Identifying idiopathic intracranial hypertension in a hospital-based chronic headache population: Utility of magnetic resonance imaging, magnetic resonance venography and trans-orbital sonography.

BACKGROUND: One of the most underestimated types of chronic headaches is headaches as a result of cerebro-spinal fluid dysregulation disorders. Idiopathic intracranial hypertension (IIH) presents with headache and visual symptoms and usually is associated with papilledema. We identified patients with IIH in a chronic headache population presenting to a hospital-based headache clinic, and studied its associations with clinical, sonographic and magnetic resonance imaging (MRI) findings. METHODS: Of 168 patients, 141 chronic headache patients were identified and completed the study procedures (semi-structured medical interview, fundus examination, MRI brain with magnetic resonance venography (MRV) and trans-orbital sonography (TOS)). Patients with abnormal findings underwent lumbar puncture for opening pressure. RESULTS: The prevalence of IIH was 27%. IIH patients were of higher age, had gnawing/throbbing headache in the vertex in most cases, and had higher body mass index. Fundus examination had a sensitivity of 79% and a specificity of 98% for the detection of IIH cases. Approximately 23% of IIH patients had no papilledema. The most sensitive MR sign was found to be transverse sinus stenosis. TOS showed optic nerve sheath dilation in 35.7% of IIH without papilledema cases. CONCLUSIONS: The prevalence of IIH is high in the chronic headache population and should be suspected in the headache clinic setting, particularly because there is significant overlap with migraine symptomatology. MRI/MR venography and TOS can be useful adjunct tests to identify IIH patients.

Predicting outcomes of unruptured intracranial artery dissection with clear symptoms onset using clinical and radiological features.

We investigated the clinical and radiologic predictors of unruptured symptomatic intracranial artery dissection (IAD) outcomes. Unruptured symptomatic IAD patients who underwent vessel wall magnetic resonance imaging (VW-MRI) and time-of-flight magnetic resonance angiography (TOF-MRA) within 1 month after symptom onset, followed for over 12 months were included. Baseline features predicting the clinical outcome of recurrent symptoms and radiologic outcomes of aneurysmal dilatation and occlusion were analyzed using logistic regression analysis. The Kaplan-Meier method calculated the median time to morphological stability. Patients with aneurysmal dilatation were categorized into progressive and non-progressive enlargement subgroups. Seventy-three IADs from 65 patients were included. All patients showed benign clinical course (mRS 0-1). No baseline features were predictive of recurrent symptoms. Aneurysmal dilatation was associated with increased outer diameter in baseline VW-MRI (OR, 23.15; 95% CI, 3.78-141.75, P < 0.001) and TOF-MRA (OR, 10.81; 95% CI, 2.16-53.99, P = 0.004). Occlusion was inversely associated with preserved patency in baseline VW-MRI (OR, 0.1; 95% CI, 0.01-0.74, P = 0.024) and TOF-MRA (OR, 0.14; 95% CI, 0.02-0.98; P = 0.048). The median time to morphological stability was 3.9 months (95% CI, 3.16-5.5). While baseline features did not significantly differ between aneurysmal dilatation subgroups, follow-up imaging revealed significant differences in remodeling index, normalized wall index, relative signal intensity of intramural hematoma, and presence of onion-skin appearance and intramural hematoma (all P < 0.05). Our findings suggest that while unruptured IAD presents a benign clinical outcome, follow-up imaging may be necessary to monitor the progressive enlargement of aneurysmal dilatation.

Shine and darkle the blood vessels: Multiparameter hypersensitive MR angiography for diagnosis of panvascular diseases.

Magnetic resonance angiography (MRA) is pivotal for diagnosing panvascular diseases. However, single-modality MRA falls short in diagnosing diverse vascular abnormalities. Thus, contrast agents combining T1 and T2 effects are sought for multiparameter MRA with clinical promise, yet achieving a balance in T1 and T2 contrast enhancement effects remains a scientific challenge. Herein, we developed a hypersensitive multiparameter MRA strategy using dual-modality NaGdF4 nanoparticles. Because of the longer tumbling time (τR), NaGdF4 nanoparticles can improve the longitudinal relaxivity (r1), brightening vessels in T1-weighted sequences. Simultaneously, the regular arrangement of Gd3+ in the crystal induces magnetic anisotropy, creating local static magnetic field heterogeneity and generating negative signals in T2-weighted sequences. Consequently, the efficacy of NaGdF4-enhanced high-resolution multiparameter MRA has been validated in diagnosing ischemic stroke and Alzheimer's disease in rodent models. In addition, the dual-contrast imaging has been realized on swine with a clinical 3.0-T magnetic resonance imaging scanner, highly emphasizing the clinical translation prospect.

