组织凝固性坏死对基于纵向弛豫时间的磁共振测温的影响

高强度聚焦超声（High Intensity Focused Ultrasound,HIFU）治疗肿瘤时,为了保证治疗的安全性和有效性,需要对组织温度分布进行实时监测.磁共振成像（Magnetic Resonance Imaging,MRI）具有对温度敏感的成像参数,可以无创检测组织温度.本文结合组织相变对测温的影响,探讨了磁共振测温（Magnetic Resonance Thermometry,MRT）技术能否用于实时监控HIFU治疗.利用两态快速交换模型,提出在组织凝固性坏死的相变前后,MRI的纵向弛豫时间（T₁）参数与组织温度之间具有不同关系.并通过实验验证了上述假设.相对于传统的磁共振测温方法模型,本文考虑了HIFU治疗过程中组织相变对检测温度的影响,对利用磁共振测温引导HIFU治疗具有重要的参考价值.     

小动物高分辨扩散加权成像在临床 MRI 上的实现

在临床用MRI系统上对小动物扩散加权成像一般采用回波平面成像序列,但是回波平面成像易受偏共振效应的影响,得到的图像伪影大、几何变形严重、图像分辨率低,无法探究微小的生物组织结构. 该文报道了在临床用3 T MRI系统上采用自旋回波序列实现了高分辨扩散加权成像. 为减少运动伪影,序列中整合了导航回波矫正技术. 对脑缺血模型大鼠脑部的扫描结果显示,自旋回波扩散加权序列获得的图像基本没有发生形变,并且具有较高的分辨率和较好的信噪比.     

用于活体温度评估的非线性超声热应变模型

热疗在肿瘤消融、高血压治疗等方面有重要应用价值.对热疗过程进行温度监控有利于实施合理的治疗规划,同时可提高治疗的安全性、减少副作用.利用基于超声回波偏移的热应变测温理论进行二维温度估计是一种常用的超声测温方法.但该理论基于组织热膨胀及声速随温度线性变化的假设,适用的温度测量范围一般限于37℃～50℃.该文基于升温组织的...     

基于同时多层激发和并行成像的心脏磁共振电影成像

磁共振成像（MRI）无创无害、对比度多、可以任意剖面成像的特点特别适合用于心脏成像,却因扫描时间长限制了其在临床上的应用.为了解决心脏磁共振电影成像屏气扫描时间过长的问题,该文提出了一种基于同时多层激发的多倍加速心脏磁共振电影成像及其影像重建的方法,该方法将相位调制多层激发（CAIPIRINHA）技术与并行加速（PPA）技术相结合,运用到分段采集心脏电影成像序列中,实现了在相位编码方向和选层方向的四倍加速,并使用改进的SENSE/GRAPPA算法对图像进行重建.分别在水模以及人体上进行了实验,将加速序列图像与不加速序列图像进行对比,结果验证了重建算法的有效性,表明该方法可以在保障图像质量以及准确测量心脏功能的前提下成倍节省扫描时间.     

激光扫描光学断层成像系统的设计与应用

设计了基于LabVIEW控制的激光扫描光学断层成像系统,该系统以准直激光器为光源,高精度四维平移台为样本定位单元,光电倍增管为采集单元,实现了针对小鼠肺等小尺寸样本的三维成像.该系统空间分辨率优于20μm,成像视野大于1cm,通过对离体小鼠肺器官的自发荧光成像,展示了系统的操作流程、成像结果和初步生物应用,并探索了它对整个生物器官组织的成像能力.与传统生物医学光学成像方法相比,该方法具有光子收集效率高、成像样本尺寸大、系统操作简单等优点.     

医学MRI系统的FSE实现

介绍了快速自旋回波成像方法（FSE）在医学磁共振成像（MRI）系统上的实现. 提出了一种简单的预扫描方案,可以有效克服FSE成像方法的固有缺陷. 软件系统的预扫描定制方案,使得本系统可以适应于不同的预扫描要求,谱仪的无关性保证了本系统可以很方便地附加在任何谱仪上. 最后给出了FSE方法在DRX谱仪上的实现和在200 mT系统上获取的实验结果.     

