Comparison of qualitative and fully automated quantitative tools for classifying severity of white matter hyperintensity.

OBJECTIVE: In this study, we aimed to compare the Fazekas scoring system and quantitative white matter hyperintensity volume in the classification of white matter hyperintensity severity using a fully automated analysis software to investigate the reliability of quantitative evaluation. MATERIALS AND METHODS: Patients with suspected cognitive impairment who underwent medical examinations at our institution between January 2010 and May 2021 were retrospectively examined. White matter hyperintensity volumes were analyzed using fully automated analysis software and Fazekas scoring (scores 0-3). Using one-way analysis of variance, white matter hyperintensity volume differences across Fazekas scores were assessed. We employed post-hoc pairwise comparisons to compare the differences in the mean white matter hyperintensity volume between each Fazekas score. Spearman's rank correlation test was used to investigate the association between Fazekas score and white matter hyperintensity volume. RESULTS: Among the 839 patients included in this study, Fazekas scores 0, 1, 2, and 3 were assigned to 68, 198, 217, and 356 patients, respectively. White matter hyperintensity volumes significantly differed according to Fazekas score (F=623.5, p<0.001). Post-hoc pairwise comparisons revealed significant differences in mean white matter hyperintensity volume between all Fazekas scores (p<0.05). We observed a significantly positive correlation between the Fazekas scores and white matter hyperintensity volume (R=0.823, p<0.01). CONCLUSIONS: Quantitative white matter hyperintensity volume and the Fazekas scores are highly correlated and may be used as indicators of white matter hyperintensity severity. In addition, quantitative analysis may be more effective in classifying advanced white matter hyperintensity lesions than the Fazekas classification.

[Evaluation of Detectability in Clinical Practice of Metal Detectors, etc. for Magnetic Resonance Imaging].

PURPOSE: In order to prevent magnetic materials from being brought into the magnetic resonance imaging (MRI) examination room, many facilities have metal detectors, etc., but there are various types of equipment with different performance and characteristics. The purpose of this study was to evaluate each detector in actual clinical practice. METHODS: At multiple facilities, gate-type magnetic detectors, pole-type magnetic detectors, handy-type magnetic detectors, and handy-type metal detectors were used to identify 9 types of objects that may be brought into the MRI examination room. We performed evaluation of detection distance measurement assuming actual operation. RESULTS: The gate type was only able to detect objects with strong magnetism. With the pole type, the closer the measurement distance was to the pole, the more objects could be detected, and the lower the pole, the shorter the detection distance. With the handy type, there were many objects that could be detected when the device and the object were brought into close contact. CONCLUSION: The detectability of the instruments varied depending on the size and type of the object. It is important to understand the characteristics of each device and use it according to the purpose in carrying-in confirmation before the examination.

[Echo Train Length (ETL) of Fluid-attenuated Inversion Recovery (FLAIR) and Extraction Volume of White Matter Hyperintensity Volume in Automated White Matter Signal Analysis].

PURPOSE: To investigate whether the volume of white matter hyperintensity (WMH) extracted from FLAIR images changes when the imaging parameters of the original images are changed. METHODS: Seven healthy volunteers were imaged by changing the imaging parameter ETL of FLAIR images, and WMHs were extracted and their volumes were calculated by the automatic extraction software. The results were statistically analyzed to examine the relationship (Experiment 1). Simulated images with different SNRs were created by adding white noise to four examples of healthy volunteer images. The SNR of the simulated images simulated the SNR of the measured images of different ETLs. The WMH was extracted from the simulated images and its volume was calculated using the automatic extraction software (Experiment 2). RESULTS: Experiment 1 showed that there was no significant difference between FLAIR imaging parameters and WMH volume in automatic white matter signal analysis, except for some conditions. Experiment 2 showed that as the SNR of the original image decreased, the volume of high white matter signal extracted decreased. CONCLUSION: In automatic white matter signal analysis, WMH was shown to be small when the ETL of the FLAIR sequence was larger than normal and/or the SNR of the image was low.

Noninvasive evaluation of collateral blood flow through circle of Willis in cervical carotid stenosis using selective magnetic resonance angiography.

BACKGROUND: Preoperative assessment of intracranial collateral circulation is helpful in predicting cerebral ischemia during surgical procedures for cervical internal carotid artery (ICA) stenosis. However, magnetic resonance angiography (MRA) and other less-invasive techniques cannot evaluate collateral blood flow because these techniques are nonselective. Hence, by using a newly developed selective MRA technique, we attempted to visualize collaterals via the circle of Willis in patients with ICA stenosis. METHODS: Twelve patients who underwent carotid endarterectomy were prospectively examined with a 1.5-T MR scanner. Both selective and nonselective MRA were obtained using a 3-dimensional time-of-flight technique, with or without a cylindrical saturation pulse that suppresses the flow signal from the region of the target ICA. Maximum intensity projection MRA images were generated and compared with digital subtraction angiography (DSA) images. RESULTS: In all patients, the distal flow signal of the ipsilateral ICA was completely suppressed on selective MRA compared with nonselective MRA. In addition, collateral blood flow through the anterior and posterior communicating arteries was visualized in 5 and 2 patients, respectively. These findings corresponded well with the DSA imaging. CONCLUSIONS: Selective MRA techniques can readily suppress signals from the distal blood flow of the target artery and visualize the presence of collateral flows through the circle of Willis in patients with cervical ICA stenosis.

