Functional

The Mind’s Eye Redux

When asked about what he’d be thinking about during his weekend rounds at the 2019 Master’s Championship at the Augusta National Golf Club, current #3 golfer in the world and 3-time major champion Brooks Koepka, thought about an article published in 2003 in the American Journal of Neuroradiology1 before answering.  “Nothing,” he said.  “I have no thoughts. When you have nothing to think about, it’s easy.”  Unfortunately for Koepka, Tiger Woods gave him something to think about when he birdied #15 to take the lead. Koepka ended up finishing 1 stroke behind Woods in a 3-way tie for second place. While Koepka has very likely never heard of the American Journal of Neuroradiology, and had not really read the paper from 2003, his simple answer is a proof-of-concept of Dr. Ross’ paper that showed decreased fMRI activity in highly skilled compared to less skilled golfers.

—Keith B. Quencer, MD, Department of Radiology,
University of Utah School of Medicine
—Kevin S. Quencer, JD, Knoxville, Tennessee

  1. Ross JS, Tkach J, Ruggieri PM, et al. The mind’s eye: functional MR imaging evaluation of golf motor imagery. AJNR Am J Neuroradiol 2003;24:1036—44

Real-Time Motor Cortex Mapping for the Safe Resection of Glioma: An Intraoperative Resting-State fMRI Study

Editor’s Choice

The authors conducted preoperative and intraoperative resting-state intrinsic functional connectivity analyses of the motor cortex in 30 patients with brain tumors. Factors that may influence intraoperative imaging quality, including anesthesia type and tumor cavity, were studied. Additionally, direct cortical stimulation was used to validate the accuracy of intraoperative resting-state fMRI in mapping the motor cortex. Fourteen patients who successfully completed both sufficient intraoperative resting-state fMRI and direct cortical stimulation were used for further analysis of sensitivity and specificity. Compared with those subjected to direct cortical stimulation, the sensitivity and specificity of intraoperative resting-state fMRI in localizing the motor area were 61.7% and 93.7%, respectively. They conclude that using intraoperative resting-state fMRI can avoid the risk of intraoperative seizures due to direct cortical stimulation and may provide neurosurgeons with valuable information to facilitate the safe resection of gliomas.

Functional Connectivity in Virally Suppressed Patients with HIV-Associated Neurocognitive Disorder: A Resting-State Analysis

Fellows’ Journal Club

Eighteen patients with active HIV-associated neurocognitive disorder (recent diagnosis with progressing symptoms) on combination antiretroviral therapy with viral suppression in both blood and CSF and 9 demographically matched control subjects underwent resting-state functional MR imaging. The connectivity in the 6 known neural networks was assessed. There were significant group differences between the control and HIV-associated neurocognitive disorder groups in the salience and executive networks. The authors conclude that active HIV-associated neurocognitive disorder in virally suppressed patients is associated with significantly decreased connectivity in the salience and executive networks, thereby making it potentially useful as a biomarker.

Resting-State Seed-Based Analysis: An Alternative to Task-Based Language fMRI and Its Laterality Index

Editor’s Choice

Eighteen healthy right-handed volunteers were prospectively evaluated with resting-state fMRI and task-based fMRI to assess language networks. The laterality indices of Broca and Wernicke areas were calculated by using task-based fMRI via a voxel-value approach. The authors performed seed-based resting-state fMRI connectivity analysis together with parameters such as amplitude of low-frequency fluctuation and fractional amplitude of low-frequency fluctuation (fALFF). fALFF can be used as an alternative to task-based fMRI for assessing language laterality. There was a strong positive correlation between the fALFF of the Broca area of resting-state fMRI with the laterality index of task-based fMRI.

Microstructure of the Default Mode Network in Preterm Infants

Editor’s Choice

A cohort of 44 preterm infants underwent T1WI, resting-state fMRI, and DTI at 3T, including 21 infants with brain injuries and 23 infants with normal-appearing structural imaging as controls. Neurodevelopment was evaluated with the Bayley Scales of Infant Development at 12 months’ adjusted age. Results showed decreased fractional anisotropy and elevated radial diffusivity values of the cingula in the preterm infants with brain injuries compared with controls. The Bayley Scales of Infant Development cognitive scores were significantly associated with cingulate fractional anisotropy. The authors suggest that the microstructural properties of interconnecting axonal pathways within the default mode network are of critical importance in the early neurocognitive development of infants.

