高原脑水肿的CT研究

在青藏高原,随着西部大开发和高原旅游业的发展,高原脑水肿(high altitude cerebral edema,HACE)时有发生,患病率为0.5%～2.O%[1].HACE是急性高山病(acute mountain sickness,AMS)最为凶险的终末阶段,发病机制可能与缺氧导致脑充血水肿、颅内压升高和细胞功能障碍有关,确切机制尚不十分明了[2].     

Prognostic value of rCBF measurements and CT in focal cerebral ischemia

Summary CT is the most effective examination technique for studying the evolution of ischemic attacks, but if performed within the first 3 weeks it does not allow prognosis of possible evolution towards necrosis. CBF measurement and vasoreactivity tests under Althesin do allow this prognosis. Thirty patients whose evolution was checked clinically and by repeated CT examinations (89 in all) underwent CBF measurements (intra-arterial xenon 133) and vasoreactivity tests. In all cases (17 patients) where vasoreactivity had completely disappeared (inverse steal), the infarct evolved towards necrosis.     

PET attenuation coefficients from CT images: experimental evaluation of the transformation of CT into PET 511-keV attenuation coefficients

The CT data acquired in combined PET/CT studies provide a fast and essentially noiseless source for the correction of photon attenuation in PET emission data. To this end, the CT values relating to attenuation of photons in the range of 40-140 keV must be transformed into linear attenuation coefficients at the PET energy of 511 keV. As attenuation depends on photon energy and the absorbing material, an accurate theoretical relation cannot be devised. The transformation implemented in the Discovery LS PET/CT scanner (GE Medical Systems, Milwaukee, Wis.) uses a bilinear function based on the attenuation of water and cortical bone at the CT and PET energies. The purpose of this study was to compare this transformation with experimental CT values and corresponding PET attenuation coefficients. In 14 patients, quantitative PET attenuation maps were calculated from germanium-68 transmission scans, and resolution-matched CT images were generated. A total of 114 volumes of interest were defined and the average PET attenuation coefficients and CT values measured. From the CT values the predicted PET attenuation coefficients were calculated using the bilinear transformation. When the transformation was based on the narrow-beam attenuation coefficient of water at 511 keV (0.096 cm(-1)), the predicted attenuation coefficients were higher in soft tissue than the measured values. This bias was reduced by replacing 0.096 cm(-1) in the transformation by the linear attenuation coefficient of 0.093 cm(-1) obtained from germanium-68 transmission scans. An analysis of the corrected emission activities shows that the resulting transformation is essentially equivalent to the transmission-based attenuation correction for human tissue. For non-human material, however, it may assign inaccurate attenuation coefficients which will also affect the correction in neighbouring tissue.     

实验性大鼠脑损伤后血脑屏障、脑水肿的变化

目的　探讨实验性大鼠脑损伤后脑水肿发生的特点 ,以及干预脑水肿发生的意义。方法　应用流体冲击装置致大鼠脑损伤 ,通过对大鼠脑组织中伊文氏蓝 (EvansBlue ,EB)含量、脑组织内百分水含量、神经功能改变等的观测 ,探讨菲尼酮对大鼠创伤性脑损伤的影响。结果　大鼠脑损伤后 4小时 ,直接冲击侧以及对侧脑EB含量达高峰 ,冲击侧脑组织百分水含量在伤后 4小时明显增加 ,伤后 4天内出现明显的神经功能障碍 ;菲尼酮不同程度地降低了脑组织EB含量、百分水含量 ,神经功能得到一定程度的恢复。结论　流体冲击致大鼠脑损伤后 ,引起明显的血管内伊文氏蓝外渗、脑水肿 ,大鼠神经功能损伤 ,菲尼酮可明显阻止以上变化 ,由此说明白三烯是引起大鼠血脑屏障 (blood brainbarrier,BBB)开放的原因之一 ,说明脑损伤后减轻脑水肿是必要的。     

