Magnetization-prepared Rapid Acquisition Gradient-echo Imaging Research Articles

Fabrication of Customizable Intraplaque Hemorrhage Phantoms for Magnetic Resonance Imaging

PurposeMagnetic resonance (MR) imaging detection of methemoglobin, a molecular marker of intraplaque hemorrhage (IPH), in atherosclerotic plaque is a promising method of assessing stroke risk. However, the multicenter imaging studies required to further validate this technique necessitate the development of IPH phantoms to standardize images acquired across different scanners. This study developed a set of phantoms that modeled methemoglobin-laden IPH for use in MR image standardization.ProceduresA time-stable material mimicking the MR properties of methemoglobin in IPH was created by doping agarose hydrogel with gadolinium and sodium alginate. This material was used to create a phantom that consisted of 9 cylindrical IPH sites (with sizes from 1 to 8 mm). Anatomical replicas of IPH-positive atherosclerosis were also created using 3D printed molds. These plaque replicas also modeled other common plaque components including a lipid core and atheroma cap. T1 mapping and a magnetization-prepared rapid acquisition gradient echo (MPRAGE) carotid imaging protocol were used to assess phantom realism and long-term stability.ResultsCylindrical phantom IPH sites possessed a T1 time of 335 ± 51 ms and exhibited little change in size or MPRAGE signal intensity over 31 days; the mean (SD) magnitude of changes in size and signal were 6.4 % (2.7 %) and 7.3 % (6.7 %), respectively. IPH sites incorporated into complex anatomical plaque phantoms exhibited contrast comparable to clinical images.ConclusionsThe cylindrical IPH phantom accurately modeled the short T1 time characteristic of methemoglobin-laden IPH, with the IPH sites exhibiting little variation in imaging properties over 31 days. Furthermore, MPRAGE images of the anatomical atherosclerosis replicas closely matched those of clinical plaques. In combination, these phantoms will allow for IPH imaging protocol standardization and thus facilitate future multicenter IPH imaging.

Quantitative MRI texture analysis in chronic active multiple sclerosis lesions

ObjectiveRecently, there has been an increasing interest in “chronic enlarging” or “chronic active” multiple sclerosis (MS) lesions that are associated with clinical disability. However, investigation of dynamic lesion volume changes requires longitudinal MRI data from two or more time points. The aim of this study was to investigate the application of texture analysis (TA) on baseline T1-weighted 3D magnetization-prepared rapid acquisition gradient-echo (MPRAGE) images to differentiate chronic active from chronic stable MS lesions. Material and methodsTo identify chronic active lesions as compared to non-enhancing stable lesions, two MPRAGE datasets acquired on a 3 T MRI at baseline and after 12 months follow-up were applied to the Voxel-Guided Morphometry (VGM) algorithm. TA was performed on the baseline MPRAGE images, 36 texture features were extracted for each lesion. ResultsOverall, 374 chronic MS lesions (155 chronic active and 219 chronic stable lesions) from 60 MS patients were included in the final analysis. Multiple texture features including “DISCRETIZED_HISTO_Energy”, “GLCM_Energy”, “GLCM_Contrast” and “GLCM_Dissimilarity” were significantly higher in chronic active as compared to chronic stable lesions. Partial least squares regression yielded an area under the curve of 0.7 to differentiate both lesion types. ConclusionOur results suggest that multiple texture features extracted from MPRAGE images indicate higher intralesional heterogeneity, however they demonstrate only a fair accuracy to differentiate chronic active from chronic stable MS lesions.

Histological validation of simultaneous non-contrast angiography and intraplaque hemorrhage imaging (SNAP) for characterizing carotid intraplaque hemorrhage.

