Feasibility study on the clinical application of CT-based synthetic brain T1-weighted MRI: comparison with conventional T1-weighted MRI.

OBJECTIVES: This study aimed to examine the equivalence of computed tomography (CT)-based synthetic T1-weighted imaging (T1WI) to conventional T1WI for the quantitative assessment of brain morphology. MATERIALS AND METHODS: This prospective study examined 35 adult patients undergoing brain magnetic resonance imaging (MRI) and CT scans. An image synthesis method based on a deep learning model was used to generate synthetic T1WI (sT1WI) from CT data. Two senior radiologists used sT1WI and conventional T1WI on separate occasions to independently measure clinically relevant brain morphological parameters. The reliability and consistency between conventional and synthetic T1WI were assessed using statistical consistency checks, comprising intra-reader, inter-reader, and inter-method agreement. RESULTS: The intra-reader, inter-reader, and inter-method reliability and variability mostly exhibited the desired performance, except for several poor agreements due to measurement differences between the radiologists. All the measurements of sT1WI were equivalent to that of T1WI at 5% equivalent intervals. CONCLUSION: This study demonstrated the equivalence of CT-based sT1WI to conventional T1WI for quantitatively assessing brain morphology, thereby providing more information on imaging diagnosis with a single CT scan. CLINICAL RELEVANCE STATEMENT: Real-time synthesis of MR images from CT scans reduces the time required to acquire MR signals, improving the efficiency of the treatment planning system and providing benefits in the clinical diagnosis of patients with contraindications such as presence of metal implants or claustrophobia. KEY POINTS: • Deep learning-based image synthesis methods generate synthetic T1-weighted imaging from CT scans. • The equivalence of synthetic T1-weighted imaging and conventional MRI for quantitative brain assessment was investigated. • Synthetic T1-weighted imaging can provide more information per scan and be used in preoperative diagnosis and radiotherapy.

Rapid three-dimensional quantification of high-intensity plaques from coronary atherosclerosis T1-weighted characterization to predict periprocedural myocardial injury.

BACKGROUND: High-intensity plaque (HIP) on magnetic resonance imaging (MRI) has been documented as a powerful predictor of periprocedural myocardial injury (PMI) following percutaneous coronary intervention (PCI). Despite the recent proposal of three-dimensional HIP quantification to enhance the predictive capability, the conventional pulse sequence, which necessitates the separate acquisition of anatomical reference images, hinders accurate three-dimensional segmentation along the coronary vasculature. Coronary atherosclerosis T1-weighted characterization (CATCH) enables the simultaneous acquisition of inherently coregistered dark-blood plaque and bright-blood coronary artery images. We aimed to develop a novel HIP quantification approach using CATCH and to ascertain its superior predictive performance compared to the conventional two-dimensional assessment based on plaque-to-myocardium signal intensity ratio (PMR). METHODS: In this prospective study, CATCH MRI was conducted before elective stent implantation in 137 lesions from 125 patients. On CATCH images, dedicated software automatically generated tubular three-dimensional volumes of interest on the dark-blood plaque images along the coronary vasculature, based on the precisely matched bright-blood coronary artery images, and subsequently computed PMR and HIP volume (HIPvol). Specifically, HIPvol was calculated as the volume of voxels with signal intensity exceeding that of the myocardium, weighted by their respective signal intensities. PMI was defined as post-PCI cardiac troponin-T > 5 × the upper reference limit. RESULTS: The entire analysis process was completed within 3 min per lesion. PMI occurred in 44 lesions. Based on the receiver operating characteristic curve analysis, HIPvol outperformed PMR for predicting PMI (C-statistics, 0.870 [95% CI, 0.805-0.936] vs. 0.787 [95% CI, 0.706-0.868]; p = 0.001). This result was primarily driven by the higher sensitivity HIPvol offered: 0.886 (95% CI, 0.754-0.962) vs. 0.750 for PMR (95% CI, 0.597-0.868; p = 0.034). Multivariable analysis identified HIPvol as an independent predictor of PMI (odds ratio, 1.15 per 10-µL increase; 95% CI, 1.01-1.30, p = 0.035). CONCLUSIONS: Our semi-automated method of analyzing coronary plaque using CATCH MRI provided rapid HIP quantification. Three-dimensional assessment using this approach had a better ability to predict PMI than conventional two-dimensional assessment.