Evaluation of micro-remnant niduses of arteriovenous malformations post-gamma knife radiosurgery by 3D-rotational angiography.

PURPOSE: Recent innovations in radiological imaging have enabled the detection of micro-remnant niduses of arteriovenous malformations (AVMs) after gamma knife radiosurgery (GKS), which have not been previously perceptible. Herein, we focus on the difficulty of evaluating micro-remnant AVMs after GKS that are hardly perceptible on conventional examinations and propose integrating follow-up three-dimensional rotational angiography (3D-RA) in the previous gamma plan as a solution. METHODS: We retrospectively searched NTT Medical Center Tokyo hospital database for patients with AVMs who underwent both two-dimensional digital subtraction angiography (2D-DSA) and 3D-RA as follow-up for GKS from February 2021 to January 2024. Patients with suspected nidus occlusion on the latest non-contrast-enhanced magnetic resonance angiography (NC-MRA) were included, and contrast-enhanced magnetic resonance angiography (CE-MRA), 2D-DSA, and 3D-RA were evaluated. RESULTS: Twelve patients with 13 AVM sites were defined as having complete nidus occlusion on upfront NC-MRA. On 2D-DSA, seven AVM sites showed the presence of slight remaining AVMs based on the detection of remnant drainage veins, however the nidus was not detected in three cases. Nevertheless, 3D-RA detected micro-remnant niduses in all seven AVM sites, and four patients underwent re-GKS. Nine patients with ten AVM sites also underwent CE-MRA, and six AVM sites were diagnosed with radiation-induced parenchymal injury. CONCLUSION: Importing the 3D-RA image into the treatment planning has the potential to be more helpful than NC-MRA or CE-MRA to detect micro-remnant AVMs and evaluate the true remnant volume, and may contribute to a more detailed treatment planning, thereby improving the results of GKS retreatment.

Use of Pretreatment Perfusion MRI-based Intratumoral Heterogeneity to Predict Pathologic Response of Triple-Negative Breast Cancer to Neoadjuvant Chemoimmunotherapy.

Background Neoadjuvant chemoimmunotherapy (NACI) has significantly increased the rate of pathologic complete response (pCR) in patients with early-stage triple-negative breast cancer (TNBC), although predictors of response to this regimen have not been identified. Purpose To investigate pretreatment perfusion MRI-based radiomics as a predictive marker for pCR in patients with TNBC undergoing NACI. Materials and Methods This prospective study enrolled women with early-stage TNBC who underwent NACI at two different centers from August 2021 to July 2023. Pretreatment dynamic contrast-enhanced MRI scans obtained using scanners from multiple vendors were analyzed using the Tofts model to segment tumors and analyze pharmacokinetic parameters. Radiomics features were extracted from the rate constant for contrast agent plasma-to-interstitial transfer (or Ktrans), volume fraction of extravascular and extracellular space (Ve), and maximum contrast agent uptake rate (Slopemax) maps and analyzed using unsupervised correlation and least absolute shrinkage and selector operator, or LASSO, to develop a radiomics score. Score effectiveness was assessed using the area under the receiver operating characteristic curve (AUC), and multivariable logistic regression was used to develop a multimodal nomogram for enhanced prediction. The discrimination, calibration, and clinical utility of the nomogram were evaluated in an external test set. Results The training set included 112 female participants from center 1 (mean age, 52 years ± 11 [SD]), and the external test set included 83 female participants from center 2 (mean age, 47 years ± 11). The radiomics score demonstrated an AUC of 0.80 (95% CI: 0.70, 0.89) for predicting pCR. A nomogram incorporating the radiomics score, grade, and Ki-67 yielded an AUC of 0.86 (95% CI: 0.78, 0.94) in the test set. Associations were found between higher radiomics score (>0.25) and tumor size (P < .001), washout enhancement (P = .01), androgen receptor expression (P = .009), and programmed death ligand 1 expression (P = .01), demonstrating a correlation with tumor immune environment in participants with TNBC. Conclusion A radiomics score derived from pharmacokinetic parameters at pretreatment dynamic contrast-enhanced MRI exhibited good performance for predicting pCR in participants with TNBC undergoing NACI, and could potentially be used to enhance clinical decision making. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Rauch in this issue.

