超声造影评价去甲肾上腺素对兔肾血流灌注的影响

目的探讨超声造影结合时间强度曲线定量评价去甲肾上腺素（NE）对兔肾血流灌注的影响。方法应用实时超声造影成像技术（Contrast Tuned Imaging,CnTi）与超声造影剂声诺维对12只健康家兔左肾进行超声造影,并在应用血管活性物质去甲肾上腺素0.3μg·kg^-1·min^-120min后对兔左侧肾进行造影,应用时间强度曲线对肾血流灌注情况进行定量分析。结果输注去甲肾上腺素后,肾皮质开始增强时间及达峰时间延长（P〈0．05）,峰值强度、曲线上升斜率、曲线下面积均减小（P〈0．01）。而肾髓质仅开始增强时间延长（P〈0．01）。结论超声造影结合时间强度曲线能反映肾血流灌注特征及变化,具有潜在临床实用价值。     

新型超声造影剂对组织器官血流灌注的研究

超声造影剂的类型与相关技术的发展(一)超声造影剂的类型　目前造影剂根据剂型及成分的不同,可分为:①自由气体;②包裹气体;③混悬液;④胶体溶液;⑤水溶液。第一代微泡造影剂为自由气体,由于在血液循环中持续时间极为短暂、微泡大小不一、不能通过肺循环等缺陷,未能在临床有效应用。第二代微泡造影剂则在微泡周围包裹以外壳成份(白蛋白或脂质)或膜稳定剂,比较具代表性的有Ａｌｂｕｎｅｘ和Ｌｅｖｏｖｉｓｔ。第三代微泡造影剂则在弹性外壳的韧性及采用低弥散度大分子量的气体成分等方面作了较大的改进(如Ｑｕａｎｔｉｓｏｎ,Ｏｐｔｉｓｏｎ,…     

经静脉心肌声学造影的研究进展

心肌声学造影 (ｍｙｏｃａｒｄｉａｃｃｏｎｔｒａｓｔｅｃｈｏｃａｒｄｉｏｇｒａｐｈｙ,ＭＣＥ)是将含有微小气泡的声学造影剂随冠脉血流灌注到心肌组织 ,通过造影剂背向散射信号较心肌组织强 ,心肌显影强度增加而确定心肌灌注范围。近年来由于新的经静脉途径造影剂的研制及超声成像技术的发展 ,使经静脉途径ＭＣＥ取得了瞩目的进展。1　经静脉途径造影剂　　　高分子量、低血液溶解性的气体有助于增强微泡的稳定性 ,为实现经静脉途径左室心肌造影奠定了基础。目前经静脉途径造影剂主要有以下几种 :1 1　Ａｌｂｕｎｅｘ　含空气的白蛋白微…     

失代偿期肝硬化肾脏血流灌注异常的影像学评价

失代偿期肝硬化（DCC）病人常常出现肾功能损害，尤其是发生肝肾综合征时，病人病死率极高，因此对DCC病人肾脏病变的诊断十分重要。影像学方法为该病的诊断提供了可能。综述DCC肾脏病变的发病机制、组织学特点以及影像学诊断方法。     

心肌声学造影估测冠脉血流储备及心内膜下心肌灌注的实？…

目的探讨心肌声学造影定量冠脉血流储备及心内膜下心肌灌注的意义。材料与方法13只开胸犬左旋支临界狭窄状态及静脉注射潘生丁后分别进行心肌声学造影并与放射性微球所测心肌血流量对比。结果静注潘生丁后,正常对照区心肌血流量及心肌造影曲线下面积、峰值强度、最大上升斜率指标均明显增加;而临界狭窄缺血区无明显变化。在临界狭窄缺血区,放射性微球所测的心内膜下／心外膜下心肌血流比率减低;但以造影曲线下面积指标所测则无明显变化。结论心肌声学造影曲线下面积、峰值强度及最大上升斜率是定量评价冠脉血流储备的可靠指标;在当前情况下心肌声学造影技术尚不能用于评价心内膜下心肌灌注。     

心肌声学造影研究进展

心肌声学造影研究进展唐志宏综述刘伊丽审校Ｘ线冠状动脉造影是一种解剖学检查方法。它能确定冠状动脉狭窄的部位及严重程度，但它仅能观察大于１００μｍ直径的血管［１］，不能提供心肌血流灌注改变的直接信息。心肌声学造影是一项活体内测量心肌组织血流灌注的影像诊断...     

