Assessment of the cut-off value of quantitative liver-portal vein contrast ratio in the hepatobiliary phase of liver MRI.

AIM: To calculate the quantitative liver-portal vein contrast ratio (Q-LPC) cut-off value based on tumour detectability by using receiver operating characteristic (ROC) curves. MATERIALS AND METHODS: Seventy-four patients with tumours (46 men and 28 women; age, 71 ± 8.1 years), who underwent liver magnetic resonance imaging (MRI) using gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) were enrolled. Some patients were found to have multiple tumours. In total, 102 tumour images were evaluated for quantitative liver-spleen contrast ratio (Q-LSC) and Q-LPC 10 minutes after the administration of Gd-EOB-DTPA. Q-LPC and Q-LSC were compared to assess the cut-off values and usefulness. The ROC curve was evaluated using the method for continuously distributed test results, with a free scale of 50 mm. A score of ≥30 out of 50 points was considered good. Cut-off values of Q-LPC and Q-LSC were then calculated. The areas under the ROC curve (AUCs) were also examined and compared. RESULTS: The AUC-ROC for Q-LPC was 0.858 (95% confidence interval [CI], 0.783-0.933). The cut-off value was determined to be at 1.462. Sensitivity was 0.747, and specificity was 0.852 at the cut-off value. The AUC-ROC for Q-LSC was 0.710 (95% CI, 0.597-0.822). The cut-off value was at 1.543, the sensitivity was 0.560, and the specificity was 0.778 at the cut-off value. A significant difference was noted between the AUCs (p=0.0016). CONCLUSION: Q-LPC can be used for hepatobiliary phase MRI evaluation.

Visualization of Nigrosome 1 from the Viewpoint of Anatomic Structure.

BACKGROUND AND PURPOSE: Parkinson disease is related to neurodegeneration and iron deposition in the substantia nigra pars compacta and nigrosome 1. However, visualization of nigrosome 1 via MR imaging is poor owing to the bilateral asymmetry, regardless of whether it is healthy. We focused on the magic angle and susceptibility effect and evaluated the anatomic slant structure of nigrosome 1 by tilting subjects' heads in the B0 direction. MATERIALS AND METHODS: To investigate the effectiveness of the magic angle, we tilted the volunteers' heads to the right and left in the B0 direction or not at all for evaluating correlations between the degree of head tilting and visualization of the right nigrosome 1 and left nigrosome 1 using 3D spoiled gradient-echo sequences with multiecho acquisitions. We evaluated the susceptibility of nigrosome 1 and the local field using quantitative susceptibility mapping to assess static magnetic field inhomogeneity. RESULTS: The heads tilted to the right and left showed significantly higher contrasts of nigrosome 1 and the substantia nigra pars compacta than the nontilted heads. No significant differences were observed in the visualization and susceptibility between the right nigrosome 1 and left nigrosome 1 for each head tilt. The effect of the magic angle was remarkable in the nontilted heads. This finding was supported by quantitative susceptibility mapping because the anatomic slant structure of nigrosome 1 was coherent between the axis of nigrosome 1 and the magic angle. CONCLUSIONS: The asymmetric visualization of nigrosome 1 is affected by the magic angle and susceptibility. The anatomic slant structure of nigrosome 1 causes these challenges in visualization.

Visual criterion for evaluating hepatobiliary phase image acquisition of gadolinium-ethoxybenzyl-diethylenetriaminepentaacetic acid-enhanced MRI.