Collateral assessment on magnetic resonance imaging/angiography up to 30 hours after stroke onset.

PURPOSE: We aimed to validate hyperintense vessel sign (HVS) on FLAIR imaging or posterior cerebral artery (PCA) laterality on MR angiography beyond 4.5 hours after stroke onset. MATERIALS AND METHODS: Data from acute ischemic stroke patients with internal carotid or middle cerebral artery occlusion who underwent CT perfusion imaging at baseline, follow-up MR perfusion imaging and angiography within 30 hours after stroke, without effective recanalization on follow-up imaging, were analysed retrospectively. Patients were separately classified as high or low HVS (>5 or ≤5 slices of HVS), and PCA laterality positive or negative group. We compared core and penumbra volumes at follow-up imaging and neurological outcomes between high or low HVS group, and between PCA laterality positive or negative group. RESULTS: Of 49 patients analyzed, four patients with artifacts were excluded and 45 were classified into high (n = 23) or low (n = 22) HVS group. High group had a smaller core volume (median 32 ml versus 109 ml, p = 0.004), larger penumbra volume at follow-up (68 ml versus 0 ml, p = 0.001), and better outcomes (modified Rankin Scale at three months, 3 versus 5, p = 0.03). For PCA laterality analysis, 1 patient with previously occluded PCA was excluded and 48 patients were classified as positive (n = 22) or negative (n = 26). Positive group had larger core volume (116 ml versus 37 ml), and no significant differences in penumbral volumes or outcomes. CONCLUSION: Prominent HVS in later time was associated with small core volume, persistent penumbra volume and favorable outcomes.

Quantitative Perfusion-Weighted Magnetic Resonance Imaging in Uveal Melanoma.

Purpose: Perfusion-weighted imaging (PWI; magnetic resonance imaging [MRI]) has been shown to provide valuable biological tumor information in uveal melanoma (UM). Clinically used semiquantitative methods do not account for tumor pigmentation and eye movement. We hypothesize that a quantitative PWI method that incorporates these, provides a more accurate description of tumor perfusion than the current clinical method. The aim of this study was to test this in patients with UM before and after radiotherapy. Methods: Perfusion-weighted 3T MRIs were retrospectively analyzed in 47 patients with UM before and after radiotherapy. Tofts pharmacokinetic modeling was performed to determine vascular permeability (Ktrans), extracellular extravascular space (ve), and reflux rate (kep). These were compared with semiquantitative clinical parameters including peak intensity and outflow percentage. Results: The effect of tumor pigmentation on peak intensity and outflow percentage was statistically significant (P < 0.01) and relative peak intensity was significantly different between melanotic and amelanotic tumors (1.5 vs. 1.9, P < 0.01). Before radiotherapy, median tumor Ktrans was 0.63 min-1 (range = 0.06-1.42 min-1), median ve was 0.23 (range = 0.09-0.63), and median kep was 2.3 min-1 (range = 0.6-5.0 min-1). After radiotherapy, 85% showed a decrease in Ktrans and kep (P < 0.01). Changes in tumor pigmentation before and after radiotherapy were small and not significant (median increase in T1 of 33 ms, P = 0.55). Conclusions: Quantitative PWI parameters decreased significantly after radiotherapy and can therefore can serve as an early biomarker for treatment response assessment. However, due to the nonsignificant changes in tumor pigmentation before and after radiotherapy, the current semiquantitative method appears to be sufficiently sensitive for detection of changes in tumor perfusion.

Comparative study of CTA/CTV and MRTA for preoperative simulation of microvascular decompression in neurovascular compression syndromes.