基于超快超声多普勒的三维脑损伤成像方法研究

三维超声微血管成像可直观呈现血流信息,对于脑血管疾病诊断和治疗具有重要意义。本文旨在将超快超声成像技术、超快超声功率多普勒技术和机械扫描相结合,实现脑血管三维成像和脑缺血区域评价。通过工程实现,完成了可同步控制微型线性位移平台移动和超声阵列超快发射、高速采集与压缩存储的三维扫描数据采集序列与系统。利用GPU并行运算,高效实现了超声图像波束合成方法,对原始射频超声数据完成重建。进而,基于SVD杂波滤除技术,从重建三维超声数据中提取了脑部的动态小血管信号,并获得了各切面的功率多普勒成像和冠状面彩色多普勒超声小血管成像。最后,采用体素方法对三维脑血管进行重建。大鼠在体实验结果表明,该成像系统可用于三维脑血管网络在体成像,以及脑血管损伤区域定位与量化评价。本工作对脑病检测技术发展与诊断方法研究具有一定的借鉴意义。此外,相关检测系统和成像算法具有一定普适性,对其他富含微血流血管的组织检测也有一定的参考价值。     

基于聚焦光声层析技术的甲状腺离体组织成像

对人体甲状腺内的病变组织进行定位和成像对于准确诊断和有效治疗甲状腺疾病是至关重要的. 本文评估了利用光声层析技术对离体甲状腺组织进行成像的可行性, 并利用基于30 MHz超声换能器的聚焦光声成像系统对甲状腺进行扫描成像. 实验中成像系统的横向分辨率和纵向分辨率分别达到了350 μupm和74 μupm. 分别对正常离体甲状腺组织和模拟病变甲状腺组织进行光声成像. 实验结果表明, 本成像系统能够有效区分和鉴别正常甲状腺组织和病变组织. 此项技术有望进一步提高甲状腺疾病诊断的准确率, 以便更为有效地指导疾病的治疗, 具有潜在的临床应用前景.     

一种基于双波长的光声测温技术

光声测温是一种利用光声效应来进行温度监控的新方法,具有非侵入式、高灵敏度和探测深度较深等优点.但现有的单波长光声测温方法极易受到系统及测量环境干扰而导致测量精度降低.为了解决这一问题,本文提出了一种双波长光声温度测量方法.在光声测温理论的基础上,分析推导了双波长光声测温的基本原理,并进行了仿体及离体组织样品的双波长光声测温实验.实验结果显示,与传统单波长模式相比,双波长模式下的光声温度测量误差明显减小,测量精度平均提高35%以上.研究结果表明双波长光声测温方法能够有效提高光声温度测量的精度和稳定性,可作为一种更精准的光声温度监控方法应用于医疗手术等领域.     

X射线成像技术在医学中应用

文章介绍了在医学中广泛应用的二维X射线摄影屏一胶片系统及三维计算机断层扫描成像技术。并对二维X射线摄影技术的发展，例如数字减影血管造影（DSA），计算机放射成像（CR）和直接数字化X射线摄影（DR）以及三维成像新技术，如螺旋计算机断层扫描技术（螺旋CT），正电子发射体层／多层螺旋CT图像融合扫描装置（简称PET-CT）和相位衬度成像技术的原理和应用作了简单描述。医学图像后处理是现代医学图像设备不可或缺的组成部分，先验医学知识的融入使现代图像设备具有辅助诊断的能力。     

Quantitative MR temperature monitoring of high-intensity focused ultrasound therapy

A new quantitative method has been developed for real-time mapping of temperature changes induced by high intensity focused ultrasound (HIFU). It is based on the temperature dependence of the T1 relaxation time and the equilibrium magnetization. To calibrate the temperature measurement, the functional relationship between T1 and temperature was examined in different samples of porcine muscle and fatty tissue. The method was validated by a comparison of calculated temperature maps with fiber-optic measurements in heated muscle tissue. The experiment showed that the accuracy of the MR method for temperature measurements is better than 1 degree C. Since the acquisition time of the employed MR sequence takes only 3 s per slice and the calculation of the temperature map can be performed within seconds, the imaging technique works nearly in real-time. The temperature measurement could be realized during HIFU showing no disturbances by ultrasound sonication. In comparison to other MR approaches, the advantages of the introduced method lie in a sufficient accuracy and time resolution combined with a reasonable robustness against motion as well as the feasibility for temperature monitoring in fatty tissues.     

