Quantitative Measurement of Blood Flow Volume in the Major Intracranial Arteries by Using 123I-Iodoamphetamine SPECT

Uncertainty quantification in cerebral circulation simulations focusing on the collateral flow: Surrogate model approach with machine learning

Collateral circulation in the circle of Willis (CoW), closely associated with disease mechanisms and treatment outcomes, can be effectively investigated using one-dimensional–zero-dimensional hemodynamic simulations. As the entire cardiovascular system is considered in the simulation, it captures the systemic effects of local arterial changes, thus reproducing collateral circulation that reflects biological phenomena. The simulation facilitates rapid assessment of clinically relevant hemodynamic quantities under patient-specific conditions by incorporating clinical data. During patient-specific simulations, the impact of clinical data uncertainty on the simulated quantities should be quantified to obtain reliable results. However, as uncertainty quantification (UQ) is time-consuming and computationally expensive, its implementation in time-sensitive clinical applications is considered impractical. Therefore, we constructed a surrogate model based on machine learning using simulation data. The model accurately predicts the flow rate and pressure in the CoW in a few milliseconds. This reduced computation time enables the UQ execution with 100 000 predictions in a few minutes on a single CPU core and in less than a minute on a GPU. We performed UQ to predict the risk of cerebral hyperperfusion (CH), a life-threatening condition that can occur after carotid artery stenosis surgery if collateral circulation fails to function appropriately. We predicted the statistics of the postoperative flow rate increase in the CoW, which is a measure of CH, considering the uncertainties of arterial diameters, stenosis parameters, and flow rates measured using the patients’ clinical data. A sensitivity analysis was performed to clarify the impact of each uncertain parameter on the flow rate increase. Results indicated that CH occurred when two conditions were satisfied simultaneously: severe stenosis and when arteries of small diameter serve as the collateral pathway to the cerebral artery on the stenosis side. These findings elucidate the biological aspects of cerebral circulation in terms of the relationship between collateral flow and CH.

Relationship between cerebral hyperperfusion syndrome and the immediate change of cerebral blood flow after carotid artery stenting evaluated by single-photon emission computed tomography

PURPOSE

Cerebral hyperperfusion syndrome (CHS) is a critical complication after carotid artery stenting (CAS). However, few CAS studies have evaluated immediate and temporary changes in ipsilateral cerebral blood flow (CBF) quantitatively. The study was performed to evaluate immediate changes in CBF after CAS and subsequent CBF changes in patients with cerebral hyperperfusion (HP) using ¹²³I-IMP SPECT.

METHODS

The subjects were 223 patients with chronic extracranial carotid artery stenosis who underwent CAS in our department between March 2010 and March 2020. Quantitative CBF and cerebrovascular reactivity to acetazolamide in the middle cerebral artery were assessed before CAS by ¹²³I-IMP SPECT. CBF was also measured immediately after CAS by ¹²³I-IMP SPECT. When HP was detected, CBF was measured again 3 and 7 days after CAS.

RESULTS

The median (interquartile range) ipsilateral quantitative CBF change after CAS was - 0.1% (- 9.5-8.2%), and the upper value of the 95% CI of the quantitative CBF change was 48.2%. Thus, we defined HP after CAS as an increase in quantitative CBF of > 48.2% compared with the preoperative value. Of 223 patients, 5 (2.2%) had HP, and 4 of these patients (80%) developed CHS. In the CHS patients, HP was maintained for about 3 days and improved after about 7 days.

CONCLUSION

An immediate CBF increase of > 48.2% after CAS may lead to development of CHS. In CHS after CAS, HP persisted for about 1 week and postoperative management may be required for at least 1 week.

A Combined Computational Fluid Dynamics and Arterial Spin Labeling MRI Modeling Strategy to Quantify Patient-Specific Cerebral Hemodynamics in Cerebrovascular Occlusive Disease

Cerebral hemodynamics in the presence of cerebrovascular occlusive disease (CVOD) are influenced by the anatomy of the intracranial arteries, the degree of stenosis, the patency of collateral pathways, and the condition of the cerebral microvasculature. Accurate characterization of cerebral hemodynamics is a challenging problem. In this work, we present a strategy to quantify cerebral hemodynamics using computational fluid dynamics (CFD) in combination with arterial spin labeling MRI (ASL). First, we calibrated patient-specific CFD outflow boundary conditions using ASL-derived flow splits in the Circle of Willis. Following, we validated the calibrated CFD model by evaluating the fractional blood supply from the main neck arteries to the vascular territories using Lagrangian particle tracking and comparing the results against vessel-selective ASL (VS-ASL). Finally, the feasibility and capability of our proposed method were demonstrated in two patients with CVOD and a healthy control subject. We showed that the calibrated CFD model accurately reproduced the fractional blood supply to the vascular territories, as obtained from VS-ASL. The two patients revealed significant differences in pressure drop over the stenosis, collateral flow, and resistance of the distal vasculature, despite similar degrees of clinical stenosis severity. Our results demonstrated the advantages of a patient-specific CFD analysis for assessing the hemodynamic impact of stenosis.

Cerebral hemodynamics associated with fluid-attenuated inversion recovery hyperintense vessels in patients with extracranial carotid artery stenosis

PURPOSE

Fluid-attenuated inversion recovery hyperintense vessels (FHVs) are linked to sluggish or disordered blood flow. The purpose of this study is to compare FHVs with digital subtraction angiography (DSA) findings and cerebral hemodynamic changes on acetazolamide challenge SPECT and to determine the clinical and imaging metrics associated with FHVs in patients with extracranial carotid artery stenosis (ECAS).

