Faculty Bibliography

PURPOSE/OBJECTIVE:In diffusion MRI, vasogenic edema manifests as a major fraction of isotropic water that dilutes the anisotropic intra-axonal portion of the signal. Many tractography algorithms mistake vasogenic edema for the white matter boundary and terminate tracking to prevent producing spurious streamlines. As a result, visual representations of fascicles traversing edema are often compromised, limiting the clinical utility of tractography. METHODS:We address this hurdle with ODF-Fingerprinting (ODF-FP)-a dictionary-based fiber reconstruction algorithm that accommodates variability of neural tissue. By adding a regularization term to the ODF-FP matching formula, we counterbalance the drop of diffusion anisotropy in edematous regions to improve white matter fiber identification. In 19 glioma cases with significant peritumoral vasogenic edema, we quantify the volume of the reconstructed white matter tracts immersed in edema, then we use the cortical regions activated during task-based functional MRI as validation for tractography. To assess the potential for clinical translation, we additionally test the performance of ODF-FP on subsampled single-shell diffusion-weighted images, which contemporary clinical scanners can acquire within a few minutes. RESULTS:Our approach produces high volumes of streamlines traversing vasogenic edema and reaches high overlap with the cortical regions activated at task-based fMRI, significantly outperforming common fiber reconstruction methods in the clinically feasible data set. CONCLUSION/CONCLUSIONS:ODF-FP proves effective on research and clinical quality dMRI, which offers an opportunity for application in neurosurgery.

BACKGROUND:Molecular imaging, particularly positron emission tomography (PET), has significantly advanced the diagnosis and management of disease by visualizing biological processes at a cellular and molecular level. PET imaging of the brain, spine, and head/neck, summarized under the umbrella term Neuro-PET, enables noninvasive diagnosis and monitoring of diseases such as dementia, epilepsy, cancer, movement, or autoimmune disorders. The rising prevalence of these conditions, as well as new treatment options necessitating response assessment, are expected to escalate Neuro-PET imaging volumes, with projections for a significant increase in the need for specialized imaging services. This increasing clinical need highlights existing workforce shortages and underscores the need for neuroradiologists to acquire proficiency in molecular imaging. This expanded role seeks to address the growing demand. To this end, we propose a rigorous, structured, patient-centered, and collaborative framework for expanding neuroradiologists' training and practice to include Neuro-PET interpretation. METHODS:This ASNR consensus statement outlines competency recommendations, training pathways, and implementation strategies to incorporate Neuro-PET into neuroradiology practice. This approach is based on existing guidelines and was informed by survey data from neuroradiologists and molecular imaging subspecialists revealing current practice patterns and training needs. For neuroradiology fellows, structured training encompasses hands-on Neuro-PET imaging experience, understanding the biologic and molecular basis of radiopharmaceuticals used in Neuro-PET, and integrating molecular insights with anatomical data. Neuroradiologists beyond fellowship can undertake practice-based curriculum involving supervised case interpretation, standardized reader training courses, continuing medical education (CME), and peer review. KEY MESSAGE/CONCLUSIONS:Neuroradiologists, with their in-depth expertise of central nervous system structure and function, are well positioned to meld molecular imaging data with traditional anatomical findings. They can achieve competency and should be granted practice privileges in interpreting Neuro-PET studies through a comprehensive combination of structured training, hands-on clinical experience, and documented CME hours. ABBREVIATIONS/BACKGROUND:PET = positron emission tomography; CME = continuing medical education; ACR= American College of Radiology.

BACKGROUND AND PURPOSE/OBJECTIVE:Accurate localization of the ventral intermediate nucleus (VIM) within the dentatorubrothalamic tract (DRTT) is critical for effective neurosurgical treatment of essential tremor (ET). This study evaluated the feasibility and anatomical specificity of quantitative susceptibility mapping (QSM) for direct VIM/DRTT visualization, comparing it with conventional diffusion tractography-based reconstructions. MATERIALS AND METHODS/METHODS:Twenty-seven participants (10 healthy controls, 17 ET patients) were enrolled across two institutions and imaged on 3T MRI systems. QSM-defined VIM/DRTT regions were manually segmented based on characteristic hypointense susceptibility contrast. Whole-brain diffusion tractography was performed to reconstruct the DRTT, pyramidal tract (PT), and medial lemniscus (ML) tracts. Spatial overlap between QSM-and tractography-defined VIM/DRTT regions was calculated, as well as overlap with neighboring PT and ML tracts to assess specificity. RESULTS:Two participants were excluded due to insufficient VIM/DRTT streamlines in tractography reconstruction. In healthy controls, QSM-and tractography-defined VIM/DRTT showed high spatial correspondence (left: 87.6 ± 5.1%; right: 85.3 ± 6.5%). ET patients exhibited slightly lower overlap (mean range: 71.5 - 85.1%). Overlap with neighboring PT and ML tracts was minimal (<3.3%), confirming high anatomical specificity of QSM-derived VIM/DRTT regions. CONCLUSIONS:QSM enables direct visualization of the VIM/DRTT with high spatial agreement to conventional tractography-based approaches while demonstrating minimal overlap with adjacent tracts. These findings support QSM as a complementary or standalone imaging modality for improved, patient-specific neurosurgical targeting in ET. ABBREVIATIONS/BACKGROUND:DBS = deep brain stimulation; DRTT = dentatorubrothalamic tract; ET = essential tremor; ML = medial lemniscus; MRgFUS = MR-guided focused ultrasound; VIM = ventral intermediate nucleus; PT = pyramidal tract; QSM = quantitative susceptibility mapping; WM = white matter.