A flexible 9-channel coil array for fast 3D MR thermometry in MR-guided high-intensity focused ultrasound (HIFU) studies on rabbits at 3 T

Signal-to-noise ratio (SNR) is a critical factor in MR-guided high-intensity focused ultrasound (HIFU) for local heating, which can affect the accuracy of temperature measurement. In order to achieve high SNR and higher temporal resolution, dedicated coil arrays for MR-guided HIFU applications need to be developed. In this work, a flexible 9-channel coil array was designed, and constructed at 3 T to achieve fast temperature mapping for MR-guided HIFU applications on rabbit leg muscle. Coil performance was evaluated for SNR, and parallel imaging capability by in-vivo studies. Compared to a commercially available 4-channel flexible coil array, the dedicated 9-channel coil array has a much higher SNR, with at least a 2.6-fold increment in the region of interest (ROI). The inverse g-factors maps demonstrated that the dedicated 9-channel coil array has a better parallel imaging capability than the Flex Small 4. With accelerations normal to the array direction, both coil arrays showed much higher g-factors than those of accelerations along the array direction. Room temperature mapping was implemented to evaluate the temperature measurement accuracy by in-vivo experiments. The precisions of the 9-channel coil, ±0.18 °C for un-acceleration and ± 0.56 °C for acceleration at R = 2 × 2, both improved by an order of magnitude than these of the 4-channel coil, which were ± 1.45 °C for un-acceleration and ± 3.52 °C for acceleration at R = 2 × 2. In the fast temperature imaging on the rabbit leg muscle with heating, a high temporal resolution of 3.3 s with a temperature measurement precision of ±0.56 °C has been achieved using the dedicated 9-channel coil. This study demonstrates that the dedicated 9-channel coil array for rabbit leg imaging provides improved performance in SNR, parallel imaging capability, and the accuracy of temperature measurement compared to a commercial 4-channel coil, and it also achieves fast temperature mapping in practical MR-guided HIFU applications.     

B模式实时成像定量监控超声空化时空行为的研究

提出一种采用B超图像实现高强聚焦超声(HIFU)治疗时声空化的时空量化监控的方法。首先,采用B模式实时成像系统对不同声辐照能量下的HIFU在凝胶仿体中引发的超声空化进行实验监测;接着,利用二维数字图像处理算法消除高强聚焦超声(HIFU)在B超图像中产生的干涉条纹,并在此基础上,对B超成像中观察到的高亮区域的面积变化情况进行量化分析;最后,进一步讨论了驱动声压或脉冲宽度对超声空化产生的高亮区域的生成速度和面积大小的影响。结果显示该方法可以有效去除B超图像中的干涉条纹,并对HIFU引发的空化现象进行实时监测。实验结果还表明辐照声能量的提高将引发更强烈的声空化行为,并且显著缩短HIFU引发的空化泡群的初始生成时间。研究结果对进一步优化HIFU治疗有重要意义。      

Model-based PRFS thermometry using fat as the internal reference and the extended Prony algorithm for model fitting

A model-based proton resonance frequency shift (PRFS) thermometry method was developed to significantly reduce the temperature quantification errors encountered in the conventional phase mapping method and the spatiotemporal limitations of the spectroscopic thermometry method. Spectral data acquired using multi-echo gradient echo (GRE) is fit into a two-component signal model containing temperature information and fat is used as the internal reference. The noniterative extended Prony algorithm is used for the signal fitting and frequency estimate. Monte Carlo simulations demonstrate the advantages of the method for optimal water-fat separation and temperature estimation accuracy. Phantom experiments demonstrate that the model-based method effectively reduces the interscan motion effects and frequency disturbances due to the main field drift. The thermometry result of ex vivo goose liver experiment with high intensity focused ultrasound (HIFU) heating was also presented in the paper to indicate the feasibility of the model-based method in real tissue.     