A robust ultrashort TE (UTE) imaging method with corrected k-space trajectory by using parametric multiple function model of gradient waveform.

Ultra-short TE (UTE) sequences with radial sampling make it possible to visualize tissues with very short T2 decay times. The UTE sequence acquires an echo signal from the central to the outer parts of k-space and is very sensitive to small trajectory errors. Therefore, k-space errors caused by imperfections in the gradient system performance, such as gradient delay and waveform distortion, must be corrected. During normal clinical use, these errors must be corrected to account for any gradient strength, or image obliquity. Because of time limitation on clinical examination, a simple, robust, and time-efficient correction method for use with UTE is needed. We demonstrated image degradation due to k-space errors by simulation and found that uncontrolled gradient time delays were the dominant cause of image degradation. They could be corrected by using a pre-scan calibration that works by comparison of half and full echo signals. Further improvements in image quality were achieved by using a one-time calibration of gradient waveform approximations that were built from multiple exponential functions and were used during image reconstruction. We have developed a robust UTE correction method that consists of a gradient waveform approximation that follows a short pre-scan for estimating gradient time delay errors.

Modified echo peak correction for radial acquisition regime (RADAR).

PURPOSE: Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B(0), some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial aquisition regime (RADAR) and expand its application sequences. METHODS: We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T(1)- and T(2)-weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence. RESULTS: The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence. CONCLUSION: Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences.

Positional lumbar imaging using a positional device in a horizontally open-configuration MR unit - initial experience.

PURPOSE: To evaluate whether positional MR images of the lumbar spine, obtained with a horizontally open-configuration MR unit, demonstrate positional changes of the dural sac, and to assess whether there are significant differences in positional changes between healthy volunteers and patients with chronic low back pain. MATERIALS AND METHODS: The study population consisted of 15 patients with chronic low back pain and 14 healthy volunteers. MR images were obtained using a horizontally open-configuration 0.4-T MR unit. After conventional lumbar MR examinations, images were obtained in the flexion, neutral, and extension positions, using a positioning device. The anteroposterior diameter of the dural sac at the level of each lumbar disk was measured in the three positions and quantitative data were compared. RESULTS: Our MR protocol was tolerated by all patients. In both patients and volunteers, the mean anteroposterior diameter of the dural sac was smaller in the extension positions than in the flexion positions. In the mean rate of change (RC) in the dural sac diameter at the site of the degenerated disks, the difference between the volunteers and patients was significant (P < 0.05). There was no significant difference in the mean RC between patients and volunteers without degenerative disks. CONCLUSION: Using a horizontally open-configuration MR unit, positional MR imaging provided position-dependent change of the dural sac. Positional changes at the site of the degenerated disks may be different in patients with and without chronic low back pain.

Interactive scan control for kinematic study in open MRI.

PURPOSE: A tool to support the subject is generally used for kinematic joint imaging with an open MRI apparatus because of difficulty setting the image plane correctly. However, use of a support tool requires a complicated procedure to position the subject, and setting the image plane when the joint angle changes is time consuming. Allowing the subject to move freely enables better diagnoses when kinematic joint imaging is performed. We therefore developed an interactive scan control (ISC) to facilitate the easy, quick, and accurate setting of the image plane even when a support tool is not used. METHODS: We used a 0.4T magnetic resonance (MR) imaging system open in the horizontal direction. The ISC determines the image plane interactively on the basis of fluoroscopy images displayed on a user interface. The imaging pulse is a balanced steady-state acquisition with rewound gradient echo (SARGE) sequence with update time less than 2 s. Without using a tool to support the knee, we positioned the knee of a healthy volunteer at 4 different joint angles and set the image plane through the patella and femur at each of the angles. Lumbar imaging is also demonstrated with ISC. RESULTS: Setting the image plane was easy and quick at all knee angles, and images obtained clearly showed the patella and femur. Total imaging time was less than 10 min, a fourth of the time needed when a support tool is used. We also used our ISC in kinematic imaging of the lumbar. CONCLUSION: The ISC shortens total time for kinematic joint imaging, and because a support tool is not needed, imaging can be done more freely in an open MR imaging apparatus.

Parallel imaging of head with a dedicated multi-coil on a 0.4T open MRI.

