Deqiang Qiu

Performance and Predictive Value of a User-Independent Platform for CT Perfusion Analysis: Threshold-Derived Automated Systems Outperform Examiner-Driven Approaches in Outcome Prediction of Acute Ischemic Stroke

BACKGROUND AND PURPOSE: Treatment strategies in acute ischemic stroke aim to curtail ischemic progression. Emerging paradigms propose patient subselection using imaging biomarkers derived from CT, CTA, and CT perfusion. We evaluated the performance of a fully-automated computational tool, hypothesizing enhancements compared with qualitative approaches. The correlation between imaging variables and clinical outcomes in a cohort of patients with acute ischemic stroke is reported. MATERIALS AND METHODS: Sixty-two patients with acute ischemic stroke and MCA or ICA occlusion undergoing multidetector CT, CTA, and CTP were retrospectively evaluated. CTP was processed on a fully operator-independent platform (RApid processing of PerfusIon and Diffusion [RAPID]) computing automated core estimates based on relative cerebral blood flow and relative cerebral blood volume and hypoperfused tissue volumes at varying thresholds of time-to-maximum. Qualitative analysis was assigned by 2 independent reviewers for each variable, including CT-ASPECTS, CBV-ASPECTS, CBF-ASPECTS, CTA collateral score, and CTA clot burden score. Performance as predictors of favorable clinical outcome and final infarct volume was established for each variable. RESULTS: Both RAPID core estimates, CT-ASPECTS, CBV-ASPECTS, and clot burden score correlated with favorable clinical outcome (P < .05); CBF-ASPECTS and collateral score were not significantly associated with favorable outcome, while hypoperfusion estimates were variably associated, depending on the selected time-to-maximum thresholds. Receiver operating characteristic analysis demonstrated disparities among tested variables, with RAPID core and hypoperfusion estimates outperforming all qualitative approaches (area under the curve, relative CBV = 0.86, relative CBF = 0.81; P < .001). CONCLUSIONS: Qualitative approaches to acute ischemic stroke imaging are subject to limitations due to their subjective nature and lack of physiologic information. These findings support the benefits of high-speed automated analysis, outperforming conventional methodologies while limiting delays in clinical management.

Dose Reduction in Contrast-Enhanced Cervical MR Angiography: Field Strength Dependency of Vascular Signal Intensity, Contrast Administration, and Arteriographic Quality.

OBJECTIVEnCervical contrast-enhanced MR angiography (MRA) has proven accurate and superior to noncontrast alternatives. We proposed the systematic investigation of dose reduction in contrast-enhanced MRA, hypothesizing heightened tolerance at 3 T vs 1.5 T. Quantitative and qualitative features were compared between full-dose and 50%-reduced dose examinations at 1.5 T and 3 T.nnnMATERIALS AND METHODSnOne hundred eight cervical contrast-enhanced MRA examinations were reviewed for qualitative and quantitative (signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) features across four dose-field strength combinations: 1.5 T, 0.05 mmol/kg; 3 T, 0.05 mmol/kg; 1.5 T, 0.1 mmol/kg; and 3 T, 0.1 mmol/kg. Quantitative features were evaluated among the following segments: aortic arch, common carotid arteries, common carotid bifurcations, and cervical internal carotid arteries. A qualitative visual rating scale was applied for the same segments as well as to the vertebral arteries along their proximal (V1), intraforaminal (V2), and distal extraforaminal (V3) courses. Significant between-group differences were reported at p < 0.05.nnnRESULTSnQualitatively good arteriography was observed in all segments for all protocols. No significant qualitative differences between protocols were noted throughout evaluation of the anterior cervical circulation. Significant qualitative differences were observed only for V2 and V3 segments at half-dose 1.5-T compared with the remaining protocols (p < 0.05). No significant quantitative differences were present between full-dose and dose-reduced 3-T MRA in any segment. At 1.5 T, significant decrement in SNR and CNR at half-dose was present only within the cervical internal carotid artery.nnnCONCLUSIONnDose reduction in cervical contrast-enhanced MRA is feasible at 3 T without significant compromise in arteriographic quality in most segments. Particularly at 3 T, arteriography is quantitatively and qualitatively robust and may be advisable in high-risk patients.