Neurovascular compression syndrome (NVCS), characterized by cranial nerve compression due to adjacent blood vessels at the root entry zone, frequently presents as trigeminal neuralgia (TN), hemifacial spasm (HFS), or glossopharyngeal neuralgia (GN). Despite its prevalence in NVCS assessment, Magnetic Resonance Tomographic Angiography (MRTA)'s limited sensitivity to small vessels and veins poses challenges. This study aims to refine vessel localization and surgical planning for NVCS patients using a novel 3D multimodal fusion imaging (MFI) technique incorporating computed tomography angiography and venography (CTA/CTV). A retrospective analysis was conducted on 76 patients who underwent MVD surgery and were diagnosed with single-site primary TN, HFS, or GN. Imaging was obtained from MRTA and CTA/CTV sequences, followed by image processing and 3D-MFI using FastSurfer and 3DSlicer. The CTA/CTV-3D-MFI showed higher sensitivity than MRTA-3D-MFI in predicting responsible vessels (98.6% vs. 94.6%) and NVC severity (98.6% vs. 90.8%). Kappa coefficients revealed strong agreement with MRTA-3D-MFI (0.855 for vessels, 0.835 for NVC severity) and excellent agreement with CTA/CTV-3D-MFI (0.951 for vessels, 0.952 for NVC). Resident neurosurgeons significantly preferred CTA/CTV-3D-MFI due to its better correlation with surgical reality, clearer depiction of surgical anatomy, and optimized visualization of approaches (p < 0.001). Implementing CTA/CTV-3D-MFI significantly enhanced diagnostic accuracy and surgical planning for NVCS, outperforming MRTA-3D-MFI in identifying responsible vessels and assessing NVC severity. This innovative imaging modality can potentially improve outcomes by guiding safer and more targeted surgeries, particularly in cases where MRTA may not adequately visualize crucial neurovascular structures.

Comparison of a new MR rapid wash-out map with MR perfusion in brain tumors.

BACKGROUND: MR perfusion is a standard marker to distinguish progression and therapy-associated changes after surgery and radiochemotherapy for glioblastoma. TRAMs (Treatment Response Assessment Maps) were introduced, which are intended to facilitate the differentiation of vital tumor cells and radiation necrosis by means of late (20-90 min) contrast clearance and enhancement. The differences of MR perfusion and late-enhancement are not fully understood yet. METHODS: We have implemented and established a fully automated creation of rapid wash-out (15-20 min interval) maps in our clinic. We included patients with glioblastoma, CNS lymphoma or brain metastases who underwent our MR protocol with MR perfusion and rapid wash-out between 01/01/2024 and 30/06/2024. Since both wash-out and hyperperfusion are intended to depict the active tumor area, this study involves a quantitative and qualitative comparison of both methods. For this purpose, we volumetrically measured rCBV (relative cerebral blood volume) maps and rapid wash-out maps separately (two raters). Additionally, we rated the agreement between both maps on a Likert scale (0-10). RESULTS: Thirty-two patients were included in the study: 15 with glioblastoma, 7 with CNS lymphomas and 10 with brain metastasis. We calculated 36 rapid wash-out maps (9 initial diagnosis, 27 follow-up). Visual agreement of MR perfusion with rapid wash-out by rating were found in 44 ± 40% for initial diagnosis, and 75 ± 31% for follow-up. We found a strong correlation (Pearson coefficient 0.92, p < 0.001) between the measured volumes of MR perfusion and rapid wash-out. The measured volumes of MR perfusion and rapid wash-out did not differ significantly. Small lesions were often not detected by MR perfusion. Nevertheless, the measured volumes showed no significant differences in this small cohort. CONCLUSIONS: Rapid wash-out calculation is a simple tool that provides new information and, when used in conjunction with MR perfusion, may increase diagnostic accuracy. The method shows promising results, particularly in the evaluation of small lesions.

Impact of microvascular decompression on wall shear stress in responsible arteries in trigeminal neuralgia and hemifacial spasm.