AIM: To evaluate the hepatobiliary phase (HBP) of liver magnetic resonance imaging (MRI) using gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid, and report a visual criterion based on the portal vein (PV), which can be used as a substitute for the quantitative liver-spleen contrast ratio (Q-LSC). MATERIALS AND METHODS: In HBP images of 167 patients, a visual criterion was established based on the sufficient contrast between the liver parenchyma (LP) and PV. The Q-LSC was calculated for patients to assess whether the cut-off value of 1.5 was exceeded. The correlation between the signal intensities in the PV and tumours were determined and comparisons were made. The contrast between LP and the tumour was visually assessed with scores ranging from 1 to 3 defined as poor, fair, and good, respectively. The correlation between Q-LSC and quantitative liver-PV contrast ratio (Q-LPC) was also assessed. RESULTS: The Q-LSC was <1.5 in all patients who did not meet the visual criterion. There was a strong correlation between the signal intensities in the PV and tumours (r=0.72), and no significant differences (p=0.99) were found between the signal intensities in PV and tumours by Wilcoxon's signed-rank test. Significant differences of all the combinations were found using Steel-Dwass multiple comparisons in the visual assessments of contrasts between LP and tumour. The correlation between Q-LSC and Q-LPC was strong (r=0.82). CONCLUSIONS: The visual criterion based on the PV was suitable for the assessment of HBP images as a substitute for Q-LSC.

The Dixon technique and the frequency-selective fat suppression technique in three-dimensional T1 weighted MRI of the liver: a comparison of contrast-to-noise ratios of hepatocellular carcinomas-to-liver.

OBJECTIVE: The use of three-dimensional T1 weighted gradient echo sequences such as the Dixon technique and the frequency-selective fat suppression (FS) technique is currently widely accepted method in MRI examinations of the liver. To assess the image qualities of the Dixon technique and the frequency-selective FS technique, the contrast-to-noise ratios (CNRs) of hepatocellular carcinoma (HCC)-to-liver and fat-to-liver were compared between the two techniques in the hepatobiliary phase (HBP) following administration of gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid. METHODS: MR images of 59 patients with a total of 86 HCCs were retrospectively evaluated. Images were consecutively obtained with the Dixon and frequency-selective FS methods in the HBP and their CNRs of HCC-to-liver and fat-to-liver were compared. CNRs and contrast ratios were calculated by the mean value of the liver parenchyma, HCC, fat and standard deviation of the liver parenchyma. The Wilcoxon signed-ranks test was used for statistical analysis. RESULTS: The median CNRs for the frequency-selective FS and Dixon techniques of HCC-to-liver were 4.3 and 5.4 (p < 0.01), mesenteric fat-to-liver were 9.9 and 12.8 (p < 0.01) and subcutaneous fat-to-liver were 9.9 and 13.2 (p < 0.01), respectively. CONCLUSION: The Dixon technique yielded higher CNRs of HCC-to-liver than that of the frequency-selective FS technique. ADVANCES IN KNOWLEDGE: There are a limited number of reports on quantitative analysis of the image qualities of the Dixon technique and the frequency-selective FS technique, particularly within the same patient and examination.

Influence of parameter settings in voxel-based morphometry 8. Using DARTEL and region-of-interest on reproducibility in gray matter volumetry.

OBJECTIVES: To investigate whether reproducibility of gray matter volumetry is influenced by parameter settings for VBM 8 using Diffeomorphic Anatomical Registration Through Exponentiated Lie Algebra (DARTEL) with region-of-interest (ROI) analyses. METHODS: We prepared three-dimensional T1-weighted magnetic resonance images (3D-T1WIs) of 21 healthy subjects. All subjects were imaged with each of five MRI systems. Voxel-based morphometry 8 (VBM 8) and WFU PickAtlas software were used for gray matter volumetry. The bilateral ROI labels used were those provided as default settings with the software: Frontal Lobe, Hippocampus, Occipital Lobe, Orbital Gyrus, Parietal Lobe, Putamen, and Temporal Lobe. All 3D-T1WIs were segmented to gray matter with six parameters of VBM 8, with each parameter having between three and eight selectable levels. Reproducibility was evaluated as the standard deviation (mm³) of measured values for the five MRI systems. RESULTS: Reproducibility was influenced by 'Bias regularization (BiasR)', 'Bias FWHM', and 'De-noising filter' settings, but not by 'MRF weighting', 'Sampling distance', or 'Warping regularization' settings. Reproducibility in BiasR was influenced by ROI. Superior reproducibility was observed in Frontal Lobe with the BiasR1 setting, and in Hippocampus, Parietal Lobe, and Putamen with the BiasR3*, BiasR1, and BiasR5 settings, respectively. CONCLUSION: Reproducibility of gray matter volumetry was influenced by parameter settings in VBM 8 using DARTEL and ROI. In multi-center studies, the use of appropriate settings in VBM 8 with DARTEL results in reduced scanner effect.