Improved Leakage Correction for Single-Echo Dynamic Susceptibility Contrast Perfusion MRI Estimates of Relative Cerebral Blood Volume in High-Grade Gliomas by Accounting for Bidirectional Contrast Agent Exchange

Editor’s Choice

The authors’ hypothesis is that incorporating bidirectional contrast agent transport into the DSC MR imaging signal model will improve rCBV estimates in brain tumors. A unidirectional contrast agent extravasation model (Boxerman-Weisskoff) was compared with a bidirectional contrast agent exchange model. For both models, they compared the goodness of fit with the parent leakage-contaminated relaxation rate curves and the difference between modeled interstitial relaxation rate curves and dynamic contrast-enhanced MR imaging in 21 patients with glioblastoma. The authors conclude that the bidirectional model more accurately corrects for the T1 or T2* enhancement arising from contrast agent extravasation due to blood-brain barrier disruption in high-grade gliomas by incorporating interstitial washout rates into the DSC MR imaging relaxation rate model.

Interrogating the Functional Correlates of Collateralization in Patients with Intracranial Stenosis Using Multimodal Hemodynamic Imaging

Editor’s Choice

The authors assessed correlations among baseline perfusion and arterial transit time artifacts, cerebrovascular reactivity, and the presence of collateral vessels on digital subtraction angiography. Arterial spin-labeling MRI and DSA were compared with BOLD MR imaging measures of hypercapnic cerebrovascular reactivity in 18 patients with symptomatic intracranial stenosis. In regions with normal-to-high signal on ASL, collateral vessel presence on DSA strongly correlated with declines in cerebrovascular reactivity (as measured on BOLD MRI). These data support the use of ASL MR imaging rather than invasive DSA to assess the presence of collateralization, even for patients with internal carotid stenosis from nonatherosclerotic etiologies. Also, collaterals identified on ASL with arterial transit artifacts correlated with decreased CVR compared with regions not perfused via collaterals.

Abstract

BACKGROUND AND PURPOSE

The importance of collateralization for maintaining adequate cerebral perfusion is increasingly recognized. However, measuring collateral flow noninvasively has proved elusive. The aim of this study was to assess correlations among baseline perfusion and arterial transit time artifacts, cerebrovascular reactivity, and the presence of collateral vessels on digital subtraction angiography.

MATERIALS AND METHODS

The relationship between the presence of collateral vessels on arterial spin-labeling MR imaging and DSA was compared with blood oxygen level–dependent MR imaging measures of hypercapnic cerebrovascular reactivity in patients with symptomatic intracranial stenosis (n = 18). DSA maps were reviewed by a neuroradiologist and assigned the following scores: 1, collaterals to the periphery of the ischemic site; 2, complete irrigation of the ischemic bed via collateral flow; and 3, normal antegrade flow. Arterial spin-labeling maps were scored according to the following: 0, low signal; 1, moderate signal with arterial transit artifacts; 2, high signal with arterial transit artifacts; and 3, normal signal.

RESULTS

In regions with normal-to-high signal on arterial spin-labeling, collateral vessel presence on DSA strongly correlated with declines

Presurgical Assessment of the Sensorimotor Cortex Using Resting-State fMRI

Editor’s Choice

Editor’s Comment

Task-based approaches to functional localization of the motor cortex have limitations such as long scanning times and exclusion of patients with severe functional or neurologic disabilities and children. Resting-state fMRI may avoid these difficulties because patients do not perform any goal-directed tasks. Nineteen patients were prospectively evaluated by using task-based and resting-state fMRI to localize sensorimotor function. Independent component analyses were performed to generate spatial independent components reflecting functional brain networks or noise. The motor cortex was successfully and consistently identified by using resting-state fMRI. Hand, foot, and face regions were defined in a comparable fashion with task-based fMRI.

Abstract

BACKGROUND AND PURPOSE

The functional characterization of the motor cortex is an important issue in the presurgical evaluation of brain lesions. fMRI noninvasively identifies motor areas while patients are asked to move different body parts. This task-based approach has some drawbacks in clinical settings: long scanning times and exclusion of patients with severe functional or neurologic disabilities and children. Resting-state fMRI can avoid these difficulties because patients do not perform any goal-directed tasks.

MATERIALS AND METHODS

Nineteen patients with diverse brain pathologies were prospectively evaluated by using task-based and resting-state fMRI to localize sensorimotor function. Independent component analyses were performed to generate spatial independent components reflecting functional brain networks or noise. Three radiologists identified the motor components and 3 portions of the motor cortex corresponding to the hand, foot, and face representations. Selected motor independent components were compared with task-based fMRI activation maps resulting from movements of the corresponding body parts.