BACKGROUND:Identifying early neuropathological changes in Alzheimer's disease (AD) is important for improving treatment efficacy. Among quantitative MRI measures, transverse relaxation time (T2) has been shown to reflect tissue microstructure relevant in aging and neurodegeneration; however, findings regarding T2 changes in both normal aging and AD have been inconsistent. The association between T2 and amyloid-beta (Aβ) accumulation, a hallmark of AD pathology, is also unclear, particularly in cognitively normal individuals who may be in preclinical stages of the disease. PURPOSE/OBJECTIVE:To investigate longitudinal hippocampal T2 changes in a cognitively normal cohort of older adults and their association with global Aβ accumulation. STUDY TYPE/METHODS:Retrospective, longitudinal. SUBJECTS/METHODS:56 cognitively normal adults between 55 and 90 years of age (17 males and 39 females). FIELD STRENGTH/SEQUENCE/UNASSIGNED:3 Tesla; multi-echo spin echo sequence for T2 mapping; 18F-florbetaben positron emission tomography for Aβ measurement. ASSESSMENT/RESULTS:Bilateral hippocampal T2 and volume were extracted to relate to Aβ PET measurements. To understand variations in AD risk, participants were separated into Aβ-high and Aβ-low subgroups using a predetermined threshold. STATISTICAL TESTS/METHODS:Linear mixed-effect models and general linear models were used. A p-value < 0.025 was considered significant to account for bilateral comparisons. RESULTS:Older age was associated with increased T2 in the bilateral hippocampus (left: β = 0.30, right: β = 0.25) and smaller hippocampal volume on the left (β = -0.12). In the Aβ-low subgroup, both longitudinal T2 increase rates (β = 0.65) in the left hippocampus and bilateral cross-sectional T2 (left: β = 0.64, right: β = 0.46) were positively correlated with Aβ PET, independent of hippocampal volume. DATA CONCLUSION/CONCLUSIONS:This study provided in vivo evidence linking hippocampal T2 to Aβ accumulation in cognitively normal aging individuals, suggesting that quantitative T2 may be sensitive to microstructural changes accompanying early Aβ pathology, such as neuroinflammation, demyelination, and reduced tissue integrity. EVIDENCE LEVEL/METHODS:3. TECHNICAL EFFICACY/UNASSIGNED:Stage 2.

The prevalence of Alzheimer's disease and other dementias is increasing as populations live longer lifespans. Imaging is becoming a key component of the workup for patients with cognitive impairment or dementia. Integrated PET-MRI provides a unique opportunity for same-session multimodal characterization with many practical benefits to patients, referring physicians, radiologists, and researchers. The impact of integrated PET-MRI on clinical practice for early adopters of this technology can be profound. Classic imaging findings with integrated PET-MRI are illustrated for common neurodegenerative diseases or clinical-radiological syndromes. This review summarizes recent technical innovations that are being introduced into PET-MRI clinical practice and research for neurodegenerative disease. More recent MRI-based attenuation correction now performs similarly compared to PET-CT (e.g., whole-brain bias < 0.5%) such that early concerns for accurate PET tracer quantification with integrated PET-MRI appear resolved. Head motion is common in this patient population. MRI- and PET data-driven motion correction appear ready for routine use and should substantially improve PET-MRI image quality. PET-MRI by definition eliminates ~50% of the radiation from CT. Multiple hardware and software techniques for improving image quality with lower counts are reviewed (including motion correction). These methods can lower radiation to patients (and staff), increase scanner throughput, and generate better temporal resolution for dynamic PET. Deep learning has been broadly applied to PET-MRI. Deep learning analysis of PET and MRI data may provide accurate classification of different stages of Alzheimer's disease or predict progression to dementia. Over the past 5 years, clinical imaging of neurodegenerative disease has changed due to imaging research and the introduction of anti-amyloid immunotherapy-integrated PET-MRI is best suited for imaging these patients and its use appears poised for rapid growth outside academic medical centers. Evidence level: 5. Technical efficacy: Stage 3.

