Effect of delayed transit time on arterial spin labeling: correlation with dynamic susceptibility contrast perfusion magnetic resonance in moyamoya disease

Multi-delay arterial spin labeling using a variable repetition time scheme in Moyamoya disease: Comparison with single-delay arterial spin labeling

PURPOSE

To present a multi-delay arterial spin labeling (ASL) protocol that obtains the cerebral blood flow (CBF) considering the arterial transit time (ATT), and to assess the correlations with an iodine-123-N-isopropyl-p-iodoamphetamine single-photon emission computed tomography (123I-IMP SPECT) reference standard between multi-delay ASL and single-delay ASL in patients with Moyamoya disease.

METHOD

We retrospectively analyzed the images of 23 patients with Moyamoya disease (4-73 years, 5 men, 18 women), each of whom was imaged with 10-delay ASL using the variable repetition time (TR) scheme, single-delay ASL, and SPECT. Pearson correlation coefficients were calculated between the CBF values of each ASL and SPECT in the three divisions of the ATT, which we categorized as fast, normal, and slow regions. The threshold for statistical significance was set atP<0.05.

RESULTS

The CBF measured by multi-delay ASL and single-delay ASL were positively correlated with that measured by SPECT, with correlation coefficients of 0.6701 and 0.5637, respectively (P < 0.001). In the fast, normal, and slow ATT divisions, the correlation coefficients between the CBF measured by multi-delay ASL and that measured by SPECT were 0.6745, 0.7055, and 0.6746, respectively. Similarly, the correlations between the CBF measured by single-delay ASL and that measured by SPECT were 0.3811, 0.5090 and 0.6178, respectively.

CONCLUSIONS

Multi-delay ASL using the variable TR scheme showed a higher correlation with 123I-IMP SPECT than single-delay ASL for measuring the CBF. The variable TR scheme potentially improved the quantification of CBF on ASL imaging.

Advances in moyamoya disease: pathogenesis, diagnosis, and therapeutic interventions

Moyamoya disease (MMD) is a type of cerebrovascular disease characterized by occlusion of the distal end of the internal carotid artery and the formation of collateral blood vessels. Over the past 20 years, the landscape of research on MMD has significantly transformed. In this review, we provide insights into the pathogenesis, diagnosis, and therapeutic interventions in MMD. The development of high-throughput sequencing technology has expanded our understanding of genetic susceptibility, identifying MMD-related genes beyond RNF213, such as ACTA2, DIAPH1, HLA, and others. The genetic susceptibility of MMD to its pathological mechanism was summarized and discussed. Based on the second-hit theory, the influences of inflammation, immunity, and environmental factors on MMD were also appropriately summarized. Despite these advancements, revascularization surgery remains the primary treatment for MMD largely because of the lack of effective in vivo and in vitro models. In this study, 16 imaging diagnostic methods for MMD were summarized. Regarding therapeutic intervention, the influences of drugs, endovascular procedures, and revascularization surgeries on patients with MMD were discussed. Future research on the central MMD vascular abnormalities and peripheral circulating factors will provide a more comprehensive understanding of the pathogenic mechanisms of MMD.

An Investigation of Cerebral Vascular Functional Properties in Middle-to-Old Age Community People With High Vascular Risk Profiles

BACKGROUND

Vascular degeneration is an important cause of brain damage in aging. Assessing the functional properties of the cerebral vascular system may aid early diagnosis and prevention.

PURPOSE

To investigate the relationships between potential vascular functional markers and vascular risks, brain parenchymal damage, and cognition.

STUDY TYPE

Retrospective.

SUBJECTS

Two hundred two general community subjects (42-80 years, males/females: 127/75).

FIELD STRENGTH/SEQUENCE

3 T, spin echo T1W/T2W/FLAIR, resting-state functional MRI with an echo-planar sequence (rsfMRI), pseudo-continuous arterial spin labeling (pCASL) with a three-dimensional gradient-spin echo sequence.

ASSESSMENT

Cerebral blood flow (CBF) in gray matter calculated using pCASL, blood transit times calculated using rsfMRI, and the SD of internal carotid arteries signal (ICAstd) calculated using rsfMRI; visual assessment for lacunes; quantification of white matter hyperintensity volume; permutation test for quality control; collection of demographic and clinical data, Montreal Cognitive Assessment, Mini-Mental State Examination.

STATISTICAL TESTS

Kolmogorov-Smirnov test; Spearman rank correlation analysis; Multivariable linear regression analysis controlling for covariates; The level of statistical significance was set at P < 0.05.

RESULTS

Age was negatively associated with ICAstd (β = -0.180). Diabetes was associated with longer blood transit time from large arteries to capillary bed (β = 0.185, adjusted for age, sex, and intracranial volume). Larger ICAstd was associated with less presence of lacunes (odds ratio: 0.418, adjusted for age and sex). Higher gray matter CBF (β = 0.154) and larger ICAstd (β = 0.136) were associated with better MoCA scores (adjusted for age, sex, and education).

