Correlation of early dynamic CT perfusion imaging with whole-brain MR diffusion and perfusion imaging in acute hemispheric stroke

BACKGROUND AND PURPOSE: Compared with MR imaging, dynamic CT perfusion imaging covers only a fraction of the whole brain. An important assumption is that CT perfusion abnormalities correlate with total ischemic volume. The purpose of our study was to measure the degree of correlation between abnormalities seen on CT perfusion scans and the volumes of abnormality seen on MR diffusion and perfusion images in patients with acute large-vessel stroke. METHODS: Fourteen patients with acute hemispheric stroke symptoms less than 12 hours in duration were studied with single-slice CT perfusion imaging and multislice MR diffusion and perfusion imaging. CT and MR perfusion studies were completed within 2.5 hours of one another (mean, 77 minutes) and were reviewed independently by two neuroradiologists. Hemodynamic parameters included cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). Extents of abnormality on images were compared by using Kendall correlation. RESULTS: Statistically significant correlation was found between CT-CBF and MR-CBF abnormalities (tau = 0.60, P =.003) and CT-MTT and MR-MTT abnormalities (tau = 0.65, P =.001). Correlation of CT-CBV with MR-CBV approached significance (tau = 0.39, P =.06). Extent of initial hyperintensity on diffusion-weighted images correlated best with extent of MR-CBV abnormality (tau = 0.69, P =.001), extent of MR-MTT abnormality (tau = 0.67, P =.002), and extent of CT-CBV abnormality (tau = 0.47, P =.02). CONCLUSION: Good correlation was seen between CT and MR for CBF and MTT abnormalities. It remains uncertain whether CT perfusion CBV abnormalities correspond well to whole-brain abnormalities.     

Dynamic CT perfusion imaging with acetazolamide challenge for evaluation of patients with unilateral cerebrovascular steno-occlusive disease

BACKGROUND AND PURPOSE: Perfusion CT (PCT) has the ability to measure quantitative values and produce maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). We assessed cerebral hemodynamics by using these parameters and acetazolamide challenge in patients with cerebrovascular steno-occlusive disease. METHODS: Fifteen patients underwent PCT with acetazolamide challenge. Comparison of mean CBF, CBV, and MTT was determined between hemispheres and before and after acetazolamide challenge. Hemispheric ratio and percent change due to acetazolamide administration were also calculated. Absolute values and percent changes 2 SDs outside the mean from the nonstenotic hemispheres were defined as abnormal. RESULTS: Significant decreases in CBF (-25.1%, P = .003) and significant increases in MTT (47.1%, P < .001) were found in stenotic hemispheres. After acetazolamide challenge, significant changes in CBF (-39.5%, P < .001) and MTT (92.9%, P < .001) were also seen. The acetazolamide test significantly decreased CBF hemispheric ratio (-20.3%, P < .001) and increased MTT hemispheric ratio (30.8%, P = .002), making both maps more asymmetric. Significance in CBF and MTT percent changes (P < .001 and P = .005, respectively) was found between hemispheres. When CBF percent changes were assumed to represent the true determinant of hemodynamic impairment, normal ranges of baseline MTT value and MTT percent changes demonstrated sensitivities of 66.7% and 100% and specificities of 58.3% and 75%, respectively, for detecting patients with hemodynamic impairment. CONCLUSION: Parameters obtained from PCT with acetazolamide are promising for the evaluation of cerebral hemodynamics in patients with cerebrovascular steno-occlusive disease.     

320排动态容积CT全脑灌注成像技术在脑梗死中的临床应用

目的:探讨320排动态容积CT全脑灌注成像技术在脑梗死诊断中的优势及临床应用价值。方法:对42例脑梗死患者行CT全脑灌注成像,一次对比剂注射得到平扫容积图像、CT血管成像图像及全脑灌注图像,综合运用这三种检查方法全面评估脑梗死。结果:42例脑梗死患者共发现18例存在缺血半暗带(IP),其中8例超急性期6例存在IP,19例急性期8例存在IP,15例亚急性期4例存在IP。42例梗死核心区与健侧对应区比较,脑血容量(CBV)、血流量(CBF)、平均通过时间(MTT)及达峰时间(TTP)值差异均具统计学意义(P<0.05)。18例IP区与梗死核心区比较,CBV、CBF、MTT及TTP值差异均具统计学意义(P<0.05),与健侧对应区比较,CBV值差异无统计学意义(P>0.05)。结论:急性期及亚急性期脑梗死仍可能存在IP。应用320排容积CT全脑灌注成像,对脑梗死患者可明确其责任血管的狭窄部位及程度,了解病变范围及有无IP存在,实现对脑梗死的全面评估。     