超声造影评价肝纤维化血流灌注特征的初步研究

目的:探讨超声造影评价肝纤维化血流灌注特征的临床应用价值。方法:肝纤维化组15例,均经超声引导下肝组织活检病理证实,选取健康志愿者15例为正常对照组。所有研究对象经肘静脉团注对比剂SonoVue 2.4ml,行实时灰阶超声造影检查,记录对比剂肝动脉到达时间(hepatic artery arrival time,HAAT)、门静脉到达时间(portal vein arrival time,PVAT)、肝静脉到达时间(hepatic vein arrival time,HVAT)及相应血管灌注强度参数(peak intensity,PI),同时计算肝动-静脉渡越时间(hepatic artery to hepatic vein transit time,HA-HVTT)、门静脉-肝静脉渡越时间(portal vein to hepatic vein transittime,PV-HVTT)及门静脉-肝动脉间隔时间(PVAT-HAAT,VVT),分析2组间上述各参数差异有无统计学意义。结果:肝纤维化组PVAT较正常对照组缩短,差异有统计学意义(P<0.05),肝纤维化组HVAT、HA-HVTT、PV-HVTT及VVT较正常对照组缩短,差异均有统计学意义(P<0.01);2组HAAT、HA-PI、PV-PI及HV-PI差异均无统计学意义。结论:超声造影定量参数PVAT、HVAT及PV-HVTT可反映肝纤维化微循环及血流动力学改变,有望成为无创评价肝纤维化的定量指标。     

失代偿期肝硬化肾脏血流灌注异常的影像学评价

失代偿期肝硬化(DCC)病人常常出现肾功能损害,尤其是发生肝肾综合征时,病人病死率极高,因此对DCC病人肾脏病变的诊断十分重要.影像学方法为该病的诊断提供了可能.综述DCC肾脏病变的发病机制、组织学特点以及影像学诊断方法.     

超声造影技术对移植肝脏血流灌注的评价应用研究

近年来,随着超声造影剂的不断改进及超声造影成像技术的迅速发展,新型超声造影方法成功地开辟了全新的超声造影领域.通过动态观察造影剂对组织的强化过程,可有效反映病变组织的血流动力学变化[1],并已成功的应用于肝脏肿瘤良恶性的鉴别诊断.在肝移植领域,超声造影技术的应用正在逐步开展[2],通过增强肝脏血管的显像来观察移植肝脏血流灌注3个时期的动态变化,分析动脉相、门静脉相、肝实质相的血管及肝实质的变化情况,有助于发现移植肝的血流异常和肝实质的血流灌注情况[3],对移植后的预后评估具有重要意义.     

电子束CT对肾脏临床血流灌注研究

目的 探讨电子束CT应用于肾脏血流灌注的价值。材料与方法 应用电子束CT血流序列对40例正常人和20例血流减少性肾病进行检查，分别测量强化高峰时间、CT值上升时间、高峰CT值、CT值增幅和血流灌注量等。结果 血流减少肾脏的强化高峰时间比正常延迟，CT值上升时间延长；血流减少肾脏皮质的CT值增幅和强化程度明显低于正常；正常和异常血流量也有非常显著差别。结论 电子束CT可对血流减少性肾病进行动态观察CT值的变化，判断肾脏血流减少程度，测量肾脏血流灌注量。     

Contrast agent dose effects in cerebral dynamic susceptibility contrast magnetic resonance perfusion imaging

Purpose

To study the contrast agent dose sensitivity of hemodynamic parameters derived from brain dynamic susceptibility contrast MRI (DSC‐MRI).