Microvascular decompression (MVD) has proven efficacy in trigeminal neuralgia (TN) and hemifacial spasm (HFS). This study utilized computational fluid dynamics (CFD) to investigate the impact of MVD on wall shear stress (WSS) of responsible arteries (RAs) at the neurovascular contact (NVC). A total of 21 cases (10 TN, 11 HFS) were analyzed, involving RAs at NVC validated through intraoperative photographs. Hemodynamic parameters (WSS, vessel diameter, flow rate, pressure drop) was calculated using CFD for the RAs based on 3D silent-magnetic resonance angiograms. The NVC was segmented into NVC-proximal, NVC-site, and NVC-distal portions using simulated 3D CFD images that correlated with surgical observations. WSS ratios of NVC-site to NVC-proximal (NVC-site/proximal) was calculated both before and after MVD. Prior to MVD, WSS in the RA at the NVC displayed a peaked curve with a maximum at NVC-site; however, post MVD, it presented a smooth curve without peaks. The WSS ratio exhibited a significant decrease after MVD. The impact of MVD on WSS of RAs at NVC was evaluated in both TN and HFS cases. Analyzing the hemodynamics of RAs through CFD and identifying WSS peaks at NVC portions before MVD provided a more detailed and localized understanding of the morphologically depicted NVC.

Aneurysm growth evaluation and detection: a computer-assisted follow-up MRA analysis.

Growing intracranial aneurysms pose a high risk of rupture, making the detection and quantification of the growth crucial for timely treatment strategy adoption. In this paper we propose a computer-assisted approach based on the extraction of IA shapes from associated baseline and follow-up angiographic scans and non-rigid morphing of the two shapes. From the obtained shape deformations we computed four novel features, including differential volume (dV), surface area (dSA), aneurysm-size normalized median deformation path length (dMPL), and integral of cumulative deformation distances (dICDD). An experienced neuroradiologist manually extracted the IA shape models from the baseline and follow-up MRAs and, by utilizing size change and visual assessments, classified each aneurysm into stable with morphology changes, stable or growing. We investigated the classification performance and found that three of the novel and one cross-sectional feature exhibited significantly different mean values (p-value < 0.05 ; Tukey's HSD test) between the stable and growing IA groups, while the mean dICDD was significantly different between all the three groups. The cross-sectional features has sensitivity to growing IAs in range 0.05-0.86, while novel features had generally higher sensitivity in range 0.81-0.90, making them promising candidates as surrogate follow-up imaging-based biomarkers for IA growth detection. These findings may offer valuable information for clinical management of patients with IAs based on follow-up imaging.

Perfusion parameter map generation from TOF-MRA in stroke using generative adversarial networks.

PURPOSE: To generate perfusion parameter maps from Time-of-flight magnetic resonance angiography (TOF-MRA) images using artificial intelligence to provide an alternative to traditional perfusion imaging techniques. MATERIALS AND METHODS: This retrospective study included a total of 272 patients with cerebrovascular diseases; 200 with acute stroke (from 2010 to 2018), and 72 with steno-occlusive disease (from 2011 to 2014). For each patient the TOF MRA image and the corresponding Dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) were retrieved from the datasets. The authors propose an adapted generative adversarial network (GAN) architecture, 3D pix2pix GAN, that generates common perfusion maps (CBF, CBV, MTT, TTP, Tmax) from TOF-MRA images. The performance was evaluated by the structural similarity index measure (SSIM). For a subset of 20 patients from the acute stroke dataset, the Dice coefficient was calculated to measure the overlap between the generated and real hypoperfused lesions with a time-to-maximum (Tmax) > 6 s. RESULTS: The GAN model exhibited high visual overlap and performance for all perfusion maps in both datasets: acute stroke (mean SSIM 0.88-0.92, mean PSNR 28.48-30.89, mean MAE 0.02-0.04 and mean NRMSE 0.14-0.37) and steno-occlusive disease patients (mean SSIM 0.83-0.98, mean PSNR 23.62-38.21, mean MAE 0.01-0.05 and mean NRMSE 0.03-0.15). For the overlap analysis for lesions with Tmax>6 s, the median Dice coefficient was 0.49. CONCLUSION: Our AI model can successfully generate perfusion parameter maps from TOF-MRA images, paving the way for a non-invasive alternative for assessing cerebral hemodynamics in cerebrovascular disease patients. This method could impact the stratification of patients with cerebrovascular diseases. Our results warrant more extensive refinement and validation of the method.