First-pass quantitative CT perfusion identifies thresholds for salvageable penumbra in acute stroke patients treated with intra-arterial therapy

BACKGROUND AND PURPOSE: The purpose of this study was to determine whether, in acute stroke patients treated with intra-arterial (IA) recanalization therapy, CT perfusion (CTP) can distinguish ischemic brain tissue destined to infarct from that which will survive. METHODS: Dynamic CTP was obtained in 14 patients within 8 hours of stroke onset, before IA therapy. Initial quantitative cerebral blood volume (CBV) and flow (CBF) values were visually segmented and normalized in the "infarct core" (region 1: reduced CBV and CBF, infarction on follow-up), "penumbra that infarcts" (region 2: normal CBV, reduced CBF, infarction on follow-up), and "penumbra that recovers" (region 3: normal CBV, reduced CBF, normal on follow-up). Normalization was accomplished by dividing the ischemic region of interest value by that of a corresponding, contralateral, uninvolved region, which resulted in CBV and CBF "ratios." Separate CBV and CBF values were obtained in gray matter (GM) and white matter (WM). RESULTS: Mean CBF ratios for regions 1, 2, and 3 were 0.19 +/- 0.06, 0.34 +/- 0.06, and 0.46 +/- 0.09, respectively (all P < .001). Mean CBV ratios for regions 1, 2, and 3 were similarly distinct (all P < .05). Absolute CBV and CBF values for regions 2 and 3 were not significantly different. All regions with CBF ratio <0.32, CBV ratio <0.68, CBF <12.7 mL/100 g/min, or CBV <2.2 mL/100 g infarcted. No region with CBF ratio >0.44 infarcted. GM versus WM CBF and CBV values were significantly different for region 2 compared with region 3 (P < .05). CONCLUSIONS: In acute stroke patients, quantitative CTP can distinguish ischemic tissue likely to infarct from that likely to survive.     

Dynamic CT perfusion imaging of acute stroke

BACKGROUND AND PURPOSE: Because cerebral perfusion imaging for acute stroke is unavailable in most hospitals, we investigated the feasibility of a method of perfusion scanning that can be performed rapidly during standard cranial CT. Our aim was to identify the scanning parameters best suited to indicate tissue at risk and to measure a perfusion limit to predict infarction. METHODS: Seventy patients who had suffered stroke and had undergone cranial CT 0.5 to 12 hours (median, 3.75 hr) after the onset of symptoms participated in the study. While undergoing conventional CT, each patient received a bolus of iodinated contrast medium. Maps of time to peak (TTP), cerebral blood volume (CBV), and CBF were calculated from the resulting dynamically enhanced scans. These perfusion images were compared with follow-up CT scans or MR images showing the final infarctions. RESULTS: CBF maps predicted the extent of cerebral infarction with a sensitivity of 93% and a specificity of 98%. In contrast, CBV maps were less sensitive and TTP maps were less specific and also showed areas of collateral flow. Infarction occurred in all of the patients with CBF reduction of more than 70% and in half of the patients with CBF reduction of 40% to 70%. CONCLUSION: Dynamic CT perfusion imaging safely detects tissue at risk in cases of acute stroke and is a feasible method for any clinic with a third-generation CT scanner.     

Perfusion CT and angio CT in the assessment of acute stroke

In order to evaluate the clinical utility of non-enhanced CT with perfusion and angio CT in the assessment of acute ischaemic stroke, 42 patients with symptoms of acute stroke were examined within the first 6 h from onset of symptoms with non-enhanced CT (NECT), perfusion CT (PCT) and CT angiography (CTA). Maps of cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) were analysed visually, and after drawing regions of interest (ROIs) in the territory of anterior, middle and posterior cerebral arteries, maximum-intensity projection and volume-rendering images of the cervical and cerebral vessels were created. All patients underwent a control CT or MR examination 24–48 h after the initial examination. Twenty-nine patients developed an area of infarction at control examinations. Significant perfusion abnormalities were found in 27 cases, whilst in two patients the perfusion studies were considered to be normal. All the cases with perfusion abnormalities showed arterial stenoses or occlusions on angio CT. Small infarctions at levels other than the ones selected for perfusion CT, and arteriosclerotic changes, were observed in the two cases with no perfusion abnormalities. In conclusion, combining non-enhanced CT with PCT and CTA is a simple and a very valuable tool in the initial assessment of acute stroke.     