Delta-ADC (apparent diffusion coefficient) analysis in patients with idiopathic normal pressure hydrocephalus.

We have developed the delta-apparent diffusion coefficient (ADC), a new parameter of the water dynamics of brain tissue using MRI. Delta-ADC is the changes in regional ADC values of the brain during the cardiac cycle. The study included 6 idiopathic normal pressure hydrocephalus (iNPH) patients (iNPH group) and 12 healthy volunteers (control group). ECG-triggered single-shot diffusion echo planar imaging (b = 0 and 1,000 s/mm(2)) was used on a 1.5-T MRI. The delta-ADC image was calculated from the maximum minus the minimum ADC value of all cardiac phase images (20 phases) on a pixel-by-pixel basis. Delta-ADC values in the white matter of the frontal, temporal, and occipital lobe were obtained. Delta-ADC values in the iNPH group were significantly higher than those in the control group in all regions. ADC values in the iNPH were also significantly higher than those in the control group, but the differences in the ADC between the groups in each region were much lower than those for the delta-ADC. Although the changes in the delta-ADC and ADC values were similar, there was no significant correlation between the delta-ADC and the ADC. These results suggest that the ADC and the delta-ADC may reflect different kinds of water dynamics. The ADC depends on the water content in brain tissue. On the other hand, delta-ADC depends on not only the water content, but also on the degree of the fluctuation of the water molecules. Delta-ADC analysis makes it possible to obtain non-invasively new and more detailed information on the regional brain condition in iNPH.

Development of a cone angle weighted three-dimensional image reconstruction algorithm to reduce cone-beam artefacts.

OBJECTIVES: Image reconstruction from cone-beam projections collected along a single circular source trajectory is commonly done using the Feldkamp algorithm, which performs well only with a small cone angle. In this report, we propose an algorithm to reduce cone-beam artefacts by increasing the cone angle by several fold to achieve satisfactory image quality at the same radiation dose. METHODS: To examine the factors involved in the occurrence of cone-beam artefacts, a microspheres-phantom was arranged longitudinally at different positions and a computer simulation was performed. Due to differences in projection angle, data projected onto the detector surface were projected along trajectories shown as different periodic functions depending on the distance and position from the mid-plane position. Therefore, projection along several detector channels based on different projection data resulting from different periodic functions is considered responsible for the increase in cone-beam artefacts associated with an increase in the distance of reconstruction planes from the mid-plane position. Our recommended algorithm to reduce such artefacts features a change in weighting with respect to projection data obtained at different projection angles, three-dimensional back-projection of corrected projection data. RESULTS: Numerical phantom simulation and real human head origin study (a prototype cone-beam CT) showed that the effect of the reduction in cone-beam artefacts of an object located at the edges was markedly enhanced at reconstruction planes at positions further from the mid-plane position. CONCLUSION: We propose a projection angle weight-based algorithm to increase the cone angle by several fold to achieve satisfactory image quality at the same radiation dose. These findings confirmed that this algorithm reduces cone-beam artefacts and generates high-quality reconstruction images.

Non-invasive measurement of intracranial compliance using cine MRI in normal pressure hydrocephalus.