Plaque enhancement of middle cerebral artery and pre-stroke diet are associated with prognosis of subacute ischemic stroke: A prospective high-resolution MR vessel wall imaging study.

OBJECTIVES: To explore the value of middle cerebral artery (MCA) plaque characteristics in predicting the outcomes of subacute ischemic stroke and the incremental value of the previous diet on predictive performance. METHODS: One hundred and thirty-seven subacute ischemic stroke patients attributed to MCA plaques were included and analyzed in this prospective study. The National Institute of Health Stroke Scale (NIHSS) score, Mediterranean Diet Adherence Screener (MEDAS) score, and other clinical data were assessed. The plaque area, degree of stenosis, plaque burden, enhancement ratio, remodeling type, and intraplaque hemorrhage were measured using high-resolution MR vessel wall imaging (HR-VWI). Multivariable logistic regression analysis and receiver operating characteristic curve analysis were performed to assess the predictive performance of clinical and plaque characteristics for subacute ischemic stroke outcomes at 3 months. RESULTS: Patients with poor outcomes exhibited high NIHSS scores, and low MEDAS scores (P<0.001). Plaque burden, enhancement ratio, and degree of stenosis were significantly higher in patients with poor outcomes (P<0.001). Multivariate analyses further indicated that NIHSS score (P=0.001), MEDAS score (P=0.013), and enhancement ratio (P=0.011) were independent predictors of subacute ischemic stroke outcomes. The three models' area under the curve (AUC) values were 0.811, 0.844, and 0.794. Combining these three factors resulted in an AUC of 0.908 (P<0.001). CONCLUSIONS: The combination of NIHSS score, MEDAS score, and enhancement ratio showed significant superiority in the prognostic evaluation of subacute ischemic stroke. Clinical data combined with plaque characteristics improves the accuracy of 3-month outcome prediction on subacute ischemic stroke.

Diagnostic accuracy of arterial spin labeling MR imaging in detecting cerebral arteriovenous malformations: a systematic review and meta-analysis.

Diagnostic accuracy of arteriovenous malformations (AVMs) is imperative for delineating management. The current standard is digital subtraction angiography (DSA). Arterial spin labeling (ASL) is an understudied noninvasive, non-contrast technique that allows angioarchitecture visualization and additionally quantifies cortical and AVM cerebral blood flow and hemodynamics. This meta-analysis aims to compare ASL and DSA imaging in detecting and characterizing cerebral AVMs. EMBASE, Medline, Scopus, and Cochrane databases were queried from inception to July 2022 for reports of AVMs evaluated by DSA and ASL imaging. Fourteen studies with 278 patients evaluated using DSA and ASL imaging prior to intervention were included; pCASL in 11 studies (n = 239, 85.37%) and PASL in three studies (n = 41, 14.64%). The overall AVM detection rate on ASL was 99% (CI 97-100%); subgroup analysis revealed no difference between pCASL vs. PASL (99%; CI 96-100% vs. 100%; CI 95-100% respectively, p = 0.42). The correlation value comparing ASL and DSA nidus size was 0.99. DSA and ASL intermodality agreement Cohen's k factor for Spetzler Martin Grading (SMG) was reported at a median of 0.98 (IQR 0.73-0.1), with a 1.0 agreement on SMG classification. A median of 25 arteries were detected by DSA (IQR 14.5-27), vs. 25 by ASL (IQR 14.5-27.5) at a median 0.92 k factor. ASL provides angioarchitectural visualization noninferior to DSA and additionally quantifies CBF. Our study suggests that ASL should be considered in the detection of AVMs, especially in patients with contrast contraindications or apprehension towards an invasive assessment.

Quantitative non-contrast perfusion MRI in the body using arterial spin labeling.