Enhancement of the lymphatic system following intravenous administration of ferumoxytol.

BACKGROUND: Lymphatic imaging is becoming increasingly important in the management of patients with congenital heart disease. However, the influence of the intravenous contrast agent ferumoxytol on lymphatic imaging is not well understood. OBJECTIVE: To evaluate the impact of intravenous ferumoxytol on T1-weighted and T2-weighted lymphatic imaging in patients with congenital heart disease. MATERIALS AND METHODS: We included consecutive patients receiving ferumoxytol-enhanced 3D angiography for congenital heart disease evaluation. The visibility of the thoracic duct was reviewed on the T1-weighted 3D inversion recovery balanced-steady-state free precession (SSFP) with respiratory navigator gating sequence which is routinely used for angiography and the heavily T2-weighted turbo spin echo sequence which is employed for lymphatic imaging. Data on demographics and time interval between contrast administration and imaging were collected. Statistical analyses were performed using t-tests for continuous variables and chi-squared tests for categorical variables. RESULTS: One hundred nineteen consecutive patients with a mean age of 12.46 years±7.7 years were included. Of these, 45 cases underwent both T1-weighted and T2-weighted imaging; the other 74 underwent only T1-weighted imaging. Of the 45 patients, 20 had thoracic duct enhancement on T1-weighted imaging; among the 26 sedated, only 2 showed enhancement, while 18 of 19 non-sedated patients showed enhancement (P<0.001), indicating a strong association between sedation and reduced thoracic duct visibility. If T2-weighted imaging was performed after contrast administration, the thoracic duct was not visible on those images. For all 45 cases of visible thoracic duct in the entire cohort, the time from contrast administration to imaging ranged from 8 min up to 75 min. CONCLUSION: The enhancement of the thoracic lymphatic duct on T1-weighted imaging, coupled with degradation observed on T2-weighted imaging, suggests that intravenously administered ferumoxytol rapidly enters the lymphatic fluid. To prevent T2 shortening from degrading the imaging results, T2-weighted imaging for lymphatic evaluation should be performed prior to the administration of ferumoxytol. Sedation and, by inference, fasting may influence this property and warrant further investigation in future studies.

Longitudinal manganese-enhanced magnetic resonance imaging of neural projections and activity.

Manganese-enhanced magnetic resonance imaging (MEMRI) holds exceptional promise for preclinical studies of brain-wide physiology in awake-behaving animals. The objectives of this review are to update the current information regarding MEMRI and to inform new investigators as to its potential. Mn(II) is a powerful contrast agent for two main reasons: (1) high signal intensity at low doses; and (2) biological interactions, such as projection tracing and neural activity mapping via entry into electrically active neurons in the living brain. High-spin Mn(II) reduces the relaxation time of water protons: at Mn(II) concentrations typically encountered in MEMRI, robust hyperintensity is obtained without adverse effects. By selectively entering neurons through voltage-gated calcium channels, Mn(II) highlights active neurons. Safe doses may be repeated over weeks to allow for longitudinal imaging of brain-wide dynamics in the same individual across time. When delivered by stereotactic intracerebral injection, Mn(II) enters active neurons at the injection site and then travels inside axons for long distances, tracing neuronal projection anatomy. Rates of axonal transport within the brain were measured for the first time in "time-lapse" MEMRI. When delivered systemically, Mn(II) enters active neurons throughout the brain via voltage-sensitive calcium channels and clears slowly. Thus behavior can be monitored during Mn(II) uptake and hyperintense signals due to Mn(II) uptake captured retrospectively, allowing pairing of behavior with neural activity maps for the first time. Here we review critical information gained from MEMRI projection mapping about human neuropsychological disorders. We then discuss results from neural activity mapping from systemic Mn(II) imaged longitudinally that have illuminated development of the tonotopic map in the inferior colliculus as well as brain-wide responses to acute threat and how it evolves over time. MEMRI posed specific challenges for image data analysis that have recently been transcended. We predict a bright future for longitudinal MEMRI in pursuit of solutions to the brain-behavior mystery.

Three-Dimensional Bioprinted MR-Trackable Regenerative Scaffold for Postimplantation Monitoring on T1-Weighted MRI.