局灶性脑缺血后脑血流变化及血流储备能力的CT评价

目的:应用动态增强CT灌注成像评价局灶性脑缺血后脑血流储备能力的变化。方法:将15只大鼠随机分为脑缺血0.5、1、3和6h组和假手术对照组,进行脑缺血静息态CT灌注测试。9只动物随机分为脑缺血0.5、1h组和假手术盐水组,进行脑缺血负荷CT灌注测试;脑缺血组动物CT扫描前给予乙酰唑胺静脉制剂Diamox,假手术盐水组CT扫描前给予相当量的生理盐水。所有动物24h行MRI和MRA扫描。结果:静息状态脑缺血后30min及以后各时间点CBF、CBV、MTT图及原始图像上均可见大脑中动脉供血区脑组织低灌注改变,0.5~1h低灌注范围逐渐扩大,程度加重,其后低灌注范围和程度变化不大。早期纹状体CBF和CBV降低,MTT延长,但皮质CBF轻度下降,CBV维持正常或略偏高水平,MTT延长,1h后CBF、CBV明显下降。负荷状态脑缺血30minCBF异常范围较静息时增大,纹状体和皮质CBF均已明显下降;脑缺血1h低灌注范围与静息状态相差无几但低灌注程度加重;提示以上两个时间点缺血区血流储备能力下降。假手术动物脑CT灌注图像上脑组织未出现灌注异常。结论:Diamox负荷前后脑灌注CT测定能够用于脑血流储备能力的评价。局灶性脑缺血后脑血流存在时间和空间上的变化规律,CBV是反映组织血流调节能力的一个指标,局灶性脑缺血后血流储备能力降低。     

Effects of dexamethasone on cerebral perfusion and water diffusion in patients with high-grade glioma

BACKGROUND AND PURPOSE: The mechanisms by which the glucocorticoid dexamethasone produces its therapeutic action in patients with intracranial tumors still remain unclear. The purpose of this study was to investigate whether dexamethasone affects cerebral perfusion and water molecule diffusion by using quantitative dynamic susceptibility contrast perfusion MR imaging (DSC-MR imaging) and diffusion tensor MR imaging (DT-MR imaging). METHODS: Ten consecutive patients with glioblastoma multiforme underwent DSC-MR imaging and DT-MR imaging before and 48-72 hours after dexamethasone treatment (16 mg/day). Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and water mean diffusivity () were measured for enhancing tumor, nonenhancing peritumoral edematous brain, and normal-appearing contralateral white matter before and after steroid therapy. The percentage change in CBF, CBV, MTT, and for the 3 tissue types was calculated for each patient, a mean value obtained for the population, and the statistical significance determined by using a paired-samples Student t test. RESULTS: After dexamethasone treatment, there was no significant change in tumor CBF, CBV, or MTT. Edematous brain CBV and MTT were also unchanged. There was, however, an increase in edematous brain CBF (11.6%; P = .05). was reduced in both enhancing tumor (-5.8%; P = .001) and edematous brain (-6.0%; P < .001). There was no significant change in CBF, CBV, MTT, or for normal-appearing contralateral white matter after treatment. CONCLUSION: These data suggest that dexamethasone does not significantly affect tumor blood flow but may, by reducing peritumoral water content and local tissue pressure, subtly increase perfusion in the edematous brain.     