NMR in experimental cerebral edema: value of T1 and T2 calculations

In an experimental investigation, the efficacy of nuclear magnetic resonance (NMR) relaxation times in measuring brain water was studied. Cerebral edema was induced in four dogs with a freeze lesion, which was produced by contact with a steel cylinder cooled in liquid nitrogen and placed on the exposed dural surface of the brain. NMR proton imaging was performed 2, 3, 6, or 24 hr after production of the lesion, at a field strength of 0.35 T, using multiparametric spin-echo (SE) technique. The animals were sacrificed immediately after imaging, and brain samples were analyzed for water content (wet-to-dry, microgravimetry). Correlation between water content, NMR imaging, and resulting T1, T2 relaxation times and mobile proton density values calculated with SE technique was performed. Brain sample analysis showed elevation of water content in the white matter subjacent to the lesion in all four dogs, rising at least 15% in each of the animals. NMR imaging detected the freeze lesion and subjacent vasogenic edema of the white matter in all animals. The 2 sec pulse interval SE technique was most sensitive in the detection of the abnormality, and provided optimal differentiation of gray and white matter. The second echo sampling (56 msec) was most sensitive to the detection of edema. The T1 and T2 relaxation values, as well as the mobile proton density values, were elevated in the normal gray matter and in the abnormal white matter when compared with normal white matter in any given animal.(ABSTRACT TRUNCATED AT 250 WORDS)     

CT and MRI demonstration of cerebral edema in preeclampsia: a report of two cases

In two patients with visual disturbances occurring in preeclampsia CT and MR imaging findings are discussed. Clinical and radiological follow-up indicate reversible edema formation as the most probable cause of the neurological symptoms described. Correspondence to: P.J. Versluis     

Serial changes in CT cerebral blood volume and flow after 4 hours of middle cerebral occlusion in an animal model of embolic cerebral ischemia

BACKGROUND AND PURPOSE: Neuroimaging techniques have the potential to improve acute stroke treatment by selecting the appropriate patients for thrombolytic therapy. In this study, we examined changes in cerebral blood flow (CBF) and cerebral blood volume (CBV) in an animal model of middle cerebral artery occlusion and used these to identify the parameters that best differentiate between oligemic and infarct regions. MATERIALS AND METHODS: Permanent middle cerebral artery occlusion was performed in 17 New Zealand white rabbits. CT perfusion imaging was performed before (baseline), 10, and 30 minutes after the stroke, and then every 30 minutes up to 3 hours. After a final scan at 4 hours, the brain was removed, cut corresponding to CT sections, and stained with 2,3,5-triphenyltetrazolium chloride (TTC) to identify infarcted tissue. A logistic regression model with the 4-hour post-CBF and -CBV values as independent variables was used to determine the binary tissue outcome variable (oligemia or infarction). RESULTS: Infarcted regions were characterized by a significant decrease (P < .005) in both CBV and CBF, whereas oligemic (CBF < 25 mL . 100 g(-1) . min(-1), not infarcted) regions showed a significant decrease (P < .005) in CBF with maintenance of CBV at or near baseline values. From the perfusion parameters at the 4-hour time point, logistic regression by using CBV*CBF resulted in a sensitivity of 90.6% and a specificity of 93.3% for infarction. CONCLUSION: CBF and CBV values obtained from CT perfusion imaging can be used to distinguish between oligemic and infarct regions. This information could be used to assess the viability of ischemic brain tissue.     

The low attenuation area on dual-energy perfusion CT: correlation with the pulmonary function tests and quantitative CT measurements

Purpose

To retrospectively investigate the distribution of the low attenuation area (LAA) on dual energy perfusion CT (DEpCT) in comparison with the results of pulmonary function tests (PFTs) and quantitative CT measurements.

Materials and methods

Twenty-eight patients (15 male and 13 female; mean age: 62.21 years) underwent DEpCT and PFTs within a 1-month interval. The ranges of the LAA on DEpCT were classified into six groups with attenuation values of 0–3, 0–5, 0–8, 0–10, 0–13 and 0–15 HU and the ratios of LAA in each group were compared with the percentage of forced expiratory volume in the 1st second (%FEV_1.0), FEV_1.0/forced vital capacity (FEV_1.0/FVC) and the relative area of the lung with attenuation coefficients lower than −950 HU (RA₋₉₅₀).