BACKGROUND: Parallel imaging is widely used for cylindrical magnetic resonance imaging (MRI); however, few studies apply parallel imaging to open MRI. We previously developed a parallel method called "RAPID" (rapid acquisition through a parallel imaging design) for imaging the heart on a 0.7T open MRI apparatus, and we have now developed a RAPID head coil and shading correction algorithm for imaging the brain with a 0.4T open MRI apparatus. Images acquired with RAPID were compared with those acquired using a conventional quadrature-detection (QD) head coil. MATERIALS AND METHODS: The images were acquired using a dedicated 4-channel RF receiving coil consisting of a solenoid coil and surface coils. For MRI of the brain, we developed 2 methods to acquire the necessary calibration data: a pre-scan method that acquires the calibration data before the main scans and a self-calibration method that acquires the calibration data and imaging data simultaneously. We also modified the algorithm for calculating the shading distribution so that it only uses acquired image data and then corrects the shading. RESULTS: RAPID was applied for T1-weighted, T2-weighted, fluid-attenuation inversion recovery (FLAIR), time-of-flight (TOF), and diffusion-weighted echo-planar (DW-EPI) imaging. The RAPID images had no visible unfolded artifacts or motion artifacts. Images with the same contrast as that with a conventional QD coil were acquired using the RAPID coil and shading correction. CONCLUSION: These preliminary results show that RAPID can be applied to imaging of the head using a 0.4T open MRI apparatus.

Utilization of low-field MR scanners.

The evident advantage of high-field MR (magnetic resonance) scanners is their higher signal-to-noise ratio, which results in improved imaging. While no reliable efficacy studies exist that compare the diagnostic capabilities of low- versus high-field scanners, the adoption and acceptance of low-field MRI (magnetic resonance imaging) is subject to biases. On the other hand, the cost savings associated with low-field MRI hardware are obvious. The running costs of a non-superconductive low-field scanner show even greater differences in favor of low-field scanners. Patient anxiety and safety issues also reflect the advantages of low-field scanners. Recent technological developments in the realm of low-field MR scanners will lead to higher image quality, shorter scan times, and refined imaging protocols. Interventional and intraoperative use also supports the installation of low-field MR scanners. Utilization of low-field systems has the potential to enhance overall cost reductions with little or no loss of diagnostic performance.

Cardiac cine parallel imaging on a 0.7T open system.

BACKGROUND: Parallel imaging can be applied to cardiac imaging with a cylindrical MRI (magnetic resonance imaging) apparatus. Studies of open MRI, however, are few. This study sought to achieve cardiac cine parallel imaging (or RAPID, for "rapid acquisition through parallel imaging design") with an open 0.7T MRI apparatus. MATERIALS AND METHODS: Imaging time was shortened in all slice directions with the use of a dedicated four-channel RF receiving coil comprising solenoid coils and butterfly coils. Coil shape was designed through an RF-coil simulation that considered biological load. The auto-calibration of a 0.7T open MRI apparatus incorporated a modified image-domain reconstruction algorithm. Cine images were obtained with a BASG, or balanced SARGE (steady-state acquisition with rewound gradient echo), sequence. Image quality was evaluated with cylindrical phantoms and five healthy volunteers. RESULTS: Multi-slice phantom images showed no visible artifacts. Cine images taken under breath-hold with an acceleration factor of two were evaluated carefully. With auto-calibration, the images revealed no visible unfolded artifacts or motion artifacts. RAPID thus improved the acquisition speed, time resolution, and spatial resolution of short-axis, long-axis, and four-chamber images. CONCLUSION: The use of a dedicated RF coil enabled cardiac cine RAPID to be performed with an open MRI apparatus.

Development of intraarterial contrast-enhanced 2D MRDSA with a 0.3 tesla open MRI system.

PURPOSE: The purpose of this study was to develop a new technique for a high temporal resolution two-dimensional MR digital subtraction angiography (2D MRDSA) sequence under intraarterial injection of contrast material to permit the visualization of vascular anatomy and hemodynamics. METHODS: 2D MRDSA was imaged on a 0.3T open MR scanner with a T(1)-weighted fast gradient echo sequence. The phantom study examined vials containing gadolinium (Gd) solutions ranging in concentration from 0.5 mmol/L to 100 mmol/L. Repetition time and echo time were fixed at minimal values in order to achieve high temporal resolution, and only the flip angle was changed in 10-degree increments between 10 and 90 degrees. The in vivo study examined a brachial artery of a human volunteer. MRDSA images were acquired continuously during intraarterial injections of Gd solutions ranging in concentration from 0.5 mmol/L to 100 mmol/L. The subtracted images were displayed on the monitor in real time at a frame rate of one frame per second and evaluated to determine the optimal concentration of contrast material. RESULTS: In the phantom study, a 10-mmol/L Gd concentration with a flip angle of 50 degrees -90 degrees and a 25-mmol/L Gd concentration with a flip angle of 60 degrees -90 degrees showed high signal-to-noise ratios. In the human brachial artery experiment, the forearm arteries were well visualized when solutions of 5-50 mmol/L Gd concentration were used. The 10- and 25-mmol/L Gd concentrations were considered optimal. The palmar digital arteries were also visualized. Higher Gd concentrations showed a paradoxical signal increase when diluted by blood. CONCLUSION: We successfully developed an intraarterial contrast-enhanced 2D MRDSA sequence. With appropriate settings of imaging parameters and Gd concentrations, we obtained acceptable vessel visualization in the human study. The low Gd concentration for optimal visualization permits repeated intraarterial injections. This technique can be a useful tool for investigating the vascular anatomy and hemodynamics required for MR-guided vascular interventions.