The Effects of Acetazolamide on the Evaluation of Cerebral Hemodynamics and Functional Connectivity Using Blood Oxygen Level–Dependent MR Imaging in Patients with Chronic Steno-Occlusive Disease of the Anterior Circulation

BACKGROUND AND PURPOSE: Measuring cerebrovascular reactivity with the use of vasodilatory stimuli, such as acetazolamide, is useful for chronic cerebrovascular steno-occlusive disease. The purpose of this study was to evaluate the effects of acetazolamide on the assessment of hemodynamic impairment and functional connectivity by using noninvasive resting-state blood oxygen level–dependent MR imaging. MATERIALS AND METHODS: A 20-minute resting-state blood oxygen level–dependent MR imaging scan was acquired with infusion of acetazolamide starting at 5 minutes after scan initiation. A recently developed temporal-shift analysis technique was applied on blood oxygen level–dependent MR imaging data before and after acetazolamide infusion to identify regions with hemodynamic impairment, and the results were compared by using contrast agent–based DSC perfusion imaging as the reference standard. Functional connectivity was compared with and without correction on the signal by using information from temporal-shift analysis, before and after acetazolamide infusion. RESULTS: Visually, temporal-shift analysis of blood oxygen level–dependent MR imaging data identified regions with compromised hemodynamics as defined by DSC, though performance deteriorated in patients with bilateral disease. The Dice similarity coefficient between temporal-shift and DSC maps was higher before (0.487 ± 0.150 by using the superior sagittal sinus signal as a reference for temporal-shift analysis) compared with after acetazolamide administration (0.384 ± 0.107) (P = .006, repeated-measures ANOVA). Functional connectivity analysis with temporal-shift correction identified brain network nodes that were otherwise missed. The accuracy of functional connectivity assessment decreased after acetazolamide administration (P = .015 for default mode network, repeated-measures ANOVA). CONCLUSIONS: Temporal-shift analysis of blood oxygen level–dependent MR imaging can identify brain regions with hemodynamic compromise in relation to DSC among patients with chronic cerebrovascular disease. The use of acetazolamide reduces the accuracy of temporal-shift analysis and network connectivity evaluation.

Cerebral Temperature Dysregulation: MR Thermographic Monitoring in a Nonhuman Primate Study of Acute Ischemic Stroke

BACKGROUND AND PURPOSE: Cerebral thermoregulation remains poorly understood. Temperature dysregulation is deeply implicated in the potentiation of cerebrovascular ischemia. We present a multiphasic, MR thermographic study in a nonhuman primate model of MCA infarction, hypothesizing detectable brain temperature disturbances and brain-systemic temperature decoupling. MATERIALS AND METHODS: Three Rhesus Macaque nonhuman primates were sourced for 3-phase MR imaging: 1) baseline MR imaging, 2) 7-hour continuous MR imaging following minimally invasive, endovascular MCA stroke induction, and 3) poststroke day 1 MR imaging follow-up. MR thermometry was achieved by multivoxel spectroscopy (semi-localization by adiabatic selective refocusing) by using the proton resonance frequency chemical shift. The relationship of brain and systemic temperatures with time and infarction volumes was characterized by using a mixed-effects model. RESULTS: Following MCA infarction, progressive cerebral hyperthermia was observed in all 3 subjects, significantly outpacing systemic temperature fluctuations. Highly significant associations were observed for systemic, hemispheric, and global brain temperatures (F-statistic, P = .0005 for all regressions) relative to the time from stroke induction. Significant differences in the relationship between temperature and time following stroke onset were detected when comparing systemic temperatures with ipsilateral (P = .007), contralateral (P = .004), and infarction core (P = .003) temperatures following multiple-comparisons correction. Significant associations were observed between infarction volumes and both systemic (P ≤ .01) and ipsilateral (P = .04) brain temperatures, but not contralateral brain temperature (P = .08). CONCLUSIONS: Successful physiologic and continuous postischemic cerebral MR thermography was conducted and prescribed in a nonhuman primate infarction model to facilitate translatability. The results confirm hypothesized temperature disturbance and decoupling of physiologic brain-systemic temperature gradients. These findings inform a developing paradigm of brain thermoregulation and the applicability of brain temperature as a neuroimaging biomarker in CNS injury.