Microvascular abnormality in relapsing-remitting multiple sclerosis: perfusion MR imaging findings in normal-appearing white matter

PURPOSE: To prospectively determine hemodynamic changes in the normal-appearing white matter (NAWM) of patients with relapsing-remitting multiple sclerosis (RR-MS) by using dynamic susceptibility contrast material-enhanced perfusion magnetic resonance (MR) imaging. MATERIALS AND METHODS: Conventional MR imaging (which included acquisition of pre- and postcontrast transverse T1-weighted, fluid-attenuated inversion recovery, and T2-weighted images) and dynamic susceptibility contrast-enhanced T2*-weighted MR imaging were performed in 17 patients with RR-MS (five men and 12 women; median age, 38.4 years; age range, 27.6-56.9 years) and 17 control patients (seven men and 10 women; median age, 42.0 years; age range, 18.7-62.5 years). Absolute cerebral blood volume (CBV), absolute cerebral blood flow (CBF), and mean transit time (MTT) (referenced to an arterial input function by using an automated method) were determined in periventricular, intermediate, and subcortical regions of NAWM at the level of the lateral ventricles. Least-squares regression analysis (controlled for age and sex) was used to compare perfusion measures in each region between patients with RR-MS and control patients. Repeated-measures analysis of variance and the Tukey honestly significant difference test were used to perform pairwise comparison of brain regions in terms of each perfusion measure. RESULTS: Each region of NAWM in patients with RR-MS had significantly decreased CBF (P <.005) and prolonged MTT (P <.001) compared with the corresponding region in control patients. No significant differences in CBV were found between patients with RR-MS and control patients in any of the corresponding areas of NAWM examined. In control patients, periventricular NAWM regions had significantly higher CBF (P =.03) and CBV (P =.04) than did intermediate NAWM regions. No significant regional differences in CBF, CBV, or MTT were found in patients with RR-MS. CONCLUSION: The NAWM of patients with RR-MS shows decreased perfusion compared with that of controls.     

Image quality in CT perfusion imaging of the brain

The purpose of this study was to evaluate the impact of various iodine contrast concentrations on image quality in computed tomography (CT) perfusion studies. Twenty-one patients with suspicion of cerebral ischemia underwent perfusion CT using two different iodine contrast concentrations: 11 patients received iomeprol 300 (iodine concentration: 300 mg/ml ) while ten received the same volume of iomeprol 400 (iodine concentration: 400 mg/ml). Scan parameters were kept constant for both groups. Maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and time to peak (TTP) were calculated from two adjacent slices. Quantitative comparisons were based on measurements of the maximum enhancement [Hounsfield units (HU)] and signal-to-noise index (SNI) on CBF, CBV, and TTP images. Determinations of grey-to-white-matter delineation for each iodine concentration were performed by two blinded readers. Only data from the non-ischemic hemispheres were considered. Both maximum enhancement and SNI values were higher after iomeprol 400, resulting in significantly better image quality in areas of low perfusion. No noteworthy differences were found for normal values of CBF, CBV, and TTP. Qualitative assessment of grey/white matter contrast on CBF and CBV maps revealed better performance for iomeprol 400. For brain perfusion studies, highly concentrated contrast media such as iomeprol 400 is superior to iomeprol 300.     

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.     

CT灌注扫描在脑肿瘤的临床应用

目的:研究颅内良恶性肿瘤多层螺旋CT各灌注参数的改变和肿瘤良恶性和脑内外肿瘤的鉴别诊断。方法:41例患者行脑血流的CT灌注扫描,其中脑内肿瘤26例(胶质瘤6例、脑脓肿2例、脑转移瘤17例、淋巴瘤1例),脑外肿瘤15例(颅骨转移瘤2例、垂体瘤7例、脑膜瘤2例、肉芽肿3例、蛛网膜囊肿1例)。应用去卷积算法模式计算相应病变区域的血流量(BF)、血容量(BV)、平均通过时间(MTT)、毛细血管通透性(PS)。根据不同肿瘤的相关参数图来评价良恶性肿瘤血流动力学状态。结果:41例脑肿瘤患者中,脑外肿瘤的CBF、CBV和PS明显高于脑内肿瘤,脑内肿瘤的恶性程度越高其CBF和PS越高,而MTT值与良性肿瘤组织无显著差异。结论:灌注参数CBF、CBV和PS可有效的评价脑肿瘤的血流状态,在脑部良恶性病变及脑内外肿瘤的鉴别诊断上有重要的临床应用价值。     