Materials and Methods

Sequential DSC‐MRI (1.5T gradient‐echo echo‐planar imaging using an echo time of 61–64 msec) was performed using contrast agent doses of 0.1 and 0.2 mmol/kg delivered at a fixed rate of 5.0 mL/second in 12 normal subjects and 12 stroke patients.

Results

1) Arterial signal showed the expected doubling in relaxation response (ΔR2*) to dose doubling. 2) The brain signal showed a less than doubled ΔR2* response to dose doubling. 3) The 0.2 mmol/kg dose studies subtly underestimated cerebral blood volume (CBV) and cerebral blood flow (CBF) relative to the 0.1 mmol/kg studies. 4) In the range of low CBV and CBF, the 0.2 mmol/kg studies overestimated the CBV and CBF compared with the 0.1 mmol/kg studies. 5) The 0.1 mmol/kg studies reported larger ischemic volumes in stroke.

Conclusion

Subtle but statistically significant dose sensitivities were found. Therefore, it is advisable to carefully control the contrast agent dose when DSC‐MRI is used in clinical trials. The study also suggests that a 0.1 mmol/kg dose is adequate for hemodynamic measurements. J. Magn. Reson. Imaging 2009;29:52–64. © 2008 Wiley‐Liss, Inc.     

Comparison of liver perfusion parameters studied with conventional extravascular and experimental intravascular CT contrast agents

RATIONALE AND OBJECTIVES: To compare liver perfusion parameters obtained by using an extravascular contrast agent and a blood-pool agent. MATERIALS AND METHODS: Fifteen rabbits were imaged with a continuous 40-second single-slice computed tomography acquisition after a bolus injection of contrast agent (physiologic bolus duration 4-5 seconds, extravascular iohexol, n = 7; experimental nanoparticulated blood-pool agent WIN8883, n = 8). Time-density curves were generated for the aorta, portal vein, and liver. From the curves, arterial, portal, and total blood flows and hepatic perfusion index (HPI, arterial-to-total perfusion ratio) were determined by using two commonly applied fundamentally different analyzing methods: the single-compartment model and the peak gradient (PG) method. Also, the gamma variate fitting method was used. RESULTS: By using the single-compartment model, the obtained HPI and total blood flow were 0.14 +/- 0.04 and 2.29 +/- 0.40 (mL/min/mL(tissue)) for WIN8883, and 0.15 +/- 0.06 (P = .54) and 4.60 +/- 1.14 (mL/min/mL(tissue)) (P = .0002) for iohexol, respectively. With the PG, HPI and total blood flow were 0.15 +/- 0.08 and 1.27 +/- 0.24 (mL/min/mL(tissue)) for WIN8883, and 0.20 +/- 0.06 (P = .12) and 2.11 +/- 0.25 (mL/min/mL(tissue)) (P = .00002) for iohexol, respectively. With the blood pool agent, similar contrast enhancement to the conventional agent was achieved with about 36% reduced dosage of iodine per body weight (mg I/kg). CONCLUSIONS: HPI was found to be quite insensitive to different contrast agent types and analyzing methods. However, the arterial, portal and total liver blood flow values strongly depend on contrast agent type and modeling method.     

Quantification of renal perfusion using an intravascular contrast agent (part 1): results in a canine model.

In this work absolute values of regional renal blood volume (rRBV) and flow (rRBF) are assessed by means of contrast-enhanced (CE) MRI using an intravascular superparamagnetic contrast agent. In an animal study, eight foxhounds underwent dynamic susceptibility-weighted MRI upon injection of contrast agent. Using principles of indicator dilution theory and deconvolution analysis, parametric images of rRBV, rRBF, and mean transit time (MTT) were computed. For comparison, whole-organ blood flow was determined invasively by means of an implanted flow probe, and the weight of the kidneys was evaluated postmortem. A mean rBV value of 28 ml/100 g was found in the renal cortex, with a corresponding mean rBF value of 524 ml/100 g/min and an average MTT of about 3.4 s. Although there was a systematic difference between the absolute blood flow values determined by MRI and the ultrasonic probe, a significant correlation (r(s) = 0.72, P < 0.05) was established. The influence of the arterial input function (AIF), T(1) relaxation effects, and repeated measurements on the precision of the perfusion quantitation is discussed.     