BACKGROUND: A three-dimensional (3D) bioprinted tissue scaffold is a promising therapeutic that goes beyond providing physical support for tissue regeneration by enabling precise spatial control over scaffold geometry and integration of different materials/cells. Critically important is in vivo confirmation of correct scaffold placement and retention during the initial 24 hours postimplantation, to detect unwanted implant migration. PURPOSE: To incorporate a safe, efficient MR contrast agent into a bioprinting workflow, and to achieve bright-contrast scaffold monitoring in vivo postimplantation. STUDY TYPE: In vitro and animal in vivo longitudinal study. ANIMAL MODEL: Two female Sprague Dawley rats (~200 g) for labeled and unlabeled scaffold implantation in the subcutaneous dorsal space flanking the vertebral column. FIELD STRENGTH/SEQUENCE: A 7.0 T/T1 -weighted spin echo (SE) sequence and T1 mapping using turbo SE with variable repetition times (TRs). ASSESSMENT: Cell viability and proliferation were assessed over 2 weeks after labeling bioprinted gelatin/alginate scaffolds with MnPNH2 (0.5 mM, 24 hours). In vitro MRI was performed 0, 12, and 24 hours postlabeling in nine labeled and three unlabeled (control) scaffolds to monitor T1 evolution. In vivo MRI was performed immediately and 24 hours postimplantation to assess T1 . Acute inflammation near surgical site was monitored in one rat to 3 days. STATISTICAL TESTS: One-way analysis of variance with Tukey-Kramer post hoc analysis (P < 0.01). RESULTS: Cell viability was unaffected by bioprinting/labeling: viability exceeded 90% in all scaffolds after 1 week. In vitro T1 's were significantly lower in labeled scaffolds compared to control (207 msec vs. 2257 msec) immediately postlabeling and 24 hours later (1227 msec vs. 2257 msec). In vivo T1 's were significantly different (243.6 msec vs. 2414.6 msec) immediately postimplantation, and no differences emerged compared to respective in vitro control/labeled counterparts. The 24-hours imaging and gross pathology confirmed migration of scaffolds beyond the imaging field. DATA CONCLUSION: We report an MR-detectable, cell-compatible bioprinted scaffold, utilizing a T1 -weighting contrast agent for high-resolution, postimplantation scaffold tracking. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 1.

Impacts of skull stripping on construction of three-dimensional T1-weighted imaging-based brain structural network in full-term neonates.

BACKGROUND: Skull stripping remains a challenge for neonatal brain MR image analysis. However, little is known about the accuracy of how skull stripping affects the neonatal brain tissue segmentation and subsequent network construction. This paper therefore aimed to clarify this issue by comparing two automatic (FMRIB Software Library's Brain Extraction Tool, BET; Infant Brain Extraction and Analysis Toolbox, iBEAT) and a semiautomatic (iBEAT with manual correction) processes in constructing 3D T1-weighted imaging (T1WI)-based brain structural network. METHODS: Twenty-two full-term neonates (gestational age, 37-42 weeks; boys/girls, 13/9) without abnormalities on MRI who underwent brain 3D T1WI were retrospectively recruited. Two automatic (BET and iBEAT) and a semiautomatic preprocessing (iBEAT with manual correction) workflows were separately used to perform the skull stripping. Brain tissue segmentation and volume calculation were performed by a Johns Hopkins atlas-based method. Sixty-four gray matter regions were selected as nodes; volume covariance network and its properties (clustering coefficient, Cp; characteristic path length, Lp; local efficiency, Elocal; global efficiency, Eglobal) were calculated by GRETNA. Analysis of variance (ANOVA) was used to compare the differences in the calculated volume between three workflows. RESULTS: There were significant differences in volumes of 50 brain regions between the three workflows (P < 0.05). Three neonatal brain structural networks presented small-world topology. The semiautomatic workflow showed remarkably decreased Cp, increased Lp, decreased Elocal, and decreased Eglobal, in contrast to the two automatic ones. CONCLUSIONS: Imperfect skull stripping indeed affected the accuracy of brain structural network in full-term neonates.

High signal-intensity abnormalities in susceptibility-weighted imaging for primary intracerebral hemorrhage.