Results

The LAAs on the DEpCT images were significantly correlated with the RA₋₉₅₀, %FEV_1.0 and FEV_1.0/FVC, and the regression analysis showed that the best values of LAA on DEpCT were 0–10 HU with RA₋₉₅₀ (r = 0.63), 0–8 HU with %FEV_1.0 (r = −0.52) and 0–8 HU with FEV_1.0/FVC (r = −0.61) per patient.

Conclusion

The iodine disturbance on DEpCT had a moderate correlation with the results of the PFTs and RA₋₉₅₀, but further examination would be needed for evaluation of iodine distribution.     

Reliability of attenuation measurements in CT of the lumbar spine: evaluation with an anthropomorphic phantom

A phantom was constructed with the intention of simulating the clinical situation at examination of the spine. Artifacts from bony vertebral structures were analyzed and the uniformity in a body-shaped object was studied. Tests were carried out on eight CT scanners. A considerable variation in uniformity was found between the tested scanner models. The CT numbers within the spinal canal and in a region anterior to the spine were elevated for most of the scanners. The deviation varied considerably, however, between models.     

Renal cyst pseudo-enhancement:influence of multidetector CT reconstrnction algorithm and renal attenuation in experimental study

目的:采用试验模型研究不同重建算法和肾强化程度对肾囊肿假性强化的影响.方法:设计一个可变化浓度的模拟肾脏的体模和模拟不同直径肾内囊肿的试管作为研究对象.将肾浓度设定为40、100、140及240 HU.两种MSCT机均采用腹部螺旋扫描模式,层厚分别为5 mm和1 mm.Siemens双能CT使用B30和B70两种重建算法,GEMSCT机使用standard和bone两种重建算法.对比分析肾强化程度及重建算法对肾囊肿CT值测定的影响;同时比较囊肿在不同层厚下CT值的差异,分析产生假性强化的原因.结果:假性强化在两种CT机型和不同的重建算法中均可发生,假性强化程度为11.47～17.46HU.虽然两种CT机均可出现假性强化现象,但GE MSCT机发生的概率高于Siemens双能CT.Siemens双源CT仅在240 HU背景浓度、B70算法时出现囊肿假性强化,重建算法对其影响较大.背景浓度为240 HU时GE MSCT机均可发生假性强化现象,GE MSCT机不同重建算法和层厚对是否产生肾囊肿假性强化影响不大(P＞0.05).结论:肾囊肿假性强化是客观存在的,它受多种因素的影响.重建算法的B值越大出现假性强化现象的概率越高,较高的肾脏强化程度同样会增加假性强化发生的概率.     

A magnetic resonance imaging study of experimental cerebral edema and its response to dexamethasone

Vasogenic edema following cortical freezing, and its response to dexamethasone were studied in cats. The time course of the edema shown by MRI was the same as that observed by invasive techniques. Dexamethasone retards early edema formation and may reduce its total volume, but does not accelerate its disappearance.     

Diagnostic value of attenuation measurements of the kidney on unenhanced helical CT of obstructive ureterolithiasis

OBJECTIVE: The objective of this study was to assess the diagnostic value of attenuation measurements of the kidney on unenhanced helical CT in patients with obstructive ureterolithiasis. MATERIALS AND METHODS: Consecutive unenhanced helical CT scans of patients referred for acute unilateral renal colic were retrospectively reviewed. Patients with CT evidence of other urinary system diseases were excluded. Included scans (n = 145) were assessed for ureteral stone and secondary signs of obstruction such as unilateral collecting system or ureteral dilatation, perinephric stranding, and periureteral edema. Renal attenuation in Hounsfield units was measured in the upper, middle, and lower portions of the parenchyma, and a mean value was determined for each kidney. RESULTS: Ureteral stones were present in 76 patients. Renal attenuation on the side with lithiasis was lower than on the opposite kidney: 27.2 +/- 3.9 H vs 32.6 +/- 3.4 H (p < 0.001). Attenuation differences between kidneys were higher for patients with ureterolithiasis: 5.4 +/- 3.2 H (range, -3.3 to 13.0 H) versus 1.2 +/- 1.0 H (range, 0-4.7 H) (p < 0.001). An attenuation difference between kidneys greater than or equal to 5.0 H had 61% sensitivity, 100% specificity, 100% positive predictive value, 69% negative predictive value, and 79% accuracy for diagnosis of ureteral lithiasis. CONCLUSION: Attenuation difference between kidneys greater than or equal to 5.0 H was a valuable sign and had diagnostic performance similar to other secondary signs of obstructive ureterolithiasis. Furthermore, attenuation difference had the advantage of being an objective, measurement-based indicator.     