High spatial resolution magnetic resonance imaging of experimental cerebral venous thrombosis with a blood pool contrast agent

Purpose

The purpose of this study was to investigate the feasibility of clot visualization in small sinus and cortical veins with contrast enhanced MRA in a cerebral venous thrombosis animal model using a blood pool contrast agent, Gadofosveset, and high spatial resolution imaging.

Material and methods

For induction of cerebral venous thrombosis a recently developed combined interventional and microsurgical model was used. Cerebral sinus and cortical vein thrombosis was induced in six pigs. Two further pigs died during the procedure. Standard structural, time-of-flight- and phase contrast-angiograms were followed by fast time resolved high resolution 3D MRA (4D MRA) and subsequent high spatial resolution 3D MRA in the equilibrium phase with and without addition of parallel imaging. Visualization of the clots using the different sequences was subjectively compared and contrast-to-noise ratio (CNR) was assessed.

Results

In the remaining six animals the procedure and MR-imaging protocol including administration of Gadofosveset was successfully completed. The 3D high resolution MRA in the equilibrium phase without the addition of parallel imaging was superior to all the other applied MR measurement techniques in terms of visualization of the clots. Only applying this sequence bridging vein thromboses were also seen as a small filling defect with a high CNR of >18.

Conclusion

Only the non-accelerated high spatial resolution 3D MRA in the equilibrium in conjunction with the blood pool agent Gadofosveset allows for high-contrast visualization of very small clots in the cerebral sinus and cortical veins.

Statement clinical impact

Detection of cortical vein thrombosis is of high clinical impact. Conventional MRI sequences often fail to visualize the clot. We could demonstrate that, in contrast to conventional sequences, with high spatial resolution 3D MRA in the equilibrium in conjunction with the blood pool agent Gadofosveset very small clots in the cerebral sinus and cortical veins could be successfully visualized. We think that with the presented approach cortical vein thrombosis might also be sufficiently visualized in patients.     

Contrast agent concentration measurements affecting quantification of bolus-tracking perfusion MRI.

Measurement of the concentration of the contrast agent using dynamic susceptibility contrast MRI relies on field inhomogeneities caused by the presence of the paramagnetic agent. The usual method for calculation of the concentration from dynamic T2*-weighted images is based on two key assumptions: 1) a linear relation between the change in R2* and the contrast agent concentration, and 2) a negligible effect on the MR signal due to concurrent T1 changes. In this study the effect of inaccuracies in these two assumptions on perfusion measurements was investigated using simulations and in vivo data. The results of the simulations provide a quantitative characterization of the magnitude of these effects for various experimental conditions (e.g., when a 1-sec TR is used with TE=20 ms, the T1 effects can introduce up to 40% cerebral blood flow underestimation depending on the flip angle). These findings can be used as a guide to estimate the errors in specific practical implementations, as well as to optimize the sequence parameters to minimize their effect. In summary, this study shows that the arterial input function measurement should be corrected for nonlinear R2* effects and that care should be taken in the study design to avoid introducing significant T1 effects in perfusion quantification.     