DATA CONCLUSION

Prolonged blood transit time, decreased ICAstd, and diminished CBF were associated with vascular dysfunction and cognitive impairment. They may serve as vascular functional markers in future studies.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 3.

Cerebral perfusion in patients with unilateral internal carotid artery occlusion by dual post-labeling delays arterial spin labeling imaging

BACKGROUND

Global and regional cerebral blood flow (CBF) changes in patients with unilateral internal carotid artery occlusion (ICAO) are unclear when the dual post-labeling delays (PLD) arterial spin labeling (ASL) magnetic resonance imaging (MRI) technique is used. Manual delineation of regions of interest for CBF measurement is time-consuming and laborious.

AIM

To assess global and regional CBF changes in patients with unilateral ICAO with the ASL-MRI perfusion technique.

METHODS

Twenty hospitalized patients with ICAO and sex- and age-matched controls were included in the study. Regional CBF was measured by Dr. Brain's ASL software. The present study evaluated differences in global, middle cerebral artery (MCA) territory, anterior cerebral artery territory, and Alberta Stroke Program Early Computed Tomography Score (ASPECTS) regions (including the caudate nucleus, lentiform nucleus, insula ribbon, internal capsule, and M1-M6) and brain lobes (including frontal, parietal, temporal, and insular lobes) between ICAO patients and controls at PLD 1.5 s and PLD 2.5 s.

RESULTS

When comparing CBF between ICAO patients and controls, the global CBF in ICAO patients was lower at both PLD 1.5 s and PLD 2.5 s; the CBF on the occluded side was lower in 15 brain regions at PLD 1.5 s, and it was lower in 9 brain regions at PLD 2.5 s; the CBF in the contralateral hemisphere was lower in the caudate nucleus and internal capsule at PLD 1.5 s and in M6 at PLD 2.5 s. The global CBF in ICAO patients was lower at PLD 1.5 s than at PLD 2.5 s. The ipsilateral CBF at PLD 1.5 s was lower than that at PLD 2.5 s in 15 regions, whereas the contralateral CBF was lower at PLD 1.5 s than at PLD 2.5 s in 12 regions. The ipsilateral CBF was lower than the contralateral CBF in 15 regions at PLD 1.5 s, and in M6 at PLD 2.5 s.

CONCLUSION

Unilateral ICAO results in hypoperfusion in the global and MCA territories, especially in the ASPECTS area. Dual PLD settings prove more suitable for accurate CBF quantification in ICAO.

Assessment of cerebral perfusion in moyamoya disease with dynamic pseudo-continuous arterial spin labeling using a variable repetition time scheme with optimized background suppression

PURPOSE

Accurate assessment of cerebral perfusion in moyamoya disease is necessary to determine the indication for treatment. We aimed to investigate the usefulness of dynamic PCASL using a variable TR scheme with optimized background suppression in the evaluation of cerebral perfusion in moyamoya disease.

METHODS

We retrospectively analyzed the images of 24 patients (6 men and 18 women, mean age 31.4 ± 18.2 years) with moyamoya disease; each of whom was imaged with both dynamic PCASL using the variable-TR scheme and ¹²³IMP SPECT with acetazolamide challenge. ASL dynamic data at 10 phases are acquired by changing the LD and PLD. The background suppression timing was optimized for each phase. CBF and ATT were measured with ASL, and CBF and CVR to an acetazolamide challenge were measured with SPECT.

RESULTS

A significant moderate correlation was found between the CBF measured by dynamic PCASL and that by SPECT (r = 0.53, P < 0.001). The CBF measured by dynamic PCASL (52.5 ± 13.3 ml/100 mg/min) was significantly higher than that measured by SPECT (43.0 ± 12.6 ml/100 mg/min, P < 0.001). The ATT measured by dynamic PCASL showed a significant correlation with the CVR measured by SPECT (r = 0.44, P < 0.001). ATT was significantly longer in areas where the CVR was impaired (CVR < 18.4%, ATT = 1812 ± 353 ms) than in areas where it was preserved (CVR > 18.4%, ATT = 1301 ± 437 ms, P < 0.001). The ROC analysis showed a moderate accuracy (AUC = 0.807, sensitivity = 87.7%, specificity = 70.4%) when the cutoff value of ATT was set at 1518 ms.

CONCLUSION

Dynamic PCASL using this scheme was found to be useful for assessing cerebral perfusion in moyamoya disease.

Evidence of cerebral hypoperfusion consecutive to ultrasound-mediated blood-brain barrier opening in rats

PURPOSE

This work aims to explore the effect of Blood Brain Barrier (BBB) opening using ultrasound combined with microbubbles injection on cerebral blood flow in rats.

METHODS

Two groups of n = 5 rats were included in this study. The first group was used to investigate the impact of BBB opening on the Arterial Spin Labeling (ASL) signal, in particular on the arterial transit time (ATT). The second group was used to analyze the spatiotemporal evolution of the change in cerebral blood flow (CBF) over time following BBB opening and validate these results using DSC-MRI.