The aim of this study is to clarify biophysics of normal pressure hydrocephalus (NPH) based on non-invasive intracranial compliance measurement using magnetic resonance imaging (MRI). Patients with NPH after subarachnoid hemorrhage (NPH group, n = 5), brain atrophy or asymptomatic ventricular dilation (VD group, n = 5), and healthy volunteers (control group, n = 12) were included in this study. Net blood flow (bilateral internal carotid and vertebral arteries, and jugular veins) and cerebrospinal fluid (CSF) flow in subarachnoid space at the C2 level of cervical vertebra were measured using phase-contrast cine MRI. CSF pressure gradient and intracranial volume changes during a cardiac cycle were calculated based on Alperin's method. Compliance index (Ci = delta V/delta P) was obtained from the maximum pressure gradient and volume changes. Pressure volume response (PVR) was measured in the NPH group during a shunt operation. Ci in the NPH group was the lowest among the three studies groups. No difference was found between the control and VD groups. There was a linear correlation between Ci and PVR. In conclusion, intracranial compliance can be determined by cine MRI non-invasively. It is well known that NPH has relatively low intracranial compliance, this non-invasive method can be used for the diagnosis of NPH.

Comparison of 99mTc-MIBI uptakes on planar images with those in excised rats organs.

The precision with which images reflect tracer uptake in the myocardium has been studied. Additionally, the degree to which Tc methoxyisobutylisonitrile (99mTc-MIBI) in the liver gave the effect to a myocardial image has been examined. After administering Tc-MIBI to normal male rats, we compared the myocardial uptakes obtained using a gamma camera with the actual uptakes in the excised organs. Twenty-nine rats were used. Following imaging, the anterior view at 5, 10, 15, 30, 45, 60, 90 and 120 min after administration of the tracer, uptakes in the heart, lung, liver and blood were estimated with a well-type scintillation counter (WC) and represented as the percentage of the injected dose per gram of tissue (%ID/g). The regions of interest (ROIs) were placed on planar images (PI) and the uptake in each organ was estimated as the percentage of the injected dose per pixel (%ID/pixel). The ratios of PI-to-WC and heart-to-organ were also evaluated. Cardiac uptake with WC was maximum (1.581%+/-1.893%) at 10 min post-injection. On the other hand, that with PI was maximum (1.493%+/-0.598%) at 45 min post-injection, but there were significant differences between both measurements (PI/WC ratio: about 1.0 time). Pulmonary uptake with WC was the maximum at 5 min (0.808%+/-0.015%) post-injection, and decreased gradually. PI measurement showed the maximum value at 45 min (0.760%+/-0.012%). Hepatic uptake with WC was the maximum at 30 min (0.594%+/-0.254%). On the other hand, PI measurement showed the same pattern with WC, but these values were higher value than WC as the whole. PI measurement showed higher uptakes in each organ than WC measurement. It was concluded that uptakes or the heart-to-organ ratio obtained clinically with PI might not represent a value that is always accurate.

Surgical treatment of chronic subdural hematoma based on intrahematomal membrane structure on MRI.

BACKGROUND: To determine the optimal surgical management of chronic subdural hematoma (CSDH), we assessed which operative procedure, burr holes or small craniotomy, was more effective on 49 consecutive patients. METHOD: We retrospectively classified all cases into two groups according to the intrahematomal membrane structure of CSDH on T2*-weighted magnetic resonance (MR) imaging. The first group, labeled type B, included hematomas which had no intrahematomal membrane and/or were monolayer multilobule. The second group, labeled type C, consisted of hematomas which were divided into multiple layers by the intrahematomal membrane. FINDINGS: The outcome of type C patients treated with burr holes was significantly inferior to that of those who underwent a small craniotomy in terms of the relative outcome of neurological grading. re-operation ratio, and postoperative hospital stay (p < 0.05). Type C hematomas treated with burr holes also had inferior outcome compared with a small craniotomy in terms of the duration of hematoma until disappearance on postoperative CT (p < 0.05). INTERPRETATION: We concluded that a considerable number of cases appeared to need craniotomy and resection of intrahematomal membrane for complete recovery in CSDH, and that T2*-weighted MR imaging could be used as a basis for selecting the operative procedure for CSDH.