Renal perfusion abnormality. Coded harmonic angio US with contrast agent

Purpose: 
Coded harmonic angio (CHA) US is a recently developed technique that can depict the effects of contrast agents. The purpose of this study was to determine the role of this technique in depicting the enhancement patterns of various renal perfusion abnormalities compared with dynamic CT. Material and Methods: 
During a 6-month period, various renal lesions including renal cell carcinoma (n=12), transitional cell carcinoma (n=5), acute pyelonephritis (n=5), and renal trauma (n=2) were evaluated with CHA US using a microbubble contrast agent. US images were obtained before contrast administration and with a bolus injection of 4 g of microbubble contrast agent (300 mg/ml) every 10 s for 1 min and every minute for 5 min. The contrast enhancement patterns of various renal masses were compared with dynamic CT. Results: 
Of 12 renal cell carcinomas, 9 (75%) showed heterogeneous enhancement and the remaining 3 (25%) showed homogeneous enhancement. Enhancement of more than adjacent renal parenchyma was seen 16-252 s after injection. The duration of enhancement was 13-208 s (mean, 80 s). All transitional cell carcinomas showed peripheral enhancement. Enhancement was seen 22-270 s after injection. The duration of enhancement was 191-238 s (mean, 291 s). Five patients with acute pyelonephritis and 2 with renal trauma showed focal perfusion defects not shown on the pre-contrast examinations. Conclusion: 
CHA US with microbubble contrast agent is an effective US technique for the evaluation of both tumor vascularity and renal perfusion abnormality.     

Influence of perfusion on high-intensity focused ultrasound prostate ablation: a first-pass MRI study.

Our aim was to evaluate the influence of regional prostate blood flow (rPBF) on high-intensity focused ultrasound (HIFU) treatment outcome. A total of 48 patients with clinically localized prostate cancer were examined by dynamic contrast-enhanced (DCE)-MRI prior to HIFU therapy. A prostate-specific antigen (PSA) nadir threshold of 0.2 ng/ml was used to define the populations of responders and nonresponders. A dedicated tracer kinetic model, namely "monoexponential plus constant" (MPC) deconvolution, was implemented to provide quantitative estimates of rPBF. The results were compared with those obtained by semiquantitative (steepest slope, mean gradient) and quantitative (Fermi deconvolution) approaches. Of the four methods studied, quantitative rPBF obtained by MPC deconvolution proved the most sensitive to the perfusion changes encountered in this study. Furthermore, blood-flow values obtained with MPC deconvolution in the prostate and muscle (12 +/- 8 and 5 +/- 3 ml/min/100 g, respectively) were in good agreement with literature data. The mean pretreatment rPBF obtained with MPC deconvolution was significantly higher in nonresponders compared to responders (16 +/- 9 vs. 10 +/- 6 ml/min/100 g), suggesting a correlation between baseline perfusion and treatment outcome. The present work describes and validates the use of dynamic MRI to estimate rPBF in patients, which in the future may help to refine the conduct of HIFU therapy.     

Perfusion imaging with a freely diffusible hyperpolarized contrast agent

Contrast agents that can diffuse freely into or within tissue have numerous attractive features for perfusion imaging. Here we present preliminary data illustrating the suitability of hyperpolarized ¹³C labeled 2‐methylpropan‐2‐ol (also known as dimethylethanol, tertiary butyl alcohol and tert‐butanol) as a freely diffusible contrast agent for magnetic resonance perfusion imaging. Dynamic ¹³C images acquired in rat brain with a balanced steady‐state free precession sequence following administration of hyperpolarized 2‐methylpropan‐2‐ol show that this agent can be imaged with 2–4s temporal resolution, 2 mm slice thickness, and 700 μm in‐plane resolution while retaining adequate signal‐to‐noise ratio. ¹³C relaxation measurements on 2‐methylpropan‐2‐ol in blood at 9.4T yield T₁ = 46 ± 4s and T₂ = 0.55 ± 0.03s. In the rat brain at 4.7T, analysis of the temporal dynamics of the balanced steady‐state free precession image intensity in tissue and venous blood indicate that 2‐methylpropan‐2‐ol has a T₂ of roughly 2–4s and a T₁ of 43 ± 24s. In addition, the images indicate that 2‐methylpropan‐2‐ol is freely diffusible in brain and hence has a long residence time in tissue; this in turn makes it possible to image the agent continuously for tens of seconds. These characteristics show that 2‐methylpropan‐2‐ol is a promising agent for robust and quantitative perfusion imaging in the brain and body. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.