This study sought to validate the performance of simultaneous non-contrast angiography and intraplaque hemorrhage (SNAP) imaging in characterizing carotid IPH by histology. Thirty-five patients with carotid atherosclerotic disease (symptomatic 50-70% stenosis or > 70% stenosis) scheduled for carotid endarterectomy underwent 3.0-T carotid MR imaging by acquiring SNAP and magnetization-prepared rapid acquisition gradient-echo (MP-RAGE) sequences. Presence and area of IPH were separately evaluated on SNAP and MP-RAGE images. Presence and area of IPH were also assessed on histology. Agreement between SNAP/MP-RAGE and histology was determined in identify and quantify IPH using Cohen kappa, Spearman correlation, and Bland-Altman analyses. Of all 35 patients (mean age: 63.1 ± 8.8 years; 27 males), 128 slices with successful registration were eligible for analysis. The accuracy, sensitivity, specificity, and positive and negative predictive values were 86.7%, 85%, 89.6%, 93.2%, and 78.2% for SNAP, and76.6%, 75%, 79.2%, 85.7%, and 65.5% for MP-RAGE in identification of IPH, respectively. In identification of IPH, the kappa value between SNAP and histology and between MP-RAGE and histology was 0.725 and 0.520, respectively. The correlation between SNAP and histology (r = 0.805, p < 0.001) was stronger than that between MP-RAGE and histology (r = 0.637, p < 0.001) in measuring IPH area. Bland-Altman analysis showed that, in measuring IPH area, the bias of SNAP (1.4 mm2, 95% CI: - 0.016 to 2.883) was smaller than that of MP-RAGE (1.7 mm2, 95% CI: - 0.039 to 3.430) compared with histology. This validation study by histology demonstrates that SNAP sequence better identifies and quantifies carotid intraplaque hemorrhage compared with traditional MP-RAGE sequence. • SNAP imaging showed better agreement with histology compared with MP-RAGE imaging, especially for the IPHs with small size. • SNAP sequence is a more effective tool to identify and quantify carotid IPH than traditional sequence of MP-RAGE that can help clinicians to optimizing the treatment strategy. • The plaque components of rich lipid pools or loose matrix and chronic/old IPH (cholesterol crystals) can lead to false positive and false negative results in SNAP and MP-RAGE imaging for identifying IPH.

Identification of carotid non-hemorrhagic lipid-rich necrotic core by magnetization-prepared rapid acquisition gradient-echo imaging: Validation by contrast-enhanced T1 weighted imaging

Identification of carotid non-hemorrhagic lipid-rich necrotic core by magnetization-prepared rapid acquisition gradient-echo imaging: Validation by contrast-enhanced T1 weighted imaging

CAIDE Dementia Risk Score Indicates Cortical Thinning in Low‐Risk, Middle‐Aged Adults

Increased risk for the future development of Alzheimer's disease begins as early as midlife and can be predicted using modifiable cardiovascular and lifestyle‐related risk factors. The Cardiovascular Risk Factors, Aging and Incidence of Dementia (CAIDE) dementia risk score has been used to predict late life risk of dementia based on midlife vascular risk factors. Additionally, in older adults with mild or subjective cognitive impairment, higher CAIDE scores were associated with greater atrophy in the middle temporal and frontal regions of the brain.PurposeWe aimed to determine if CAIDE score is associated with cortical thickness in middle‐aged cognitively intact adults at risk for cardiovascular disease. We hypothesized individuals with higher CAIDE scores would have reduced cortical thickness in a priori regions associated with memory and attention‐executive function.MethodsA total of 155 middle‐age adults (49±6 years, 52.4% female) classified as cognitively normal were studied. CAIDE score was calculated using the original model that excludes ApoE e4 genotype. This includes age, sex, education level, systolic blood pressure, body mass index, total cholesterol, and physical inactivity. Each factor is given a specific weight and the total score ranges from 0 to 14. Cortical thickness was obtained from high resolution magnetization‐prepared rapid acquisition gradient‐echo images. Thickness values for 24 a priori regions of interest associated with memory and executive function were extracted and analyzed.ResultsA majority of the participants (95.5%) in this sample were categorized as low‐risk, having a CAIDE score of 8 or lower. After using a corrected p‐value (p=0.006) for multiple correlations, there were several significant negative associations between CAIDE score and cortical thickness. These include the right parahippocampal (r=−0.251, p=0.002), left pars opercularis (r=−0.244, p=0.002), right superior frontal (r=−0.229, p=0.004) and left superior frontal (r=−0.247, p=0.002) regions.ConclusionsHigher CAIDE scores in midlife are associated with lower cortical thickness in middle‐age adults at risk for cardiovascular disease. This finding supports the notion that cardiovascular risks may contribute to early alteration of brain structure. We propose that the CAIDE dementia risk score may be useful in predicting future risk of dementia even in low‐risk populations who have no indication of clinically significant cognitive impairment.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Identification of carotid lipid-rich necrotic core and calcification by 3D magnetization-prepared rapid acquisition gradient-echo imaging

