impact in the near future; however, further technological advances tailored to ultrahigh-field systems as well as the accumulation of scientific evidence will be needed to establish its clinical significance.

Purpose We aimed to show that correcting image distortion significantly affects brain volumetry using voxel-based morphometry (VBM) and to assess whether the processing of distortion correction reduces system dependency. Materials and methods We obtained contiguous sagittal T(1)-weighted images of the brain from 22 healthy participants using 1.5- and 3-tesla magnetic resonance (MR) scanners, preprocessed images using Statistical Parametric Mapping 5, and tested the relation between distortion correction and brain volume using VBM. Results Local brain volume significantly increased or decreased on corrected images compared with uncorrected images. In addition, the method used to correct image distortion for gradient nonlinearity produced fewer volumetric errors from MR system variation. Conclusion This is the first VBM study to show more precise volumetry using VBM with corrected images. These results indicate that multi-scanner or multi-site imaging trials require correction for distortion induced by gradient nonlinearity.

Object: To propose a new arterial spin labeling (ASL) perfusion-imaging method (alternate slab width inversion recovery ASL: AIRASL) that takes advantage of the qualities of 3.0 T. Materials and methods: AIRASL utilizes alternate slab width IR pulses for labeling blood to obtain a higher signal-to-noise ratio (SNR). Numerical simulations were used to evaluate perfusion signals. In vivo studies were performed to show the feasibility of AIRASL on five healthy subjects. We performed a statistical analysis of the differences in perfusion SNR measurements between flow-sensitive alternating inversion recovery (FAIR) and AIRASL. Results: In signal simulation, the signal obtained by AIRASL at 3.0 and 1.5 T was 1.14 and 0.85%, respectively, whereas the signal obtained by FAIR at 3.0 and 1.5 T was 0.57 and 0.47%, respectively. In an in vivo study, the SNR of FAIR (3.0 T) and FAIR (1.5 T) were 1.73 ± 0.49 and 1.02 ± 0.20, respectively, whereas the SNRs of AIRASL (3.0 T) and AIRASL (1.5 T) were 3.93 ± 1.65 and 1.34 ± 0.31, respectively. SNR in AIRASL at 3.0 T was significantly greater than that in FAIR at 3.0 T. Conclusion: The most significant potential advantage of AIRASL is its high SNR, which takes advantage of the qualities of 3.0 T. This sequence can be easily applied in the clinical setting and will enable ASL to become more relevant for clinical application. © 2012 ESMRMB., Article in Press エンバーゴ設定 Thesis of Fujiwara, Yasuhiro / 藤原 康博 博士学位論文(金沢大学 / 大学院医薬保健学総合研究科)

Purpose: To depict supraaortic arteries using (3D fast spin echo (FSE) combined with slab selective inversion recovery for noncontrast magnetic resonance angiography (MRA) in healthy volunteers, and to investigate the property of the inflow enhanced inversion recovery FSE (IFIR-FSE) for background suppression and inflow effects. Materials and Methods: IFIR-FSE with no image subtraction was used to visualize the aortic arch, subclavian arteries, carotid arteries, and vertebral arteries in 10 healthy volunteers. Simulations were performed to achieve both high background suppression and inflow effects by adjusting the inversion time (TI) and wait time after data acquisition. The effect of inflow was investigated with TIs of 800, 1200, 1600, and 2000 msec. Contrast between artery and these background tissues were measured with scan protocols based on simulation results. Results: IFIR-FSE images showed good visualization of the supraaortic arteries and allowed separation of arteries from veins without image subtraction. The proposed method demonstrated that a high contrast between arteries and background tissues can be acquired with various TIs, which was in good agreement with the simulation. A TI over 1600 msec was favorable in terms of background suppression, arterial signal intensity, and inflow effects. Conclusion: Inflow enhanced inversion recovery cardiac-triggered 3D FSE imaging can be used for supraaortic artery imaging without contrast agents. J. Magn. Reson. Imaging 2012;35:957–962. © 2011 Wiley Periodicals, Inc.

Purpose To clarify age-related structural changes specific to hippocampal volume by hierarchizing according to age, gender, and menopausal status. Many studies report the neuroprotective effects of estrogen and age-related brain volume changes; however, there are no studies regarding age-related change specific to hippocampal volume in terms of age, gender, and menopausal status. Materials and Methods T1-weighted MR images were obtained in 412 healthy adults divided into eight groups according to age and gender, to analyze brain volume change focusing on hippocampal volume. Results Voxel-based morphometry (VBM) revealed significantly smaller gray matter volume in the hippocampus bilaterally in females aged in their fifties (51 of 59 females were at menopause) compared with females in their forties (3 of 46 females were at menopause). No significant difference was found, however, between female groups in their fifties versus sixties, or sixties versus seventies; or between male groups in their forties versus fifties, fifties versus sixties, or sixties versus seventies. In addition, VBM revealed significant hippocampal volume reduction bilaterally in all postmenopausal women compared with all premenopausal women. Conclusion The results of the current study suggest that the menopause may be associated with hippocampal volume reduction. J. Magn. Reson. Imaging 2011;33:48–53. © 2010 Wiley-Liss, Inc.