Validation of PET/MRI attenuation correction methodology in the study of brain tumours

Background This study aims to compare proton density weighted magnetic resonance imaging (MRI) zero echo time (ZTE) and head atlas attenuation correction (AC) to the reference standard computed tomography (CT) based AC for 11C-methionine positron emission tomography (PET)/MRI. Methods A retrospective cohort of 14 patients with suspected or confirmed brain tumour and 11C-Methionine PET/MRI was included in the study. For each scan, three AC maps were generated: ZTE–AC, atlas-AC and reference standard CT-AC. Maximum and mean standardised uptake values (SUV) were measured in the hotspot, mirror region and frontal cortex. In postoperative patients (n = 8), SUV values were additionally obtained adjacent to the metal implant and mirror region. Standardised uptake ratios (SUR) hotspot/mirror, hotspot/cortex and metal/mirror were then calculated and analysed with Bland–Altman, Pearson correlation and intraclass correlation reliability in the overall group and subgroups. Results ZTE–AC demonstrated narrower SD and 95% CI (Bland–Altman) than atlas-AC in the hotspot analysis for all groups (ZTE overall ≤ 2.84, − 1.41 to 1.70; metal ≤ 1.67, − 3.00 to 2.20; non-metal ≤ 3.04, − 0.96 to 3.38; Atlas overall ≤ 4.56, − 1.05 to 3.83; metal ≤ 3.87, − 3.81 to 4.64; non-metal ≤ 4.90, − 1.68 to 5.86). The mean bias for both ZTE–AC and atlas-AC was ≤ 2.4% compared to CT-AC. In the metal region analysis, ZTE–AC demonstrated a narrower mean bias range—closer to zero—and narrower SD and 95% CI (ZTE 0.21–0.48, ≤ 2.50, − 1.70 to 2.57; Atlas 0.56–1.54, ≤ 4.01, − 1.81 to 4.89). The mean bias for both ZTE–AC and atlas-AC was within 1.6%. A perfect correlation (Pearson correlation) was found for both ZTE–AC and atlas-AC compared to CT-AC in the hotspot and metal analysis (ZTE ρ 1.00, p < 0.0001; atlas ρ 1.00, p < 0.0001). An almost perfect intraclass correlation coefficient for absolute agreement was found between Atlas-, ZTE and CT maps for maxSUR and meanSUR values in all the analyses (ICC > 0.99). Conclusions Both ZTE and atlas-AC showed a good performance against CT-AC in patients with brain tumour.

Increased blood-brain barrier permeability in contralateral hemisphere predicts worse outcome in acute ischemic stroke after reperfusion therapy

AimsWe sought to investigate the risk factors of blood-brain barrier (BBB) disruption, and its potential impact on 90-day clinical outcome in acute ischemic stroke (AIS) patients after reperfusion therapy.MethodsConsecutive acute anterior circulation AIS patients imaged with computed tomographic perfusion (CTP) before reperfusion therapy were included. Tmax >6 s was used for the volumetric measurement of the hypoperfusion area. BBB permeability (BBBP) was calculated as the average relative permeability-surface area product (rPS) within the hypoperfusion region (rPShypo-i) and its contralateral mirror region (rPShypo-c) on CTP-derived PS color maps. Modified Rankin Scale (mRS) score was obtained at 90-day post-stroke.ResultsA total of 187 patients were included, among whom the median age was 73 (61–80) years and 76 (40.6%) were women. Median baseline NIHSS score was 12 (7– 16). Ninety-eight (52.4%) patients had mRS score >2. Increased rPShypo-i and rPShypo-c were both independently associated with males and large infarct volume. The increased rPShypo-i was also independently associated with a history of atrial fibrillation and high NIHSS score. Multivariable analysis showed higher rPShypo-c was independently associated with higher mRS (OR: 1.064, 95% CI 1.011 to 1.121; P=0.018).ConclusionBBBP in both the hypoperfusion region and its contralateral mirror region are associated with stroke severity, but only increased BBBP in the contralateral mirror hypoperfusion region relates to worse outcome after reperfusion therapy.

GHOSTS IN A MIRROR

We look at some dynamic geometries produced by scalar fields with both the "right" and the "wrong" signs of the kinetic energy. We start with anisotropic homogeneous universes with closed, open and flat spatial sections. A non-singular solution to the Einstein field equations representing an open anisotropic universe with the ghost field is found. This universe starts collapsing from t→-∞ and then expands to t→∞ without encountering singularities on its way. We further generalize these solutions to those describing inhomogeneous evolution of the ghost fields. Some interesting solutions with the plane symmetry are discussed. These have a property that the same line element solves the Einstein field equations in two mirror regions |t|≥z and |t|≤z, but in one region the solution has the right and in the other, the wrong sign of the kinetic energy. We argue, however, that a physical observer cannot reach the mirror region in a finite proper time. Self-similar collapse/expansion of these fields are also briefly discussed.

Scanning tunneling microscope observations of the mirror region of silicate glass fracture surfaces

We report scanning tunneling microscope images of gold-coated fracture surfaces of soda lime glass and fused silica in the mirror region. The scans show a variety of nanometer scale features that are attributed to fracture phenomena at this scale. We find considerable similarity to the structures observed in regions of extensive crack branching (e.g., “mist”). The density of these features increases as one progresses away from the crack origin toward the mirror-mist boundary. Comparisons are made between soda lime glass and fused silica, revealing differences in the local deformation behavior of these two materials. Self-similarity of the observed structures is probed by measurements of the fractal dimension, Df, of the surfaces created in soda lime glass near the mirror-mist boundary, where we observe 2.17 > Df > 2.40.