Background and purposeThis study sought to investigate the feasibility of three-dimensional MPRAGE in identifying the lipid-rich necrotic core (LRNC) and calcification (CA) of carotid atherosclerotic plaques. Materials and methodsTwelve patients (mean age 68.4 ± 11.8 years; 7 males) with carotid atherosclerotic plaques on ultrasound were included and underwent multicontrast magnetic resonance (MR) vessel wall imaging. The contrast enhanced T1W (CE-T1W) images were considered as reference for identifying LRNC. The signal intensity of LRNC, CA, sterno-cleidomastoid muscle and fibrous tissue (FT) was measured on CE-T1W, T1W, T2W, and MPRAGE images, respectively. The relative signal intensity (rSI) of LRNC and CA against muscle or FT was compared among four sequences. Area under the curve (AUC) of rSIs of LRNC, CA and FT against muscle on MPRAGE, T1W and T2W images in discriminating the LRNC or CA from FT and the other plaque component was calculated. ResultsOf 352 slices, 88 (25.0%) had LRNC, 31 (8.8%) had CA, 14 (4.0%) had both LRNC and CA, and 247 (70.2%) had no components. Among four imaging sequences, MPRAGE images showed the lowest rSI of LRNC (0.34 ± 0.18) and CA (0.20 ± 0.16) against muscle, followed by T1W (0.48 ± 0.18 and 0.33 ± 0.21), CE-T1W (0.58 ± 0.23 and 0.40 ± 0.21) and T2W (0.71 ± 0.47 and 0.43 ± 0.40) images. In addition, the MPRAGE images showed the lowest rSI of LRNC (0.57 ± 0.26) and CA (0.33 ± 0.23) against FT. MPRAGE showed greater AUC than T2W and T1W in discriminating the LRNC (0.827 vs. 0.703 vs. 0.635) and CA (0.917 vs. 0.838 vs. 0.825). ConclusionMPRAGE sequence might be a potential non-contrast enhanced imaging tool for identification of carotid LRNC and CA.

Spinal cord volume loss: A marker of disease progression in multiple sclerosis.

Cross-sectional studies have shown that spinal cord volume (SCV) loss is related to disease severity in multiple sclerosis (MS). However, long-term data are lacking. Our aim was to evaluate SCV loss as a biomarker of disease progression in comparison to other MRI measurements in a large cohort of patients with relapse-onset MS with 6-year follow-up. The upper cervical SCV, the total brain volume, and the brain T2 lesion volume were measured annually in 231 patients with MS (180 relapsing-remitting [RRMS] and 51 secondary progressive [SPMS]) over 6 years on 3-dimensional, T1-weighted, magnetization-prepared rapid-acquisition gradient echo images. Expanded Disability Status Scale (EDSS) score and relapses were recorded at every follow-up. Patients with SPMS had lower baseline SCV (p < 0.01) but no accelerated SCV loss compared to those with RRMS. Clinical relapses were found to predict SCV loss over time (p < 0.05) in RRMS. Furthermore, SCV loss, but not total brain volume and T2 lesion volume, was a strong predictor of EDSS score worsening over time (p < 0.05). The mean annual rate of SCV loss was the strongest MRI predictor for the mean annual EDSS score change of both RRMS and SPMS separately, while correlating stronger in SPMS. Every 1% increase of the annual SCV loss rate was associated with an extra 28% risk increase of disease progression in the following year in both groups. SCV loss over time relates to the number of clinical relapses in RRMS, but overall does not differ between RRMS and SPMS. SCV proved to be a strong predictor of physical disability and disease progression, indicating that SCV may be a suitable marker for monitoring disease activity and severity.

