Non-parametric deconvolution using Bézier curves for quantification of cerebral perfusion in dynamic susceptibility contrast MRI

Objective Deconvolution is an ill-posed inverse problem that tends to yield non-physiological residue functions R(t) in dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI). In this study, the use of Bézier curves is proposed for obtaining physiologically reasonable residue functions in perfusion MRI. Materials and methods Cubic Bézier curves were employed, ensuring R(0) = 1, bounded-input, bounded-output stability and a non-negative monotonically decreasing solution, resulting in 5 parameters to be optimized. Bézier deconvolution (BzD), implemented in a Bayesian framework, was tested by simulation under realistic conditions, including effects of arterial delay and dispersion. BzD was also applied to DSC-MRI data from a healthy volunteer. Results Bézier deconvolution showed robustness to different underlying residue function shapes. Accurate perfusion estimates were observed, except for boxcar residue functions at low signal-to-noise ratio. BzD involving corrections for delay, dispersion, and delay with dispersion generally returned accurate results, except for some degree of cerebral blood flow (CBF) overestimation at low levels of each effect. Maps of mean transit time and delay were markedly different between BzD and block-circulant singular value decomposition (oSVD) deconvolution. Discussion A novel DSC-MRI deconvolution method based on Bézier curves was implemented and evaluated. BzD produced physiologically plausible impulse response, without spurious oscillations, with generally less CBF underestimation than oSVD.

Comparison of MR Perfusion and FDG-PET Brain Studies in Patients With Alzheimer’s Disease and Amnestic Mild Cognitive Impairment

Background: The aim of this study was to compare Dynamic Susceptibility Contrast Enhanced MRI (DSC-MRI) and PET with flurodeoxyglucose (FDG-PET) in the diagnosis of Alzheimer’s Disease (AD) and amnestic Mild Cognitive Impairment (aMCI).Methods: Age and sex matched 27 patients with AD, 39 with aMCI and 16 controls underwent brain DSC-MRI followed by FDG-PET. Values of relative Cerebral Blood Volume (rCBV) and rCBV z-scores from frontal, temporal, parietal and PCG cortices were correlated with the rate of glucose metabolism from PET. Sensitivity, specificity and accuracy of DSC-MRI and FDG-PET in the diagnosis of AD and aMCI were assessed and compared.Results: In AD hypoperfusion was found within all examined locations, while in aMCI in both parietal and temporal cortices and left PCG. FDG-PET showed the greatest hypometabolism in parietal, temporal and left PCG regions in both AD and aMCI. FDG-PET was more accurate in distinguishing aMCI from controls than DSC-MRI. In AD and combined group (AD + aMCI ) there were numerous correlations between DSC-MRI and FDG-PET results. Conclusions: In AD the patterns of hypoperfusion and glucose hypometabolism are similar thus DSC-MRI may be a competitive method to FDG-PET. FDG-PET is a more accurate method in the diagnosis of aMCI.

NI-11 Usefulness of the magnetic resonance imaging arterial spin labeling method for diagnosing posterior fossa hemangioblastoma

Purpose: It is sometimes challenging to diagnose hemangioblastoma by MRI when the tumor is a solid mass in the posterior fossa. We therefore evaluated perfusion images and diffusion-weighted images to diagnose hemangioblastoma in order to obtain the most useful quantitative features. Methods: Thirty-one posterior fossa tumors whose pathological diagnosis was confirmed by surgery were included in groups A (12 hemangioblastomas) and B (non-hemangioblastoma 19 cases: metastatic tumor 6 cases, pilocytic astrocytoma 3 cases, malignant lymphoma 3 cases, glioblastoma 2 cases, medulloblastoma 2 cases, and other 3 cases). All cases were imaged by 3.0-Tesla MRI, with the apparent diffusion coefficient (ADC) on diffusion-weighted imaging as the parameter, arterial spin labeling (ASL) as the relative value from the CBF map to the region of interest (ROI) in the contralateral hemisphere as perfusion image, dynamic susceptibility contrast (DSC) as rCBF, rCBV, corrected CBV, and K2. The ROI was set to match the contrast-enhanced part, and the two groups were compared and examined. Results: The relative ASL value of group A and the corrected CBV in DSC were significantly higher than group B (p<0.001). In contrast, the ADC showed no marked difference between the two groups. In the distinction between the two groups, the receiver operating characteristic (ROC) analysis showed that the area under the curve (AUC) of the relative ASL value was significantly higher than the other parameters (AUC 0.995, cut-off value 2.34, sensitivity 100%, specificity 99.5%). Discussion/Conclusion: The non-contrast ASL method was extremely useful for diagnosing hemangioblastoma in posterior fossa tumors. The ASL method has been reported helpful for the follow-up of residual tumors or recurrence after surgery. Contrast-enhanced DSC is not always essential for diagnosing posterior fossa hemangioblastoma. It should be noted that measuring the ROI by ASL is difficult when the size of the mural nodule is small.

Usefulness of arterial spin labeling perfusion as an initial evaluation of status epilepticus

This study aimed to evaluate the sensitivity and prognostic value of arterial spin labeling (ASL) in a large group of status epilepticus (SE) patients and compare them with those of other magnetic resonance (MR) sequences, including dynamic susceptibility contrast (DSC) perfusion imaging. We retrospectively collected data of patients with SE in a tertiary center between September 2016 and March 2020. MR images were visually assessed, and the sensitivity for the detection of SE and prognostication was compared among multi-delay ASL, DSC, fluid-attenuated inversion recovery (FLAIR), and diffusion-weighted imaging (DWI). We included 51 SE patients and 46 patients with self-limiting seizures for comparison. Relevant changes in ASL were observed in 90.2% (46/51) of SE patients, a percentage higher than those for DSC, FLAIR, and DWI. ASL was the most sensitive method for initial differentiation between SE and self-limiting seizures. The sensitivity of ASL for detecting refractory SE (89.5%) or estimating poor outcomes (100%) was higher than those of other MR protocols or electroencephalography and comparable to those of clinical prognostic scores, although the specificity of ASL was very low as 9.4% and 15.6%, respectively. ASL showed a better ability to detect SE and predict the prognosis than other MR sequences, therefore it can be valuable for the initial evaluation of patients with SE.

Cerebral perfusion imaging: Hypoxia-induced deoxyhemoglobin or gadolinium?

Assessment of resting cerebrovascular perfusion measures (mean transit time, cerebral blood flow and cerebral blood volume) with magnetic resonance imaging currently requires the intravascular injection of the dynamic susceptibility contrast agent gadolinium. An initial comparison between hypoxia-induced deoxyhemoglobin and gadolinium was made for these measures in six healthy participants. A bolus of deoxyhemoglobin is generated in the lung via transient hypoxia induced by an available computer-controlled gas blender technology employing sequential gas delivery (RespirAct). We hypothesised and confirmed perfusion measures from both susceptibility contrast agents would yield similar spatial patterns of cerebrovascular perfusion measures. We conclude that hypoxia-induced deoxyhemoglobin, an endogenously, non-invasively generated, non-allergenic, non-toxic, recyclable, environmentally innocuous molecule, may be suitable to become the first new magnetic resonance imaging susceptibility contrast agent introduction since gadolinium.