RESULTS

Using pCASL, a decrease in CBF of up to 29 . 6 ± 15 . 1 % $$ 29.6\pm 15.1\% $$ was observed in the target hemisphere, associated with an increase in arterial transit time. The latter was estimated to be 533 ± 121ms $$ 533\pm 12\mathrm{1ms} $$ in the BBB opening impacted regions against 409 ± 93ms $$ 409\pm 93\mathrm{ms} $$ in the contralateral hemisphere. The spatio-temporal analysis of CBF maps indicated a nonlocal hypoperfusion. DSC-MRI measurements were consistent with the obtained results.

CONCLUSION

This study provided strong evidence that BBB opening using microbubble intravenous injection induces a transient hypoperfusion. A spatiotemporal analysis of the hypoperfusion changes allows to establish some points of similarity with the cortical spreading depression phenomenon.

Imaging methods for surgical revascularization in patients with moyamoya disease: an updated review

Neuroimaging is crucial in moyamoya disease (MMD) for neurosurgeons, during pre-surgical planning and intraoperative navigation not only to maximize the success rate of surgery, but also to minimize postsurgical neurological deficits in patients. This is a review of recent literatures which updates the clinical use of imaging methods in the morphological and hemodynamic assessment of surgical revascularization in patients with MMD. We aimed to assist surgeons in assessing the status of moyamoya vessels, selecting bypass arteries, and monitoring postoperative cerebral perfusion through the latest imaging technology.

Diagnostic Accuracy of Screening Arterial Spin-Labeling MRI Using Hadamard Encoding for the Detection of Reduced CBF in Adult Patients with Ischemic Moyamoya Disease

BACKGROUND AND PURPOSE

Adult patients with ischemic Moyamoya disease are advised to undergo selective revascularization surgery based on cerebral hemodynamics. The purpose of this study was to determine the diagnostic accuracy of arterial spin-labeling MR imaging using Hadamard-encoded multiple postlabeling delays for the detection of reduced CBF in such patients.

MATERIALS AND METHODS

Thirty-seven patients underwent brain perfusion SPECT and pseudocontinuous arterial spin-labeling MR imaging using standard postlabeling delay (1525 ms) and Hadamard-encoded multiple postlabeling delays. For Hadamard-encoded multiple postlabeling delays, based on data obtained from the 7 sub-boluses with combinations of different labeling durations and postlabeling delays, CBF corrected by the arterial transit time was calculated on a voxel-by-voxel basis. Using a 3D stereotaxic template, we automatically placed ROIs in the ipsilateral cerebellar hemisphere and 5 MCA territories in the symptomatic cerebral hemisphere; then, the ratio of the MCA to cerebellar ROI was calculated.

RESULTS

The area under the receiver operating characteristic curve for detecting reduced SPECT-CBF ratios (<0.686) was significantly greater for the Hadamard-encoded multiple postlabeling delays-CBF ratios (0.885) than for the standard postlabeling delay-CBF ratios (0.786) (P = .001). The sensitivity and negative predictive value for the Hadamard-encoded multiple postlabeling delays-CBF ratios were 100% (95% confidence interval, 100%-100%) and significantly higher than the sensitivity (95% CI, 44%-80%) and negative predictive value (95% CI, 88%-97%) for the standard postlabeling delay-CBF ratio, respectively.

CONCLUSIONS

ASL MR imaging using Hadamard-encoded multiple postlabeling delays may be applicable as a screening tool because it can detect reduced CBF on brain perfusion SPECT with 100% sensitivity and a 100% negative predictive value in adult patients with ischemic Moyamoya disease.

Time to peak and full width at half maximum in MR perfusion: valuable indicators for monitoring moyamoya patients after revascularization

Moyamoya disease (MMD) is a chronic, steno-occlusive cerebrovascular disorder of unknown etiology. Surgical treatment is the only known effective method to restore blood flow to affected areas of the brain. However, there are lack of generally accepted noninvasive tools for therapeutic outcome monitoring. As dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI) is the standard MR perfusion imaging technique in the clinical setting, we investigated a dataset of nineteen pediatric MMD patients with one preoperational and multiple periodic DSC MRI examinations for four to thirty-eight months after indirect revascularization. A rigid gamma variate model was used to derive two nondeconvolution-based perfusion parameters: time to peak (TTP) and full width at half maximum (FWHM) for monitoring transitional bolus delay and dispersion changes respectively. TTP and FWHM values were normalized to the cerebellum. Here, we report that 74% (14/19) of patients improve in both TTP and FWHM measurements, and whereof 57% (8/14) improve more noticeably on FWHM. TTP is in good agreement with Tmax in estimating bolus delay. Our study data also suggest bolus dispersion estimated by FWHM is an additional, informative indicator in pediatric MMD monitoring.

Clinical utility of arterial spin labeling imaging in disorders of the nervous system

Neuroimaging is an indispensable tool in the workup and management of patients with neurological disorders. Arterial spin labeling (ASL) is an imaging modality that permits the examination of blood flow and perfusion without the need for contrast injection. Noninvasive in nature, ASL provides a feasible alternative to existing vascular imaging techniques, including angiography and perfusion imaging. While promising, ASL has yet to be fully incorporated into the diagnosis and management of neurological disorders. This article presents a review of the most recent literature on ASL, with a special focus on its use in moyamoya disease, brain neoplasms, seizures, and migraines and a commentary on recent advances in ASL that make the imaging technique more attractive as a clinically useful tool.