Arterial spin labeling (ASL) is a non-invasive magnetic resonance imaging (MRI) method that enables the assessment and the quantification of perfusion without the need for an exogenous contrast agent. ASL was originally developed in the early 1990s to measure cerebral blood flow. The utility of ASL has since then broadened to encompass various organ systems, offering insights into physiological and pathological states. In this review article, we present a synopsis of ASL for quantitative non-contrast perfusion MRI, as a contribution to the special issue titled "Quantitative MRI-how to make it work in the body?" The article begins with an introduction to ASL principles, followed by different labeling strategies, such as pulsed, continuous, pseudo-continuous, and velocity-selective approaches, and their role in perfusion quantification. We proceed to address the technical challenges associated with ASL in the body and outline some of the innovative approaches devised to surmount these issues. Subsequently, we summarize potential clinical applications, challenges, and state-of-the-art ASL methods to quantify perfusion in some of the highly perfused organs in the thorax (lungs), abdomen (kidneys, liver, pancreas), and pelvis (placenta) of the human body. The article concludes by discussing future directions for successful translation of quantitative ASL in body imaging.

Improved visualization of intracranial distal arteries with multiple 2D slice dynamic ASL-MRA and super-resolution convolutional neural network.

PURPOSE: To develop a novel framework to improve the visualization of distal arteries in arterial spin labeling (ASL) dynamic MRA. METHODS: The attenuation of ASL blood signal due to the repetitive application of excitation RF pulses was minimized by splitting the acquisition volume into multiple thin 2D (M2D) slices, thereby reducing the exposure of the arterial blood magnetization to RF pulses while it flows within the brain. To improve the degraded vessel visualization in the slice direction due to the limited minimum achievable 2D slice thickness, a super-resolution (SR) convolutional neural network (CNN) was trained by using 3D time-of-flight (TOF)-MRA images from a large public dataset. And then, we applied domain transfer from 3D TOF-MRA to M2D ASL-MRA, while avoiding acquiring a large number of ASL-MRA data required for CNN training. RESULTS: Compared to the conventional 3D ASL-MRA, far more distal arteries were visualized with higher signal intensity by using M2D ASL-MRA. In general, however, the vessel visualization with a conventional interpolation was prone to be blurry and unclear due to the limited spatial resolution in the slice direction, particularly in small vessels. Application of CNN-based SR transferred from 3D TOF-MRA to M2D ASL-MRA successfully addressed such a limitation and achieved clearer visualization of small vessels than conventional interpolation. CONCLUSION: This study demonstrated that the proposed framework provides improved visualization of distal arteries in later dynamic phases, which will particularly benefit the application of this approach in patients with cerebrovascular disease who have slow blood flow.

A generalized signal model for dual-module velocity-selective arterial spin labeling.

PURPOSE: To develop a generalized signal model for dual-module velocity-selective arterial spin labeling (dm-VSASL) that can integrate arbitrary saturation and inversion profiles. THEORY AND METHODS: A recently developed mathematical framework for single-module VSASL is extended to address the increased complexity of dm-VSASL and to model the use of realistic velocity-selective profiles in the label-control and vascular crushing modules. Expressions for magnetization difference, arterial delivery functions, labeling efficiency, and cerebral blood flow (CBF) estimation error are presented. Sources of error are examined and timing requirements to minimize quantification errors are derived. RESULTS: For ideal velocity-selective profiles, the predicted signals match those of prior work. With realistic profiles, a CBF-dependent estimation error can occur when velocity-selective inversion (VSI) is used for the labeling modules and velocity-selective saturation (VSS) is used for the vascular crushing module. The error reflects a mismatch between the leading and trailing edges of the delivery function for the second bolus and can be minimized by choosing a nominal labeling cutoff velocity that is lower than the nominal saturation cutoff velocity. In the presence of B 0 $$ {\mathrm{B}}_0 $$ and B 1 $$ {\mathrm{B}}_1 $$ inhomogeneities, the labeling efficiency of dual-module VSI is more attenuated than that of dual-module VSS. CONCLUSION: The proposed signal model will enable researchers to more accurately assess and compare the performance of realistic dm-VSASL implementations and improve the quantification of dm-VSASL CBF measures.

High-Resolution Magnetic Resonance Angiography of Tumor Vasculatures with an Interlocking Contrast Agent.