Quantitative MRI of uterine leiomyomas during triptorelin treatment: Reproducibility of volume assessment and predictability of treatment response

Magnetic resonance (MR) imaging is increasingly applied for the quantitative evaluation of uterine leiomyomas. MR is thought to be more accurate in comparison to ultrasound (US) techniques. MR signal intensity (SI) may prove to be predictive of myoma response to GnRH agonist treatment. This study aimed to evaluate the precision of uterine volume assessment by a parallel planimetric MR method and the accuracy of the ellipsoid formula based calculations from MR and US images. It was also attempted to analyze the precision of MR leiomyoma volume measurements and examine the relation between pretreatment myoma SI patterns and the response to agonist therapy. Twenty-seven women with a myomatous uterus were scanned three times during GnRH agonist treatment for 6 months. T₁- and T₂-weighted, as well as T₁ contrast-enhanced sequences of the uterus were obtained in the transverse and sagittal plane. Abdominal US of the uterus was performed with a conventional sector scanner. By the use of a software system for analysis of three-dimensional images obtained by MR, uterine volume was measured by a parallel planimetric method (MR-ROI) as well as the use of the ellipsoid formula (MR-ELL). Myoma volume was assessed by the MR-ROI method. SI of the myomas was estimated from selected tissue samples as well as from the integral myoma region of interest. By abdominal US, volume was assessed by the ellipsoid equation (US-ELL). Within- and between-observer and method reliability (Rw/Rb) was calculated from mean squares obtained by analysis of variance. For uterine volume assessment, reliability between observers and between methods when the MR-ROI and MR-ELL methods were analyzed was excellent. For the US-ELL measurements, the between-observer reliability was limited. Moreover, the reliability of the US-ELL was low when the MR-ROI method was used as the standard. Myoma volume assessment with the MR-ROI method showed high between-observer and between-method agreement. The myoma/fat SI ratio and the mean SI coefficient of variation failed to show a correlation with the degree of response to triptorelin treatment of individual myomas. In MR uterine volume assessment the MR-ELL method is very accurate compared with the more complicated MR-ROI method. The agreement between MR and US is limited. Therefore, the ellipsoid method on MR images is to be regarded as the method of choice for quantitative assessment of uterine volume response to hormonal treatment. Myoma SI patterns were shown to be of no value in the response prediction of myomas to treatment with GnRH agonists.     

Differential ultrasonic imaging for the characterization of lesions induced by high intensity focused ultrasound

High intensity focused ultrasound (HIFU) is an effective technique for noninvasive local creating coagulative necrotic lesions in deep target volumes without damage to the overlaying or surrounding tissues. It is very important to detect and evaluate lesions generated by HIFU during treatment procedures. This study describes the development of several differential ultrasonic imaging techniques to characterize lesions based on estimation of relative changes in tissue properties derived from backscattered RF data. A single, spherical HIFU transducer was used to produce lesions in soft tissues. The RF signals were recorded as outputs from a modified diagnostic ultrasound system. After some preprocessing, the integrated backscatter values, which can be used as an indicator of the microstructure and backscattering property of tissues, were calculated before and after HIFU treatment. The differential integrated backscatter values were subsequently used to form images revealing the lesion areas. The differential attenuation imaging with the same RF data was also performed, which has been proposed by a few researchers. The results of the differential integrated backscatter imaging were compared with that of the differential attenuation imaging and the former method offers some advantages over the latter method. The two methods above are both based on spectrum analysis and would spend much computational time. Therefore, some simple digital differential imaging methods, including absolute difference (AD), sum absolute differences (SAD), and sum squared differences (SSD) algorithms, were also proposed to detect HIFU-induced lesions. However, these methods cannot provide the information of the degree of tissue damage. Experiments in vitro bovine muscle and liver validated the method of differential integrated backscatter imaging for the characterization of HIFU-induced lesions. And the AD, SAD, and SSD algorithms can be implemented in real-time during HIFU therapy to visualize the lesions.     