Intravoxel incoherent motion diffusion-weighted imaging for discrimination of benign and malignant retropharyngeal nodes

PURPOSE

Anatomical imaging criteria for the diagnosis of malignant head and neck nodes may not always be reliable. This study aimed to evaluate the diagnostic value of conventional diffusion-weighted imaging (DWI) and intravoxel incoherent motion (IVIM) DWI in discriminating benign and malignant metastatic retropharyngeal nodes (RPNs).

METHODS

IVIM DWI using 14 b-values was performed on RPNs of 30 patients with newly diagnosed metastatic nasopharyngeal carcinoma (NPC) and 30 patients with elevated plasma Epstein-Barr virus (EBV)-DNA without NPC who were part of an EBV-based NPC screening program. Histogram measurements of the two groups were compared for pure diffusion coefficient (D), pseudo-diffusion coefficient (D*), perfusion volume fraction (f) and apparent diffusion coefficient (ADC) using the Mann-Whitney U test. Area under the curves (AUCs) of significant measurements were calculated from receiver-operating characteristics analysis and compared using the DeLong test.

RESULTS

Compared with metastatic RPNs, benign RPNs had lower ADC_mean (0.73 vs 0.82 × 10^-3 mm²/s) and D_mean (0.60 vs 0.71 × 10^-3 mm²/s) and a higher D*_mean (35.21 vs 28.66 × 10^-3 mm²/s) (all p < 0.05). There was no difference in the f measurements between the two groups (p = 0.204 to 0.301). D_mean achieved the highest AUC of 0.800, but this was not statistically better than the AUCs of the other parameters (p = 0.148 to 0.991).

CONCLUSION

Benign RPNs in patients with EBV-DNA showed greater restriction of diffusion compared with malignant metastatic RPNs from NPC. IVIM did not show a significant advantage over conventional DWI in discriminating benign and malignant nodes.

Monitoring Cerebral Perfusion Changes after Revascularization in Patients with Moyamoya Disease by Using Arterial Spin-labeling MR Imaging

Purpose To determine whether arterial spin-labeling (ASL) magnetic resonance (MR) imaging could be used to identify changes in cerebral blood flow (CBF), collateral blood flow, and anastomosis site patency after revascularization in patients with moyamoya disease. Materials and Methods This retrospective study was conducted in 145 patients with moyamoya disease who underwent middle cerebral artery (MCA)-superficial temporal artery anastomosis. Preoperative, early postoperative, and late postoperative ASL and digital subtraction angiography images were analyzed. In the MCA territory, absolute CBF (hereafter, CBF_MCA) and normalized CBF values adjusted to nonanastomosis side (hereafter, nCBF_MCA) and to cerebellum (hereafter, nCBF_Cbll) were calculated. Collateral grading in the MCA territory was assessed according to Alberta Stroke Program Early CT Score methodology, and anastomosis site patency were also assessed. Changes in CBF were compared by using one-way analysis of variance with Bonferroni correction for multiple comparisons. Intermodality agreement was determined by κ statistics. Results Significant increases in CBF_MCA, nCBF_MCA, and nCBF_Cbll were found after revascularization (preoperative and postoperative values of CBF_MCA, 35.2 mL/100 g per minute ± 7.8 [mean ± standard deviation] and 51.5 mL/100 g per minute ± 12.0; nCBF_MCA, 0.73 mL/100 g per minute ± 0.14 and 1.01 mL/100 g per minute ± 0.18; nCBF_Cbll, 0.74 mL/100 g per minute ± 0.12 and 1.12 mL/100 g per minute ± 0.16; all P < .001). Agreements for collateral grading and anastomosis patency between ASL MR imaging and digital subtraction angiography were moderate to good, with weighted κ values of 0.77 (95% confidence interval: 0.73, 0.81) and 0.57 (95% confidence interval: 0.37, 0.76), respectively. Conclusion ASL MR imaging can be used to identify perfusion changes in patients with moyamoya disease after revascularization as a noninvasive monitoring tool.

Transit time corrected arterial spin labeling technique aids to overcome delayed transit time effect

PURPOSE

This study aimed to evaluate the usefulness of transit time corrected cerebral blood flow (CBF) maps based on multi-phase arterial spin labeling MR perfusion imaging (ASL-MRP).

METHODS

The Institutional Review Board of our hospital approved this retrospective study. Written informed consent was waived. Conventional and multi-phase ASL-MRPs and dynamic susceptibility contrast MR perfusion imaging (DSC-MRP) were acquired for 108 consecutive patients. Vascular territory-based volumes of interest were applied to CBF and time to peak (TTP) maps obtained from DSC-MRP and CBF maps obtained from conventional and multi-phase ASL-MRPs. The concordances between normalized CBF (nCBF) from DSC-MRP and nCBF from conventional and transition time corrected CBF maps from multi-phase ASL-MRP were evaluated using Bland-Altman analysis. In addition, the dependence of difference between nCBF (ΔnCBF) values obtained from DSC-MRP and conventional ASL-MRP (or multi-phase ASL-MRP) on TTP obtained from DSC-MRP was also analyzed using regression analysis.

