Correspondence of CT perfusion imaging to pathological manifestations in rabbit models of hyperacute cerebral infarction

BACKGROUND： Could the infarction be diagnosed quickly and accurately at the acute stage by CT perfusion imaging （CTPI） technology？ Whether the images of CTPI will correspond with the pathological changes or not？ All the questions need to be solved by experimental and clinical studies. OBJECTIVE： To reveal the rules of perfusion map changes and guide the early diagnosis of hyperacute cerebral infarction by analyzing the correlation of CTPI with pathological manifestations for hyperacute cerebral infarction. DESIGN： A randomized controlled animal experiment. SETTING： Experimental Center of Medical Radiology, Longgang Central Hospital of Shenzhen City. MATERIALS： Forty-two adult New Zealand rabbits of （2.6±0.5） kg, either male or female, were randomly divided into experimental group （n =36） and control group （n =6）. Six rabbits in the experimental group were observed after ischemia for 0.5, 1, 2, 3, 4 and 6 hours respectively, and 1 rabbit in the control group was observed at each corresponding time point. METHODS： The experiments were carried out in the Experimental Center of Medical Radiology, Longgang Central Hospital of Shenzhen City from March 2003 to July 2004. Rabbit models of cerebral infarction were established by modified O＇Brein method. （1） The rabbits in the experimental group were scanned at 0.5, 1, 2, 3, 4 and 6 hours after ischemia respectively. The dynamic CT scan slice was 13 mm from the anterior edge of the frontal cortex, and six fake color functional images were obtained, including cerebral blood flow map （CBF map）, cerebral blood volume map （CBV map）, peak to enhancement map （PE map）, flow without vessels map, time to peak map （TP map）, time to start map （TS map）. The manifestations and changes of the functional maps in different interval were observed. （2） Bilateral symmetric ranges of interest （ROI） were drawn separately on the CBF map, CBV map, TP map and TS map. The blood flow parameters of focal and contralateral cerebral tissues could be obtained to calculate relative cerebral blood flow （rCBF, rCBF=focal CBF/contralateral CBF）, relative cerebral blood volume （rCBV, rCBV= focal CBV/contralateral CBV）, a relative time to peak （rTP, rTP= focal TP - contralateral TP）, a relative time to start （rTS, rTS= focal TP - contralateral TP）. （3） The perfusion maps were input into AutoCAD software. The percents of ischemic cores and peri-ischemic areas accounting for contralateral cerebral hemisphere were calculated. （4） The animals were anesthetized and killed, then the cerebellum and low brain stem were taken out. The brain tissues were cut on coronal plane at 14 mm from the anterior edge of the frontal cortex, a 2-mm piece anterior to the incision, and a 3-mm piece posterior to the incision. The anterior piece was fixed, stained and observed. A 1-mm slice was cut from the front of the posterior piece tissues as electron microscope sample, the remnant was fixed and then taken out, and the location and size of stained ＂white＂ areas were observed as the reference for electron microscope sample. （5） The correlation between CTPI and pathological manifestations was observed. MAIN OUTCOME MEASURES： （1） Laws of time and spatial changes of ischemic areas; （2） Pathological changes of the ischemic tissues; （3） Correspondency between CTPI and pathological manifestations. RESULTS： （1） Laws of time and spatial changes of ischemic areas： Relative ischemic-core areas were consistent in each perfusion map, increased incessantly along with the ischemic times. Relative peri-ischemic areas were inconsistent in each perfusion map, on CBF map from 1 to 6 hours after ischemia, the area of ischemic core increased from （1.503±0.523）% to （7.125± 1.054）%, the ascending trend occurred. But the peri-ischemic areas showed a descending trend on CBF map, the areas decreased from （8.960±0.719）% to （5.445 ± 0.884）% from 0.5 to 6 hours; The relative areas were the largest one on TP maps, the average value was （32.796±3.029）% at 0.5 hour after ischemia happening （60.540±1.683）% at 6 hours. The trend of ischemic areas was increased. No obvious change was observed on TS maps. （2） Pathological changes of the ischemic tissues： Under light microscope, there was no obvious change at 0.5- 2 hours after ischemia, edema at 3 hours, karyopycnosis at 4 hours and eosinophilous changes at 6 hours; Under electron microscope, there was edema in ischemic cores within 4 hours after ischemia, whereas karyopycnosis or structure vanished after 4 hours; Edema was observed in peri-ischemic areas. （3） Correlation between CTPI and pathological manifestations： On CTPI maps, the ischemic core was blue on CBF and CBV maps, black on TP and TS maps. Along with the ischemic times, the rCBF and rCBV decreased, whereas the rTP and rTS prolonged. Hemodynamic parameters were not significantly different within 2 hours of ischemia and 2 hours after ischemia. The rTP and rTS became 0 after 1 and 2 hours respectively. On CTPI maps the peri-ischemic area was red on CBF and CBV maps, red and yellow on TS maps, red on TP maps. Along with the ischemic times, the rCBF decreased, and the lowest level was always at about 20%, whereas the rTP and rTS prolonged. CONCLUSION： （1） CTPI manifestations corresponded well with pathological findings, and it is a sensitive, stable and reliable technique to diagnose hyperacute cerebral infarction. （2） TP map was more sensitive than CBF map and TS map in exhibiting the peri-ischemic areas, thus TP maps could be a good choice for observing peri-ischemic areas.