Serial CT and MRI of ischaemic cerebral infarcts: frequency and clinical impact of haemorrhagic transformation

The frequency, predisposing factors and clinical consequences of haemorrhagic infarcts and damaged blood-brain barrier as shown by contrast enhancement (CE) in ischaemic cerebral infarcts are controversial. We prospectively compared the sensitivity of CT and MRI to haemorrhagic transformation (HT) and CE. We also wished to investigate the clinical significance of HT and factors possibly associated with it. We studied 36 patients with acute ischaemic infarcts in the middle cerebral artery territory during the first 2 weeks after the ictus. After CT and rating of the neurological deficit on admission, serial examinations with clinical neuromonitoring, contrast-enhanced CT and MRI were done on the same day. The occurrence and severity of HT were correlated with CE, stroke mechanism, infarct size, development of neurological deficits and antithrombotic treatment. The frequency of HT detected by MRI was 80 %. CE usually preceded HT or was seen simultaneously. MRI had a higher sensitivity than CT to HT and CE. Severity of HT was positively correlated with infarct size (P < 0.01). HT had no influence on patient's neurological status. Neither the type of antithrombotic treatment nor the stroke mechanism was associated with the severity of HT. No parenchymal haemorrhage occurred. Received: 10 November 1998 Accepted: 29 July 1999     

The role of aortic wall CT attenuation measurements for the diagnosis of acute aortic syndromes

Objectives

To determine if measurements of aortic wall attenuation can improve the CT diagnosis of acute aortic syndromes.

Methods

CT reports from a ten year period were searched for acute aortic syndromes (AAS). Studies with both an unenhanced and a contrast enhanced (CTA) series that had resulted in the diagnosis of intramural hematoma (IMH) were reviewed. Diagnoses were confirmed by medical records. The attenuation of aortic wall abnormalities was measured. The observed attenuation threshold was validated using studies from 39 new subjects with a variety of aortic conditions.

Results

The term “aortic dissection” was identified in 1206, and IMH in 124 patients’ reports. IMH was confirmed in 31 patients, 21 of whom had both unenhanced and contrast enhanced images. All 21 had pathologic CTA findings, and no CTA with IMH was normal. Attenuation of the aortic wall was greater than 45 HUs on the CTA images in all patients with IMH. When this threshold was applied to the new group, sensitivity for diagnosing AAS was 100% (19/19), and specificity 94% (16/17). Addition of unenhanced images did not improve accuracy.

Conclusions

Measurements of aortic wall attenuation in CTA have a high negative predictive value for the diagnosis of acute aortic syndromes.     

急性脑静脉闭塞CT灌注成像的实验研究

目的观察脑静脉闭塞模型脑实质损害区CT灌注成像（CTP）变化规律,探讨该模型在该病研究中的价值。方法新西兰大白兔28只,随机分为2组（实验组24只,对照组4只）。一侧颈内静脉注入醋酸纤维素聚合物（CAP）合并双侧颈外静脉结扎术后1、3、6、12、24和48h行CTP检查对各组模型的脑血流动力学改变进行观察。结果实验组21只造模成功,其中3h及12h组各有1只在CTP上无明显异常表现,有19只CTP检查示脑血流灌注异常。术后1～3h,病变区脑血容量（CBV）轻度增加或正常,脑血流量（CBF）轻度降低,平均通过时间（MTT）稍延长;6～12h后病变中心区主要表现为CBV和CBF降低,MTT延长,而病变边缘区CBV增加或正常或轻度降低,CBF降低,MTT缩短;12～24h后病变中心区和边缘区CBV和CBF均明显降低,MTT明显延长。各时段病变中心区和边缘区的CBV%、CBF%、MTT%的差异均有统计学意义（P值均〈0.05）。对照组未见上述各种异常表现。结论 CT灌注成像可准确、敏感地反映急性脑静脉闭塞模型的血流动力学改变。     

CT attenuation measurements are valuable to discriminate pledgetsused in prosthetic heart valve implantation from paravalvular leakage

Objectives

Sutures with polytetrafluorethylene (PTFE) felt pledgets are commonly used in prosthetic heart valve (PHV) implantation. Paravalvular leakage can be difficult to distinguish from PTFE felt pledgets on multislice CT because both present as hyperdense structures. We assessed whether pledgets can be discriminated from contrast-enhanced solutions (blood/saline) on CT images based on attenuation difference in an ex vivo experiment and under in vivo conditions.