Purpose: To identify the regularity of signal evolution of intracerebral hemorrhage on susceptibility-weighted imaging (SWI) at different stages compared with T1-weighted imaging (T1WI) and T2-weighted imaging (T2WI). Methods: We retrospectively evaluated a series of 365 patients who underwent T1WI, T2WI, and SWI examination simultaneously or sequentially in our hospital from January 2015 to May 2017. Two neuroradiologists assessed the images and discrepancies between their interpretations were resolved by consensus. Statistical analysis was performed using Chi-squared and Kappa tests. Results: Of the 365 patients on SWI sequence, 94 were enrolled. SWI detected the cases at different stages; T1WI detected 89 cases and T2WI detected 91 cases. The signal intensity of intracerebral hemorrhage on SWI was significantly associated with T1WI imaging and T2WI (χ2 = 4.651; p < 0.05; χ2 = 26.396; p < 0.01, respectively), especially at the late subacute stage. There was moderate consistency between the signal intensity of intracerebral hemorrhage on T2WI and SWI (Kappa coefficient = 0.530). Conclusion: Intracerebral hemorrhage has a varied appearance on SWI, and the evolution of signal of intracerebral hemorrhage on SWI sequence is influenced by T1WI and T2WI. Hematoma detection should be closely combined with clinical manifestation.

[Improvement of Brain Contrast Using Spin Echo T1-weighted Image at 3 T MRI].

Brain T1-weighted images using spin echo (SE) sequence has poor contrast at 3.0 Tesla magnetic resonance imaging (3.0 T MRI) systems from the influence of crosstalk and magnetized transfer (MT) effect, and prolongation of the T1 value. Therefore, improving of scan parameters has been reported such as excitation flip angle (FA) and interleave data acquisition. The purpose of this study was to show the effects of alterations of presaturation pulse amplitude and chemical shift selective (CHESS) pulse amplitude. Gray-to-white matter contrast increased with decreasing amplitude of presaturation pulse in whole brain imaging. Presaturation and CHESS pulse consist of radio frequency pulse. Therefore, both pulses have a similar effect on MT pulse. Manual alteration of presaturation pulse amplitude for each scan lacks versatility on clinical use. However, decreasing amplitude of presaturation pulse is equal to decreasing thickness of presaturation pulse. About CHESS pulse, it requires no manual alteration for each scan. For example, switching fat suppression mode from strong to weak increase T1 contrast. Our study demonstrated that using not only low excitation FA and interleave date acquisition but also low amplitude of presaturation and CHESS pulse increase the contrast in T1 SE brain scans at 3.0 T MRI.

Age-Related Effects and Sex Differences in Gray Matter Density, Volume, Mass, and Cortical Thickness from Childhood to Young Adulthood.

Developmental structural neuroimaging studies in humans have long described decreases in gray matter volume (GMV) and cortical thickness (CT) during adolescence. Gray matter density (GMD), a measure often assumed to be highly related to volume, has not been systematically investigated in development. We used T1 imaging data collected on the Philadelphia Neurodevelopmental Cohort to study age-related effects and sex differences in four regional gray matter measures in 1189 youths ranging in age from 8 to 23 years. Custom T1 segmentation and a novel high-resolution gray matter parcellation were used to extract GMD, GMV, gray matter mass (GMM; defined as GMD × GMV), and CT from 1625 brain regions. Nonlinear models revealed that each modality exhibits unique age-related effects and sex differences. While GMV and CT generally decrease with age, GMD increases and shows the strongest age-related effects, while GMM shows a slight decline overall. Females have lower GMV but higher GMD than males throughout the brain. Our findings suggest that GMD is a prime phenotype for the assessment of brain development and likely cognition and that periadolescent gray matter loss may be less pronounced than previously thought. This work highlights the need for combined quantitative histological MRI studies.SIGNIFICANCE STATEMENT This study demonstrates that different MRI-derived gray matter measures show distinct age and sex effects and should not be considered equivalent but complementary. It is shown for the first time that gray matter density increases from childhood to young adulthood, in contrast with gray matter volume and cortical thickness, and that females, who are known to have lower gray matter volume than males, have higher density throughout the brain. A custom preprocessing pipeline and a novel high-resolution parcellation were created to analyze brain scans of 1189 youths collected as part of the Philadelphia Neurodevelopmental Cohort. A clear understanding of normal structural brain development is essential for the examination of brain-behavior relationships, the study of brain disease, and, ultimately, clinical applications of neuroimaging.