Acetazolamide-augmented dynamic BOLD (aczBOLD) imaging for assessing cerebrovascular reactivity in chronic steno-occlusive disease of the anterior circulation: An initial experience

The purpose of this study was to measure cerebrovascular reactivity (CVR) in chronic steno-occlusive disease using a novel approach that couples BOLD imaging with acetazolamide (ACZ) vasoreactivity (aczBOLD), to evaluate dynamic effects of ACZ on BOLD and to establish the relationship between aczBOLD and dynamic susceptibility contrast (DSC) perfusion MRI. Eighteen patients with unilateral chronic steno-occlusive disease of the anterior circulation underwent a 20-min aczBOLD imaging protocol, with ACZ infusion starting at 5 min of scan initiation. AczBOLD reactivity was calculated on a voxel-by-voxel basis to generate CVR maps for subsequent quantitative analyses. Reduced CVR was observed in the diseased vs. the normal hemisphere both by qualitative and quantitative assessment (gray matter (GM): 4.13% ± 1.16% vs. 4.90% ± 0.98%, P = 0.002; white matter (WM): 2.83% ± 1.23% vs. 3.50% ± 0.94%, P = 0.005). In all cases BOLD signal began increasing immediately following ACZ infusion, approaching a plateau at ~ 8.5 min after infusion, with the tissue volume of reduced augmentation increasing progressively with time, peaking at 2.60 min (time range above 95% of the maximum value: 0–4.43 min) for the GM and 1.80 min (time range above 95% of the maximum value: 1.40–3.53 min) for the WM. In the diseased hemisphere, aczBOLD CVR significantly correlated with baseline DSC time-to-maximum of the residue function (Tmax) (P = 0.008 for the WM) and normalized cerebral blood flow (P = 0.003 for the GM, and P = 0.001 for the WM). AczBOLD provides a novel, safe, easily implementable approach to CVR measurement in the routine clinical environments. Further studies can establish quantitative thresholds from aczBOLD towards identification of patients at heightened risk of recurrent ischemia and cognitive decline.

The Brain Thermal Response as a Potential Neuroimaging Biomarker of Cerebrovascular Impairment

The authors evaluated the use of noninvasive MR thermometry in patients with cerebrovascular disease, and hypothesized that the presence of a measurable brain thermalresponse would reflect the tissue hemodynamic state. MR imaging and MR thermometry were performed in 10 patients undergoing acetazolamide challenge for chronic, anterior circulation steno-occlusive disease. Cerebrovascular reactivity was calculated with BOLD imaging and arterial spin-labeling methods. Brain temperature was calculated pre- and post-acetazolamide using previously established chemical shift thermometry. They observed significant, voxelwise quadratic relationships between cerebrovascular reactivity from BOLD imaging and the brain thermal response and baseline brain temperatures, concluding that brain thermal response is a potential noninvasive biomarker for cerebrovascular impairment. BACKGROUND AND PURPOSE: Brain temperature is critical for homeostasis, relating intimately to cerebral perfusion and metabolism. Cerebral thermometry is historically challenged by the cost and invasiveness of clinical and laboratory methodologies. We propose the use of noninvasive MR thermometry in patients with cerebrovascular disease, hypothesizing the presence of a measurable brain thermal response reflecting the tissue hemodynamic state. MATERIALS AND METHODS: Contemporaneous imaging and MR thermometry were performed in 10 patients (32–68 years of age) undergoing acetazolamide challenge for chronic, anterior circulation steno-occlusive disease. Cerebrovascular reactivity was calculated with blood oxygen level–dependent imaging and arterial spin-labeling methods. Brain temperature was calculated pre- and post-acetazolamide using previously established chemical shift thermometry. Mixed-effects models of the voxelwise relationships between the brain thermal response and cerebrovascular reactivity were computed, and the significance of model coefficients was determined with an F test (P < .05). RESULTS: We observed significant, voxelwise quadratic relationships between cerebrovascular reactivity from blood oxygen level–dependent imaging and the brain thermal response (x coefficient = 0.052, P < .001; x2coefficient = 0.0068, P < .001) and baseline brain temperatures (x coefficient = 0.59, P = .008; x2 coefficient = −0.13, P < .001). A significant linear relationship was observed for the brain thermal response with cerebrovascular reactivity from arterial spin-labeling (P = .001). CONCLUSIONS: The findings support the presence of a brain thermal response exhibiting complex but significant interactions with tissue hemodynamics, which we posit to reflect a relative balance of heat-producing versus heat-dissipating tissue states. The brain thermal response is a potential noninvasive biomarker for cerebrovascular impairment.