METHODS

The subjects were patients with chronic ECAS who underwent carotid artery stenting in our department between March 2011 and October 2018. Relationships of FHVs with age, sex, medical history, cerebral angiographic findings using DSA, and quantitative values of cerebral blood flow (CBF) were examined. The resting CBF (rCBF) and cerebrovascular reactivity (CVR) in the middle cerebral artery territory were measured quantitatively using SPECT with acetazolamide challenge. We used multivariate logistic regression analysis to identify independent predictors of FHVs.

RESULTS

Of 173 patients included, 92 (53.2%) had FHVs. Patients with FHVs had more severe stenosis (P < 0.01) and more leptomeningeal collateral vessels (P < 0.01). FHV-positive cases had significantly reduced CVR compared with FHV-negative cases (P < 0.01), although there was no significant difference in rCBF between FHV-positive and FHV-negative cases. Logistic regression analysis showed that ipsilateral rCBF and ipsilateral CVR were significant predictors for FHVs (P < 0.01).

CONCLUSION

In patients with ECAS, cerebral hemodynamic metrics, especially ipsilateral rCBF and ipsilateral CVR, are associated with the presence of FHVs.

Significance of N-isopropyl-[123I] p-iodoamphetamine single-photon emission computed tomography in detection of responsible hypoperfusion in hemichorea

Hemichorea is relatively an uncommon clinical presentation while its known etiology are vascular, metabolic, neoplastic, infectious, autoimmune, and inherited disorders. In the acquired case of hemichorea, the most common cause is the cerebrovascular insult, which is often diagnosed by the magnetic resonance (MR) imaging. An 84-year-old woman reported a one-week history of involuntary movements in the left side of her face and left limbs. Blood tests were normal and brain MR imaging showed no responsible hyperintense lesion on T1-, FLAIR, and diffusion-weighted imaging. N-isopropyl-[¹²³I] p-iodoamphetamine single-photon emission computed tomography (SPECT) detected hypoperfusion in the right thalamus. Further three-dimensional tomography clearly detected the hypoperfusion in the right subthalamic nucleus. The hypoperfused lesion was MR-negative and remained unchanged in SPECT one year after the onset. After the treatment with 0.35 mg of oral haloperidol was initiated, the hemichorea was gradually decreased and completely disappeared in 9 months. Because the three-dimensional analysis performs voxel-by-voxel analysis, it possibly detects the precise hypoperfusion in a specific region. In conclusion, evaluation of cerebral blood flow using SPECT on patients presenting with acute hemichorea can lead to the detection of responsible lesion when the routine examinations are negative.

Idiopathic basal ganglia calcification associated with cerebral micro-infarcts: a case report

Background

Idiopathic basal ganglia calcification (IBGC) is a rare neurodegenerative disorder characterized by symmetric intracranial calcium deposition. We report a patient with IBGC associated with cerebral infarction due to impairment of cerebrovascular reactivity based on single-photon emission computed tomography (SPECT) with acetazolamide challenge.

Case presentation

A 66-year-old male presented with right conjugate deviation, right hemiparesis and total aphasia due to a convulsive seizure. Brain computed tomography showed symmetric calcifications in the bilateral basal ganglia, thalamus, cerebellar dentate nuclei, which were consistent with IBGC. Diffusion-weighted brain magnetic resonance imaging showed multiple small infarctions in the bilateral cerebral subcortical area. In the search for the cause of cerebral infarction, SPECT with acetazolamide challenge revealed heterogeneous impairment of cerebrovascular reactivity in the whole brain, despite the absence of evidence for steno-occlusive changes in proximal arteries.

Conclusion

Cerebrovascular insufficiency due to the lack of elasticity caused by microvascular calcification might have been one of the pathophysiological features of IBGC in this case. Thus, vascular calcification may cause cerebrovascular disturbance and could lead to ischemic stroke in patients with IBGC.

Intra- and extracranial atherosclerotic disease: casting a new light on emerging trends

Intra- and extracranial atherosclerotic stenosis has been shown to be associated with an increased risk of secondary stroke mortality. Advances in invasive and non-invasive imaging modalities have improved analysis of hemodynamic changes and allowed better delineation of the integrity of intracranial collateralization and plague morphology in patients with artery stenosis. This review focuses on new imaging modalities and clinical applications of currently available techniques, and provides significant insight into future directions in comprehensive analysis of intra- and extracranial atherosclerotic stenosis.

Development of a Numerical Method for Patient-Specific Cerebral Circulation Using 1D-0D Simulation of the Entire Cardiovascular System with SPECT Data

The detailed flow information in the circle of Willis (CoW) can facilitate a better understanding of disease progression, and provide useful references for disease treatment. We have been developing a one-dimensional-zero-dimensional (1D-0D) simulation method for the entire cardiovascular system to obtain hemodynamics information in the CoW. This paper presents a new method for applying 1D-0D simulation to an individual patient using patient-specific data. The key issue is how to adjust the deviation of physiological parameters, such as peripheral resistance, from literature data when patient-specific geometry is used. In order to overcome this problem, we utilized flow information from single photon emission computed tomography (SPECT) data. A numerical method was developed to optimize physiological parameters by adjusting peripheral cerebral resistance to minimize the difference between the resulting flow rate and the SPECT data in the efferent arteries of the CoW. The method was applied to three cases using different sets of patient-specific data in order to investigate the hemodynamics of the CoW. The resulting flow rates in the afferent arteries were compared to those of the phase-contrast magnetic resonance angiography (PC-MRA) data. Utilization of the SPECT data combined with the PC-MRA data showed a good agreement in flow rates in the afferent arteries of the CoW with those of PC-MRA data for all three cases. The results also demonstrated that application of SPECT data alone could provide the information on the ratios of flow distributions among arteries in the CoW.