64层螺旋CT脑灌注成像评价急性脑梗死溶栓前后脑血流动力学改变

目的探讨64层螺旋CT脑灌注成像(CTP)在评价急性脑梗死溶栓疗效中的应用价值。资料与方法20例急性脑梗死患者于发病3~10h行常规CT平扫和CTP检查,其中16例行静脉溶栓、4例行动脉溶栓治疗。溶栓后2~7天复查CT平扫和CTP。对溶栓治疗前后病变区的脑血流量(CBF)、脑血容量(CBV)和达峰时间(TTP)进行定性和定量比较分析。结果20例中5例头颅CT平扫发现早期脑梗死征象,15例常规CT平扫未发现异常,CTP均发现与临床症状对应的脑灌注异常区,表现为CBF、CBV降低,TTP延迟。溶栓后15例脑灌注异常范围缩小,CBF和CBV增加,TTP缩短;3例脑灌注异常区范围扩大,CBF、CBV进一步降低,TTP延迟更加显著;2例出现局部过度灌注。统计学分析结果显示溶栓治疗后多数患者脑灌注情况明显改善,缺血边缘区CBF和TTP与溶栓前差异有统计学意义(P<0.05),缺血中心区CBF和CBV与溶栓前差异无统计学意义(P>0.05)。结论脑CTP检查能够观察溶栓治疗前后脑血流动力学指标的变化,为评价急性脑梗死患者的溶栓疗效提供重要依据。     

256层螺旋CT全脑灌注联合CTA在急性脑梗死诊断中的价值

目的 探讨256层MSCT全脑CTP与CTA技术相结合在急性脑梗死中的应用价值,并评估脑梗死与供血动脉状况的关系.方法 对21例临床拟诊急性脑梗死患者行常规CT平扫、CTP和CTA检查,重建并分析CT平扫图像、CTP及CTA图像,所有病例在CTP检查后24h内进行MRI＋ DWI检查.结果 21例脑梗死患者CTA发现33条动脉不同程度狭窄及闭塞,其中包括轻度狭窄4例,中度狭窄13例,重度狭窄7例,闭塞9例.21例患者CTP发现32处梗死灶,脑梗死中心区及周边区rCBF下降、TTP延长的差异在统计学上有显著性意义.结论 256层螺旋CT全脑CTP联合CTA扫描方法简便,可对缺血后脑组织供血动脉状况及血流动力学改变进行有效评价.     

Predicting cerebral ischemic infarct volume with diffusion and perfusion MR imaging

BACKGROUND AND PURPOSE: Diffusion and perfusion MR imaging have proved useful in the assessment of acute stroke. We evaluated the utility of these techniques in detecting acute ischemic infarction and in predicting final infarct size. METHODS: Diffusion and hemodynamic images were obtained in 134 patients within a mean of 12.3 hours of onset of acute ischemic stroke symptoms. We retrospectively reviewed patient radiology reports to determine the presence or absence of lesion identification on initial diffusion- (DW) and perfusion-weighted (PW) images. Radiologists were not blinded to the initial clinical assessment. For determination of sensitivity and specificity, the final discharge diagnosis was used as the criterion standard. Neurologists were not blinded to the DW or PW imaging findings. In 81 patients, acute lesions were compared with final infarct volumes. RESULTS: Sensitivities of DW imaging and cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) perfusion parameters were 94%, 74%, 84%, and 84%, respectively. Specificities of DW imaging, CBV, CBF, and MTT were 96%, 100%, 96%, and 96%, respectively. Results were similar in 93 patients imaged within 12 hours. In 81 patients with follow-up, regression analysis yielded r(2) = 0.9, slope = 1.24 for DW imaging; r(2) = 0.84, slope = 1.22 for CBV; r(2) = 0.35, slope = 0.44 for CBF; and r(2) = 0.22, slope = 0.32 for MTT, versus follow-up volume. A DW-CBV mismatch predicted additional lesion growth, whereas DW-CBF and DW-MTT mismatches did not. Results were similar in 60 patients imaged within 12 hours. CONCLUSION: Diffusion and hemodynamic images are sensitive and specific for detecting acute infarction. DW imaging and CBV best predict final infarct volume. DW-CBV mismatch predicts lesion growth into the CBV abnormality. CBF and MTT help identify additional tissue with altered perfusion but have lower correlation with final volume.     

Improvement of image quality and radiation dose of CT perfusion of the brain by means of low-tube voltage (70 KV)

Objectives

To investigate the feasibility of 70 kV cerebral CT perfusion by comparing image quality and radiation exposure to 80 kV.

Methods

Thirty patients with suspected cerebral ischemia who underwent dual-source CT perfusion were divided into group A (80 kV, 150 mAs) and group B (70 kV, 150 mAs). Quantitative comparisons were used for maximum enhancement, signal-to-noise index (SNI), and values of cerebral blood flow (CBF), cerebral blood flow (CBV), mean transit time (MTT) on CBF, CBV, and MTT images, and radiation dose from these two groups. Qualitative perfusion images were assessed by two readers.