Methods

PTFE felt pledgets were sutured to the suture ring of a mechanical PHV and porcine aortic annulus, and immersed and scanned in four different contrast-enhanced (Ultravist®; 300 mg jopromide ml⁻¹) saline concentrations (10.0, 12.0, 13.6 and 15.0 mg ml⁻¹). Scanning was performed on a 256-slice scanner with eight different scan protocols with various tube voltage (100 kV, 120 kV) and tube current (400 mAs, 600 mAs, 800 mAs, 1000 mAs) settings. Attenuation of the pledgets and surrounding contrast-enhanced saline were measured. Additionally, the attenuation of pledgets and contrast-enhanced blood was measured on electrocardiography (ECG)-gated CTA scans of 19 patients with 22 PHVs.

Results

Ex vivo CT attenuation differences between the pledgets and contrast-enhanced solutions were larger by using higher tube voltages. CT attenuation values of the pledgets were higher than contrast-enhanced blood in patients: 420±26 Hounsfield units (mean±SD, range 383–494) and 288±41 Hounsfield units (range 202–367), respectively.

Conclusions

PTFE felt pledgets have consistently higher attenuation than surrounding contrast-enhanced blood. CT attenuation measurements therefore may help to differentiate pledgets from paravalvular leakage, and detect paravalvular leakage in patients with suspected PHV dysfunction.In 2003, approximately 290 000 patients underwent prosthetic heart valve (PHV) implantation worldwide [1]. During PHV implantation, the affected native valve is excised and replaced by a mechanical or biological PHV. The PHV is fixated by sutures that are placed through the suture ring of the PHV and the aortic or mitral annulus. To prevent the suture from being pulled through the annular tissue, polytetrafluoroethylene (PTFE) pledged sutures are commonly used. These sutures have a PTFE absorbent pad attached to the suture, which disperses the pressure of the single suture on the annulus [2,3].Paravalvular leakage, defined as blood flow outside the suture ring through the annulus, is a relatively common echocardiographic finding after PHV implantation [4]. Paravalvular leakage is reported in up to 15% of patients after mitral valve replacement (MVR) and in up to 10% of patients after aortic valve replacement (AVR) [5-7]. Paravalvular leakage is mainly caused by (i) incomplete apposition of the PHV suture ring to the native annular tissue, (ii) suture dehiscence or rupture, or (iii) infective PHV endocarditis [8]. Paravalvular leakage is one of the most common causes for reoperation after PHV implantation.In daily clinical routine, suspected PHV dysfunction is evaluated by transthoracic and transoesophageal echocardiography (TTE and TOE). TTE is the first-line imaging method to detect paravalvular leakage. In patients with acoustic shadowing caused by the PHV material, TOE can be of additional diagnostic value especially for valves in the mitral position.Multislice CT (MSCT) has recently been shown to have complementary value to echocardiography to evaluate PHV dysfunction [9,10]. Paravalvular leakage is visualised on MSCT as contrast-enhanced blood next to the valve prosthesis at the level of the annulus. In our experience, it can be difficult to differentiate paravalvular leakage from the PTFE felt pledgets on CT angiography (CTA) scans, because of the similar location and hyperdense appearance. Thus diagnostic dilemmas may arise. Additional non-contrast-enhanced scans may help to differentiate paravalvular leakage from pledgets, but with the disadvantage of additional radiation exposure.Currently no data are available on the normal MSCT imaging characteristics of PTFE felt pledgets. The purpose of this study was (i) to determine normal MSCT imaging characteristics of PTFE felt pledgets both ex vivo and in vivo, and (ii) to examine the possibility of distinguishing PTFE felt pledgets from contrast-enhanced blood (paravalvular leakage) based on the level of Hounsfield units.