Non-contrast-enhanced T1 -weighted MRI of myocardial radiofrequency ablation lesions.

PURPOSE: To demonstrate imaging of radiofrequency ablation lesions with non-contrast-enhanced T1 -weighted (T1w) MRI. METHODS: Fifteen swine underwent left ventricular ablation followed by MRI using different preparations: endocardial or epicardial ablation of naïve animal, or endocardial ablation of animal with myocardial infarction. Lesion imaging was performed using free-breathing, non-contrast-enhanced, T1w sequence with long inversion time (TI). Also acquired were T1 maps and delayed contrast-enhanced (DCE) imaging. Hearts were excised for ex vivo imaging, and sliced for gross pathology and histology. RESULTS: All ablations were visibly enhanced in non-contrast-enhanced T1w imaging using TI = 700 ms. T1w enhancement agreed with regions of necrosis in gross pathology and histology. Enhanced lesion cores were surrounded by dark bands containing contraction band necrosis, hematoma, and edema. In animals with myocardial infarction, chronic scar was hypointense in T1w, whereas acute ablations were enhanced, allowing discrimination between chronic scar and acute lesions, unlike DCE. Contrast was sufficient to create 3D volume renderings of lesions after minor postprocessing. CONCLUSIONS: Non-contrast-enhanced T1w imaging with long TI promises to be an effective method for visualizing necrosis within radiofrequency ablation lesions. Enhancement is more specific and stationary than that from DCE. The imaging can be repeated as needed, unlike DCE, and may be especially useful for assessing ablations during or after a procedure. Magn Reson Med 79:879-889, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Methods for the computation of templates from quantitative magnetic susceptibility maps (QSM): Toward improved atlas- and voxel-based analyses (VBA).

PURPOSE: To develop and assess a method for the creation of templates for voxel-based analysis (VBA) and atlas-based approaches using quantitative magnetic susceptibility mapping (QSM). MATERIALS AND METHODS: We studied four strategies for the creation of magnetic susceptibility brain templates, derived as successive extensions of the conventional template generation (CONV) based on only T1 -weighted (T1 w) images. One method that used only T1 w images involved a minor improvement of CONV (U-CONV). One method used only magnetic susceptibility maps as input for template generation (DIRECT), and the other two used a linear combination of susceptibility and T1 w images (HYBRID) and an algorithm that directly used both image modalities (MULTI), respectively. The strategies were evaluated in a group of N = 10 healthy human subjects and semiquantitatively assessed by three experienced raters. Template quality was compared statistically via worth estimates (WEs) obtained with a log-linear Bradley-Terry model. RESULTS: The overall quality of the templates was better for strategies including both susceptibility and T1 w contrast (MULTI: WE = 0.62; HYBRID: WE = 0.21), but the best method depended on the anatomical region of interest. While methods using only one modality resulted in lower WEs, lowest overall WEs were obtained when only T1 w images were used (DIRECT: WE = 0.12; U-CONV: WE = 0.05). CONCLUSION: Template generation strategies that employ only magnetic susceptibility contrast or both magnetic susceptibility and T1 w contrast produce templates with the highest quality. The optimal approach depends on the anatomical structures of interest. The established approach of using only T1 w images (CONV) results in reduced image quality compared to all other approaches studied. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1474-1484.

The Prevalence of and Factors Related to Vascular Hyperintensity on T1-Weighted Imaging in Acute Ischemic Stroke.