RESULTS

The values of nCBFs from conventional and multi-phase ASL-MRPs had lower values than nCBF based on DSC-MRP (mean differences, 0.08 and 0.07, respectively). The values of ΔnCBF were dependent on TTP values from conventional ASL-MRP technique (F = 5.5679, P = 0.0384). No dependency of ΔnCBF on TTP values from multi-phase ASL-MRP technique was revealed (F = 0.1433, P > 0.05).

CONCLUSION

The use of transit time corrected CBF maps based on multi-phase ASL-MRP technique can overcome the effect of delayed transit time on perfusion maps based on conventional ASL-MRP.

Can Arterial Spin-Labeling with Multiple Postlabeling Delays Predict Cerebrovascular Reserve?

BACKGROUND AND PURPOSE

The effect of delayed transit time is the main source of error in the quantitative measurement of CBF in arterial spin-labeling. In the present study, we evaluated the usefulness of the transit time-corrected CBF and arterial transit time delay from multiple postlabeling delays arterial spin-labeling compared with basal/acetazolamide stress technetium Tc99m-hexamethylpropylene amineoxime (Tc99m-HMPAO) SPECT in predicting impairment in the cerebrovascular reserve.

MATERIALS AND METHODS

Transit time-corrected CBF maps and arterial transit time maps were acquired in 30 consecutive patients with unilateral ICA or MCA steno-occlusive disease (severe stenosis or occlusion). Internal carotid artery territory-based ROIs were applied to both perfusion maps. Additionally, impairment in the cerebrovascular reserve was evaluated according to both qualitative and quantitative analyses of the ROIs on basal/acetazolamide stress Tc99m-HMPAO SPECT using a previously described method. The area under the receiver operating characteristic curve was used to evaluate the diagnostic accuracy of arterial spin-labeling in depicting impairment of the cerebrovascular reserve. The correlation between arterial spin-labeling and cerebrovascular reserve was evaluated.

RESULTS

The affected hemisphere had a decreased transit time-corrected CBF and increased arterial transit time compared with the corresponding values of the contralateral normal hemisphere, which were statistically significant (P < .001). The percentage change of transit time-corrected CBF and the percentage change of arterial transit time were independently differentiating variables (P < .001) for predicting cerebrovascular reserve impairment. The correlation coefficient between the arterial transit time and cerebrovascular reserve index ratio was -0.511.

CONCLUSIONS

Our results demonstrate that the transit time-corrected CBF and arterial transit time based on arterial spin-labeling perfusion MR imaging can predict cerebrovascular reserve impairment.

Perfusion magnetic resonance imaging in pediatric brain tumors

PURPOSE

The use of DSC-MR imaging in pediatric neuroradiology is gradually growing. However, the number of studies listed in the literature remains limited. We propose to assess the perfusion and permeability parameters in pediatric brain tumor grading.

METHODS

Thirty children with a brain tumor having benefited from a DSC-MR perfusion sequence have been retrospectively explored. Relative CBF and CBV were computed on the ROI with the largest lesion coverage. Assessment of the lesion's permeability was also performed through the semi-quantitative PSR parameter and the K2 model-based parameter on the whole-lesion ROI and a reduced ROI drawn on the permeability maps. A statistical comparison of high- and low-grade groups (HG, LG) as well as a ROC analysis was performed on the histogram-based parameters.

RESULTS

Our results showed a statistically significant difference between LG and HG groups for mean rCBV (p < 10^-3), rCBF (p < 10^-3), and for PSR (p = 0.03) but not for the K2 factor (p = 0.5). However, the ratio K2/PSR was shown to be a strong discriminating factor between the two groups of lesions (p < 10^-3). For rCBV and rCBF indicators, high values of ROC AUC were obtained (> 0.9) and mean value thresholds were observed at 1.07 and 1.03, respectively. For K2/PSR in the reduced area, AUC was also superior to 0.9.

CONCLUSIONS

The implementation of a dynamic T2* perfusion sequence provided reliable results using an objective whole-lesion ROI. Perfusion parameters as well as a new permeability indicator could efficiently discriminate high-grade from low-grade lesions in the pediatric population.

Concomitant carotid aplasia and basilar artery occlusion in a child with PHACES syndrome

We report a case of an 8-year-old girl with posterior fossa abnormalities, haemangioma, arterial lesions, cardiac abnormalities or coarctation of the aorta and eye abnormalities syndrome with right carotid aplasia and complete basilar occlusion. The patient initially presented at 2.5 weeks of age with a growing right facial haemangioma involving segments 1, 3 and 4. Initial MRI at 2.5 weeks of age revealed an extraconal right orbital haemangioma without posterior fossa abnormalities and MR angiography (MRA) 3 weeks later showed right internal carotid aplasia. A follow-up MRA and cerebral angiography at 8 years of age revealed a complete occlusion of the basilar artery that was not appreciated on previous imaging. Neurological function remains normal, meeting all age-appropriate milestones.