RESULTS

The motor cortex was successfully and consistently identified by using resting-state fMRI by the 3 radiologists for all patients. When they subdivided the motor cortex into 3 segments, the sensitivities of resting-state and task-based fMRI were comparable. Moreover, we report a good spatial correspondence …

The Contribution of Common Surgically Implanted Hardware to Functional MR Imaging Artifacts

Editor’s Choice

Editor’s Comment

The authors calculated the BOLD-dependent MR imaging artifact impact arising from surgically implanted hardware through a retrospective analysis of fMRIs acquired from 2006–2014. Mean artifact volume associated with intracranial hardware was 4.3 cubic centimeters. The mean artifact volume from extracranial hardware in patients with cerebrovascular disease was 28.4 cubic centimeters. Artifacts had no-to-mild effects on clinical interpretability in all patients with intracranial implants. Extracranial hardware artifacts had no-to-moderate impact on clinical interpretability. The exceptions to interpretability in the face of hardware were ventriculoperitoneal shunts, particularly those with programmable valves and siphon gauges, and large numbers of KLS-Martin maxDrive screws.

Abstract

BACKGROUND AND PURPOSE

Blood oxygenation level–dependent MR imaging is increasingly used clinically to noninvasively assess cerebrovascular reactivity and/or language and motor function. However, many patients have metallic implants, which will induce susceptibility artifacts, rendering the functional information uninformative. Here, we calculate and interpret blood oxygenation level–dependent MR imaging artifact impact arising from surgically implanted hardware.

MATERIALS AND METHODS

A retrospective analysis of all blood oxygenation level–dependent MRIs (n = 343; B0 = 3T; TE = 35 ms; gradient echo EPI) acquired clinically (year range = 2006–2014) at our hospital was performed. Blood oxygenation level–dependent MRIs were most commonly prescribed for patients with cerebrovascular disease (n = 80) or patients undergoing language or motor localization (n = 263). Artifact volume (cubic centimeters) and its impact on clinical interpretation were determined by a board-certified neuroradiologist.

RESULTS

Mean artifact volume associated with intracranial hardware was 4.3 ± 3.2 cm3 (range = 1.1–9.4 cm3). The mean artifact volume from extracranial hardware in patients with cerebrovascular disease was 28.4 ± 14.0 cm3 (range = 6.1–61.7 cm3), and in patients with noncerebrovascular disease undergoing visual or motor functional mapping, it was 39.9 3± 27.0 cm3 (range = 6.9–77.1 cm3). The mean artifact …

Seizure Frequency Can Alter Brain Connectivity: Evidence from Resting-State fMRI

Editor’s Choice

Editor’s Comments

Resting-state fMRI data from 36 patients with hot-water epilepsy (18 with infrequent seizures) and 18 healthy age- and sex-matched controls were analyzed for seed-to-voxel connectivity. Patients in the frequent-seizure group had increased connectivity within the medial temporal structures and widespread areas of poor connectivity, including the default mode network. Seizure frequency can alter functional brain connectivity, which can be visualized by resting-state fMRI.

Abstract

BACKGROUND AND PURPOSE

The frequency of seizures is an important factor that can alter functional brain connectivity. Analysis of this factor in patients with epilepsy is complex because of disease- and medication-induced confounders. Because patients with hot-water epilepsy generally are not on long-term drug therapy, we used seed-based connectivity analysis in these patients to assess connectivity changes associated with seizure frequency without confounding from antiepileptic drugs.

MATERIALS AND METHODS

Resting-state fMRI data from 36 patients with hot-water epilepsy (18 with frequent seizures [>2 per month] and 18 with infrequent seizures [≤2 per month]) and 18 healthy age- and sex-matched controls were analyzed for seed-to-voxel connectivity by using 106 seeds. Voxel wise paired t-test analysis (P < .005, corrected for false-discovery rate) was used to identify significant intergroup differences between these groups.

RESULTS

Connectivity analysis revealed significant differences between the 2 groups (P < .001). Patients in the frequent-seizure group had increased connectivity within the medial temporal structures and widespread areas of poor connectivity, even involving the default mode network, in comparison with those in the infrequent-seizure group. Patients in the infrequent-seizure group had focal abnormalities with increased default mode network connectivity and decreased left entorhinal cortex connectivity.

CONCLUSIONS

The results of this study suggest that seizure frequency can alter functional brain connectivity, which can be visualized by using resting-state fMRI. Imaging features such as diffuse network abnormalities, involvement of