Noninvasive Assessment of Intracranial Pressure Status in Idiopathic Intracranial Hypertension Using Displacement Encoding with Stimulated Echoes (DENSE) MRI: A Prospective Patient Study with Contemporaneous CSF Pressure Correlation

Nine patients with suspected elevated intracranial pressure and 9 healthy control patients were included in this prospective study. Control patients underwent DENSE MR imaging through the midsagittal brain while patients underwent DENSE MR imaging followed immediately by lumbar puncture with opening pressure measurement, CSF removal, closing pressure measurement, and immediate repeat DENSE MR imaging. All patients had elevated opening pressure (median, 36.0 cm water), decreased by the removal of CSF to a median closing pressure of 17.0 cm water. Measured CSF pressure in patients pre= and post=lumbar puncture correlated significantly with pontine displacement. The authors conclude that DENSE MR imaging may providing a method to noninvasively assess intracranial pressure status in idiopathic intracranial hypertension. BACKGROUND AND PURPOSE: Intracranial pressure is estimated invasively by using lumbar puncture with CSF opening pressure measurement. This study evaluated displacement encoding with stimulated echoes (DENSE), an MR imaging technique highly sensitive to brain motion, as a noninvasive means of assessing intracranial pressure status. MATERIALS AND METHODS: Nine patients with suspected elevated intracranial pressure and 9 healthy control subjects were included in this prospective study. Controls underwent DENSE MR imaging through the midsagittal brain. Patients underwent DENSE MR imaging followed immediately by lumbar puncture with opening pressure measurement, CSF removal, closing pressure measurement, and immediate repeat DENSE MR imaging. Phase-reconstructed images were processed producing displacement maps, and pontine displacement was calculated. Patient data were analyzed to determine the effects of measured pressure on pontine displacement. Patient and control data were analyzed to assess the effects of clinical status (pre–lumbar puncture, post–lumbar puncture, or control) on pontine displacement. RESULTS: Patients demonstrated imaging findings suggesting chronically elevated intracranial pressure, whereas healthy control volunteers demonstrated no imaging abnormalities. All patients had elevated opening pressure (median, 36.0 cm water), decreased by the removal of CSF to a median closing pressure of 17.0 cm water. Patients pre–lumbar puncture had significantly smaller pontine displacement than they did post–lumbar puncture after CSF pressure reduction (P = .001) and compared with controls (P = .01). Post–lumbar puncture patients had statistically similar pontine displacements to controls. Measured CSF pressure in patients pre– and post–lumbar puncture correlated significantly with pontine displacement (r = 0.49; P = .04). CONCLUSIONS: This study establishes a relationship between pontine displacement from DENSE MR imaging and measured pressure obtained contemporaneously by lumbar puncture, providing a method to noninvasively assess intracranial pressure status in idiopathic intracranial hypertension.

Effects of Height and Blood Volume on Venous Enhancement After Gadolinium-Based Contrast Administration in MR Venography: A Paradigm Challenge and Implications for Clinical Imaging.

OBJECTIVEnThe purpose of this study was to analyze quantitative and qualitative effects of estimated blood volume on venous enhancement in patients undergoing cerebral MR venography (MRV) with standard weight-based dosing of a gadolinium-based contrast agent.nnnMATERIALS AND METHODSnFifty-two patients with normal 1.5-T cerebral MRV findings and contemporaneous height and weight measurements were included. Estimated blood volume was calculated with the Nadler formula for blood volume. Standard weight-based cerebral MRV was performed after administration of gadobenate dimeglumine (0.1 mmol/kg up to 20 mL). Venous enhancement within the superior sagittal sinus, right jugular bulb, and left jugular bulb was measured. Patients were dichotomized on the basis of administration of less than versus a maximum weight-based gadolinium-based contrast dose of 20 mL. Venographic quality was assigned by two neuroradiologists. Correlational and multiple linear regression analyses were performed.nnnRESULTSnAmong patients receiving less than the maximum 20 mL of gadolinium, no significant correlations were observed between weight and vascular enhancement (p > 0.05). Significant correlations between height and enhancement were observed in the superior sagittal sinus and left jugular bulb. This finding suggests that differences in estimated blood volume driven by height remain unaccounted for (p < 0.05). With the 20-mL maximal dose, a significant inverse relation was noted between estimated blood volume and contrast enhancement of all vascular segments (p < 0.05). Within all vascular segments, significant correlations were observed between enhancement and user-defined quality scores (p < 0.05). This finding suggests that optimized dosing may affect reader confidence.nnnCONCLUSIONnStandard weight-based dosing for cerebral MRV insufficiently accounts for differences in circulating blood volume. An expanded biometric dosing paradigm leveraging readily attainable subject data may mitigate unintended variations in enhancement affecting venography and other clinical imaging modalities.