Hiroyuki Kabasawa

Diffusion-weighted echo planar imaging of ovarian tumors: is it useful to measure apparent diffusion coefficients?

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 T1-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 T1-weighted imaging, and hyperintensity in T2-weighted imaging had similar ADCs, ranging from 1.54 to 1.84 × 10−3 mm2 /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.

Voxel-based analysis of the diffusion tensor

IntroductionDiffusion 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).MethodsWe 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.ResultsWith 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.ConclusionThe 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.

Fat-suppressed T2-weighted MRI of the liver: Comparison of respiratory-triggered fast spin-echo, breath-hold single-shot fast spin-echo, and breath-hold fast-recovery fast spin-echo sequences

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.

Effect of scanner in longitudinal diffusion tensor imaging studies

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.

Evaluation of super paramagnetic iron oxide-enhanced diffusion-weighted PROPELLER T2-fast spin echo magnetic resonance imaging: Preliminary experience.

Objective: To evaluate the usefulness of super paramagnetic iron oxide-enhanced, diffusion-weighted, periodically rotated overlapping parallel lines with enhanced reconstruction (SPIO DWI PROPELLER) T2-fast spin echo (FSE) magnetic resonance imaging (MRI) for the detection of hepatic metastases. Methods: Fourteen patients were examined with SPIO-enhanced T2-FSE (SPIO FSE) imaging and SPIO DWI PROPELLER T2-FSE imaging. The b-value of the diffusion-sensitizing gradient was 10 s/mm2 so as to suppress the signal of the hepatic vessels. Hepatic resections were performed on all patients, and the number of lesions on MRI was compared between the 2 pulse sequences with references from pathologic reports. Results: Nearly all metastases 1 cm or larger, totalling 38 metastases, were detected with both pulse sequences. Among the 30 metastases less than 1 cm, more lesions were detected on SPIO DWI PROPELLER T2-FSE imaging than on SPIO FSE imaging (16 for SPIO FSE imaging and 24 for DWI PROPELLER T2-FSE imaging; P < 0.05, McNemar test). Conclusion: Super paramagnetic iron oxide-enhanced DWI PROPELLER T2-FSE is useful for detecting small hepatic metastases.

Sex dimorphism in gray/white matter volume and diffusion tensor during normal aging

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. Copyright

Three-dimensional susceptibility-weighted imaging at 3 T using various image analysis methods in the estimation of grading intracranial gliomas

OBJECT Although three-dimensional (3D), high-spatial resolution susceptibility-weighted imaging (SWI) appears to be valuable in the evaluation of central nervous system gliomas, several evaluation methods are proposed in the literature. The purpose of this study was to evaluate the use of 3D SWI for grading intracranial gliomas with various analysis methods. MATERIALS AND METHODS Twenty-three patients suspected of having gliomas participated in this study. SWI was performed in addition to conventional MR sequences. In 15 cases, post-gadolinium enhanced SWI was also obtained. Imaging evaluation criteria were conventional grade, hypointensity ratio in the tumor-dominant structure of hypointensity on SWI (hemorrhage or vascular structure) and presence of abnormal enhancement surrounding the tumor. RESULTS Mean grading scores of conventional grade showed no statistically significant difference among WHO grades. Mean grading scores of hypointensity ratios in the tumor were higher for WHO Grades 3 and 4 than for lower grade tumors (P=.05, Mann-Whitney U test). Hemorrhagic foci were more frequently seen in the higher grade tumor. Post-contrast susceptibility-weighted images of five of 11 WHO Grade 3 and 4 cases showed bright enhancement surrounding the tumor, suggesting a breakdown of the blood-brain barrier. CONCLUSIONS SWI at 3 T may be a useful method to analyze the structural characteristics of gliomas and to evaluate pathology in vivo. Assessment of hypointensity ratios in the glioma was the most preferable method in grading glioma. However, more studies, specifically concerning a suitable method for image analysis, are needed to establish SWI at 3 T as a useful tool in clinical routine.