Mapping altered brain connectivity and its clinical associations in adult moyamoya disease: A resting-state functional MRI study

Detection of subtle ischemic injuries in moyamoya disease may enable optimization of timing of revascularization surgery, and could potentially improve functional outcomes. Resting-state functional magnetic resonance imaging (rs-fMRI) is widely used to study functional organization of the brain, but it remains unclear whether rs-fMRI could elucidate distinct characteristics in moyamoya disease. Here, we aimed to determine changes in a conventional rs-fMRI measure and analyze any associations with clinical symptoms and cerebral hemodynamics. Thirty-one adults with moyamoya disease and 25 adult controls underwent rs-fMRI, in which we measured brain connectivity via temporal correlations of low-frequency BOLD signals. We identified the extent of between-group differences with multivoxel pattern analysis. Seed-based analysis was performed to determine associations with vascular lesions, symptoms, and regional cerebral blood flow (rCBF). There was significantly altered connectivity in the precentral gyrus, operculo-insular region, precuneus, cingulate cortex, and middle frontal gyrus in moyamoya disease. There was reduced connectivity in the left insula, left precuneus, right precentral, and right middle frontal regions, which form part of the salience, default mode, motor, and central executive networks, respectively. Patients with ischemic motor-related symptoms showed significantly decreased connectivity in precentral homotopic regions compared with those without, while there were no differences in vascular lesions or rCBF. Connectivity between the right occipital and left hippocampus was significantly associated with cognitive performance and posterior cerebral artery involvement. Our results demonstrate distinct alterations in the temporal correlations of low-frequency BOLD signals, predominantly in resting-state networks in moyamoya disease. Additionally, rs-fMRI measures were associated with ischemic motor-related symptoms and cognitive performance in the patients. Thus, rs-fMRI may offer a useful non-invasive method of acquiring additional information beyond cerebral perfusion as part of clinical investigations in patients with moyamoya disease.

Long-Delay Arterial Spin Labeling Provides More Accurate Cerebral Blood Flow Measurements in Moyamoya Patients: A Simultaneous Positron Emission Tomography/MRI Study

BACKGROUND AND PURPOSE

Arterial spin labeling (ASL) MRI is a promising, noninvasive technique to image cerebral blood flow (CBF) but is difficult to use in cerebrovascular patients with abnormal, long arterial transit times through collateral pathways. To be clinically adopted, ASL must first be optimized and validated against a reference standard in these challenging patient cases.

METHODS

We compared standard-delay ASL (post-label delay=2.025 seconds), multidelay ASL (post-label delay=0.7-3.0 seconds), and long-label long-delay ASL acquisitions (post-label delay=4.0 seconds) against simultaneous [¹⁵O]-positron emission tomography (PET) CBF maps in 15 Moyamoya patients on a hybrid PET/MRI scanner. Dynamic susceptibility contrast was performed in each patient to identify areas of mild, moderate, and severe time-to-maximum (Tmax) delays. Relative CBF measurements by each ASL scan in 20 cortical regions were compared with the PET reference standard, and correlations were calculated for areas with moderate and severe Tmax delays.

RESULTS

Standard-delay ASL underestimated relative CBF by 20% in areas of severe Tmax delays, particularly in anterior and middle territories commonly affected by Moyamoya disease (P<0.001). Arterial transit times correction by multidelay acquisitions led to improved consistency with PET, but still underestimated CBF in the presence of long transit delays (P=0.02). Long-label long-delay ASL scans showed the strongest correlation relative to PET, and there was no difference in mean relative CBF between the modalities, even in areas of severe delays.

CONCLUSIONS

Post-label delay times of ≥4 seconds are needed and may be combined with multidelay strategies for robust ASL assessment of CBF in Moyamoya disease.

Implication of cerebral circulation time in intracranial stenosis measured by digital subtraction angiography on cerebral blood flow estimation measured by arterial spin labeling

PURPOSE

Arterial spin labeling (ASL) magnetic resonance imaging to assess cerebral blood flow (CBF) is of increasing interest in basic research and in diagnostic applications, since ASL provides similar information to positron emission tomography about perfusion in vascular territories. However, in patients with steno-occlusive arterial disease (SOAD), CBF as measured by ASL might be underestimated due to delayed bolus arrival, and thus increased spin relaxation. We aimed to estimate the extent to which bolus arrival time (BAT) was delayed in patients with SOAD and whether this resulted in underestimation of CBF.

METHODS

BAT was measured using digital subtraction angiography (DSA) in ten patients with high-grade stenosis of the middle carotid artery (MCA). Regional CBF was assessed with pseudocontinuous ASL.

RESULTS

BATs were nonsignificantly prolonged in the stenotic hemisphere 4.1±2.0 s compared with the healthy hemisphere 3.3±0.9 s; however, there were substantial individual differences on the stenotic side. CBF in the anterior and posterior MCA territories were significantly reduced on the stenotic hemisphere. Severe stenosis was correlated with longer BAT and lower quantified CBF.