Cerebrospinal fluid flow in empty sella syndrome and normal sellar regions measured by phase-contrast quantitative magnetic resonance

We used MRI to examine 38 healthy females and 38 female patients with empty sella syndrome. Cerebrospinal fluid flow was examined in six regions of interest, including the anterior clinoid processes, posterior clinoid processes, and 1.0 mm, 1.0 mm, 2.0 mm, --2.0 mm from the midpoint of the line between the anterior and posterior clinoid processes. The results revealed no significant differences in cerebrospinal fluid flow velocity and discharge in a single cardiac cycle, or indicators of cardiac cycles in the control group, indicating that the cerebrospinal fluid flow was relatively steady in the saddle area of the normal brain. In the empty sella syndrome group, cerebrospinal fluid hernia into the saddle area triggered a fluctuation of the anterior and posterior clinoid processes in the saddle area, while the flow in other regions in the saddle area was relatively steady this resulted in significant differences in cerebrospinal fluid flow velocity and discharge, as well as the cardiac cycle.

Multi-time Collaborative Restoration for Integrated Electrical-gas Distribution Systems Based on Rolling Optimization

This paper proposes a multi-time collaborative restoration model for integrated electricity-gas distribution sys-tems(IEGDSs)considering multiple resources after extreme weather events.Based on the linearized power flow constraints of the unbalanced electrical distribution system(EDS)and gas distribution system(GDS),this problem can be formulated as a mixed-integer linear programming(MILP)model.To improve the efficiency and veracity of the solution,a rolling optimiza-tion based two-stage method is developed with the first stage solved by a linear approximation model,and the second stage solved by real-time updated rolling optimization.By solving the MILP problem using rolling optimization,the proposed model and solution method achieve efficient and reliable collaborative restoration of IEGDS considering multiple resources and unbal-anced operation characteristics of EDS.The effectiveness of the proposed model and method is validated by using an IEGDS made of a 37-bus unbalanced EDS and 11-node GDS.Index Terms-Electricity-gas system,mix-integer linear programming,power system restoration.

Estimation of ballistic coefficients of space debris using the ratios between different objects

This paper proposes a new method to estimate the ballistic coefficient（BC） of low earth orbit space debris.The data sources are the historical two-line elements（TLEs）.Since the secular variation of semi-major axes is mainly caused by the drag perturbation for space objects with perigee altitude below 600 km,the ballistic coefficients are estimated based on variation of the mean semi-major axes derived from the TLEs.However,the approximate parameters used in the calculation have error,especially when the upper atmosphere densities are difficult to obtain and always estimated by empirical model.The proportional errors of the approximate parameters are cancelled out in the form of ratios,greatly mitigating the effects of model error.This method has been also been validated for space objects with perigee altitude higher than 600 km.The relative errors of estimated BC values from the new method are significantly smaller than those from the direct estimation methods used in numerical experiments.The estimated BC values are used for the prediction of the semi-major axes,and good performance is obtained.This process is also a feasible method for prediction over a long period of time without an orbital propagator model.