Comparison of T2-FLAIR images obtained at 3 T and 7 T.

<p>In all patients, all lesions detected at 3 T were also visible at 7 T. Boxed areas are shown at higher magnification. A) Patient No. 3, with a small chronic lesion consisting of hyperintense postischemic tissue (white arrowheads) surrounding a tissue defect area (asterisk); compare also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037631#pone-0037631-g002" target="_blank">figure 2</a> A. At 7 T, the intensity values of the tissue defect area were comparable to CSF, while at 3 T, the intensity values were comparable to white matter. Contrast between postischemic and healthy brain tissue was higher at 3 T. However, small white matter lesions (red arrowheads) were easier to identify at 7 T. B) Patient No. 1, with a chronic stroke lesion (white arrowheads) and a subacute lesion (red arrowheads). Both lesion types were readily identifiable at both field strengths. As in A), contrast between the lesion and healthy tissue appeared to be higher at 3 T. C) Patient No. 4, with a large chronic infarct, consisting of hyperintense lesion areas (white arrowheads) and hypointense defect areas (asterisks). Again, CSF-filled tissue defect areas were easier to identify at 7 T, while the lesion to healthy tissue contrast was higher at 3 T. Compare also fig. 2 A–C.</p

Comparison of T2-weighted imaging performed at 3 T and 7 T.

<p>Boxed areas are shown at higher magnification. A) In patient No. 3, artifacts were present (red arrowheads). Contrast and detail level of the lesion (white arrowhead) and of Virchow-Robin spaces were not higher at 7 T. B) In contrast, in patient No. 1 no artifacts were present. Virchow Robin spaces (white arrowheads) were depicted in higher detail at 7 T and the delineation of the lesion (red arrowheads) from healthy tissue was higher at 7 T. C) Same patient as in B). Also in the region of the deep nuclei T2-weighted imaging at 7 T showed better delineation, e.g. between deep nuclei (red asterisks) and fibre bundles of the internal capsule (white asterisks).</p

Synopsis of the parameters of the imaging techniques used.

<p> <i>TR: repetition time; TE: echo time; BW: Bandwidth; FA: flip angle; t = time.</i></p

Comparison of T₁-weighted images derived from T1-MPRAGE at 3 T and 7 T.

<p>In all patients, MPRAGE at 7 T depicted the internal structure of stroke lesion in higher detail compared with 3 T. Boxed areas are shown at higher magnification. A) Patient No. 3. The tissue defect area appeared larger and less well confined at 3 T in contrast to 7 T (white arrowheads). Virchow-Robin spaces were seen in more detail and higher frequency at 7 T (red arrowheads). B) In patient No. 1, the chronic stroke lesion (white arrowheads) presented as an hypointense area – indicating gliosis – and as a disruption of the cortical band. These characteristics of the lesion were depicted in higher detail level and contrast at 7 T. The subacute lesion (red arrowheads) showed a different internal structure of the cortical band compared with healthy cortex. Within the lesion, the cortical band was divided into a superficial hyperintense layer and a deeper hypointense layer (asterisks). Differentiation of the two layers was much easier at 7 T. C) Patient No. 4. In this large infarct, differentiation of hypointense gliosis (white arrowheads) and healthy tissue was again clearer at 7 T. Inhomogeneities between the frontal and occipital cortex and paramedian deep structures – typical for 7 T – were more pronounced in this patient compared to A) and B).</p

Comparison of T2*-weighted images acquired with HemoFLASH at 3 T and 7 T.

<p>In all patients, HemoFLASH provided higher anatomic detail level at 7 T. Moreover, hypointense perilesional hemosiderin deposits were much more pronounced at 7 T. Boxed areas are shown at higher magnification. A) In patient No 3, anatomical detail level and contrast of the lesion (white arrowheads) to healthy tissue were higher at 7 T imaging. T2-FLAIR weighted high magnification images are shown for comparison below. A perilesional hypointense area, indicating hemosiderin deposits, was much more pronounced at 7 T (red arrowheads). B) In patient No. 4, again both anatomical details as well as the imaging of hemosiderin (white arrowheads) were superior at 7 T. C) Incidental finding of a cavernous angioma (white arrowhead) in patient No. 5. The internal structure of the lesion, showing a nodular characteristic with a hypointense rim, and the depiction of feeding vessels were more pronounced at 7 T, facilitating the diagnosis.</p

Comparison of MR-angiographies derived from 3D TOF acquisitions at 3 T and 7 T.

<p>In all patients, TOF at 7 T was able to depict the branches of the main cerebral arteries in higher anatomical detail. In patients No. 4 (A) and No. 7 (B), the left MCA territory is shown in higher magnification. In comparison with 3 T, clearly more first and second order branches were visible at 7 T in comparison with 3 T (white arrowheads).</p

Visual rating of DSC-CBF/ASL.

<p>Results of the visual qualitative analysis. As hypoperfusion in ASL occurred exclusively as part of ATDA and not isolated, for ASL only the categories ATDA and normal are presented.</p><p>Rows show imaging findings for ASL-CBF, columns show imaging findings for DSC-CBF. Patients rated uninterpretable were excluded.</p><p>Of 11 patients with hypoperfusion in DSC-CBF, 9 patients showed ATDAs in ASL (specificity: 82%; false negative rate: 18%). 6 patients had normal DSC-CBF findings, 3 of them showed ATDAs in ASL (false positive: 50%).</p><p>DSC-CBF: Dynamic Susceptibility Contrast - Cerebral Blood Flow; ASL: Arterial Spin Labeling; ATDA: Arterial Transit Delay Artifact.</p

Visual rating of TTP/ASL.

<p>Results of the visual qualitative analysis. As hypoperfusion in ASL occurred exclusively as part of ATDA and not isolated, for ASL only the categories ATDA and normal are presented.</p><p>Rows show imaging findings for ASL-CBF, columns show imaging findings for DSC-TTP. Patients rated uninterpretable were excluded. Of 14 patients with a TTP delay, 10 showed Arterial Transit Delay Artifacts in ASL (specificity: 71%; false negative rate: 29%). Out of 3 patients with normal findings in TTP, 1 showed ATDAs in ASL (false positive rate: 67%).</p><p>DSC-TTP: Dynamic Susceptibility Contrast - Time to Peak; ASL: Arterial Spin Labeling; ATDA: Arterial Transit Delay Artifact.</p

Clinical data of all patients.

<p>y: years; p: points; mRS: Modified Rankin Scale, NIHSS: National Institute of Health Stroke Scale; GoS: Grade of Stenosis; ICA: Internal Carotid Artery; MCA: Middle Cerebral Artery.</p

Arterial Transit Delay Artifact.

<p>Origin of the Arterial Transit Delay Artifact in ASL (labeling slice = green, imaging slices = blue). If arterial transit time is prolonged as it is the case in our patients, the inflow time is too short. Imaging slices capture high signal of labeled blood that is still in small arteries (as indicated by hyperintensities inside the labeling slices; red arrow) and hypointense areas, which the labeled blood has not yet reached. In parts of the brain where the arterial transit time is normal, blood has already exchanged with residual water and the ASL image appears normal (white arrow).</p