CONCLUSION

ASL-based perfusion measurement involves a race between the decay of the spins and the delivery of labeled blood to the region of interest. Special caution is needed when interpreting CBF values quantified in individuals with altered blood flow and delayed circulation times. However, from a clinician's point of view, an accentuation of hypoperfusion (even if caused by underestimation of CBF due to prolonged BATs) might be desirable since it indexes potentially harmful physiologic deficits.

Noninvasive Evaluation of CBF and Perfusion Delay of Moyamoya Disease Using Arterial Spin-Labeling MRI with Multiple Postlabeling Delays: Comparison with 15O-Gas PET and DSC-MRI

BACKGROUND AND PURPOSE

Arterial spin-labeling MR imaging with multiple postlabeling delays has a potential to evaluate various hemodynamic parameters. To clarify whether arterial spin-labeling MR imaging can identify CBF and perfusion delay in patients with Moyamoya disease, we compared arterial spin-labeling, DSC, and ¹⁵O-gas PET in terms of their ability to identify these parameters.

MATERIALS AND METHODS

Eighteen patients with Moyamoya disease (5 men, 13 women; ages, 21-55 years) were retrospectively analyzed. CBF values of pulsed continuous arterial spin-labeling using 2 postlabeling delays (short arterial spin-labeling, 1525 ms; delayed arterial spin-labeling, 2525 ms) were compared with CBF values measured by ¹⁵O-gas PET. All plots were divided into 2 groups by the cutoff of time-based parameters (the time of the maximum observed concentration, TTP, MTT, delay of MTT to cerebellum, and disease severity [symptomatic or not]). The ratio of 2 arterial spin-labeling CBFs (delayed arterial spin-labeling CBF to short arterial spin-labeling CBF) was compared with time-based parameters: time of the maximum observed concentration, TTP, and MTT.

RESULTS

The short arterial spin-labeling-CBF values were significantly correlated with the PET-CBF values (r = 0.63; P = .01). However, the short arterial spin-labeling-CBF value dropped in the regions with severe perfusion delay. The delayed arterial spin-labeling CBF overestimated PET-CBF regardless of the degree of perfusion delay. Delayed arterial spin-labeling CBF/short arterial spin-labeling CBF was well correlated with the time of the maximum observed concentration, TTP, and MTT (ρ = 0.71, 0.64, and 0.47, respectively).

CONCLUSIONS

Arterial spin-labeling using 2 postlabeling delays may detect PET-measured true CBF and perfusion delay in patients with Moyamoya disease. Provided its theoretic basis and limitations are considered, noninvasive arterial spin-labeling could be a useful alternative for evaluating the hemodynamics of Moyamoya disease.

Arterial Spin Labeling Techniques 2009-2014

PURPOSE

Arterial spin labeling (ASL) techniques have been implemented across a diverse range of clinical and experimental applications. This review aims to evaluate the current feasibility of ASL in clinical neuroradiology based on recent improvements to ASL sequences and highlight areas for potential clinical applications.

METHODS AND MATERIALS

In December 2014, a literature search was conducted on PubMed Central, EMBASE, and Scopus using the search terms: "arterial spin labeling, neuroradiology," for studies published between 2009 and 2014 (inclusive). Of 483 studies matching the inclusion criteria, the number of studies using continuous, pseudocontinuous, pulsed, and velocity-selective ASL sequences was 42, 209, 226, and 3, respectively. Studies were classified based on several common clinical applications according to the type of ASL sequence used. Studies using pulsed ASL and pseudo-continuous ASL were grouped based on common sequences.

RESULTS

The number of clinical studies was 264. Numerous studies applied ASL to stroke management (43 studies), drug testing (21 studies), neurodegenerative diseases (40 studies), and psychiatric disorders (26 studies).

CONCLUSIONS

This review discusses several factors hindering the implementation of clinical ASL and ASL-related radiofrequency safety issues encountered in clinical practice. However, a limited number of search terms were used. Further development of robust sequences with multislice imaging capabilities and reduced radiofrequency energy deposition will hopefully improve the clinical acceptance of ASL.

3D GRASE pulsed arterial spin labeling at multiple inflow times in patients with long arterial transit times: comparison with dynamic susceptibility-weighted contrast-enhanced MRI at 3 Tesla