The comprehensive evaluation of tumor vasculature that is crucial for the development, expansion, and spread of cancer still remains a great challenge, especially the three-dimensional (3D) evaluation of vasculatures. In this study, we proposed a magnetic resonance (MR) angiography strategy with interlocking stratagem of zwitterionic Gd-chelate contrast agents (PAA-Gd) for continuous monitoring of tumor angiogenesis progression in 3D. Owing to the zwitterionic structure and nanoscale molecular diameter, the longitudinal molar relaxivity (r1) of PAA-Gd was 2.5 times higher than that of individual Gd-chelates on a 7.0 T MRI scanner, resulting in the higher-resolution visualization of tumor vasculatures. More importantly, PAA-Gd has the appropriate blood half-life (69.2 min), emphasizing the extended imaging window compared to the individual Gd-chelates. On this basis, by using PAA-Gd as the contrast agent, the high-resolution, 3D depiction of the spatiotemporal distribution of microvasculature in solid tumors formed by different cell lines over various inoculation times has been obtained. This method offers an effective approach for early tumor diagnosis, development assessment, and prognosis evaluation.

High-resolution MR vessel wall imaging and cardiovascular health for evaluating the occurrence of ischemic stroke.

OBJECTIVES: To explore the value of high-resolution MR vessel wall imaging (HR-VWI) based plaque characteristics combined with cardiovascular health (CVH) metrics in the risk evaluation of ischemic stroke attributed to middle cerebral artery (MCA) atherosclerotic stenosis. METHODS: Retrospective analysis of 209 participants with middle cerebral atherosclerosis, 146 patients with high signal in the MCA area on DWI were included in the symptomatic group, and 63 patients were included in the asymptomatic group. The degree of stenosis, enhancement ratio, plaque burden, remodeling index, and intraplaque hemorrhage were measured and compared between groups. Seven CVH metrics and other clinical data were obtained. The association between these factors and ischemic stroke was investigated by univariate and multivariate analysis. RESULTS: The degree of stenosis [OR, 1.036 (95 % CI, 1.014-1.058); P = 0.001], plaque burden [OR, 0.958 (95 % CI, 0.928-0.989); P = 0.009], intraplaque hemorrhage [OR, 3.530 (95 % CI, 1.233-10.110); P = 0.019], physical activity [OR, 4.321 (95 % CI, 1.526-12.231); P = 0.006], and diet [OR, 8.986 (95 % CI, 2.747-29.401); P < 0.001] were the independent characteristics associated with the occurrence of ischemic stroke. ROC curve showed that the combination of plaque characteristics, diet, and physical activity achieved the highest AUC of 0.828 (95 % CI 0.770-0.877; P < 0.001), with sensitivity and specificity being 86.30 % and 66.67 %, respectively. CONCLUSION: Plaque characteristics combined with CVH metrics may identify high-risk populations for ischemic stroke and offer novel insights into risk evaluation and stratification.

Application of the 2022 ACR/EULAR criteria for Takayasu arteritis to previously diagnosed patients based on the 1990 ACR criteria.

OBJECTIVES: Recently, a joint group of the American College of Rheumatology (ACR) and the European Alliance of Associations for Rheumatology (EULAR) proposed new criteria for Takayasu arteritis (TAK) (the 2022 ACR/EULAR criteria). This study applied the 2022 ACR/EULAR criteria to patients with previously diagnosed TAK based on the 1990 ACR criteria and investigated the concordance rate between the two criteria according to the four imaging modalities. METHODS: This study reviewed the medical records of 179 patients who met the 1990 ACR criteria for TAK. The imaging modalities included conventional angiography, computed tomography angiography, fluorodeoxyglucose-positron emission tomography, and magnetic resonance angiography. RESULTS: Regardless of the imaging modalities, the concordance rate between the two criteria was 85.5% when including all patients, whereas it increased to 98.1% when only patients aged ≤60 years were included. Among the four imaging modalities, computed tomography angiography exhibited the highest concordance rate between the two criteria (85.6%). The concordance rate among patients aged >60 years was 95.7%. Only one patient aged 50-60 years was reclassified as having both TAK and giant cell arteritis. CONCLUSIONS: The concordance rate was 85.5% regardless of the imaging modalities and increased to 86.9% on simultaneous computed tomography angiography and fluorodeoxyglucose-positron emission tomography imaging.