BACKGROUND: Thrombus visualization in patients with acute ischemic stroke has been detected and reported using various imaging modalities. T1-weighted imaging (T1-WI) can depict thrombi as hyperintense signals within vessels. Moreover, in addition to thrombi, T1-WI hyperintensities in arteries may suggest arterial dissection. However, the frequency of and factors related to the T1-hyperintense vessel sign (T1-HVS) are not fully known. The aim of this study was to clarify the prevalence of and related factors for the T1-HVS in patients with acute ischemic stroke. METHODS: From September 2014 through December 2015, consecutive acute ischemic stroke patients who were admitted to our stroke unit within 7 days from symptom onset were retrospectively recruited from the prospective registry. A T1-HVS was defined as the presence of a hyperintense signal, with intensity higher than surrounding brain, within the vessel lumen. Moreover, T1-HVSs were separated into filled T1-HVSs (hyperintensity fills whole vessel lumen) and non-filled T1-HVSs. The frequency of the T1-HVS and the timing of emersion and the relationship between the presence of the T1-HVS and arterial occlusion were assessed. RESULTS: A total of 399 patients (139 women; median age 73 years; National Institutes of Health Stroke Scale score 3) were enrolled in the present study. Of these, 327 (82%) patients had T1-WI on admission. Two hundred and sixty-seven (67%) subjects had at least one follow-up T1-WI (median 6 days after admission), and 134 (34%) cases had ≥2 follow-up T1-WI examinations. The T1-HVS was observed in 18 patients during admission; therefore, the frequency of the T1-HVS in acute ischemic stroke patients was 4.5% (95% CI 2.5-6.5%). All but one (94%) of the T1-HVSs were first observed on follow-up imaging, and the median number of days from onset to T1-HVS appearance was 9. For patients having initial major artery occlusion and follow-up MRI (n = 95), sensitivity and specificity of the T1-HVS for persistent arterial occlusion on follow-up MR angiography were 22 and 100%, respectively. T1-HVS persisted for a few months and then normalized. Although there were no significant differences between filled and non-filled T1-HVS, more patients with non-filled T1-HVS had arterial dissection (43%) than those with filled T1-HVS (9%, p = 0.245). CONCLUSION: The T1-HVS was observed in 4.5% of acute ischemic stroke patients. T1-HVSs appeared in the subacute phase in arteries with persistent occlusion and remained for a few months.

Comparison of T1-weighted 2D TSE, 3D SPGR, and two-point 3D Dixon MRI for automated segmentation of visceral adipose tissue at 3 Tesla.

OBJECTIVES: To evaluate and compare conventional T1-weighted 2D turbo spin echo (TSE), T1-weighted 3D volumetric interpolated breath-hold examination (VIBE), and two-point 3D Dixon-VIBE sequences for automatic segmentation of visceral adipose tissue (VAT) volume at 3 Tesla by measuring and compensating for errors arising from intensity nonuniformity (INU) and partial volume effects (PVE). MATERIALS AND METHODS: The body trunks of 28 volunteers with body mass index values ranging from 18 to 41.2 kg/m2 (30.02 ± 6.63 kg/m2) were scanned at 3 Tesla using three imaging techniques. Automatic methods were applied to reduce INU and PVE and to segment VAT. The automatically segmented VAT volumes obtained from all acquisitions were then statistically and objectively evaluated against the manually segmented (reference) VAT volumes. RESULTS: Comparing the reference volumes with the VAT volumes automatically segmented over the uncorrected images showed that INU led to an average relative volume difference of -59.22 ± 11.59, 2.21 ± 47.04, and -43.05 ± 5.01 % for the TSE, VIBE, and Dixon images, respectively, while PVE led to average differences of -34.85 ± 19.85, -15.13 ± 11.04, and -33.79 ± 20.38 %. After signal correction, differences of -2.72 ± 6.60, 34.02 ± 36.99, and -2.23 ± 7.58 % were obtained between the reference and the automatically segmented volumes. A paired-sample two-tailed t test revealed no significant difference between the reference and automatically segmented VAT volumes of the corrected TSE (p = 0.614) and Dixon (p = 0.969) images, but showed a significant VAT overestimation using the corrected VIBE images. CONCLUSION: Under similar imaging conditions and spatial resolution, automatically segmented VAT volumes obtained from the corrected TSE and Dixon images agreed with each other and with the reference volumes. These results demonstrate the efficacy of the signal correction methods and the similar accuracy of TSE and Dixon imaging for automatic volumetry of VAT at 3 Tesla.

Improved spoiling efficiency in dynamic RF-spoiled imaging by ghost phase modulation and temporal filtering.