基于电阻抗层析成像的高强度聚焦超声温度监测技术

作为一种对正常组织无损伤且不易引起癌细胞转移的非入侵肿瘤治疗手段,高强度聚焦超声(HIFU)治疗过程中焦域的温度监测是实现剂量精准控制的关键.本文基于生物组织的温度-电阻抗的关系,将电阻抗层析成像(EIT)和HIFU治疗相结合,提出了一种利用组织焦平面的表面电压实现电阻抗重构的检测技术.建立了HIFU治疗和EIT综合系统模型,在考虑组织的声吸收条件下,对三维Helmholtz方程在柱坐标下的声场计算进行了二维简化,并引入Pennes生物热传导方程来计算HIFU焦域的声压和温升分布特性;引入生物组织的温度-电阻抗关系,基于麦克斯韦电磁场理论,建立了具有温度分布HIFU焦域的电流和电压计算模型,利用恒流注入的边界条件实现电场计算,获得焦平面的表面电压分布.在数值计算中,利用实验聚焦换能器参数,模拟了在固定声功率下组织焦域的声场和温度场分布,以及中心和偏心聚焦条件下不同治疗时刻的电导率分布;然后通过对称电极的循环电流注入,计算了组织模型焦平面内的电流密度和电势分布,获得了焦平面圆周分布的表面电极电压;进一步采用修正的牛顿-拉夫逊算法,利用32×32的表面电极电压实现了焦平面内电导率分布的重建.结果表明,基于温度-电阻抗关系的EIT电导率重建技术不但能准确定位HIFU焦域中心,还能恢复HIFU治疗中焦域的温度分布,证明了EIT用于HIFU治疗中温度监测的可行性,为其疗效评估和剂量控制提供了一种无创电阻抗测量和成像新方法.     

Characterization of high intensity focused ultrasound transducers using acoustic streaming

A new approach for characterizing high intensity focused ultrasound (HIFU) transducers is presented. The technique is based upon the acoustic streaming field generated by absorption of the HIFU beam in a liquid medium. The streaming field is quantified using digital particle image velocimetry, and a numerical algorithm is employed to compute the acoustic intensity field giving rise to the observed streaming field. The method as presented here is applicable to moderate intensity regimes, above the intensities which may be damaging to conventional hydrophones, but below the levels where nonlinear propagation effects are appreciable. Intensity fields and acoustic powers predicted using the streaming method were found to agree within 10% with measurements obtained using hydrophones and radiation force balances. Besides acoustic intensity fields, the streaming technique may be used to determine other important HIFU parameters, such as beam tilt angle or absorption of the propagation medium.     

Ultrasound line-by-line scanning method of spatial–temporal active cavitation mapping for high-intensity focused ultrasound

This paper presented an ultrasound line-by-line scanning method of spatial–temporal active cavitation mapping applicable in a liquid or liquid filled tissue cavities exposed by high-intensity focused ultrasound (HIFU). Scattered signals from cavitation bubbles were obtained in a scan line immediately after one HIFU exposure, and then there was a waiting time of 2 s long enough to make the liquid back to the original state. As this pattern extended, an image was built up by sequentially measuring a series of such lines. The acquisition of the beamformed radiofrequency (RF) signals for a scan line was synchronized with HIFU exposure. The duration of HIFU exposure, as well as the delay of the interrogating pulse relative to the moment while HIFU was turned off, could vary from microseconds to seconds. The feasibility of this method was demonstrated in tap-water and a tap-water filled cavity in the tissue-mimicking gelatin–agar phantom as capable of observing temporal evolutions of cavitation bubble cloud with temporal resolution of several microseconds, lateral and axial resolution of 0.50 mm and 0.29 mm respectively. The dissolution process of cavitation bubble cloud and spatial distribution affected by cavitation previously generated were also investigated. Although the application is limited by the requirement for a gassy fluid (e.g. tap water, etc.) that allows replenishment of nuclei between HIFU exposures, the technique may be a useful tool in spatial–temporal cavitation mapping for HIFU with high precision and resolution, providing a reference for clinical therapy.