Three-Dimensional Radial VIBE Sequence for Contrast-Enhanced Brain Imaging: An Alternative for Reducing Motion Artifacts in Restless Children.

The purpose of this study was to evaluate the usefulness of radially sampled 3D fat-suppressed T1-weighted gradient-echo sequences (radial volumetric interpolated breath-hold examination [radial VIBE]) for contrast-enhanced brain MRI of children through comparison with a magnetization-prepared rapid-acquisition gradient-echo (MP-RAGE) sequence. Sixty-five consecutive contrast-enhanced brain MRI examinations performed with axial MP-RAGE and radial VIBE sequences were included. For quantitative analysis, coefficients of variation of gray matter and white matter and CSF and relative contrast between tissue types (gray matter and white matter, gray matter and CSF, and white matter and CSF) for each sequence were calculated. For qualitative assessment, motion, pulsation artifacts, overall image quality, and lesion conspicuity were retrospectively scored on a 5-point scale. Quantitative and qualitative subgroup analyses were performed for patients with serious motion artifacts. Images obtained with the radial VIBE sequence had fewer motion and pulsation artifacts than those obtained with the MP-RAGE sequence (MP-RAGE vs radial VIBE motion score, 3.57 ± 1.00 vs 4.52 ± 0.51; pulsation score, 3.57 ± 0.60 vs 4.91 ± 0.21; all p < 0.001). Among 25 images with serious motion artifacts, radial VIBE images had significantly higher scores for all qualitative parameters, including overall image quality, than did MP-RAGE images (overall image quality for MP-RAGE vs radial VIBE, 2.63 ± 0.82 vs 3.42 ± 0.55, p < 0.001). The study showed that a radial fat-suppressed T1-weighted gradient-echo sequence is a viable alternative to conventional cartesian acquisition for contrast-enhanced brain imaging of restless children.

Incidental ferumoxytol artifacts in clinical brain MR imaging

Ferumoxytol (Feraheme) is a parenteral therapy approved for treatment of iron deficiency anemia. The product insert for ferumoxytol states that it may affect the diagnostic ability of MRI for up to 3months. However, the expected effects may not be commonly recognized among clinical neuroradiologists. Our purpose is to describe the artifacts we have seen at our institution during routine clinical practice. We reviewed the patients at our institution that had brain MRI performed within 90days of receiving intravenous ferumoxytol. The imaging was reviewed for specific findings, including diffusion-weighted imaging vascular susceptibility artifact, gradient-echo echo-planar T2*-weighted vascular susceptibility artifact, SWI/SWAN vascular susceptibility artifact, hypointense vascular signal on T2-weighted images, pre-gadolinium contrast vascular enhancement on magnetization-prepared rapid acquisition gradient echo (MPRAGE) imaging, and effects on post-gadolinium contrast T1 imaging. Multiple artifacts were observed in patients having a brain MRI within 3days of receiving intravenous ferumoxytol. These included susceptibility artifact on DWI, GRE, and SWAN/SWI imaging, pre-gadolinium contrast increased vascular signal on MPRAGE imaging, and decreased expected enhancement on post-gadolinium contrast T1-weighted imaging. Ferumoxytol can create imaging artifacts which complicate clinical interpretation when brain MRI is performed within 3days of administration. Recognition of the constellation of artifacts produced by ferumoxytol is important in order to obviate additional unnecessary examinations and mitigate errors in interpretation.

Central Adiposity and Cortical Thickness in Midlife.