PURPOSE: Radiofrequency-spoiled steady-state sequences offer rapid data acquisition with T1- or T2*-weighting. The spoiler gradients in these sequences must be large enough to suppress ghost artifacts, and are chosen empirically. However, certain factors such as the need to minimize gradient first moments or acoustic noise can limit the spoiler size and, hence, the ability to suppress ghosts. We present an acquisition and preprocessing strategy for improved spoiling efficiency in conventional and echo-shifted dynamic radiofrequency-spoiled 3D imaging. THEORY AND METHODS: By requiring each time-frame in a dynamic imaging sequence to contain a particular (restricted) number of total radiofrequency shots, the ghost signal can be made to alternate in sign every other frame. The ghost is then suppressed by Fourier transforming along the temporal dimension, and removing the Nyquist frequency in preprocessing (similar to UNFOLD). The method works for both Cartesian and non-Cartesian imaging. RESULTS: We demonstrate improved ghost suppression with the proposed approach, for both conventional and echo-shifted spoiled gradient echo imaging in stationary phantoms and in vivo. Cartesian echo-shifted spoiled gradient echo imaging produces two ghosts shifted in opposite directions, both of which are suppressed with our method. CONCLUSION: For a given spoiler gradient area, the proposed approach substantially suppresses the ghost signal in both conventional and echo-shifted dynamic radiofrequency-spoiled imaging. Magn Reson Med 75:2388-2393, 2016. © 2015 Wiley Periodicals, Inc.

Mathematical optimization of contrast concentration for T1-weighted spoiled gradient echo imaging.

PURPOSE: To develop and validate closed form mathematical expressions that predict the optimal contrast agent concentration for the maximum T1-weighted spoiled gradient echo (SGRE) signal. THEORY AND METHODS: Gadolinium and iron-based contrast agents can have significant transverse relaxivity that leads to signal dropout with increasing contrast agent concentration. A mathematical expression for the "optimal" contrast agent concentration where recovery of longitudinal magnetization is offset by increasing transverse signal decay was derived. Expressions for the maximum possible SGRE signal were also derived. Three phantoms were constructed, each with varying concentrations of one of the following three agents: gadoteridol, gadobenate dimeglumine, and ferumoxytol. After measuring the longitudinal and transverse relaxivity of the three agents, the SGRE signal was measured in the phantoms over a wide range of flip angles and echo times. RESULTS: Excellent qualitative agreement between the SGRE signal behavior, optimal concentration, and optimal flip angle were observed between experimental measurements and theoretical predictions. CONCLUSION: This work provides validated mathematical expressions for contrast enhanced T1-weighted SGRE imaging and may provide guidance for contrast dosing and injection protocols, as well as for novel pulse sequence design.

MPnRAGE: A technique to simultaneously acquire hundreds of differently contrasted MPRAGE images with applications to quantitative T1 mapping.

PURPOSE: To introduce a new technique called MPnRAGE, which produces hundreds of images with different T1 contrasts and a B1 corrected T1 map. THEORY AND METHODS: An interleaved three-dimensional radial k-space trajectory with a sliding window reconstruction is used in conjunction with magnetization preparation pulses. This work modifies the SNAPSHOT-FLASH T1 fitting equations for radial imaging with view-sharing and develops a new rapid B1 correction procedure. MPnRAGE is demonstrated in phantoms and volunteers, including two volunteers with eight scans each and eight volunteers with two scans each. T1 values from MPnRAGE were compared with those from fast spin echo inversion recovery (FSE-IR) in phantoms and a healthy human brain at 3 Tesla (T). RESULTS: The T1 fit for human white and gray matter was T1MPnRAGE = 1.00 · T1FSE-IR + 24 ms, r(2) = 0.990. Voxel-wise coefficient of variation in T1 measurements across eight time points was between 0.02 and 0.08. Region of interest-based T1 values were reproducible to within 2% and agree well with literature values. CONCLUSION: In the same amount of time as a traditional MPRAGE exam (7.5 min), MPnRAGE was shown to produce hundreds of images with alternate T1 contrasts as well as an accurate and reproducible T1 map that is robust to B1 errors.

Magnetic resonance imaging assessment of degenerative cervical myelopathy: a review of structural changes and measurement techniques.