Pulsed arterial spin labeling (PASL) at multiple inflow times (multi-TIs) is advantageous for the measurement of brain perfusion in patients with long arterial transit times (ATTs) as in steno-occlusive disease, because bolus-arrival-time can be measured and blood flow measurements can be corrected accordingly. Owing to its increased signal-to-noise ratio, a combination with a three-dimensional gradient and spin echo (GRASE) readout allows acquiring a sufficient number of multi-TIs within a clinically feasible acquisition time of 5 minutes. We compared this technique with the clinical standard dynamic susceptibility-weighted contrast-enhanced imaging-magnetic resonance imaging in patients with unilateral stenosis >70% of the internal carotid or middle cerebral artery (MCA) at 3 Tesla. We performed qualitative (assessment by three expert raters) and quantitative (region of interest (ROI)/volume of interest (VOI) based) comparisons. In 43 patients, multi-TI PASL-GRASE showed perfusion alterations with moderate accuracy in the qualitative analysis. Quantitatively, moderate correlation coefficients were found for the MCA territory (ROI based: r=0.52, VOI based: r=0.48). In the anterior cerebral artery (ACA) territory, a readout related right-sided susceptibility artifact impaired correlation (ROI based: r=0.29, VOI based: r=0.34). Arterial transit delay artifacts were found only in 12% of patients. In conclusion, multi-TI PASL-GRASE can correct for arterial transit delay in patients with long ATTs. These results are promising for the transfer of ASL to the clinical practice.

Increased SNR efficiency in velocity selective arterial spin labeling using multiple velocity selective saturation modules (mm-VSASL)

PURPOSE

Velocity-selective arterial spin labeling (VSASL) is theoretically insensitive to transit delay (TD) effects. However, it uses saturation instead of inversion, resulting in compromised signal to noise ratio (SNR). In this study we explore the use of multiple velocity-selective saturation (VSS) modules in VSASL (mm-VSASL) to improve SNR.

METHODS

Theoretical SNR efficiency improvement and optimized parameters were calculated from simulations for mm-VSASL. VSASL with two VSS modules (VSASL-2VSS) was implemented to measure cerebral blood flow in vivo, compared with conventional VSASL (VSASL-1VSS), pulsed ASL (PASL), and pseudo-continuous ASL (PCASL). TDs and bolus durations (BDs) were measured to validate the simulations and to examine the TD sensitivity of these preparations.

RESULTS

Compared with VSASL-1VSS, VSASL-2VSS achieved a significant improvement of SNR (22.1 ± 1.9%, P = 1.7 × 10(-6) ) in vivo, consistent with a 22.7% improvement predicted from simulations. The SNR was comparable to or higher (in gray matter, P = 4.3 × 10(-3) ) than that using PCASL. VSASL was experimentally verified to have minimal TD effects.

CONCLUSION

Utilizing multiple VSS modules can improve the SNR efficiency of VSASL. Mm-VSASL may result in an SNR that is comparable to or even higher than that of PCASL in applications where long postlabeling delays are required.

Serum miRNA signature in Moyamoya disease

Moyamoya disease (MMD) is a cerebrovascular disease characterized by progressive stenosis of the intracranial internal carotid arteries and their proximal branches. However, the etiology of this rare disease remains unknown. Serum microRNA (miRNA) profiles have been screened to identify novel biomarkers of prognostic values. Here, we identified serum miRNAs that might play an important role in the pathogenesis of MMD. A genome-wide miRNA array analysis of two pooled serum samples from patients with MMD and controls revealed 94 differentially expressed serum miRNAs, including 50 upregulated and 44 downregulated miRNAs. In an independent MMD cohort, real-time PCR confirmed that miR-106b, miR-130a and miR-126 were significantly upregulated while miR-125a-3p was significantly downregulated in serum. GO analysis showed that the differentially expressed serum miRNAs were enriched in metabolic processes, transcription and signal transduction. Pathway analysis showed that the most enriched pathway was mTOR signaling pathway with 16 potential, functional targets. Finally, we found that 16 and 13 aberrant serum miRNAs coordinately inhibited RNF213 and BRCC3 protein expression at the posttranscriptional level, respectively, resulting in defective angiogenesis and MMD pathogenesis. To our knowledge, this is the first study to identify a serum miRNA signature in MMD. Modulation of the mechanism underlying the role of serum miRNAs in MMD is a potential therapeutic strategy and warrants further investigations.

An optimized design to reduce eddy current sensitivity in velocity-selective arterial spin labeling using symmetric BIR-8 pulses

PURPOSE

Velocity-selective arterial spin labeling (VSASL) tags arterial blood on a velocity-selective (VS) basis and eliminates the tagging/imaging gap and associated transit delay sensitivity observed in other ASL tagging methods. However, the flow-weighting gradient pulses in VS tag preparation can generate eddy currents (ECs), which may erroneously tag the static tissue and create artificial perfusion signal, compromising the accuracy of perfusion quantification.

METHODS

A novel VS preparation design is presented using an eight-segment B1 insensitive rotation with symmetric radio frequency and gradient layouts (sym-BIR-8), combined with delays after gradient pulses to optimally reduce ECs of a wide range of time constants while maintaining B0 and B1 insensitivity. Bloch simulation, phantom, and in vivo experiments were carried out to determine robustness of the new and existing pulse designs to ECs, B0 , and B1 inhomogeneity.

RESULTS

VSASL with reduced EC sensitivity across a wide range of EC time constants was achieved with the proposed sym-BIR-8 design, and the accuracy of cerebral blood flow measurement was improved.

CONCLUSION

The sym-BIR-8 design performed the most robustly among the existing VS tagging designs, and should benefit studies using VS preparation with improved accuracy and reliability.