Optimal treatment of glioma has been a subject of debate over the last few decades, since maximal resection can improve survival, whereas preservation of functional peritumoral brain tissue minimizes the risk of postoperative neurological deficits. Our preliminary study uses tractography and neural tissue microstructure modeling based on diffusion MRI to quantify progressive axonal degeneration in proximity to frontotemporal glioma. For this, we sample major white matter pathways that traverse peritumoral penumbra at two time points. The results show a pattern of decreased intra-axonal water fraction beyond anatomical MRI abnormalities, which may indicate a tumor invasion of normal-appearing white matter that potentially advocates supratotal resection.

INTRODUCTION/BACKGROUND:Blood-based biomarkers (BBMs) are promising tools for Alzheimer's disease (AD) diagnosis, but their accuracy may be affected by body mass index (BMI) and blood volume (BV) through dilution. We investigated how BMI and BV influence BBM concentrations and PET prediction. METHODS:, glial fibrillary acidic protein [GFAP], neurofilament light chain [NfL]) and BBM-based PET predictions. RESULTS:and NfL, independent of brain amyloid burden. BMI-stratified thresholds improved amyloid PET prediction, with higher BBM thresholds and area under the curve (AUC) values seen in normal weight compared to overweight or obese participants. Drastic BMI/BV declines due to weight loss increased BBM variability and systematic PET misclassification. DISCUSSION/CONCLUSIONS:Adjusting for BMI/BV in BBM-based diagnostics appears to improve accuracy and reliable detection of AD pathology, especially in preclinical stages. HIGHLIGHTS/CONCLUSIONS:Body mass index (BMI) and blood volume (BV) significantly influenced plasma BBM concentrations in cognitively unimpaired (CU) individuals. Blood-based biomarkers (BBMs) associated more strongly with BV than with BMI. Dilution effects were independent of brain amyloid burden. BMI-stratified BBM thresholds improved amyloid positron emission tomography (PET) classification accuracy. Declines in BMI/BV resulted in PET prediction bias and systematic errors.

OBJECTIVES/OBJECTIVE:Anti-amyloid-beta immunotherapy requires frequent MRI screening for amyloid-related imaging abnormalities-hemorrhage subtype (ARIA-H), consisting of cerebral microbleeds (CMB) and/or superficial siderosis (SS), using gradient-recalled echo (GRE) or susceptibility-weighted imaging (SWI). Screening MRI sequences for ARIA-H may benefit from acceleration to maximize patient enrollment by increased throughput and reduced motion degradation. This study assessed the diagnostic performance of standard GRE and SWI to echo-planar imaging (EPI) accelerated substitutions for detecting CMB and SS. MATERIALS AND METHODS/METHODS:This retrospective single-center rater study included 50 patients, 25 with CMB and 25 patients without CMB (median age 77 y, IQR: 70 to 82 y; 30 of 50 female) who were imaged with FDG PET-3T MRI from April to July 2023. Standard GRE (90 s) and SWI (192 s) were compared with an EPI-accelerated GRE (aGRE; 13 s, 86% time reduction) and an EPI-accelerated SWI substitution (aSWI; 33 s, 83% time reduction). Three board-certified neuroradiologists independently reported CMB and SS (per ARIA-H monitoring guidelines), perceived image quality and motion for each sequence. There were 240 total assessments per rater (the 4 different sequences for the 50 patients plus 10 duplicated patients). Sensitivity, specificity, positive and negative predictive values, area under the curve (AUC), inter-rater and intrarater agreement were determined for each sequence and rater. RESULTS:The aggregate AUCs for the 4 individual sequences were excellent for detecting CMB (0.84 to 0.94) and SS (0.89 to 1.00) without statistical differences observed between standard and EPI-accelerated substitutions. Both aGRE and aSWI had high negative predictive values (96.5% to 100%). There were modest quantitative correlations between standard and accelerated sequences (0.606 and 0.391 for GRE and SWI, respectively), no differences in CMB count for aGRE (bias 0.01, P=0.895), but reduced CMB count with aSWI (bias -1.12, P=0.014). Inter-rater agreements were mildly reduced for both GRE versus aGRE (eg, 0.757 to 0.622 for CMB detection) and SWI versus aSWI (eg, 0.834 to 0.649 for SS detection). Perceived image quality for accelerated sequences was reduced, but with less motion observed with aSWI. CONCLUSIONS:The aGRE and aSWI sequences shorten scan times 86% and 83%, respectively, with similar diagnostic performance for ARIA-H screening, but reduced rater agreement and perceived image quality.

Fahr disease is a rare neurodegenerative syndrome characterized by abnormal symmetric calcium deposition in the white matter, cerebral cortex, deep gray, and cerebellar nuclei. The characteristic CT pattern is well known, but descriptions of molecular imaging in Fahr disease remain sparse. We present the characteristic imaging patterns of Fahr disease by CT, I-123-Ioflupane SPECT, and integrated FDG PET/MRI in a single patient.