Degenerative cervical myelopathy encompasses a spectrum of age-related structural changes of the cervical spine that result in static and dynamic injury to the spinal cord and collectively represent the most common cause of myelopathy in adults. Although cervical myelopathy is determined clinically, the diagnosis requires confirmation via imaging, and MRI is the preferred modality. Because of the heterogeneity of the condition and evolution of MRI technology, multiple techniques have been developed over the years in an attempt to quantify the degree of baseline severity and potential for neurological recovery. In this review, these techniques are categorized anatomically into those that focus on bone, ligaments, discs, and the spinal cord. In addition, measurements for the cervical spine canal size and sagittal alignment are also described briefly. These tools have resulted collectively in the identification of numerous useful parameters. However, the development of multiple techniques for assessing the same feature, such as cord compression, has also resulted in a number of challenges, including introducing ambiguity in terms of which methods to use and hindering effective comparisons of analysis in the literature. In addition, newer techniques that use advanced MRI are emerging and providing exciting new tools for assessing the spinal cord in patients with degenerative cervical myelopathy.

Prediction of Infarct Lesion Volumes by Processing Magnetic Resonance Apparent Diffusion Coefficient Maps in Patients with Acute Ischemic Stroke.

OBJECTIVE: We aimed to investigate the diagnostic value of apparent diffusion coefficient (ADC) maps in magnetic resonance imaging (MRI) in the volume of acute cerebral infarction (ACI). METHODS: A total of 207 ACI patients were selected in our study. The cerebral infarction (CI) volume in the initial diffusion-weighted imaging examination, minimum ADC value, relative apparent diffusion coefficient (rADC) value, and mean ADC value were measured. The correlations between age, smoking, drinking, hypertension, diabetes, coronary heart disease, clinical stage, the lowest ADC value, the mean ADC value, and the mean rADC value with CI volume were analyzed by logistic regression analysis. A receiver operating characteristic (ROC) curve was used to analyze the diagnostic value of the ADC value in the ACI volume. RESULTS: There was a significant difference in the distribution of the CI volume in ACI patients (P <.05). A significant difference was found in the signal intensity and percentage distribution of ADC map in patients of different CI groups with different CI volumes (P <.05). The signal of the ADC map was positively correlated with the CI volume. The mean ADC and rADC values had significant differences between different CI volumes (all P <.05). Logistic regression analysis revealed that the mean ADC value was significantly correlated with the CI volume (P <.05). Analysis of the ROC curve showed that the quantitative value of ADC has a diagnostic value for the ACI volume. CONCLUSION: This study has shown that the signal intensity change on the ADC map in MRI and quantitative analysis of the ADC value can be used as a reference for predicting the ACI volume.

Linking contemporary high resolution magnetic resonance imaging to the von Economo legacy: A study on the comparison of MRI cortical thickness and histological measurements of cortical structure.

The cerebral cortex is a distinctive part of the mammalian nervous system, displaying a spatial variety in cyto-, chemico-, and myelinoarchitecture. As part of a rich history of histological findings, pioneering anatomists von Economo and Koskinas provided detailed mappings on the cellular structure of the human cortex, reporting on quantitative aspects of cytoarchitecture of cortical areas. Current day investigations into the structure of human cortex have embraced technological advances in Magnetic Resonance Imaging (MRI) to assess macroscale thickness and organization of the cortical mantle in vivo. However, direct comparisons between current day MRI estimates and the quantitative measurements of early anatomists have been limited. Here, we report on a simple, but nevertheless important cross-analysis between the histological reports of von Economo and Koskinas on variation in thickness of the cortical mantle and MRI derived measurements of cortical thickness. We translated the von Economo cortical atlas to a subdivision of the commonly used Desikan-Killiany atlas (as part of the FreeSurfer Software package and a commonly used parcellation atlas in studies examining MRI cortical thickness). Next, values of "width of the cortical mantle" as provided by the measurements of von Economo and Koskinas were correlated to cortical thickness measurements derived from high-resolution anatomical MRI T1 data of 200+ subjects of the Human Connectome Project (HCP). Cross-correlation revealed a significant association between group-averaged MRI measurements of cortical thickness and histological recordings (r = 0.54, P < 0.001). Further validating such a correlation, we manually segmented the von Economo parcellation atlas on the standardized Colin27 brain dataset and applied the obtained three-dimensional von Economo segmentation atlas to the T1 data of each of the HCP subjects. Highly consistent with our findings for the mapping to the Desikan-Killiany regions, cross-correlation between in vivo MRI cortical thickness and von Economo histology-derived values of cortical mantle width revealed a strong positive association (r = 0.62, P < 0.001). Linking today's state-of-the-art T1-weighted imaging to early histological examinations our findings indicate that MRI technology is a valid method for in vivo assessment of thickness of human cortex.