Results

Maximum enhancement for group B was higher than group A (P?<?0.05). There were no significant differences between the two groups for SNI on CBF and CBV maps (P?=?0.06 – 0.576), but significant differences for MTT when SNI was measured on frontal white matter and temporo-occipital white matter (P?<?0.05). There were no differences among values of CBF, CBV, and MTT for both groups (P?=?0.251–0.917). Mean image quality score in group B was higher than group A for CBF (P?<?0.05), but no differences for CBV (P?=?0.542) and MTT (P?=?0.962). Radiation dose for group B decreased compared with group A.

Conclusions

70 kV cerebral CT perfusion reduces radiation dose without compromising image quality.

Key Points

? Radiation dose is a key concern with the increased using cerebral CT perfusion. Cerebral CT perfusion of 70 kV reduces radiation dose without compromising image quality. ? A 70-kV protocol could be used for cerebral CT perfusion.     

CT sign of brain swelling without concomitant parenchymal hypoattenuation: comparison with diffusion- and perfusion-weighted MR imaging

PURPOSE: To retrospectively evaluate the apparent diffusion coefficient (ADC) on magnetic resonance (MR) images and the perfusion parameters of lesions that show brain swelling without concomitant parenchymal hypoattenuation on computed tomographic (CT) scans. MATERIALS AND METHODS: Review board approval was obtained, and informed consent was waived. A total of 14 patients (seven men and seven women; mean age, 64 years +/- 11) were retrospectively selected from the consecutive 172 patients with acute cerebral ischemia who underwent CT within 6 hours of symptom onset. All patients had brain swelling without parenchymal hypoattenuation, including loss of gray-white matter distinction on CT scans, and they underwent diffusion- and perfusion-weighted MR imaging shortly after CT. CT attenuation, ADC, and perfusion parameters of relative cerebral blood volume (CBV), time to peak (TTP), and relative cerebral blood flow (CBF) were calculated for gray and white matter of the lesion. The measured values were compared with those of the contralateral hemisphere by using the paired t test; comparison of values of perfusion parameters among three subgroups was performed with the Kruskal-Wallis test. Arterial occlusions were determined with MR angiography or conventional angiography. RESULTS: The mean interval between initial CT and MR imaging was 2.4 hours +/- 0.9 (range, 0.4-3.4 hours). The ADC of lesions was similar to that of contralateral normal tissue (mean ADC ratio for gray matter and white matter, 0.99 and 0.97, respectively) (P > .05). Lesions had an increased relative CBV (P < .001), a mild to moderate TTP delay (P < .001), and a variable but not statistically significant reduction of relative CBF. The mean relative CBF of gray matter was less in patients who had complete infarction (0.81 +/- 0.16) than that in patients with partial infarction (0.99 +/- 0.16) or those with a normal radiologic outcome (1.12 +/- 0.22), but this difference was not statistically significant (P > .05). Proximal cerebral artery occlusions were found in all patients. In five (36%) patients, the lesion did not progress to infarction at follow-up. CONCLUSION: The CT sign of brain swelling without concomitant parenchymal hypoattenuation in patients with acute cerebral ischemia does not represent severe ischemic damage and may suggest ischemic penumbral or oligemic tissue.     

Relationship between brain tissue oxygen tension and CT perfusion: feasibility and initial results