Excessive visceral fat is associated with greater metabolic fluctuation and increased risk for dementia in older adults. The aim of the current study is to directly determine the impact of central adiposity on brain structure at midlife by examining the thickness of the cerebral cortex. High-resolution magnetization-prepared rapid acquisition gradient-echo images were obtained from 103 participants aged 40 to 60 years (mean [standard deviation] = 49.63 [6.47] years) on a 3-T Siemens Skyra scanner. Visceral fat was measured using dual-energy x-ray absorptiometry. Individuals with higher visceral fat mass and volume had significantly thicker cortex in the right posterior cingulate gyrus (β = 0.29 [p = .019] and β = 0.31 [p = .011], respectively), controlling for age, systolic blood pressure, total cholesterol level, and blood glucose level. Visceral fat was significantly associated with thicker cortex in the posterior cingulate gyrus. Although future studies are necessary, these results indicate that central adiposity is associated with significant metabolic changes that impinge upon the central nervous system in middle age.

Non-Enhanced MR Imaging of Cerebral Aneurysms: 7 Tesla versus 1.5 Tesla

PurposeTo prospectively evaluate 7 Tesla time-of-flight (TOF) magnetic resonance angiography (MRA) in comparison to 1.5 Tesla TOF MRA and 7 Tesla non-contrast enhanced magnetization-prepared rapid acquisition gradient-echo (MPRAGE) for delineation of unruptured intracranial aneurysms (UIA).Material and MethodsSixteen neurosurgical patients (male n = 5, female n = 11) with single or multiple UIA were enrolled in this trial. All patients were accordingly examined at 7 Tesla and 1.5 Tesla MRI utilizing dedicated head coils. The following sequences were obtained: 7 Tesla TOF MRA, 1.5 Tesla TOF MRA and 7 Tesla non-contrast enhanced MPRAGE. Image analysis was performed by two radiologists with regard to delineation of aneurysm features (dome, neck, parent vessel), presence of artifacts, vessel-tissue-contrast and overall image quality. Interobserver accordance and intermethod comparisons were calculated by kappa coefficient and Lin's concordance correlation coefficient.ResultsA total of 20 intracranial aneurysms were detected in 16 patients, with two patients showing multiple aneurysms (n = 2, n = 4). Out of 20 intracranial aneurysms, 14 aneurysms were located in the anterior circulation and 6 aneurysms in the posterior circulation. 7 Tesla MPRAGE imaging was superior over 1.5 and 7 Tesla TOF MRA in the assessment of all considered aneurysm and image quality features (e.g. image quality: mean MPRAGE7T: 5.0; mean TOF7T: 4.3; mean TOF1.5T: 4.3). Ratings for 7 Tesla TOF MRA were equal or higher over 1.5 Tesla TOF MRA for all assessed features except for artifact delineation (mean TOF7T: 4.3; mean TOF1.5T 4.4). Interobserver accordance was good to excellent for most ratings.Conclusion7 Tesla MPRAGE imaging demonstrated its superiority in the detection and assessment of UIA as well as overall imaging features, offering excellent interobserver accordance and highest scores for all ratings. Hence, it may bear the potential to serve as a high-quality diagnostic tool for pretherapeutic assessment and follow-up of untreated UIA.

Focal multiple sclerosis lesions abound in ‘normal appearing white matter’

Background: The ‘normal appearing white matter’ (NAWM) in multiple sclerosis (MS) is known to be abnormal using quantitative magnetic resonance (MR) techniques. The aetiology of the changes in NAWM remains debatable. Objective: To investigate whether high-field and ultra high-field T1-weighted magnetization prepared rapid acquisition gradient echo (MPRAGE) MRI enables detection of MS white matter lesions in areas defined as NAWM using high-field T2-weighted fluid attenuation inversion recovery (FLAIR) MRI; that is, to ascertain whether undetected lesions are likely contributors to the burden of abnormality in similarly defined NAWM. Methods: Fourteen MS patients underwent MRI scans using 3T FLAIR and MPRAGE and 7 Tesla (7T) MPRAGE sequences. Independent observers identified lesions on 3T FLAIR and (7T and 3T) MPRAGE images. The detection of every individual lesion was then compared for each image type. Results: We identified a total of 812 white matter lesions on 3T FLAIR. Using 3T MPRAGE, 186 additional lesions were detected that were not detected using 3T FLAIR. Using 7T MPRAGE, 231 additional lesions were detected that were not detected using 3T FLAIR. Conclusions: MRI with 3T and 7T MPRAGE enables detection of MS lesions in areas defined as NAWM using 3T FLAIR. Focal MS lesions contribute to the abnormalities known to exist in the NAWM.