Evaluating Middle Cerebral Artery Atherosclerotic Lesions in Acute Ischemic Stroke Using Magnetic Resonance T1-weighted 3-Dimensional Vessel Wall Imaging

BACKGROUND Atherosclerotic lesions in intracranial arteries are a leading cause of ischemic stroke. Magnetic resonance angiography (MRA) is often used to assess atherosclerotic changes by detecting luminal narrowing, whereas it cannot directly visualize atherosclerotic lesions. Here, we used a 3-dimensional vessel wall imaging (3D-VWI) technique to evaluate intracranial arterial wall changes in acute stroke. METHODS Eighteen consecutive patients with acute noncardioembolic stroke in the middle cerebral artery (MCA) territory who were prospectively examined with a 1.5-T magnetic resonance scanner were studied. T1-weighted (T1-W) 3D-VWI was obtained using a flow-sensitized 3D fast-spin echo technique. Wall thickening of MCA that suggests atherosclerotic plaques was visually evaluated and the contrast ratio (CR) of signal intensity of the lesions to that of the corpus callosum was calculated and compared with stenotic changes by MRA. RESULTS Wall thickenings of the MCA ipsilateral and contralateral to the lesion were observed in almost all patients on 3D-VWI (94.4% and 94.4%, respectively), whereas MRA showed stenotic changes of 50% only in 1 patient (5.9%; P < .001). The CR of the thickened wall in the ipsilateral MCA was significantly higher than that in the contralateral MCA (median, .53 and .45, respectively; P = .028), suggesting of unstable plaques consisting of hemorrhage or lipid. CONCLUSIONS The T1-W 3D-VWI can provide direct visualization of atherosclerotic lesions of the intracranial arteries in stroke patients, and it can detect signal change suggestive of unstable plaque.

Precontrast and postcontrast susceptibility-weighted imaging in the assessment of intracranial brain neoplasms at 1.5 T

PurposeThe goal of this study was to estimate pre- and post-gadolinium-enhanced high-spatial resolution susceptibility-weighted imaging (SWI) in patients with brain neoplasms.Materials and methodsA total of 17 patients (8 women, 9 men) with brain neoplasms participated in this study. In addition to conventional magnetic resonance imaging, pre- and post-gadolinium-enhanced SWI was performed. The contrast-to-noise ratio (CNR) and major diameters of the brain tumor were measured for quantitative analyses, and intratumoral susceptibility signal intensity (ITSS) was graded for semiquantitative analysis.ResultsBoth bright and dark enhancement were observed at the pathological lesion on postcontrast SWI. Some postcontrast SWI results suggested leakage of contrast material due to breakdown of the blood-brain barrier. There were no statistical differences (Student’s t-test) between postcontrast SWI and three-dimensional (3D) T1-weighted images regarding the major diameters of the brain tumors. CNR of postcontrast 3D T1-weighted images was statistically superior to that of postcontrast SW images (P < 0.01, Wilcoxon signed-rank test). Malignant tumors tended to have a higher ITSS score.ConclusionSWI clearly visualized the architecture of brain neoplasms. This imaging technique may be useful for evaluating tumor characterization in clinical use.

Flexible ex vivo phantoms for validation of diffusion tensor tractography on a clinical scanner

PurposeThe aim of this study was to develop ex vivo diffusion tensor (DT) flexible phantoms.Materials and methodsMaterials were bundles of textile threads of cotton, monofilament nylon, rayon, and polyester bunched with spiral wrapping bands and immersed in water. DT images were acquired on a 1.5-Tesla clinical magnetic resonance scanner using echo planar imaging sequences with 15 motion probing gradient directions. DT tractography with seeding and a line-tracking method was carried out by software originally developed on a PC-based workstation.ResultsWe observed relatively high fractional anisotropy on the polyester phantom and were able to reconstruct tractography. Straight tracts along the bundle were displayed when it was arranged linearly. It was easy to bend arcuately or bifurcate at one end; and tracts followed the course of the bundle, whether it was curved or branched and had good agreement with direct visual observation. Tractography with the other fibers was unsuccessful.ConclusionThe polyester phantom revealed a diffusion anisotropic structure according to its shape and would be utilizable repeatedly under the same conditions, differently from living central neuronal system. It would be useful to validate DT sequences and to optimize an algorithm or parameters of DT tractography software. Additionally, the flexibility of the phantom would enable us to model human axonal projections.