Characteristics of acoustic noise in echo-planar imaging.

Characteristics of the acoustic noise generated by magnetic resonance imagers of different systems and performance levels were studied when operating in echo-planar imaging (EPI) sequence. Continuous equivalent A-weighted sound pressure levels (Leq) and peak impulse sound pressure levels (Lpeak) during EPI were measured in 12 clinical super-conducting MRI systems (0.5-1.5 T). Sound pressure levels and frequency spectra of EPI were compared with those of nine different pulse sequences. EPI sound pressure levels differed among institutions (Leq = 94.2 +/- 2.7 dBA. Lpeak = 109.1 +/- 3.5 dB), but these were within permissible noise exposure levels. Sound pressure levels during EPI were not significantly different from those during other pulse sequences. However, compared to other pulse sequences. EPI had a significantly greater proportion of acoustic noise in the high octave-frequency band. Single-shot EPI had relatively higher frequency noise and greater Leq than multishot EPI, but the difference in Leq decreased when the number of slices in multishot EPI was increased.

Acoustic noise analysis in echo planar imaging: multicenter trial and comparison with other pulse sequences.

The purpose of this study was to evaluate acoustic noise in echo planar imaging (EPI) at various magnetic resonance imaging (MRI) centers and to compare EPI acoustic noise with that in other fast pulse sequences. We measured A-weighted root-mean-square sound pressure levels and peak impulse sound pressure levels for EPI, under the same conditions, in eleven clinical super-conducting MRI systems. We also compared sound pressure levels for the EPI and six different pulse sequences and analyzed the acoustic noise spectra. Sound pressure levels during the use of the EPI differed greatly among institutions. Moreover, sound pressure levels of the EPI were not significantly different from those of other fast pulse sequences and were within permissible noise exposure levels. In comparison to other fast sequences, the EPI had significantly greater acoustic noise in the high-octave band frequency.

Dual dynamic contrast-enhanced MR imaging.

A method was devised for obtaining dynamic contrast-enhanced T1-weighted and relaxation rate (delta R2*) images simultaneously to evaluate regional hemodynamics of the brain tumors. On a 1.5-T MR system, dual dynamic contrast-enhanced images were obtained using a gradient echo (dual echo fast field echo) pulse sequence with the keyhole technique to improve temporal and spatial resolution during a rapid bolus injection of gadopentetate dimeglumine. The dynamic T1 contrast images were obtained from the first echo: moreover. integral delta R2*dt values were calculated from the first and the second echo images. The dynamic T1 contrast images provided information about characteristic enhancement pattern (vascularization and disruption of blood-brain barrier), and the integral delta R2*dt values provided a map of regional blood pool in tumor site, peritumoral edema, and other surrounding regions of the brain. The ability to obtain dynamic contrast-enhanced T1 contrast and delta R2* imaging at the same time allows optimization of the advantages of each and thereby more information about the microvascular circulation of the brain lesions.

Fast RARE MR imaging with variable flip angle excitation.

A method was developed for performing T1-weighted magnetic resonance imaging with the rapid acquisition with relaxation enhancement (RARE) sequence by altering the excitation flip angle. This method was called variable flip angle turbo spin-echo (VF-TSE) imaging. When the effective echo time corresponds to the first echo, the resolution worsens as the echo train length becomes longer. For this reason, the echo train length was set at three, the repetition time (TR) was shortened (100- 200 msec) to decrease imaging time, and the initial flip angle was adjusted (120 degrees-140 degrees) to improve image quality. Another advantage of this method is that the initial flip angle can be reduced to below 90 degrees when a longer TR is needed. Measured signal intensities for VF-TSE imaging matched theoretic predictions. VF-TSE imaging yielded high contrast-to-noise and signal-to-noise ratios without sacrificing resolution. The VF-TSE technique was useful for breath-hold, three-dimensional, and cardiac synchronization imaging.