Inflammation and atrophy in multiple sclerosis: MRI associations with disease course

Brain atrophy may be a useful surrogate marker of axonal loss and disease progression in multiple sclerosis (MS). Several studies have suggested that inflammatory disease activity is a risk factor for atrophy in the early stages of the disease, but may become less important later in the disease course. We aimed to investigate the relationships between atrophy and active inflammation at different stages of the disease course using brain volume measurements from magnetic resonance imaging (MRI) in patients with both relapsing–remitting (RR) ( n=95) and secondary progressive (SP) ( n=76) MS. Conventional dual echo and three-dimensional magnetization-prepared rapid-acquisition gradient echo imaging were performed in all patients and in 31 healthy controls. Supratentorial and infratentorial brain, and lateral ventricular volumes were determined using modern design stereology. Patients with SP MS had smaller supratentorial ( p=0.003) and infratentorial brain volumes ( p=0.0003), and larger lateral ventricles ( p=0.02) than patients with RR MS. RR MS patients with T 1-enhancing lesions had smaller supratentorial ( p=0.02) and infratentorial ( p=0.002) brain volumes and larger ventricles ( p=0.002) than those without enhancing lesions. SP MS patients with enhancing lesions also had significantly larger lateral ventricles ( p=0.03). Categorical analysis showed that more RR MS patients with enhancing lesions had smaller supratentorial brain ( p=0.005), or larger lateral ventricular ( p=0.028) volumes, and more SP MS patients with enhancing lesions had increased lateral ventricle volumes ( p=0.013), than patients without enhancements. The number of enhancing lesions was significantly correlated with lateral ventricular volumes in both RR MS ( r=0.39, p=0.0001) and SP MS ( r=0.46, p<0.0001). Our data shows that the presence of active inflammation on a single MRI in the course of RR and SP MS, is associated with a higher risk and higher level of brain atrophy. These findings emphasise the important long-term relationship between inflammation and atrophy in MS and provide additional support for the strategy of early anti-inflammatory treatment to protect tissue integrity.

3D MPRAGE evaluation of the internal auditory canals.

A heavily T1-weighted three-dimensional (3D) gradient echo sequence utilizing a 180 degrees inversion pulse has become available for clinical use, called magnetization prepared rapid acquisition gradient echo (MPRAGE). With the appropriate choice of repetition time, echo time, flip angle, and inversion time (TI), T1-weighted imaging can be performed with excellent anatomic detail and a good signal-to-noise ratio. We performed an initial evaluation of this sequence for detection of abnormalities of the internal auditory canals compared with conventional spin echo (SE) imaging. Fifteen men and 15 women were evaluated. Diagnoses included normal (n = 15 patients), acoustic neuromas (n = 7 tumors in 4 patients), cerebellopontine angle meningiomas (n = 3), postoperative for acoustic neuroma without residual tumor (n = 2), postoperative with evidence of residual tumor (n = 3), glomus jugulare (n = 1), Bell palsy (n = 1), and vestibular enhancement of probable viral etiology (n = 1). The 3D MPRAGE study consisted of 128 coronal partitions, (10/4/1), 10 degrees flip angle, 130 x 256 matrix, 2 mm slice thickness. TI time of 350 ms, 1 s recovery time, and 5.43 min examination time. All enhancing lesions identified on the conventional SE T1-weighted imaging were also identified on the MPRAGE imaging. No diagnostic difference existed between the MPRAGE and conventional SE sequences when pathology was present, but the MPRAGE sequence did have poorer resolution in the axial reformats related to the 130 x 256 in-plane matrix. While not currently able to replace conventional two-dimensional SE imaging, 3D MPRAGE may provide a valuable adjunct to the routine imaging protocol. This technique could replace the coronal T1-weighted SE sequence and provide excellent gray-white differentiation and many contiguous thin sections without a great increase in overall examination time.