BACKGROUND AND PURPOSE: Monitoring of intraparenchymal brain tissue oxygen tension (P(br)O(2)) is an emerging tool in neurocritical care. The purpose of this study was to determine if there is a relationship between CT perfusion (CTP) imaging parameters and P(br)O(2). METHODS: Nineteen patients underwent continuous P(br)O(2) monitoring with probes placed to target white matter in the cerebral hemisphere. Twenty-two CTP studies were performed at the level of the oxygen electrode, as identified on concurrent nonenhanced CT. CTP analysis software was used to measure mean transit time (MTT) and cerebral blood volume (CBV) and to derive cerebral blood flow (CBF) for a region of interest (ROI) surrounding the oxygen probe. For correlation, P(br)O(2) levels and other physiologic parameters were recorded at the time of CTP. RESULTS: P(br)O(2) values at the time of CTP were 2.7-54.4 mm Hg, MTT was 1.86-5.79 seconds, CBV was 1.18-8.76 mL/100 g, and CBF was 15.2-149.2 mL/100 g/min. MTT but not CBV or CBF was correlated with P(br)O(2) (r = -0.50, P = .017). MTT, CBV, or CBF were not correlated with other physiologic parameters, including mean arterial pressure, cerebral perfusion pressure, intracranial pressure, and fraction of inspired oxygen. On multivariable analysis, only P(br)O(2) was independently associated with MTT. CONCLUSION: CTP assessment of ROI surrounding an oxygen probe in the intraparenchymal brain tissue is feasible and showed a significant correlation between P(br)O(2) and MTT. Further studies are warranted to determine the role of CTP in assessing acute brain injury and whether it can be used to prospectively identify brain regions at risk for tissue hypoxia that should be targeted for advanced neuromonitoring.     

The effect of varying user-selected input parameters on quantitative values in CT perfusion maps

RATIONALE AND OBJECTIVES: Deconvolution-based software can be used to calculate quantitative maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) from first-pass computed tomography perfusion (CTP) datasets. The application of this software requires the user to select multiple input variables. The purpose of this study was to investigate the degree to which both major and minor variations of these user-defined inputs would affect the final quantitative values of CBF, CBV, and MTT. MATERIALS AND METHODS: A neuroradiologist constructed CBF, CBV, and MTT maps using standard methodology with commercially available software (GE Functool Version 1.9s) from CTP datasets of three acute stroke patients. Each map was reconstructed multiple times by systematically and independently varying the following parameters: postenhancement and preenhancement cutoff values, arterial and venous region-of-interest (ROI) placement, and arterial and venous ROI size. The resulting quantitative CTP values were compared using identical ROIs placed at the infarct core. RESULTS: Major variations of either arterial ROI placement or arterial and venous ROI size had no significant effect on the mean CBF, CBV, and MTT values at the infarct core (p > .05). Even minor variations, however, in the choice of venous ROI placement or in pre- and postenhancement cutoff values significantly altered the quantitative values for each of the CTP maps, by as much as threefold. CONCLUSION: Even minor variations of user-defined inputs can significantly influence the quantitative, deconvolution-based CTP map values of acute stroke patients. Although quantitation was robust to the choice of arterial ROI placement and arterial or venous ROI size, it was strongly dependent on the choice of venous ROI location and pre- and postenhancement cut-off values. Awareness of these results by clinicians may be important in the creation of quantitatively accurate CTP maps.     

Whole-brain CT perfusion: reliability and reproducibility of volumetric perfusion deficit assessment in patients with acute ischemic stroke

Introduction

The aim of this study was to examine reliability and reproducibility of volumetric perfusion deficit assessment in patients with acute ischemic stroke who underwent recently introduced whole-brain CT perfusion (WB-CTP).

Methods

Twenty-five consecutive patients underwent 128-row WB-CTP with extended scan coverage of 100 mm in the z-axis using adaptive spiral scanning technique. Volumetric analysis of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), time to peak (TTP), and time to drain (TTD) was performed twice by two blinded and experienced readers using OsiriX V.4.0 imaging software. Interreader agreement and intrareader agreement were assessed by intraclass correlation coefficients (ICCs) and Bland–Altman Analysis.

Results

Interreader agreement was highest for TTD (ICC 0.982), followed by MTT (0.976), CBF (0.955), CBV (0.933), and TTP (0.865). Intrareader agreement was also highest for TTD (ICC 0.993), followed by MTT (0.988), CBF (0.981), CBV (9.953), and TTP (0.927). The perfusion deficits showed the highest absolute volumes in the time-related parametric maps TTD (mean volume 121.4 ml), TTP (120.0 ml), and MTT (112.6 ml) and did not differ significantly within this group (each with p?>?0.05). In comparison to time-related maps, the mean CBF perfusion deficit volume was significantly smaller (92.1 ml, each with p?<?0.05). The mean CBV lesion size was 23.4 ml.

Conclusions

Volumetric assessment in WB-CTP is reliable and reproducible. It might serve for a more accurate assessment of stroke outcome prognosis and definition of flow-volume mismatch. Time to drain showed the highest agreement and therefore might be an interesting parameter to define tissue at risk.