Correlation of Regional Cerebral Blood Flow Measured by Stable Xenon CT and Perfusion MRI

Background and Purpose-Recent advances in neuroimaging have raised hopes of early and accurate identification of ischemic brain and the discrimination of dead from salvageable tissue. We sought to determine whether the data published so far are enough to establish the roles of these techniques in everyday clinical practice. Methods-A systematic review of studies of MR diffusion-weighted imaging (DWI), perfusion imaging (PI), or a combination of the two, in human stroke, excluding abstracts and case reports. One reviewer extracted information on the size of each study, its main purpose, methodological details, and results. Results-We identified 47 studies of DWI, 18 studies of MR PI alone or in combination with another advanced imaging modality, and 19 studies of DWI and PI together. Although high proportions of the studies were prospective and gave good details of the imaging sequences used, the majority gave very limited details on patient selection and clinical characteristics or blinded imaging assessment. Pathophysiological changes were inferred from DWI/PI patterns that were not supported by other data. Conclusions-Despite considerable enthusiasm for and promise of these techniques, there is not sufficient information available in these studies to enable us to draw firm conclusions about the sensitivity and specificity of these techniques for identification of either ischemic lesions not visible by other means or salvageable tissue. Future studies should include larger numbers of carefully described patients, assess the contribution of DWI over and above other imaging, obtain follow-up at an appropriate time interval to determine accurate clinical and neuroradiological outcomes, and assess DWI/PI abnormality with reperfusion in randomized treatment trials. Investigators should also be encouraged to combine their individual patient data in meta-analyses to obtain a more robust assessment of the value of DWI and PI from larger sample sizes. Key Words: magnetic resonance imaging, diffusion-weighted Ⅲ magnetic resonance imaging, perfusion-weighted Ⅲ stroke, acute Ⅲ stroke, ischemic R ecent advances in brain imaging may likely underpin the future of stroke care. In particular, the introduction of MR and development of advanced imaging-like spectroscopy (MRS) and diffusion-weighted and perfusion imaging (DWI and PI, respectively) have raised hopes of greater ability to discriminate dead from salvageable tissue and thus to target new treatments. Several reviews 1,2 have summarized the technical aspects and possible applications of these advances, and considerable enthusiasm has been expressed for the use of these techniques in stroke; relatively few, however, have highlighted the problems that need to be overcome to maximize the potential of these exciting techniques. 3,4 DWI works on the principle that sensitizing a standard MR image to diffusion weighting identifies regions of abnormal water movement, occurring very early after onset of ischemia, resulting in increased (bright) signal intensity. 5 It is thought ...

Section: Studies Of Pi Alonementioning

confidence: 88%

Systematic Review of Diffusion and Perfusion Imaging in Acute Ischemic Stroke

Keir

Wardlaw

2000

“…81 Several studies have demonstrated a good correlation between the absolute CBV and CBF values obtained according to this approach compared with PET or XeCT. [82][83][84] Note that to interpret the DSC perfusion maps quantitatively or semiquantitatively, it is necessary to mask out the large vessels (very prominent with GRE sequences). Low perfusion values can be accurately measured until 8 mL/minute per 100 g. Under this level, the signal-to-noise ratio becomes too low for a precise quantification.…”

Section: Discussionmentioning

confidence: 99%

Comparative Overview of Brain Perfusion Imaging Techniques

Wintermark

Sesay

Barbier

et al. 2005

420

209

Background and Purpose-Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are positron emission tomography, single photon emission computed tomography, Xenonenhanced computed tomography, dynamic perfusion computed tomography, MRI dynamic susceptibility contrast, arterial spin labeling, and Doppler ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow or cerebral blood volume. All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks. Summary of Review-This

“…Because we followed a clinical approach, we performed no individual PET-based correction. MR-based individual correction factors are highly desirable and the respective studies 17,42,57 yielded promising results. However, because the optimal correction factor and tissue-specific differences are still a matter of ongoing debate 38 and because technically challenging methods are not yet feasible in the acute stroke setting, we did not apply a MR-based correction factor in line with previous studies.…”

Section: Zaro-weber Et Al Mri-cbf In Acute Stroke Compared With H 2 Omentioning

confidence: 99%

The Performance of MRI-Based Cerebral Blood Flow Measurements in Acute and Subacute Stroke Compared With 15O-Water Positron Emission Tomography

Zaro-Weber

Moeller-Hartmann

Heiss

et al. 2009

Background and Purpose-Perfusion-weighted MRI-based maps of cerebral blood flow (CBF MRI ) are considered a good MRI measure of penumbral flow in acute ischemic stroke but are seldom used in clinical routine due to methodical issues. We validated CBF MRI on quantitative CBF measurement by 15O-water positron emission tomography (CBF PET ). Material and Methods-Comparative CBF MRI and CBF PET were performed in patients with acute and subacute stroke. In a voxel-based seed-growing technique, predefined CBF MRI thresholds (Ͻ40, Ͻ30, Ͻ20, Ͻ10 mL/100 g/min) were applied and the resulting volumes were compared with the hypoperfusion volume detected by the penumbral threshold (Ͻ20 mL/100 g/min) on CBF PET . The volumetric comparison was expressed as the C-ratio (volume CBF MRI /volume CBF PET ) to identify the best MRI threshold. The influence of vessel pathology, hypoperfusion size, and time point of imaging was described. The proportion of voxels correctly classified as hypoperfused and the proportion of voxel correctly classified as nonhypoperfused of the best CBF MRI threshold was calculated and a Bland-Altman plot illustrated the method-specific differences. Results-In 24 patients (median time MRI to PET: 68 minutes; 16 patients imaged within 24 hours after stroke), the median volume of hypoperfusion Ͻ20 mL/100 g/min (CBF PET ) was 78.5 cm 3 . Median hypoperfusion volume on CBF MRI ranged from 245.9 cm 3 (Ͻ40 mL/100 g/min) to 35.5 cm 3 (Ͻ10 mL/10 g/min). On visual inspection, an excellent qualitative congruence was found. The quantitative congruence was best for the MRI-CBF threshold Ͻ20 mL/100 g/min (median C-ratio: 1.0), reaching a proportion of voxels correctly classified as hypoperfused of 76% and a proportion of voxel correctly classified as nonhypoperfused of 96%, but a wide interindividual range (C-ratio 0.3 to 3.5) was found. Ipsilateral vessel pathology, time point of imaging, and size of hypoperfusion did not significantly influence the C-ratio. The Bland-Altman analysis for the volumetric difference of CBF MRI and CBF PET found a good overall agreement but a large SD. Conclusion-Hypoperfusion