Assessment of blood flow velocity and pulsatility in cerebral perforating arteries with 7-T quantitative flow MRI.

Thus far, blood flow velocity measurements with MRI have only been feasible in large cerebral blood vessels. High-field-strength MRI may now permit velocity measurements in much smaller arteries. The aim of this proof of principle study was to measure the blood flow velocity and pulsatility of cerebral perforating arteries with 7-T MRI. A two-dimensional (2D), single-slice quantitative flow (Qflow) sequence was used to measure blood flow velocities during the cardiac cycle in perforating arteries in the basal ganglia (BG) and semioval centre (CSO), from which a mean normalised pulsatility index (PI) per region was calculated (n = 6 human subjects, aged 23-29 years). The precision of the measurements was determined by repeated imaging and performance of a Bland-Altman analysis, and confounding effects of partial volume and noise on the measurements were simulated. The median number of arteries included was 14 in CSO and 19 in BG. In CSO, the average velocity per volunteer was in the range 0.5-1.0 cm/s and PI was 0.24-0.39. In BG, the average velocity was in the range 3.9-5.1 cm/s and PI was 0.51-0.62. Between repeated scans, the precision of the average, maximum and minimum velocity per vessel decreased with the size of the arteries, and was relatively low in CSO and BG compared with the M1 segment of the middle cerebral artery. The precision of PI per region was comparable with that of M1. The simulations proved that velocities can be measured in vessels with a diameter of more than 80 µm, but are underestimated as a result of partial volume effects, whilst pulsatility is overestimated. Blood flow velocity and pulsatility in cerebral perforating arteries have been measured directly in vivo for the first time, with moderate to good precision. This may be an interesting metric for the study of haemodynamic changes in aging and cerebral small vessel disease. © 2015 The Authors NMR in Biomedicine Published by John Wiley & Sons Ltd.

Influence of personalized extended interval dosing on the natalizumab wearing-off effect - a sub-study of the NEXT-MS trial.

BACKGROUND AND OBJECTIVES: Wearing-off symptoms during natalizumab treatment in multiple sclerosis are characterized by an increase of MS-related symptoms prior to natalizumab administration. The influence of extended interval dosing (EID) on wearing-off symptoms are important to consider, as this might cause hesitancy in initiating or continuing EID. METHODS: Participants of the NEXT-MS trial, in which treatment intervals are adjusted based on drug concentrations, were divided into two groups: an extended group containing participants with at least one week of additional interval extension, and a group with a fixed interval during the trial (range 4-7 weeks). Changes in the occurrence, frequency, onset, and severity of wearing-off symptoms were evaluated. RESULTS: 255 participants were included (extended group n = 171, fixed group n = 84). The odds on occurrence of wearing-off symptoms in the extended group did not increase after extending the treatment interval. Additional analyses for frequency, onset, and severity of wearing-off symptoms showed no changes over time. Mean decrease in natalizumab drug concentration did not influence the frequency of wearing-off symptoms. DISCUSSION: Wearing-off symptoms were not reinforced by further extending the natalizumab interval. Wearing-off symptoms might increase in a minority of patients after EID, although our data support the view that wearing-off symptoms appear to be unrelated to the decrease in natalizumab trough drug concentrations.

Automatic quantification of perivascular spaces in T2-weighted images at 7 T MRI.

Perivascular spaces (PVS) are believed to be involved in brain waste disposal. PVS are associated with cerebral small vessel disease. At higher field strengths more PVS can be observed, challenging manual assessment. We developed a method to automatically detect and quantify PVS. A machine learning approach identified PVS in an automatically positioned ROI in the centrum semiovale (CSO), based on -resolution T2-weighted TSE scans. Next, 3D PVS tracking was performed in 50 subjects (mean age 62.9 years (range 27-78), 19 male), and quantitative measures were extracted. Maps of PVS density, length, and tortuosity were created. Manual PVS annotations were available to train and validate the automatic method. Good correlation was found between the automatic and manual PVS count: ICC (absolute/consistency) is 0.64/0.75, and Dice similarity coefficient (DSC) is 0.61. The automatic method counts fewer PVS than the manual count, because it ignores the smallest PVS (length <2 mm). For 20 subjects manual PVS annotations of a second observer were available. Compared with the correlation between the automatic and manual PVS, higher inter-observer ICC was observed (0.85/0.88), but DSC was lower (0.49 in 4 persons). Longer PVS are observed posterior in the CSO compared with anterior in the CSO. Higher PVS tortuosity are observed in the center of the CSO compared with the periphery of the CSO. Our fully automatic method can detect PVS in a 2D slab in the CSO, and extract quantitative PVS parameters by performing 3D tracking. This method enables automated quantitative analysis of PVS.