Hypercapnic BOLD MRI compared to H215O PET/CT for the hemodynamic evaluation of patients with Moyamoya Disease

Abstract

Background and purposePatients with Moyamoya Disease (MMD) need hemodynamic evaluation of vascular territories at risk of stroke. Today's investigative standards include H215O PET/CT with pharmacological challenges with acetazolamide (ACZ). Recent developments suggest that CO2-triggered blood‑oxygen-level-dependent (BOLD) functional MRI might provide comparable results to current standard methods for evaluation of territorial hemodynamics, while being a more widely available and easily implementable method. This study examines results of a newly developed quantifiable analysis algorithm for CO2-triggered BOLD MRI in Moyamoya patients and correlates the results with H215O PET/CT with ACZ challenge to assess comparability between both modalities.MethodsCO2-triggered BOLD MRI was performed and compared to H215O PET/CT with ACZ challenge in patients with angiographically proven MMD. Images of both modalities were analyzed retrospectively in a blinded, standardized fashion by visual inspection, as well as with a semi-quantitative analysis using stimuli-induced approximated regional perfusion-weighted data and BOLD-signal changes with reference to cerebellum.Results20 consecutive patients fulfilled the inclusion criteria, a total of 160 vascular territories were analyzed retrospectively. Visual analysis (4-step visual rating system) of standardized, color-coded cerebrovascular reserve/reactivity maps showed a very strong correlation (Spearman's rho = 0.9, P < 0.001) between both modalities. Likewise, comparison of approximated regional perfusion changes across vascular territories (normalized to cerebellar change) reveal a highly significant correlation between both methods (Pearson's r = 0.71, P < 0.001).ConclusionsThe present analysis indicates that CO2-triggered BOLD MRI is a very promising tool for the hemodynamic evaluation of MMD patients with results comparable to those seen in H215O PET/CT with ACZ challenge. It therefore holds future potential in becoming a routine examination in the pre- and postoperative evaluation of MMD patients after further prospective evaluation.

Investigation of the BOLD-Based MRI Signal Time Course During Short Breath-Hold Periods for Estimation of the Cerebrovascular Reactivity

“…Reduced cerebrovascular reactivity can be used to assess the severity of cerebrovascular diseases and constitutes an important risk factor for ischemic stroke [33,34]. The evaluation of CVR can serve as an indication for neurosurgical revascularization [3,4,11,14,[35][36][37][38], as well as the evaluation of the clinical outcome after cerebrovascular interventions [35][36][37][38].…”

“…A recent retrospective study showed that in patients with MMD, the hypercapnia-triggered fMRI by use of short breathhold periods leads to comparable results to the more complex and expensive positron emission tomography (PET) with acetazolamide challenge [11]. An open question in this investigation was the necessary duration of the breath-hold periods for clinical use.…”

“…Nuclear medicine imaging techniques are much used to investigate the cerebrovascular reactivity, but are limited available due to the requirement of short-lived radiopharmaceutical tracers and relatively expensive [5]. Functional magnetic resonance imaging (fMRI) technique can also be employed in clinical routine to determine remaining cerebrovascular reactivity at patients with MMD using the exogenous vasoactive stimulus acetazolamide (ACT) [6] or hypercapnic challenges such as inhalation of CO 2 -enriched gas [7][8][9][10] or breath-holding [11]. Hypercapnia is known to induce cerebral vasodilatation in healthy brain tissue and increased cerebral blood flow (CBF) [6].…”

“…Long breath-hold periods are associated with difficulties in carrying out the tasks, particularly for patients with limited state of health; too short breath-hold periods do not provide sufficient BOLD signals. In the implementation of breath-hold tasks, a distinction is made between breath-hold (BH) following inspiration (end-inspiration) [12,[16][17][18] and BH following expiration (end-expiration) [11,12,[19][20][21][22][23]. BH periods after expiration are supposed to lead to earlier and higher signal increases [21].…”

“…To overcome this disadvantage, patient respiratory movements could be monitored by use of a respiratory belt to ensure correct execution of the breath-hold periods. Another way of verifying patient compliance is to evaluate the signal time course of the cerebellum, where distinct BOLD signal increases are expected, and to exclude individual breath-hold periods from further evaluation, in which the expected cerebellar response curve is not observed [11]. Dlamini et al recently showed that breath-hold paradigms are well feasible even for children and lead to reliable results [47].…”